CT observation of the effect of controlled stress and micromovement on fracture healing

Abstract

Objective To observe by CT images the effects of controlled axial stresses on the healing of fracture ends at different stages. Methods Thirty-two grey goats were randomized into 4 equal groups (n=8), in which stresses of 0 (control group), 1/6(group A), 1/3 (group B) and 1/2(group C) of their body weight were applied respectively. Transverse osteotomy at the middle shaft of the femur was performed in all groups to create animal fracture models. The goats were sacrificed in batch at 4 and 8 weeks after operation separately for CT scanning and measurement of the Hounsfield unit (HU) and callus area at the fracture ends. Results At 4 weeks after operation, the average HU of bony callus at the fracture ends was 164.9±16.8, 214.4±27.3, 287.7±30.6 and 313.6±33.5 respectively in control group and groups A, B and C; the callus area at the fracture ends was 0.40±0.15 cm2, 0.78±0.19 cm2, 0.84±0.22 cm2 and 0.88±0.21 cm2 respectively in control group and groups A, B and C. On average, groups A, B and C had signif-icantly higher HU and significantly large callus area than control group while groups B and C had significantly higher HU than group A (P<0.05). At 8 weeks after operation, the average HU of bony callus at the fracture ends was 334.3±38.1, 415.6±45.1, 505.8±45.6 and 512.8±41.8 respectively in control group and groups A, B and C; the callus area at the fracture ends was 0.70±0.21 cm2, 1.11±0.23 cm2, 1.63±0.28 cm2 and 1.65±0.20 cm2 respectively in control group and groups A, B and C. On average, groups A, B and C had significantly higher HU and significantly large callus area than control group while groups B and C had significantly higher HU and significantly large callus area than group A (P<0.05). There were significant differences between the 4 and 8 weeks after operation in average HU of bony callus in all the 4 groups (P<0.05). There were also significant differences between the 4 and 8 weeks after operation in average callus area in groups B and C (P<0.05). Angulation deformity of the fracture ends was observed in one case in control group, in one in group A, in 2 cases in group B and in 4 in group C. Conclusions As stress at the fracture ends can improve callus formation, it can be strengthened to enhance the effect, but a strengthened stress at fracture ends may increase incidence of angulation deformity during fracture healing. Application of a stress of 1/3 of the body weight may promote callus formation at fracture ends with a low incidence of angulation deformity. Key words: Biomechanics; Fracture healing; Bony callus; Animal experimentation