What Is the Role of Anterior Vertebral Tethering?: Commentary on an article by Peter O. Newton, MD, et al.: "Anterior Spinal Growth Modulation in Skeletally Immature Patients with Idiopathic Scoliosis. A Comparison with Posterior Spinal Fusion at 2 to 5 Years Postoperatively".

Abstract

Commentary The article by Newton et al. addresses a timely and important question. It is important in that it compares a relatively new and relatively untested procedure, anterior vertebral tethering, with a long-established one, posterior fusion and instrumentation for idiopathic scoliosis. It is timely in that many centers are very interested in this newer surgical procedure. It is also especially important in that it reports on outcomes at least 2 years postoperatively. The data, which are honestly reported in detail, are not favorable to vertebral tethering. Indeed, some of the data contradict portions of the authors’ earlier reports. The discussion of the results presents a more favorable interpretation than is deserved, an opinion noted by each reviewer prior to publication. Although the initial patient selection for tethering is not presented, the study group and the control group are well-matched as to severity and maturity. The tethering group achieved significantly less reduction of deformity and had more complications and revisions. The proposed advantages of tethering, progressive postoperative correction and maintenance of spinal motion, were not demonstrated. The lack of progressive correction with growth is unexpected and worthy of note. In a 2014 article, Samdani et al. reported significant gradual correction from 44° preoperatively to 20° immediately postoperatively and 13.5° at 2 years after vertebral tethering1. The frequency of breakage of the tethers, 52%, is alarming. It is alarming because it represents failure of the construct and especially because we do not know what will happen to the spine in the future. Will the untethered segment(s) allow continued progression, and will the patient have pain? It is also concerning because, in this study, with longer follow-up, the incidence of breakage of tethers has increased. I noted in a prior commentary that we simply do not have enough follow-up of this surgical procedure to promote wider usage, and this article by Newton et al. reinforces my conclusion2. For certain, we need development of a more durable, fatigue-resistant cable prior to generalized use. It is interesting that, although we should congratulate the authors for openly publishing these unfavorable results, we also have to be critical of some of their statements. Newton et al. state that they were able to prevent or delay posterior spinal fusion in a majority of patients. They note that 52% of patients were successful in having curves of <35° and 74% were successful in having curves of <50°. This is not good enough. We have to ask what did the patients gain in that transaction? They had more subsequent surgical procedures, more than half with broken tethers, and no demonstrated advantage in mobility. They paid a price in terms of greater residual spinal rotation and coronal deformity. Nine of 23 patients had a revision surgical procedure, with 3 patients who underwent spinal fusion and 3 patients who were scheduled to undergo spinal fusion. In their earlier work, Newton et al. and others showed proof of the concept that anterior tethering of vertebrae can alter spinal growth to correct deformity with continued growth. This an important finding and will certainly be of use in the future. To get a real benefit from the technology, we must perform studies that identify the circumstances of deformity and maturity in which the advantages of gradual correction and lack of fusion can be appreciated. Can we achieve gradual correction without overcorrection? Should this technique replace brace management of smaller curves in younger patients? Surely, we can come up with more fatigue-resistant cable materials, and continuing to use current models with >50% failure is not wise.