Surgical outcome of locked facet in distractive flexion injury of the subaxial cervical spine: Single institution retrospective study

1. Introduction

Distractive flexion injury (DFI) is the most common injury mechanism of the subaxial cervical spine, caused by a combination of anterior column compression and posterior column distraction.[1] Allen first described the current biomechanical aspect and injury pattern of DFI in detail.[2] In severe DFI, the facet joint can be subluxated or dislocated unilaterally or bilaterally. Although facet subluxation/dislocation is usually reducible preoperatively by traction maneuvers, subaxial cervical spine facet joint dislocations are difficult to reduce when complicated by posterior facet fractures or ligamentous injury.[3,4] In particular, surgical treatments are required for cases with a locked facet (LF), which is defined as a subluxation/dislocation that is irreducible preoperatively, even at a maximum load of skeletal traction, or for which further traction is impossible because of worsening neurologic symptoms.[5] Although the DFI treatment has been previously introduced,[6,7] the treatment option for such locked facet distractive flexion injury (LF-DFI) remains controversial, and the optimal strategies and approaches to reduce the LF have not been fully evaluated. The joystick maneuver via the anterior approach or open reduction via the posterior approach are the current reduction options. An anterior approach is generally considered to be safe in the case of patients with traumatic herniation of the nucleus pulposus (HNP).[6–8] However, other studies have reported that a posterior approach with or without HNP does not cause neurologic worsening.[9,10] In this case series, we analyzed the surgical outcomes of patients with LF-DFI, with a particular focus on the surgical approach and reduction maneuver.

2. Methods

This study was approved by the Institutional Review Board of our institution (approval number 2022-06-031). We retrospectively analyzed patients who underwent surgical treatment for DFI at a single institution between November 2006 and April 2021. After excluding patients with reducible subluxated/dislocated facet joints, we examined clinical outcomes, including the American Spinal Cord Injury Association (ASIA) scale score, radiological changes, and postoperative complications. We could not assess the risk of postoperative neurologic deterioration in 1 patient who had been preoperatively classified as ASIA scale A; therefore, the patient was excluded from this study. We also excluded patients with impaired mental status because their neurologic status could not be assessed perioperatively.

Before undergoing closed reduction, all patients with DFI of the subaxial cervical spine underwent preoperative magnetic resonance imaging (MRI) to determine the presence of HNP, thereby avoiding any cord compression by the disc fragment after reduction. Closed reduction was attempted in patients who were mentally alert with identifiable changes in neurologic symptoms.

Patients with LF-DFI were divided into 2 groups based on their initial surgical approach. The anterior-first patients underwent an anterior approach that involved open reduction with distraction using a Cobb retractor and joystick maneuver, if necessary, followed by discectomy and interbody fusion with an allogenic bone graft or cage. The posterior-first patients underwent a posterior approach that involved open reduction by removing the superior portion of the superior articular facet that was obstructing subluxated/dislocated facet joint reduction, followed by posterior instrumentation and additional anterior cervical discectomy and fusion, if necessary.

All patients wore a Philadelphia neck collar for 4 weeks after surgery. Plain radiographs were obtained regularly after surgery. During the follow-up period, complications such as infection and wound dehiscence were confirmed, and the final plain radiograph revealed nonunion, cage subsidence, and screw loosening.

All statistical analyses were performed using Statistical Package for Social Sciences (version 25.0; IBM Corp., Armonk, NY). Values are presented as the mean or mean ± standard deviations. Fisher exact test used to compare the initial anterior and posterior approach groups. A P < .05 was considered to indicate statistical significance.

3. Results

Based on the exclusion criteria, 12 patients with LF-DFI were enrolled in this study. All patients were men, with a mean age of 52.1 years (Table 1). The mean duration of follow-up was 19.9 months. Patients were injured at the following levels: C3-4 for 1 patient, C4-5 for 5 patients, C5-6 for 3 patients, and C6-7 for 3 patients. According to the Allen classification of subaxial cervical spine injury, there were no stage 1 or stage 4 cases in this study.[2] Six patients each had unilateral and bilateral facet dislocations. Regarding the initial surgical approach, 4 and 8 patients underwent the anterior and posterior approaches, respectively. Anterior fusion was performed following discectomy in 4 patients. In contrast, posterior fixation or fusion was performed in 8 patients, followed by additional anterior fusion on the same day in 7 of these patients. The cohort included 8 patients who had HNP without any significant cord compression. Table 2 presents the perioperative ASIA scale scores. The preoperative ASIA scale scores of the patients were as follows: A for 1 patient, B for 1 patient, C for 3 patients, D for 4 patients, and E for 3 patients. Ten patients showed no neurologic deterioration after surgery, whereas 2 had aggravated neurologic status. Of these 2 patients, 1 patient showed deterioration in scores from E to D, whereas the other showed deterioration from D to C, and both patients underwent an initial anterior approach. There was a marginal statistically significant difference between the 2 approaches in terms of change in neurologic status (P = .054). At the final follow-up, all patients achieved radiological fusion. Other than neurologic deterioration, no complications were detected.

Table 1 - Patient demographics with radiologic, surgical, and neurologic status. Case Sex Age Injury level Facet dislocation DF stage Initial approach Fusion HNP Initial ASIA Final ASIA Injury mechanism Interval between trauma and surgery (h) 1 Male 48 C6–7 B III P Both X C D TA 33 2 Male 56 C4–5 U II P Both O D D Direct blow 13 3 Male 52 C5–6 U II P Both O D D FFH 8 4 Male 64 C6–7 B III P Both O B B FFH 6 5 Male 66 C3–4 U II P Both O E E FFH 25 6 Male 54 C4–5 U II P Both X C D TA 25 7 Male 22 C4–5 U II P Both O D D TA 5 8 Male 36 C5–6 B III A Anterior O B B TA 21 9 Male 34 C4–5 U II A Anterior O E E TA 7 10 Male 75 C4–5 B III A Anterior O E D TA 22 11 Male 52 C7–T1 B III P Posterior X C D TA 15 12 Male 67 C5–6 B III A Anterior X D C Slip down 11

A = anterior, ASIA = American Spinal Cord Injury Association, B = bilateral facet dislocation, DF = distractive flexion injury, FFH = fall from height, HNP = herniation of nucleus pulposus, P = posterior, TA = traffic accident, U = unilateral facet dislocation.


Table 2 - Clinical outcomes and radiologic findings grouped by initial approach. Anterior approach Posterior approach P value Neurologic change .054  Deterioration 2 0  No deterioration 1 8 HNP 1  Present 3 5  Absent 1 3 Facet dislocation .545  U 1 5  B 3 3 Complications* 0 0

B = bilateral facet dislocation, HNP = herniation of nucleus pulposus, U = unilateral facet dislocation.

* Nonunion, infection, wound dehiscence cage subsidence, screw loosening.


4. Discussion

The optimal treatment for acute traumatic cervical spine subluxation injuries remains controversial. Closed reduction using Gardner–Wells skull tong traction has been reported to be safe and effective for traumatic cervical dislocations.[11] With the increasing availability of MRI facilty across hospitals, patients progressively tend to undergo prompt prereduction MRI; thus, the reported incidence of traumatic HNP has increased from < 5% to approximately 40%.[11–13] Although some studies have reported a risk of neurologic deterioration after closed reduction of cervical spine injuries with traumatic HNP,[14,15] no patient in our series presented with neurologic aggravation after closed reduction. Thus, we concluded that closed reduction is feasible for treating cooperative and alert patients, even those with disk herniation detected by prereduction MRI. Nevertheless, in the case of LF-DFI, it is important to perform surgical intervention for reduction and stabilization. The current trend is to confirm the presence of traumatic HNP before undergoing surgery.[6] However, in the case of patients with HNP and significant cord compression, removing the ruptured HNP via an anterior approach may be more rational. Surgeons must exercise caution to avoid spinal cord injury while distracting the vertebral bodies with a Casper pin or any other device that may also cause nerve tissue distraction.

The term “locked facet” was originally used for DFI stage 2, a unilateral facet dislocation interchangeable with interlocked facet or facet luxation.[2] However, most LF stage 2 DFI cases in our series were reducible preoperatively by Gardner–Wells tongue traction using weight or manual force. Weights were added in increments until the patient could withstand the weight. Manual traction was performed in the operating room, where urgent surgery could be performed if an acute neurologic exacerbation occurred during the maneuver. Although the DFI stage reflects the severity of the injury, we assumed that the initial degree of force, facet arthrosis, soft tissue integrity, and cervical alignment were additional factors that influence the reducibility of facet subluxation/dislocation. Further studies are warranted to evaluate the potential factors for an actual LF.

In our study, no patients who underwent an initial posterior approach experienced neurologic deterioration. All 12 patients with LF were men. We believe that the soft tissue tension by the muscle, which is generally greater among men, may contribute to such a bias. As expected, most patients were admitted following a high-energy injury, such as a car accident. Open reduction was performed in all 8 patients who underwent the posterior approach by removing the upper portion of the superior articular facet (Fig. 1). Resection of the superior articular facet allows for gentle or automatic reduction of the bony structures without any distractive force to the nerve tissues (Fig. 2). A previous study revealed that posterior open reduction had positive clinical and radiological outcomes in patients with fracture-dislocation, even when accompanied with disk herniation.[9,10] In contrast, 2 of the 4 patients who underwent an initial anterior approach experienced neurologic deterioration after surgery. One of the remaining 2 patients exhibited improved neurologic symptoms, whereas the other showed no change in symptoms. Two patients with worsening neurologic symptoms underwent open reduction using a Cobb elevator to distract the vertebral bodies (Fig. 3). Such distraction was required for reduction, allowing the dislocated inferior facet to migrate over the tip of the superior facet. However, because the cord is compromised before reduction, this maneuver may be harmful to the spinal cord due to distraction injury (Fig. 4). Spinal cord ischemia owing to vascular compromise and direct traction-induced spinal cord tract disturbances may cause distraction spinal cord injury.[16]

F1Figure 1.:

Intraoperative view of the locked facet. The blue-shaded superior facet of the lower vertebra overrides the yellow-shaded superior facet of the upper vertebra and prevents the reduction of the dislocated facet joint.

F2Figure 2.:

Preoperative and postoperative computed tomography scans reveal the superior part of the superior articular facet that was removed using the posterior approach. PRE = preoperative, POST = postoperative.

F3Figure 3.:

Intraoperative C-arm image representing the distraction of the vertebral bodies using a Cobb elevator.

F4Figure 4.:

Preoperative sagittal MRI showing severe cord compression at the dislocated C5–6 level. MRI = magnetic resonance imaging.

A previous animal study demonstrated that axial tension of the spinal cord caused a histologic injury.[17] In a rat study, distraction caused considerable tissue enlargement and structural alteration in the white matter as well as the most extensive lesion cavity, particularly in the dorsal white matter.[18] Another potential disadvantage of an anterior approach is that the patient may require additional posterior surgery if there is an obvious posterior ligamentous injury or anterior implant failure in a biomechanical aspect of the construct.[19]

There are some limitations in this study. First, the study was conducted retrospectively at a single institution. There may be a risk of implicit bias due to the surgeon skill or preferred technique. Second, due to the small number of patients included, there are statistical limitations. Upon comparing the 2 approaches in terms of neurologic aggravation after surgery, the P value was .054, which is not statistically significant in the conventional manner. However, no complications, such as nonunion, infection, wound dehiscence, malalignment, cage subsidence, or screw breakage, were reported.

In conclusion, whereas anterior reduction of LF-DFI by axial traction or retraction of vertebral bodies may cause iatrogenic distraction cord injury, gentle reduction by removing the superior part of the superior articular facet via a posterior approach would be safer in terms of avoiding intraoperative cord injury.

Acknowledgment

The authors would like to thank Enago for the English language review.

Author contributions

Conceptualization: Eugene J. Park, Woo-Kie Min.

Data curation: Kang-San Lee, Eugene J. Park.

Formal analysis: Kang-San Lee, Eugene J. Park, Woo-Kie Min.

Investigation: Kang-San Lee, Woo-Kie Min.

Methodology: Woo-Kie Min.

Project administration: Kang-San Lee.

Supervision: Eugene J. Park, Woo-Kie Min.

Validation: Woo-Kie Min.

Visualization: Kang-San Lee, Eugene J. Park, Woo-Kie Min.

Writing – original draft: Kang-San Lee.

Writing – review & editing: Eugene J. Park, Woo-Kie Min.

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