Influence of mini approach instrumentation on component alignment in unicondylar knee replacement.
Dr Vinod Kumar, Dr Deepak Gupta, Dr Ananya Sharma
Department of Orthopaedics, MAMC and Lok Nayak Hospital, New Delhi 110002.
AIM- to evaluate the accuracy of placements of implants using mini approach instrumentation.
Methods- It was an Interventional Prospective Clinical Study in thirty-three knees of primary Symptomatic Medial compartment osteoarthritis having full thickness articular cartilage loss with or without bone loss in the medial compartment. On AP views, the alignments of the femoral and tibial components were measured. On lateral views, flexion/extension of the femoral and tibial component was. A 7° posterior–inferior tilt of the tibial component was taken as neutral. Tilting beyond this gave a positive value, whereas tilting less than this was negative.
Summary- Position of varus/ valgus femoral component (recommended range of alignment as 10° varus to 10° valgus) was within acceptable ranges in all the patients with a mean of 4.21° varus (SD:2.98°, range:3.3° valgus to 8.6° varus).
Position of flexion/ extension femoral component (recommended range of alignment as 5° extension to 10° flexion) was within acceptable ranges in 72.73% of knees with a mean of 7.21° flexion (SD:4.3°, range:1.2° flexion to 14.4° flexion). Posterior fit of femoral component with proposed acceptable range of 0 to 4 mm posterior overhang was achieved in all patients except three with mean: 0.73 mm overhang (range 1 mm short to 2.5 mm overhang). Medial/ lateral fit of femoral component was achieved in 54.55% of knees with the mean femoral component placement was 0.82 mm lateral (range: 1 mm medial to 5 mm lateral). Position of varus/valgus tibial component (recommended range of alignment as 5° varus to 5° valgus) was achieved in 54.55% patients with mean alignment of 5.8° varus (SD:3.89°, range:3° valgus to 13.2° varus).
Superior/ Inferior tilt of tibial component (recommended range of alignment from 5° superior tilt to 5° inferior tilt) was achieved in 72.73% of the knees with mean tibial alignment was 3.6° superior tilt. Anterior fit of tibial component of all except three patient, were within the acceptable range (flush or <5mm short). Posterior fit of tibial component was 0.2 mm short (range: 3 mm short to 2 mm overhang). This was achieved in 72.73% of patients. Medial fit of tibial component was 0.4 mm short (range: 2 mm short to flush). Nine patients were outside the acceptable range of medial fit of tibial component. Lateral fit of tibial component of all patients were within the acceptable range. Meniscal bearings were placed centrally in all the patients.
Conclusion- Components of UKR i.e. Femoral component, Tibial component and Meniscal bearing can be placed with high accuracy using mini-approach instrumentation. In this study, two implant position namely Femoral central position and Tibia varus alignment had maximum error rate. This can be attributed to technical errors and learning surgical curve.