Bone Microarchitecture And Biomechanics Of Necrotic Femoral Head

Objective: Femoral head necrosis is a common and refractory disease with poor prognosis,bringing huge economic and social burden to patients and country.Treatments for femoral head necrosis mainly are core decompression,free vascularized fibular grafts,derotation osteotomy and limited or total hip arthroplasty,the effect of which is uncertain.Specific pathogenesis is the premise of effective treatments.The pathogenesis of femoral head necrosis is still unclear yet.In recent years,increasingly importance has been attached to the effect of biomechanics on the development of femoral head necrosis.The aim of our study is to explore the changing of space structure and biomechanical property of the femoral head in the development of femoral head necrosis,and provide theoretical basis for the pathogenesis and treatment of femoral head necrosis.Methods:(1)Fifteen femoral heads after total hip arthroplasty for patients with femoral neck fracture or femoral head necrosis were selected respectively,excluding deformities and bone tumors,etc.Take Micro-CT scan for these specimens by Siemens,Inveon~TM system,observe and compare the space structure of these femoral heads,and calculate the parameters of bone morphometry.(2)Get bone blocks of uniform size(1cm×1cm×1cm)from different zone of femoral head by diamond band cutting system,and test the biomechanical property of these bone blocks by BOSE-ELF3510 biomechanical property testing system.Compare the biomechanical property of bone blocks from corresponding zone of normal and necrotic femoral head.Results:(1)The arrange of trabecular bone of any zone of normal femoral head is regular and ordered,while the arrange of trabecular bone of necrotic zone and sclerotic zone of necrotic femoral head is messy and unordered.(2)Comparing with the proximal compressive trabeculae of normal femoral head,bone surface vs.bone volume(BV/TV)of necrotic zone of necrotic femoral head drops,number of trabecular bones(Tb.N)decreases,trabecular separation(Tb.Sp)increases;comparing with the junctional zone of normal femoral head,BV/TV of sclerotic zone of necrotic femoral head increases,Tb.Sp decreases,trabecular thickness(Tb.Th)increases;comparing with distal compressive trabeculae of normal femoral head,BV/TV,Tb.N,Tb.Sp,Tb.Th of distal compressive trabeculae of necrotic femoral head have no statistical differences;comparing with tensile trabeculae zone of normal femoral head,the BV/TV and Tb.Th of tensile trabeculae zone of necrotic femoral head have no statistical differences(3)Comparing with the proximal compressive trabeculae of normal femoral head,the biomechanical property of necrotic zone of necrotic femoral head becomes weak,the elastic modulus of it decreases 70%,yield strength decreases 35%,ultimate strength decreases 35%;comparing with the junctional zone of normal femoral head,the elastic modulus,yield strength and ultimate strength of sclerotic zone of necrotic femoral head all increase;comparing with distal compressive trabeculae of normal femoral head,the biomechanical property of distal compressive trabeculae of necrotic femoral head have no statistical differences;comparing with tensile trabeculae zone of normal femoral head,the biomechanical property of tensile trabeculae zone of necrotic femoral head have no statistical differencesConclusion: Comparing with the femoral head of normal people,the space structure and biomechanical property of necrotic zone and sclerotic zone of femoral head of patients with femoral head necrosis change a lot.In my opinion,the essence of the development of femoral head necrosis is the changing of the space structure and biomechanical property of femoral head.I hypothesize that: the hip joint is the major weight-bearing joint,stress on the femoral head is very large,hormone using,alcohol abuse,etc non-traumatic factors makes the bone strength of femoral head decrease,leading to fatigue fracture;for traumatic femoral head necrosis,after the treatment of internal/external fixation,anatomical reduction is not achieved mostly,the arrange of trabeculae is altered,the structure and function is not harmonious,fatigue fracture occurs after long-term stimulation of stress.After fatigue fracture of trabeculae,the small-scale,original necrotic zone develops,reparative reaction is activated,the biomechanical property of old trabeculae are strengthened or new trabeculae are produced,sclerotic zone are formed around the necrotic zone.Although the formation of sclerotic zone can provide biomechanical protection for necrotic zone,when the reparative process and fatigue fracture are unbalanced,the normal trabeculae is replaced by granulation tissue or fibrous connective tissue,stress shielding occurs at the marginal line of necrotic zone and sclerotic zone,leading to the increasing of stress on sclerotic zone.And fatigue fracture occurs at the sclerotic zone,reparative reaction is activated,then vicious circle starts,the range of necrotic zone enlarged,collapse occurs finally.