Magnetic Resonance Imaging Findings of the Lateral Collateral Ligament and Popliteus Tendon in Symptomatic Knees Without Instability

Purpose: To describe normative values of the thicknesses of the lateral collateral ligament (LCL) and popliteus tendon in patients who underwent knee surgery but had no evidence of knee instability and identify factors associated with the variations, and to estimate the prevalence and associated factors of abnormal magnetic resonance imaging (MRI) findings of the LCL and popliteus tendon. Methods: MRI scans in 120 patients without knee instability were evaluated to measure the thicknesses of the LCL and popliteus tendon and estimate the prevalence of signal alteration and abnormal thickening and thinning. We then investigated the factors associated with the thicknesses and abnormal MRI findings. Results: The mean thicknesses of the LCL and popliteus tendon were 5.3 +/- 1.0 mm and 3.8 +/- 0.6 mm, respectively. Elderly, heavier patients and patients with more varus alignment had thicker LCLs, whereas taller, heavier, and male patients had thicker popliteus tendons. Signal alterations of the LCL and popliteus tendon were found in 33% and 23%, respectively, of the knees; abnormal thickening was found in 33% and 8%, respectively. Regression analyses found the mechanical tibiofemoral angle (more varus angle) to be the only predictor for abnormal MRI findings of the LCL (odds ratio of 0.81 [95% confidence interval, 0.66 to 0.98] for signal alteration and odds ratio of 0.73 [95% confidence interval, 0.59 to 0.90] for abnormal thickening); however, no predictors were found for abnormal MRI findings of the popliteus tendon. Conclusions: Even in patients without varus and posterolateral rotary instability, signal alteration and thickening of the LCL and/or popliteus tendon can be frequently found with MRI. In particular, abnormal MRI findings of the LCL were likely to be more frequent in the patients with more varus knee alignment. These findings may be considered when interpreting MRI evaluation to diagnose patients with chronic posterolateral corner injury.