Abstract
Dislocation after primary total hip replacement (THR) can occur within days or weeks after the index procedure because of malpositioned components or be of late onset years later due to trauma or excessive wear.
Regardless of timing, the culprit causing dislocation is catastrophic neck-cup impingement, which levers the prosthetic head out of the prosthetic socket. Prosthetic range of motion (P-ROM), which is determined by the diameter of the femoral neck at the ball-neck junction and the distance to the edge of the prosthetic cup, must be considered during initial THR insertion to allow internal and external hip rotation of 45° at 90° of hip flexion in neutral abduction-adduction. Failure to achieve satisfactory P-ROM by accurate placement of the acetabular cup and femoral component may result in multiple re-dislocations, especially if periprosthetic capsular reformation is interrupted by an initial dislocation, which disrupts the primary surgical repair.
If component position is satisfactory but traumatic disruption of the periprosthetic capsule results in recurrent posterior THR dislocation, a posterior capsular reefing and reinforcement with mersilene tape can be used. A postoperative 30° hip abduction brace with a 60° flexion stop is recommended for continuous use for 6 to 12 weeks. If component position is unsatisfactory or excessive wear causes impingement, removal and repositioning of the acetabular cup in 30° anteversion and 60° abduction with 15° of femoral neck anteversion is recommended.
The abstracts were prepared by Mrs Dorothy L. Granchi, Course Coordinator. Correspondence should be addressed to her at PMB 295, 8000 Plaza Boulevard, Mentor, Ohio 44060, USA.
