Objectives: To evaluate the biomechanical performance of the Femoral Neck System (FNS) versus the Hansson Pin System (Hansson Pins) with two parallel pins in a Pauwels II femoral neck fracture model with posterior comminution.
Methods: Forty-degree Pauwels II femoral neck fractures AO 31-B2.1 with 15° posterior wedge were simulated in fourteen paired fresh-frozen human femora, followed by instrumentation with either FNS or Hansson Pins in pair-matched fashion. Implant positioning was quantified by measuring shortest implant distances to inferior cortex (DI) and posterior cortex (DP) on anteroposterior and axial X-rays, respectively. Biomechanical testing was performed in 20° adduction and 10° flexion with simulated iliopsoas muscle tension. Progressively increasing cyclic loading was applied until construct failure. Interfragmentary femoral head-to-shaft movements were measured with optical motion tracking.
Results: Cycles to 10° varus deformation were significantly higher for FNS (23007 ± 5496) versus Hansson Pins (17289 ± 4686), P = 0.027. Cycles to 10° femoral head dorsal tilting (FNS: 12765 ± 3425; Hansson Pins: 13357 ± 6104) and cycles to 10° rotation around the femoral neck axis (FNS: 24453 ± 5073; Hansson Pins: 20185 ± 11065) were comparable between the implants, P ≥ 0.314. For Hansson Pins, the outcomes for varus deformation and dorsal tilting correlated significantly with DI and DP, respectively (P ≤ 0.047), whereas these correlations were not significant for FNS (P ≥ 0.310).
Conclusions: From a biomechanical perspective, by providing superior resistance against varus deformation and performing in a less sensitive way to variations in implant placement, the angular stable Femoral Neck System can be considered as a valid alternative to the Hansson Pin System for the treatment of Pauwels II femoral neck fractures.
Level of evidence: therapeutic, Level V.
The translational potential of this article: The translational potential of this article is to compare the performance of the FNS with Hansson Pins in a AO 31-B2.1 fracture model featuring a 15 posterior wedge to show the implants behavior concerning the dorsal tilting tendency.
Keywords: Biomechanics; Dorsal tilting; Femoral Neck System; Femoral neck fracture; Hansson Pin System; Posterior comminution.
© 2020 The Authors.