Delayed bilateral facet dislocation at L4-5: A case report.

RATIONALE: Traumatic bilateral facet dislocation in the lumbar (L) spine has rarely been reported. All reported cases were presented with acute facet dislocation. However, we present the first case of delayed bilateral facet dislocation at L4-5. PATIENT CONCERNS: A 34-year-old woman presented with back pain after a head-on collision. The patient was treated conservatively for 3 months with rigid orthosis and activity restriction. Even after this conservative treatment, she continued to suffer from persistent back pain that radiated down her left leg and a progressively kyphotic posture. DIAGNOSES: Initial imaging studies revealed a fracture of the left L5 superior articular process with a posterior ligament complex (PLC) injury. Subsequent radiographs showed the locked facet dislocation with kyphotic changes.
INTERVENTIONS: The patient underwent surgical reduction and fusion, and the operative findings revealed the L4-5 bilateral facet dislocation and rupture of the PLC at the index level. OUTCOMES: After surgical reduction and fusion at L4-5 by posterior interbody fusion, we achieved a satisfactory clinical outcome. LESSONS: Injury of the PLC in the lower lumbar region deserves careful attention for the development of sequelae. The anatomic transition from lordosis to kyphosis, in the lumbosacral region may be related to this type of injury.

Introduction

Traumatic bilateral facet dislocation at L4-5 is extremely rare and to date only 4 cases have been reported (Table 1).[ This dislocation is generally associated with high-energy trauma induced by rapid deceleration such as motor vehicle accidents (MVAs).[ In this regard, all reported cases were presented with acute facet dislocation. To the best of our knowledge, we present the first case of delayed bilateral facet dislocation at L4–5 and discuss the probable pathophysiologic mechanism.

Table 1

Previous case reports.

Case report

A 34-year-old woman without any medical history was the passenger in a head-on collision. She complained of mild low back pain and was neurologically intact. A lumbar (L) spine computed tomography (CT) scan revealed the fracture of the L5 left superior articular process and sacralization of the L5 vertebra. Magnetic resonance (MR) images showed the disruption of the posterior ligament complex (PLC) at L4-5 (Fig. 1).

Figure 1

Initial lumbar spine CT images showing the fracture of the L5 left superior articular process (A) and MR images showing the disruption of the PLC at L4-5 (B). CT = computed tomography, MR = magnetic resonance, PLC = posterior ligament complex.

The patient was treated conservatively at another hospital for 3 months. After the initial 3 weeks of absolute bed rest, she was permitted to ambulate with a lumbosacral orthosis and restricted activity. Even after the conservative treatment, she continued to suffer from persistent back pain that radiated to her left leg and a progressively kyphotic posture. She was transferred to our hospital for further evaluation and treatment. Subsequent radiographs showed wide separation of the L4-5 interspinous space and locked facet dislocation with kyphotic changes (Fig. 2). Subsequent MR images further identified a rupture of the intervertebral disc and PLC. The extruded disc was mildly compressing the left L5 nerve root (Fig. 3).

Figure 2

Subsequent preoperative radiographs showing wide separation of the L4-5 interspinous space and bilateral facet dislocation at L4-5 (arrow head). (A) Lumbar AP view. (B) Lumbar lateral view. (C) Whole spine AP view. (D) Whole spine lateral view.

Figure 3

Subsequent preoperative MR sagittal images showing a rupture of the intervertebral disc (A) and axial images showing PLC and extruded disc mildly compressing the left L5 nerve root (B). MR = magnetic resonance, PLC = posterior ligament complex.

We performed the surgery based on diagnosis of an L4-5 bilateral facet dislocation. The operative findings revealed a rupture of the PLC and severe adhesion of the ligament to the dura at the index level. The L5 superior articular facets were resected in order to reduce the dislocation. Pedicle screw fixation and posterolateral arthrodesis with autologous bone grafts were followed by posterior interbody fusion (Fig. 4). The patient ambulated on second postoperative day and was discharged home without neurologic deficit. The patient reported no low back pain at her 1-year follow-up.

Figure 4

Postoperative radiographs showing reduction of the facet dislocation and restored alignment of L4 and L5. (A) Lumbar AP view (B) Lumbar lateral view. (C) Whole spine AP view. (D) Whole spine lateral view.

This study was approved by the institutional review of board of Seoul St. Mary's hospital (KC17ZESI0255). Informed written consent was obtained from the patient for publication of this case report and accompanying images.

Discussion

Bilateral facet dislocation at L4-5 is extremely rare and, to date, only 4 cases have been reported. All reported cases presented with acute facet dislocation.[ However, in this case, the dislocation developed with a delayed onset.

It is plausible that disruption of the PLC had a significant impact on the delayed onset of the bilateral facet dislocation. The PLC is composed of the facet capsules, ligamentum flavum, supraspinous ligament, and interspinous ligament and is thought to maintain the stability of the spine. Traumatic injury of the PLC can potentially cause spinal instability.[

In addition, Gillespie et al performed a biomechanical study of the effect of the posterior ligaments on spinal stability in a porcine model. The supraspinous and interspinous ligaments are the most significant structures which restrict flexion motion of the lumbar spine.[ Although the PLC is thought to contribute significantly to the stability of the spine, a pathophysiologic mechanism of PLC injury of the lumbar spine is not completely understood.

In most reports, traumatic bilateral facet dislocations have been reported at the lumbosacral junction, which is vulnerable due to its transition from lordosis to kyphosis.[ Lordosis of the lumbar spine makes it difficult for the kyphosis and dislocation to occur following trauma, which may help explain the relative rarity of dislocations at L4-5 compared to lumbosacral dislocations. Interestingly, in our case, the sacralization of L5 vertebra changed the inflection point of lordosis to kyphosis from the lumbosacral junction to L4-5, which may have accelerated the development of the dislocation.

An open reduction of the dislocation may be achieved by resecting L5 superior articular process.[ Intra-operative neuromonitoring is helpful to avoid iatrogenic nerve root injury during the reduction.[ Posterolateral fusion and posterior pedicle screw fixation is the surgery of choice.[ In our case, posterior lumbar interbody fusion was performed due to the spinal instability.

The disruption of the integrity of PLC combined with anatomic transition from lordosis to kyphosis in the lumbosacral region may have altered the biomechanics of the lower L spine, resulting in the delayed bilateral facet dislocation. Patients who have experience this type of trauma should be watched closely for the development of delayed dislocation. If such a delayed dislocation does occur, our experience demonstrates that satisfactory clinical outcomes may be achieved through surgical reduction and posterior interbody fusion of L4-5.

Author contributions

Conceptualization: Hyung-Youl Park.

Funding acquisition: Hyung-Youl Park.

Investigation: Hyung-Youl Park, Sang-Il Kim, Hyung-Ki Min, In-Soo Oh, Jun-Yeong Seo, Dong-Gune Chang, Mohammed Ali Alhazmi, Joon-Hyung Cho.

Supervision: Kee-Yong Ha, Young-Hoon Kim.

Writing - original draft: Hyung-Youl Park.

Writing - review & editing: Kee-Yong Ha, Young-Hoon Kim.