Introduction: An increasing number of young and active patients are undergoing total hip replacement (THR), placing greater demands on the longevity of the implant. One of the most common modes of failure of a THR is aseptic loosening secondary to wear. This study aims to evaluate wear rates seen in a ceramic on polyethylene bearing, and to produce a mathematical model that could be used to predict wear which would have a role in a day-to-day clinic environment.

Methods: Radiographs were examined from 59 uncemented total hip replacements performed between March 1993 and April 2004 comprising a ceramic head on a polyethylene liner. Wear measurements were made using a manual Livermore technique employing digital callipers (accuracy 0.01mm). Multiple radiographic parameters were analysed so that those affecting wear could be identified and included in a mathematical model to predict wear.

Results: 59 hips were measured in 43 patients. Average age at time of follow-up was 53 (34–76). The mean length of time between postoperative and follow-up x-rays was 53 months (11–162). Overall wear rates were 0.05mm/year and total wear increased with the length of time an implant had been in place. There was no correlation between femoral stem alignment or acetabular inclination and wear rates. Multivariate linear regression analysis revealed that sex and cup type were significant contributing variables to wear. A predictive model was produced with an R2 value of 0.543.

Conclusion: This study confirms low wear rates with a ceramic on polyethylene bearing. The mathematical model produced can predict the variability of wear in 54.3% of hips. Further refinement may enable the model to be used to identify risk factors and therefore patients that require greater scrutiny at follow-up.

Introduction: A recent JBJS(Br) article examined skin markers after contamination with a standard MRSA inoculum and cultured on MRSA-indicator nutrient agar. The Penflex™ marker showed no survival after 15 minutes, whereas the Viomedex™ marker produced MRSA cultures for up to three weeks.

Research undertaken at Wrightington has shown that in primary joint replacement coagulase-negative staphylococci account for 67.2% – 76% of contaminants isolated from the ultra clean zone. It is the most prevalent and persistent species on human skin and mucous membranes and accounts for 58% of failures due to deep infection of primary THR.

Further studies of nosocomial infection transmission show bacterial contamination of healthcare workers’ scissors, ballpoint pens, stethoscopes and lab coats with MRSA, VRE and gram-negative bacilli.

Multiuse skin markers may become colonised, possibly with MRSA, MRSE and gram-negative bacilli. This may contaminate patients and cause premature failure of arthroplasty, leading some units to adopt a single use policy.

Our aim was to ascertain bacterial colonisation of multiuse skin markers.

Method: Multiuse indelible skin markers were collected from Orthopaedic staff, wards and Day Surgery Units within the Mid-Yorkshire Hospitals.

Pens identified by a number, brand, location and approximate pen age.

Pen tips were neutralised with 10ml sterile Peptone water and this was used as the inoculum.

Cap interior swabbed with sterile swab (pre-dipped in sterile water).

Both were inoculated into enrichment broth and plated onto Blood and McConkey media.

Incubation at 37°c for 18 hours with plates read at 7 days for colony forming units.

Results: 31 pens. 15 different brands. Age 1 month– 3yrs

No growth on all plates after incubation for 7 days.

Conclusion: These results indicate that multiuse indelible skin markers are safe. There is no evidence to support subsequent cross contamination or the need for sterile single use pens for preoperative marking.

Aims: Prosthesis malpositioning and inadequate cement mantles have been shown to adversely affect outcomes in cemented total hip arthroplasty. Although this has been extensively studied and reported for anteroposterior (AP) radiographs, we have found a paucity of literature concerning lateral radiographs which this study addresses. Methods: We analysed radiographs of 100 patients (Group I) with cemented Charnley total hip replacements (52 ßanged, 48 round back) performed through the lateral approach to determine the relationship between stem positioning and cement mantles in both AP and lateral radiographs. The measurements were made by a single observer and the data was analysed using chi squared tests to compare categorical data. Results: The most common stem malpositioning was seen in the lateral radiographs with þfty þve percent of stems directed 4 or more degrees from anterior to posterior (A to P). In contrast on the AP radiographs 18% of stems were directed from medial to lateral (Varus) and 3% of stems were directed from lateral to medial (Valgus) 4 or more degrees. There was no relationship between the different malpositions. Adequate resection of the posterior femoral neck gave better alignment of the stem in the lateral radiograph (p< 0.001). The ßanged stems were signiþcantly more in varus as compared to round back stems (p< 0.01). Cement mantles were most often deþcient in Gruen zone 12. There was a strong association between sagittal malpositioning and deþcient zones 12 and 9 (p< 0.001). Conclusions: This study demonstrates that sagittal mal-positioning of the stem is most important and surgical technique has a signiþcant inßuence on the same.

A radiological study of 50 patients with thoracic Scheuermann's disease revealed two types of lateral spinal curvature. A total of 43 lateral curves was present in 35 of the patients. Thirteen were apical at the same level as the Scheuermann's kyphosis and were due to vertebral-body wedging in the coronal plane; these curves had a mean Cobb angle of 15 degrees, occurred with equal prevalence in boys and girls and were directed equally to right and left. Thirty curves occurred in regions of compensatory lordosis (mean 5.6 degrees) situated above or, more commonly, below the Scheuermann's kyphosis. These scolioses had a mean Cobb angle of 16 degrees, were more often convex to the right than to the left and were significantly more prevalent in girls than in boys. The presence of these kyphoses and scolioses in the same spine, separated by only a few vertebrae, emphasises the importance of the sagittal plane in idiopathic spinal deformities and strongly suggests that idiopathic scoliosis and Scheuermann's disease share a common pathological process.

Eleven articulated scoliotic spines were examined radiographically and morphometrically. Measurement of the curve on anteroposterior radiographs of the specimens gave a mean Cobb angle of 70 degrees, though true anteroposterior radiographs of the deformity revealed a mean Cobb angle of 99 degrees (41% greater). Lateral radiographs gave the erroneous impression that there was a mean kyphosis of 41 degrees while true lateral projections revealed a mean apical lordosis of 14 degrees. Morphometric measurements confirmed the presence of a lordosis at bony level, the apical vertebral bodies being significantly taller anteriorly (P less than 0.02). There were significant correlations (P less than 0.01) between the true size of the lateral scoliosis, the amount of axial rotation and the size of the apical lordosis. This study illustrates the three-dimensional nature of the deformity in scoliosis and its property of changing in character and magnitude according to the plane of radiographic projection.