MEDIUM TERM RESULTS OF PFC SIGMA TOTAL KNEE REPLACEMENT- THE WRIGHTINGTON EXPERIENCE

Abstract

Aim: PFC Sigma total knee was introduced in 1997 incorporating a number of design changes. We report our medium-term results of a consecutive series of PFC sigma knees performed between Nov 1997 and Dec 1998.

Method: Between November 1997 and December 1998 a consecutive series of 166 TKAs (156 patients)were carried out using the PFC Sigma total knee replacement system at Wrightington Hospital. Out of the 156 patients 9 were lost to follow-up. This left 147 patients (156 knees) with a mean follow-up of 90 months (range 84 – 96 months). 137 patients (88%) had primary osteoarthritis, 14(9%) had R.A and 5(3%) had post-traumatic arthritis. The mean age was 70 yrs (53 – 88 yrs).85 were female and 62 male. All patients were followed at 3 months, 6 months,1 year and then yearly. Clinical evaluation was done by American Knee Society and Oxford knee scores. Knee society score was used to assess the postoperative radiographs.

Results: The mean Knee society score improved from the preoperative mean of 45 (range 30 – 65) to postoperative mean of 84 points(range 45 – 92). The mean preoperative functional score was 38(range 25 –5) and mean postoperative functional score was 73 points(range 50–95). According to the final scoring 90 % of the knees were rated excellent, 4% good, 4 % fair and 2 % poor. The mean preoperative Oxford knee score was 43 (range 33–52) and mean postoperative score was 17 (14–29). Range of motion improved from a mean of 90(range 50–125) to 105(range 65–130). There was no significant difference (p = 0.03) in the American Knee Society score and Oxford knee score when comparing patients with and without resurfacing of the patella and PCL-retaining with PCL-substituting implants.1 knee (0.6%) was revised within 18 months due to aseptic loosening.1 knee(0.6%) had superficial wound infection which cleared with oral antibiotics.2 patients(2 knees) developed deep infection out of which one resolved following early debridement, the other developed chronic infection requiring long term suppressive antibiotics. 3 patients had proven below knee deep venous thrombosis; one of them developed a non-fatal pulmonary embolism. Radiological review using radiological knee society scoring showed radiolucent lines under 35 % of the tibial components(56 knees)and 11 % of Femoral components(18 knees). For survivorship analysis, the actuarial life- table method was used with calculation of the numbers at risk and the survival rates at annual intervals. The 95% confidence limits were calculated by the method of Rothman. The survivorship at the end of eight year follow-up was 99.40. None of the patellar components failed.

Conclusion: Our study shows excellent clinical results of PFC Sigma Total knee replacement after almost eight years follow-up. We plan to continue monitoring this cohort of patients for long-term results.