Mechanics of Psoas Tendon Snapping. A Virtual Population Study

Abstract

Internal snapping of the psoas tendon is a frequently reported condition, especially in young adolescents involved in sports. It is defined as an increased tendon excursion over bony or soft tissue prominence causing local irritation and inflammation of the tendon leading to groin pain and often is accompanied by an audible snap. Due to the lack of detailed dynamic visualization means, the exact mechanism of the condition remains poorly understood and different theories have been postulated related to the etiology and its location about the hip. In the present study we simulated psoas tendon behavior in a virtual population of 40,000 anatomies and compared tendon movement during combined abduction, flexion and external rotation and back to neutral extension and adduction. At risk phenotyopes for tendon snapping were defined as the morphologies presenting with excess tendon movement. There were little differences in tendon movement between the male and female models. In both populations, abnormal tendon excursion correlated with changes in mainly the femoral anatomy (male r = 0.72, p < 0.001, female r = 0.66, p < 0.001): increased anteversion and valgus as well as a decreasing femoral offset and ischiofemoral distance. The observed combination of shape components correlating with excess tendon movement in essence presented with a medial positioning of the minor trochanter. This finding suggest that psoas snapping and ischiofemoral impingement are possibly two presentations of a similar underlying rotational dysplasia of the femur.

Keywords: geometric morphoinetric analysis; ischiofemoral impingement; muscle wrapping; tendon mechanics; virtual population.

FIGURE 1

Cumulative male and female variance explained by PCA.

FIGURE 2

Motion sequence enforced on the virtual models.

FIGURE 3

Relevant osteological structures were segmented and use for the construct of a PCA model describing male and female anatomical variance. From each model 20,000 virtual anatomies were created to study psoas tendon behavior in the population created.

FIGURE 4

Effect size and statistical significance of the different shape components relating to the observed peak tendon velocity.

FIGURE 5

Tendon velocity in the female population studied (Above). Reconstructed shapes correlating with decreased and increased tendon velocity upon return to the neutral position (Below).

FIGURE 6

Tendon velocity in the male population studied (Above). Reconstructed shapes correlating with decreased and increased tendon velocity upon return to the neutral position (Below).

FIGURE 7

Digitally reconstructed images of the female and male anatomies correlating with decreased and increased psoas tendon excursion upon return to the neutral position.