Polyethylene wear in a non-congruous unicompartmental knee replacement: a retrieval analysis.

Polyethylene wear is considered a threat to the long-term survival of unicompartmental knee replacement (UKR). This study aims to determine the linear penetration and volumetric wear associated with a non-congruent commonly used UKR, the St Georg Sled. This prosthesis has a biconvex femoral component which articulates with a flat polyethylene tibial component resulting in point contact. Components were retrieved from the knees of 19 patients undergoing revision for a failed UKR after primary replacement. Linear penetration and volumetric wear was measured using a coordinate measuring machine. Using an un-used implant, a three-dimensional computer model of the surface was generated and compared to the explanted specimen. Most patients had revisions because of disease progression to other compartments rather than specific wear related pathology. The mean linear wear for the sample was 0.89 mm (S.D. 0.59 mm) over an average period of 5.6 years giving the mean linear penetration rate of 0.15 mm/year. The mean volumetric wear was 99.7 mm3 (S.D. 79.3 mm3) over the same period giving a mean annual volumetric wear rate of 17.3 mm3/year. The results in this study indicate that clinically significant wear is not necessarily a feature of this fixed bearing unicompartmental knee replacement. The pattern of wear is consistent with clinical findings and indicates excavation of the polyethylene after implantation but at a slower rate than would be anticipated.

Topical anaesthesia to reduce pain associated with carpal tunnel surgery.

This randomized, double-blinded study assessed the effectiveness of a topical anaesthetic, eutectic mixture of local anaesthetics (EMLA), in reducing pain associated with carpal tunnel release performed under local anaesthetic. Fifty-six patients undergoing carpal tunnel release under local anaesthetic were randomized into either EMLA (n = 29) or placebo (n = 27) groups. Visual analogue pain scores were obtained for needle insertion, injection of anaesthetic and surgery itself. Pain scores were significantly less for needle insertion (P = 0.001) and injection of anaesthetic (P = 0.0005). Scores related to surgery were also lower in the EMLA group, but this did not reach statistical significance.

The prognostic value and reproducibility of the radiological features of the fractured scaphoid.

We investigated whether the radiological features of the fractured scaphoid could be reproducibly measured and used to predict the likelihood of union with conservative plaster cast immobilization. We found that the inter- and intra-observer reproducibility of the Compson, Herbert and Russe classification systems were only fair and that none predicted fracture union. Assessments of fracture level, comminution and displacement showed moderate inter- and intra-observer reproducibility but did not predict the likelihood of fracture union. We conclude that the radiological features of acute scaphoid fractures cannot be used to predict the likelihood of fracture union.

Acute fractures of the scaphoid. Treatment by cast immobilisation with the wrist in flexion or extension?

Acute fractures of the scaphoid were randomly allocated for conservative treatment in a Colles'-type plaster cast with the wrist immobilised in either 20 degrees flexion or 20 degrees extension. The position of the wrist did not influence the rate of union of the fracture (89%) but when reviewed after six months the wrists which had been immobilised in flexion had a greater restriction of extension. We recommend that acute fractures of the scaphoid should be treated in a Colles'-type cast with the wrist in slight extension.