The Effects Of Different Grade Of Medial Cortical Support Reduction On Biomechanical Stability In Intertrochanteric Fractures

Objective: At present,the incidence of intertrochanteric fractures in the elderly is increasing.Surgical treatment for intertrochanteric fractures has been more suggested.However,there is still a higher failure rate of internal fixation in clinical practice,which might be directly related to the unstable biomechanics.To ensure the biomechanical stability after fixation,fully and reliable reduction is the prerequisite.Therefore,the theory of medial cortical support reduction is popularized and applied in femoral intertrochanteric fractures.For type-A2 intertrochanteric fractures,previous clinical studies and biomechanical experiments have confirmed its effects.However,there are lack of related studies to explore what kind of medial cortical reduction is more stable in type-A1 and type-A3 femoral intertrochanteric fractures.Hence this article aimed to analyze the difference of stability in three different types of intertrochanteric fractures(A1.1/A2.1/A3.2)under different grade of medial cortical support reduction.Methods: A total of 36 SYNBONE models were purchased and selected in the present study.According to the AO/OTA classification,three different types of fracture were established,including type-A1.1 fractures with complete medial cortex,type-A2.1 fractures with medial cortical defects and type-A3.2 anti-trochanteric fractures,respectively.Each type of fracture included 12 cases of models.The anterior cortex in all fracture models were anatomically reduced(neutral support),after which fracture models were further divided into three groups based on different grade of medial cortical support,including the positive support group where the medial cortex of head-neck fragment was displaced and located a little bit superomedially to the medial cortex of femoral shaft,the neutral support group(anatomical reduction)and the negative support group where the medial cortex of head-neck fragment was placed superolaterally to the medial cortex of femoral shaft.Each group included 4cases of models.The fixation technique using Proximal Femoral Nail Anti-rotation(PFNA)was manipulated in all fracture models of the present study.The static axial compression test was used to assess the displacement of proximal head-neck fragment under different loads of400 N,800N,1200 N,1500N,and the axial stiffness of fracture models,so as to analyze the biomechanical stability in different types of intertrochanteric fractures under different grade of medial cortical support reduction.Results: For type-A1.1 fractures,the static axial compression test revealed that the subsidence of proximal head-neck fragment in positive support group and neutral support group were lower than the negative support group,and the axial stiffness were greater than negative support group(P<0.05),but there was no significant difference between the positive and neutral support group(P>0.05).To compare the subsidence of proximal head-neck fragment in type-A2.1fractures,the positive support group was the smallest,followed by neutral support group,and negative support group was the largest.The axial stiffness was the largest in positive support group,followed by neutral support group and the smallest in negative support group,with statistically significant difference between the groups(P<0.05).The subsidence of proximal head-neck fragment in neutral support group was less than both the positive support group and negative support group in type-A3.2 fractures,and the axial stiffness was greater than the latter two groups(P<0.05).However,there was no significant difference between the positive and negative support group(P>0.05).Conclusion: For type-A1 intertrochanteric fractures with intact medial cortex,the biomechanical stability provided by positive cortex support is approximately equal with neutral support,both of which can be regarded as effective medial cortex support.However,it is may be difficult to obtain the true neutral support reduction during surgery in clinical practice.Hence it is feasible to accept positive cortex support when anatomical reduction cannot be achieved;For type-A2 fractures with medial cortical defects,we found that the biomechanical stability of positive cortex support is the best,and the negative support is the worst.Therefore,type-A2 fractures should be reduced with medial cortical positive support and as far as possible to avoid negative support reduction;For type-A3 anti-trochanteric fractures,neutral cortex support is more stable compared with positive and negative support reduction.Therefore,the theory of medial cortical support reduction may not be suitable for type-A3 anti-trochanteric fractures.As the load increased,medial cortex with non-anatomical reduction can only make the fracture more unstable.