ACQUIRED PATELLA BAJA AFTER TOTAL KNEE ARTHROPLASTY–COMPARISON OF TWO SURGICAL TECHNIQUES: WITH AND WITHOUT PATELLA EVERSION

Background: Acquired patella baja occurs after both trauma and surgery of the knee including TKA, with prevalences between 30%–60%. The inferior position of the patella leads to alterations in the joint mechanics, reduction of range of motion, anterior knee pain, and can cause increased wear of the tibial and patellar polyethylene. Our aim was to evaluate the prevalence of patella baja after TKA and to assess the clinical effects of patella tendon torsion and twisting during surgical exposure of the knee. Methods: Postoperative changes in patella height were measured on serial radiographs of 74 TKA implanted without patella eversion (group 1) and 57 TKA implanted with patella eversion (group 2). Pre- and postoperative Knee Society Scores, operative data, and complications were compared. Results: With a cut-off level of 5% shortening, the prevalence was 12% (9 cases) in group 1 and 37% (21 cases) in group 2 (p=0.001). With the 10% cut-off level the prevalences were 5% (4 cases/group 1) and 14% (8 cases/group2) (p=0.1). The presence of patella baja was related to reduced flexion and increased pain 1 year after TKA. Conclusion: Our study has shown that tension and twisting of the patellar tendon leads to shortening which was associated with reduced flexion and increased pain after TKA. By avoiding patella eversion the prevalence of acquired patella baja was reduced significantly.