Subspine Impingement

Femoroacetabular impingement is typically described as occurring between the femoral head-neck junction and the acetabular rim and secondary to pathomorphologic osseous changes in these areas. Extra-articular sources of femoroacetabular impingement have been increasingly recognized and treated. One of the more commonly described sources has been subspine impingement, the mechanical conflict between the anterior inferior iliac spine (AIIS) and the distal femoral neck. The etiologies of AIIS pathomorphology include apophyseal avulsions of the AIIS, rectus femoris avulusions with ossification, overcorrection after periacetabular osteotomy, and developmental. Patients often present with groin pain with deep hip flexion. Cadaveric studies have noted a reproducible bare area on the inferior aspect of the AIIS, and a corresponding footprint of the direct head of the rectus femoris measuring 2.2 × 1.6 cm on average. Arthroscopic decompression of the AIIS has been performed with good short-term outcomes and significant improvement in end terminal range of motion.