The aim of this study was to assess the risks and benefits of mini-incision TKR. The limited exposure afforded by the small skin incision in the new technique of mini-incision TKR has the potential for increasing the risk of mal-positioning of components. Minor mal-positioning of components has the potential to increase polyethylene wear and may lead to early loosening and poor functioning of the TKR. The literature supports the concept that alignment within +/- 3 degrees of neutral mechanical alignment in the coronal plane is associated with a better outcome. If the mechanical axis falls outside this range it may have up to a 30% failure rate at 10 years.

We report the results of 166 mini-incision TKR that have been undertaken in 154 patients (96F; 58M; mean age 72; mean BMI 29; 96% OA) since November 2003. The pre-operative mechanical axis ranged from 8 degrees valgus to 15 degrees varus. Surgery was undertaken with a precise skin incision and a midvastus split approach. Specialised cutting blocks were used to facilitate a smaller incision. The prosthesis inserted was a cemented Zimmer NexGen TKR of either posterior stabilised or cruciate retaining form.

Long leg weight bearing alignment radiographs were available in 52% of patients. The mechanical axis was measured in the coronal plane and found to lie within +/- 3 degrees of neutral in 86% of patients. This compares favourably with the current literature which reports the mechanical axis falling within this range in between 72% and 85% of cases.

We believe the mini-incision TKR is a safe, reliable and reproducible technique offering substantial savings to the patient and health service without compromising accuracy.

Purpose: X-Ray analysis of a subset of TKR’s performed using the mini-incision technique has been undertaken to assess the accuracy of alignment, as TKR through limited exposure lends itself to a potential risk of mal-positioning of the components.

Methods and Results: The limited exposure afforded by the small skin incision and mid-vastus approach in the new technique of Mini Incision TKR, has a potential for increasing the risk of mal positioning components without the use of navigation systems. 128 mini-incision TKR’s have to date of submission, been undertaken in 125 patients (67F: 58M: mean age 72: mean BMI 29). A prospective assessment of these patients has been ongoing since its introduction in November 2003. The mean hospital stay is 5.5 days and mean range of flexion at six weeks is 106°. Two patients have required manipulation under anaesthetic for poor flexion at six weeks and blood transfusion has only been required in 4%. In patients with a minimum 6 months follow up, long leg alignment X-rays have shown the mechanical axis to be within 3° of normal in 4/5.

Conclusion: We believe that Mini Incision TKR is a safe reliable and reproducible technique offering substantial savings to the patient and health service without compromising accuracy.