Introduction Bilateral total knee replacement under one anaesthetic is a common procedure. Claimed benefits include: shorter hospital stays, fewer complications of some kinds, lower over all cost and more efficient use of staff time. In general the literature supports these concepts though some writers caution against the procedure. Most studies come from large university hospitals but most joint replacements are done in smaller hospitals. At Calvary Hospital we instituted a quality assessment review of our experience to determine patient safety and cost savings.

Methods A medical records review between 1997 and 2001 showed 63 patients had bilateral total knee replacement (126 knees). We further identified 38 patients who had both knees replaced at separate admissions within one year (76 knees), these were the staged knee replacements. We selected a matched subset of the patients who had only one joint replaced in this period (125 knees). A review was carried out over a wide variety of parameters on a relation database.

Results The incidence of infection, unplanned return to theatre and DVT was too low for this study to have statistical power and little difference was noted. Amongst the more common post-operative respiratory, cardiovascular and gastrointestinal complications no significant difference was noted per hospital admission. Post-operative confusion was not more common in bilateral replacements and we felt that fat embolism syndrome was not increased. Neither, type of anaesthesia, previous medical history nor post-operative care predicted for confusion but we did note a strikingly increased incidence in patients of low BMI. Contrary to common views obese patients did not have more complications or longer hospital stays. Mobilisation in heavy patients is not prolonged provided they have good upper limb strength. Blood transfusion is more likely in bilateral cases but our review has allowed us to formulate a nomogram based on weight and pre-operative haemoglobin to improve blood management. High admission rates to ICU were noted but mostly for precautionary reasons, the unplanned admission rate was not greater. Pre-operative urinary tract infection and use of an IDC were not associated with any infective events.

Conclusions Bilateral total knee replacement was found to be a safe proceedure with complication rates equivalent to single knee replacement. For the patient who has severe arthritis in both knees it is prefered to repeated single knee replacement as the exposure to complications is halved. A nomogram to predict blood transfusion requirements has allowed a reduction in the transfusion rate for all groups. Twenty-three hour recovery admission covers the needs of bilateral replacement patients in the immediate post-opertaive setting. Cost savings are identified allowing four knees to be replaced, if done bilaterally, for each three knees replaced as seperate admissions.