The objective of the study was to find out to what extent anatomical changes due to high osteotomy of the tibia affect knee function after total knee arthroplasty.
Of the patients with knee osteoarthritis treated by cemented total PFC prostheses in 1995, two groups were selected. Group I consisted of 50 patients who had knee replacement without previous tibial osteotomy; the average age of the patients was 71.2 years and the average follow-up was 5.7 years. Group II comprised 50 patients with high tibial osteotomy before total knee replacement. The average age was 73.5 years and average follow-up was 5.4 years. Before arthroplasty, all patients showed knee motion in the range from 10 degrees valgus to 15 degreEs varus, flexion of the knee was up to 20 degrees and there was no marked instability.
The results of knee arthroplasty were evaluated, in terms of function, according to the Knee Society Clinical Rating System, using the knee scoring system (KSS) and functional system (FS). The length of the patella and patellar ligament were measured, the Insall-Salvati index was calculated and the height of the patella was determined.
The average KSS scores were 86.6 and 84.2 points for groups I and II, respectively. Excellent and good outcomes were achieved in 38 group I patients and in 37 group II patients. The average FS scores were 82.7 and 81.4 points in groups I and II, respectively. The average Insall-Salvati indices in groups I and II were 1.09 and 0.91, respectively. No patella infera was recorded in group I but it was found in 21 (42%) patients of group II.
There was no difference in knee function, as shown by KSS and FS scores, between the two groups. This is in agreement with the results of Billings et al. and Meding et al. who studied 21 and 81 patients with knee arthroplasty, respectively. On the other hand, Windsor et al. and Katz et al., in groups of 45 and 21 patients, respectively, found that high tibial osteotomy prior to knee replacement adversely affected the outcome of arthroplasty in terms of knee function. The authors draw attention to the fact that, after high osteotomy, the detachment of soft tissues around the proximal tibia is more difficult. The surgeon has to deal with changes in shape and sloping of the proximal part of the tibia and its altered position in relation to the diaphysis.
The outcomes of total knee arthroplasty, as assessed by functional scores, were similar in the patients both without and with preceding high tibial osteotomy. This condition had some effect on the development of a patella infera (present in 21 out of 50 patients) but only to a mild degree (Insall-Salvati Index, 0.91).