Effect Of Changes In Bohler’s Angle Of Calcaneus On Ankle Contact Areas And Pressures

Objective:To observe the effect of changes in Bohler’s angle of calcaneus on ankle contact areas and pressures, to provide a theoretical foundation for treatment.Methods:Two flat and smooth stainless steel blocks with double leaf pressure-sensitive films of2cm×2cm in size were placed on the force platform, vertically downward load(200-1000N) was given. The pressure-sensitive response curve was obtained by computer image analysis of pressure-sensitive tablets and calculation. Eight fresh specimens consisting of feet and lower legs were harvested. A specimen included an intact foot and20cm of the distal tibia and fibula, and was prepared by removing the skin, muscle and achilles tendon. The important ligaments were kept intact in order to maintain the stability of the ankle joint. The eight specimens with pressure-sensitive films well placed in each ankle joint were first immobilized with denture powder by the proximal, and then placed on the test machine for load test.500-N load along the axial tibial was applied on each specimen in the neutral position for2minutes. After that, Bohler’s angle of each specimen was decreased to0degrees with its one-fifth for the difference by osteotomy. Osteotomy and fixed every time after the replacement of the pressure-sensitive films, then repeated load test. Took all pressure-sensitive films for image analysis in order to measure the articular surface contact area and to calculate the pressure according to the baseline.Results:Medial malleolus:There was no significant difference between each groups on contact area. The pressure was significantly bigger in the Bohler’s angle decreased by three fifths group and decreased by four fifths group and0degree group than in the normal group. Tibial astragaloid joint:The contact area were significantly smaller in the Bohler’s angle decreased by three fifths group and decreased by four fifths group and0degree group than in the normal group. The pressure was significantly bigger in the Bohler’s angle decreased by three fifths group and decreased by four fifths group and0 degree group than in the normal group. External malleolus:The contact area were significantly bigger in the Bohler’s angle decreased by three fifths group and decreased by four fifths group and0degree group than in the normal group. The pressure was significantly smaller in the Bohler’s angle decreased by three fifths group and decreased by four fifths group and0degree group than in the normal group.Conclusion:There is no significant difference on stress of the ankle joint if the Bohler’s angle decreased by40%or less. If the Bohler’s angle decreases more than40%, the stress of the ankle joint will change significantly. Stress concentration on medial malleolus and tibial astragaloid joint will inevitable and ankle instability or traumatic arthritis will likely to occur. So we suggest Bohler’s angle should be recovered to60%at least.