Abstract
Total knee arthroplasty (TKA) is one of the commonest orthopaedic procedures. Traditionally the surgeon, based on experience, releases the medial structures in knees with varus deformity and lateral structures in knees with valgus deformity until subjectively they feel that they have achieved the intended alignment. The aim of this prospective study was to record the frequency of medial and lateral releases for computer navigated TKAs.
Seven four consecutive patients operated on by a single surgeon were included in this study. All patients had TKA using either Stryker or Orthopilot computer navigation systems. The implants used were Scorpio NRG or Columbus. The biomechanical axis was taken as the reference for distal femoral and proximal tibial cut. The trans-epicondylar axis was taken as the reference for frontal femoral and posterior condylar cuts. A soft tissue release was undertaken after the bony cuts had been made if the biomechanical axis did not come to within 2° of neutral as shown by computer readings in extension. The post-operative alignment was recorded on the navigation system and also analysed with long leg hip knee ankle radiographs.
There were 43 female and 31 males in the study, 34 left and 40 right knees with an age range of 43 to 87 years. The range of pre-operative deformities on long leg radiographs was 15° varus to 27° valgus with a mean of −5.0° and SD 7.4°. Only two patients needed a medial release. None of the patients needed a lateral release. The fixed flexion deformities needed posterior release. None of the patients needed lateral release for patellar tracking. Post-operative alignment was available for 71 patients. The post implant navigation value was within 2° of neutral in all cases. The mean biomechanical axis on radiographs was 0.1° valgus with a SD 2.1° and range from 6° varus to 7° valgus. From the radiographs six patients were outside the ±3° range.
If one sticks to biomechanical axis and transepicondylar axis as the reference for bony cuts, there will be minimal requirement for medial or lateral soft tissue release. According to our results the use of computer navigation gives a low frequency of medial and lateral release in total knee replacement. Other authors have also found that navigation data can help to give a lower rate of soft tissue release, such as Picard et al. who had decreased their soft tissue release to 25%.
Correspondence should be addressed to Mr K Deep, Consultant Orthopaedic Surgeon, Golden Jubilee National Hospital NHS Trust, Beardmore Street, Clydebank, Glasgow G81 4HX, Scotland. Email: caosuk@gmail.com
