Short-segment posterior fixation with index level screws versus long-segment posterior fixation for thoracolumbar spine fracture: angle of correction and pain

Thoracolumbar fractures occur when the vertebra is subjected to a significant axial and possibly flexion force vector that brings the failure of the anterior vertebral body in compression. This region (T10–L2) is uniquely susceptible to this mechanism of injury as a result of its location between the stiff kyphotic thoracic spine and the more mobile lordotic lumbar region [1].

The successful diagnosis and management of thoracolumbar fractures depend on an accurate assessment of spinal stability and the neurologic state of the patient [2].

As a simple and commonly used technique, short-segment pedicle instrumentation of thoracolumbar instability seems to have a high rate of implant failure and recurrence of instability. In the literature, there are biomechanical studies aimed to determine the effect of adding pedicle screws at the level of a burst fracture [3].

Data obtained from those studies suggested that the use of transpedicular screws at the fractured level provides the advantages of a stiffer construct, an increased biomechanical stability, and the effect of 3-point fixation of the unstable segment guard against failure of the construct [4].

Currently, short-segment pedicle instrumentation for thoracolumbar fractures is gaining popularity. Otherwise, long-segment fixation may be chosen as another treatment method [5].

The aim of this study was to compare between short-segment posterior stabilization including index level versus long-segment posterior stabilization for management of thoracolumbar spine fracture instability as regards post-operative pain and angle of correction.

This is a prospective study which was performed in the period between February 2012 and February 2016. Patients included in this study had thoracolumbar spine instability including wedge fracture or burst fracture with Thoraco-Lumbar Injury Classification and Severity (TLICS) score ≥ 4 and fulfilling the study inclusion criteria which were (1) single-level fracture, (2) less than 50% of spinal canal compromised, (3) mild kyphosis or scoliosis, Cobb’s angle ≤ 25°, and (4) with or without neurological deficit.

The exclusion criteria were patients with multiple-level fractures, patients with more than 50% spinal canal compromise, patients who needed anterior approach to decompress the canal, and those who have fracture dislocation and/or marked kyphosis and scoliosis with Cobb’s angle > 25°, who needed 360° fixation with long-segment fixation to maintain the angle of correction.

Ninety-one patients were carefully selected, randomly grouped (per surgeon preference), and operated after obtaining the ethical approval from the local ethical committee. Forty-four patients underwent short-segment posterior stabilization including index level (fractured level), and the other 47 underwent long-segment posterior stabilization skipping the index level.

Short-segment approach

After exposure of laminae and facets of the index level with one level above and one level below, the trans-pedicular screws have been inserted under C-arm guidance in biplanar technique to all three levels. Laminectomy was done to decompress the canal if needed then postero-lateral fusion using bone graft was done Fig. 1. Cross connectors were not used in such short construct with screws in index levels.

Long-segment approach

After exposure of the laminae and facets of the index level with two levels above and two levels below, the trans-pedicular screws have been inserted under C-arm guidance to the above and below levels sparing the index level. Then, laminectomy and lateral fusion had been done like in short-segment approach Fig. 2. Cross connectors were used in only two patients over the index level in osteoporotic patients.

Ninety-one patients were included in this study: 80 males (87.9%) and 11 females (12.1%) with a mean age 38 ± 9 years. The highest incidence of thoracolumbar vertebrae fracture was at the level of L1 (37.7%) then L2 (29.6%) followed by D12 (23%) and least incidence in D11 (6.6%) and D10 (3.3%).

The type of fractures were variable, 38 patients presented with burst fracture (41.75%), 26 patients with wedge fracture (28.57%), 15 patients had hyperextension fractures (16.48%), and 12 patients with shears fracture (13.18%). Most of burst and wedge fractures were due to falling from a height while most of hyperextension and shears fractures were due to road traffic accident.

The Oswestry Disability Index (ODI)

The mean pre-operative ODI in the short-segment fixation group was 34.66 ± SD 26.92, while it was 41.49 ± SD 22.09 in the long segment group. Both groups have shown a statistically significant changes in the mean ODI scores at the 1 year follow-up period with (P value = 0.000) in both groups (Table 4 and Fig. 3).

Paired sample test
	Paired differences					t	df	Sig. (two-tailed)
	Mean	Std. deviation	Std. error mean	95% confidence interval of the difference
				Lower	Upper
short_segment	10.45455	9.38939	1.41550	7.59991	13.30918	7.386	43	.000
long_segment	9.78723	10.05190	1.46622	6.83589	12.73858	6.675	46	.000

Traumatic spinal fractures of the thoracolumbar area represent approximately 90% of all spinal fractures; these injuries can result in loss of neurological function, pain, disability, and deformity, and represent a great economic burden to society [6].

Although short-segment stabilization approach, one level above and one level below, has high failure rate, it become preferred approach after renovation by addition of screws into the fractured level (index level). Several studies were done to ensure biomechanical stability of this short construct, and most of studies revealed its low failure rate and high pull out resistance [7].

In a prospective, randomized study of 80 patients, Farrokhi et al. in 2010 found that placement of pedicle screws into the pedicles of the fractured level during short-segmental fixation for thoracolumbar fractures led to better kyphosis correction, fewer instrument failures, and comparable or better clinical outcomes [8].

Eno et al. in 2012 found that pedicle screw fixation at the fractured level did not achieve greater correction of the segmental kyphotic angle compared to conventional intersegmental fixation; however, pedicle screw fixation more effectively restored the height of the fractured vertebra. Recovery of height is as important as the recovery of the angle, and it is helpful for the recovery of the integrity in the adjacent segments and the whole spine [9].

Interestingly, the additional pedicle screw fixation (six-screw fixation) at the fractured vertebra allowed patients to ambulate approximately 10 days earlier than patients who underwent conventional four-screw intersegmental fixation [10]. On the other hand, our study results revealed that pedicular screws into the fracture level in short-segment fixation can correct the kyphotic angle provided that kyphotic angle range from 10° to 25° with minimum correction angle 4° and maximum correction angle 14°.

Adding bilateral index level screws to short-segment fixation increased the stability of the construct by 25%. The increase in stability was significant during flexion and lateral bending [11].

In vitro burst fracture model with pig spines was done to compare short fixation (so-called one above–one below) with short fixation plus intermediate screws. They found that intermediate screws significantly decreased segmental flexibility in all axes of motion by an average of 26%. The reduction in flexibility was least prominent during axial rotation [12].

There is no superiority of long-segment over short-segment stabilization with index level screws in the correction of kyphotic angle and maintaining sagittal plane. Moreover, short-segment stabilization has faster relief of pain, lesser tissue destruction than long segment with the same biomechanical stability.