A Temporary Costo-pelvic Distractor for Safe Intraoperative Spinal Deformity Reduction in the Treatment of Severe Scoliosis

Despite continuous advancements in surgical techniques and technological improvements within the operating theater, the surgical correction of severe scoliosis remains a challenge. With rigid deformity of a high magnitude, there is a considerable risk of complications, perhaps the most feared of these being partial or complete spinal cord injury resulting in permanent ensuing neurological deficit. Several adjunct measures to reduce curve severity intraoperatively have been described and utilized. These strategies include intraoperative halo-femoral traction (HFT), preoperative halo-gravity traction (HGT), vertebral column resection techniques, and more rarely now, combined anterior and posterior surgery. Although there are reports of satisfactory perioperative correction with the use of these strategies, they are not without their technical challenges and complications. Combined anterior-posterior surgery results in increased operative time, blood loss, and can have a detrimental effect on pulmonary function.1 Figures from the morbidity and mortality database of the Scoliosis Research Society indicate that combined anterior-posterior instrumentation and fusion have double the complication rate of either anterior or posterior instrumentation and fusion alone.2 Vertebral column resection enables powerful translation and shortening necessary to correct large rigid deformities. It is, however, a complex osteotomy in the territory of the cord. It is, therefore, technically demanding and has a very high risk of neurological compromise. In addition, surgeon fatigue is a genuine concern as these procedures can be time-consuming. They are also associated with profuse intraoperative blood loss.3 The utilization of halo-traction either preoperatively or intraoperatively carries less risk than the techniques previously described; however, complications related to the traction and pin sites are not uncommon. Preoperative halo-gravity traction also couples the patient to a bulky device and involves prolonged phases of treatment. Furthermore, both techniques are contraindicated in several circumstances, such as cervical instability, stenosis, and fixed cervical kyphosis. To address some of the deficiencies associated with these previously described techniques, we have developed an alternative technique at our institution. This technique utilizes an outrigger distractor to apply an intraoperative costo-pelvic distraction force to the concave side of the major curve in severe scoliosis. It is quick to implement, can be utilized efficiently when needed, and has shown itself in our clinical practice to be an effective and safe aid in partially correcting severe scoliosis on-table, thereby addressing the challenges associated with major curve instrumentation. Here we report on our experience of this technique with all patients who were treated with intraoperative costo-pelvic distraction. The technique was deployed either during the insertion of growing rods or during definitive posterior spinal correction and fusion for severe scoliosis. TECHNIQUE We acknowledge the heterogeneity in terms of scoliosis etiology, preop Cobb angle and age of patients in our study. The specific indications for the use of the costo-pelvic distractor in this study included those with a preop Cobb angle of 60 degrees or greater or in those who achieved only modest corrections on traction films. Intraoperative neurophysiological monitoring (both somatosensory-evoked potentials and motor-evoked potentials) was used for each procedure, and we strongly advise against attempting to perform this technique without such monitoring in place. Patients were positioned prone on a Jackson table and prepped and draped in a conventional manner. The costo-pelvic distractor outrigger is applied early into the case to take advantage of the viscoelastic nature of the spine. The distractor is applied on the concave side of the major curve. A pelvic anchor point is created by making a small skin incision over the dorsal iliac crest. Using blunt dissection in an atraumatic manner, a passage is created to the bone, and a subperiosteal plane is developed, large enough to allow the hook to engage onto the posterior iliac crest. A rib above the cranial end vertebra is used as the second anchor point. A skin incision is made at the inferior aspect of the rib, and again a subperiosteal plane is carefully created to allow safe passage of the hook underneath the rib, in an upgoing manner. The subperiosteal plane created allows us to avoid the intercostal bundle and to stay extra-pleural. Once the anchor points have been established, the remainder of the outrigger is assembled and costo-pelvic distraction is applied, with continuous background spinal cord monitoring. To fully harness the power of tissue stress-relaxation and further correction, the distractor is gradually and gently ‘finger-tensioned’ throughout the case, resulting in continuous correction of the deformity until rod insertion and connections are completed. Application of the costo-pelvic distractor device takes, on average, 12 minutes to apply. There is of course also time during the case to apply a gradual increase in distraction, but this is minimal and, over the course of a procedure, would be no more than 10 minutes. The device effectively acts as a paraspinal outrigger and is remote from the spinal dissection. Therefore, the midline dissection, any osteotomies, and instrumentation techniques are performed in the standard manner (Figs. 1, 2). Both anchor points are sufficiently lateralized to facilitate access to the spine for conventional spine exposure and instrumentation as required. Once the posterior instrumentation is completed, the costo-pelvic distraction is slowly de-tensioned to allow for a controlled transfer of load from the distraction device to the bilateral rod-anchor construct. The distraction outrigger device was fabricated in-house. There is currently no intellectual property or ownership of the device. It is based on the old Harrington rod that was historically used in spinal deformity correction. It is not, however, a Harrington rod as this is a discontinued implant. The outrigger device consists of hooks placed under a rib and under the iliac crest. These are fixed. There is a connecting device, to which the hooks and the rod are attached. The connection is all outside the skin, but well away from the main incision and operative field. Part of this connecting device has a tightening or distracting mechanism that slides cranially to distract and caudally to relax.FIGURE 1: Graphical representation of costo-pelvic distractor.FIGURE 2: Intraoperative image of costo-pelvic distractor.EXPECTED OUTCOMES Our institutional experience suggests that costo-pelvic distraction is a safe alternative to other forms of correction. We utilized the technique in over 25 patients; ages ranged from 3 to 17, with a broad range of underlying diagnoses. In terms of a breakdown of diagnoses, there were 10 neuromuscular EOS patients, 4 idiopathic EOS patients, 4 syndromic EOS patients, and 1 congenital EOS patient. Of the 10 neuromuscular patients, there were 6 patients with cerebral palsy, 2 patients with spinal muscular atrophy, and 1 patient with spina bifida. There were also 6 AIS patients. Indeed, the technique is a good option in patients who have contraindications to halo-traction, such as patients with cervical spine abnormalities or instability. It can also be used in other scenarios where HFT has been found to be less effective. This is particularly useful in patients with hip flexion contractures or hyperlordosis, as HFT in this setting tends to antevert the pelvis and aggravate lordosis.4 It should be noted that our technique is purely intraoperative and thus perhaps best compared with intraoperative HFT for a fair comparison. Indeed, preoperative HGT allows for gradual correction of the curve over the course of several weeks, thus decreasing the risk of neurologic injury. Our experience indicates that the technique can be a useful adjunct in the management of severe scoliotic deformity, particularly with single major curve patterns (Fig. 3). We report a mean correction of 67.5% (from a mean Cobb angle of 82.2 to 26.5 deg) to the major curve in the coronal plane. This compares favorably with what has been reported by those who use other recognized strategies in the management of complex rigid curves—namely preoperative HGT, intraoperative HFT, vertebral column resection, and anterior release.5FIGURE 3: Three-year-old patient with early-onset scoliosis. A, Preoperative standing AP radiograph showing a thoracic scoliosis measuring 110 degrees. B, Intraoperative screening images with costo-pelvic distraction applied. C, Postoperative AP and lateral radiograph showing curve correction to 30 degrees.A clear advantage that costo-pelvic distraction has over other strategies is that it can be used in the event of an unforeseen intraoperative finding. Even temporary intraoperative traction requires the insertion of the distal femoral traction pin and the application of a halo. Although not overly time-consuming in the hands of a senior surgeon, it still needs to be completed before the final positioning and draping of the patient. HFT, therefore, cannot be used in an impromptu manner. Costo-pelvic distraction can be applied without any change to standard preparation and draping of the patient, allowing the surgeon more flexibility during an operation. It also prevents undue harm to the patient as a result of increased operative time necessitated by the need to re-drape. Another potential merit, and perhaps the most significant, is that the distractor device allows the surgeon to respond rapidly to changes in neuromonitoring. We believe that the technique is particularly useful in the insertion of growing rods. These are low-density constructs with a significant concentration of force at the fixation points. Costo-pelvic distraction helps limit excess stress on the bone-screw interface by allowing the surgeon to delay the loading of the anchor points until the final construct is complete. The device can then be slowly de-tensioned to facilitate a graduated and controlled transfer of load to the rod-screw construct. A unique feature of the technique is that the operating surgeon can remain scrubbed and de-tension the device while having a direct view of the surgical field. This allows them to immediately intervene should there be any concern for a fixation point failure. COMPLICATIONS Many of the complications associated with this patient cohort are common to all scoliosis patients, and not as a direct result of implementing the costo-pelvic distractor. Perioperative neurological complications are mitigated with the use of intraoperative neurophysiological monitoring. In our cohort, we had no incident of neurological dysfunction or monitoring change throughout the application of the distractor. Wound complications and infections are prevented with standard prep and draping including surgical spirits and chlorhexidine. Betadine is used intraoperatively for wound irrigation, and prophylactic antibiotics are administered perioperatively. We had only one minor wound complication with partial dehiscence at the caudal incision site. This did not necessitate a return to the operating theater. As with all patients undergoing spinal deformity correction surgery in the thoracic region, the risk of pneumothorax should be considered, and a postoperative chest radiograph ordered. This is particularly relevant when placing the upgoing hook of the distractor with careful dissection to remain extra-pleural. Implant-related complications were observed in 2 cases. These were both screw pull-outs in growth rod constructs. On both occasions, the event occurred >6 months postoperatively. There were no focal complications observed secondary to the use of costo-pelvic distraction (i.e., rib fracture, pneumothorax, intercostal nerve injury, or local wound issues). As mentioned, we had only one minor wound complication and this did not necessitate a return trip to the theater. The implant-related complications were managed nonoperatively with close observation on an outpatient basis. It is worth mentioning some minor limitations of the technique, which will help to prevent complications if used incorrectly or in an inappropriate patient cohort. We would consider it relatively contraindicated in patients with pre-existing bone fragility or connective tissue disorders or those patients with severe kyphosis deformity. It would also be contraindicated in patients with poor skin/soft tissue quality or even infection in the proposed area of use or surgical field, for example, spina bifida cases. CONCLUSION Our experience indicates that the costo-pelvic distractor is a safe intraoperative technique and a useful aid in the management of severe scoliotic curves. The technique is quick to implement, offers more surgical options to the surgeon and allows for unimpeded access to the spine during difficult procedures. We recommend its use in all high-volume, high-complexity scoliosis units worldwide as a safe, effective adjunct to challenging scoliosis correction procedures.