No difference in flexion power despite iliopsoas fatty degeneration in healed hip fractures with large lesser trochanter displacement

OBJECTIVE: To evaluate iliopsoas atrophy and loss of function after displaced lesser trochanter fracture of the hip. DESIGN: Cohort study. SETTING: District hospital. PATIENTS: Twenty consecutive patients with pertrochanteric fracture and displacement of the lesser trochanter of > 20 mm. INTERVENTION: Fracture fixation with either an intramedullary nail or a plate. OUTCOME MEASUREMENTS: Clinical scores (Harris hip, WOMAC), hip flexion strength measurements, and magnetic resonance imaging findings. RESULTS: Compared with the contralateral non-operated side, the affected side showed no difference in hip flexion force in the supine upright neutral position and at 30° of flexion (205.4 N vs 221.7 N and 178.9 N vs. 192.1 N at 0° and 30° flexion, respectively). However, the affected side showed a significantly greater degree of fatty infiltration compared with the contralateral side (global fatty degeneration index 1.085 vs 0.784), predominantly within the psoas and iliacus muscles. CONCLUSION: Severe displacement of the lesser trochanter (> 20 mm) in pertrochanteric fractures did not reduce hip flexion strength compared with the contralateral side. Displacement of the lesser trochanter in such cases can lead to fatty infiltration of the iliopsoas muscle unit. The amount of displacement of the lesser trochanter did not affect the degree of fatty infiltration. LEVEL OF EVIDENCE: II.