Correction of kyphotic deformity before and after transection of the anterior longitudinal ligament - a cadaver study

With a custom-made measuring unit, two separate experiments, involving six and five cadaveric torsos with intact rib cages and sternums, respectively, were carried out to determine the effect of the transection of the anterio r longitudinal ligament with and without osteodiscectomy and its influence on the thoracic kyphosis. The open or thoracoscopically assisted anterior r elease, as part of the operative treatment of scoliosis or kyphosis, usuall y consists of a transection of the anterior longitudinal ligament (ALL) and an additional discectomy. A complete osteodiscectomy, however, is not alwa ys possible with a minimally invasive approach. As part of our biomechanica l research, we attempted to quantify the amount of correction achievable wi th a defined force prior to and following the isolated transection of the a nterior longitudinal ligament. The aim of the study was to clarify whether or not an isolated transection of the anterior longitudinal ligament iv suf ficient to obtain an adequate anterior release of the spine. In the surgica l treatment of kyphotic deformities, anterior release of the spine is perfo rmed in the form of a transection of the ALL and discectomy. Recently, vide o-assisted thoracic surgery has become increasingly popular in spine surger y. As part of this change in surgical technique, the question has arisen as to what extent an isolated transection of the ALL provides an adequate rel ease of the thoracic spine. Eleven human spines were retrieved from fresh c adavers, dissected, and attached to a specially constructed apparatus. The spine was attached to the construct at the twelfth vertebral body. C6 and C 7 were fixed in synthetic resin. We installed the instruments in such a man ner as to reproducibly apply a torsional moment of 10 Nm to the spine. Moti on was only permitted in the sagittal plane. Segmental transactions of the ALL were carried out from T3 to T7. For comparison, the sagittal Cobb angle was also documented following an anterior release combined with an osteodi scectomy. With the isolated transection of the ALL, an average correction o f the sagittal Cobb angle of 4 degrees in each functional spinal motion seg ment was recorded. In comparison, the additional osteodiscectomy led to a f urther average increase of only 2 degrees per level. The measurements perfo rmed on human cadavers showed that the isolated transection of the ALL lead s to a sufficient anterior release of the thoracic spine, allowing a correc tion of the kyphotic deformity. The release with a concomitant osteodiscect omy represents a more time-consuming and more invasive procedure resulting in only a slightly greater amelioration of the sagittal Cobb angle, while b eing associated with a greater patient morbidity.