Introduction: The Sheffield Ring Fixator (SRF) uses wires in the metaphysis and screws in the diaphysis for bone stabilisation. It has four 2mm wires tensioned to 1400N in two parallel groups to stabilise the ring in the metaphysis. For maximum stability, these parallel wires should cross at 60 degrees or greater and the position of the crossing should be in the centre of the bone. Fixation stability and clinical outcome may well depend on the accuracy of surgical application.

Aims: To review the consistency with which the SRF frames were applied by a single surgeon.

Materials and Methods: The fixators of 39 patients aged between 6 and 75 years of age (11.5 years mean age in children and 38.7 years mean age in adults) were examined. 7 patients had proximal and distal metaphyseal wires making a total of 46 recording sites. The angle of the wires was calculated using the number of holes between the wire clamps since each hole subtends an arc of 7.5 degrees. The crossing angles were divided into two groups with crossing angles of greater than 60 degrees and less than 60 degrees. The position of the crossing of the wires was determined by creating a cross section of the metaphyseal rings, reducing the size of the ring to 100mm and transposing a cross section of the tibia of the correct size and at the correct level. Scaling down the distances measured between the inner ring and the patient limb, the position of the cross section and consequently of the wire crossing was determined. Using contour lines the tibia was divided into four zones. Zone 1 was central tibia and zone 4 was the tibial cortex. All crossing within zone 1 and 2 were considered satisfactory, and zone 3 and 4 poor.

Results: 67.5% of patients had crossing angles greater than 60 degrees and 32.5 % had crossing angles of less than 60 degrees. 85% of the rings had zone 1 or 2 crossing positions. 6.5% of the rings had subcortical crossing positions and 8.5% of the rings had cortical crossing positions. 8.5% of rings had crossing angles of less than 60 degrees as well as wire crossing positions in zone 3 and 4.

Discussion: In a carefully controlled situation a surgeon’s surgical technique was consistent in 67.5% of the rings, with satisfactory crossing angles and wire crossing positions. Only 8.5 % of the rings had poor crossing angles and crossing positions. Inability to achieve ideals may be due to technical errors or anatomical variations. There were increased infection rates in patients with reduced crossing angles, however the position of the crossing had no apparent effect on infection rates and patient mobility. A further study would be required to separate the relative importance of these two factors on patient complications.

Introduction and Aims: A previous study showed the inhibitory effect of 30% metaphyseal lengthening on tibial growth (Lee 1993). This study was to investigate the effect of 30% diaphyseal lengthening of tibia on tibial growth plate and growth.

Method: 32 immature rabbits were equally divided into two groups: lengthening and sham. A bilateral external fixator was applied to the tibia and a mid-diaphyseal osteotomy performed. The lengthening group had their tibia distracted on the fifth day after the surgery at a rate of 0.4 mm twice daily until the achievement of 30% lengthening. In each group, half were sacrificed at the end of lengthening and another half after an additional five weeks. Standard radiographs were used to measure the lengths of the tibiae from the most proximal part of the intercondylar eminence to the most distal part of the medial malleollus. The actual length gained was measured by subtracting the pre-operative distance from the lengthened distance using the central points of two middle wires in the tibia as reference points. Specimens from the proximal and distal tibia were sectioned longitudinally in the midcoronal plane and the mean growth plate thickness was calculated from several measurements taken at the middle third of both medial and lateral halves of the section.

Results: In the sham group, the thickness of the growth plates continued to increase with skeletal development showing an increase in total tibial length compared with the contra-lateral control. In contrast, the lengthening group showed no increase in total tibial length compared to the contra-lateral control, suggesting that the stimulation due to the osteotomy may be matched by an inhibitory effect of 30% lengthening.

Conclusion: Thirty percent diaphyseal lengthening of tibia did not change the longitudinal growth of the tibia.

Previous studies in animal models of limb lengthening have shown a wide spectrum of histopathological changes during distraction phase. Much less is known about the structural response of muscle during the consolidation phase. This study aimed to observe and score changes in morphology, weight, length and maximal perimeter of gastrocnemius during the distraction and consolidation phases.

Thirty two immature New Zealand white rabbits were divided into two equal groups: lengthening and sham. In each group, half of the rabbits were killed at the end of lengthening and half 5 weeks later. A bilateral external fixator was applied to tibia and a mid-diaphysis osteotomy performed. The lengthening rate was 0.4 mm twice daily with an initial delay of 7 days. 30% lengthening was achieved in 4 to 5 weeks. After sacrifice, the whole gastrocnemius was taken from its attachments. Its weight, length and maximal perimeter were measured. At the middle of belly, a specimen 0.5cm in length was taken from the medial gastrocnemius for H& E and Masson trichrome staining. A scoring system was used to achieve a semi-quantitative analysis of the histopathological changes in gastrocnemius.

No abnormal changes were observed in the sham side. Degeneration, atrophy and endomysial fibrosis were all found in the lengthened side. The scores of histopathological changes between the end of lengthening and 5 weeks later showed a decreasing trend, but no significant difference. The weight and perimeter decreased and length increased in the lengthening side. The weight, perimeter and length of gastrocnemius in both lengthening and control sides increased at 5 weeks after the end of lengthening.

Muscular atrophy, as shown by a decrease in weight, perimeter and muscle fibre size, occurred and might be due to the combined effect of continuous muscle stretching and inactivity. Continuous stretching of muscles beyond a certain point produced damage. Some studies reported that damage to muscle fibres, which has been shown as degeneration and fibrosis in this study, can release and activate satellite cells. As myoblast precursors, satellite cells become myoblasts, which proliferate and fuse into the microlesioned areas, regenerating and repairing myofibrils. Also, the immature muscles have more active abilities of proliferation, regeneration, growth and healing. In this study gastrocnemius growth shown by an increase in weight, perimeter and length occurred during the consolidation phase of 5 weeks. The mean scores of histopathological changes in gastrocnemius decreased during consolidation period, indicating some recovery of damage to muscle. It is not clear whether this reflects a normal response, which would have been seen in other studies had samples been taken later or whether it is a unique response of the immature animal.