Elsevier

Clinical Biomechanics

Volume 33, March 2016, Pages 42-48
Clinical Biomechanics

Femorotibial kinematics and load patterns after total knee arthroplasty: An in vitro comparison of posterior-stabilized versus medial-stabilized design

https://doi.org/10.1016/j.clinbiomech.2016.02.002Get rights and content

Highlights

  • A medial and posterior-stabilized total knee arthroplasty design was tested in a rig.

  • Medial stabilized system had a reduced rollback in the lateral compartment with flexion.

  • The medial stabilized system enables a lateral translation with a medial pivot.

Abstract

Background

Femorotibial kinematics and contact patterns vary greatly with different total knee arthroplasty (TKA) designs. Therefore, guided motion knee systems were developed to restore natural knee kinematics and make them more predictable. The medial stabilized TKA design is supposed to replicate physiological kinematics more than the posterior-stabilized TKA system. We conducted this study to compare a newly developed medial stabilized design with a conventional posterior-stabilized design in terms of femorotibial kinematics and contact patterns in vitro.

Methods

Twelve fresh-frozen knee specimens were tested in a weight-bearing knee rig after implantation of a posterior stabilized and medial-stabilized total knee arthroplasty under a loaded squat from 20° to 120° of flexion. Femorotibial joint contact pressures in the medial and lateral compartments were measured by pressure sensitive films and knee kinematics were recorded by an ultrasonic 3-dimensional motion analysis system.

Findings

The medial stabilized design showed a reduction of medial femorotibial translation compared to posterior-stabilized design (mean 3.5 mm compared to 15.7 mm, P < 0.01). In the lateral compartment, both designs showed a posterior translation of the femur with flexion, but less in the medial stabilized design (mean 14.7 mm compared to 19.0 mm, P < 0.01). In the medial femorotibial compartment of medial stabilized design, we observed an enlarged contact area and lower peak pressure, in contrast in the lateral compartment there was a reduced contact area and an increased peak pressure.

Interpretation

While posterior-stabilized design enforces a medio-lateral posterior translation, the medial stabilized arthroplasty system enables a combination of a lateral translation with a medial pivot, which restores the physiological knee kinematics better.

Introduction

Femorotibial kinematics and load patterns after total knee arthroplasty (TKA) vary greatly. Non-physiological motion after TKA, for example, paradoxical anterior translation of the femur on the tibia with flexion or posterior subluxation of the femur are described (Dennis et al., 1998, Dennis et al., 2003). Besides the necessary stability of a TKA, physiological femoral posterior translation provides a more natural motion of the knee, resulting in a better functional outcome and satisfaction for the patient after TKA (Pritchett, 2011). Implant design directly influences the kinematics after TKA (Banks and Hodge, 2004). Therefore, “guided motion” knee systems like the PS system were developed in the late 1970s by Insall et al. (Insall et al., 1982) to restore physiological kinematics and make kinematics more predictable. A post on the inlay interacts with an integrated cam in the femoral component, providing a medial and lateral femoral posterior translation with flexion of the knee. With specific investigations of normal knee kinematics (Blaha et al., 2003, Iwaki et al., 2000), other guided motion systems were further developed in the 2000s. The MS design is supposed to provide an antero-posterior (AP) translation of the femur in the lateral compartment, while the medial condyle interacts like a “ball and socket” joint. This medial convexity of the inlay might reduce contact stress and might replicate physiological kinematics more than the PS design. On the other hand, studies have described an antero-lateral pain with guided motion TKA systems and it is assumed that a higher forced lateral AP translation might cause pain in this area (Halewood et al., 2014, Luyckx et al., 2010).

Especially for newly designed or modified implants, an in vitro analysis should be extensively performed for implementation of the implants in vivo. In vitro studies with human specimens are an established method of investigating femorotibial knee kinematics and load patterns after TKA (Arnout et al., 2014, Blaha et al., 2003, Heyse et al., 2010, Steinbruck et al., 2015, Varadarajan et al., 2009, Walker et al., 2011). A specific comparison in terms of kinematics and joint pressure of a PS and a MS knee system was—to the authors knowledge—not performed before. Therefore, the goal of this study was to compare a newly developed MS TKA system with a conventional PS design of the same manufacturer. We firstly hypothesized that the MS design had a higher AP translation and secondly a higher maximum pressure in the lateral femorotibial compartment during flexion of the knee. By having the same bone cuts, fixation points, and tibial baseplate for both the PS and MS knee systems, a direct comparison and interpretation of the results within every single knee specimen could be performed.

Section snippets

Human knee specimens

Twelve human knee specimens (Table 1) were used to investigate knee kinematics after TKA. The local ethics committee of the university approved the acquisition and usage of the human specimens. None of the chosen specimens had any severe varus or valgus deformity ≥ 10°. Muscles were dissected and fat tissue was removed carefully. Special care was taken to preserve the joint capsule and the tendons of the vastus medialis muscle, vastus lateralis muscle, intermedius and rectus femoris muscle, as

Femorotibial translation

According to the mixed effect model, the MS design showed a significant decrease of femorotibial translation in the medial compartment compared to PS design (Table 2, Fig. 4). At 120° of flexion, the PS design displayed a mean posterior translation of the femur related to the tibia of 15.7 mm (SD 7.6 mm), while the MS design translated in the medial compartment of an average of 3.5 mm (SD 4.8 mm) (Fig. 5).

In the lateral compartment, both designs showed a posterior translation of the femur in

Discussion

Our study shows that the PS design enforces a ML posterior translation, while the MS TKA system enables a combination of a posterior translation in the lateral compartment with a medial pivot. According to in vivo and in vitro studies of the physiological movement of the knee during flexion the medial femoral condyle also hardly translates in AP direction while the lateral condyle significantly moves backwards (Iwaki et al., 2000, Johal et al., 2005, Karrholm et al., 2000). Johal et al.

Conclusions

The MS TKA system enables a combination of medial pivot with a lateral translation, which is slightly lower compared to PS TKA. This provides AP stability of the knee and the appearance of antero-lateral pain after implantation is unlikely. Regarding femorotibial pressure distribution, future in vivo analysis and long-term studies are needed in order to support the good outcome and survivorship of medial stabilized knee systems.

Conflict of interest

The authors declare no conflict of interest for this study.

Acknowledgments

We especially thank Professor Michael A Freeman for his personal support in critically reviewing the manuscript. We also thank Tatjana Müller for the preparation of the specimens and her help during the tests. We like to thank the Medacta Company to support this study by donating the used knee prosthesis and their technical and logistical support. The Medacta Company had no involvement in the collection, analysis and interpretation of data and no involvement in the writing of the report; and in

References (35)

  • D.A. Dennis et al.

    In vivo fluoroscopic analysis of fixed-bearing total knee replacements

    Clin. Orthop. Relat. Res.

    (2003)
  • D.A. Dennis et al.

    A multicenter analysis of axial femorotibial rotation after total knee arthroplasty

    Clin. Orthop. Relat. Res.

    (2004)
  • D.A. Fitch et al.

    Mid- to long-term outcomes of a medial-pivot system for primary total knee replacement: a systematic review and meta-analysis

    Bone Joint Res.

    (2014)
  • C. Halewood et al.

    Kinematic behaviour and soft tissue management in guided motion total knee replacement

    Knee Surg. Sports Traumatol. Arthrosc.

    (2014)
  • T.J. Heyse et al.

    Patellofemoral pressure after TKA in vitro: highly conforming vs. posterior stabilized inlays

    Arch. Orthop. Trauma Surg.

    (2010)
  • P.F. Hill et al.

    Tibiofemoral movement 2: the loaded and unloaded living knee studied by MRI

    J. Bone Joint Surg. (Br.)

    (2000)
  • F. Hossain et al.

    Knee arthroplasty with a medially conforming ball-and-socket tibiofemoral articulation provides better function

    Clin. Orthop. Relat. Res.

    (2011)
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