Cross-Sectional Analysis of Iliopsoas Muscle-Tendon Units at the Sites of Arthroscopic Tenotomies

Background: Arthroscopic iliopsoas tenotomies are performed at the level of the labrum, femoral neck, and lesser trochanter. The composition and percentage of the iliopsoas muscle-tendon unit (MTU) that is released when the tendon is cut at these sites has not been reported to date. Hypothesis: Cutting the iliopsoas tendon at the 3 common sites of arthroscopic tenotomies does not release the entire iliopsoas MTU. Study Design: Descriptive laboratory study. Methods: Forty iliopsoas MTUs from 20 embalmed cadavers were isolated at the level of the hip joint and released from their insertion on the lesser trochanter. Circumferential measurements of the composite MTU and the isolated iliopsoas tendon were then made at (1) the MTU's insertion on the lesser trochanter, (2) the Wettstein et al site of transcapsular release, and (3) the Alpert et al release site at the level of the labrum. Single proportion testing was performed using the Student t test to determine if significant differences existed between the average circumference of the iliopsoas MTUs or the isolated tendons at the 3 levels at which they were measured. Results: The average circumference of the iliopsoas-muscle belly complex at the level of the labrum, the transcapsular release site, and the lesser trochanter was 68, 58, and 46 mm, respectively. The average circumference of the iliopsoas tendon at these same levels was 27, 31, and 27 mm, respectively. Thus, at the level of the labrum, transcapsular release site, and lesser trochanter, the iliopsoas MTU is composed of 40% tendon/60% muscle belly, 53% tendon/47% muscle belly, and 60% tendon/40% muscle belly, respectively. Conclusion: Cutting the iliopsoas tendon at the labrum, head-neck junction, or lesser trochanter does not result in a release of the entire iliopsoas MTU. Clinical Relevance: The results of this study document that releasing the iliopsoas tendon at the lesser trochanter preserves 40% of the MTU and does not result in a complete detachment of the iliopsoas MTU.