Current concepts in the management of facet joint dislocations of the cervical spine

Introduction
Facet joint injuries even though very rare, are serious injuries which usually affect the cervical spine. In most cases the lower part of the cervical spine is involved due to anatomical issues. A combination of lower height, smaller anteroposterior diameter of the superior facet, and a more horizontally oriented superior facet at C6 and C7 levels in vivo may explain the predilection of translation relative to one another in the lower cervical spine1. The most common causes for these injuries are high velocity impact accidents like motor vehicle and sporting injuries. The injury mechanism usually involves a combination of flexion or extension in combination with a rotatory component. While the flexion/rotation injury tends to produce facet joint dislocations, the extension/rotation mechanism commonly result in facet fractures with or without dislocations. This has been explained in detail by Allens classification20. Management of cervical facet joint injuries is still controversial in many aspects. This starts from the diagnostic work-up with respect to the timing of an MRI (magnetic reasonance image) scan of the spine and the issue of closed reduction. This article is intended to summarize the current treatment concepts for facet joint injuries of the cervical spine.

Analysis of the problem
In the clinical setting, isolated facet joint dislocations are an exception. Most unilateral facet joint dislocations are associated with at least a fractured facet. This type of facet joint dislocation seems to be less harmful or debilitating than dislocation without a fracture because latter is more likely to injure the spinal cord and may be more difficult to reduce⁴ In this study 50% of the patients with unilateral facet joint dislocation presented with a neurological deficit Frankel A (ie complete pralysis below the level of the injury), whereas in the group with a unilateral facet fracture only 4 out of 28 patients had a significant neurological deficit Frankel C, 12 out of 28 patients were neurologically intact (Frankel E).

There are also coincidental fractures of the spinous process, the lamina, lateral mass and the pedicle/s in any kind of combination -isolated, combined, uni- or bilateral. Therefore a variety of combinations exist. The important question is the stability of the affected motion segment. Bifacet dislocations are unstable regardless of whether it is associated with bony injury or not. Contrary to what was thought previously, unifacet dislocations without bony injury are also considered unstable. In their study, Crawford et al³ investigated the biomechanics of unilateral facet joint dislocation without fracture in a cadaveric model and the biomechanical behaviour of the cervical spine after reduction. They demonstrated that the cervical spine became overtly unstable after reduction.

The decision about the treatment plan will also be influenced by the fact that a certain amount of the facet joint injuries and dislocations are accompanied by injuries and displacement of the disc in the affected motion segment. It has been shown, that disruption of more than half of the annulus fibrosus of the disc (besides other soft tissue injuries) is necessary in the genesis of a unilateral facet joint dislocation¹³. In a prospective study with MRI evaluation before and after closed reduction of cervical spine dislocations, Vaccaro¹⁰ showed that two out of 11 patients had disc herniations before reduction, but 5 out of 9 patients after successful closed reduction. None of the patients suffered neurological harm through reduction despite the persisting or newly developed disc herniation.

Furthermore, the decision about the treatment algorithms will be drastically influenced by the presence or absence of any neurological disturbance and the degree of deficit present clinically. While there is a broad consent about a treatment algorithm for the neurologically severely impaired patient (Frankel A and B), there is still significant controversy about the management of a patient without or only minor neurological impairment. In facet dislocations with Frankel A and B neurological deficit, the patient can undergo immediate reduction to relieve the compression on the spinal cord. However, in the neurologically intact patients there is still an ongoing discussion about the timing of spinal cord imaging with MRI. Whereas some authors insist on MRI-imaging before reduction with respect to the above mentioned problem of potential disc prolapse during reduction or also an already prolapsed disc sitting behind the dislocated vertebra could be pushed posteriorly during the reduction manoeuvre causing neurological injury.There are also authors arguing for an immediate reduction without MRI aiming for an immediate removal of a potentially harmful misalignment of the spine^{11, 12}.

Investigations
The diagnostic work-up should include:

1. Plain x-rays of cervical spine AP and lateral, transoral, if necessary swimmers view.
2. CT (computed tomography) scan of cervical spine from Occiput to T4 to determine the degree of bony injuries. The importance of a computed tomography of the cervical spine in suspected injuries derives from the fact, that in the majority of cases the injury will not be detected to the full extent on plain radiographs. It has been shown that correct diagnosis based on plain radiographs can only been made in 25 % (6 out of 24 patients)14 or in another study¹⁵ in 36% (9 out of 24 patients) of the cases. It is also well known that especially the assessment of the cervico-thoracic junction with plain x-rays is very difficult if not impossible in a lot of patients.
3. MRI scanThere is still ongoing discussion about the timing of a MRI-diagnostic as mentioned above. But under any circumstances imaging via MRI is necessary to judge involvement of the spinal cord and soft tissue and a possible disc prolapse.

Treatment
In any case reduction of dislocation should be achieved first. Authors recommend closed reduction in the awake patient by means of continous axial traction using a scull tong or a halo-ring with increasing weights even over a period over several days⁹ under close neurological and radiological control^8,9,21. Additional manipulative reduction is not recommended. Traction weight up to 140 pounds are reported²², closed reduction could be achieved in 80 - 90% with traction usually below 80 pounds10,21,22. In other studies less successful reduction rates are reported using traction up to 45 pounds^7,8,9. Reasons for abandoning the reduction procedure prior to successful reduction are neurologic deterioration and mechanical reasons like vertebral distraction greater than 1cm at the zone of injury and/or an other location or the belief that further attempts will not warrant successful reduction²¹. If closed reduction is not possible, open reduction must be achieved as further goals of treatment are to preserve functional and anatomical continuity of the spinal cord and nerve roots, restore spinal alignment, establish spinal stability and provide freedom from postinjury pain or delayed neurological problems. Reviewing the literature it is quite obvious that the conservative treatment of facet joint injuries has a high failure rate achieving the above mentioned treatment goals.

In a multicenter study⁶, Dvorak et al. assessed clinical outcome in 90 patients (72 operatively, 18 non-operatively) with unilateral facet fracture, subluxation or dislocation between C3 and C7, and maximally unilateral single nerve root deficit. The authors suggest in their study, that the surgically treated patients have a better outcome concerning pain and disability compared to the conservatively treated group despite suffering a more benign fracture pattern. Beyer et al⁷ showed that surgical treatment had a better outcome clinically and radiographically in analyzing 34 patients with cervical spine injuries. Anatomical reduction was achieved in 60% in the operative group versus 25% in the conservative group. Also fewer patients treated surgically had complained of pain and stiffness. In an other study of 26 patients⁸, 20 patients (76.9%) could not be reduced with traction up to 45 lb. In the same study, ten patients were treated surgically and were pain-free at follow-up even if there had been an incomplete reduction achieved with surgery². Out of the 10 conservatively treated patients with unsuccessful reduction, seven had significant disabling pain which led to secondary surgery in five of the seven patients. Koivikko⁹ analysed 106 consecutive patients with cervical fracture dislocations and compared the results between conservative treatment (51/106) and surgical treatment (55/106). Late deformities and instability were very common in the conservatively treated group and 29% of the patients had to have late surgical stabilization. There was also a correlation between residual displacement and the incidence of late neck pain. Lifeso¹⁷ compared a retrospectively matched group of 29 conservatively treated patients with a prospectively collected patient group of 18 patients treated with anterior cervical decompression and fusion. In only 21% of the patients treated conservatively had adequate results at follow-up, whereas all patients in the operated group had successful treatment.

Therefore we advocate surgical treatment for all patients with facet joint dislocation injuries. The further development of minimally invasive techniques will also support this treatment plan in the future. In his article Wang¹⁶ describes three patients with cervical facet dislocations who were stabilized with a minimally-invasive approach by lateral mass screws, two patients after anterior stabilisation, one patient only with posterior minimally invasive approach with good post-operative results.

Regarding the surgical approach, we advocate anterior decompression and fusion in all cases where MRI scan was not performed after reduction. This is based on the fact of the high incidence of more than 50% of relevant disc injury¹⁹ and the observation of possible disc prolapse after reduction¹⁰. With the anterior discectomy and fusion even an unrecognised new herniation after reduction in the neurologically normal patient will be taken care of. The anterior approach seems to have a lower incidence of neurologic complications vs. the posterior approach (0.64% vs 2.18%) according to a study of the Cervical Spine Research Society¹⁸ in a 5-year survey of 5356 major spine cases. To achieve anatomical alignment it might be necessary to add a posterior reduction and fusion in a patient where there is no complete reduction achievable in the first place.

References

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2. Bono CM, Vaccaro AR, Fehlings M et al: Measurement techniques for lower cervical spine injuries: consensus statement of the Spine Trauma Study Group. Spine 2006; 31; 603 - 609
3. Crawford NR, Duggal N, Chamberlain H, Park SC, Sonntag VKH and Dickman CA; Unilateral cervical facet joint dislocation: Injury mechanism and biomechanical consequences. Spine 2002; 27 (17), 1858 – 1864
4. Argenson C, Lovet J, Sanouiller JL and de Peretti F: Traumatic rotary displacement of the lower cervical spine: Spine 1988, 13 (7), 767 - 773
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6. Dvorak MF, Fisher, CG, et al; Clinical outcomes of 90 isolated unilateral facet fractures, subluxations and dislocations treates surgically and nonoperatively; Spine 2007, 32 (26), 3007 – 3013
7. Beyer CA, Canabela ME, Berquist TH; Unilateral facet dislocations and fracture-dislocations of the cervical spine; J Bone Joint Surg Br 1991; 73, 977 - 981
8. Rorabeck CH, Rock MG, Hawkins RJ and Bourne RB.; Unilateral facet dislocation of the cervical spine. An analysis of the results of treatment in 26 patients; Spine 1987; 12 (1), 23 - 27
9. Koivikko MP, Myllynen P, Santavirta S.; Fracture dislocation of the cervical spine: a review of 106 conservatively and operatively treated patients; Eur Spine J. 2004; 13; 610 – 616
10. Vaccaro AR, Falatyn SP, Flanders AE, Balderston RA, Northrup BE and Cotler JM; Magnetic resonance evaluation of the intervertebral disc, spinal ligaments, and the spinal cord before and after closed traction reduction of cervical spine dislocations; Spine 1999, 24 (12), 1210 - 1217
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17. Lifeso RM and Colucci MA: Anterior fusion for rotationally unstable cervical spine fractures; Spine 2000, 25 (16), 2028 - 2034
18. Graham JJ; Complications of cervical spine surgery; A five year report on a survey of the membership of the Cervical Spine Research Society by the Morbidity and Mortality Committee. Spine 1989; 14; 1046 – 1050
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20. Allen BL, Ferguson RL, Lehmann TR and O'Brien RP; A mechanistic classification of closed, indirect fractures and dislocations of the lower spine; Spine 1982; 7, 1 – 27

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