Unintended femoral valgization after distal femoral derotational osteotomy in a patient with recurrent patella dislocation: A case report.

RATIONALE: Distal femoral derotational osteotomy (DFDO) is widely performed to correct excessive femoral anteversion in patients with patellofemoral instability. However, unintended changes in coronal alignment can occur depending on the orientation of the cutting plane. We present a case of unintentional femoral valgization after DFDO in a patient with a recurrent patellar dislocation. PATIENT CONCERNS: A 23-year-old female presented with multiple episodes of recurrent patellar dislocation of her right knee. DIAGNOSES: Physical examination revealed a positive apprehension test, positive J-sign, and generalized joint laxity. An effusion was observed in the right knee. Radiologic findings included increased femoral anteversion (30.3°), ruptured medial patellofemoral ligament (MPFL), mild varus alignment (hip-knee-ankle angle 0.4°), mechanical lateral distal femur angle (mLDFA) of 86.6°, patella alta, and increased tibial tuberosity-trochlear groove (TT-TG) distance. INTERVENTIONS: The patient underwent MPFL reconstruction and DFDO with target correction of femoral anteversion of 15°. Osteotomy was performed perpendicular to the real anatomical shaft axis. OUTCOMES: Postoperative imaging revealed an unintended valgus malalignment (HKA angle -3.0°) and decrease of mLDFA (83.6°). Despite the altered alignment, no recurrence of dislocation was noted during the 18-month follow-up period, and the clinical outcome was satisfactory. LESSONS: Unintentional valgus alignment may result from osteotomies oriented perpendicular to the real anatomical shaft axis. Surgeons should consider using the virtual anatomical shaft axis to determine the cutting plane and minimize the risk of iatrogenic malalignment during DFDO.