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The success of growth modulation for the correction of limb angular deformity has renewed interest in applying related methods to correct spine deformities without fusion. We review the history of growth modulation, which dates back almost 100 years. We describe recent preclinical studies and early human clinical use, with our primary focus on non-idiopathic early onset scoliosis and techniques that limit growth on the convex curve side. Just as neuromuscular, syndromic, traumatic, and congenital deformities of the limb usually respond to growth modulation, non-idiopathic scoliosis can respond to growth modulation. Because the human spinal growth plates adjoin the disc, a non-fusion growth modulation device must span the mobile intervertebral joint, which raises technical challenges beyond those of growth modulation techniques for long bones. If these challenges are solved, non-fusion spinal growth modulation may join convex hemifusion techniques as an important surgical option for scoliosis in young children with non-idiopathic scoliosis.

Evaluation of the intervertebral joint force in vivo is very important for clinical spine problems, for example, spinal instability, disorder of intervertebral disc, compressive fracture of osteoporotic vertebra, etc. Direct measurement of the joint force is difficult to get permission, so computational method to calculate the force is expected. Spine structure is mainly constructed of many vertebrae and flexible intervertebral disks, and it is unstable by itself under standing condition. Supporting by erector muscles and ligaments keep the spine standing condition, so that loading condition of each vertebra depend on the muscle and ligament forces. Biomechanical analysis of musculoskeletal system taking into account of large number of muscle and ligament forces is necessary to determine the intervertebral joint force. Commercial software to deal with the musculoskeletal system is available nowadays, and it has been applied to clinical, ergonomic or sport biomechanics problem.

A fusion cage is used to aid fusion of an intervertebral joint. To date, cages have been commonly made of materials (metals or polymers) that remain in the body. Postoperative complications with these permanent fixtures might be overcome by using biodegradable/bioabsorbable composite (BBC) cages. There are requirements for the BBC to be used as a cage material, including load bearing ability. The aim of this study was to evaluate the feasibility of using a BBC as a cage material. This composite would degrade gradually to be simultaneously replaced by bone. Post-operative complications are reduced as no foreign bodies remain within the patient and bone growth is unrestricted. The design of the cage has also been optimized based on BBC material properties. Cage features such as teeth and holes have been investigated to obtain a suitable cage design using BBC. Finite Element Analysis was carried out on cage concept models, using the material properties of BBC and polyetheretherketone (an existing cage material) for comparison purposes. The results, from an engineering view point, determined the feasibility of BBC as cage material.

A mid-line incision is made between the spinous processes of L4 and S1 (for spondylolysis L5 and S1). The soft tissues are dissected subperiostially on both sides, and the entire neural arch, the spondylolysis and the inferior circumference of the upper intervertebral joint are exposed. A clear exposure of these structures is mandatory to avoid technical faults (Fig. 9.1). The spondylolysis is cleared, the ‘ pseudoarthritic’ connective tissue is removed and the spondylolysis is freshened (Fig. 9.2).