Abstract
Injuries of the cervical spine can be classified into six categories according to a mechanistic system describing the biomechanical deficiencies incurred in a cervical spine injury. However high velocity flexion compression loads cause multiple contiguous and noncontiguous fractures due to multiple force vectors. A universal classification system cannot be applied.
Instability exists if there is greater than 3.5 mm of translation or greater than 11 degrees of angulation as compared to other segments. The degree of ligamentous injury on MRI correlates with instability in patients with lateral mass facet fractures, with rupture of multiple ligaments including the anterior longitudinal, posterior longitudinal, interspinous, or facet capsule. Patients with less than 13 mm of narrowing of the sagittal canal are predisposed to neurologic injury. Vertical compression injuries cause canal occlusion and vertebral column shortening. The timing of surgery in cases of spinal cord injury is controversial. There is no difference in outcome between early (< 72 hours) and late (> 5 days) surgery. However, there remains at least a theoretical benefit to early surgery.
Compression-flexion injuries result in loss of the anterior column by compression followed by the posterior column in distraction. The injury is considered unstable if there is a vertical cleavage fracture of the vertebral body or displacement. Treatment includes a cervical orthosis or halo for minor injuries, depending on the degree of kyphosis. Major injuries with displacement should be treated surgically by anterior corpectomy and plate or an anterior/posterior fusion, depending on the degree of posterior instability.
The most common level of vertical-compression injuries is at the C6 or C7 level. Minimally displaced injuries can be treated with a collar or halo. Fragmentation and peripheral displacement of the bony fragments needs a halo followed by surgery and this may include an anterior corpectomy and plating.
Distraction-flexion injuries may result in facet sub-luxation with less than 25% displacement, or dislocation of one (UFD) or both (BFD) facet joints. When there is 3 mm of translation (25%), the canal is occluded 20–25%. With 6mm of translation (50%), there is 40–50% canal occlusion. MRI can help analyse the soft tissue and ligamentous injuries. In UFD, all posterior ligamentous structures including joint capsule, and half the disc annulus are disrupted. Disruption of ALL and PLL is not necessary to create a UFD. In addition to the posterior structures, the ALL, the PLL and disc are disrupted in BFD. Rupture of the intervertebral disc may include posterior herniation or circumferential disruption. All distraction flexion injuries should be reduced closed. The necessity of a preoperative MRI is undetermined. Preoperative MRI is recommended if there is an unreliable exam due to the patient being uncooperative, if there is neurological worsening with, or failure of closed reduction. If the patient is neurologically intact and closed reduction successful, a posterior cervical fusion is advocated if there is no evidence of an extruded disc on the post reduction MRI. If the closed reduction failed, or MRI indicated, and there is no evidence of a herniated disc, an open posterior reduction followed by fusion is performed. Anterior discectomy with reduction, a graft and a plate is performed for a herniated disc.
Compression-extension injuries fail by compression of the posterior elements followed by distraction of the anterior elements. There are unilateral or bilateral fractures of the laminae/neural arch with degrees of displacement. Undisplaced neural arch fractures can be treated with a cervical orthosis or halo. Displaced neural arch fractures are treated with a posterior cervical fusion.
There are two stages in the distraction-extension injury group. The anterior longitudinal ligament is disrupted with possibly a transverse fracture of the body. With more major injuries, there is a significant displacement injuring the posterior column. Stage 1 injuries can be treated with a halo and Stage 2 with an anterior decompression and fusion with a plating device. There are two stages to lateral flexion injuries. Minor injuries include asymmetric centrum fracture and a unilateral arch fracture. In addition, there is displacement of the body with contralateral ligamentous failure in major injuries. The treatment for Stage 1 is usually a collar while treatment for Stage 2 is usually a posterior cervical fusion.
Posterior stabilization procedures may be performed with wires and cables with or without rods. Posterior clamps usually are not recommended; while plates and screws are preferred. The plates and screws are biomechanically superior to wiring and avoid canal penetration. They are ideal when there is loss of the posterior elements. Pedicle fixation should be considered when operating on the C2 or C7 level.
One in five patients may have complete disruption of vertebral artery blood flow. This occurs most commonly with flexion-distraction or flexion-compression injuries. Vertebral artery evaluation is recommended in patients with flexion injuries and symptoms consistent with vertebral artery insufficiency.
It is important to understand the mechanism of injury; to understand which elements are compromised. We have to get the appropriate imaging studies, we have to be cognizant of the fact that the vertebral artery may be injured, or there may be an associated herniated disc. We have to understand the degree of instability, which dictates the appropriate treatment and we have to understand the risk benefit of the specific internal fixation systems that we use.
The abstracts were prepared by Assoc Prof Bruce McPhee. Correspondence should be addressed to him at the Division of Orthopaedics, The University of Queensland, Clinical Sciences Building, Royal Brisbane Hospital, Herston, Brisbane, 4029, Australia.
