Biomechanical Comparison And Analysis Of Four Kinds Of Internal Fixations For The Treatment Of The Femoral Subtrochanteric Fractures

Purpose:To compare the biomechanical properties of four kinds of internal fixations (PFN, DHS, DCS and PFLCP) for the treatment of different types of subtrochanteric fractures, and explore the best method of fixation in different types of fracture and provide experimental evidences for clinical treatment.Methods:(1)32antiseptic femurs were randomly divided into four groups. After internal fixations implanted respectively, Seinsheimer type Ⅰ, type Ⅲa with medial fragment restoration, type ⅢA with medial fragment discarded and type IV subtrochanteric fracture models were sequentially produced. Each fracture model was tested under vertical load (0～1200N, velocity:10mm/min), torsional load (the direction of femoral torsion was external rotation, torque:10Nm) and vertical damage load (the model V was compressed until it damaged at the velocity10mm/min after vertical load test and torsional load test). The strain distributions on both medial and lateral side of subtrochanteric region were recorded and the stiffness of bone-implant construct was calculated. Then the torsional stiffness of each fracture model was calculated. At last, the loads of failure were recorded. The strain ratio was calculated by dividing the recorded strain by the strain on self-control femur, the stiffness ratio and torsional stiffness ratio was calculated by the same method.(2)20antiseptic femurs were randomly divided into four groups. After standard surgical procedures to install the fixations,2cm long cylindrical bone fragment was removed1cm below the lesser trochanter to simulate type IV subtrochanteric fracture. All specimens were pre-loaded five times. Formal load:five groups were performed, each loop contained300cycles, and1,500cycles in all; each group started from100N, maximum load was200N～600N (body weight was60kg), the loading rate was1Hz. And the increments load between groups was100N. The interval period between the two groups was30minutes, letting the femur elastic recover. We recorded the sinking displacement of the femur head, the load and the number of cycles.Results:(1) The strain ratios on medial and lateral side of proximal femur of PFN decreased evenly. The stiffness ratio in each fracture model and load of failure were the highest among the four groups, but the torsional stiffness ratio was the lowest. The strain ratio curves of DHS and DCS like upward arches. Tension strain ratios on lateral side became higher compress strain ratio with medial fragment restored. Stiffness ratio of DHS was lower than PFLCP in each fracture model, torsional stiffness ratio was the highest in fracture model ⅡtoⅤ, and the load of failure was only lower than PFN. The stiffness ratio and load of failure of DCS were both the lowest, torsional stiffness ratio was similar to PFLCP’s in fracture model Ⅱ to Ⅴ. The strain ratio decreased was similar to PFLCP’s. while stain ratio distribution had little changes. The stiffness ratio was only lower than PFN’s in each fracture model, but the load of failure was lower than DHS’s.(2) The average sinking displacement of different internal fixation group after1500times:PFN,(1.09±0.13) mm; DHS.(1.78±0.25) mm; DCS,(2.63±0.46) mm; PFLCP,(2.26±0.16) mm. The difference was statistically significant (P<0.05). The required load to reach1mm mean sinking displacement of each fixation group:PFN.(563.04±58.34) N; DHS.(485.73±147.27) N; DCS.(258.44±97.23) N; PFLCP.(332.68±100.34) N. There was significant difference between any two (P<0.05). The number of cycles when each fixation group reached1mm mean sinking displacement:PFN,(1458±277) cycles; DHS,(908±184) cycles; DCS.(369±116) cycles; PFLCP (603±162) cycles. There was significant difference between any two (P<0.001).Conclusions:Four kinds of internal fixations could achieve better stabilities for type Ⅰ subtrochanteric fractures. PFN and PFLCP could achieve reliable stabilities for type Ⅲa subtrochanteric fractures. And, if the medial buttress was restored, we could consider of using the DHS. For type IV subtrochanteric fractures (also the subtrochanteric comminuted fractures), only PFN could provide stable fixation. Under cyclic loading, the biomechanical property of the PFN was best, the DHS followed, the PFLCP third, and the DCS worst for the treatment of subtrochanteric comminuted fractures.