Abstract
Introduction
The Accolade II taper stem incorporates design features which maximize proximal stem fit and bone contact and avoids more distal taper engagement which has been shown to be problematic. RSA was used in this study to analyze stem micromotion to 2 years post-surgery, providing an indication of long-term fixation. Pain, function and health-related quality of life were also compared before and after total hip arthroplasty (THA.)
Method
This prospective, single centre case-series enrolled 35 patients into Parts A and B. The first 5 subjects were recruited to Part A of the study (learning curve), the subsequent 30 patients to part B. Radiopaque tantalum beads were inserted intra-operatively into each patient, with RSA radiographs taken immediately post-operatively, and at 3, 6, 12 and 24 months. These radiographs were digitized to DICOM file format and exported, allowing for independent analysis using the UmRSA system. Three Patient Reported Outcome Measurements; WOMAC, EQ-5D-3L and VAS pain were collected pre-operatively and at 6, 12 and 24 month intervals for all patients.
Results
A total of 33 patients completed the study, with 1 patient from Part A lost to follow up and 1 patient from part B withdrawing voluntarily. The 4 completed patients from part A of the study did not have RSA X-rays analysed since Part A was included for surgeon training purposes only. Hence RSA X-rays at the 2 year timepoint for 29 completed Part B patients were compared to immediate post-op RSA X-rays. The Average Maximum Total Point Motion (MTPM) of the Accolade II femoral stem was 0.764mm (SD +/− 0.340), with a clinical precision (defined as the standard deviation of double RSA examinations taken during the post-operative interval) of +/− 0.195mm. Additionally, the mean distal, medial and posterior migrations for the 29 patients at 24 months were all less than 0.1mm. When comparing with the literature, these MTPM values show less than average stem migration. A systematic review conducted by de Vries et al (2014) recorded 2 year MTPM values between 0.66 and 2.73mm for clinically successful uncemented collarless stems, with an average of 1.50mm.
The average WOMAC and VAS pain scores for 33 completed patients from parts A and B demonstrated decreased pain and functional limitations at 24 months when compared with pre-operative PROM results. In addition, average UK Time Trade-Off scores calculated from the EQ-5D-3L improved from 0.47 (SD +/− 0.29) pre-operatively to 0.86 (SD +/− 0.27) at 24 months, equating to improved health-related quality of life for all patients.
Conclusions
The mean MTPM from this study falls well below the average for uncemented collarless stems suggested by de Vries et al (2014). This, together with the negligible distal stem migration, affirms excellent immediate stability of the Accolade II design. These RSA results imply successful biologic fixation and a high survival rate can be expected with the Accolade II stem.
