Study On The Relationship Of Collapse Of The Femoral Head And Thickness Of Subchondral Bone

Objective: Avascular necrosis of the femoral head is a common disease in orthopedics with partial revascularization of the femoral head for viraous reasons, further appears intraosseous hypertension, bone trabecular fracture and femoral head collapse, the resulte is the loss of hip joint function. ANFH affect the patient's life and work seriously, and the rate of collapse is very high. Once the femoral head collapse, about 87% of patients have to take total hip arthroplasty, the medium and long-term effects of which are worse. Most patients can avoid collapse if effective measures were taken to restore normal mechanics structure of the femoral head in early stage. Present study has confirmed that there is a relationship between collapse of the femoral head and necrosis location,necrotic area,weight,age and other factors. The location and extent of necrosis impact greatly. The purpose of this study is to discuss the relationship between collapse of the femoral head and the subchondral bone thickness. Different thickness of subchondral bone of femoral head necrosis models were maded and taken biomechanical testing to discuss the change of Bio-mechanical properties of different thickness of subchondral bone,which will predict collapse in early to take effective measures to prevent the progress and provide a reasonable basis of retainning the thickness of subchondral bone when taking debridement surgeryMethods: Choose 60 femurs of British Landrace pigs, Femurs were sawed under 4cm of greater trochanter, preserving the part of the femoral head. The part of the femoral head are sawed along the median coronal plane using pendulum saws, preserving the side which has round ligament,The BMD of the femoral head were tested immediatly. In order to reduce differences in biomechanical properties effected by BMD,we use randomized block design. We marked the dates of BMD from small to large and put six of similar BMD values into one block. Then we slected two figures as a random number from random number table,which were ranked by size.The number 1-5 of each block were maded into the femoral head necrosis models with the subchondral bone thickness of 1mm, 2mm, 3mm, 4mm, 5mm.The number 6 was a normal control group without any treatment. Making methods: Connecting the two point of the junction of the head and neck, from 9-3 o'clock on average 13 position were taked, where the thickness of subchondral bone was measured accuratly and marked. Then all points were connected with arc. The cancellous bone were removed with crescent saws along the mark and polished carefully. In order to ensure the accuracy of models,we use Caliper to measure the thickness of the femoral head at many parts timely. All models of femoral head necrosis will do:①To observe imaging study: through the X-ray and CT to observe whether the thickness of subchondral bone of each model is consistent②To do biomechanical test of each femoral head necrosis model to obtain yield load .All datas wil be expressed in X±s. and analyzed with SPSS 13.0 statistical software.Results:(1) Bone mineral density Results: Bone mineral density measurements is 0.307~0.520g/cm2 , the mean±standard deviation is 0.417±0.041g/cm2. there are 14 cases between 0.307~0.399g/cm2, there are 38 cases between 0.400~0.499g/cm2 and 8 cases above 0.500g/cm2.(2) General observation after biomechanical test: All specimens of the femoral head collapsed and subchondral bone fractured.(3) Imaging study results: The thickness of the subchondral bone are uniform in 1-5Groups.(4)Biomechanical results:The yield load of 1-6 groups are: 70.29±8.72,83.02±9.22,167.95±12.28,186.65±13.65,204.15±10.44,931.69±55.46.Conclusion:1 Different thickness models of subchondral bone of femoral head necrosis can be made in vitro animal bones exactly and examed by imaging equipment.2 The collapse of ANFH is closely related with the thickness of subchondral bone. The bearing capacity of subchondral bone decreased and prone to collapse when ANFH happened. The femoral heads have a more collapsing risk when the thickness of the subchondral bone is less than 3mm.3 After debridement the thickness of subchondral bone should be controlled above 3mm in the operation of ANFH through the application of X-ray.