Cup orientation in primary and revision total hip arthroplasty

Abstract

Abstract Cup orientation in primary and revision total hip arthroplasty Degree Project thesis, Programme in Medicine by Ida Lindman Supervisor: Henrik Malchau Background Total hip arthroplasty (THA) is one of the most common surgical procedures today. Accurate orientation of the acetabular component is an important contributor to the survivorship of the prosthesis. Studies have considered different factors that may influence positioning of the cup but few have analyzed the difference between primary and revision procedures performed by a single surgeon. Purpose The purpose of this study was to determine whether there was a significant effect on overall cup orientation between primary and revision THA. Patients and Methods Three hundred sixty four consecutive THA procedures operated by a single surgeon at a tertiary hospital between 2011 and 2013 were identified. Among these, 172 primary and 133 revision THAs had proper radiographs. The version and inclination angles were determined by evaluating the Anterior Posterior Pelvic radiograph in Hip Analysis Suite TM. The cross-table lateral radiograph was then used to confirm anteversion or retroversion. Acetabular cups were considered acceptable if they were within the acceptable range zone 5-30° of anteversion and 30-50° of inclination, angles corresponding to conclusions made from prior studies. Furthermore were demographic data as age, Body Mass Index (BMI), gender, laterality of surgery, femoral head size, acetabular cup size and preoperative diagnosis considered if they have any association with cup positioning. Results 63.4 % of the primary THAs and 68.4 % of the revision THAs were within acceptable range for both anteversion and inclination. No statistical significance was found in cup positioning between the two groups. In the revision group, “Moderately obese” (BMI>30 but <35) was associated with a significant risk of malpositioned cups, where they tended to exceed the acceptable degree of anteversion. Males had a lower risk of having their cups placed outside of the range than female in the revision group with an OR of 0.39 (p-value 0.016). In the primary group, age was found significant where >70 years of age were more likely to have their cups within acceptable ranges for anteversion with an OR of 0.40 (p-value 0.018) when compared to age 50-70 years old. Conclusion The acetabular component orientation was similar between primary and revision THA which indicate that an experienced surgeon is able to position the cup accurately in most cases even at revision surgery. However, in the revision group patients with BMI indicating “Moderately obese” and female gender were associated with malpositioned cups even when controlling for surgeon experience. Further, in the primary group lower age was associated with a higher risk of malpositioned cups. These results accentuate some of the many important factors that even the qualified surgeon must consider when performing either a primary or a revision THA. Key words Total hip arthroplasty, revision arthroplasty, acetabular cup positioning, anteversion, inclination.