ASYMMETRICAL ECCENTRIC COMPRESSION EFFECT OVER THE IMMATURE SPINE ASYMMETRICAL ECCENTRIC COMPRESSION EFFECT OVER THE IMMATURE SPINE. Experimental scoliosis by scapula to contralateral ilium tethering procedure in growing rabbits N. Ventura PhD.

OBJECTIVES To create structural, idiopathic-type, scoliotic curves in growing rabbits using a subcutaneous right scapula-to-contralateral ilium tethering procedure without producing any trauma to the spine elements. To study the anatomic, radiographically and histologically alteration in the in the scoliotic vertebra.

SURGICAL TECHNIQUE: under general anaesthesia, through 2 separate incisions one over the right scapula and other over the left iliac crest were done, a wire (fixed length) attached to the scapula through to 2 holes made in the bone or previously passed through the holes of a button, was connected to pelvis around the sciatic notch through a subcutaneous tunnel. MATERIAL AND METHODS: 121 growing rabbits (2-3 weeks of age) were included in this study: 45 (37.1%) of them developed left thoracic scoliosis. The animals were randomly assigned in 2 groups: Group I (29 cases): the suture was shortened so that the scapula and pelvis were drawn together, which made the spine convex toward left side and instantaneously produced approximately a Cobb angle of 35/40° in the coronal plane. This group was subdivided in 2: Group IA: the animals were allowed to reach skeletal maturity. Group IB: tethering sutures were cut between 1-6 weeks after surgery. Group II (16 cases): no curve was induced during surgery in the hope that a scoliosis deformity would develop with growth.

MATERIAL AND METHODS Posteroanterior and lateral radiographs of the spine were taken with animals under general anesthesia at preoperative, immediate postoperative and weekly intervals. In group IA, 6 rabbits developed severe single left thoracic scoliosis deformity that reached 100º-130º at the 10th week. The incidence of vertebral rotation and the evidence vertebra wedging was significantly higher in this group. 30 D 50 D 70 D Postoperative

In group IB, a minimum of 15 days was enough to develop a mild structural scoliosis which reached 60º/70º at the 6th week. The degree of scoliosis deformity was not significantly altered after tether release. 2 W 7 W Group I B Group I B Group II Group II, 16 rabbits, structural scoliosis developed gradually and steadily progressed throughout the whole period of growth. 4 rabbits developed a 40º left thoracic scoliosis. In this group, some cases developed a double thoracic curve, the primary curve at M.T. On the sagittal plane, proximal thoracic lordosis combined with medial thoracic khyphosis were observed but, in general, deformity never became very remarkable

Spinous process displaced to the concavity (1) RESULTS MACROSCOPIC changes Spinous process displaced to the concavity (1) Lamina (2) much lower and thicker on the concave side Pedicle (3) thiker on the the concave side Transverse process short, thick and more horizontal on the convex side (4) and ascendant,long and narrowon on the concave side (7) Vertebral body wedged shape and lighted rotated toward the convexity (5) Vertebral canal was oval and displaced toward the concavity (6) 1 4 7 4 2 6 3 7 6 3 5

HISTOLOGICAL changes FRONTAL plane: Decrease height of the vertebral body (1) on the concave with Increase sclerosis on this side (trabecular bone for apposition) (2) Epiphyseal growth plate compressed, narrowed and partially fused on the concave site where cartilage columns were uneven, irregular and disarranged (3). On the convex side the cartilage columns showed a more regular arrangement (4) Nuclei pulposi displaced towards the convexity (5) 2 4 3 4 1 5 2 3 4 3

Scoliotic vertebra, concave side, epiphyseal growth plate Normal vertebra, epiphyseal growth cartilage columns with regular arrangement Epiphyseal growth plate, cartilage columns with normal arrangement cartilage columns uneven, irregular and disarranged

Cord displaced toward convexity (2) HISTOLOGICAL changes CORONAL plane: Bone structure, lamina and pedicle thicker with increased trabeculation by aposition on the concave side (3), convex pedicle showed less trabeculation (1) Transverse process , short and thick on the convex side (6) and ascendent, long and narrow on the concave side (5) Cord displaced toward convexity (2) Neurocentral epiphysis was more narrow, partially ossified with celular structure extremely irregular on the convex side (4) and wider an more normal on the concave side (7) 4 7 7 4 3 1 2 5 3 1 5 6 2

Neuro-central epiphysis, broder on the concave side Neuro-central epiphysis, broder on the concave side. Normal cartilage structure with cells maturing in 2 directions, Neurocentral epiphysis partly ossified on the convex side with celular structure extremily irregular and bone birdge formation partialy fused

CONCLUSIONS Scoliosis deformity can be induced in growing rabbits by keeping the spine in a fixed lateral position . In growing rabbits of 2-3 weeks of age, keeping the spine curved during 2 weeks was enough to induced a mild structural scoliosis which did not change after tether release The longer the time the spine remained curved, the more severe the deformity was Macroscopic changes in the rabbit scoliotic vertebrae, were similar to the human scoliotic vertebrae, posterior elements toward concavity and vertebralbody toward convexity Epiphyseal plate cartilage was compressed on the concave side and wider with normal catilage columns arrangement on the convex side. Neurocentral epiphysis was partly ossified with celular dissanrage on the convex side.

THANK YOU VERY MUCH REFERENCES Karaharju, E.O. Deformation of vertebrae in experimental scoliosis. Acta Orthop.Scand. Supple. 105. 1967 Michelssonn J.E. The developement of spine deformity in experimental scoliosis. Acta Orthp. Scand. Suppl. 81, 1965 Lifeng Liu , MD el al, The creation of scoliosis by scapula to contralateral ilium tethering procudure in bipedal rats. Spine, 36,17, 1340-49. 2011 THANK YOU VERY MUCH