Increasing the precision of intramedullary nailing in femoral derotation osteotomies by larger core locking bolts. A biomechanical study

Anders Grønseth; Jan Egil Brattgjerd; Joachim Horn

doi:10.1016/j.clinbiomech.2025.106449

Increasing the precision of intramedullary nailing in femoral derotation osteotomies by larger core locking bolts. A biomechanical study

Clin Biomech (Bristol). 2025 Mar:123:106449. doi: 10.1016/j.clinbiomech.2025.106449. Epub 2025 Feb 4.

Authors

Anders Grønseth¹, Jan Egil Brattgjerd², Joachim Horn³

Affiliations

¹ Department of Orthopaedic surgery, Division of Orthopaedic Surgery, Oslo University Hospital, Oslo, Norway; Institute for Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway. Electronic address: andgro@ous-hf.no.
² Department of Orthopaedic surgery, Division of Orthopaedic Surgery, Oslo University Hospital, Oslo, Norway; Biomechanics Laboratory, Division of Orthopaedic Surgery, Oslo University Hospital, Oslo, Norway; Institute of Rehabilitation Science and Health Technology, Faculty of Health Sciences, Oslo Metropolitan University, Oslo, Norway.
³ Department of Orthopaedic surgery, Division of Orthopaedic Surgery, Oslo University Hospital, Oslo, Norway; Institute for Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.

PMID: 39922080
DOI: 10.1016/j.clinbiomech.2025.106449

Abstract

Background: To correct increased femoral anteversion, surgeons perform femoral derotational osteotomies in symptomatic adolescents. Using an intramedullary nail as fixation in this setting, undersized locking screws reduce rotational precision by allowing nail toggling. However, the extent to which better-fitting locking bolts improve rotational precision in femoral derotational osteotomies remains unclear. Accordingly, we tested the hypothesis that adequately sized locking bolts enhance rotational stiffness and limit displacement, thereby decreasing nail toggling in femoral derotational osteotomies in vitro.

Methods: We evaluated rotational stiffness, angular displacement, and laxity at zero-loading in 12 synthetic femurs with a transverse gap osteotomy to the shaft. After inserting a pediatric intramedullary nail, femurs were fixed with either conventional 4.5 mm locking screws or locking bolts with a 0.3 mm larger core diameter. Non-destructive quasi-static rotational testing of 4 Nm external and internal torque was performed according to a predefined protocol.

Findings: We found significantly higher mean rotational stiffness with locking bolts than with locking screws, demonstrating a 150 % increase (0.4 Nm/degree vs. 1.0 Nm/degree, P < 0.001). Mean angular displacement was significantly lower with locking bolts than with locking screws, exhibiting a 61 % decrease (21.9 vs. 8.6 degrees, P < 0.001). Additionally, laxity with locking bolts was 69 % lower than with locking screws (3.2 degrees vs. 10.4 degrees, P = 0.0027).

Interpretation: Locking bolts with a larger core diameter enhances rotational stability and fixation precision, making them a valuable advancement in intramedullary nailing for femoral derotational osteotomies. These findings may also have implications for fracture treatment.

Keywords: Biomechanical testing; Femoral anteversion; Femoral derotational osteotomy; Intramedullary nail; Locking screw design; Locking screws.

MeSH terms

Biomechanical Phenomena
Bone Nails*
Bone Screws*
Femoral Fractures* / physiopathology
Femoral Fractures* / surgery
Femur* / physiopathology
Femur* / surgery
Fracture Fixation, Intramedullary* / instrumentation
Fracture Fixation, Intramedullary* / methods
Humans
Osteotomy* / instrumentation
Osteotomy* / methods
Rotation
Torque