Biomechanical characteristics of two geometric configurations of cannulated compression screws in the fixation of femoral neck fracture

Wei SHI; Jie FAN; Yingze ZHANG; Bogui YANG; Weidou JIA; Suhong LI

ABSTRACT

BACKGROUND:

After femoral neck fracture, incidences of ischemic necrosis and bone non-healing are closely related to biomechanical characteristics of internal fixation devices. Compression stress can improve fracture healing, tension force can delay fracture healing, and shear stress can inhibit fracture healing. How to relieve shear stress and expand compression stress is of significance for theories and clinical applications.

OBJECTIVE:

To compare the biomechanical characteristics of the two geometric configurations of three cannulated compression screws in the fixation for femoral neck fracture and to provide a theoretical foundation in the treatment of femoral neck fracture.

DESIGN:

Observational contrast study.

SETTING:

Department of Orthopaedics, the 251 Hospital of Chinese PLA; Department of Orthopaedics, the Third Hospital, Hebei Medical University.

PARTICIPANTS:

The experiment was carried out in the Hebei Orthopaedic Institute from November 2002 to March 2003. Five cadavers including 4 males and 1 female with similar bone mineral density (BMD) were provided by Department of Anatomy, Hebei Medical University. X-ray photographs proved that all the cadavers did not have rheumatism, tuberculosis, tumor, fracture or deformity.

METHODS:

Ten femurs were randomly divided into inverted and upright isosceles triangle with 5 in each group. Femur samples with femoral neck fracture were fixed with three cannulated screws and measured with the biomechanical machine (CSS-44020, made in Changchun Experimental Researching Institute, provided by Hebei Orthopaedics Institute). The compression strength, torsibility and the maximal vertical loading were compared between the two configurations of screws.MAIN OUTCOME

MEASURES:

①Displacement of femoral head at 600 N and 750 N during torsibility test; ②torque-moment at 2°and 4°during torsibility test;③load during maximal vertical loading test.

CONCLUSION:

The effect of three cannulated compression screws configured as an inverted isosceles triangle on the treatment of femoral neck fracture is superior to that of three cannulated compression screws as an upright isosceles triangle.