Abstract
Background
The most important factors affecting the outcome of a TKA are restoring the normal mechanical axis and achieving optimum soft tissue balance. In the measured resection technique may have accompanying problems in imbalanced patients. Secondly individual variability of the reference points may affect the alignment of the bony cuts and thereby the alignment of the implant. The gap balance technique blends the soft tissue balance with the bony cuts and tries to overcome this problem. However proponents of the measured resection technique argue that no consideration is given to the coronal and rotational alignment of the femoral component in the gap balance technique. The ligament specific navigation assisted gap balance technique, tries to overcome these fallacies. The lateral ligaments and soft tissues act as a reference against which the medial soft tissues are balanced. Thus the reference becomes individualized and any variability is taken care of. Navigation assistance ensures control of the coronal and rotational alignment of the femoral component. The aim of the present study was two fold: - To describe our methodology of ligament specific navigation assisted gap balance technique and analyze the clinico-radiological outcome of our technique over an eight year follow up.
Methods
79 patients (98 knees) with primary osteoarthritis with varus deformity and flexion deformity of were followed up for eight year duration. After obtaining an optimum gap balance and neutral axis in extension, tibial osteotomy perpendicular to the mechanical axis in both the coronal and sagittal planes was done. At this stage joint gaps were distracted in extension and 90â�° flexion. Based on the gap values patients were classified into three groups. Group 1 was the balanced group with flexion extension gap difference ≤2mm, group 2 was the flexion tight group with flexion gap smaller than the extension gap by ≥3mm and group 3 was the extension tight group with the extension gap smaller than the flexion gap by ≥3mm. Thereafter flexion gap balance was achieved only by adjusting the cutting levels of the distal and posterior condyles and adjusting the axial rotation of the femoral component without any further soft tissue release. Intraoperative navigation readings were recorded. All patients were followed clinico-radiologically at 1, 4, and 8 years post operatively.
Results
The level of posterior condylar cut was significantly higher in the flexion tight group. The level of distal cut was higher in the extension tight group. Mean external rotation of the femoral component was 3.14â�°. Mean joint line change in all patients was < ±2.5mm. There was significant improvement in all the clinical scores, and ROM till the last follow up. There were no differences among the patients in the three groups.
Conclusion
The ligament specific navigation assisted gap balance technique is a reliable technique for TKA with excellent clinico-radiological results over an eight year follow up period.
