Summary
In valgus knees of more than 5°, high strain values within the medial collateral ligament are observed.
Abstract
Purpose
To analyze, how lower limb alignment affects the strain within the Medial Collateral Ligament (MCL).
Methods
For this study 12 human cadaveric knees (average age 80 years) were tested. Before biomechanical testing of the knees, long leg standing radiographs of the lower limbs of the full human body donors were obtained to assess lower limb alignment. Then, knee joints and surrounding tissues were harvested and dissected, preserving muscles and ligaments. Specimens were then mounted on a testing rig enabling the modification of knee flexion and lower limb alignment. Mounted specimens were radiographed again at 0° knee flexion. MCL maximum unloaded length in the anterior, middle and posterior regions was measured using a 3D optical tracking system (Aramis, GOM, Braunschweig). Valgus alignment was simulated to reach a valgus angulation of 8° or the ligament's elastic limit, examining axis-dependent strain behavior within the MCL at 2° intervals. Simulating weight-bearing conditions, cycles were conducted bearing 20 kg and 40 kg load.
Results
At full extension and 6° of valgus, the ligament strain was 2.6%, 3.6%, and 3.9% in the anterior, middle and posterior portion of the sMCL with 20 kg of weight bearing. With 40kg weight bearing, the corresponding strain was 3.1%, 4.0%, and 4.5%, respectively. At 30° of flexion and 8° valgus, MCL elongation was 3.9%, 4.3%, and 4.5% with 20 kg weight bearing and 4.2%, 4.5%, and 4.6% with 40 kg.
Discussion
The findings indicate that knees with a higher initial valgus alignment exhibit a greater MCL strain during valgus stress and could therefore be more prone to injury or failure following reconstruction. Strain levels associated with microdamages to the ligament of more than 5% were observed at 5 - 6° of valgus. Thus, in subjects with a medial sided injury and a valgus alignment of > 5°, a realigning osteotomy should be considered if a MCL reconstruction is performed.