Computer navigation systems enable precise measurement and intra- operative knee range of movement analysis. We present a series of five knees that demonstrated unusual kinematics.

Five of 80 computer navigated knee replacements that were part of a prospective randomised trial were found to have unusual joint lines. Range of motion assessment was performed with computer assisted navigation after exposure and registration of bony landmarks and before bony resection was commenced. This revealed valgus alignment in extension that drifted into varus with knee flexion. We referred to these unusual patterns as ‘oblique joint lines’.

The data from the navigation log files of these five knees was analysed in detail. Average age of patients in this series was 68years and all were female. The average pre- operative angle between femoral axis and distal femoral articular surface was 101 degrees. All five knees had a tibial varus with average angle between the tibial axis and articular surface being 85 degrees. In two knees, more bone was resected from the medial posterior femoral condyle using 4 degrees external rotation. These two knees showed improved kinematics and horizontal joint line post- operatively.

Computer assisted navigation provides a precise understanding of the pre- operative knee kinematics. Bony cuts can be tailored to suit the pre- operative deformity. Increased external rotation of the femur with adequate medial soft tissue release is an alternate approach for difficult knees with ‘oblique joint lines’.

The ligament balancing technique involves precise measurement and equalisation of flexion and extension gaps. A force tension distractor that has separate arms for the medial and lateral joint compartments was used. We describe our experience of 40 total knee replacements (TKR) using this technique.

We undertook a prospective randomised trial using computer assisted navigation in TKRs applying two different soft tissue balancing techniques. The aim was to see how balancing techniques help us achieve a rectangular flexion extension gap. The 40 TKR that underwent the ligament balancing procedure were part of this trial. The distractor used was derived from the Freeman-Swanson knee instrumentation which measures the gap and tension in the medial and lateral compartments. The options to make the gap rectangular were: 1. adjustment of femoral cut by change in external rotation (for the flexion gap); 2. soft- tissue release or 3. a combination of both. Using computer assisted navigation it was possible to perform real time motion analysis during surgery.

We found that three degrees of external rotation for the femoral component was adhered to in only 16 out of 40 knees. The remaining 60% had external rotation of femoral component varying between two and eight degrees. No maltracking of the patella resulted in any of the TKR with increased rotation of the femoral component. The axis of movement was plotted on a graph at the end of the surgery by passive extension to flexion to which the operating surgeon was blinded.

Varying external rotation of femoral component might be an option in balancing difficult knees. Computer navigation enables precise tailoring of bony resection to suit different deformities.

A randomised, prospective trial comparing the percutaneous compression plate (PCCP) and the classic hip screw was performed for intertrochanteric fractures of the femur in 108 patients. The PCCP offers the ability to stabilise fractures with a minimal exposure and periosteal stripping thus preserving soft tissue cover.

Over a 19-month period all patients with extra-capsular fractures apart from subtrochanteric and pathologic fractures were included. They were classified as per Evans classification.

The patient’s pre-operative haemoglobin, premorbid mobility, medical and mental status were noted. The duration of the procedure, screening time, blood loss and any technical difficulty encountered along with the post-operative haemoglobin, drainage and transfusion requirements, as well as the length of stay in the orthopaedic unit and total length of stay in the hospital were recorded. Results were analysed using the Chi-square test and Student’s test.

The operating time was significantly longer in the PCCP group (mean 59vs49mins,P< 0.05). There was no significant difference between the two groups with regard to the other parameters measured.

There was no difference in the failure rate (2 cut-outs in the CHS group and one screw back-out in the PCCP.) With the device being of fixed single angled design it proved to be unsuitable for 3 patients.

The PCCP would appear to be as good as the more conventional device though it does not confer the perceived advantages of decreased duration of stay or significant reduction in transfusion requirement which are associated with other percutaneous procedures. The device is a single fixed angle one and is therefore not universally applicable to all patients.