12.44 Post-traumatic spinal reconstruction

In the United States of America approximately 50 000 fractures of the spine occur each year. Between 7000 and 10 000 of these are associated with neurological deficit. The thoracolumbar junction (T10–L2) is the commonest site for such injury. This predilection may be explained by virtue of its unprotected position between two rigid lever arms formed by the upper thoracic and lower lumbar spine.

Post-traumatic kyphosis (PTK) is a common sequel to fractures in this region, particularly following neglected flexion–compression, flexion–distraction, and burst fractures. The resultant late deformity may result in pain, neurological deficit, or unacceptable cosmesis requiring complex reconstruction of the spine.

The spine has a characteristic alignment in the coronal and sagittal planes. In the coronal plane the spine is straight. In the sagittal plane, the spine is lordotic in the cervical and lumbar regions and kyphotic in the thoracic region. The normal cervical lordosis is 30–50 degrees, with the majority occurring at the C1–C2 level. The normal thoracic kyphosis is 10-40 degrees. The normal lumbar lordosis is 40–60 degrees with up to 75% occurring between L4 and S1. The thoracolumbar junction measured between the superior endplate of T10 and the inferior endplate of L2 usually measures 0 degrees.

In stance, the C7 plumb line should pass within a few millimetres of the posterosuperior corner of S1. The lordotic and kyphotic segments of the spine must ultimately balance the occiput over the sacropelvic axis for posture to be energy-efficient.

PTK may occur in the cervical, thoracic, or lumbar spine. Loss of cervical lordosis and lumbar lordosis may occur following posterior spinal decompressive procedures. The commonest site of PTK however is thoracolumbar junction. The thoracolumbar junction is the biomechanical transition zone between the relatively rigid thoracic spine and the highly flexible lumbar spine and is relatively unprotected.

Several classification systems for thoracolumbar injuries have been described. However, these often lack validity and reproducibility, serving only as descriptors of injury and not necessarily as predictors of outcome. The thoracolumbar injury classification severity score (TLICS) attempts to address this by assessing the fracture morphology, the integrity of the posterior ligamentous complex, and the neurological status of the patient. Careful use of this classification may improve the diagnostic accuracy of such injuries, resulting in more aggressive early treatment, potentially minimizing the risk of PTK.

The present site and severity of pain should be ascertained. Pain may be localized to the original fracture site. It may result from a pseudarthrosis or failure of the fracture to heal, or it may be secondary to adjacent level intervertebral disc degeneration or facet joint degeneration. Alternatively, the pain may be remote from the fracture site. Malcolm et al. highlighted the problem of low back pain resulting from muscle fatigue as the posterior spinal muscles attempt to correct the sagittal imbalance produced by a more cranial PTK.

Patients may complain of loss of height or progressive deformity. Others will complain of discomfort when sitting in hard-backed chairs when the gibbus makes contact with the back of the chair. Others still will complain of unacceptable cosmesis. Neurological dysfunction may be evident with radicular-type symptoms suggestive of individual nerve root compromise or in more severe cases there may be spinal cord involvement with lower limb weakness, bladder, bowel, or sexual dysfunction.

The patient should be examined in the standing position with attention paid both to frontal and sagittal alignment. The spinal balance should be formally assessed with a plumb line in both posterior and lateral views. The site and size of the gibbus should be noted. This will become more obvious if the patient is asked to bend forward. The range of motion in the spine should be assessed. An attempt should be made to ascertain whether the deformity is fixed or flexible. This may be done, for example, by asking the patient to lie on a flat couch to see if the deformity corrects. A complete neurological examination including abdominal reflexes and rectal examination should be carried out.

Standing anteroposterior and lateral radiographs of the whole spine will allow assessment of the focal kyphosis by measurement of the Cobb angle. This is the angle subtended by a line drawn over the superior endplate and a line drawn over the inferior endplate of the vertebral body above and below the level of injury. These standing radiographs will also allow for an assessment of the global sagittal balance. The C7 sagittal plumb line should pass on average 40mm anterior to the posterosuperior margin of the S1 endplate. A hyperextension film over a bolster placed at the apex of the deformity will allow for an accurate assessment of the flexibility of the deformity (important in planning the surgical strategy). Serial lateral standing radiographs will allow assessment of progression of the deformity over time.

Computed tomography with fine cuts (1–3mm) will allow a detailed evaluation of the bony architecture and fracture geometry. Sagittal and coronal reconstructions may confirm the presence of a pseudarthrosis at the site of the original fracture and also allow for detailed planning including the need for spinal osteotomy.

Magnetic resonance imaging is invaluable for assessing the integrity of the posterior ligamentous complex, the surrounding intervertebral discs, and subtle neural compression and changes within the spinal cord, such as myelomalacia or the presence of a post-traumatic syrinx.

This is useful to confirm the source of pain. Under conscious sedation, the intervertebral discs adjacent to the injured vertebra are cannulated using a two-needle technique, followed by injection of radiographic contrast. If such an injection produced concordant pain reproduction, there would be a strong argument for inclusion of this level in the proposed fusion.

Baseline somatosensory evoked potentials (SSEPs) are important to assess before surgery. If reproducible, they will allow the use of continuous intraoperative spinal cord monitoring to detect intraoperative spinal cord dysfunction before it becomes irreversible.

The treatment of PTK depends primarily on the location and magnitude of the deformity, its stiffness on hyperextension films, and the anatomical source of pain. Conservative measures including non-steroidal anti-inflammatory medication and physiotherapy (aimed at optimizing the spinal extensor muscle activity and postural readjustment) should be given a fair trial before surgery is considered.

Indications for surgery include pain, progressive neurological deficit, progressive spinal deformity, and unacceptable cosmesis. Patients who have a localized kyphotic deformity of greater than or equal to 30 degrees have been noted to have an increased risk of chronic pain at the site of the kyphosis.

Goals of surgery include correction of the deformity, restoration of sagittal balance, provision of immediate stability, improvement of neurological function, and reduction in pain. In so doing, it is important to recreate a load-sharing and tension band system and to fuse only the damaged segments.

The basic principles used in the treatment of fractures still apply, however the surgical technique differs. This is because the kyphosis is often fixed, correction is more difficult to achieve than is the case for acute fractures because of the presence of osseous deformity, soft tissue retraction, and elongation. Also there is a higher risk of neurological impairment because of dural adhesions. Very rarely is only one segment damaged, in the majority of cases two segments are involved.

In any surgical correction it is important to use spinal cord monitoring during the procedure. The combination of SSEPs and transcortical magnetic stimulation motor-evoked potentials (MEPs) are extremely useful in detecting spinal cord lesions before they become irreversible. Prompt intervention during loss of spinal cord monitoring can lead to a return of normal spinal cord monitoring, thereby preventing a permanent neurological deficit.

A number of different surgical procedures have been described, depending on the magnitude and location of the deformity and whether the deformity is fixed or mobile.

This is particularly useful for flexible multisegmental deformities which lack focal angular kyphosis. Multiple extension (Chevron) osteotomies with segmental fixation may allow return of a normal sagittal contour. In this type of surgery, the importance of a comprehensive resection of the facet joints or fusion mass cannot be overemphasized.

This technique requires either a thoracotomy or a thoracoabdominal approach, depending on the level of the PTK. For fixed kyphotic deformity, the anterior-only approach provides a less reliable and sometimes incomplete correction.

Benli et al. (2007) treated 40 patients with PTK with a mean age of 44.7 years (range 18–65 years) with anterior vertebrectomy, decompression and anterior fusion with costal or iliac crest bone graft. The preoperative kyphosis measured 51.4 degrees ± 13.8 degrees compared to a postoperative kyphosis of 7.0 degrees ± 7.6 degrees. At a minimum of 5-year follow-up, the mean loss of correction was 1.4 degrees ± 1.8 degrees. These authors reported complete resolution of pain in 36 patients with partial resolution of pain in the remainder. For those patients with neurological deficit before surgery (24 patients), all noted an improvement following surgery. Improvements in pain and functional assessment were noted, as well as total SRS-22 scores and each individual domain score (pain, function, mental status, self-image, and satisfaction).

Gertzbein (1992) in a study of 1019 acute spinal fractures noted that anterior surgery was more beneficial in improving complete bladder impairment to partial impairment when compared to posterior surgery. For those patients with an incomplete neurological deficit, several authors have reported significant neurological recovery after anterior decompressive procedures even as late as two years after injury.

This is an excellent posterior technique ideally suited for localized kyphosis requiring a large magnitude correction. Surgery below the conus medullaris (circa L1) is generally regarded as safer than that above the conus.

The technique involves removal of a posteriorly-based wedge involving the spinous process, pedicles and vertebral body followed by segmental fixation (Figure 12.44.1). This is a closing-wedge osteotomy thereby shortening the neuraxis. For this reason arguably it is safer than an opening-wedge osteotomy, which is now rarely performed.

Wu (1996) treated 13 patients with rigid PTK by pedicle subtraction osteotomy. All patients were male between the ages of 20 and 45 years. The initial fractures were all between T12 and L4. The mean kyphosis before correction measured 40 degrees (range 30–60 degrees), reducing to a mean kyphosis of 1.5 degrees (range −5 degrees to +5 degrees) postoperatively. The authors reported no neurological deficit, no implant failures, no infections and bony union was said to occur in all 13 cases at the osteotomy site.

Harms describes surgery consisting of three stages, usually performed in one operation. The first stage consists of a posterior release via a transversotomy. This consists of resection of the lig amentum flavum and undermining of the upper neural arch (to avoid posterior compression of the cord during and after the reduction), resection of the facet joints. Only rarely is a complete laminectomy required. Pedicle screws for segmental fixation are inserted at this stage. The second stage involves an anterior release consisting of excision of the anterior longitudinal ligament and intervertebral discs, along with a vertebrectomy if required. The anterior release is then followed by reduction of deformity, grafting and anterior instrumentation. The third stage involves return to the posterior approach for completion of the posterior instrumentation. The structure is loaded in compression to restore the tension band (Figure 12.44.2). Only in those cases where the bending films show full reduction without neural compromise, can the surgery be performed in two approaches (anterior and posterior).

This technique provides exceptional correction of sagittal plane deformity through segmental and progressive release/excision. The initial posterior approach allows an aggressive facetectomy ± osteotomy followed by anterior decompression/release allowing for a comprehensive correction of the kyphotic deformity. Finally the posterotension band is restored through an instrumented posterior arthrodesis. Disadvantages of this procedure are the prolonged anaesthesia, significant blood loss, and it may well be tiring for the surgeon.

Been et al. (2004) compared an anterior procedure alone (10 patients) with a one-stage combined anterior and posterior procedure (13 patients) for post-traumatic thoracolumbar kyphosis after simple type A fractures. The main indication for this surgery was pain. No significant difference was observed in the clinical or radiological outcome between the two techniques. The authors concluded that monosegmental correction with an anterior procedure alone was preferable to the more complex combined procedures.

Complications of post-traumatic spinal reconstruction include approach-related complications (e.g. pneumothorax, diaphragmatic hernia, paralytic ileus, chylothorax, retrograde ejaculation, dural laceration), neurological deficit (spinal cord, cauda equina, individual nerve roots), bleeding, infection, pseudarthrosis, and implant failure.

One study reported an overall complication rate for PTK surgery at 48%. Postoperative neurological deficit was observed in 8.3% of patients and 12.5% suffered a pseudarthrosis. Forty-two per cent reported a loss of correction of more than 10 degrees and 2% had further problems with instrumentation.

In PTK, the spinal cord is often draped over the anterior vertebral column. Pre-existing spinal cord injury, neural scarring, and cord tethering will all potentially increase the risk of neurological injury. Intraoperative neural injury to the spinal cord may occur as a result of traction, correction, mechanical damage or vascular events. Nerve roots or cauda equina may be injured as a result of a misplaced pedicle screw or inadequate decompression prior to reduction. Dural laceration is not infrequently reported and may relate to previous scarring. Major vessel injury has been reported involving the aorta and inferior vena cava caused by too vigorous retraction. Posterior screws that are too long may perforate the anterior cortex and cause vessel injury.

PTK is a common occurrence following fractures of the thoracolumbar and lumbar spine, the presence of which often indicates a failure of initial treatment. The resultant pain, progressive deformity, progressive neurological deficit or unacceptable cosmesis may offer compelling indications for surgical intervention. With careful planning and meticulous technique these symptoms can be treated with a degree of success, justifying such invasive and complex surgery.