The clinical results of bilateral total knee replacement staged at a one-week interval during a single hospital admission were compared with bilateral total knee replacements performed under the same anaesthetic and with bilateral total knee replacements performed during two separate admissions. The data were retrospectively reviewed. All operations had been performed by the same surgeon using the same design of prosthesis at a single institution. The operative time and length of stay for the one-week staged group were comparable with those of the separate admission group but longer than for the patients treated under one anaesthetic. There was a low rate of complications and good clinical outcome in all groups at a mean follow-up of four years (1 to 7.2). The group staged at a one-week interval had the least blood loss (p = 0.004). With appropriate patient selection, bilateral total knee replacement performed under a single anaesthetic, or staged at a one-week interval, is a safe and effective method to treat bilateral arthritis of the knee.

The Unispacer knee system is a cobalt-chrome self-centring tibial hemiarthroplasty device for use in the treatment of isolated medial compartment osteoarthritis of the knee. The indications for use are similar to those for high tibial osteotomy, but insertion does not require bone cuts or component fixation, and does not compromise future knee replacement surgery. A prospective study of a consecutive series of 18 patients treated with the Unispacer between June 2003 and August 2004 was carried out to determine the early clinical results of this device. The mean age of the patients was 49 years (40 to 57). A total of eight patients (44%) required revision within two years. In two patients revision to a larger spacer was required, and in six conversion to either a unicompartmental or total knee replacement was needed. At the most recent review 12 patients (66.7%) had a Unispacer remaining in situ. The mean modified visual analogue score for these patients at a mean follow-up of 19 months (12 to 26) was 3.0 (0 to 11.5). The mean pain level was 30% that of the mean pre-operative level of 10. The early clinical results using this device have been disappointing. This study demonstrates that use of the Unispacer in isolated medial compartment osteoarthritis is associated with a high rate of revision surgery and provides unpredictable relief of pain.

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We welcome letters to the Editor concerning articles which have recently been published. Such letters will be subject to the usual stages of selection and editing; where appropriate the authors of the original article will be offered the opportunity to reply. Letters should normally be under 300 words in length, doublespaced throughout, signed by all authors and fully referenced. The edited version will be returned for approval before publication. Pain related to the psoas muscle after total hip replacement Sir, I read with interest the article in the September 2002 issue by Jasani, Richards and Wynn-Jones 1 entitled 'Pain related to the psoas muscle after total hip replacement'. I entirely agree with the authors that when investigating a painful hip following total hip replacement (THR), causes other than infection and loosening of the prosthesis have to be considered. However, I would like to highlight psoas haematoma as another cause of groin pain, particularly in patients on anticoagulant medication. Although this complication of anticoagulant therapy is well recognised, its importance in relation to THR has only been recently reported. 2 Early clinical diagnosis can be established by looking for weakness of the hip flexors and a sluggish quadriceps reflex following compression of the femoral nerve by the haematoma inside the psoas sheath. The diagnosis may be confirmed by a CT scan. Prompt intervention by stopping the anticoagulation may lead to a good outcome. If not, surgical decompression will be required.