13.1 Introduction

Halo traction is an adjunctive therapy that may be employed in the treatment of large idiopathic curves. Large or rigid deformities are challenging to correct safely, as rapid or excessive correction can increase the risk of neurologic injury. ^{1 , 2} Instrumentation sites can also fail when extreme corrective forces are applied to these deformities. ³ The use of preoperative traction techniques may therefore allow severe deformities to be corrected slowly and safely prior to fusion.

The halo device itself was first described by Perry and Nickel in 1959. ⁴ The French surgeons Cotrel and Morel pioneered the notion of preoperative traction a few years later in 1964, an adaptation of older spine-straightening techniques dating to the previous century. ^{2 , 5} Nickel et al ⁶ then popularized the utilization of halos for preoperative traction in 1968. In 1971, Stagnara et al ⁷ coupled this technique with the use of the body as a counterweight, and HGT for scoliosis has gained regular use ever since.

Halo traction is most often used for several weeks either preoperatively to lengthen the affected segment or perioperatively after an initial mobilizing surgery such as an anterior release. ^{3 , 8 , 9 , 10 , 11 , 12} It is sometimes used as a delaying measure in early-onset scoliosis (EOS) to be followed by casting and bracing, though this is a less common use. ¹³ Traction may also be used intraoperatively to facilitate and maintain alignment, easing the instrumentation itself. Unlike pre- or perioperative traction, intraoperative traction may be applied either externally or internally. This chapter will focus primarily on methods of pre- and perioperative external traction.

13.2 Traction: The Risks and Benefits

The primary benefit of pre- or perioperative halo traction is its gradual step-up in axial corrective force. Pre-/perioperative traction thus may stretch the skin and muscle around the deformity as well as the spinal cord itself. It also decreases the force per anchor at each bone–anchor interface during instrumentation. Finally, it allows for neurologic monitoring when the patient is awake.

In cases where respiratory capacity is compromised, preoperative traction can improve pulmonary function. In their study of 33 patients with severe scoliosis (15 idiopathic) who underwent an average of 71 days of preoperative HGT, Bogunovic et al ¹⁴ showed a 9% increase in pulmonary function from traction alone, which occurred without complications and was either maintained or improved after surgery. Pre-/perioperative traction can also lead to improved gastrointestinal function, which is hypothesized to occur by decreasing the pressure that the deformed spine places on the abdomen. ¹⁵ Traction may thus allow for weight gain and improve nutrition in underweight or malnourished patients.

Preoperative traction may or may not lead to improved coronal correction. An article by Sponseller et al examining preoperatively distracted adolescent idiopathic scoliosis (AIS) patients showed no difference in the percent correction of 30 idiopathic patients who underwent traction (62%) compared to 23 without traction (59%). ¹² However, a more recent study by Koptan and ElMiligui ⁹ showed improved postoperative correction in 21 AIS patients who had 2 weeks of perioperative traction (59% correction) compared to 26 who did not receive traction (47% correction; p < 0.01). The amount of additional correction achieved, if any, may vary between centers, given differences not only in patient populations but also in each institutions’ traction protocols. ^{14 , 16}

Preoperative traction may reduce the need for vertebral column resection (VCR) during definitive fixation. In the aforementioned study by Sponseller et al, ¹² VCR was used in 30% of control patients but in only 3% of preoperatively distracted patients. In cases where VCR is planned, preoperative traction may make it safer and easier. Two studies have observed no difference in blood loss or operative time between patients with and without preoperative distraction, ^{12 , 17} but Koptan and ElMiligui ⁹ reported decreased operative times after preoperative traction in their population. While several additional weeks of in-hospital observation markedly increase the total cost of a patient’s care, the observation period may allow respiratory improvement, nutritional optimization, or more regular neurologic monitoring. Select patients may also safely undergo HGT at home, provided their parents and caregivers have demonstrated good compliance and receive adequate discharge instructions. ¹⁵

There remains variability in the use of halo traction. A 2011 survey of 195 pediatric orthopaedic surgeons in North America found that only 27% of respondents reported using HGT to treat idiopathic EOS patients in their practice, compared to 62% of respondents who used casting. ¹³ This variance in practice was further illuminated by a later survey of 48 deformity surgeons from 29 countries. When asked specifically about large, rigid AIS curves, 63% of respondents felt that some form of preoperative traction was useful, compared to 37% who thought that it was not useful. ¹⁰

13.3 Preferred Methods of Preoperative Traction

External traction is applied by affixing a halo with countertraction through the femur, tibia, or pelvis, or the force of the patient’s own body (HGT). The literature contains reports of the use of each of these methods without untreated controls. Baseline radiographs of the lateral cervical spine must always be obtained before halo traction is applied, given that cervical ligamentous laxity, fixed kyphosis, or other instability is a contraindication to its use. In one case report, 2 weeks of perioperative HGT was used to assist in the correction of a 145-degree curve in a patient with Marfan syndrome. This patient developed progressive cervical kyphosis associated with neck pain and stiffness after her thoracolumbar fusion, and she ultimately required anteroposterior cervical fusion 2 years after her scoliotic correction (Fig. 13‑1a–d). This complication was attributed to the increased ligamentous laxity found in patients with Marfan syndrome and illustrates the necessity of c-spine evaluation and stability prior to the initiation of halo traction. ¹⁸

A halo may be applied under general anesthetic or sedation with local infiltration, according to the age and maturity of the patient. The hair should be locally trimmed and the skin prepared antiseptically. Temporary positioning pins may be helpful in centering the halo. During its application, one person should be dedicated to monitoring the positioning of the halo. Compared to an adult patient, a greater number of halo pins must be used in children, as the insertional torque is less. Six to eight pins are the authors’ preferred number for children younger than 6 years, although ten may be needed if the patient is osteopenic. ¹⁵ The pins should be placed equatorially, 1 cm above the lateral eyebrow (to avoid injury to the supraorbital and supratrochlear nerves and the frontal sinus), above and posterior to the pinnae of the ears but slightly below the greatest circumference of the skull. This placement can help prevent pin migration caudocranially. ¹⁹ Avoiding the temporalis muscle will help avoid both skull penetration and pain after placement. Posterior pins should be placed diametrically opposite the anterior pins. Pins should be tightened to 4 inch-pounds of torque in children younger than 6 years or 6 to 8 inch-pounds of torque in older children or adults, assuming normal cranial bone density. The amount of weight used for traction should be increased incrementally, moving up gradually to tolerance with neurologic monitoring. ²⁰ Nursing care includes cleaning the pins twice daily. ¹⁶

13.3.2 Halo-Gravity Traction

Halo-gravity traction is generally a safer and simpler method for preoperative external traction of severe IS curves compared to HFT. HGT can correct deformity in the frontal and sagittal planes in addition to improving truncal decompensation. One major advantage of HGT is that it can be maintained while the patient is in bed, in a wheelchair, or in a walking frame, whereas HFT requires that the patient remain bedbound. The bed should be inclined in reverse Trendelenburg while the patient is in HGT, although the traction weight may be lessened while the patient sleeps, if desired, especially once the weight nears its maximum.

In the authors’ experience, pretraction release can be a useful adjunct for patients with unusually stiff curves, such as those with bony apical fusions or flexibility of less than 20% on traction radiographs. Nevertheless, most patients begin traction without a preceding release, which likely results in lower overall infection risk. The halo is usually applied with sedation and local anesthesia. HGT should be initiated at 5 pounds for young children and 10 pounds for older children. It may be slowly increased as tolerated by 2 to 3 pounds per day, or by 10% body weight per week, until the maximum amount of desired traction is achieved. ²⁰ Surgeons have different thresholds for the percent body weight they will allow. Most authors advocate for a maximum of 33 to 50% of body weight to obtain the full correction that may be achieved safely prior to surgery. Patients may divide their time between bed (Fig. 13‑2), wheelchair (Fig. 13‑3), and walker (Fig. 13‑4). Some surgeons recommend decreasing the weight during sleep, while others have found it safe to leave it constant. The ability to self-adjust the resistance can be provided by the use of a fish-scale if constant weight is not preferred.

In addition to daily pin-site checks, peripheral neurologic assessments of both the upper and lower body should be performed three times per day. Cranial nerve (CN) exams should be performed once per day. Posteroanterior and lateral radiographs of the full spine should be obtained once per week during traction, which may last up to 12 weeks preoperatively, to assess the improvement in the patient’s spine. The authors prefer a maximum of 2 to 3 weeks of traction, having observed that curve correction benefits tend to taper after 3 weeks. However, some experts prefer to use longer periods of time, especially if this allows patients to improve their nutrition and pulmonary reserve.

Several studies have examined pre- and perioperative HGT’s effectiveness in severe IS. In their study of 33 all-cause spinal deformity patients treated with perioperative HGT, Rinella et al ¹ described four IS patients who achieved 54% correction in their major coronal curves, with rod migration being the only complication. In a similar study of 19 all-cause deformity patients, Sink et al reviewed 4 IS patients who underwent 14 to 18 weeks of perioperative HGT. ³ Of the three who had not had prior fusions, 43% correction was achieved after perioperative traction, followed by 51% after fusion. HGT is typically not advised in patients who have had prior fusions, as it will result in additional hospitalization and minimal added correction.

Recent evidence further supports the notion that HGT allows preoperative optimization for surgery. A 2018 retrospective review by Iyer et al ²⁰ examined 96 patients with severe scoliosis treated with preoperative HGT (mean = 97 days), of whom 55 had IS. Among all patients, average body mass index increased from 17.7 to 19.6 kg/m² during HGT. When these patient’s 100-point Foundation of Orthopedics and Complex Spine (FOCOS) scores were calculated to estimate their risk of complications, the use of HGT was associated with an 18-point decrease in complication risk, with IS patients receiving the greatest benefit from HGT risk reduction. These authors also noted that the planned rate of three-column osteotomy reduced from 91% before HGT to 38% after HGT, and that FOCOS score was an independent risk factor for surgical complications, with scores over 74 having a four times greater risk than those with a score under 74. Medical complications, which occurred in 20% of this study’s patients, were chiefly gastrointestinal (n = 10) or pulmonary (n = 5), further emphasizing the importance of medical optimization for patients with severe scoliosis. However, these authors observe that HGT use itself was not without complication, with halo-related complications occurring in 34% of patients and with 8.3% of patients requiring halo revision because of infection or pin-site loosening. ²⁰

13.4 Complications and Contraindications

Potential complications of halo use may include pin-site loosening or infection, cerebrospinal fluid leak, nerve palsy, paralysis, pressure sores, or cranial suture separation. In the authors’ opinion, there is no minimum age that constitutes a contraindication to halo placement, as halo traction can be useful in patients of all ages, and many of the bigger curves in the realm of spine deformity occur in younger children. To prevent complications, the weight applied should be approximately the same percent of body weight regardless of age. The torque of the pins should be progressively decreased with age to about 2 inch-pounds in infants, but the number of pins can be correspondingly increased.

One of the largest studies of halo-related complications, which reviewed a single institution’s population of 68 preoperatively treated all-cause scoliosis patients, estimated a 53% complication rate associated with halo use alone. ²⁸ However, not all of these patients underwent preoperative traction, and only four had a diagnosis of IS. In comparison, a multicenter study of 15 AIS patients treated with preoperative halo traction observed a total complication rate of 33%, which was not found to be significantly different (p = 0.68) from the 25% complication rate of its nontraction AIS control group. ¹² Of the different methods for pre- or perioperative traction, HGT has the lowest incidence of neurologic complications. The true incidence of halo-traction–related complications for IS remains difficult to study, given both its greater use in nonidiopathic scoliosis and the high variability of traction protocols between centers. ^{12 , 16} Since preoperative traction is typically reserved for the most severe cases of IS, however, caution is warranted whenever it is employed. Compared to pre- or perioperative traction, the use of intraoperative traction alone is associated with a lower complication rate. A recent systematic review examining 150 AIS patients found an intraoperative traction-related complication rate of 13.3%, representing 19 reversible neuromonitoring changes and one pressure sore. ²⁹

Pin loosening and pin-site infections, both deep and superficial, are the principal complications related to pre- or perioperative halo application. Daily pin-site checks are therefore appropriate so that pin sites may be monitored for signs of infection. ²⁸ Likelihood of pin-site complication may also be associated with the length of time spent in the halo. ³⁰ Deep infections, in particular, represent a devastating complication, with several reports documenting intracerebral abscesses that presented anywhere from 2 weeks to 5 years after the application of the traction tongs or halo unit. ^{31 , 32 , 33} Proper pin positioning, number, and torque are all necessary to prevent skull penetration. Regarding placement, however, a study of computed tomography (CT) has suggested that there may be no true osseous “safe zone” anteriorly in children aged 10 years and younger, given the variable thickness of the pediatric skull. ³⁴ Families of halo-wearing children must therefore also be cautioned about fall risk, which poses the greatest threat to skull penetration. ²⁸ CT may be used to confirm penetration when suspected. A CT study of pediatric skull thickness by Loder ³⁵ looked at four standard pin placement sites (right and left anterolateral, and right and left posterolateral) and found that age accounted for only 40% of the variation in skull thickness for children ranging from infancy to 16 years, indicating that even healthy children of similar chronologic ages can still have a wide variation in skull thickness. However, this variation did not correlate with patients’ race or sex. For all age groups, the region superior to the ear pinna was the thinnest part of the skull.

Peripheral nerve palsy represents another possible complication of pre-/perioperative traction. A study of 30 IS patients treated with perioperative traction following anterior release reported three cases of transient brachial plexus palsy (10%). ⁸ Transient brachial plexus palsy was likewise observed in 1 of 33 patients (3%) in a study of perioperative HGT ¹ and also in a case report of a patient with Ehlers–Danlos syndrome undergoing preoperative traction. ³⁶ When brachial plexus symptoms have been observed, reducing the amount of traction has led to full resolution. Early recognition of these symptoms will also minimize their risk. Keeping traction at or below 33 to 40% of body weight may further help avert brachial plexus palsies. ³⁷ In the lower extremities, the development of ankle clonus or a positive Babinski sign has been noted in patients undergoing preoperative traction. ³⁸ Horner syndrome and urinary retention are rare but more concerning findings that can also be seen during preoperative halo traction. ³⁸ Any of the aforementioned findings call for the reduction or removal of traction, and their mention here further underscores the necessity of a well-documented neurologic exam every time the patient is seen.

CN palsies during preoperative halo traction have also been reported. In their series on 70 patients, Wilkins and MacEwen ³⁸ reported 6 cases of CN palsy during preoperative traction, with CN VI (abducens) palsy being the most common (4 of 6 cases) and presenting as loss of lateral gaze (Fig. 13‑5). They attributed this symptom to nerve impingement at the petrosphenoidal junction. In a case report, Ginsburg and Bassett ³⁹ also described a pattern of CN IX, X, and XII (glossopharyngeal, vagus, and hypoglossal) palsy after preoperative HGT at 40% body weight that presented as dysphagia, loss of palatopharyngeal reflexes, and tongue weakness in a 12-year-old with myelomeningocele. Although his symptoms resolved with traction removal, later authors have noted that in an immobilized patient difficulty swallowing represents a potentially lethal CN palsy, ¹ if one that may be more common in myelodysplastic than idiopathic patients. ³⁹

Paralysis, a catastrophic and much-feared complication of scoliosis treatment, has become increasingly rare as treatment methods have improved. Many of the complications historically seen from traction occurred because the distraction force was applied too forcefully and too rapidly, whether internally or externally. ² A Scoliosis Research Society (SRS) review of 7,885 patients reported an incidence of 0.72% in 1975, including a case of IS in whom permanent paraplegia developed during perioperative HFT following a soft-tissue release. ⁴⁰ In six patients with postoperative paraplegia after Harrington rod insertion, however, peripheral or CN symptoms had developed previously during preoperative traction. This sequence suggests that the distraction force of these patients’ Harrington rods thus exacerbated a neurologic insult that had been introduced during preoperative halo traction. The SRS authors concluded that applying traction more slowly and more gradually might have avoided these outcomes. Ransford and Manning ⁴¹ also reported two cases of paraplegia in 1975, one permanent, that presented during perioperative halo-pelvic traction of IS. These neuropathies were likewise attributed primarily to the excess internal force applied by the patients’ solid Harrington rods, rather than to their external traction alone. The shift toward treating severe IS with gradually increased halo traction and instrumentation with less force-per-anchor, such as dual-rod pedicle-screw constructs, has further decreased the risk of pre- or postoperative paralysis.

Cranial suture separation is another rare but dramatic potential complication associated with halo use in spinal deformity. Woon and Mardjetko ⁴² recently reported on their experience using halo-vest treatment in a patient with Hajdu–Cheney syndrome, an ultra-rare (< 100 reported cases) autosomal dominant disorder that causes severe osteoporosis and open skull sutures. This patient was found to have symptomatic separation of her lambdoid sutures, which presented only when her halo vest was removed after a suboccipital craniectomy and fusion. When intraoperative neuromonitoring (IONM) is used, intraoperative traction must always be examined as a potential source of neuromonitoring events. Some recent evidence has suggested that traction alone is rarely a cause of signal loss. A multicenter study of 579 IS patients found that 21 cases (3.6%) had IONM changes, and that only 2 of these 21 events (9.5%) were associated with the application of intraoperative traction, with low blood pressures or misplaced screws accounting for a much greater percentage (71%) of events. ⁴³ In this study, both episodes of a traction-related neuromonitoring change resolved when traction was removed. However, a study of 36 consecutive patients by Lewis et al found that intraoperative traction had a significant association with loss of motor evoked potentials (MEPs), with three patients recovering to less than 50% of their baseline function. ⁴⁴ In this sample, rigidity, major curve size, and thoracic location were risk factors for loss of MEP, and recovery of any MEPs by the time of skin closure resulted in retention of neurologic function.

While intraoperative traction is being established, consideration must be given to the patient’s positioning on the operating table, given that the traction may alter the placement of hip and shoulder cushioning. In the event of an intraoperative cardiac arrest, the need to remove traction weights might delay the initiation of chest compressions and could thus present another possible complication. ³⁷

Preoperative halo traction is not a panacea for severe IS curves, and several other factors may indicate against its use. Any observation of stenosis, ligamentous laxity, fixed kyphosis, or other instability in the cervical spine is an absolute contraindication, as the risk of upper spinal cord injury outweighs the benefits of preoperative traction. In patients with these findings, temporary internal distraction may be used as an alternative. Additionally, patients with sagittal plane deformities alone are least likely to respond to HGT. ²⁰ Halo traction should also not be used in patients with significant behavioral disorders. Falls or high-energy blows to the head present a major risk to skull penetration by the halo pins, and children who may be predisposed to violence or otherwise have difficulty mediating their behavior while in traction are poor candidates for this technique.