Graded limb lengthening by callus distraction is a widely used surgical procedure to correct tubular bone deformities and can result in dramatic functional improvements in children. We used a model of tibial lengthening in rabbits to study the postoperative pain pattern during limb lengthening and morphological changes in the dorsal root ganglia (DRG), including alteration of substance P (SP) expression. Four groups of animals (naïve; OG: osteotomised only; SDG/FDG: slow/fast distraction with 1mm/3mm lengthening a day) were used. Signs of increasing postoperative pain were detected till the10th postoperative day in all groups; then it decreased in OG, whereas remained higher in SDG/FDG until the distraction finished. This suggests that pain response is based mainly on surgical trauma until the 10th day: the lengthening extended its duration and increased its intensity. The only morphological change observed in the DRGs was the presence of large vacuoles in large neurons of all operated groups. Although osteotomy was conducted in OG/SDG/FDG groups, significant de novo SP-expression in the large DRG cells appeared only in OG and significant decrease in the number of SP-immunoreactive small DRG neurons was detected solely in the SDG/FDG groups. Faster and larger distraction resulted in more severe pain sensation and lowered further the number of SP-positive small cells. Our data suggest that down-regulation of SP in the small cells in lengthened animals is associated with the stretch nerve injury, whereas de novo expression of the peptide in the large cells in OG is likely to correspond to the undergoing regeneration.

The response of the muscle is critical in determining the functional outcome of limb lengthening. We hypothesised that muscle response would vary with age and therefore studied the response of the muscles during tibial lengthening in ten young and ten mature rabbits. A bromodeoxyuridine technique was used to identify the dividing cells.

The young rabbits demonstrated a significantly greater proliferative response to the distraction stimulus than the mature ones. This was particularly pronounced at the myotendinous junction, but was also evident within the muscle belly.

Younger muscle adapted better to lengthening, suggesting that in patients in whom a large degree of muscle lengthening is required it may be beneficial to carry out this procedure when they are young, in order to achieve the optimal functional result.

Little is known about the increase in length of tendons in postnatal life or of their response to limb lengthening procedures. A study was carried out in ten young and nine adult rabbits in which the tibia was lengthened by 20% at two rates 0.8 mm/day and 1.6 mm/day.

The tendon of the flexor digitorum longus (FDL) muscle showed a significant increase in length in response to lengthening of the tibia. The young rabbits exhibited a significantly higher increase in length in the FDL tendon compared with the adults. There was no difference in the amount of lengthening of the FDL tendon at the different rates. Of the increase in length which occurred, 77% was in the proximal half of the tendon.

This investigation demonstrated that tendons have the ability to lengthen during limb distraction. This occurred to a greater extent in the young who showed a higher proliferative response, suggesting that there may be less need for formal tendon lengthening in young children.

Children who present late with hip dislocation may require femoral osteotomy after reduction, to correct valgus and anteversion deformity of the femoral neck. After these procedures proximal femoral growth is unpredictable. We have studied proximal femoral growth in 40 children who had been treated by femoral osteotomy.

Preoperatively, the mean femoral neck-shaft angle was 5° greater on the affected side than on the contralateral side. Postoperatively, it was 28° less. There was progressive recorrection; after five years the angle was not significantly different from that on the contralateral side. In our series 70% of the capital epiphyses became abnormally shaped, taking the appearance of a ‘jockey’s cap’. All the growth plates became angulated but this corrected with time.

Correction of the neck-shaft angle probably results from the more normal mechanical environment provided by reduction. The abnormal radiographic appearance of the epiphysis and growth plate is probably due to the rotation produced by the osteotomy.