THE METAPHYSEAL-DIAPHYSEAL INDEX SCORE: A NOVEL METHOD OF PREVENTING INTRA-OPERATIVE PERIPROSTHETIC FRACTURES IN MODERN UNCEMENTED HEMIARTHROPLASTY IN OSTEOPOROTIC NECK OF FEMUR FRACTURES

Abstract

Introduction: The JRI Furlong HAC LOL hemiarthroplasty stem has shown increased periprosthetic fracture rates compared to previous literature (15.2% vs 7.4%) [1,2,3]. This study seeks 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: A 5 year prospective cohort of 560 consecutive patients underwent hemiarthroplasty (cemented or uncemented). A nested case-control study to determine risk factors affecting intra-operative fracture was carried out.

Clinical outcomes and radiographic analysis was performed. The Vancouver Classification was used to classify periprosthetic fracture.

The MDI score was calculated using radiographs, as a control (gold standard), Yeung’s CBR score was calculated [4]. See Figure 1. A receiver operating characteristic (ROC) curve was formulated for both and area under the curve (AUC) compared. Intra and inter-observer correlations were determined.

Cost analysis was also worked out.

Results: 407 uncemented and 153 cemented stems were implanted. The use of uncemented implants was the main risk factor for intra-operative periprosthetic fracture.

62 periprosthetic fractures occurred in the uncemented group (15.2%), 9 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 and 90 day mortality 19.7%, p< 0.03.

MDI’s AUC was 0.985 compared to CBR’s 0.948, p< 0.001. See Figure 2. The MDI score cut-off to predict fracture was 21, sensitivity 98.3%, specificity 99.8%, PPV 90.5%, NPV 98%. ANCOVA 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 £93,780.

Discussion: The MDI score is a 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: Development of diagnostic criteria on basis of consecutive patients (with universally applied reference “gold” standard).