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Introduction

Presbyopia – the reduced ability of the natural lens to accommodate – affects almost all individuals by the age of 50, leaving them with decreased near visual acuity (VA). In 2011 alone, it is estimated that from a total of 244 million cases of uncorrected or under-corrected presbyopia in people aged less than 50 years, there was an approximate worldwide $11.023 billion loss in potential productivity.¹ One novel way to manage presbyopia is by the implantation of phakic intraocular lenses (IOLs) – IOLs that are placed over the natural lens rather than replacing it. These lenses refract light either via distinct regions with various radii of curvature, or diffractively by inducing add powers through Fresnel zones, which refract the light differently than their lens-base.² Phakic IOLs allow for patients to maintain their residual ability to accommodate, receive a refractive intraocular lens if needed, and avoid an increased risk of retinal detachment during this procedure if they are highly myopic.^3–6 Previous studies have extensively reported positive outcomes on various phakic IOLs in refractive surgery,^3,7–9 however few studies have explored their outcomes in presbyopia management.^10–13

In 2020, Schmid and Luedtke established promising results for the use of phakic IOLs in correcting presbyopia, where 8 patients undergoing presbyopia correction with a diffractive posterior chamber phakic IOL reached a median uncorrected distance VA of at least 0.1logMAR with no need for reading glasses at one-month post-operation.¹⁴ Four prospective studies by Stodulka et al, Takahashi et al, Bianchi et al, and Güel et al have found patients undergoing presbyopic phakic IOL correction to have significantly improved VA at follow-ups.^15–18 While such studies have reported positive outcomes for phakic IOL use in presbyopia management, they are limited in numbers and no previous study has yet directly compared a refractive and a diffractive phakic IOL for presbyopia management.

In this study, we evaluated and compared the optical quality of a diffractive phakic IOL – the IPCL with +2.5 diopters (D) add power (Care Group) – and a recently introduced refractive phakic model designed for presbyopia correction – the Artiplus (Ophtec). By measuring their optical-quality metrics and simulating postoperative VA at various aperture sizes and near, intermediate, and far distances, we aimed to provide comprehensive information on the optical properties of both approaches in the same study, allowing for better direct comparison of the models and a more personalized selection of phakic IOL based on patients’ needs.

Methods

Phakic IOLs

The Artiplus Model 470 (Artiplus) is a polysiloxane iris-fixated refractive phakic IOL (Ophtec, Groningen, the Netherlands),¹⁹ which has recently obtained a CE-marking. Its multi-segmented optic using the continuous transitional focus technology allows for improved VA at near, intermediate, and far distances (Figure 1). Its refractive index is 1.43, with dioptric powers ranging from +2.0 to −15.0D in 0.5D increments. Artiplus has an overall diameter of 8.5mm with a 6.0mm convex-concave body. We used an Artiplus IOL with a power of −3D.

The IPCL V2.0 is a hybrid hydrophilic acrylic phakic IOL with a refractive index of 1.465. It features a central hole to allow aqueous flow and six haptic pads to ensure its stability in the ciliary sulcus (Care Group, Gujarat, India).²⁰ It has an optic diameter of 6.60mm that can be customized up to 7.25mm with sizes ranging from 11.00 to 14.00mm (0.25mm step).²¹ The IPCL is available in the broad power range of −30.0D to +15.0D in 0.5D increments. The added power can also be customized by offering +1.5D, 2D, 2.5D, 3D, and 3.5D secondary foci. In the current study, we used an IPCL with a power of −3D and an add power of +2.5D, aligning with the range of the Artiplus model.

In our experiments, the optical power of the natural lens was modeled with a 23D Precizon Monofocal (Ophtec, Groningen, the Netherlands), with no spherical aberration. When assembling the 23D monofocal and phakic IOL with one another, the overall corneal aberration (0.27 µm) was similar to the mean of 0.280 µm (±0.086 µm) reported in the literature.²²

Optical Setup

The 23D monofocal and phakic IOLs were assembled into a custom-made and 3D-printed insert with the 23D monofocal placed posterior to the phakic IOL to simulate the in-vivo condition of the natural lens being posterior to a phakic IOL (Supplemental Figure 1). An estimated distance between the two lenses was 0.5mm, determined based on the IOL geometry and a dedicated spacer incorporated into the 3D-printed holder, which had a designed gap of 1.2 mm. The printing accuracy was approximately ±0.1mm. This resulting distance was comparable to the separation found between phakic IOLs and the crystalline lens (0.609±0.165mm) in the literature.²³

The optical quality of the phakic IOLs was evaluated with the Laboratory’s OptiSpheric IOL PRO2 (Trioptics GmbH, Wedel, Germany), with its design adhering to ISO 11979-2.^24,25 Two samples of each phakic IOL were tested for all experiments after placing them in a balanced salt solution (BSS, Bausch+Lomb, United States). Two samples sufficed for the experiments given the OptiSpheric’s accuracy against a reference lens (2% for MTF testing)²⁶ and the lab’s previous studies indicating high reproducibility^27,28 and repeatability²⁹ of the optical quality of IOLs, regardless of type or refractive power, using the laboratory’s OptiSpheric. Measurements were conducted with a photopic filter, and 3.0- and 4.5-mm apertures. A corneal model with 0.27µm of spherical aberration at 5.15mm was used representing the average value reported in the normal population,^22,28–31 and simulations were performed in polychromatic light to more closely mimic natural viewing conditions.

Image Quality Metrics

Variables measured with the setup included modulation transfer function (MTF). In addition to comparing the phakic IOLs’ MTF curves, the area under the curve of the MTFs (MTFa) up to 50 lp/mm with the simulated VA conversion was calculated using the methods outlined elsewhere.³² The through-focus MTF (TF MTF) was compared at 25, 50, and 100 lp/mm. Lastly, the 1951 USAF resolution test images were recorded. The results were graphed and analyzed with custom-made software (MATLAB, MathWorks, USA).

Results

Figure 2 shows the MTF levels of the IPCL and Artiplus phakic IOLs for a 3mm pupil measured at far, intermediate, and near focus. At this aperture, the lenses showed close MTF values at all distances.

Supplemental Figure 2 shows the TF MTF of the tested phakic IOLs for a 3mm pupil at 25, 50, and 100 lp/mm at a defocus range of 1 to −3D at the spectacle plane. At all tested frequencies, both the IPCL and Artiplus IOLs had a primary peak at 0D. At approximately −1.9D, IPCL had a higher secondary peak compared to Artiplus, but at the expense of a lower contrast at the intermediate range with a steep decline from the primary to the secondary focus. Given IPCL being a diffractive phakic IOL, such a bimodal shape of the TF MTF curve is expected.

Figure 2 Modulation transfer function curves of the tested lenses at three foci for a 3mm aperture. The tested foci included best far, intermediate, and near focus. The dotted lines show the values of each lens separately; the solid lines refer to the average of two lenses. Abbreviation: MTF, modulation transfer function.

Figure 3 presents the MTFa and simulated VA (logMAR) for the two lenses at a 3mm aperture. The two lenses had a similar primary peak at 0D, but IPCL had a second primary peak at approximately −1.9D. At an intermediate defocus of −1D, Artiplus showed a higher MTFa (0.32 versus 0.25) and better simulated VA (0.05 versus 0.13logMAR) than the IPCL.

Figure 3 The area under MTF curve and simulated VA of the tested lenses at 3mm aperture. The MTFa and simVA are graphed as a function of spectacle defocus. The dotted lines show the values of each lens separately; the solid lines refer to the average of two lenses. Abbreviations: MTFa, area under the modulation transfer function; simVA, simulated visual acuity.

At a 4.5mm aperture as shown in Figure 4, the MTF level of lenses at far, intermediate, and near focuses showed decreased values compared to the 3.0mm aperture, due to the presence of corneal spherical aberration. Notably at the near focus, IPCL had a lower MTF at all spatial frequencies compared to the Artiplus lens with the 4.5mm aperture, indicating a deficiency in near performance at higher apertures.

With the 4.5mm aperture, TF MTF values of the lenses at 25, 50, and 100 lp/mm decreased for all lenses compared to the 3.0mm aperture (Supplemental Figure 3). Still, both models preserved their multifocal properties extending the depth of focus at 4.5mm.

Figure 4 Modulation transfer function curves of the lenses at three foci for a 4.5mm aperture. The tested foci included best far, intermediate, and near focus. The dotted lines show the values of each lens separately; the solid lines refer to the average of two IOLs. Abbreviaton: MTF, modulation transfer function.

Nevertheless, the IPCL’s tolerance to hyperopic and negative defocus appeared further reduced at the extreme ends of the MTFa and simulated VA presented in Figure 5, demonstrating a steeper decline in its optical quality. Artiplus demonstrated a bimodal simulated VA with peaks of 0.05logMAR at −0.5D and 0.13logMAR at −2.4D. In contrast to the Artiplus, IPCL demonstrated a narrower simulated VA curve with a primary peak of 0.05logMAR at −0.25D. Testing with larger apertures also revealed that the optical performance of both the IPCL and the Artiplus was comparable in the intermediate range, with the two curves overlapping at −1.0D, which contrasts with the lens IPCL performance measured at 3mm.

Figure 5 The area under MTF curve and simulated VA of the tested lenses at 4.5mm aperture. The MTFa and simVA are graphed as a function of spectacle defocus. The dotted lines show the values of each lens separately; the solid lines refer to the average of two lenses. Abbreviations: MTFa, area under the modulation transfer function; simVA, simulated visual acuity.

The USAF resolution target images presented in Figure 6 confirmed the MTFa results. At −1.0D, Artiplus has better image resolution than IPCL with the 3.0mm aperture, while its resolution became more similar to IPCL at the 4.5mm aperture. At −2.0D with the 3.0mm aperture, IPCL had a better image resolution than the Artiplus, but at the same defocus value with the 4.5mm aperture, IPCL had a worse contrast than the Artiplus. Overall, at both pupil sizes, especially the 4.5mm size, Artiplus had an improved image quality at the ends of the defocus range, compared to the IPCL.

Figure 6 The United States Air Force target images for tested lenses across defocus range. The defocus range included +1.0D to −3.0D, at 0.5D increments at 3-mm and 4.5-mm apertures.

Discussion

Given phakic IOL’s recent introduction to presbyopia treatment, the literature on laboratory studies evaluating such lenses is still limited. Our study tested and compared the optical performance of refractive versus diffractive phakic IOLs – IPCL (+2.5D add) and Artiplus – at 3.0 and 4.5mm apertures for surgical management of presbyopia. We demonstrated good optical quality of the two models across the studied focus range, with the Artiplus providing a flatter simulated defocus curve. While expected differences in VA between the two approaches were minimal, they may become more pronounced in patients with larger pupils.

Our study’s MTF values of the IPCL with +2.5D added power at the 3.0mm aperture decreased with spatial frequency, and the curves decreased to lower MTF values with an increased aperture size of 4.5mm. The IPCL phakic IOL for presbyopia has been studied in a laboratory by Yu et al with additional powers of 2D and 4D at a 3.0mm aperture.³³ Yu et al found the MTF values at 100 cycles/mm to be 27% and 24% with the 2D and 4D add powers respectively, compared to our study with MTF values closer to 11% at 100 cycles/mm. The reason for this discrepancy and the lower MTF value reported in our study results from differences in the optical setups applied in both studies. The primary factor limiting the IOL performance using our approach is the presence of corneal spherical aberration. In contrast, the corneal lens used by Yu et al was designed to minimize spherical aberration, as inferred from its resemblance to the corneal model outlined in the ISO standard. Another contributing factor is the use of polychromatic light in our evaluation of IOL performance. By contrast, the optical bench used by Yu et al employed a 546 nm light source, which is free of chromatic aberration effects and may therefore yield higher objective quality metrics.²⁸ However, in agreement with our study, they found that the IPCL MTF levels gradually worsen with increasing apertures. This change was also seen in a prospective cohort study by Stodulka et al where highly myopic patients undergoing presbyopic treatment with IPCL had difficulty seeing under dim light conditions.¹⁷ They found the mean uncorrected distance visual acuity (UDVA) to be 0.11logMAR, with uncorrected near visual acuity (UNVA) improving to J1 for 15 of 17 eyes as the other 2 eyes were J1 at baseline. Schmid and Luedtke retrospectively studied the use of IPCL for presbyopia treatment in 16 eyes of 8 patients and found 9 out of 16 to be emmetropic with UDVA of at least 0.1logMAR with no need for reading glasses at one-month post-operation.¹⁴ Similarly, in our study, with apertures of 3.0 and 4.5mm, we respectively found the simulated VA to be −0.01logMAR and 0.07logMAR at distance. At the near focus, ie, at −2D, we found simulated VA to be 0.03 and 0.16logMAR for the two apertures respectively, which may show a lack of need for reading glasses. Overall, based on our and other studies, we can conclude that IPCL for the treatment of presbyopia can result in significantly improved near and far distances, but the len’s design appears to be susceptible to pupil-size changes.

The Artiplus lens studied is currently being clinically investigated by Güel et al as part of a prospective non-controlled multicenter clinical trial.¹⁸ The one-year clinical trial has shown that at 6 months post-operation, mean monocular UDVA, uncorrected intermediate VA (UIVA) at 80cm, and UNVA at 40cm were 0.01±0.08, 0.03±0.08, and 0.07±0.09logMAR respectively, with binocular UDVA, UIVA, and UNVA being −0.06±0.08, −0.01±0.07, and 0.02±0.08logMAR respectively.³⁴ The results of this study appear to agree with ours for far and intermediate, but not fully for near distance. With the 3mm aperture, we found the simulated VA to be approximately −0.02, 0.06, and 0.12 logMAR at far, intermediate, and near focuses (respectively 0, −1.25, and −2.5 defocus values). It is important to note; however, that our results simulate the scenario of complete accommodation loss, which can differ from real-world clinical cases. In practice, the loss of accommodation is a gradual process, and patients receiving such lenses often retain some ability to accommodate.³⁵ Laboratory studies thus can predict the maximum lens-related depth-of-focus improvement that patients may experience at various distances, with possibly better outcomes for those whose lenses may still have residual accommodation.

Lastly, our work did not study the EVO Visian Implantable Collamer Lens by STAAR Surgical (Monrovia, California, USA). This lens is a collagen and poly-hydroxyethyl methacrylate iris-fixated refractive phakic IOL with dioptric powers ranging from −0.5 to –18.0D.³⁶ It has a plate-haptic design with a central convex/concave optical zone ranging from 4.9 to 5.8mm diameter and a 0.36mm diameter central port allowing aqueous flow.^36,37 The STAAR phakic IOL for the treatment of presbyopia has been studied prospectively by Rateb et al showing uncorrected VA improving from 1.3±0.06logMAR to 0.76±0.2logMAR post-operatively.³⁸ Alfonso et al studied the STAAR lens to correct moderate to high myopia and presbyopia and found postoperative UDVA and corrected DVA (CDVA) values of 0.09 ± 0.19 and 0.02 ± 0.03logMAR, following bilateral implantation in 40 patients.³⁹ To be able to offer a comprehensive review of phakic IOL options available for patients with presbyopia, future studies comparing the STAAR phakic IOL to the Artiplus and IPCL phakic IOLs can be significantly beneficial.

In addition to the range of vision, which typically distinguishes presbyopia-correcting IOL solutions, another key differentiating factor is the occurrence and severity of photic phenomena. These unwanted light effects involve the perception of glare, halos, or starbursts when looking at light sources, such as streetlights or headlights of cars at night.⁴⁰ In studying presbyopia-correcting IOLs, literature has found photic phenomena to greatly vary between lens types, and to be one of the most common complaints of patients undergoing IOL procedures – as high in 32.9% of eyes found by de Vries et al.^40,41 Generally, a lower incidence of photic phenomena has been associated with the refractive rather than the diffractive principle in the context of multifocal IOLs implanted into the capsular bag.⁴² It is of interest to confirm whether this can also be observed in the context of phakic multifocal IOLs. Therefore, by studying photic phenomena rates with phakic IOLs and their comparison to other methods of presbyopia treatment, we can gather more information on the rate of side effects associated with phakic IOLs, which warrants further clinical and laboratory investigations. Additionally, due to the limitation of the OptiSpheric setup, this study did not evaluate the effects of IOL decentration or tilt on the IOL performance– factors that have been shown to impact visual outcomes resulting in symptoms such as glare or visual halos.^43,44 Future studies on the impact of tilt and decentration on phakic IOL outcomes may add insights into the side effects of such IOLs.

Conclusion

Our study evaluated and contrasted the optical quality of diffractive versus refractive phakic IOL models – IPCL with added power of 2.5D and Artiplus – for the management of presbyopia at near, intermediate, and far distances simulating various pupil sizes. We found that both IPCL and Artiplus can effectively expand the range of vision, potentially alleviating visual symptoms in presbyopic patients and restoring vision at intermediate and near distances. Although the optical quality of both models was comparable at a 3mm pupil size, an increase to 4.5mm led to reduced defocus tolerance, with the IPCL model appearing more affected. While our study aids in directly comparing the two models and choosing a phakic IOL more appropriate based on patients’ individualized needs, it still needs to be considered that lens performance may differ under in vivo conditions due to the interaction between the IOL optics and the eye’s intrinsic aberrations and residual accommodation. Future studies evaluating the impact of these aspects and the perception of photic phenomena in presbyopic patients undergoing phakic IOL implantation can provide physicians and patients with a more comprehensive understanding of their treatment options.

Abbreviations

BSS, balanced salt solution; CDVA, corrected distance visual acuity; D, diopters; IPCL, implantable phakic contact lens; IOL, intraocular lens; MTF, modulation transfer function; MTFa, area under the modulation transfer function; TF MTF, through-focus modulation transfer function; UDVA, uncorrected distance visual acuity; UIVA, uncorrected intermediate visual acuity; UNVA, uncorrected near visual acuity; VA, visual acuity.

Data Sharing Statement

The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising, or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Funding

Supported by a research grant from OPHTEC BV, Groningen, The Netherlands. The David J Apple Laboratory receives support from the Klaus Tschira Foundation, Heidelberg, Germany.

Disclosure

GU Auffarth reports grants, personal fees, non-financial support and consulting fees from Afidera, Johnson&Johnson and Alcon, grants, personal fees, and non-financial support from Carl Zeiss Meditec, Hoya, Kowa, Oculentis/Teleon, Rayner, Santen, Sifi, Ursapharm, grants, and personal fees from Biotech, Oculus, EyeYon grants from Acufocus, Anew, Contamac, Glaukos, Physiol, Rheacell, outside the submitted work. The University of Heidelberg holds a patent application (No. WO2024/023230) entitled “Lens with extended depth of focus by inducing an excess of longitudinal chromatic aberration,” with GU Auffarth and G Łabuz as inventors. G Łabuz reports non-financial support from Contamac outside the submitted work. R Khoramnia reports grants, personal fees, and non-financial support from Alcon, Johnson&Johnson, Hoya, Physiol, Rayner, personal fees, and non-financial support from Kowa, Ophtec, Oculentis/Teleon, Santen, Staar, 1stQ, BVI, Zeiss, SIFI, and Acufocus, outside the submitted work. The remaining authors have nothing to disclose.

References

1. Frick KD, Joy SM, Wilson DA, Naidoo KS, Holden BA. The global burden of potential productivity loss from uncorrected presbyopia. Ophthalmology. 2015;122(8):1706–1710. doi:10.1016/j.ophtha.2015.04.014

2. Schwiegerling J. Refractive and diffractive principles in presbyopia-correcting IOLs – an optical lesson. Available from: https://us.alconscience.com/sites/g/files/rbvwei1736/files/pdf/Refractive-and-Diffractive-Principles-in-Presbyopia-Correcting-IOLs-An-Optical-Lesson-US-REF-1900001.pdf. Accessed August 14, 2025.

3. Namdev V, Kaur M, Sharma VK, Mulay A, Raj R, Titiyal JS. Current paradigms in refractive surgery. Med J Armed Forces India. 2024;80(5):497–504. doi:10.1016/j.mjafi.2024.08.003

4. Kumar K, Kohli P, Babu N, Khare G, Ramasamy K. Incidence and management of rhegmatogenous retinal detachment after pars plana vitrectomy and sutureless scleral-fixated intraocular lens. Indian J Ophthalmol. 2020;68(7):1432–1435. doi:10.4103/ijo.IJO_1974_19

5. Jafarinasab M, Kalantarion M, Hooshmandi S, et al. Indications and outcomes of intraocular lens exchange among pseudophakic eyes in a Tertiary Referral Center. BMC Ophthalmol. 2023;23(1):127. doi:10.1186/s12886-023-02871-y

6. Rodríguez-calvo-de-mora M, Rocha-de-lossada C, Rodríguez-Vallejo M, Zamora-de-la-cruz D, Fernández J. Retinal detachment after refractive lens exchange: a narrative review. Archivos de la Sociedad Española de Oftalmología. 2023;98(9):507–520. doi:10.1016/j.oftale.2023.06.013

7. Vasavada V, Srivastava S, Vasavada SA, Sudhalkar A, Vasavada AR, Vasavada VA. Safety and efficacy of a new phakic posterior chamber IOL for correction of myopia: 3 years of follow-up. J Refract Surg. 2018;34(12):817–823. doi:10.3928/1081597X-20181105-01

8. Kamiya K, Shimizu K, Igarashi A, et al. Posterior chamber phakic intraocular lens implantation: comparative, multicentre study in 351 eyes with low-to-moderate or high myopia. Br J Ophthalmol. 2018;102(2):177–181. doi:10.1136/bjophthalmol-2017-310164

9. Sachdev GS, Singh S, Ramamurthy S, Rajpal N, Dandapani R. Comparative analysis of clinical outcomes between two types of posterior chamber phakic intraocular lenses for correction of myopia and myopic astigmatism. Indian J Ophthalmol. 2019;67(7):1061–1065. doi:10.4103/ijo.IJO_1501_18

10. Pérez-Vives C, Ferrer-Blasco T, Cerviño-Expósito A, Madrid-Costa D, Montés-Micó R. Simulated prototype of posterior chamber phakic intraocular lens for presbyopia correction. J Cataract Refract Surg. 2015;41(10):2266–2273. doi:10.1016/j.jcrs.2015.10.050

11. Ferraz CA, Allemann N, Chamon W. Phakic intraocular lens for presbyopia correction. Arq Bras Oftalmol. 2007;70(4):603–608. doi:10.1590/s0004-27492007000400009

12. Alió JL, Mulet ME. Presbyopia correction with an anterior chamber phakic multifocal intraocular lens. Ophthalmology. 2005;112(8):1368–1374. doi:10.1016/j.ophtha.2005.02.029

13. Baïkoff G, Matach G, Fontaine A, Ferraz C, Spera C. Correction of presbyopia with refractive multifocal phakic intraocular lenses. J Cataract Refract Surg. 2004;30(7):1454–1460. doi:10.1016/j.jcrs.2003.12.051

14. Schmid R, Luedtke H. A novel concept of correcting presbyopia: first clinical results with a phakic diffractive intraocular lens. Clin Ophthalmol. 2020;14:2011–2019. doi:10.2147/OPTH.S255613

15. Bianchi GR, Paredes A, Puccio B, Parra-Hernández A. Implantable phakic contact lens: vault evaluation 5 years postoperatively. J Cataract Refract Surg. 2024;50(10):1000–1005. doi:10.1097/j.jcrs.0000000000001496

16. Takahashi M, Kamiya K, Shoji N, Kato S, Igarashi A, Shimizu K. Intentional undercorrection by implantation of posterior chamber phakic intraocular lens with a central hole (Hole ICL) for early presbyopia. Biomed Res Int. 2018;2018:6158520. doi:10.1155/2018/6158520

17. Stodulka P, Slovak M, Sramka M, Polisensky J, Liska K. Posterior chamber phakic intraocular lens for the correction of presbyopia in highly myopic patients. J Cataract Refract Surg. 2020;46(1):40–44. doi:10.1097/j.jcrs.0000000000000033

18. Truong D. Ophtec’s artiplus shows promising one-year clinical results. CAKE. 2024. Available from: https://cakemagazine.org/ophtecs-artiplus-shows-promising-one-year-clinical-results/. Accessed November 1, 2024.

19. Artiplus. Available from: https://www.ophtec.com/product-overview/artiplus. Accessed November 2, 2024.

20. Care Group. Available from: https://caregroupiol.com/products/phakic-lenses/ipcl/. Accessed November 2, 2024.

21. Spectrum Ophthalmics. IPCL – the customised refractive solution. Available from: https://www.spectrumophthalmics.uk/app/uploads/2022/08/IPCL-Presbyopic-Surgeons-Brochure.pdf. Accessed August 14, 2025.

22. Wang L, Dai E, Koch DD, Nathoo A. Optical aberrations of the human anterior cornea. J Cataract Refract Surg. 2003;29(8):1514–1521. doi:10.1016/s0886-3350(03)00467-x

23. Du C, Wang J, Wang X, Dong Y, Gu Y, Shen Y. Ultrasound biomicroscopy of anterior segment accommodative changes with posterior chamber phakic intraocular lens in high myopia. Ophthalmology. 2012;119(1):99–105. doi:10.1016/j.ophtha.2011.07.001

24. Łabuz G, Yan W, Baur ID, Khoramnia R, Auffarth GU. Chromatic aberration and spectral dependency of extended-range-of-vision intraocular lens technology. Sci Rep. 2023;13(1):14781. doi:10.1038/s41598-023-41634-z

25. ISO 11979-2:2014. ISO. Available from: https://www.iso.org/standard/55682.html. Accessed October 10, 2024.

26. TRIOPTICS GmbH. Technische Daten OptiSpheric^® AF 500. INV; 2019. Available from: www.trioptics.com. Accessed August 14, 2025.

27. Son HS, Tandogan T, Liebing S, et al. In vitro optical quality measurements of three intraocular lens models having identical platform. BMC Ophthalmol. 2017;17:108. doi:10.1186/s12886-017-0460-0

28. Lee Y, Łabuz G, Son HS, Yildirim TM, Khoramnia R, Auffarth GU. Assessment of the image quality of extended depth-of-focus intraocular lens models in polychromatic light. J Cataract Refract Surg. 2020;46(1):108–115. doi:10.1097/j.jcrs.0000000000000037

29. Łabuz G, Papadatou E, Khoramnia R, Auffarth GU. Longitudinal chromatic aberration and polychromatic image quality metrics of intraocular lenses. J Refract Surg. 2018;34(12):832–838. doi:10.3928/1081597X-20181108-01

30. Łabuz G, Auffarth GU, Knorz MC, Son HS, Yildirim TM, Khoramnia R. Trifocality achieved through polypseudophakia: optical quality and light loss compared with a single trifocal intraocular lens. J Refract Surg. 2020;36(9):570–577. doi:10.3928/1081597X-20200715-01

31. Łabuz G, Son HS, Naujokaitis T, Yildirim TM, Khoramnia R, Auffarth GU. Laboratory Investigation of Preclinical Visual-Quality Metrics and Halo-Size in Enhanced Monofocal Intraocular Lenses. Ophthalmol Ther. 2021;10(4):1093–1104. doi:10.1007/s40123-021-00411-9

32. Alarcon A, Canovas C, Rosen R, et al. Preclinical metrics to predict through-focus visual acuity for pseudophakic patients. Biomed Opt Express. 2016;7(5):1877–1888. doi:10.1364/BOE.7.001877

33. Yu C, Kamiya K, Kawamorita T. Modulation transfer function of implantable phakic intraocular contact lens (IPCL) for myopia and presbyopia. Graefes Arch Clin Exp Ophthalmol. 2024;262(10):3201–3206. doi:10.1007/s00417-024-06539-1

34. Ophtec. Artiplus Model 470. Available from: https://www.ophtec.com/product-overview/artiplus. Accessed October 30, 2024.

35. Pérez-Prados R, Piñero DP, Pérez-Cambrodí RJ, Madrid-Costa D. Soft multifocal simultaneous image contact lenses: a review. Clin Exp Optometry. 2017;100(2):107–127. doi:10.1111/cxo.12488

36. STAAR Surgical. EVO Visian Implantable Collamer Lens; 2021. Available from: https://edfu.staar.com/edfu/5c784538fd5dd20001d67c89/ICL%20eDFU’s/eDFU-0016_Rev_01_EVO%20Visian%20ICL.pdf. Accessed August 14, 2025.

37. Packer M. Evaluation of the EVO/EVO+ sphere and toric visian ICL: six month results from the United States Food and Drug Administration Clinical Trial. Clin Ophthalmol. 2022;16:1541–1553. doi:10.2147/OPTH.S369467

38. Rateb M, Gad AAM, Tohamy D, Elmohamady MN. A prospective comparative study between implantable phakic intraocular contact lens and implantable Collamer lens in treatment of myopia in adults. J Ophthalmol. 2022;2022:9212253. doi:10.1155/2022/9212253

39. Alfonso JF, Fernández-Vega-Cueto L, Lisa C, Alfonso-Bartolozzi B, Palacios A, Madrid-Costa D. Clinical and aberrometric outcomes of a new implantable Collamer lens for myopia and presbyopia correction in phakic patients. J Refract Surg. 2023;39(9):589–596. doi:10.3928/1081597X-20230726-02

40. Ukai Y, Okemoto H, Seki Y, et al. Quantitative assessment of photic phenomena in the presbyopia-correcting intraocular lens. PLoS One. 2021;16(12):e0260406. doi:10.1371/journal.pone.0260406

41. de Vries NE, Webers CAB, Touwslager WRH, et al. Dissatisfaction after implantation of multifocal intraocular lenses. J Cataract Refract Surg. 2011;37(5):859–865. doi:10.1016/j.jcrs.2010.11.032

42. Łabuz G, Khoramnia R, Naujokaitis T, Auffarth GU. Optical benchtop evaluation of special intraocular lens optics. Ophthalmologie. 2024;121(9):698–705. doi:10.1007/s00347-024-02064-y

43. Ashena Z, Maqsood S, Ahmed SN, Nanavaty MA. Effect of intraocular lens tilt and decentration on visual acuity, dysphotopsia and wavefront aberrations. Vision. 2020;4(3):41. doi:10.3390/vision4030041

44. Chen XY, Wang YC, Zhao TY, et al. Tilt and decentration with various intraocular lenses: a narrative review. World J Clin Cases. 2022;10(12):3639–3646. doi:10.12998/wjcc.v10.i12.3639

Leon Neal/Getty Images

‘Support they need’

Total Knee Arthroplasty (TKA) is an orthopedic surgical procedure that replaces a damaged human joint with a prosthesis made of artificial materials. TKA aims to alleviate joint pain, instability, deformities, and severe functional impairment caused by various types of arthritis, traumatic arthritis, and non-pyogenic arthritis, thereby reconstructing a joint with near-normal functionality and enhancing joint performance. Recognized as the safest and most effective treatment for alleviating pain and improving limb function in patients with knee arthritis, the utilization of TKA has been on a steady rise, increasing annually by 5% to 17%.¹ However, systematic reviews indicate that only 3 randomized controlled trials (RCTs) with a total sample size of less than 100 participants have evaluated the efficacy of MET in post-TKA rehabilitation. These studies suggest limited evidence regarding the efficacy of MET post-TKA, warranting further investigation into its impact on functional recovery. Despite undergoing TKA, many patients still experience suboptimal functional recovery, which is primarily characterized by persistent postoperative pain, joint stiffness, and limited ability to perform daily activities.^2–4 Conventional rehabilitation methods have not significantly improved postoperative knee joint mobility, possibly due to early postoperative symptoms like pain and swelling.⁴ Hence, with the increasing number of patients undergoing TKA (growing annually by 5–17%), implementing effective early rehabilitation training is crucial for enhancing postoperative knee joint function and improving the quality of life for TKA patients.

Muscle Energy Technique (MET) is a manipulative treatment targeting disorders of the soft tissues, muscles, and skeletal system. It involves precise therapist-controlled direction and force application, coupled with active patient participation, utilizing isometric muscle contractions to mitigate pain, stretch tight muscles and fascia, reduce muscle rigidity, improve local blood circulation, strengthen weak muscles, and increase mobility in stiff joints. Common MET techniques include Reciprocal Inhibition (RI), Contract Relax (CR), Contract Relax Antagonistic Contraction (CRAC), and Annulare Muscle Energy Technique (A-MET), each serving distinct purposes. For instance, RI primarily relaxes agonist muscles through the active contraction of antagonist muscles, thereby increasing joint Range of Motion (ROM) and reducing adhesions in joints, ligaments, and fascia. CR involves isometric contraction of the agonist muscle, causing tendon tissues to stretch, passively elongating and alleviating abnormal collagen tissue adhesions, thereby releasing collagen in tendons and facilitating more freedom in muscle fiber contraction and extension, along with enhanced mobility in the connected fibrous tissue.⁵

MET has gained widespread recognition in global fields of rehabilitation medicine, rehabilitative therapy, and sports rehabilitation. Its primary treatment targets include individuals with sports injuries, post-traumatic injuries from traffic accidents, chronic injury-related pain complications, and patients with limb joint functional impairments. As China’s aging population grows, the incidence of knee arthritis is also increasing and is expected to continue to rise significantly. However, the effectiveness of existing post-TKA rehabilitation methods in China is inadequate for achieving rehabilitation goals. This study challenges traditional rehabilitation approaches by incorporating novel rehabilitation techniques. By comparing the effects of conventional rehabilitation methods (Routine Rehabilitation Treatment, RRT) and Muscle Energy Technique (MET) on knee joint functional rehabilitation in post-TKA patients, the study explores the impact of MET on functional recovery and long-term prognosis in these patients. The findings not only optimize the rehabilitation treatment pathway, providing more effective rehabilitation methods for TKA patients, but also align with the current objectives of “Healthy China 2030”, playing a significant role in improving postoperative functional recovery and the quality of life for patients.

Clinical Data and Methodology

Baseline Data Patient Records

The study selected 80 patients who underwent Total Knee Arthroplasty (TKA) between January 2021 and December 2021 at the Department of Orthopedics, The First Affiliated Hospital of Nanjing Medical University. All procedures were performed by the same team of doctors, utilizing prostheses of the same material provided by the same company, and followed a uniform postoperative treatment protocol.

Sample Size Calculation

Based on ROM data (α=0.05, β=0.2), A sample size of 36 patients per group was required to achieve adequate statistical power, with 40 patients enrolled per group to account for potential dropout. The actual study included 36 patients in the MET group and 42 patients in the RRT group, which was slightly different from the planned 36/group.

Inclusion Criteria

a. Patients diagnosed with osteoarthritis undergoing unilateral Total Knee Arthroplasty; b. Patients undergoing Total Knee Arthroplasty for the first time; c. Patients aged between 50 and 80 years; d. Patients with good compliance, capable of participating in functional exercises; e. Patients willing to participate in the study, agree to follow-up appointments, and provide signed informed consent.

Exclusion Criteria

a. Patients with a history of knee surgery or rheumatoid arthritis; b. Patients with concurrent lower limb acute infection or other joint functional impairments; c. Patients with preoperative coagulation disorders or lower limb Deep Vein Thrombosis (DVT); d. Patients with consciousness, cognitive impairments, or severe mental illness. Elimination Criteria: a. Patients who need to discontinue the treatment plan for personal reasons; b. Patients who experience severe adverse reactions and are unable to adhere to the set treatment plan; c. Patients who withdraw from the clinical study midway; d. Patients who fail to attend scheduled clinic follow-ups, resulting in incomplete follow-up or assessment data.

Research Methodology

Prospective data collection was performed from January 2021 to December 2021, involving 80 patients who met the inclusion and exclusion criteria and underwent TKA at our facility. Block randomization (size=4) via opaque envelopes was employed to allocate patients into two groups. A computerized random number sequence was generated, and the allocation sequence was concealed in opaque, sequentially numbered envelopes. The assessors, who were blinded to group allocation, opened the envelopes according to the patient’s hospital admission order, ensuring a randomized and blinded assignment. The patients, in accordance with their hospital admission order, opened these envelopes and were subsequently randomly assigned to either the Muscle Energy Technique (MET) rehabilitation group or the conventional rehabilitation group.

The conventional rehabilitation treatment methods for the control group are as follows: Preoperative rehabilitation assessment, including the evaluation of muscle strength, Range of Motion (ROM), and circumference of different parts of the operative limb. Development of a rehabilitation plan based on the assessment results, which includes ankle pump dorsiflexion and plantarflexion exercises, muscle strength training, joint ROM exercises, gait training, and Activities of Daily Living (ADL) training. Muscle strength training, encompassing quadriceps muscle strength training, hamstring muscle strength training, and straight leg raise exercises. Each exercise is held for 10 seconds, with 20 repetitions per set and two sets conducted daily. Joint ROM exercises, involving both active and passive knee flexion exercises. Each exercise is held for 5 seconds, with 20 repetitions per set and two sets conducted daily. Gait training, which includes guidance on how to perform body position transitions, stand up from the ground, and walk correctly using a walker, all within the first 24 hours post-surgery. Rehabilitation evaluation, assessing the patient’s muscle strength, joint ROM, gait, walking distance, and ADL status after undergoing the rehabilitation training. The Muscle Energy Technique (MET) intervention rehabilitation treatment methods specifically implemented in the experimental group include:

The MET intervention comprised 2 sessions per day for 6 consecutive days during inpatient rehabilitation, followed by 3 sessions per week for 8 weeks during outpatient rehabilitation. Specifically, the intervention included Post-Isometric Relaxation (PIR) and Post-Facilitation Stretch (PFS) techniques to target the quadriceps muscle. These techniques aim to enhance neuromuscular activation by engaging Type II muscle fibers and improving the extensibility of antagonist muscles, ultimately leading to enhanced knee extension function. The specific implementation is as follows: The patient lies supine with the knee passively flexed to 15 degrees. The patient is instructed to perform isometric contractions of the quadriceps against resistance, followed by relaxation, then the therapist rapidly stretches to the next resistance point. Each quadriceps isometric contraction lasts 10 seconds, performed 10 times per set, with one stretch after completing a set and two sets per day. After each stretch, the knee extension angle is remeasured to maximize the improvement of knee extension limitations. Once the patient’s knee joint can fully extend, they are guided through regular muscle strength training, including isometric contractions of the quadriceps, assessing the strength of medial muscle contractions, ensuring proper contraction and relaxation of key muscles, straight leg raise exercises, active knee flexion exercises, and bedside passive knee flexion exercises. The training starts on the second day post-TKA and continues for six consecutive days until discharge, aiming to achieve full knee extension and mastery of the isometric contraction technique of the quadriceps. Eccentric contraction of the quadriceps combined with conventional straight leg raise training, which further strengthens the muscle strength of the knee extensors, activates the power of the quadriceps, particularly the strength of the vastus medialis muscle. This approach ensures more coordinated contraction within the different muscles of the quadriceps, laying the foundation for the completion of straight leg raise exercises. The specific implementation is as follows: The patient is guided to sit at the edge of the bed, actively extending the knee, then, under the therapist’s control, passively flexing the knee to 60 degrees. The patient exerts force toward the resistance point in the direction of stretch, and the therapist provides single-handed equal resistance (isometric contraction) or uses a sequential progressive resistance. The patient is instructed to extend the knee (isotonic contraction), activating the quadriceps muscle. The therapist rapidly stretches to the next resistance point, the patient extends the knee again, and the therapist observes the contraction response, especially in the position of the vastus medialis muscle, to ensure the quadriceps are in an activated state. Each resistance contraction lasts 5 seconds, followed by one stretch, repeated 10 times per set, with two sets per day. The training begins on the second day post-TKA and continues for six consecutive days until discharge. The goal is to correctly master the force application method of the adductor muscles of the thigh, activate the quadriceps early, and complete the straight leg raise training regimen.

Conventional Range of Motion (ROM) training followed by Reciprocal Inhibition (RI) technique (knee flexor muscle training) effectively stimulates the electrical response rate of knee flexor muscles and induces neuromuscular activation. This method also alleviates pain through reciprocal inhibition and stimulation of mechanoreceptors. The specific implementation is as follows: Before starting the therapy, the patient is seated at the edge of the bed with the thigh snug against the bed edge and the leg dangling. The therapist, facing the patient, stabilizes the operative thigh with one hand and places the other hand under the distal end of the affected calf. The patient is instructed to take deep breaths; if the thigh muscles of the operative limb are tense, they are gently tapped to induce relaxation. The patient is then guided to actively flex the knee for 5 seconds. Simultaneously, the therapist, while seated, places a hand on the patient’s posterior ankle, providing equal resistance against the patient’s hamstring muscle contraction. After maintaining the knee flexion resistance for 5 seconds, the therapist relaxes the pressure. When the patient’s muscles are balanced and coordinated, the therapist continually advances the joint’s range of motion until the highest resistance point of knee flexion is reached. Each resistance contraction lasts 5 seconds, with the joint’s range of motion advanced once. This is performed 10 times per set, with two sets per day. The training begins on the second day post-TKA and continues for six consecutive days until discharge. The objective is to correctly master the hamstring muscle’s force application method, activate the hamstring muscle early, and successfully complete the active knee flexion training regimen.

Observation Indicators

Knee Joint Active Range of Motion

The goniometer is used to measure the active range of motion of the patient’s knee joint, including the flexion angle in the supine and sitting positions, and the extension angle in the sitting position. Each movement is measured twice, and the best value is taken. Measurements are taken at 3 days, 7 days, 1 month, and 3 months, with a planned follow-up at 6 months.

Time Up and Go Test (TUG)

Initially, the patient sits on a chair 45 cm high. Timing starts when the patient stands up, walks 3 meters, turns, returns to the chair, and sits down again. The total time taken for this process is recorded. This scale is simple, easy to operate, and has high reliability and validity, making it suitable for evaluating short-term and long-term rehabilitation effects post-knee arthroplasty.¹ The TUG test is performed and recorded 7 days and 1 month postoperatively.

Hospital for Special Surgery (HSS) Knee Score

The HSS knee scoring system, proposed by the Hospital for Special Surgery in the USA, includes six dimensions: pain, function, range of motion, muscle strength, knee flexion deformity, and knee instability. Each question has five multiple-choice options, with the scores converted to a 100-point scale, where 0 points indicate the most severe symptoms, and 100 points indicate the least severe. The HSS knee scores are recorded 1 month and 3 months postoperatively.

Visual Analogue Scale for Pain (VAS)

A 10 cm ruler is used, divided into ten equal parts, with the ends labeled “0” and “10”, representing no pain and unbearable extreme pain, respectively. The middle part of the scale corresponds to the respective pain levels. Subjects assess their pain level based on their sensation and mark it on the appropriate scale. VAS scoring criteria: 0–2 points are considered “excellent”, 3–5 points “good”, 6–8 points “fair”, and 8–10 points “poor”. VAS pain scores are recorded at 3 days, 7 days, 1 month, and 3 months postoperatively.

Statistical Methods

All clinical research data are recorded in a standardized observation chart created with Microsoft Excel and are managed by a dedicated person responsible for clinical data. Analysis is conducted using SPSS software version 22.0. For comparing quantitative data between two groups, repeated-measures ANOVA was employed to account for time-related effects and group differences. Paired-sample t-tests were utilized to compare pre- and post-treatment outcomes within each group, with a significance level set at P < 0.05. All measurement data should fit a normal or approximately normal distribution and are presented as mean ± standard deviation. The independent samples t-test is used for analyzing the aforementioned indicators, with P < 0.05 considered statistically significant.

Results

MET Significantly Enhances Patients’ Knee Joint ROM

The range of motion (ROM) of the knee joint can reach 135 degrees during flexion and 0 degrees during extension, with internal and external rotation angles being approximately 10 degrees each. Limited joint mobility may be a result of knee injuries or degeneration. When the quadriceps muscles are weak, complete extension of the knee joint is not possible. This study compared the intergroup effects, time effects, and interaction effects on the ROM of the knee joint post-TKA between the two patient groups. As indicated in Table 1, the experimental results were statistically significant (P < 0.001). The results of the repeated-measures ANOVA demonstrated that, over time, the active ROM of the knee joint in the experimental group was significantly superior to that in the control group (P < 0.001). Notably, on the third day post-surgery, the knee joint activity degree of the patients in the experimental group was 19.3% higher than that in the control group. These results suggest that, compared to conventional rehabilitation methods, the rehabilitation treatment utilizing MET can significantly improve the ROM of the knee joint in patients post-TKA (Figure 1).

Figure 1 Comparison results of ROM (Range of Motion) between the two groups of patients.

MET Does Not Improve Patients’ TUG Scores

This study compared the Time Up and Go (TUG) test scores post-TKA between the two patient groups, and the experimental results are presented in Table 2. The data reveal that there was no significant difference in the TUG scores between the two groups one month post-surgery (P > 0.05), indicating no statistical significance. However, the TUG scores three months post-surgery were statistically significant (P < 0.001), with the scores of the Routine Rehabilitation Treatment (RRT) group being higher than those of the MET group. These results suggest that, compared to conventional rehabilitation methods, the MET rehabilitation approach does not enhance patients’ TUG scores.

Table 2 Comparison of Time Taken for the Timed Up and Go (TUG) Test After Intervention Between Two Groups of Patients () Unit: seconds

MET Significantly Improves Patients’ HSS Scores

This study compared the differences in the Hospital for Special Surgery (HSS) scores between the two patient groups, focusing on intergroup effects, time effects, and interaction effects. The scoring results, as shown in Table 3, were statistically significant (P < 0.001). The data indicate that before the commencement of the rehabilitation treatment, the scores of both groups were similar. However, as time progressed, one month post-intervention, the HSS scores of patients in the MET group were 22.2% higher than those in the RRT group; and three months post-intervention, the HSS scores in the MET group still surpassed those in the RRT group by 14.2%. These results demonstrate that, compared to conventional treatment methods, the MET rehabilitation approach can significantly enhance patients’ postoperative HSS scores, and this improvement is sustained over time.

Table 3 Comparison of HSS Scores Before and After Intervention Between Two Groups of Patients () Unit: Points

MET Significantly Reduces Postoperative VAS in Patients

Postoperative pain management is one of the critical factors affecting early mobility in patients undergoing Total Knee Arthroplasty (TKA), and effective postoperative analgesia can reduce hospital stay duration and medical expenses. This study compared the postoperative pain conditions between the two patient groups. The differences in pain scores between the groups, considering intergroup effects, time effects, and interaction effects, were statistically significant (P < 0.001), indicating different therapeutic effects from the two intervention measures. Over time, the condition of knee joint pain in patients in the MET group was better than that in the control group. The differences in pain levels at 3 days, 7 days, one month, and three months post-surgery for both groups are presented in Table 4. The data clearly indicate that patients who underwent rehabilitation with the MET method experienced a significant reduction in knee joint pain perception. On the third day post-surgery, the pain scores in the conventional group were 1.34 times higher than those in the MET group; three months post-surgery, the pain scores in the conventional group were 3.67 times higher than those in the MET group. The results of this study indicate that using the MET method for patient rehabilitation can significantly suppress postoperative pain in patients. Moreover, this suppressive effect becomes more pronounced as the recovery time increases.

Table 4 Comparison of Knee Joint Pain Scores Between Two Groups of Patients () Unit: Points

Discussion

Currently, domestic rehabilitation techniques for Total Knee Arthroplasty (TKA) primarily include isometric muscle contraction, isometric resistance contraction, active and passive Range of Motion (ROM) training, Continuous Passive Motion (CPM) device training for sustained passive activity, gait training, and more.⁶ Singular isometric contraction training, however, may not sufficiently activate muscle strength and lacks coordination during contraction and relaxation. ROM training without resistance can lead to inadequate active knee flexion strength, failing to aid in patient recovery effectively. Additionally, post-TKA patients may exhibit exercise-induced muscle force errors due to kinesiophobia, leading to compensatory movements, making it challenging to control the direction of force application, rendering the exercise ineffective and failing to achieve the true purpose of the exercise. The hallmark of the Muscle Energy Technique (MET) is its active, gentle, and non-impactful nature. During the alternating active contraction and relaxation of muscles, the soft tissues surrounding the joint form a spiraling and unwinding effect. The therapeutic characteristic of this technique necessitates the active participation of the patient, continuous cooperation during treatment, and muscle contractions of specific degrees and directions as set by the operator. Various muscle contraction methods, including isometric, concentric, and eccentric contractions, are often combined in application. This training can improve tissue fluid metabolism, accelerate the synthesis of new cells, promote tissue fiber repair and strengthening, improve joint angles, relax tense muscles and fascia, alleviate pain, balance the muscle strength around the joint, and restore the normal biomechanics of the joint and surrounding tissues.^5,7

TKA is regarded as one of the surgeries with significant effects on severe knee joint diseases, capable of reconstructing knee joint function and alleviating knee pain. However, the incidence of severe postoperative pain after TKA can be as high as 60%, lasting 48–72 hours, and may even develop into chronic pain.⁸ Some patients experience pain, knee joint dysfunction, and muscle weakness after TKA, severely affecting their ability to walk. Postoperative pain can severely impede the recovery of knee joint function and even affect patients’ daily lives. Studies suggest that MET can alleviate patients’ pain through mechanisms such as stimulating mechanoreceptors or reciprocal inhibition, and strength training of the quadriceps can improve the motor function of the knee joint.⁹ This conclusion aligns with the experimental group’s knee joint pain score results, and our experimental findings indicate that MET significantly alleviates patients’ pain with a sustained effect (remaining significant after three months). Starting from the third day post-surgery, each test result showed that the pain scores of patients in the experimental group were significantly lower than those in the control group. Currently, MET is widely used domestically and internationally for soft tissue pain treatment, such as for muscle strains, lateral epicondylitis of the humerus,⁷ periarthritis of the shoulder¹⁰, piriformis syndrome¹¹, and elbow joint stiffness¹². Recently, MET has also been applied for functional rehabilitation training post-ACL reconstruction¹³, post-meniscus repair surgery¹⁴, and more, though the literature is sparse and further exploration in knee joint applications is needed.

This experiment has direct evidence indicating that MET can enhance active knee joint mobility, accelerate knee joint recovery, and alleviate pain. Therefore, compared to conventional rehabilitation treatments, MET is considered to have better therapeutic effects, shorter recovery periods, and higher patient satisfaction. Thus, MET can be regarded as a rehabilitation treatment method for TKA patients worthy of widespread promotion and application.

Data Sharing Statement

The experimental data used to support the findings of this study are available from the corresponding author upon request.

Ethical Approval

Approved by the Ethics Committee of The First Affiliated Hospital of Nanjing Medical University (Approval number: 2022-SR-666), informed consent obtained.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Funding

The work was not funded by any funding.

Disclosure

The authors declared that they have no conflicts of interest regarding this work.

References

1. Mistry JB, Elmallah RDK, Bhave A, et al. Rehabilitative guidelines after total knee arthroplasty: a review. J Knee Surg. 2016;201(03):201–217. doi:10.1055/s-0036-1579670

2. Zuin M, Gentili V, Cervellati C, et al. Viral load difference between symptomatic and asymptomatic COVID-19 patients: systematic review and meta-analysis. Infect Dis Rep. 2021;13(3):645–653. doi:10.3390/idr13030061

3. Thomas E, Cavallaro AR, Mani D, et al. The efficacy of muscle energy techniques in symptomatic and asymptomatic subjects: a systematic review. Chiropr Man Therap. 2019;27(1):1–18. doi:10.1186/s12998-019-0258-7

4. Mascarenhas VV, Rego P, Dantas P, et al. Imaging prevalence of femoroacetabular impingement in symptomatic patients, athletes, and asymptomatic individuals: a systematic review. Eur J Radiol. 2016;85(1):73–95. doi:10.1016/j.ejrad.2015.10.016

5. Sbardella S, La Russa C, Bernetti A, et al. Muscle energy technique in the rehabilitative treatment for acute and chronic non-specific neck pain: a systematic review. Healthcare. 2021;9(6):746. doi:10.3390/healthcare9060746

6. Wang T, Gu H, Gao H. Research on the best evidence application of postoperative rehabilitation exercises for knee arthroplasty patients based on the concept of accelerated recovery. Chin J Mod Nurs. 2020;26(5):595–599.

7. Li J, Zhang J, Hei G, et al. Therapeutic effect observation of muscle intramuscular effect patch combined with muscle energy technique in treating lateral epicondylitis of humerus. Chin J Phys Med Rehabil. 2018;40(3):208–210.

8. Luo G, Wang W, Han X. Current research on postoperative analgesia after total knee arthroplasty. Gansu Med. 2017;36(11):921–923.

9. Wang L, Lv L, Zhang H, et al. Effectiveness of deep hyperthermia combined with dynamic traction in the treatment of knee osteoarthritis. J Clin Rehabil. 2021;35(3):367–377. doi:10.1177/0269215520966702

10. Yu H, Shang J, Yan Z. Clinical efficacy analysis of muscle energy technique combined with muscle intramuscular effect patch in the treatment of periarthritis of shoulder. Liaoning Sports Sci Technol. 2021;43(3):59–62.

11. Zhou Y, Gao H, Qiu J, et al. Observation on the therapeutic effect of needle knife combined with muscle energy technique on piriformis syndrome. Chin Rehabil. 2018;33(3):237–239.

12. Wang X, Xu L. Application of static progressive stretching technique combined with muscle energy technique in the rehabilitation treatment of post-traumatic elbow joint stiffness. Chin Rehabil. 2020;35(8):409–412.

13. Li J, Zhang W, Guan S, et al. Application of muscle energy technique in rehabilitation training of patients after anterior cruciate ligament reconstruction. Nurs Res Mid-Month Ed. 2017;31(8):2925–2927.

14. Ye Z, Li S. The impact of rehabilitation training nursing based on muscle energy technique on functional rehabilitation after meniscus injury surgery. China Med Herald. 2020;17(29):171–174.