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Indications and pitfalls of surgical management

J-M. Mac-Thiong

Most insufficiency fractures of the spine are amenable to non-surgical management. However, open surgical treatment is indicated for certain cases. Although uncommon, insufficiency vertebral fractures can be associated with immediate neurological compromise that necessitates decompression and fixation (Fig. 1). Early surgery may also be preferred over non-surgical treatment when there is significant increase in local kyphosis between supine and standing radiographs initially, particularly if the fracture is not amenable to vertebroplasty or kyphoplasty.

 

Fig. 1. 1a and 1b) CT images of a 65-year-old male with a T12 burst fracture and ASIA D neurological deficit. 1c and 1d) anteroposterior (c) and lateral (d) radiographs showing treatment with posterior decompression, instrumentation and fusion from T10 to L2.

 

Patients presenting with late neurological deficit due to progressive collapse or instability also require surgery. When vertebroplasty and kyphoplasty are not indicated, patients with progressive deformity (kyphosis or scoliosis) may benefit from surgery, as well as those with stable deformity and intractable pain. Indications for surgery also include the presence of neurologic symptoms, persisting pain or progressive deformity despite non-surgical treatment, vertebroplasty or kyphoplasty (Fig. 2).

 

Fig. 2. 2a and 2b) anteroposterior (a) and lateral (b) radiographs of a patient with a history of T7 burst fracture treated with vertebroplasty showing marked local kyphosis. The patient presented with intractable pain despite appropriate non-surgical treatment and paresthesia in his lower extremities.
The MRI (2c) also showed compression of the spinal cord at the level of T7 due to a bony fragment retropulsed into the spinal canal. Figures 2d and 2e – anteroposterior (d) and lateral (e) radiographs after T7 vertebral column resection as well as instrumentation and fusion from T4 to T10 through a posterior-only approach, with restoration of a normal sagittal alignment.

 

Patients affected by insufficiency fractures of the spine are often of advanced age with multiple comorbidities. These must be taken into account when surgery is considered in addition to the location and type of fracture. Thorough assessment and optimisation of the patient’s medical condition and nutritional status are essential for decreasing the mortality rate, improving healing potential and facilitating recovery.

In patients with insufficiency fractures of the spine, it is often preferable to avoid the open anterior approach due to the associated morbidity and increased risk of complications, especially when the diaphragm is taken down. For patients aged > 60 years with multiple comorbidities, the risk of complications is increased further,1 and a posterior-only approach is usually preferred even when anterior decompression is needed (Fig. 2).

The major challenge in the open surgical treatment of insufficiency fractures of the spine is poor fixation in osteoporotic bone (Fig. 3). Pedicle screws are most often used for short segment constructs because biomechanically they provide enhanced strength and rigidity.2 Pedicle screws are associated with the greatest pullout strength when compared to sublaminar hooks and wires.3 However when tested individually, the strength of each pedicle screw is related to bone mineral density, more so than hooks and wires that encircle the bone cortex.3 Therefore, the superiority of pedicle screws over hooks and wires is less marked in highly osteoporotic bone. Other strategies such as cannulated pedicle screws for cement augmentation, pedicle screws with particular thread design, and expandable pedicle screws have been devised to strengthen the fixation in the osteoporotic spine, but have not gained wide acceptance. The use of cement augmentation in vertebral bodies instrumented with pedicle screws can sometimes be beneficial in order to decrease the risk of pullout.4

 

Fig. 3. The same patient as in Figure 1 sustained a fracture of the upper instrumented vertebra four weeks after the initial surgery (3a and 3b). He then underwent revision surgery with proximal extension of the construct up to T8. At two weeks after revision surgery (3c and 3d), he presented for upper wound dehiscence and was diagnosed with pullout of transverse process hooks at T8 and upper endplate fracture at T9. He underwent a second revision surgery to remove the transverse process hooks at T8 and close the wound dehiscence.

 

The other main challenge in the surgical management of insufficiency vertebral fractures is the risk of proximal junctional fracture (Figs 3a and 3b). While stronger spinal fixation is needed in the osteoporotic bone to decrease the risk of implant failure, it comes with the drawback of greater local stress proximally at the upper instrumented and supra-adjacent levels. Accordingly, two types of proximal junctional fractures can occur, either a fracture of the supra-adjacent uninstrumented vertebra, or a fracture of the upper instrumented vertebra potentially associated with supra-adjacent vertebral subluxation.5 In order to decrease the risk of proximal junctional fractures, prophylactic cement augmentation of upper instrumented and supra-adjacent vertebrae has been proposed.4 However, prophylactic augmentation carries the same risks as for any percutaneous vertebroplasty performed without concurrent instrumentation, including the risk of adjacent fracture. Other authors have also proposed using less rigid anchors (hooks or wires) at the top of the construct in an attempt to decrease stress concentration between upper instrumented and supra-adjacent levels.6,7 In order to minimise the risk of proximal adjacent fracture, restoration of adequate sagittal alignment and avoidance of overcorrection in patients with pre-existing sagittal malalignment are important.5

 

This article was originally published in the Canadian Orthopaedic Association’s COA Bulletin #92, Spring 2011 edition.

 

References

1. Faciszewski T, Winter RB, Lonstein JE, Denis F, Johnson L. The surgical and medical perioperative complications of anterior spinal fusion surgery in the thoracic and lumbar spine in adults: a review of 1223 procedures. Spine (Phila Pa 1976) 1995;20:1592– 1599.

2. Jones GA, Kayanja M, Milks R, Lieberman I. Biomechanical characteristics of hybrid hook-screw constructs in short-segment thoracic fixation. Spine (Phila Pa 1976) 2008;33:173–177.

3. Hitchon PW, Brenton MD, Black AG, et al. In vitro biomechanical comparison of pedicle screws, sublaminar hooks, and sublaminar cables. J Neurosurg Spine 2003;99:104–109.

4. Aydogan M, Ozturk C, Karatoprak O, et al. The pedicle screw fixation with vertebroplasty augmentation in the surgical treatment of the severe osteoporotic spines. J Spinal Disord Tech 2009;22:444–447.

5. Watanabe K, Lenke LG, Bridwell KH, et al. Proximal junctional vertebral fracture in adults after spinal deformity surgery using pedicle screw constructs: analysis of morphological features. Spine (Phila Pa 1976) 2010;35:138–145.

6. Hongo M, Gay RE, Zhao KD, et al. Junction kinematics between proximal mobile and distal fused lumbar segments: biomechanical analysis of pedicle and hook constructs. Spine J 2009;9:846–853.

7. Ogawa H, Hori H, Oshita H, et al. Sublaminar wiring stabilization to prevent adjacent segment degeneration after lumbar spinal fusion. Arch Orthop Trauma Surg 2009;129:873–878.