CHRONIC PATELLA DISLOCATION DUE TO EXCESSIVE FEMORAL NECK ANTEVERSION. TREATMENT WITH A COMBINATION OF DEROTATIONAL FEMORAL SHAFT OSTEOTOMY AND ELMSLIE-TRILLAT PROCEDURE.

We report a case of a 20-year-old microcephalic patient who suffered from symptomatic patellar dislocation since his early days. His patella was laterally dislocated from full extension to 40° of flexion and would remain subluxated thereafter. His CT-scan revealed excessive ipsilateral femoral neck anteversion (45°) that resulted in substantial internal femoral torsion and subsequently led to patella dislocation. He was treated in one stage with a stepwise procedure, that involved arthroscopic assessment of patellar tracking followed by derotational femoral shaft osteotomy. Tracking was reassessed arthroscopically and although improved was still suboptimal. Therefore an arthroscopic lateral release and an Elmslie-Trillat tibial tubercle transfer were undertaken. This led to very satisfactory patellar tracking. One year postoperatively he had significant functional improvement, no further episodes of patellar dislocation and a ROM of 0–110°. His Lysholm score improved from 45 to 88, his Tegner activity scale from 2 to 4 and his Knee Outcome Score from 38/80 to 70/80. This complex case highlights excessive femoral neck anteversion as a causative factor for patella dislocation. A combination of proximal and distal bony realignment procedures is proposed and the role of arthroscopy is emphasised.