Correction of Femoral Acetabular Impingement at the Time of Primary THA

Abstract

Background: Primary total hip arthroplasty (THA) is considered one of the most cost effective and functionally beneficial procedures to treat end-stage coxarthrosis worldwide. However, in all regions of the world, there is a small percentage of patients that are plagued by residual anterior hip pain and have limited hip flexion. One explanation for this problem is bone and soft tissue impingement in the anterior hip region. In the native hip, the problem is described as femoral acetabular impingement (FAI). FAI is a form of developmental dysplasia of the hip (DDH). Not infrequently, these dysplastic acetabula are also retroverted. In primary THA, a retroverted boney acetabulum adversely affects prosthetic hip function. Specifically, when the acetabular cup is inserted in an anteverted position and the native acetabulum is retroverted, the proximal femur will still impinge upon the retroverted acetabular bone with flexion and internal rotation. This causes mechanical instability, pain, and prosthetic subluxation. We aptly name this condition prosthetic femoral acetabular impingement (PFAI).Methods: In this study we address PFAI with an anterior acetabular bone wall reduction (AABWR). In a consecutive series of 426 primary THA’s, we prospectively removed all impinging anterior retroverted bone during the THA procedure. All acetabular cups were placed between 25-35 degrees of anteversion. Retroverted acetabular bone extending beyond the acetabular cup was removed along with impinging capsular tissues. All femoral stems were positioned between 15-20 degrees.Results: The study group consisted of 426 THA’s. Three hundred patients (70%) had an AABWR. There were 140 females (47%) and 160 males (53%). The average amount of bone resected in the AABWR group was 1.32 cm (0.3 cm to 3.4 cm). For females, the average bone resection measured 1.1 cm (0.3 to 2.0 cm). For males, the average bone resection measured 1.53 cm (0.3 cm to 3.4 cm). Harris Hip Scores (HHS) at minimum of 1 year follow-up (range 1 to 11.5 years) averaged 91 (64 to 100) for the entire group. In the AABWR group, HHS averaged 92 (71 to 100). Average hip flexion was 110 degrees (100 to 130 degrees). In the non-AABWR group, HHS averaged 87 (71 to 100). Average flexion was 109 degrees (88 to 125 degrees). In the AABWR group, 12 patients (4%) experienced groin pain symptoms. On a scale from 0 to 4, the peak groin pain rating was 1 in 10 of the 12 patients and the remaining 2 rated his/her pain at a 2. As time progressed, 50% of these patients saw their groin pain resolve. In the non-AABWR group, 2 patients (1.6%) experienced groin pain and both patients rated his/her pain at a 1.Discussion: Maximizing hip flexion and function for the active patient undergoing primary THA requires meticulous surgical technique. PFAI may be one reason for unexplained anterior hip pain in the highly active patient that demands higher hip flexion and rotation. Our experience shows that the anterior acetabular rim and part of the anterior column can be removed at the time of primary THA without compromising the THA procedure. The AABWR is now an integral part of our primary THA technique.