Several proponents of minimally invasive surgery-total knee arthroplasty (MIS-TKA) have suggested patellar eversion during
a standard exposure of the knee may cause shortening of the patellar tendon and poorer outcomes secondary to acquired patella
baja. To explore this suggestion, we retrospectively reviewed 135 consecutive TKAs in 110 patients to ascertain the effect
of TKA on the postoperative Insall-Salvati ratio. All surgeries were performed using standard TKA techniques with a midline
incision, medial parapatellar arthrotomy, partial excision of the fat pad, and routine eversion of the patella. One patient
developed a postoperative patella baja, defined as an Insall-Salvati ratio of less than 0.8. The Knee Society score for knee
and function in this patient was 75 and 70, respectively. Five additional patients had a decrease in Insall-Salvati ratio
by 10% or more but without patella baja. Mean Knee Society score for knee and function in these five patients was 94 (range,
73–99) and 96 (range, 90–100), respectively, as compared with 93 (range, 37–99) and 94 (range, 40–100) in the remaining 104
patients. Our data suggest the incidence of patella baja is low after TKA despite routine patellar eversion. Furthermore,
a 10% or more decrease in the Insall-Salvati ratio without patella baja was not associated with a worse clinical outcome.
Level of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.
The research foundation of one or more of the authors (ASR, CSR) has received funding from DePuy Orthopaedics, Inc, Johnson
& Johnson (Warsaw, IN) and Stryker Orthopaedics, Inc (Mahwah, NJ). One or more of the authors (ASR, CSR) has received royalties
from DePuy Orthopaedics, Inc, Johnson & Johnson (Warsaw, IN) and Stryker Orthopaedics, Inc (Mahwah, NJ). ASR is a consultant
for DePuy Orthopaedics, Inc, Johnson & Johnson (Warsaw, IN) and Stryker Orthopaedics, Inc (Mahwah, NJ). CSR is designer/consultant
for DePuy Orthopaedics, Inc, Johnson & Johnson (Warsaw, IN) and Stryker Orthopaedics, Inc (Mahwah, NJ).
Each author certifies that his or her institution has approved the human protocol for this investigation, that all investigations
were conducted in conformity with ethical principles of research, and that informed consent for participation in the study
was obtained.