Limb lengthening by epiphyseal distraction in chondrodystrophic bone: An experimental study in the canine femur

Epiphyseal distraction of the left distal femur was accomplished in 18 chondrodystrophic dogs (age 19–22 weeks). A distraction rate of 0.5 mm/day was applied by means of a unilateral device. Epiphysiolysis occurred after 4 to 9 days. Lengthening was continued for 3 weeks. The animals were killed at 3 (Group 1; n = 5), 19 (Group 2; n = 10), and 71 (Group 3; n = 3) weeks after the end of distraction to verify the magnitude of elongation at removal of the device (Group 1) and at the time of growth cessation (Groups 2 and 3), and to register possible permanent secondary joint changes (Group 3). The average lengthening of 1.2 cm (12.3%) at removal of the device was reduced to 0.7 cm (6.4%) at cessation of growth. The middiaphyseal diameter of the elongated femur was enlarged after the lengthening procedure in all animals. The average torsional strength of the elongated femur compared with the contralateral control was 83% in Group 1, 98% in Group 2, and 107% in Group 3. Degenerative changes were observed in the knee joints of three animals in each group. A two‐way analysis of variance was applied for all data sets to test differences between control and elongated bones and between time periods. The reduction in gained length by retardation of residual growth in the distal femur was significant (p < 0.05). The difference in external diameter between lengthened and control bones was significant in Groups 1 and 3 (p < 0.05). We conclude that early onset of bilateral lengthening by epiphyseal distraction in chondrodystrophic bone required in successive treatment of bone segments may result in significant loss of gained length due to reduction of residual growth. The observed degenerative changes in the knee joint are a sequela that calls into question the use of the method in the femur.