The tension of the iliopsoas tendon more than doubles during extension of the dysplastic hip in open reduction.

The role of the iliopsoas as an obstructing and re-dislocating factor in developmentally dislocated hips is unclear. The purpose of this article is to determine the change in the iliopsoas' tension during flexion and extension when performing an open reduction. We evaluated 34 hips undergoing an anterior open reduction for a developmental dislocation. At the time of surgery, we identified the iliopsoas, and before sectioning it as part of the open reduction, we measured the tension while cycling the reduced hip through flexion and extension. We performed statistical analysis using Pearson and Spearman correlation tests. We created an initial tension artificially at 20 N with the hip held in 90º of flexion, which then doubled to a mean of 42 N when placed in extension. We found a significant increase in tension when the hip went below 20º of flexion. We also found the correlation between the angle of the hip and the force of tension to be statistically significant ( P  = 0.003). This study provides quantitative support that the tension of the iliopsoas tendon increases significantly in extension when performing an open reduction of a developmentally dislocated hip.