Effect of the Number, Size, and Location of Cannulated Screws on the Incidence of Avascular Necrosis of the Femoral Head in Pediatric Femoral Neck Fractures: A Review of 153 Cases

Abstract

Background:The correlation between the number, size, and location of cannulated screws and the incidence of avascular necrosis (AVN) in children with femoral neck fractures treated surgically is uncertain. Methods: We retrospectively reviewed 153 children (mean age: 10.6 ± 3.7 y) with femoral neck fractures treated by internal fixation with 2 (n = 112) or 3 (n = 41) cannulated screws. The severity of initial displacement was divided into incomplete (type I) and complete (type II, angulation <50 degrees; type III, angulation > 50 degrees) fractures. The diameter of the screw was measured and recorded as a percentage of the femoral neck width. The distance (D) between the mid-point of each screw at the base (B) of the femoral neck and at the tip (T) of each screw and the superior and anterior cortices of the femoral neck, respectively, were measured on anteroposterior (AP) and lateral (L) radiographs. Values were expressed as the ratio between the measured distance and the width of the femoral neck (BD AP %, TD AP %, BD L %, and TD L %). The correlation between the number, size, and location of the screws and AVN was analyzed. Results: Patients with type II of initial displacement treated with 2 cannulated screws had a lower AVN rate (21.4%) than those treated with 3 screws (44.8%) (P = 0.027). Screw diameter (19%) in patients with AVN was larger than (17%) in patients without AVN (P < 0.001); patients with AVN had a lower BD AP % (48.6%) than those without AVN (56.4%) (P < 0.001). Screw size and BD AP % were risk factors for AVN (P < 0.05). Further, screw diameter > 16.5% and BD AP % <51.6% of the femoral neck width were the cutoff values for an increased AVN rate (P < 0.05). Conclusions: Patients treated with 2 cannulated screws showed a lower rate of AVN than patients treated with 3 screws. Screws of larger size and screws closer to the piriformis fossa on AP radiographs increased the risk of AVN in children with femoral neck fractures treated surgically. Level of Evidence: Level III.

The Duration of Hardware Retention After Radiologic Union of Surgically Treated Femoral Neck Fractures in Children May Predict the Aggravation or Occurrence of Avascular Necrosis of the Femoral Head or Neck After Hardware Removal

“…In particular, in patients with AVN, the presence of particularly vulnerable vascular structures and the reduced number of vessels predisposes to a decreased blood supply to the femoral head during the process of removing hardware 22,23 . Several studies have reported similar findings indicating that the intraosseous vascular system can be damaged to varying degrees during implant insertion 3,4 . In addition, due to the stress shielding caused by implants, the removal of internal fixation is inevitably associated with the imposition of greater mechanical stresses on the bone structure that were not previously applied to the trabecular bone 7,8 .…”

“…The inclusion criteria were as follows: 1) diagnosis of unilateral PFNF with the absence of additional injuries or nutritional metabolic diseases; 2) age at the time of injury: below 17 years; 3) type II or type III PFNF according to the Delbet-Colonna classification; 9 4) complete clinical and radiographic data, including standard postoperative anterior-posterior and cross-table or frog-leg lateral pelvic radiographs; 10,11 5) hardware in place for more than 6 months; 3 and 6) consecutive postoperative radiographs with a follow-up interval of less than 2 months before hardware removal 12 and follow-up data covering a period of at least 6 months after hardware removal 2 …”

“…Pediatric femoral neck fractures (PFNFs) account for ∼0.3% to 0.5% of pediatric fractures 1,2 . Fracture location and treatment are associated with an increased risk of avascular necrosis (AVN) of the femoral neck and head due to damage to the circumflex arteries and intraosseous vascular system 3,4 . However, it is unclear whether hardware removal after achievement of radiologic fracture healing can cause or exacerbate AVN of the femoral neck and head; the risk factors associated with this complication are also unclear.…”

Is Femoral Neck System a Valid Alternative for the Treatment of Displaced Femoral Neck Fractures in Adolescents? A Comparative Study of Femoral Neck System versus Cannulated Compression Screw

“…However, too large an internal fixation can disrupt hemoperfusion of the femoral head, as reported by Wang et al [ 14 ]. The FNS consists of a bolt and an anti-rotation screw with an angle of 5°.…”

“…Song et al [ 13 ] and Wang et al [ 14 ] classification system was used to evaluate initial fracture displacement: type I, incomplete fractures without translation or mild angulation <30°; type II, complete fractures with any amount of translation or angulation <50°; and type III, complete fractures with any translation or angulation >50°.…”