Patella alta in patellofemoral instability.

In a retrospective study of 90 realignment procedures for patellar instability, a high percentage of patella alta was diagnosed based upon the preoperative radiographs: 53% or 48 knees. The LP-LT index, described by Insall and Salvati, averaged 0.80 for this group of patients. Post-operative measurements of this index showed a definite correction of the craniocaudal position of the patella, with a mean increase of 0.10 (0.80 to 0.90). In evaluating the severity of the eliciting trauma, it is suggested that the alta position makes the patella more prone to instability: only 14.5% of the alta knees (n = 48) sustained a significant trauma versus 28.5% in the non-alta population (n = 42). The altaposition, however, had no influence on the final outcome, (at a mean follow-up time of 57 months), after a latero-medial realignment procedure, using a proximal or a combined proximal and distal procedure.