Treatment of the unstable total hip arthroplasty using modularity, soft tissue, and allograft reconstruction.

This is a retrospective analysis of a stepwise approach to the treatment of the unstable total hip arthroplasty. Thirty-two hips in 32 patients were analyzed 9 months to 7 years (average, 3.6 years) after reoperation for instability. Half of the patients underwent revisions of primary total hip arthroplasties, and the other half underwent multiple procedures. Of the patients, 26 dislocated posteriorly, 4 dislocated anteriorly, and 2 were multidirectional. The commonest cause for the dislocation was soft tissue deficiency (n = 17). Other common causes included anterior soft tissue impingement (n = 10), unsatisfactory head-to-neck ratio (n = 5), hypoanteversion of the socket (n = 4), and deficient abductor mechanism (n = 4). Multiple causes were present in 75% of the patients, with a combination of 2 (48%) or > or =3 (28%) factors of instability. Management of the instability by addressing the soft tissue and modification of modular components was successful in 25 patients and unsuccessful in 1 patient. Three unstable hips were treated successfully with an innovative soft tissue augmentation using an Achilles tendon-bone allograft.