THE PATELLA BAJA AS A COMPLICATION OF TOTAL KNEE REPLACEMENT. USE OF INSALL’S APPROACH IN ITS PREVENTION

Abstract

The total knee replacement is one of the most common operations in an Orthopaedics Department. Despite of being a frequent procedure, it’s been calculated that between 18 and 20% of the patients aren’t satisfied with the result. One of the complications that may occur after TKR is patella baja, which has been related to poor outcomings. The main factor that may produce it after TKR is the shortening of the patellar tendon. As it has been published, the medial parapatellar approach and the eversion of the patella may cause patella baja. Many authors defend the use of minimally invasive approaches to prevent this complication. We studied if the use of the variation of the traditional approach that Insall described produces low patella. We have also analysed if this complication produces poorer outcomings. To know if the patellar tendon’s length was reduced, we used the Insall–Salvati Ratio. We measured it before and after the operation. We considered low patella if the IIS value was lower than 0,8. All the analyses were also done considering low patella if the ISR had decreased more than 10% after the operation. We reviewed 200 consecutive TKR performed in the Orthopaedics Department of Marqués de Valdecilla Hospital, from 1997 to 2001. All of the patients were operated by seniors surgeons. 2 patients were excluded because they died before we had finished the study. We analysed the influence of age, gender, BMI, preoperative diagnosis, degree of joint’s erosion and some surgical maneuvers. We also analysed the outcome, using the KSS score, paying special attention to the postoperative pain, the ability of walking and using stairs and the maximal postoperative extension and flexion degrees. SPSS v15.0 program was used for the statistical analysis. For the proportion analysis was used the ji-squared test or the Fisher test. For the main comparation we used the t-student test or the Wilcoxon test. The p values under 0,05 were considered to be significant. 3,3% of the TKR developed postoperative low patella. We founded statistically significant differences considering BMI, age and diagnosis. The shortening of the patellar tendon caused poorer outcomes:statistically significant differences were found in the maximal postoperative flexion and in climbing stairs. Considering low patella if the ISR decrease > 10% after the operation, the results were similar. It’s not been published the influence of the Insall’s variation in developing low patella after TKR. We couldn’t found references about the influence of age, BMI, diagnosis or level of joint’s erosion in the developing of this complication. In our study, obesity seems to protect and being young seems to predispose to suffer it;no surgical maneuver seems to have any influence. The outcome is worse if low patella is present. We concluded that the Insall variation is a comparable option to the MIS approaches in preventing the low patella after TKR.