Review Question - QID 219547

Piriformis-entry nails are contraindicated in pediatric patients due to the risk of osteonecrosis from damaging the posterosuperior, posteroinferior, or retinacular vessels of the medial femoral circumflex artery (Answer 1).

Osteonecrosis occurs in up to 30% of pediatric proximal femur fractures secondary to vascular disruption. Damage can be a result of direct trauma, kinking of vessels with fracture displacement, or tamponade from intracapsular distension. Vascular supply to the pediatric femoral head changes through aging. At birth, the medial and lateral femoral circumflex arteries (MFCA, LFCA) provide the predominant supply to the epiphysis with significant contribution from the artery of the ligamentum teres. At about 3 or 4 years of age, the artery of the ligamentum teres diminishes and contributes minimally. The MFCA provides the predominant supply by way of the posterosuperior and posteroinferior retinacular branches, with the posterosuperior branch being arguably a stronger contributor from the lateral cervical ascending artery of the MFCA. The LFCA also contributes at this stage, but it is minimal compared to the MFCA. By adulthood, the MFCA is the primary vascular supply through an extracapsular ring formed at the base of the neck. Due to the increased risk of avascular necrosis with piriformis-entry intramedullary nails in pediatric patients, this technique has been abandoned. For pediatric patients with femoral neck fractures that require fixation, percutaneous pins or screws can be placed (either short of the physis or transphyseal). When an intramedullary nail is indicated, a lateral or trochanteric start point is used to avoid damaging the vascular supply in pediatric patients.

Patterson et al. published a 2018 JAAOS review article on the management of pediatric femoral neck fractures. Along with fracture management, the authors make note of the blood supply to the proximal femur. After the age of 3 or 4, the medial femoral circumflex artery provides the majority of the blood supply to the eipiphysis via the posterosuperior branch of the lateral ascending circumflex artery and the posteroinferior branch as well as posterior retinacular vessels. The authors report a rate of osteonecrosis in 16% to 47% of pediatric proximal femur fractures, presumably as a result of disruption of the femoral head vasculature. To reduce the rate of this disabling complication, an astute understanding of the vascular supply is critical.

Spence et al. performed a retrospective review of pediatric patients with femoral neck fractures to evaluate the risk factors of osteonecrosis. 70 patients between the ages of 1 and 18 years were treated for femoral neck fractures, of which 20 (29%) developed osteonecrosis. The authors found that fracture displacement and fracture location were significant predictors of osteonecrosis. The authors concluded that osteonecrosis is a common and devastating complication of pediatric femoral neck fractures that is complicated by the changing vascular supply to the femoral epiphysis.

Figures/Illustrations
Figure A is a radiograph with significant displacement of a pediatric femoral neck fracture (Delbet III).

Incorrect Answers:
Answer 2: The artery of the ligamentum teres provides a contribution to the epiphyseal blood supply at a young age but diminishes by around the age of 4 years. Furthermore, a piriformis-entry nail does not place this artery at risk.
Answer 3: The proximal femoral physis is an important contributor to overall limb growth (3-4 mm/year or 13%). However, stable fracture fixation is a higher priority than physeal preservation. Fixation may be achieved proximal to the physis, but only if this does not compromise stability.
Answer 4: Infection of the hip is a rare complication of pediatric femoral neck fractures, occurring less than 5% of the time. This can occur with open or closed fracture reduction and fixation. A piriformis-entry nail does not necessarily increase the risk of infection in this scenario.
Answer 5: The transverse branch of the LFCA is not a strong contributor to the epiphyseal blood supply. As the transverse branch of the LFCA courses just distal to the lateralis ridge, it would not be at risk with a piriformis-entry nail.