Abstract
Objectives This biomechanical study was conducted to compare fixation stability of the proximal fragments and their mechanical characteristics in proximal femur models of unstable basicervical IT fractures fixed by cephalomedullary nailing using 3 different types of the femoral head fixation. Methods A total of 36 composite femurs corresponding to osteoporotic human bone were used. These specimens were fixed with Gamma 3 (hip screw type; group 1) in 12, Gamma 3 U-blade (screw-blade hybrid type; group 2) in 12, and proximal femoral nail antirotation-II (helical blade type; group 3) in 12, respectively, and an unstable basicervical IT fracture was created by an engraving machine. After preloading and cyclic loading, the migration of the proximal fragment according to 3 axes was assessed by the stereophotogrammetric method and the migration of screw or blade tip within the femoral head was measured radiographically. Next, the vertical load was continued at a speed of 10 mm/min until the construct failure occurred. Finite element analysis was additionally performed to measure the stress and compressive strain just above the tip of screw or blade within the femoral head. Results The rotational change of the proximal fragment according to the axis of screw or blade was much greater in group 1 than in groups 2 and 3 (p=0.016 and p=0.007, respectively). Varus collapse was greater in group 3 than in group 2 (p=0.045). Cranial and axial migration of screw or blade within the femoral head were significantly greater in group 3 than in both group 1 (p=0.001 and p=0.002, respectively) and group 2 (p=0.002 and p=0.016, respectively). On finite element analysis, group 3 showed the highest peak von-Mises stress value (13.3 MPa) and compressive strain (3.2%) just above the tip of the blade within the femoral head. Meanwhile, groups 1 and 2 showed similar results on two values. Conclusions Screw-blade hybrid type and blade type would be more effective in minimizing rotation instability of the proximal fragment in unstable basicervical IT fractures. However, varus collapse of the proximal fragment and cranial and axial migration within the femoral head were greater with blade type than screw-blade hybrid type.
Highlights
Basicervical intertrochanteric (IT) fractures are a specific type of trochanteric fracture that has rarely been reported as a separate entity [1,2,3,4]
Bojan et al [16] reported that a basicervical fracture pattern is 1 of 3 variables associated with a high risk of screw cut-out
Watson et al [14] reported that all fixation failure after cephalomedullary nailing (CMN) for basicervical proximal femoral fractures developed in patients who had appropriate tip-apex distance (TAD)
Summary
Basicervical intertrochanteric (IT) fractures are a specific type of trochanteric fracture that has rarely been reported as a separate entity [1,2,3,4]. In comparison with typical trochanteric fractures reported in earlier series, the fracture line crosses close to the base of the femoral neck and its junction with the IT region on radiographs [2, 5,6,7] These fractures have not been well characterized in existing classification systems and are relatively rare. Because cephalomedullary nailing (CMN) has shown a clear advantage over the compression hip screw, the indications for CMN have been broadened greatly [8,9,10] These expanded indications have led to increased CMN use for BioMed Research International almost all peritrochanteric fractures, including basicervical fracture patterns [11,12,13]. Very little has been reported regarding biomechanical analysis or surgical outcomes focusing on basicervical IT fractures as a separate entity, especially when fixed with CMN
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