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We often don’t consider anatomical differences within our bodies, even though there are many cases where anatomical differences exist. One recent study looked at the anatomical differences in hip musculature of fifty-three nomatched, fresh-frozen, cadaveric hemipelvis specimens (~62 years; M=29, F=24). Dissections were performed by 2 fellowship-trained orthopaedic surgeons with a 10 – 15-cm longitudinal incision at the level of the anterior superior iliac spine. The incision was between the tensor fasciae latae and the Sartorius, then continued between the rectus femoris and gluteus medius interval. The hip was then carried through a range of motion to determine the location where the ilipsoas tendon crossed the anterior hip joint capsule over the equator of the femoral head.
The width of each tendon was measured as well as the distance from the trochanter to the level of the transverse incision.
Prevalence of Differences
The prevalence of a single-, double-, and triple-banded iliopsoas tendon was 28.3%, 64.2%, and 7.5% respectively. Two tendinous slips were found in 72.4% of male and 54.2% of females. The average distance from the less trochanter to the location of the musculotendinous unit of the iiopsoas tendon on the anterosuperior hip joint capsule was 6.9 cm. The psoas major tendon was found most medially. The iliac was found most laterally. When found, the additional iliacus tendon was located adjacent to the primary iliacus tendon and lateral to the psoas major tendon.
The average width of the psoas major for all single tendon specimens was 1.4 cm, which was significantly larger than the most lateral tendon for all double and triple tendon specimens. There was a significant combined tendon width difference between single (1.4 cm) double (1.8 cm) and triple (2.4 cm) tendons.
Discussion
Understanding the presence of variability in the iliopsoas tendon is essential, as the rate of hip surgeries is rising. In those with anterior snapping hip syndrome, it is postulated that the snapping mechanism is created when the medial part of the iliac muscle is trapped between the ilopsoas tendon and the pubic bone during an abduction/flexion/external rotation movement. This may be more common in those with larger musculatures like the people with three iliopsoas tendons.
Also, the presence of more tendons (and greater cross-sectional area) may provide force production and sporting benefits.
Dr. John, DPT, CSCS