The Effect of Size for a Hydroxyapatite-Coated Cementless Implant on Component Revision in Total Hip Arthroplasty: An Analysis of 41,265 Stems.

BACKGROUND: The cementless Corail is one of the most commonly used stems in total hip arthroplasty (THA). The aim of this study was to investigate whether there was a difference in revision rate for smaller stems. METHODS: All primary THA procedures recorded by the Australian Joint Replacement Registry from September 1999 to December 2017 performed for osteoarthritis using the Corail stem, a cementless acetabular cup, modern bearing surfaces (ceramic/ceramic, ceramic/cross-linked polyethylene, and metal/cross-linked polyethylene), and 28 mm, 32 mm, and 36 mm head sizes were included. The primary outcome measure was femoral component revision. Data were analyzed and adjusted for age, gender, and head size. Further analysis investigated the effects of surgical approach. RESULTS: There was 41,265 primary THAs recorded. The cumulative percent revision (CPR) at 13 years was 7.7% (5.5, 10.7) for stem sizes 8 and 9 and 3.0% (2.4, 3.8) for sizes 10-20 (P < .001). When adjusted for age and gender, the sizes 8 and 9 collared (hazard ratio [HR]: 6.22 [3.84-10.06], P < .001) and collarless (HR: 3.28 [2.41-4.45], P < .001) had a higher CPR than the collared and collarless size 10-20. The size 8 and 9 stems performed with an anterior approach had the highest CPR (HR: 14.44 [6.21-33.56], P < .001). The main reason for revision of size 8 and 9 femoral stems was loosening (65.2%, compared to 31.5% for 10-20 femoral stems). CONCLUSIONS: Smaller Corail stems have 4 times the rate of revision compared with the larger femoral sizes with loosening being the most common diagnosis. This is most evident when using an anterior approach.

The long leg radiograph is a reliable method of assessing alignment when compared to computer-assisted navigation and computer tomography.

BACKGROUND: The mechanical alignment of the knee is an important factor in planning for, and subsequently assessing the success of a knee replacement. It is most commonly measured using a long-leg anteroposterior radiograph (LLR) encompassing the hip, knee and ankle. Other modalities of measuring alignment include computer tomography (CT) and intra-operative computer navigation (Cas). Recent studies comparing LLRs to Cas in measuring alignment have shown significant differences between the two and have hypothesized that Cas is a more accurate modality. This study aims to investigate the accuracy of the above mentioned modalities. METHODOLOGY: A prospective study was undertaken comparing alignment as measured by long-leg radiographs and computer tomography to intra-operative navigation measurements in 40 patients undergoing a primary total knee replacement to test this hypothesis. Alignment was measured three times by three observers. Intra- and inter-observer correlation was sought between modalities. RESULTS: Intra-observer correlation was excellent in all cases (>0.98) with a coefficient of repeatability <1.1°. Inter-observer correlation was also excellent measuring >0.960 using LLRs and >0.970 using CT with coefficient of repeatability <2.8°. Inter-modality correlation proved to be higher when comparing LLRs and CT (>0.893), than when comparing either of these modalities with Cas (>0.643 and >0.671 respectively). Pre-operative values had the greatest variability. CONCLUSION: Given its availability and reduced radiation dose when compared to CT, LLRs should remain the mainstay of measuring the mechanical alignment of the lower limb, especially post-operatively. LEVEL OF EVIDENCE: II.