Background and Introduction

A marked increase in Total Knee Replacement (TKR) procedures has been observed over the last decades in the US and Europe, with around 720,000 TKR performed in Europe in 2019 (1). This rising trend of TKR procedures is projected to plateau around 2030 (2).

For example, in France, Le Stum et al. (1) reported the highest increase in the TKR rate (82%, 20.9 to 37.9) in male patients in the age group >64 years for the years 2009 - 2019. The same authors also reported an increased TKR rate in patients with fewer comorbidities. These younger patients, undergoing TKR procedures, have not only a higher functional demand and higher expectations of the outcome but also have a significantly higher risk for revision as shown in a recently published survival analysis of a regional Italian arthroplasty register (6). In this survival analysis, the relative risk of failure was 3.1 higher (CI 95, 2.2 - 4.3) in patients younger than 50 years of age compared to the age group >65 years. Furthermore, patients in the age group 50-65 years of age also showed a 1.8 higher (CI95, 1.6-2 - 2.0) risk of failure. To address these problems, adult reconstruction surgeons must continue to strive for the optimal implant and select the best alignment.

Total knee replacement has undergone significant advancements in design and alignment over the years. The development of medial pivot designs and recently, the philosophy of more personalized alignments combined with enabling technologies, represent a notable stride in improving clinical outcomes.

This article provides a brief overview of the historical progression of the use of medially stabilized total knee designs, highlighting the impact on patient satisfaction and functional outcomes, especially when combined with modern alignment strategies and technological surgical aids.

History of the medial stabilised knee - back to the future?

The first description of the native knee kinematics was given by Giovanni Alfonso Borelli, who showed the medial pivot kinematic and the femoral rollback mechanism in cadaveric specimens back in the late 17th century (7). However, it took almost 300 years until this concept achieved wide acceptance following the publication of Freeman and Pinskerova (8). Thanks to those authors, it has been shown that the tibio-femoral flexion axis translates posteriorly during knee flexion and the tibio-femoral contact remains, at the same time, constant in the medial compartment of the knee.

The first medial stabilized knee design dates back to 1998 and was the Advance Medial Pivot (MicroPort Orthopedics Inc, Arlington, TN). Since then, other orthopaedic companies have developed a medial stabilised knee design. While early knee replacement designs focused on achieving stability and durability, often sacrificing physiological knee motion, the evolution of medially congruent knee designs aimed at addressing these limitations by incorporating more anatomical features. In 2023, it is mandatory to distinguish between pure Medial Pivot (MP) and Medial Congruent (MC) or other forms of Medial Stabilized designs. The pure MP design concept is based on mimicking the natural knee's biomechanics, where the medial condyle serves as a pivot during flexion: this type of implant is usually designed as a “ball in socket” where the medial femoral condyle is defined and designed as the ball and the polyethylene insert, medially ultracongruent with a 1/1 ratio, acts as the socket, whereas the lateral compartment is generally flatter. In contrast to this “pure” concept, the most popular form of MC design (Persona MC, Zimmer Biomet, Warsaw, USA) incorporates a standard femoral component (J-curve) which articulates with a polyethylene insert that is medially more congruent with respect to the lateral side; this medial high-congruence is also increased by the use of a higher anterior lip in the medial compartment, favouring a lateral roll back kinematic during the gait cycle.

All medial pivot/medial congruent/medial stabilized designs aim to restore not only stability but also normal knee kinematics, potentially improving patient satisfaction and function. However, the current literature on the benefits of medial stabilized designs compared to other designs is still inconclusive.

A recent meta-analysis by Kakoulidis et al. (3) published in KSSTA, did not yield any ROM and PROMs statistical differences between PS and medially stabilized groups. In contrast to this study, a systematic review and meta-analysis by Shi (4) showed better WOMAC and HSS scores and a lower complication rate (OR 0.53) in medial pivot cohorts compared to PS while ROM, radiographic results and revision rates showed no differences.

When looking at outcomes, however, adult reconstruction surgeons should also consider alignment philosophies that are currently changing towards more personalized and kinematic strategies. Historically, mechanical alignment has been a dogma over the last decades. With the rise of technological aids, precision for the targeted component placement is dramatically improving. Therefore, the comparison between a mechanical aligned PS knee (historically the gold standard in TKA) and a medially stabilized knee, might not yield the full potential of the second one. A systematic review of the literature comparing gait data following PS and medial pivot primary TKRs, published by Risitano et al. (5) in 2023, confirmed important kinematic and kinetic differences between medial pivot and PS TKA designs; this review also confirmed that both designs kinematic is still quite distant from that one of the native knee.

Clinical Implications

Medial pivot total knee replacement designs in combination with a personalized or kinematically aligned implantation philosophy may show promising results in terms of improved kinematics and patient-reported outcomes. The preservation of natural knee motion may contribute to enhanced functional performance and long-term implant survivorship of medial pivot total knee replacement as shown in a study by Karachilios et al. (9) where an overall survival rate of 97.3% at 15 years was reported. However, challenges and controversies exist, and ongoing research is essential to further validate the clinical benefits.

Conclusion

The evolution of total knee replacement designs has witnessed a paradigm shift towards achieving more natural knee kinematics. The development of medial stabilised total knee replacement designs represents a significant advancement in this pursuit. Scientific literature supports the notion that medial pivot designs may offer improved patient satisfaction and functional outcomes. As research continues to refine and validate these designs, the future of total knee replacement holds the promise of better replicating the intricate biomechanics of the native knee.

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References
1. Le Stum, M., Gicquel, T., Dardenne, G., Le Goff-Pronost, M., Stindel, E. and Clavé, A., 2023. Total knee arthroplasty in France: Male-driven rise in procedures in 2009–2019 and projections for 2050. Orthopaedics & Traumatology: Surgery & Research, 109(5), p.103463.
2. Daugberg, L., Jakobsen, T., Nielsen, P.T., Rasmussen, M. and El-Galaly, A., 2021. A projection of primary knee replacement in Denmark from 2020 to 2050. Acta Orthopaedica, 92(4), pp.448-451.
3. Kakoulidis, P., Panagiotidou, S., Profitiliotis, G., Papavasiliou, K., Tsiridis, E. and Topalis, C., 2023. Medial pivot design does not yield superior results compared to posterior-stabilised total knee arthroplasty: a systematic review and meta-analysis of randomised control trials. Knee Surgery, Sports Traumatology, Arthroscopy, 31(9), pp.3684-3700.
4. Shi, W., Jiang, Y., Wang, Y., Zhao, X., Yu, T. and Li, T., 2022. Medial pivot prosthesis has a better functional score and lower complication rate than posterior-stabilized prosthesis: a systematic review and meta-analysis. Journal of Orthopaedic Surgery and Research, 17(1), pp.1-14.
5. Risitano, S., Cacciola, G., Capella, M., Bosco, F., Giustra, F., Fusini, F., Indelli, P.F., Massé, A. and Sabatini, L., 2023. Comparison between gaits after a medial pivot and posterior stabilized primary total knee arthroplasty: a systematic review of the literature. Arthroplasty, 5(1), pp.1-11.
6. Perdisa, F., Bordini, B., Salerno, M., Traina, F., Zaffagnini, S. and Filardo, G., 2023. Total knee arthroplasty (TKA): when do the risks of TKA overcome the benefits? Double risk of failure in patients up to 65 years old. Cartilage, p.19476035231164733.
7. Piolanti, N., Polloni, S., Bonicoli, E., Giuntoli, M., Scaglione, M. and Indelli, P.F., 2018. Giovanni Alfonso Borelli: the precursor of medial pivot concept in knee biomechanics. Joints, 6(03), pp.167-172.
8. Freeman, M.A. and Pinskerova, V., 2005. The movement of the normal tibio-femoral joint. Journal of biomechanics, 38(2), pp.197-208.
9. Karachalios, T., Varitimidis, S., Bargiotas, K., Hantes, M., Roidis, N., amd Malizos, K. N., 2016. An 11-to 15-year clinical outcome study of the Advance Medial Pivot total knee arthroplasty: pivot knee arthroplasty. The Bone & Joint Journal, 98(8), pp. 1050-1055.

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