[Postoperative low patella. Treatment by lengthening of the patellar tendon]

Abstract

Purpose of the study: Patella infera is a post operative complication that can be prevented in most cases. This study was undertaken to determine etiological factors and to determine the means to avoid patella infera following knee surgery. The authors describe a new surgical technic to correct this complication and describe prognostic factors for achieving good results.

Material and methods: From 1985 to 1991, 35 patellar tendon lengthenings were performed in 35 patients. There were 28 female and 7 male patients with an average age of 37 years (21 to 72). Follow-up averaged 27 months and all patients had radiographic follow-ups. All patients had previous knee surgery: 21 for patellar pain (= patellar pain), 9 ACL reconstructions, 5 traumatic lesions. The range of motion of the knee was between 5 and 120 degrees. Patients complained of a burning pain in the patellar region and the sensation that the knee was held in a vice. The average Insall index was 0.55 (0.3 to 0.87). 25 patients had osteoporosis of the patella and 31 patients had a typical "sunrise" aspect on axial radiographs in 30 degrees of flexion. The usual diagnosis was that of algodystrophy. All patients underwent patellar tendon lengthening.

Results: Intra operative findings showed transverse retractions leading to resection of the medial and lateral retinaculum. The patellar tendon was short but its histological structure was normal. 15 patients had excellent results with no residual pain and were able to resume sports activities. 11 had good results with residual pain in hyperflexion and 9 had poor functional results, however nocturnal pain disappeared. Range of motion was between 0 and 130 degrees. Radiographic results were excellent since the preoperative average Insall score of 0.55 increased to 1.02 at follow-up.

Discussion: Patella infera is caused by combination of two factors: patellar surgery (painful patellar syndrome, patellar instability, ACL reconstruction using the mid third of the patellar tendon) and painful post operative rehabilitation with no active quadriceps contractions. To avoid this complication, the knee should be braced in 20 degrees of flexion to tense the patellar tendon and rehabilitation should be undertaken with active quadriceps contractions. Patellar lengthening is a successful procedure with the results being dependent upon number of previous surgeries, cartilage damage and, most importantly, the patellar index: between 0.8 and 0.65 the results are uncertain, < 0.6, the results are usually good.

Conclusion: Patella infera is not a frequent complication of knee surgery. It is important to diagnose it early in order to prevent it. For chronic cases, surgical criteria should be strict: sensation of burning pain, lack of motion, unstable flexed monopodal stance, "sunrise" aspect on axial radiographs and a patellar index < 0.6. Patella infera differs from algodystrophy and re operation by retinacular release is indicated if the delay from previous surgery is < 2 months. In older cases, patellar tendon lengthening should be undertaken.