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.

Background: Recently, less invasive techniques for total knee arthroplasty (TKA) were introduced and the early results suggest a more rapid return of flexion and functional activities, while requiring fewer analgesics after surgery. Despite these findings, there is concern over the possibility of a steep learning curve and the potential risks of implant misalignment or poor fixation that may compromise long-term results. The purpose of this study was to analyze the potential learning curve effect on clinical and radiographic Results: Methods: This retrospective review compares the first 30 (Group 1) to the latest 30 cases (Group 2) in one surgeon’s consecutive series of 152 mini-incision mid-vastus TKA. Pre- and postoperative Knee Society Scores were compared, implant alignment was measured, and flexion was evaluated during hospital stay, at 6 weeks and 3 months after surgery. Complications and operative data were collected.

Results: Flexion was significantly higher in group 2 during hospitalization and at all clinical follow-up evaluations. At last follow-up mean flexion was 111° ± 8 (95–125) in group 1 and 121° ± 11 (90–140) in group 2 (p= 0.001). The mean length of skin incision was 11.7 cm ± 1.5 (8–15) with a mean incision length of the vastus medialis oblique muscle of 3.2 cm ± 1.0 (1–5). A steady improvement of knee and function scores was found in the entire series which were significantly greater in group 2. There were no complications and the radiographic evaluation found no implant or limb misalignment, or signs of early loosening.

Conclusion: The introduction of a mini-incision technique is an evolutionary process. The clinical and functional results show continued improvement after more than 100 cases. There was no classical learning curve effect and no increased complication rate in the earlier series. Thus far, the benefits of the mini-incision mid-vastus approach outweigh the new technique related difficulties and possible new risks. There are no signs of compromise that will affect the long-term results of mini-incision TKA.