Vertebral Body Tethering in an Adult With Lumbar Idiopathic Scoliosis

Abstract

Case:

We report a case of adolescent-onset idiopathic scoliosis of the lumbar spine in a 43-year-old woman treated with nonfusion vertebral body tethering (VBT), a controversial and unreported technique in this age group. At 6-year follow-up, clinical and radiographic improvements are maintained. She continues to live an active lifestyle and reports being pain free.

Conclusion:

We demonstrate intermediate term safety and efficacy of VBT in a single adult patient. Careful ongoing assessment of this patient is needed to determine if this procedure will have a durable outcome and lend support for adequately powered prospective multicenter studies.

The standard surgical treatment for the adult with scoliosis is a spinal fusion. Outcomes remain reliable in terms of radiographic correction and pain relief, but the complication and reoperation rates can be as high as 39% and 26%, respectively^1-4. Disadvantages of a fusion include decreased motion at the fused segments, adjacent segment degeneration (ASD)^5,6, junctional failure⁷, pseudoarthrosis⁸, significant morbidity, and prolonged recovery. Given the morbidity associated with spinal fusion for adult scoliosis, surgeons have an obligation to innovate and search for alternative procedures to improve outcomes.

We present a case of a 43-year-old woman with lumbar adolescent-onset idiopathic scoliosis (AIS) treated with nonfusion vertebral body tethering (VBT), a controversial and never before reported technique in this age group. The potential advantages of this procedure include maintenance of spinal flexibility^9,10, decreased operative morbidity, reduced blood loss, more rapid recovery, and decreased potential for ASD. The rationale for the procedure and 6-year outcomes are discussed.

The patient was informed that data concerning the case would be submitted for publication, and she provided consent.

Case Report

A 43-year-old woman with AIS presented with back pain, disability (Table I), and increasing deformity refractory to nonoperative treatment that included PT, aerobic exercises, and nonsteroidal anti-inflammatory medication. Radiographs revealed a flexible right lumbar idiopathic scoliosis of 46⁰ (Figs. 1-A and 1-B, Table II). There was a 13° rotational prominence (Table III). Magnetic resonance imaging (MRI) of the lumbar spine demonstrated type 1 Modic changes at L4-L5.

Fig. 1.

Fig. 1-A Preoperative erect, (Fig. 1-B) bending, (Fig. 1-C) first erect, and (Fig. 1-D) 6-year postoperative posteroanterior and lateral radiographs demonstrating maintenance of coronal plane correction and satisfactory sagittal alignment.

TABLE I.

Scoliosis Research Society Scores

	Activity	Pain	Image	Mental	Satisfaction	Mean
Preoperative	4.0	3.4	3.0	3.6	2.0	3.5
6-year follow-up	4.4	5.0	4.8	4.6	4.5	4.6

TABLE II.

Radiographic Measurements

	Preoperative	Immediate Postoperative	6-year Follow-up
Coronal major Cobb angle, T11-L3 (°)	46	20	21
Coronal minor Cobb angle, T6-T11 (°)	28	20	18
Sagittal Cobb angle, T5-T12 (°)	55	31	37

TABLE III.

Clinical Measurements

	Preoperative	6-year Follow-up
Thoracic rotational prominence (°)	3	6
Thoracolumbar rotational prominence (°)	13	2

In light of her symptoms and failure to respond to treatment, a posterior spinal fusion was recommended. Given the patient’s active lifestyle, she implored the surgeon to consider VBT as a surgical option to maintain spinal motion and flexibility. The patient was told that this would be a controversial approach to her condition with a device that did not yet have regulatory approval but had clinical acceptance for skeletally immature patients. She was informed of the likelihood of tether breakage and the potential for her pain and deformity to recur. The patient understood that no data were available for this procedure in her age group. The surgeon, given his extensive experience with the procedure, believed this was a reasonable, albeit unproven approach which would not preclude spinal fusion in the future should the outcome be unacceptable.

Before induction, a thoracic epidural was placed for postoperative analgesia. Under general anesthesia using single lung ventilation, a left thoracoabdominal approach between the 10th and 11th ribs and a retroperitoneal dissection carried down to access T11 to L3 was performed. A double row of screws were placed with bicortical fixation in the vertebral bodies. The Dynesys spinal tether, with the outer sheath of the polyethylene cord removed (Zimmer Biomet, Warsaw, IN), was positioned in the posterior screws, and the T11 screw, set screws were applied and tightened after tensioning each level. A second tether was seated in the anterior screws and tensioned appropriately. A chest tube was placed through a 5-mm anterior axillary portal that had been used for endoscopic visualization. Operative time was 145 minutes and EBL 300 mL.

The chest tube was removed on the fourth postoperative day (POD), and the patient was discharged on the fifth POD. First erect radiographs demonstrated major curve correction to 20° (Fig. 1-C, Table II).

Follow-up confirmed maintenance of the correction and a high level of patient satisfaction. At 3 years, an MRI was obtained, which demonstrated neither deterioration of the L4-5 disk nor disk or facet degeneration within or adjacent to the construct (Fig. 2). At 6 years, there was a 2° thoracolumbar prominence (Table III and Fig. 3). The curve was maintained at 21° (Fig. 1-D). SRS-22 scores improved in all domains (Table I), and she exercised multiple days per week. The patient remarked to the surgeon on her 6-year postoperative date, “I am grateful this was an option for me and am thankful for my results, as I have remained largely pain-free.”

Fig. 2.

Three-year postoperative lumbar spine MRI. T1 (Fig. 2-A) and T2 (Fig. 2-B) midsagittal representative cuts demonstrating no deterioration of intervertebral disks and facets. MRI = magnetic resonance imaging.

Fig. 3.

Clinical photographs, taken preoperatively at 6-year follow-up, demonstrating correction of trunk shift, shoulder height, and rib hump, with maintenance of global balance.

Discussion

The treatment of a majority of medical and surgical conditions has been largely developed through trial and error, evolution of approaches and innovative concepts not previously attempted, to improve outcomes of established approaches. Paul Harrington introduced his implant to treat scoliosis during the polio pandemic. Harrington was initially derided, but eventually the Harrington rod represented the “state of the art” in spinal instrumentation at that time¹¹. This led to innovations in spinal implants that persist today. Initially, pedicle screws were used in an “off-label” manner and it was not until 1998 that pedicle screws were down-classified from a Food and Drug Administration Class III to Class II device¹². In an ideal world, all innovative techniques would go through the highest level of scientific rigor through prospective randomized clinical trials; however, that is not practical in many cases.

Keeping the above in mind, a surgeon introducing a new technique must approach it with equipoise and inform the patient of its novel nature, lack of outcomes data, and potential ramifications of failures¹³. The surgeon in this case did not offer this procedure in a vacuum; rather, he gained a large experience with the technique in standardly indicated skeletally immature patients. As time went on and the procedure was noted to be a success, he gradually offered it to more skeletally mature adolescent patients, who had less growth remaining, for curves in the lumbar spine due to its potential advantages. This eventually led to performing the VBT procedure in this middle-aged adult.

In the case reported here, the patient herself was the driving force for the adaptation of this technique. After extensive discussion with the patient, the decision to proceed was one of the shared decision making^14,15.

The rationale for performing VBT in an adult was twofold. First, the standard operation, a spinal fusion, has significant morbidity and potentially high rates of major complications and reoperations^1-4. Second, it was an attempt to maintain spinal flexibility and function^9,10,16 as well as the potential to minimize disk degeneration that may be observed caudal to the instrumented lumbar levels following spinal fusion⁶. Studies assessing the outcomes of VBT in skeletally mature adolescents with little or no growth remaining have shown promising results^17,18. Posterior motion-sparing constructs that incorporate the use of polyethylene cords could be considered as an alternative to the anterior approach. However, a posterior-based solution will limit flexion and potentially extension of the spine. This approach also requires extensive dissection of the paraspinal musculature, leading to increased morbidity.

VBT uses its growth-modulating effect according to the Hueter-Volkmann principle, which addresses the response of growing bone to mechanical pressure. If this were the only effect of VBT, it would be illogical to apply this technique to fully grown individuals. This reasoning, however, overlooks the role of the intervertebral disk (IVD) as an important stabilizer of the spinal column, both in immature and mature patients.

In immature patients, the intervertebral disk-vertebral body (IVD-VB) complex matures at its own rate while body dimensions increase rapidly¹⁹. Nonsurgical scoliosis treatment at this age relies not only on growth modulation of bone but also on allowing the IVD-VB complex to mature into an optimal shape, with endplates as parallel as possible.

In mature patients, disk changes also occur, but this process is called degeneration. Disk degeneration occurs according to well-defined phases²⁰ that imply a loss of torsional stiffness in its early stages, with restabilization of the segment as its end stage. If the end stage of disk degeneration is a well-aligned, stable spine, there is no need for further fusion surgery. Temporarily supporting the spine in a better-aligned position will prevent rotatory subluxation, while segmental stability gradually improves over time. In this sense, VBT works as an internal brace that temporarily protects the spine from decompensation into a more severe deformity, while the spine restabilizes.

VBT can thus be considered a device that protects the vulnerable disk in an optimal position during 2 crucial time windows: the first one when the IVD-VB complex matures and stabilizes into its adult form with hopefully well-aligned endplates and the second one when that IVD degenerates, first becoming unstable, and later restabilizing, hopefully in an improved position²¹. The assumption is that well-aligned spines at later stages will lead to better outcomes than rotated segments with asymmetric segmental pressure distribution. Thus, protection of the spine only needs to occur during a limited number of years, and once the spine has stabilized either through maturation or degeneration, further progression of deformity is no longer expected.

Despite excellent intermediate term outcomes for this patient, potential issues may arise that require further treatment. While it is unknown whether the correction obtained in our patient will be maintained if the tether breaks, previous literature has demonstrated that tether breakage is not necessarily associated with a large loss of correction or need for reoperation²².

Conclusion

The present report demonstrates the intermediate term safety and efficacy of VBT in a single adult patient. Careful ongoing assessment of our patient will be needed to determine if this procedure will have a durable outcome and lend support for adequately powered prospective multicenter studies.