Purpose of the study: There remains some debate on the proper treatment of congenital dislocation of the patella in children and adolescents. Ligament-periosteum transfer (green-stick method) is a technique adapted for pediatric patients which realigns the distal extensor system.
Material and methods: Between 1979 and 2000, 36 children (51 knees) were treated with this method described by Grammont. Section of the lateral wing and medial capsulomyoplasty were associated in all procedures. Other complementary procedures used as needed included lengthening of the quadriceps, trochleoplasty, and quadriceps release. Mean age at surgery was 11 years (range 5–15 years). All patients were reviewed at bone maturity with a mean follow-up of 7.5 years for functional (IKC criteria) and radiographic assessment. A computed tomography and/or magnetic resonance imaging was obtained preoperatively and at last follow-up to assess TAGT, patellar height, trochlear angle, femoral anteversion, external tibial torsion, and knee rotation. Tibial slope was specifically studied to assess the possible epiphysiodesis effect.
Results: Two groups of patients were distinguished: congenital dislocation of the patella (persistent or usual) and objective patellar instability. Functional outcome was good in 74% and 87% of the knees. There were eight cases of recurrent dislocation: five knees were operated on with good outcome. The trochlear angle was improved in both groups, more significantly in the congenital dislocation group. There was one case of an inverted tibial slope (−2°) and two cases of cancelled slope.
Discussion: Our functional results are in agreement with earlier reports (Grammont, Bensahel, Langeskiold) but comparison is hindered by the heterogeneous nature of the different cohorts. Radiographically, we observed that trochlear remodeling, a sign of good stability, is better if the operation is performed early (before the age of ten years). On the contrary, in adolescents with major patellar instability, complementary trocheloplasty should be performed in addition to the recentering procedure. We observed that a small tibial slope became smaller in eleven knees in comparison with the nonoperated knee and in comparison with the preoperative slope for the bilateral cases. There appears to be a discrete epiphysiodesis effect but with no functional consequence.
Conclusion: We propose a classification of congenital dislocation of the patella in children. The ligament-periosteum transfer technique, associated with other procedures as needed, enables stabilizing the extensor system and a normal trochlear angle if surgery is performed at a young age. Remodeling of the tibial tubercle may result from transient disruption of the vascular supply.
