Primary Total Knee Arthroplasty: How Does Residual Patellar Thickness Affect Patient-Oriented Outcomes?

BACKGROUND: Maintenance of the native patellar thickness has been deemed important for proper clinical outcomes after total knee arthroplasty (TKA). Our objective was to study the effects of the change in patellar thickness on patient-perceived outcomes (PPOs) after TKA. We hypothesized that reestablishing native patellar thickness after TKA results in better PPOs.

METHODS: 819 consecutive patients undergoing primary TKA were studied. Patients were classified according to their postoperative patellar thickness into: (1) less than native patella thickness; (2) equal to native patella thickness; and (3) greater than native patella thickness. Difference in postoperative range of motion (ROM), PPOs and clinical scores, and delta-Δ-change were assessed. MANCOVA was used to assess for differences.

RESULTS: No significant differences found based on postoperative patellar thickness (mean follow-up: 4.9 ± 2.1 years) for each ROM assessments. Those who reported more stiffness (Western Ontario and McMaster Universities Arthritis Index stiffness; P = .011) and lower knee active flexion (P = .046) preoperatively had "greater than native patella thickness" after surgery. Postoperatively, the "equal to native patella thickness" group reported significantly better quality of life (quality of well-being scale 7 total; P = .008) as well as better physical score (Short Form-36 role physical score; P = .03). The amount of improvement (delta-Δ-change), when restoring patellar thickness equal to the native demonstrated greatest improvements in quality of life (quality of well-being scale 7 total; P = .016) physical measures (Short Form-36 role physical [P = .025], and Western Ontario and McMaster Universities Arthritis Index stiffness scores [P = .006]).

CONCLUSION: When compared with the native patellar thickness, a final postoperative difference (delta thickness) that ranges from -1.06 to 2.58 mm provides satisfactory results and does not seem to affect ROM after surgery.