A Lateral Fracture Line Affects Femoral Trochanteric Fracture Instability and Swing Motion of the Intramedullary Nail: A Biomechanical Study

Takuya Usami; Naoya Takada; Weerachai Kosuwon; Permsak Paholpak; Masami Tokunaga; Hidetoshi Iwata; Yusuke Hattori; Yuko Nagaya; Hideki Murakami; Gen Kuroyanagi

doi:10.2106/JBJS.OA.23.00118

A Lateral Fracture Line Affects Femoral Trochanteric Fracture Instability and Swing Motion of the Intramedullary Nail: A Biomechanical Study

JB JS Open Access. 2024 Feb 13;9(1):e23.00118. doi: 10.2106/JBJS.OA.23.00118. eCollection 2024 Jan-Mar.

Authors

Takuya Usami^{1

2}, Naoya Takada³, Weerachai Kosuwon⁴, Permsak Paholpak⁴, Masami Tokunaga⁵, Hidetoshi Iwata³, Yusuke Hattori^{1

2}, Yuko Nagaya², Hideki Murakami¹, Gen Kuroyanagi^{1

6}

Affiliations

¹ Department of Orthopaedic Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya, Aichi, Japan.
² Department of Orthopaedic Surgery, Nagoya City University East Medical Center, Nagoya, Aichi, Japan.
³ Department of Orthopaedic Surgery, Kainan Hospital, Yatomi, Aichi, Japan.
⁴ Department of Orthopaedics, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
⁵ Department of Orthopaedic Surgery, Fukuoka Orthopaedic Hospital, Fukuoka, Fukuoka, Japan.
⁶ Department of Rehabilitation Medicine, Nagoya City University Graduate School of Medical Sciences, Nagoya, Aichi, Japan.

Abstract

Background: An unstable trochanteric femoral fracture is a serious injury, with a 1-year mortality rate of 5.4% to 24.9%, for which there is currently no standard treatment method. The lag screw insertion site is one of the primary contact areas between the cortical bone and an intramedullary nail. We hypothesized that a posterolateral fracture causes intramedullary nail instability when the posterolateral fracture line interferes with lag screw insertion. The purpose of the present study was to investigate the effect of posterolateral fracture line morphology on intramedullary nail stability by simulating unstable trochanteric femoral fractures with a posterolateral fracture fragment.

Methods: Eighteen custom-made synthetic osteoporotic bone samples were used in the present study. Nine samples had a posterolateral fracture line interfering with the lag screw insertion hole (Fracture A), and the other 9 had a fracture line 10 mm away from the hole (Fracture B). Cyclic loading (750 N) was applied to the femoral head 1,500 times. Movement of the end cap attached to the intramedullary nail was recorded. The amplitudes of motion in the coronal plane (coronal swing motion), sagittal plane (sagittal swing motion), and axial plane (total swing motion) were evaluated. The change in the neck-shaft angle was evaluated on photographs that were made before and after the test. Medial cortical displacement was measured before and after the test.

Results: Two Fracture-A samples were excluded because the amplitude of sagittal swing motion was too large. The mean values for coronal, sagittal, and total swing motion were 1.13 ± 0.28 mm and 0.51 ± 0.09 mm (p < 0.001), 0.50 ± 0.12 mm and 0.46 ± 0.09 mm (p = 0.46), and 1.24 ± 0.24 mm and 0.69 ± 0.11 mm (p < 0.001) for Fractures A and B, respectively. The mean neck-shaft angle change was -8.29° ± 2.69° and -3.56° ± 2.35° for Fractures A and B, respectively (p = 0.002). The mean displacement of the medial cortex was 0.38 ± 1.12 mm and 0.12 ± 0.37 mm for Fractures A and B, respectively (p = 0.57).

Conclusions: This study showed that an unstable trochanteric femoral fracture with a posterolateral fracture line that interferes with the lag screw insertion holes is a risk factor for increased intramedullary nail instability.