Biomechanical and Clinical Evaluation of a Novel Technique for Surgical Repair of Spondylolysis in Adolescents

Abstract

A biomechanical comparison of a novel spondylolysis repair technique method to established spondylolysis repair constructs accompanied by a case series of 5 adolescent patients with spondylolysis treated with this technique. To provide retrospective data on these patients treated with an intralaminar link construct, as well as present comparative biomechanical data on this construct and that of an intact spine, lytic spine, and known methods of repair. Spondylolysis is a unilateral or bilateral defect in the pars interarticularis, and most commonly occurs at L5 and less frequently at L4. Surgical treatment may be indicated in patients with persistent pain and impairment despite conservative treatment. Unlike posterolateral fusion, direct pars repairs may benefit adolescents by sparing motion segments. Biomechanical testing of 5 cadaver lumbar spines was completed to provide comparative biomechanical data on this intralaminar link construct, and that of an intact spine, destabilized spondylolytic spine, Scott wiring technique, pedicle screw-cable system, and the pedicle screw-rod-hook constructs. There were 5 adolescent patients with spondylolysis treated with multiaxial pedicle screws, with a modular linkage that passes beneath the spinous process of the same segment. Biomechanical evaluation of the intralaminar link construct showed the least displacement (across pars defect) followed by the pedicle screw-rod-hook system, Scott wiring, and, finally, the pedicle screw-cable system. Interbody flexion and extension stiffness was highest for pedicle screw-rod-hook followed by normal, intralaminar link construct, Scott wiring, pedicle screw-cable system, and, finally, the destabilized spine. Interbody torsional stiffness was highest for pedicle screw-rod-hook followed by intralaminar link construct, normal, pedicle screw-cable system, Scott wiring, and lytic spine. Retrospective follow-up (average 4.6 years) of patients showed complete radiographic healing or pain relief in all 5 patients. There was 1 patient with solid healing of L3 spondylolysis who later had onset pain despite evidence of solid fusion on computerized tomographic images. In this patient, pain resolved after implant removal. Biomechanical evaluation of the intralaminar link construct showed excellent stability of a spondylolytic defect in comparison to established methods. Clinical follow-up of this method reflects the results of biomechanical testing with excellent clinical results.