Fusion mass to pelvis internal distraction technique using multiple-hook fixation for scoliosis correction: illustrative case

Abstract

BACKGROUND

Internal distraction rods have been described as an alternative to halo gravity traction for the treatment of severe scoliosis. Distraction rods can be challenging to use in patients with existing fusion masses. The authors report an internal distraction, construct-to-construct rod technique using multiple-hook fixation in a patient with a sharply angulated cervicothoracic scoliosis fusion mass.

OBSERVATIONS

A 12-year-old female with previously diagnosed congenital scoliosis who had undergone cervical fusion in situ at age 2 presented to the clinic with shortness of breath exacerbated by increased levels of activity. Standing anteroposterior and lateral scoliosis radiographs revealed a left >150° cervicothoracic curve, right 140° thoracolumbar curve, and left 28° lumbosacral fractional curve with pelvic obliquity. The authors indicated this patient for a 3-stage all-posterior approach for spinal fusion and deformity correction. In the final fusion surgery, the authors set up a construct-to-construct internal distraction configuration connecting the left hemipelvis to the cervicothoracic fusion mass to aid in deformity correction.

LESSONS

A construct-to-construct internal distraction rod technique connecting a fusion mass to the pelvis can assist with curve correction in severe scoliosis.

Temporary internal distraction has been applied for the correction of severe spinal deformity. Internal distraction involves placing cephalad anchors on the ribs or spine and caudad anchors on the spine or pelvis to apply gradual distraction forces to the spine directly.¹ Internal distraction is employed for single or staged procedures prior to pursuing final fusion. Studies using internal distraction rod constructs have demonstrated greater curve correction in severe scoliosis, improved pulmonary function tests, lower rates of permanent neurological injury, and lower rates of infection.^2,3 Internal distraction can also serve as an alternative or adjunct to halo gravity traction (HGT), ameliorating the need for an inpatient hospital stay and circumventing common complications of neck pain, pin pain, pin infections, or other neurological sequelae.⁴ Previous studies have described a multiple-hook technique as a method for fixating a multilevel fusion mass in revision spinal deformity surgery.⁵ We report a construct-to-construct internal distraction rod technique using multiple-hook fixation in a patient with a sharply angulated cervicothoracic scoliosis fusion mass.

Illustrative Case

A 12-year-old female who was previously diagnosed with congenital scoliosis and who had undergone cervical fusion in situ at age 2 presented to the clinic with shortness of breath exacerbated by increased levels of activity. She denied recent falls, gait instability, difficulty with fine motor hand movements, or urinary/bowel incontinence. Her relevant past medical history included asthma, which was well controlled. Recent forced expiratory volume in the first second (FEV1) and forced vital capacity (FVC) were low at 0.88 and 1.13 L, respectively (FEV1/FVC = 77.7%). On physical examination, she stood 4 ft. 9 in. and weighed 124 lb for a body mass index of 26.8 kg/m². Her right shoulder was elevated; there was a right thoracolumbar rib hump and paraspinal prominence and a marked left thoracic skin crease, and her right patellar deep tendon reflex was 3+ without clonus. She had full strength in all muscle groups.

Standing anteroposterior and lateral scoliosis radiographs revealed a left >150° cervicothoracic curve, right 140° thoracolumbar curve, and left 28° lumbosacral fractional curve with pelvic obliquity (left hemipelvis higher than right; Fig. 1A–D). Because her sweeping thoracolumbar curve showed reasonable flexibility on supine radiographs, we used preoperative HGT with a slow increment in weight up to a goal of 30 lb over a 3-week period (Fig. 1E and F). Three-dimensional (3D) computed tomography (CT) reconstruction showed the severe extent of her rotational deformity and thoracolumbar lordosis (Fig. 2A and B). A 3D printed model highlighted her sharply angulated cervicothoracic curve and fusion mass (Fig. 2C and D). Magnetic resonance imaging showed a syrinx, split cord malformation, and a type 3 spinal cord (based on the spinal cord shape classification system) at the apex of the cervicothoracic curve and against the lamina of the thoracolumbar curve with no tethering noted.

FIG. 1.

Preoperative anteroposterior (AP) standing (A) and supine (B) and lateral standing (C) and supine (D) radiographs. Standing AP radiographs in HGT with increasing weight (E). Standing lateral radiographs in HGT with increasing weight (F). Asterisk indicates unable to obtain accurate measurement.

FIG. 2.

3D CT reconstruction of the spinal deformity showing a left-sided cervicothoracic fusion mass in the posterior (A) and anterior (B) planes. 3D model showing the cervicothoracic spinal deformity in the ventral (C) and dorsal (D) planes. Asterisk indicates the cervicothoracic fusion mass.

We indicated this patient for a 3-stage all-posterior approach for spinal fusion and deformity correction. Stage 1 involved a 3-week period of HGT. Stage 2 involved spinal cord decompression at the cervicothoracic junction via T3 and T4 hemilaminectomies and right-sided pediculectomies, L2 to the pelvis spinal instrumentation, and L5–S1 transforaminal lumbar interbody fusion. The T3 and T4 pediculectomies were performed because these were the spinal levels corresponding to the coronal apex of the cervicothoracic deformity. At stage 3, C4–S1 posterior spinal fusion and instrumentation, T6–L2 posterior column osteotomies, and left T8–10 pediculectomies were performed. In the third stage of this procedure, the patient was positioned prone on a standard operating room table with bolsters under her chest and pelvis. Intraoperative HGT was applied with 10 lb of weight. Posterior column osteotomies were started distally at L1–2 and continued at serial levels proximally until T10. Next, complete laminectomies and concave pediculectomies from T8 to T10 were performed to decompress the thoracic spinal cord. Additional posterior column osteotomies were performed from T6 to T8. Pedicle screw placement was achieved via a freehand technique, and final placement was confirmed with fluoroscopy.⁶ Next, we set up a construct-to-construct internal distraction configuration connecting the left hemipelvis to the fusion mass of the cervicothoracic region. Two hooks were placed in claw fashion above at the C4 and C6 levels (Fig. 3), and another hook was placed in an upgoing fashion at approximately the T3 level. The process for placing the fusion mass hooks began with drilling into the fusion mass to create an entry hole. This was followed by deepening the entry hole using an angled curette or laminar finder to dig a horizontal tunnel into which the incoming hook could attach. We captured these 3 hooks with a 4.75-mm rod linked by 2 side-to-side domino connectors to a 5.5-mm rod in a construct-to-construct configuration caudally fixed to a lateral iliac screw (Fig. 4). We then employed multiple rounds of distraction to push the hemipelvis down and improve the coronal malalignment. At this point, we contoured and engaged a left-sided, 6-mm, cobalt-chrome, concave correcting rod first distally into the lumbosacral fixation points, and we used in situ contouring up to T6 and T7. Using this same technique, we contoured and engaged a right-sided, 6-mm, cobalt-chrome rod going from the S2 alar-iliac screw up to T6. We then placed 2 additional rods on the left side going from the lateral iliac screw after we removed our temporary internal distraction rod and connected one of the rods to a variable-angle domino connector from the T11–12 region as a kickstand construct.⁷ Kickstand distraction was performed to further improve the pelvic obliquity and coronal alignment. The second additional rod was a 4.75- to 5.5-mm transition rod that replaced the initial 4.75-mm rod used for distraction at the fusion mass anchor sites. Finally, we placed an additional right-sided 6-mm rod to go from the T12 to L1 variable-angle domino connector down to the iliac screw. Thus, we had 4 rods crossing the thoracolumbar and lumbosacral junction along with a fifth left-sided, lateral transition rod that connected the entire construct to the C4 fusion mass via the multihook fixation technique. There were no changes in intraoperative neuromonitoring, and the patient woke up neurologically intact. Postoperative standing radiographs showed good spinal realignment in the sagittal and coronal planes (Fig. 5).

FIG. 3.

Illustration showing the operative procedure. Burring the placement site for a hook on the fusion mass (A). Preparing a tunnel to accommodate the hook (B). The claw formation is made up of 2 hooks facing each other (C, D). Copyright Ning Liu. Adapted from Liu et al.⁵

FIG. 4.

Intraoperative photograph showing a construct-to-construct internal distraction rod technique using multiple-hook fixation in a patient with a sharply angulated cervicothoracic scoliosis fusion mass.

FIG. 5.

Preoperative standing anteroposterior (AP) (A) and lateral (C) radiographs. Postoperative standing AP (B) and lateral (D) radiographs showing good spinal realignment in the sagittal and coronal planes.

Patient Informed Consent

The necessary patient informed consent was obtained in this study.

Discussion

Observations

In this case, we describe a construct-to-construct internal distraction rod technique using multiple-hook fixation in a patient with a sharply angulated cervicothoracic scoliosis fusion mass. Obtaining reliable proximal anchor points for internal distraction can be challenging in patients with existing fusion masses, especially in those who also have dysplastic ribs or congenitally fused ribs. The loss of anatomical landmarks in cases of fusion masses makes pedicle screw placement technically more difficult. Skipping the fusion mass and connecting an internal distraction construct to an adjacent pedicle screw either proximal or distal to the fusion mass is a viable alternative to our technique. However, by not incorporating the fusion mass in the internal distraction construct, we lose an important opportunity to distract against a rigid proximal fixation point that could aid in gradual curve correction. Furthermore, excluding long fusion masses from fixation can significantly increase the risk of instrumentation failure, as reported in previous cases.⁸ A more reasonable alternative to fixate a fusion mass in a revision scoliosis surgery would be to use a stereotactic navigation system to accurately guide pedicle screw placement.⁹

One of the first studies that described a multiple-hook technique to fixate a multilevel fusion mass in revision spinal deformity surgery was reported in 2017 by Liu et al.⁵ In that study, multiple laminar hooks were placed in a clawlike configuration directly within the fusion masses and were incorporated into the final rod construct in revision spinal deformity surgeries. The indications for this technique included 1) the inability to identify pedicle screw tracts and other anatomical landmarks because of a previous massive fusion mass that spanned 3 or more levels and 2) an adequate thickness (usually 2 cm and above) of the fusion mass for hook placement, which was confirmed preoperatively by CT sagittal reconstruction. Eight patients underwent this technique over an 8-year period with a mean 30-month follow-up. There was no evidence of hook loosening or displacement in this case series. There were also no dural tears reported during hook placement site preparation. It should be noted that the stability and strength of the authors’ claw configuration was reinforced with compression forces after the rod was engaged, which is also a technique that we used in our case. The main advantage of this extrapedicular, multiple-hook fixation technique is its simplicity to execute, and it provides a less invasive alternative to fixate large fusion masses that obscure normal spinal anatomical landmarks.

An additional method of screw fixation in cases of revision spinal deformity surgery with multilevel fusion masses is freehand placement of fusion mass screws. These screws are placed coronally or obliquely across a posterior fusion mass. A recent 2022 retrospective study by Mittal et al.¹⁰ reported 6 patients who had undergone revision spinal deformity surgery with fusion mass screw placement. Bone mineral density and dimensions of the posterolateral fusion masses were determined on the basis of preoperative CT to assess possible levels for fusion mass screw placement. Fifteen freehand screws were placed in the 6 patients. All fusion mass screws were combined with pedicle screws, and all screws were either 5.0 or 5.5 mm in diameter. There were no neurophysiological alerts observed during screw placement, and no neurological deficits were reported postoperatively. On postoperative CT, 1 of 15 screws had a low-grade breach into the spinal canal. Although fusion mass screws can be used to achieve a stable fixation in revision spinal deformity cases, it is a more technically challenging technique than the multihook technique for fusion mass fixation. Lastly, we are hesitant to choose a fusion mass screw over laminar hooks in a claw configuration as proximal anchors in an internal distraction construct because of the dangerous consequences of a fusion mass screw plowing into the spinal canal during distraction maneuvers.

Historically, HGT has been used as an adjunct for treating severe scoliosis. In our case, the patient’s sweeping thoracolumbar curve showed reasonable flexibility on supine radiographs, so preoperative HGT was applied over a 3-week period. In the literature, the preoperative use of HGT showed up to 38% deformity correction in curves surpassing 100° and sometimes obviated the need for 3-column osteotomies.^11,12 Intraoperative temporary internal distraction has been described as an effective adjunct technique for correction and maintenance of sagittal and coronal alignment.¹³ This technique takes advantage of the viscoelasticity properties of the spine to achieve gradual spinal deformity correction and decreases the risk of intraoperative neurological injury.^3,14 When employing internal distraction techniques, the proximal rod anchors are typically either a thoracic rib or a pedicle screw at the proximal concavity of the curve. Distal rod anchors can be either pelvic fixation or a pedicle screw at the distal concavity of the curve to correct potential pelvic obliquity and improve coronal malalignment. The construct-to-construct internal distraction configuration was converted to a kickstand rod after the spine was reduced with the main thoracolumbar rods to help realign the spine in the coronal plane. In the final construct, 4 rods spanned the thoracolumbar and lumbosacral junctions along with a fifth left-sided rod connecting to the C4 fusion mass to maintain the internal distraction forces employed during the initial deformity correction steps.

Lessons

A construct-to-construct internal distraction rod technique connecting a fusion mass to the pelvis can assist with curve correction in severe scoliosis.

Acknowledgments

Dr. Lenke has received grants and nonfinancial support for travel from the Scoliosis Research Society, as well as grants from the Setting Scoliosis Straight Foundation, AOSpine, and the International Spine Study Group outside the submitted work.

Author Contributions

Conception and design: Sarmiento, Lenke. Acquisition of data: Sarmiento, Kozan. Analysis and interpretation of data: Rymond, Kozan. Drafting the article: Sarmiento, Rymond, Kozan. Critically revising the article: Sarmiento, Rymond, Lenke. Reviewed submitted version of manuscript: Rymond, Lenke. Approved the final version of the manuscript on behalf of all authors: Sarmiento. Administrative/technical/material support: Rymond, Kozan. Study supervision: Lenke.