The role of computer-assisted surgery in maintaining the level of the joint in primary knee joint replacement (TKR) has not been well defined. We undertook a blinded randomised controlled trial comparing joint-line maintenance, functional outcomes, and quality-of-life outcomes between patients undergoing computer-assisted and conventional TKR. A total of 115 patients were randomised (computer-assisted, n = 55; conventional, n = 60).

Two years post-operatively no significant correlation was found between computer-assisted and conventional surgery in terms of maintaining the joint line. Those TKRs where the joint line was depressed post-operatively improved the least in terms of functional scores. No difference was detected in terms of quality-of-life outcomes. Change in joint line was found to be related to change in alignment. Change in alignment significantly affects change in joint line and functional scores.

We carried out a prospective, continuous study on 529 patients who underwent primary total knee replacement between January 2006 and December 2007 at a major teaching hospital. The aim was to investigate weight change and the functional and clinical outcome in non-obese and obese groups at 12 months post-operatively. The patients were grouped according to their pre-operative body mass index (BMI) as follows: non-obese (BMI < 30 kg/m²), obese (BMI ³ 30 to 39 kg/m²) and morbidly obese (BMI > 40 kg/m²). The clinical outcome data were available for all patients and functional outcome data for 521 (98.5%). Overall, 318 (60.1%) of the patients were obese or morbidly obese.

At 12 months, a clinically significant weight loss of ≥ 5% had occurred in 40 (12.6%) of the obese patients, but 107 (21%) gained weight. The change in the International Knee Society score was less in obese and morbidly obese compared with non-obese patients (p = 0.016). Adverse events occurred in 30 (14.2%) of the non-obese, 59 (22.6%) of the obese and 20 (35.1%) of the morbidly obese patients (p = 0.001).

Introduction: Inadequate cementation of the acetabular component in hip replacement surgery leads to early aseptic loosening, the most common cause of revision. The optimum method of cementation has not been fully evaluated. This study aimed to determine the effect of the acetabular component flange on mean and peak pressure during component insertion.

Method: A 53mm deepened hemisphere was machined from aluminium. Pressure transducers were positioned at the rim, at 45 degrees, and at the base. Polyethelene acetabular components of different sizes and flange designs were mounted onto a materials testing machine and inserted at a constant rate into Palacos R cement within the aluminium hemisphere. Insertion was stopped at a pre-determined point when an even cement mantle was achieved. The same components were then tested without a flange. Each test was repeated six times. Output data from the transducers was analysed.

Results: Components with a flange create a mean pressure 6–18 times higher at the rim than those without a flange. At the base pressures are 2–4 times higher. A stiffer flange generates higher peak and mean pressures than a more malleable flange. Delaying insertion by one minute does not increase the pressures achieved unless a flange is used.

Discussion: These results strongly support the use of a flange to contain cement during insertion of the acetabular component. Unflanged components fail to achieve satisfactory mean or peak pressures, even if insertion is delayed. This is likely to result in poor cement penetration into bone and reduced longevity of interface fixation.