Dislocation after total hip arthroplasty (THA) via the posterior approach remains a serious complication. This cadaveric study compared two soft tissue repair techniques—trans-osseous and direct suturing—regarding their effect on dislocation torque and angle.

Ten hips from five fresh-frozen cadavers were used. A Posterior approach identified the short external rotators. Following standard THA, each limb was mounted on a motorized torque wrench. Hips were tested first with no posterior repair (NPR), then with either transosseous or direct repair techniques. Dislocation torque and angle were recorded, with each hip serving as its own control.

Posterior repair significantly increased the force required for dislocation compared to NPR (mean 9.12 Nm vs. 2.73 Nm; p = 0.004). Trans-osseous repair led to a 4.41-fold increase in torque (p = 0.04), and direct repair a 2.47-fold increase (p = 0.03), with a significant difference between the two (p = 0.016). The dislocation angle increased with repair (mean 54.6° vs. 45.1°; p = 0.09), though not significantly. Trans-osseous and direct repairs increased the angle by 1.70× and 1.18×, respectively.

Posterior soft tissue repair improves hip stability in THA performed via a posterior approach. Trans-osseous repair provides significantly greater resistance to dislocation torque than direct suturing and may be the preferred technique to reduce postoperative instability.