Unilateral hypoplastic facet joint

A 34-year-old female presented with on and off lower back pain for four years, associated with occasional right-sided sciatica symptoms. It was aggravated after childbirth. There was no associated weakness, numbness of the extremities or sphincter dysfunction. The physical examination was unremarkable. The patient had a surgical history of caesarian sections and laparoscopic cholecystectomy.

Magnetic resonance imaging of the lumbar spine revealed a multilevel diffuse disc bulge, more pronounced at the level of L5-S1 causing bilateral foraminal narrowing and abutment of L5 nerves (Figure 1).   

There was a hypoplastic appearance of the right facet joint of L5-S1 level with hypertrophy and mild sclerosis of the contralateral facet joint. There was no surrounding muscle and fat plane disruption to suggest any infection and old or recent spine surgery (Figure 2 and 3).

Background

The facet joint, also called the zygapophyseal or apophyseal joint, is a synovial joint formed between the superior articular process of a vertebra and the inferior articular process of the other vertebra immediately above. Anatomically, they are situated between the pedicle and the lamina of the same vertebra. The posterior ligamentous complex strengthens the vertebral columns and stabilizes the facet joints of the adjacent vertebrae.

The bilateral facet joints, along with intervertebral discs, are responsible for transferring weight and direct and limit motions in the spine due to their biomechanical function(1).

Clinical Perspective

Facet joint syndrome is an entity in which structural or mechanical abnormalities of the facet joints can cause back pain. It is the common cause of lower back pain with the prevalence of 15-41%(2).

The factors that contribute to the degeneration of the facet joint are multiple, including osteoarthritis, secondary to inflammation or trauma or subluxation (2).

The unilateral hypoplastic facet joint is a rare condition that leads to facet joint syndrome. The exact aetiology of this anomaly is still unclear but is thought to be the result of a failure of ossification and impaired ossification due to insufficient blood supply in fetal life (3).

Imaging Perspective

The congenital hypoplastic facet joint and pedicle can be seen on conventional radiographs as an absent pedicle with associated abnormal enlargement of the neural foramen. Multidetector Computer Tomography and Magnetic Resonance Imaging demonstrates additional findings such as small anteriorly displaced transverse process, hypoplastic pedicle and facet joint, tilt of the spinous process and contralateral facet joint or pedicle hypertrophy and sclerosis (4). However, not all the cases will show the additional features and will present as isolated finding of unilateral hypoplastic facet joint and pedicle.

Outcome

Numerous anatomic variations and congenital anomalies in the neural arch and its process can affect the ossification process. Most of the patients are asymptomatic and these findings are incidentally noted on imaging for another cause. Some of the variations and anomalies can cause symptoms and  the diagnosis is made on the imaging to rule out fracture, dislocation or degenerative changes.

Unilateral hypoplastic facet joint is a rare cause of the chronic back pain. If this is an isolated finding, conservative therapy is usually recommended. However, if there is associated disc herniation or canal stenosis, orthopedic surgery should be sought if the condition is debilitating.

Take-Home Message / Teaching Points

Unilateral hypoplastic facet joint is uncommon but should be considered as possibility if the patient has chronic back pain.

Written informed patient consent for publication has been obtained.