Is Flexion Gap Rectangular in Native Indian Knees? Results of an MRI Study

BACKGROUND: The purpose of this study was to evaluate the flexion-gap of the native knees in the normal population and to assess any gender-specific variations in the flexion gap of the knees. METHODS: A total of 50 normal asymptomatic volunteers with normal knee radiographs were selected for MRI of the knee. The left knee was scanned in an open MRI using a T1-weighted sequence. Imaging was performed in neutral, passive varus and valgus stress at 90° of knee flexion by placing custom-made blocks on a special board consecutively below the distal part of the leg. RESULTS: The study population consisted of 26 males and 24 females with a mean age of 25.77 years. Under varus stress, the mean lateral flexion gap increased to 9.28 ± 1.53 mm and under valgus stress, the mean medial flexion gap increased to 2.75 ± 1.22 mm from neutral. The increase in the flexion gap on the lateral side was 5.28 ± 1.79 mm, which was significantly higher compared to that on the medial side. In gender-specific analysis, the mean lateral flexion gap was 10.21 mm in females and 8.46 mm in males under varus stress. CONCLUSION: The findings of the study indicate that the lateral soft tissues are more lax compared to the medial soft tissue structures and this laxity is higher in females as compared to males. The study provides evidence of the existing physiological variations of these soft tissue structures resulting in a trapezoidal flexion gap in the native knees rather than the recommended rectangular gap.