Effect of varus and valgus alignment on implant loading after proximal femur fracture fixation.
BACKGROUND
More than 10 % of proximal femur fractures repaired with either a sliding hip screw and side plate (SHS-P) or a sliding hip screw and intramedullary nail (SHS-IMN) demonstrate varus malreduction. The purpose of this study was to compare the effect of varus or valgus loading on comminuted intertrochanteric fractures repaired with SHS-P or SHS-IMN constructs.


METHODS
Unstable intertrochanteric fractures with segmental comminution were generated in 12 cadaver proximal femurs, six of which were fixed with an SHS-P and six with an SHS-IMN. Both implants had a strain gauge at the lag screw-nail-plate interface to assess implant load bearing. The load on the implants was measured with the specimens in neutral position and at 5°, 10°, and 15° of varus and valgus.


RESULTS
Loads on both SHS-IMN and SHS-P constructs were significantly increased when loading the implants in varus and significantly decreased when loading the implants in valgus. Unlike the SHS-IMN, the SHS-P trended toward increased load bearing at 15° varus (159.1 vs. 118.5 %, P = .065) and trended toward less load bearing at 15° valgus (42.3 vs. 59.8 %, P = .06).


CONCLUSIONS
Regardless of implant choice, avoiding varus loading on the fixation construct reduces the load on the implant. SHS-P constructs may be more affected by varus or valgus malalignment than SHS-IMN constructs.
Orthopaedic Trauma Institute, San Francisco General Hospital, University of California, San Francisco, 2550 23rd Street, Building 9, 2nd Floor, San Francisco, CA, 94110, USA.
Meir
M
Marmor
UCSF School of Medicine, San Francisco, CA, 94101, USA.
Kate
K
Liddle
Department of Mechanical Engineering, University of Delaware, 106 Spencer Lab, Newark, DE, 19716, USA.
Jenni
J
Buckley
Orthopaedic Trauma Institute, San Francisco General Hospital, University of California, San Francisco, 2550 23rd Street, Building 9, 2nd Floor, San Francisco, CA, 94110, USA. amir.matityahu@ucsf.edu.
Amir
http://orcid.org/0000-0003-0783-0376
A
Matityahu
D017760:Bone Malalignment / Q000601:surgery; D001858:Bone Nails; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000379:methods*; D006620:Hip Fractures / Q000601:surgery*; D006801:Humans; D013312:Stress, Physiological / Q000502:physiology
Biomechanical testing; Fracture fixation; Hip fracture; Intertrochanteric fracture; Intramedullary nailing; Malreduction; Pertrochanteric fracture; Proximal femur fracture; Varus