Aims

The main objective of this study is to analyze the penetration of bone cement in four different full cementation techniques of the tibial tray.

Computer-assisted surgical techniques in knee replacement procedures have been shown to increase the accuracy of implant positioning and reduce the incidence of alignment and soft-tissue balancing “outliers”. The use of this technology as a training tool is less widely reported. However, the recent implementation of the EWTD 48-hour working week for junior doctors has focussed attention on the issues of surgical training and experience. Recent evidence from trainee logbooks has shown a significant downward trend in operative exposure and this is forcing changes in the principles of how training should be delivered. Trainees are actively required to demonstrate operative competence in order to progress but are increasingly faced with limited opportunities to acquire these skills. On the other hand, trainers also face difficulties with the prospect of supervising less accomplished trainees which raises ethical issues of patient protection. We present a trainee’s perspective of experience gained in a unit routinely using computer-assisted technology and highlight the potential to enhance the learning process. Navigation systems provide constant visual and numerical feedback via a computer simulated interpretation. Initially this displays relevant functional anatomy, helps in the identification of anatomical landmarks and demonstrates sagittal and coronal plane deformities which can be difficult to accurately assess “by eye”. Computer-assisted systems have the benefit of displaying only bony anatomy which improves visualisation. This can then be compared to the palpable, clinical deformity on the table. The geometry of the native knee is also made clear with the navigation system leading to a better understand of the objectives of TKR. There are some aspects of the biomechanics of the knee which are difficult to appreciate, such as the changes in varus-valgus alignment during flexion and extension. This may be very subtle and difficult to pick up manually but can look quite dramatic on the computer. The position of cutting jigs which are held to the bone by pins can be altered by inadvertently lifting or hanging on them with the saw, when making the bone cuts. Additionally the cut can be altered by advancing the cutting block closer to the bone, for example if cutting the tibia with a posterior slope. Both these effects can be quantified by using the navigation tools to confirm the cut that has been made. Trainers can have the benefit of seeing the alignment and confirming the cuts made by a trainee without having to get closely involved with the operation. Cementation technique is also open to scrutiny with the ability to compare pre and post cementation alignment. The positive feedback obtained from computer assisted surgery is educational to the trainee, by giving an undisputable computer generated graphic of what they are doing during the different stages of total knee arthroplasty. It also shows what has been achieved at the end of the procedure. This can give both the trainer and trainee more confidence in the procedure and ensures patient safety

Introduction: Osteolysis is a significant problem associated with hip replacement. In the early stages of osteolysis, when the implant is still stable, formal revision is technically demanding and may result in signififant bone loss. A recently described technique for acetabular component revision addresses osteolysis, retaining the acetabular cup and cementing a new polyethylene liner.

Materials and Methods: Between January 2000 and December 2003, 29 liner cementation revisions in 27 patients were performed. The mean age was 61 years (range 37–77), the mean time elapsed after the original surgery was 6.7 years (3–14). 23 of the hips (79%) were ABG (Howmedica). Only 20 (69%) of the patients were clinically symptomatic. At surgery the polyethylene was removed and osteolytic cysts were debrided. Then, the metal acetabular component was tested for stability. Obviously, only stable metal implants were not revised. The cysts were filled with bone graft or bone substitute and a new polyethylene liner was cemented in with methylmetacrilate augmented gentamicin. The patients were evaluated by modified Harris Hip Score (HHS) and by SF-12 score. The mean follow up was 25 months (10–45).

Results: The average HHS was 86/4 and its pain component was 38.8. The average physical component of SF-12 was 45.9 (19.5–57.2) and the average metal component was 54.6 (29–66.9). The post-operative HHS and the SF-12 scores were high (good or excellent) in all patients reflecting good clinical outcome. In patients who were asymptomatic prior to surgery, both the HHS and the pain score were significantly higher compared to the symptomatic patients (p< 0.01). One patient with extensive bone loss needed revision surgery due to early postoperative fracture of the acetabulum, and another patient had recurrent dislocations that required revision.

Summary: We conclude that revision of the polyethylene liner and cementation of a new one is a safe and useful technique in patients with stable acetabular shell. This is especially true for asymptomatic patients with osteolysis.