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.

The aim of the present study is to compare the Oxford Shoulder Score (OSS), the Shoulder Pain and Disability Index (SPADI) and the SF36 in terms of their correlation and sensitivity to change in a group of patients with subacromial impingement.

Patients attending a specialist shoulder clinic over a six-month period with a diagnosis of subacromial impingement completed the OSS, SPADI and SF36 on each of up to four attendances at six-week intervals, regardless of treatment. The data were analysed by creating scatter plots for each scoring system compared with each other, calculation of correlation coefficients, and calculating the effect size for each scale between subsequent visits (the difference in mean score divided by the standard deviation of the change in score for all individuals). This is a measure of sensitivity to change.

Three-hundred and twenty-three sets of scores were obtained in 110 patients. Scores were recorded across the whole range of the OSS and SPADI in our population. Similarly, the physical functioning component of the SF 36 ranged from 0 to 100. However, total SF 36 scores ranged only from 478 to 831.

There was good correlation between the OSS and SPADI scores (correlation coefficient = 0.86), although in 71% of observations the SPADI score was greater than the OSS when expressed as a percentage. The correlation between the OSS and SPADI was less good with the physical functioning component of the SF 36 (0.57 and 0.51 respectively), and worse with the total SF 36 (0.37 and 0.27 respectively) The OSS and SPADI showed good effect sizes (0.211 and 0.212) compared to the physical functioning and total SF 36 scores (0.104 and 0.063).

The OSS and SPADI show close correlation between each other, and were similarly sensitive to change in a group of patients with impingement. However, the SF 36 shows a poor spread of scores and less sensitivity to change in this group. These data support the use of the OSS or SPADI in these patients.

A prospective study to assess the long-term outcome of ASAD (arthroscopic subacromial decompression) in the presence of un-reconstructable large and massive cuff tears using a modified Constant score.

All patients under the care of the senior author admitted for ASAD had a modified Constant score recorded pre-operatively, excluding the power component. Review of patient notes between May 1994 and August 2000 identified 40 patients (45 shoulders) with un-reconstructable rotator cuff tears found at the time of surgery. Nine patients failed to attend. Thirty-one patients (35 shoulders) were scored by a single independent observer. Five shoulders were excluded having undergone subsequent surgery. Five pre-operative scores could not be retrieved. The preoperative and review scores were compared in the remaining 25 patients (25 shoulders).

The average age at review was 75 years (range 39–85) with mean review of 51 months from surgery (range 20–94). In the studied population the mean score increased as follows (95% confidence limits in parentheses). Mean pain score improved from 4.8 (+/−2) to 8.5 (+/−1.6), the mean activities of daily living score increased from 8.9 (+/−1.5) to 12.6 (+/−2.4) and the range of motion improved from 22.9 (+/−2.9) to 31.3 (+/−3.3) points.

The total score improved from 36.6 (+/−4.6) to 52.4 (+/−6.5). The average gain for each patient was 15.8 (+/−6.5)

The 95% confidence limits indicate significant improvement for pain, range of motion and total score.

In our study population of patients undergoing ASAD in the presence of un-reconstructable cuff tears, the 95% confidence limits of the preoperative and follow up scores do not overlap. ASAD confers significant benefit in patients with large cuff defects.