Abstract
At present bone scan is the only objective indicator of homeostasis in the bone and adjacent joint. This prospective study of 19 consecutive osteotomies in 17 patients was undertaken to see whether homeostasis is achieved around the knee after high tibial osteotomy for medial compartment osteoarthritis.
All cases underwent preoperative clinical, radiological and bone scan evaluation. Clinical evaluation included an SF12 score. Radiographs included standard anteroposterior, lateral, intercondylar and skyline patellar views, as well as standing views for measuring the mechanical axis and calculating the degree of correction. The three-phase technecium-99 m scan included blood-flow, blood pool uptake and delayed static imaging. As part of the surgical procedure an arthroscopic examination was performed and the degree of degeneration in all three compartments of the knee were noted. An excision wedge osteotomy was performed, aiming to achieve a 3° mechanical valgus alignment. Tension wire fixation allowed immediate mobilisation. One year postoperatively the clinical examination, standing radiographs and bone scans were repeated and the results statistically analysed.
One year postoperatively the mean SF12 score had improved from a preoperative 13.6 to 21.2 and the mean mechanical alignment from 6.3° of varus (3° to 12°) to 2° of valgus (0° to 4°). The significant decrease in isotope uptake in the medial compartment correlated with the clinical improvement and improved alignment. There was a significant reciprocal change from high uptake in the medial compartment preoperatively to high uptake in the lateral compartment one year postoperatively.
Medial compartment homeostasis was achieved one year after tibial osteotomy, but homeostasis was not achieved in the whole joint. Although correction was so conservative that it resulted in a mean of only 2° of mechanical valgus alignment, the area of increased uptake shifted from medial to lateral compartment. It is probable that the preoperative varus alignment led to reduced load-bearing and disuse osteoporosis in the lateral compartment, and that the increased uptake represents metabolic response to greater load. Possibly lateral compartment homeostasis will be restored over time.
This study shows that even a mild realignment improves homeostasis in the medial compartment. With the development of biological resurfacing, the importance of osteotomy may increase.
The abstracts were prepared by Professor M. B. E. Sweet. Correspondence should be addressed to him at The Department of Orthopaedic Surgery, Medical School, University of Witwatersrand, 7 York Road, Parktown, Johannesburg, 2193 South Africa
