Chronic patellar dislocation due to excessive femoral neck anteversion. Treatment with a combination of derotational femoral shaft osteotomy and Elmslie-Trillat procedure

A number of factors may contribute to symptomatic patellar instability. The case of a 20-year-old male patient suffering from symptomatic patellar dislocation since his early days is reported; his patella was laterally dislocated from full extension to 40° of flexion and would remain subluxated thereafter. A 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 with a staged procedure that involved arthroscopic assessment of patellar tracking followed by derotational femoral shaft osteotomy and subsequently arthroscopic lateral release and Elmslie-Trillat tibial tubercle transfer. This led to very satisfactory patellar tracking. Two years postoperatively he had significant functional improvement and a ROM of 0-110°.This complex case highlights excessive femoral neck anteversion as a causative factor for patellar dislocation. A combination of proximal and distal bony realignment procedures is proposed and the role of arthroscopy is emphasised