Acetabular Abduction Research Articles

Early outcomes following minimally invasive total hip arthroplasty using a two-incision approach versus a mini-posterior approach

We evaluated early clinical results and radiographic findings of MIS THA using 2-incsion approach and mini-posterior approach. A consecutive series of 35 patients (40 hips) with 2-incision THA and a consecutive series of 35 patients (36 hips) with mini-posterior THA performed in the same period were evaluated. The patient groups were not randomised. At the mean follow-up of 20.2 months (range, 12-36 months), the 2-incision group had significantly earlier ambulation, driving ability and return to work. However, it had significantly more operative time, blood loss, blood transfusion and complications. Regarding radiographic findings of 2-incision group and mini-posterior group, the mean radiographic acetabular abduction of was 46.7 degrees (89% was within 35- 55) and 44.8 degrees (84% was within 35-55), respectively. The femoral stem was in neutral position in 80% and 83%, respectively. There was no statistical difference of the implant position between groups. Although MIS 2-incison THA provided faster, early ambulation than the mini-posterior THA, surgeons have to weigh the advantages and disadvantages of this technique including, increased operative time, blood loss and their familiarity with similar standard incisions and landmarks.

Clinical Outcome of Current Generation Hydroxyapatite Coated Acetabular Design

Hydroxyapatite (HA) coatings for femoral stems have been successful in short- to intermediate-term follow up. However, the outcomes of HA-coated cups have not been as successful as comparable non-HA-coated designs. This has been attributed to component design and to poor quality HA-coating processes. This is a clinical outcome study of a newer generation acetabular design with an improved plasma-sprayed HA-coat. Ninety consecutive primary total hip replacements implanted with a HA-coated metal-backed cup were prospectively followed up for 2–5 years after surgery. Mean age was 69 years, male:female ratio was 36:47; mean-weight was 77 kg. Polyethylene wear was measured on digitized images. Component position, component migration, and implant-bone interface radiolucent lines were analyzed by computerized image analysis. Hip-scores improved from preoperative mean 59(±12) to a final follow-up mean of 91(±12). One hip was revised for recurrent dislocation. No hips were revised for aseptic loosening. Mean acetabular abduction angle was 46°(±8.5) and anteversion was 18°(±8.7). Incomplete lucent lines were noted on early postoperative radiographs in 5% of the cases. With ongoing follow up radiolucent line thickness decreased by mean 13% and radiolucent line density increased by 11%. No cup had complete continuous radiolucent lines or lysis. Mean polyethylene linear and volumetric wear rates were 0.14(± 0.15) mm/year and 73(± 70) mm3/year respectively. Wear rates were higher in males (p<0.03). No other factor (age, body weight, cup abduction or anteversion angle) correlated significantly with wear rate. This study presents encouraging short-term results. The improvement in radiolucent lines suggests a beneficial effect of the HA-coat on bone ingrowth. None of the cups loosened or migrated. Wear rates were comparable to published reports of successful non-HA-coated cups. Long-term follow up is ongoing to corroborate these early findings.

The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios.

Prosthetic impingement due to poor positioning can limit the range of motion of the hip after total hip arthroplasty. In this study, a computer model was used to determine the effects of the positions of the acetabular and femoral components and of varying head-neck ratios on impingement and range of motion. A three-dimensional generic hip prosthesis with a hemispherical cup, a neck diameter of 12.25 millimeters, and a head size ranging from twenty-two to thirty-two millimeters was simulated on a computer. The maximum range of motion of the hip was measured, before the neck impinged on the liner of the cup, for acetabular abduction angles ranging from 35 to 55 degrees and acetabular and femoral anteversion ranging from 0 to 30 degrees. Stability of the hip was estimated as the maximum possible flexion coupled with 10 degrees of adduction and 10 degrees of internal rotation and also as the maximum possible extension coupled with 10 degrees of external rotation. The effects of prosthetic orientation on activities of daily living were analyzed as well. Acetabular abduction angles of less than 45 degrees decreased flexion and abduction of the hip, whereas higher angles decreased adduction and rotation. Femoral and acetabular anteversion increased flexion but decreased extension. Acetabular abduction angles of between 45 and 55 degrees permitted a better overall range of motion and stability when combined with appropriate acetabular and femoral anteversion. Lower head-neck ratios decreased the range of motion that was possible without prosthetic impingement. The addition of a modular sleeve that increased the diameter of the femoral neck by two millimeters decreased the range of motion by 1.5 to 8.5 degrees, depending on the direction of motion that was studied. There is a complex interplay between the angles of orientation of the femoral and acetabular components. Acetabular abduction angles between 45 and 55 degrees, when combined with appropriate acetabular and femoral anteversion, resulted in a maximum overall range of motion and stability with respect to prosthetic impingement. During total hip arthroplasty, acetabular abduction is often constrained by available bone coverage, while femoral anteversion may be dictated by the geometry of the femoral shaft. For each combination of acetabular abduction and femoral anteversion, there is an optimum range of acetabular anteversion that allows the potential for a maximum range of motion without prosthetic impingement after total hip arthroplasty. These data can be used intraoperatively to determine optimum position.

Minor column structural acetabular allografts in revision hip arthroplasty.

A minor column (shelf) allograft is used for uncontained defects that involve less than 50% of the acetabulum. The prospectively collected records and radiographs of 47 patients (51 hips) who had undergone minor column structural acetabular allograft reconstruction during revision hip arthroplasty were reviewed. The purpose was to identify the long-term results (minimum 5 years) and factors that may influence longevity of the allograft and predispose the patient to subsequent acetabular component failure. The mean duration of followup was 119 months (range, 68-195 months). There was one perioperative death and six patients were lost to followup. Eleven patients (22%) required additional surgery. Three acetabular cups could not be revised successfully, despite multiple attempts, and the patients were treated with Girdlestone excisions. Eight patients underwent successful revision surgery with only three requiring a repeat structural allograft. Survival time for the acetabular cup as determined by Kaplan-Meier analysis was 153 months (95% confidence interval; range, 136-169 months). Cup failure was associated with more operative procedures performed before revision surgery (mean, 3.2 procedures), and failure to restore the vertical center of hip rotation to within 12 to 14 mm of the predicted value. The acetabular abduction angle was not a predictor for failure. The current study shows that good results can be achieved with structural acetabular allograft reconstruction with mid-term to long-term implant survival (cup aseptic survival, 80.4% and allograft re-construction survival, 94.1%), especially if there is restoration of near normal hip biomechanics.

Effects of acetabular abduction on cup wear rates in total hip arthroplasty

This study was designed to determine the effect of acetabular abduction on the polyethylene wear rates of the acetabular component. The hypothesis of this study is that acetabular placement, in particular abduction, effects contact forces and therefore polyethylene wear. A total of 364 total hip arthroplasties that were performed between 1974 and 1976 were included in this study. The cemented all-polyethylene acetabular components were the same for each case and came from a single supplier. The polyethylene wear rates were calculated by measuring the shortest radius from the center of the prosthetic femoral head to a point on the outer surface of the acetabular cup. An immediate postoperative radiograph was compared with a follow-up radiograph at least 9.5 years later. A standardized radiograph was used to prevent differences due to magnification. The abduction or inclination of the acetabular cups was measured in all of the patients. The amount of acetabular cup abduction was measured relative to the ischial tuberosity line. The mean abduction was 44.1° with a standard deviation of 9.2° and a median of 44°. The range of abduction was from 0° to 85°. This analysis failed to show a correlation between the amount of acetabular abduction and polyethylene wear rates (Pearson's correlation coefficient = 0.0679; P = .20). With a sample size of 364, there is over a 95% change (statistical power) of detecting an underlying true correlation between wear and abduction that is greater than or equal to 0.20. We were unable to demonstrate a difference in wear that would correlate with the differing degrees of abduction of the acetabular socket. We felt that the radiographic measurements of wear were quite accurate. This method of determining acetabular abduction has also been documented and supported in previous literature and has allowed us to accurately determine acetabular abduction. The results of our study demonstrate that within the normal ranges described by our study, polyethylene wear did not significantly increase with increased abduction of the acetabular component.

Constrained acetabular components

Between May 1987 and October 1990, 21 constrained acetabular components were used in revision total hip arthroplasty at the University of California, San Francisco. In 18 patients, the device was placed for a chronically dislocating total hip arthroplasty. In the remaining three, intraoperative instability during revision total hip arthroplasty necessitated its use. At the minimum 2-year follow-up evaluation (average, 31 months; range, 24–64 months), 15 patients (71%) experienced no further dislocations or subluxations. There were eight dislocations in the remaining six patients (29%). The average Harris hip score at the follow-up evaluation was 76 points (range, 32–100 points). For those patients who redislocated (n = 6), an increased acetabular abduction angle of the metallic acetabular cup, averaging 70°, was the only predictive factor of failure of the constrained cup ( P < .05). No radiographic or clinical evidence of loosening in the 19 porous ingrowth acetabular components was observed. This device will relieve the complication of severe hip instability in the majority of patients, but is not universally successful.