Introduction: The workload of a bone and soft tissue tumour (BSTT) multidisciplinary team (MDT) is varied. Only a proportion of the workload attracts specific funding from the National Commissioning Group (NCG) but many patients who do not have primary malignant bone tumours are also seen and treated. We analysed the workload of our supra-regional BSTT MDT to determine the variety of conditions seen, the proportion that does not attract specific funding and the expertise required to run the service.

Methods: A prospective database was used to identify all new patients discussed at our weekly BSTT MDT meetings between 2004 and 2008 inclusively. Patients were divided by diagnosis into eight categories and further identified as to whether or not they attracted funding under NCG regulations.

Results: 1743 new patients were identified of which 83 were excluded. Of the remaining 1660, 65% were non-sarcoma and 50% were benign. 31% of the malignant workload was non-sarcoma. Only 11% of patients were eligible for NCG funding. Of those requiring surgery, the orthopaedic team managed 93% of benign and 77% of malignant cases; general, plastic, or thoracic surgical teams managed the remainder.

Discussion: NCG funds the management of all malignant primary bone tumours and the investigation and/or treatment of other selected conditions; the majority of our workload does not qualify. Despite fluctuations in the total workload, the ratio of benign to malignant cases remains relatively constant. Considerable expertise across many different specialties is essential for an effective and efficient MDT.

There are many methods for analysing wear volume in failed polyethylene acetabular components. We compared a radiological technique with three recognised ex vivo methods of measurement.

We tested 18 ultra-high-molecular-weight polyethylene acetabular components revised for wear and aseptic loosening, of which 13 had pre-revision radiographs, from which the wear volume was calculated based upon the linear wear. We used a shadowgraph technique on silicone casts of all of the retrievals and a coordinate measuring method on the components directly. For these techniques, the wear vector was calculated for each component and the wear volume extrapolated using mathematical equations. The volumetric wear was also measured directly using a fluid-displacement method. The results of each technique were compared.

The series had high wear volumes (mean 1385 mm³; 730 to 1850) and high wear rates (mean 205 mm³/year; 92 to 363). There were wide variations in the measurements of wear volume between the radiological and the other techniques. Radiograph-derived wear volume correlated poorly with that of the fluid-displacement method, co-ordinate measuring method and shadowgraph methods, becoming less accurate as the wear increased. The mean overestimation in radiological wear volume was 47.7% of the fluid-displacement method wear volume.

Fluid-displacement method, coordinate measuring method and shadowgraph determinations of wear volume were all better than that of the radiograph-derived linear measurements since they took into account the direction of wear. However, only radiological techniques can be used in vivo and remain useful for monitoring linear wear in the clinical setting.

Interpretation of radiological measurements of acetabular wear must be done judiciously in the clinical setting. In vitro laboratory techniques, in particular the fluid-displacement method, remain the most accurate and reliable methods of assessing the wear of acetabular polyethylene.

Introduction The ABG I acetabular insert is an ultra high molecular weight polyethylene (UHMWPE) component used in primary hip arthroplasty. Studies have shown early osteolysis and aseptic loosening of the ABG I uncemented cup compared with other implants. Theories advocate that loosening is initiated by the biological response to insert wear debris; wear volume and the distribution of particle size are considered to be important parameters. This study analysed explanted plastic inserts to identify any mechanical properties that may have contributed to early failure.

Materials and Methods 21 ABG I acetabular components were revised due to aseptic loosening over a 16 month period. Silicone casts of the insert sockets were made and volumetric analysis performed using a shadowgraphing technique and a coordinate measuring machine (CMM). The UHMWPE inserts were divided into uniform pieces with a diamond-tipped microsaw and analysed for hardness, wear, stress and strain properties using a microhardness tool, pin-on-plate analysis and small punch testing. We performed identical tests on explanted inserts from other manufacturers.

Results We present the findings of the above tests and provide suggestions as to why these particular implants are more prone to early failure when compared with other common implants. We also discuss the results of volumetric analysis by shadowgraphing compared with CMM.