To assess the effectiveness of unilateral sublaminar and concave rib tethering with convex rib resection through the period of peak growth in lambs. Morphometric growth data from 10 experimental Scottish Blackface sheep were compared to those from 5 control animals (no intervention) over 12 months. Standardized AP and Lateral radiographs were taken before and at monthly intervals after scoliosis creation. The Cobb angle was measured in the coronal and sagittal planes. Rotational mal-alignment was assessed by axial CT 7 months post surgery. In the supine position the control animals had no coronal plane deformity and a mean 5° lordosis (T4-T12). These figures did not alter with growth (doubling of body weight). Tethering (at age 5 weeks) produced an immediate scoliosis of 22±11° and a lordosis of 24±8° (means(sd). The degree of scoliosis was maintained over 7 months (at 20°) but lordosis increased (to 59±11°, p<0.01). There was an associated change in vertebral rotation. Surgery had no influence on rate of growth or animal development. Two animals died from Clostridium associated enterocolitis. There were no deaths associated with the surgical intervention. This ovine model gives a progressive spinal deformity in the sheep but primarily in the sagittal plane. This fact should be considered in studies designed to evaluate the effectiveness of surgical implants.
Damage Control techniques involve primary external fracture fixation to reduce the ‘second hit’ of surgery. This study used a large animal (ovine) trauma model to compare pathophysiological responses of primary external femoral fixation and intramedullary stabilisation. Under terminal anaesthesia bilateral femoral fractures and hypovolaemia were produced using a pneumatic ram. 24 sheep were randomised into 4 groups and monitored for 24 hours. Group 1 – Control; Group 2 – Trauma only; Group 3 – Trauma and external fixation; Group 4 – Trauma and reamed intramedullary stabilisation. Outcome measures: pulmonary embolic load (transoesophageal echocardiography); plasma coagulation markers; bronchoalveolar lavage differential cell counts (neutrophils, lymphocytes and macrophages). Total embolic load was significantly higher (p<0.001) in the intramedullary fixation group (median score 42 versus 20). All trauma groups had a significant increase (p < 0.05) in prothrombin time with a fall in antithrombin III and fibrinogen levels. No significant differences occurred between trauma groups with any coagulation or alveolar lavage marker. Intramedullary femoral fracture fixation produced a relatively higher pulmonary embolic load. However, the initial fracture fixation method did not affect any of the changes seen in the measured coagulation or inflammatory markers during the first 24 hours of injury.
An experimental model was established to investigate the possibility of repairing cervical nerve roots avulsed from the spinal cord, as occurs in traction injuries of the brachial plexus. In five sheep the C6 root was avulsed and the ventral root was reattached using freeze-thawed muscle as a short graft (0.5 cm). Recovery was assessed after one year by electrophysiology and histology. Stimulation of the root produced muscle contractions in four out of five sheep. Action potentials were recorded distal to the grafts in all five sheep. Histological examination showed regenerated fibres in the ventral roots in all cases. These fibres could be traced distally to the brachial plexus. Our study confirms that motor fibres can regenerate out of the spinal cord into the ventral roots and reinnervate muscles, and suggests that reimplantation of avulsed roots is a surgical option in selected cases of traction injury of the brachial plexus.
