A Magnetic Resonance Imaging Study Comparing Varus Arthritic to Normal Knees Indicates that the Medial Collateral Ligament Does Not Contract in up to 15° of Varus Deformity, Whereas the Lateral Collateral Ligament May Elongate.

BACKGROUND

The question of whether the superficial medial collateral ligament (MCL) undergoes contracture in the presence of osteoarthritic changes remains unresolved. Addressing this fundamental scientific inquiry is crucial for determining the surgical technique of correcting varus deformity and evaluating the need for deploying alternative alignment philosophies.

METHODS

Magnetic resonance (MR) images of 100 knees with established osteoarthritis were compared to those of 100 normal control knees. We measured the width of the transepicondylar axis (TEA), lengths of the MCL and lateral collateral ligaments (LCL) along their tortuosity, the straight line distance between their attachments (MCL1 line and LCL1 line), the hip-knee-ankle angle, and the width of medial femoral and tibial osteophytes.

RESULTS

The MCL/TEA ratios did not differ significantly with deformity. The mean MCL length was reduced by five mm in knees greater than 15° varus (P < 0.001). The LCL/TEA ratios were greater in knees with 5 to 10° (P = 0.001) and 10 to 15° varus (P = 0.007). The MCL difference (MCL1 line minus MCL length) significantly correlated with femoral (P = 0.009) and tibial osteophyte width (P = 0.044).

CONCLUSIONS

In varus arthritic knees, the MCL does not shorten but is tented over medial osteophytes. The LCL may elongate by up to two mm with increasing deformity. At extreme deformity (greater than 15°), possibly due to bone loss and subluxation, the unstressed lengths of superficial MCL and LCL appear to be reduced. This study questions the need for releasing the MCL in knees with up to 15° varus, as anatomical contracture may not be the primary cause of tightness; alternative techniques such as osteophyte excision should be prioritized. It may suggest reconsideration of alternative alignment philosophies solely to avoid superficial MCL release.