Long term outcome analysis of fixed bearing total knee arthroplasty

Abstract

Introduction: Survivorship of TKA is directly related to appropriate alignment and balance. Surgeons should evaluate the biomechanics of knee alignment and determine the proper position of the implant. Malalignment of total knee prostheses has been implicated in few difficulties, including tibiofemoral instability, patellofemoral instability, patellar fracture, stiffness, accelerated polyethylene wear, and implant loosening. The aim of this study is to analyse the long term follow up of functional and radiological results of twenty cases of fixed bearing Total Knee Arthroplasty prospectively done in our institute during the period April 2008 to September 2009. Materials & Methods: This is a prospective study done in our department form 2008- 2009 which included total knee arthroplasty done for bicompartmental osteoarthritis without gross deformity. 20 cases were included in the study. The age range was 32 to 65 years. There were 5 male patients and 15 female patients. The accuracy of component position was assessed by mechanical axis restoration, coronal tibio femoral angle, sagittal femoral angle, posterior tibial slope by X-ray and the transepicondylar line-posterior condyle component angle by CT. We used Depuy PFC fixed bearing knee in 17 patients, Stryker knee in 2 patients and Indus knee in 1 patient. Knee society score was used to measure the functional outcome of the surgery. Results: The average postoperative flexion in the rheumatoid group was 105.4 degrees and in the osteoarthritis group was 115.8 degrees. There was no incidence of periprosthetic fractures. No patients had neurological deficit or dislocations. One case had valgus instability postoperatively. In our study all our patients showed an improvement in knee score with mean preop score of 50.4 (range: 46-57) improved to 75.6 (range: 65-88). 2 patients had excellent score (80-100).16 patients had good score (70-79) and 2 patients had fair results (60-69). No patients had maltracking of patella clinically.one patient with anterior knee pain and two patients with limited flexion post operatively were evaluated with axial view of knee. There were no evidence of patellar tilt or subluxation. No patients had loosening and osteolysis noted around the femoral and tibial components. No implant needed to be revised during the period of study. There was no incidence of superficial or deep infection. Of the 20 patients 18 cases returned to their premorbid condition. Two patients who were rheumatoid has persistent pain. The average follow up was 9.2 years (range 8.4 to 10.7 years). Conclusion: In patients with ideal placement of the components i.e. with mechanical axis and the rotational alignment accurate better knee flexion and knee score was obtained provided other factors are normal. We conclude that the correct positioning of the components both axially and rotationally improves the functional outcome of fixed bearing knee in low demand patients with an excellent long term clinical outcome.