Medial Congruent and Medial Pivot Inserts in Total Knee Arthroplasty: A Scoping Review

Abstract

Background and Objectives: Total knee arthroplasty (TKA) is one of the most common medical procedures worldwide. However, 10 to 20% of patients are still dissatisfied despite implants and surgical technique advancements. Recently, several medial-stabilized TKAs have been developed in attempts to replicate the native kinematics of the knee. The aim of this scoping review on medial-stabilized TKA inserts-medial congruent (MC) and medial pivot (MP)-is to focus on their clinical outcomes and the role of the posterior cruciate ligament (PCL), aiming to systematically map the existing research and highlight current knowledge gaps. Materials and Methods: A search of the PubMed, Embase and Cochrane databases was performed to identify relevant studies on the kinematics and outcomes of medial pivot (MP) or medial congruent (MC) inserts. The following Mesh terms were used in combination with the Boolean operators "AND" and "OR": "total knee arthroplasty", "total knee replacement", "medial pivot", "medial congruence", "outcomes" and "kinematic". Original studies reporting on clinical outcomes assessed with validated patient-reported scales, surgical techniques and reoperation rates for any reason with a minimum follow-up of 18 months were included. Results: A total of 39 articles met the inclusion criteria, accounting for 6143 total knee replacements. The overall reoperation-free survivorship rate was 98.4% (6047 out of 6143 knees) at a weighted average follow-up of 6.3 years (range 1.5-15.2 years, SD 0.7). Both MP and MC inserts demonstrated good outcomes, with no differences between groups. Few studies evaluated the role of the PCL in MP and MC inserts, with no differences in terms of clinical outcomes between retaining and sacrificing the PCL. Conclusions: MS-TKA demonstrated good outcomes in the literature independently of the specific design (medial pivot or medial congruent). Different possible biases may be present when evaluating the outcomes of these inserts, including different types of alignment and soft tissue balancing philosophies.

Keywords: medial congruence; medial pivot; outcomes; total knee arthroplasty.

Figure 1

In the upper part of the figure, an MC insert is shown: (A) Axial view demonstrating the anatomic asymmetric shape of the tibial plateau with a larger medial surface. (B) AP view demonstrating a more concave medial surface for a more constrained medial compartment compared to the lateral one. (C) Lateral view showing the deep anterior and posterior lips to achieve AP stability. In the lower part of the figure, an MP insert is shown. (D) Axial view demonstrating the symmetric shape of the tibial plateau. (E) AP view demonstrating a more concave medial surface and a flat lateral one, reproducing the “medial pivot” kinematics of the knee. (F) Lateral view showing the deep anterior lip to achieve AP stability.

Figure 2

PRISMA diagram.

Figure 3

Post-operative anteroposterior (a) and lateral (b) radiographs of a medial pivot TKA from the senior author’s case series.

Figure 4

Post-operative anteroposterior (a) and lateral (b) radiographs of a medial congruent TKA from the senior author’s case series.