DTI-based muscle fiber tracking of the quadriceps mechanism in lateral patellar dislocation.

PURPOSE: To determine the feasibility of using diffusion tensor MRI (DT-MRI) -based muscle fiber tracking to create biomechanical models of the quadriceps mechanism in healthy subjects and those with chronic lateral patellar dislocation (LPD).

MATERIALS AND METHODS: Four healthy (average 14.5 years old; BMI 21.8) and four chronic LPD (average 17.3 years old; BMI 22.4) females underwent DT and axial T1W MRI of the thighs. The anatomical and physiologic cross-sectional areas (ACSA and PCSA, respectively) and pennation angle were calculated of the vastus lateralis oblique (VLO) and vastus medialis oblique (VMO) muscles. The predicted resultant force vector on the patella was calculated.

RESULTS: The VLO pennation angles in healthy and LPD subjects were 18.7 and 14.5 degrees, respectively (P=0.141). The VMO pennation angles in healthy and LPD subjects were 11.4 and 14.8 degrees, respectively (P=0.02). The ACSA and PCSA VLO:VMO ratios in healthy and LPD subjects were 1.9:1.6 and 2.1:1.6, respectively (P=0.025 and 0.202, respectively). Regardless of whether ACSA or PCSA was used to predict resultant lateral force vectors, the values differed between healthy and LPD subjects (approximately 2 and approximately 5.3 degrees, respectively; P<0.05).

CONCLUSION: Chronic LPD patients had more laterally directed predicted resultant force vectors than healthy subjects. Our preliminary results suggest that biomechanical models of the quadriceps mechanism in patients with chronic LPD and healthy subjects can be created in healthy subjects and patients with chronic LPD using DT-MRI.