A longitudinal study was done assessing the latest radiographs available in a series of collarless Corail uncemented stems which have reported survival rates of 95% at 20 years. Parameters scored included the degree of “Ghosting” or delamination, the Gruen, the stem fit in the femoral canal and the degree of calcar resorption. Patient and implant demographics were noted. At 3 years the loosening rate was 23% reaching 64% at 6 years after the index procedure. It was present in all age groups, with a peak in the 24 to 49 year age group. Males and females had the same occurrence. When it was present this was always in zone 1. It was present in 6% of patients in zone 7, but then always associated with zone 1 changes. High and standard off-set stems had the same loosening rates. The looser fit of the stem the higher the incidence of loosening. There was no correlation to the type of bearing surface or the degree of calcar resorption. Those patients with a BMI of 25 – 35 had lower loosening rates compared to those with higher or lower BMI's. We postulate that cancellous bone on-growth onto the hydroxyapatite coating associated with loading flexural micro-motion leads to hydroxyapatite being pulled off the smooth stem substrate in zone 1. Progressive delamination of the hydroxyapatite then occurs. The triple-tapered design though imparts continued stability. We report high loosening rates in the Corail stem and suggest a mechanism for its development.
We have developed a technique with the underlying principle being that the difference in height between what is removed and what is inserted will determine the leg length correction (Figure 1). The height of the implant to be inserted is determined from the manufacturer's specifications. We have developed a Vertical Measurement Tool to accurately and reproducibly determine the height of the resected bone (Figure 2). Leg length correction = a−b−c+d Vertical Measurement Tool validation was performed by 4 separate surgeons on 20 resected femoral heads in the laboratory. Inter and intra-observer error was assessed. Fifty patients were assessed clinically and radiologically, to assess if desired leg length correction was achieved. Statistical analysis showed the device to be accurate with high intra and inter observer reliability. Differences between the observers were tested using a general linear model in a repeated measure design. No main effect and interaction effects were found. Intra operatively the resected head was measured and the formula was applied. The range of desired correction was 0mm to 18mm. In all cases the post-operative correction was within 4mm of the pre-operative planned correction. Statistical analysis showed that a linear Regression with ‘Actual’ as dependent and ‘Lambda’ as independent variables resulted in R= 0.889. We believe that it is consistently possible to achieve a leg length correction to within 5 mm of the pre-operative plan using the Vertical Measurement System. The system is simple and reproducible even in the hands of relatively inexperienced surgeons. For any figures or tables, please contact the authors directly by clicking on ‘Info & Metrics’ above to access author contact details.
