Abstract
The purpose of this study was to review our entire primary THR experience using large diameter femoral heads in order to prevent dislocation.
83 hips in 77 patients (average age 61years) had a total hip replacement using femoral heads at least 36 mm in diameter. Average follow-up was 4.4 years (range 1 to 17). 22% of the bearings used were conventional UHMWPE, 25% Metal on Metal (two thirds of which were one-piece sockets), and 53% cross-linked polyethylene.
UCLA hip scores improved significantly (p< 0.001) to 9.4, 8.4, 7.5, and 5.2, for pain, walking, function and activity respectively. All of the hips were stable at last follow-up although 3 hips had to be revised: 2 for instability in the early post-op period for poorly positioned socket and one for acetabular component aseptic loosening, which was rectified by revision surgery. Two out of these 3 hips had an etiology of DDH. The dislocations occurred in hips reconstructed with a head size less of 36mm only and none of the hips that dislocated had to be revised with a constrained acetabular liner.
As the safety of new wear-resistant joint bearings has improved, an increase of femoral head size leads to a lower prevalence of dislocation in THR potentially without adverse wear consequences. However, adequate positioning of the acetabular component remains a key factor in the success of this type of hip arthroplasty. Metal-on-metal, which provides the largest ball size for a given socket diameter, especially with a one-piece socket, best addresses component-to-component impingement by increasing the range of motion. Bone-to-bone impingement risks are also minimized as the travel distance to dislocation is increased by maximizing the head diameter and minimizing the socket shell thickness.
Correspondence should be addressed to Richard Komistek, PhD, International Society for Technology in Arthroplasty, PO Box 6564, Auburn, CA 95604, USA. E-mail: ista@pacbell.net
