Abstract
OBJECTIVES
The use of a mobile bearing has been suggested to decrease the rate of patellar complications after total knee arthroplasty (TKA). However, to resurface or retain the native patella remains debated. Few long-term results have been documented. The present retrospective study was designed to evaluate the long-term (more than 10 years) results of mobile bearing TKAs on a national scale, and to compare pain results and survivorship according to the status of the patella.
The primary hypothesis of this study was that the 10 year survival rate of mobile bearing TKAs with patella resurfacing will be different from that of mobile bearing TKAs with native patella retaining.
METHODS
All patients operated on between 2001 and 2004 in all participating centers for implantation of a TKA (whatever design used) were eligible for this study. Usual demographic and peri-operative items have been recorded. All patients were contacted after the 10 year follow-up for repeat clinical examination (Knee Society score (KSS), Oxford knee questionnaire). Patients who did not return were interviewed by phone call. For patients lost of follow-up, family or general practitioner was contacted to obtain relevant information about prosthesis survival. TKAs with resurfaced patella and TKAs with retained native patella were paired according to age, gender, body mass index and severity of the coronal deformation (with steps of 5°). Pain score, KSS and Oxford knee score were compared between two groups with a Student t-test at a 0.05 level of significance. Survival curve was plotted according to the actuarial technique, using the revision for mechanical reason as end-point. The influence of the patella status was assessed with a logrank test at a 0.05 level of significance.
RESULTS
1,604 TKAs were implanted during the study time-frame. 849 cases could be paired according to age, gender, BMI and severity of the pre-operative coronal deformation (2/1 ratio) into two groups: resurfaced patella (496 cases) and retained patella (243 cases). There was no difference in any baseline criteria between both groups. 150 patients deceased before the 10 year follow up (18%). Final follow-up was obtained for 489 cases (58%). 31 reoperations (prosthesis exchange or patellofemoral revision) were performed during the study time frame (4%), with 17 reoperations for mechanical reasons (3%). KSS and Oxford knee score were significantly higher for TKAs without patella resurfacing, there was a significant difference between the 13 year survival rates of TKAs with resurfaced patella (97%) and TKAs with retained native patella (93%).
CONCLUSIONS
The primary hypothesis was confirmed: 10 year survival rate of mobile bearing TKAs with patella resurfacing was better than mobile bearing TKAs with native patella retaining. Patella resurfacing may lead to a better survival after mobile bearing TKA. However, the clinical results were better after patella resurfacing when the index TKA was not revised.
