[Soft tissue balanced navigation of total knee arthroplasties].

OBJECTIVE: Implantation of a total knee arthroplasty with a correct mechanical axis, a rectangular joint gap and a reconstructed joint line by use of an imageless computer navigation device INDICATIONS: Symptomatic gonarthrosis if non operative treatment or joint preserving operations remains ineffective CONTRAINDICATIONS: Infections; soft tissue damage in the approach area; massive instability of the collateral ligaments SURGICAL TECHNIQUE: Medial parapatellar approach to the knee joint; diminution of the patella; fixation of the reference arrays in tibia and femur; registration of leg axis, ligament balance and surface of the knee joint by use of the navigation system; tibial resection perpendicular to the mechanical axis; ligament balancing to achieve a rectangular extension gap; femoral implant planning to maintain the original joint line and reconstruct an equal joint gap in extension and flexion; femora resection perpendicular to the mechanical axis; reconstruction of the rectangular flexion gap by rotation of the femoral resection; two stage cementing technique for fixation of the original implants; check of the final mechanical axis and symmetry of the joint gap over the whole range of motion; wound closure. POSTOPERATIVE MANAGEMENT: Physiotherapy; continuous passive motion treatment; mobilization with 20 kg weight bearing with 2 crutches for 2 weeks, thereafter with 2 crutches and incremental full weight bearing for 4 weeks.
RESULTS: The analysis of 582 consecutive navigated total knee arthroplasties showed one case of extension gap instability  > 3 mm (0.2%) and 8 patients with flexion gap instability  > 3 mm (1.4%). A too tight flexion gap was registered in 23 patients (4.4%), a too wide flexion gap in 13 cases (2.5%). The joint line was reconstructed with an average inaccuracy of 0 mm, in 17 patients the joint line was elevated  > 3 mm (2.9%).