A Biomechanical Study Of Lesser Trochanter Defected Intertrochanteric Fracture Fixed With PFLCP

Objective: The intertrochanteric fractures is defined as fractures from thebase of femoral neck to lesser trochanter above, which belongs toextracapsular fractures and accounts for55%of hip fractures. It mostly strikeselder patient suffering from osteoporosis, hence it becomes one of the biggestthreat to the health of old people as a traumatic disease. Early surgicaltreatment has been recognized due to the benefit of early ambulation and freefrom complications of long-time bed. What’s more, its postoperativefunctional recovery and significantly reducing mortality are superior toexpectant treatment.However, in terms of unstable intertrochanteric fractures,it experienced a high failure rate in internal fixation, which seriously impedespatients’ functional restoration. Therefore, great attention should be paid onthis kind of fracture to choose proper way of internal fixation according to its“personality”. During recent years, the development of biologicalosteosynthesis(BO) principle and minimally invasive percutaneous plateosteosynthesis(MIPPO) technique made locking plate an alternative ofintramedullary fixation. Nevertheless, the failure clinical cases of applyingproximal femur locking compression plate(PFLCP) to the treatment ofunstable intertrochanteric fractures, especially those fractures accompany withdefect around the lesser trochanter, still happened occasionally. Thisexperiment aims to study the influence of two factors upon the stability ofPFLCP internal fixation from the biomechanical view, that is, the defect levelof lesser trochanter and the length of the screw, and therefore provides atheory foundation for clinical treatment.Methods: Chose three adult antisepsis corpse specimens of close height,male and32to46years old, an average of40. Then rejected the muscles andother soft tissue attached, with only a layer of periosteum retained. Measured the geometric parameter of six femur specimens. After macroscopicobservation and x-ray examination, no bone tumour, skeletal deformity, bonedestruction and obvious osteoporosis of the skeletal system of femur werediscovered. Besides, all the specimens were preserved in formalin. Took themout12hours before the experiment, cross sectioned them from femoralcondyle above, with the segment from femoral neck to upper middle sectionleft at a length about35cm.Six femur samples each for a set. Before making the fracture model, allthe specimens were fixed by10-hole PFLCP with the standard techniques.Three hollow locking screws were fixed into the femoral head while fivedouble cortical screws were fixed into the distal end. Having finished thefixation, the positive lateral X-ray was made to ensure a right position ofinternal fixation.All specimens were embedded with type Ⅱdenture base resin andmounted on a jig. Then four sites on the proximal femur were selected to pastestrain gauges. With the strain gauges affixed, the fractures internal model andjigs were placed on electronic universal testing machine, followed by thestrain gauges and deformeter connected accordingly. Dial indicator pointerwas placed horizontally against the edge of the first hole on proximal femorallocking plate and firmly fixed. Before the formal load,1000N vertical loadwas delivered to minimum the error caused by creep. Then loaded verticalload at the speed of20N/S from0~1000N, and record the strain values.Meanwhile, record the corresponding vertical displacement and horizontaldisplacement under corresponding load. In addition, According to thegeometric parameter of the specimens and imaging measurements, eachfracture model was in turn using90mm,85mm,80mm, three types of headscrew for testing. The distance between three types of screws to the cartilagesurface of femoral head were correspondingly about10mm,15mm and20mm.In this experiment,the groups wrer called simplified as90mm group,85mmgroup, and80mm group.After finishing the test of internal fixation of simplefracture model, made each specimen with different internal fixation fracture models for lesser trochanter basal defect, lesser trochanter moderate defect andlesser trochanter extensive defect, then, in turn, loaded the vertical pressurewith the loading method mentioned above, and record correspondingindexes.At last, applied SPSS20.0statistical software for statistical processing,repeated measure designed variance analysis, in which P﹤0.05wasconsidered as statistically significant differences.Results:1No statistically significant differences existed between the six femoralspecimens in terms of femoral neck length, femoral neck diameter，femoralhead diameter, and femoral neck-shaft angle.2Displacement value: the results of horizontal displacement value andvertical displacement value were similar. In the simple fracture model andlesser trochanter basal defect fracture model,there was no statisticallysignificant difference between90mm group and85mm group but differ fromthat of80mm group. In the lesser trochanter moderate defect fracture modeland lesser trochanter extensive defect fracture model, three lengths of screwshad significant difference between any two lengths. With the increase of thedefect degree,the displacement value increased,the stability of the fracturereduced gradually.3Strain values: Site one and two were both detected as positive, whichmeans they were under the tensile stress. While site three and four weremeasured as negative, which means they were under the compressive stress.With the changes in the length of head screws, the strain value of four siteschanged in the same way.In the simple fracture model and lesser trochanterbasal defect fracture model,there was no significance between90mm groupand85mm group but differ from that of80mm group. In the lesser trochantemoderate defect and extensive defect fracture model, three lengths of screwshad significant difference between any two lengths.Meanwhile,with theincrease of the defect degree,the strain value of four sites didn’t change in thesame way.Among them, the strain value of sites one, two and three increasedas the defect widened. In contrast, the strain value of site four decreased as the defect widened.Conclusion: This experiment research shows that, as to the application ofthe proximal femur locking compression plate（PFLCP） for the treatment oflesser trochanter defected intertrochanteric fractures, the best biomechanicalstability can be achieved with the head screws fixed under the femoral headcartilage at the distance of about10mm. If the degree of the defect of lessertrochanter is relatively lighter, then the distance at15mm can also achieve thesimilar stabilizing effect. Nevertheless, the distance of20mm will not berecommended.