Abstract
Introduction: The JRI Furlong HAC LOL hemiarthroplasty stem has shown increased periprosthetic fracture rates compared to previous literature(15.2% vs 7.4%). This study will seek to identify a measurable radiographic index, the Metaphyseal-Diaphyseal Index (MDI) score to determine whether intra-operative fracture in osteoporotic bone can be predicted to influence the type of prosthesis used (cemented or uncemented).
Methodology: Over 5 years prospectively, a cohort of 560 consecutive patients undergoing hemiarthroplasty (cemented and uncemented) were evaluated. Clinical outcomes and radiographic analysis was performed. The Vancouver Classification was used to classify peri-prosthetic fracture. The MDI score was calculated using radiographs from the uncemented group. As a control (gold standard), Yeung et al’s CBR score was also calculated. From this, a receiver operating characteristic (ROC) curve was formulated for both scores and area under the curve (AUC) compared. Intra and inter-observer correlations were determined. Cost analysis was also worked out for adverse outcomes.
Results: 407 uncemented and 153 cemented stems were implanted. 62 periprosthetic fractures occurred in the uncemented group (15.2%), 9 occurred in the cemented group (5.9%), p< 0.001. The revision rate for sustaining a periprosthetic fracture (uncemented group) was 17.7%, p< 0.001. MDI’s AUC was 0.985 compared to CBR’s 0.948, p< 0.001. The MDI score cut-off to predict fracture was 21, sensitivity 98.3%, specificity 99.8%, positive predictive value 90.5% and negative predictive value 98%. ANCOVA analysis ruled out any other confounding factors as being significant. The intra and inter-observer Pearson correlation scores were r=0.99, p< 0.001. The total extra cost due to the intra-operative fractures was ú40,140.
Discussion: The MDI score has been shown to be a potentially useful, cost effective way of preventing this serious complication from occurring. We recommend that any femur scoring 21 or less on the MDI score be considered for cemented hemiarthroplasty. Level of evidence: Level 2 Diagnostic Study: Investigating a diagnostic test against gold standard.
Correspondence should be addressed to Dr Roger Bayston, Division of Orthopaedic and Accident Surgery, Queen’s Medical Centre, Nottingham, NG7 2UH, England.
