Patella baja after unicompartmental knee arthroplasty

The literature data on patellar height following unicompartmental knee arthroplasty (UKA) are scarce. A total of 41 knee joints in 37 patients after UKA were prospectively evaluated for patellar height by using the Insall-Salvati and modified Insall-Salvati ratio. Patellar height was measured preoperatively, postoperatively, at 6, 12 weeks, and, at 1 year postoperatively. Patients were categorized according to age, gender, operated side, and rehabilitation program. Regarding all the patients, the Insall-Salvati ratio demonstrated a significant decrease only for the time period "postoperatively-1 year postoperatively", whereas the modified Insall-Salvati ratio showed a significant decrease only for the period "preoperatively-postoperatively". The Insall-Salvati ratio showed a significant decrease in the patellar height of men and left knees, whereas the modified Insall-Salvati ratio revealed a significant decrease in patients older than 65 years and those who followed a specific rehabilitation program. The decrease in the patellar height after UKA occurs within the first postoperative year. Women, right knees, patients younger than 65 years and those who do not follow a specific rehabilitation program are less prone to decrease in the patellar height; ratio-specific differences are evident for each subgroup. Diagnostic study, Level III.