Abstract
Introduction
The pathogenesis of primary knee osteoarthritis is due to excess mechanical loading of the articular cartilage. Previous studies have assessed the impact of muscle forces on tibiofemoral kinematics and force distribution. A cadaveric study was performed to evaluate the effect of altering the moment arm of the iliotibial band (ITB) on knee biomechanics.
Method
A robotic system consisting of a 6-DOF manipulator capable of measuring forces on the medial and lateral condyle of a cadaveric knee at various flexion angles and muscle forces was utilized [1]. The system measured the compartment forces at flexion angles between 0° and 30° under 3 simulated loading conditions (300N quadriceps, 100N hamstrings and: i. 0N ITB; ii. 50N ITB; iii. 100N ITB).
Eight fresh frozen human cadaver knee specimens (4 males, 4 females); age range 36 – 50 years; weight range 49 – 90 kg; height range 154 – 190 cm were used in the study.
The ITB and associated lateral soft tissue structures were laterally displaced from the lateral femoral condyle by fixing a metal implant (like in Figure 1) to the distal lateral femur. Mechanical loads on the medial and lateral compartments (with and without the implant) were measured using piezoelectric pressure sensors.
Results
For each specimen, lateral displacement of the ITB due to the implant was measured (15 – 20 mm). The % average unloading of the medial compartment for all the specimens ranged from 34% – 65% (Figure 2). Also observed was a concomitant increase in lateral compartment load. Medial unloading was even observed with no ITB force (0N) which indicates a role for other lateral structures attached to the ITB in unloading the medial compartment [2]. In addition, under these non-weight bearing conditions, on average, there was an increase in valgus tibial angulation through the flexion range.
Discussion
Increasing mechanical leverage of muscles across a joint is accomplished in nature through sesamoid bones (e.g., patella) which increase the muscle moment arm. By increasing the moment arm of the ITB and lateral soft tissue structures by lateralizing these structures, our model demonstrates a 34–65% unloading of the medial compartment.
Studies of knee braces and weight loss have shown that reducing mechanical load on the medial condyle by even 10% provides clinical benefits in terms of reduced pain and improved function. Based on the results of this study, unloading the medial compartment by displacing the ITB laterally may be a means of treating medial osteoarthritis (Figure 3). A prospective, multi-center, non-randomized, open label, single-arm study is currently underway to establish the safety and efficacy of providing medial osteoarthritis pain relief by displacing the ITB using Cotera, Inc.'s Latella™ Knee Implant.
