Comparison Between Medial Pivot Versus Symmetric Insert Total Knee Arthroplasty

Comparison Between Medial Pivot Versus Symmetric Insert Total Knee Arthroplasty: A Randomized Controlled Study

The functional outcome and longevity of total knee arthroplasty (TKA) is still a concern. Despite various developments in TKA designs, including fixed or mobile bearing, cruciate retaining or posterior stabilized, multi or single radius, it remains unclear which design is superior for achieving a physiological kinematic.

In normal healthy knees the medial and lateral tibial condyles are different: the medial is almost flat while the lateral is somewhat convex. Thus, the movement during flexion is asymmetric: during the flexion, the medial condyle is stable throughout the range of motion while the lateral condyle slides anteroposteriorly with respect to femur). Therefore, the native knee requires a specific degree of rollback of the lateral compartment coupled with a medial pivot, which leads to an external axial rotation of the femur. This rollback is thought to be even more pronounced with increasing knee flexion angles to enable deep flexion without excessive shear forces acting at the patella or overloading the extensor mechanism.

In addition, stability throughout flexion is a crucial element to normal knee function. Most TKA designs removal of the ACL, and the PCL in posterior-stabilized design, but the TKA do not fully restore the function of those ligaments.

Based on this philosophy, the medial pivot TKA was designed to provide better function, patient satisfaction and increased survival.

The objective of this study is to analyze whether the medial pivot design provides better outcome and prosthesis survival than conventional total knee arthroplasty.

Candidates for the study will be consecutive patients eligible for total knee arthroplasty (TKA) at our center. All patients meeting inclusion criteria will be recruited for enrollment into the study. Informed consent will be obtained from the patient prior to randomization.

At that time, each patient will be randomized into one of two groups by an independent staff using computer generated randomization and allocation concealment. The two patient groups will include:

1. Study group: patients treated with a medial pivot TKA.
2. Control group: patients treated with a conventional TKA. Patients will be preoperatively assessed and postoperatively at regular intervals (6mo, 12 mo, and then annually) by orthopaedic surgeons not involved in the surgeries or cares.

Inclusion Criteria:

• Primary osteoarthritis of the knee
• 50 years and older
• Participants must be able to give informed consent

Exclusion Criteria:

• Inflammatory arthritis
• Traumatic etiology
• Neurologic disease
• Neoplastic disease
• Morbid obesity
• Severe collateral ligament instability (> 10° varus/valgus)
• Severe knee misalignment (greater than 10° of varus or valgus)
• Flexion contracture greater than 15º
• Prior surgery on the affected knee (except meniscus)
• Knee arthroplasty in the contralateral knee