Diminished abductor muscular strength in patients with valgus-impacted femoral neck fractures treated by internal fixation: Clinical study and biomechanical considerations

Abstract

Background: Valgus-impacted femoral neck fractures treated with internal fixation occasionally result in unsatisfactory postoperative locomotive function, partially due to muscle shortening and a decrease in the moment arm. This study quantifies the degree of diminished abduction strength both clinically and biomechanically. Methods: Fifteen patients were enrolled in this study. Twelve patients with fracture healed in valgus-impacted position were further evaluated. Muscular strength around hip was examined, and values between the nonoperated and operated side were compared and analyzed. For the biomechanical study, two three-dimensional models were prepared: model I (control model without displacement) and model II (simulated malunion of a 15 valgus-impacted fracture). Two sets of hip flexion angles in each of the models were simulated with flexion angles of 0 and 23 . Results: Mean and standard deviation values for muscle strength from the nonoperative/operative side among the valgus group are as follows: flexion strength was 9.2 + 4.0/9.2 + 3.2, extension strength was 5.8 + 2.8/6.1 + 3.2, abduction strength at 0 was 9.1 + 3.7/7.4 + 3.6, abduction strength at 10 was 6.7 + 3.0/5.5 + 2.2, and knee extension strength was 15.3 + 6.2/15.1 + 6.0 (kgf). When comparing values between the nonoperative and operative sides, statistical significance was only observed in abduction strength (p < 0.01). The biomechanical models prove that valgus impaction decreases the moment arm by approximately 10% at both flexion angle. Conclusions: A significant decrease in abductor strength at 0 and 10 was observed in the valgus-healed group. This may be related to a decrease in the moment arm. Further research should be done to define the acceptable limit of deformity for the satisfactory postoperative functioning.

Innovative technique of minimally invasive closed reduction for impacted femoral neck fractures (MICRIF)

“…7,8 Our previous study also demonstrated that a 15° valgus impaction, using biomechanical computerized bony models, decreases the moment arm of abduction by approximately 10% and that only abduction of hip joint at the operated side was significantly lesser when compared with the healthy contralateral side during clinical examination. 9 This clinical result coincides with the report of Zlowodzki et al 8…”

A Simple Percutaneous Technique to Reduce Valgus-Impacted Femoral Neck Fractures

“…We expect that this simple reduction technique will increase the bone contact area by restoring the femoral neck alignment. 2,6) Previous reports suggested that the optimal posi- tioning of screws over a wide area would reduce the risk of nonunion after multiple-screw fixation. 1) Valgus deformity in the femoral neck leads to a decrease in the femoral neck dimension, which reduces the contact area and space for screw insertion.…”

“…2,4) A significant decrease in abductor strength was observed in patients with a valgus-healed femoral neck due to a decrease in the moment arm. 6) In addition, many studies verified that a healed valgus-impacted FNF can cause anterior femoroacetabular impingement (FAI) because of a large bump on the anterolateral side of the femoral headneck transition that causes a cam lesion on the femoral neck and leads to progressive hip arthrosis. 5) Steinmann pins (S-pins) are a thin metal rod commonly used in orthopedic procedures to hold large bone fractures together or control the reduction of the fracture.…”

Reverse fracture displacement direction closed reduction technique (RCRT) for the treatment of valgus impacted femoral neck fracture

“…High rate of fracture re-displacement has been found in valgus impacted femoral neck fracture patients with Conservative treatment [4,5,6] . Fracture fixed in situ without anatomical reduction contributed to increasing reports of complications, which would reduce the Harris Hip Score such as femoral neck shortening, inferior offset and femoroacetabular impingement syndrome [3,7,8] . Anatomical reduction and internal fixation has been considered necessary to enhance bony healing and reduce the rate of avascular necrosis and complications.…”