2023 Volume 10 Pages 51-54
We report a rare case presenting radiculopathy caused by unilateral lumbosacral facet abnormality resembling facet interlocking. The patient was a 57-year-old man with no medical and traumatic history. He began to exhibit numbness below his left ankle followed by pain at the left buttock with no obvious causes. He visited our hospital approximately 1 year after the onset of his symptom. Preoperative images revealed a left lumbosacral facet abnormality resembling facet interlocking. His left S1 nerve root was compressed by the dislocated left L5 inferior articular process and bone fragment. His symptom was consistent with left S1 radiculopathy without an obvious stenosis of the left L5 intervertebral foramen; thus, we performed partial facetectomy of the left L5/S1, posterior decompression of the S1 nerve root tunnel, and removal of bone fragment. After the operation, his symptom completely disappeared with satisfactory result. There are several types of congenital facet anomalies in the lumbosacral facet joint; however, congenital unilateral lumbosacral facet abnormality resembling facet interlocking described in this paper has not been reported. His clinical symptom was completely recovered after simple decompression surgery. In this paper, we report the interesting and unique findings of facet abnormality resembling facet interlocking.
Several types of congenital facet anomalies in the lumbosacral facet joint have been reported; however, congenital lumbosacral facet abnormality resembling facet interlocking has not been described. In this paper, we report the interesting and unique findings of unilateral lumbosacral facet abnormality resembling facet interlocking, causing left S1 radiculopathy by compression of the dislocated left L5 inferior articular process and bone fragment.
The patient was a 57-year-old man with no abnormal delivery, medical and traumatic history. He began to exhibit numbness below his left ankle followed by pain at the left buttock with no obvious causes. He visited our hospital approximately 1 year after symptom onset.
Physical examinations showed intermittent claudication for 500 m, lower back pain, and numbness between the posterior side of the left crus and sole. No muscle weakness, sensory disturbance, and abnormal deep tendon reflex were found.
Plain X-ray films showed something abnormal at the left lumbosacral facet region, the details of which could not be confirmed by this examination (Fig. 1A). We could not detect the spinal instability on dynamic flexion and extension X-ray films. Computed tomography (CT) scan showed the left L5 inferior articular process located at the ventral side of the left S1 superior articular process, resembling "facet interlocking" (Fig. 1B). A small bone fragment at the tip of the L5 inferior articular process and hypoplasia of the left S1 pedicle were also noticed (Fig. 1C1-3, D). Magnetic resonance image (MRI) revealed stenosis of the left side of the spinal canal at the L5/S1 level. MRI constructive interference in steady state (CISS) showed the left S1 nerve root compressed toward the medial side by the ventrally dislocated left L5 inferior articular process and bone fragment (Fig. 2A). He was diagnosed as having left S1 radiculopathy caused by the compression of the dislocated left L5 inferior articular process and bone fragment, and we planned decompressive procedure for the left S1 nerve root.
Preoperative images (A, X-ray; B, 3D-CT; and C and D, CT).
Preoperative X-ray shows lumbosacral facet abnormality at the left side (A, white arrows).
Preoperative 3D-CT shows the left L5 inferior articular process dislocated ventrally to the S1 superior articular process, resembling facet interlocking (B; C2, white circle). Bone fragment by the tip of the left L5 inferior articular process (C1; C3, arrowhead), mild spondylosis at the left L5/S1 facet, severe spondylosis at the right L5/S1 facet, and hypoplasia of the left S1 pedicle (D, white arrow) are confirmed via preoperative CT.
Preoperative MRI CISS (A), intraoperative view (right), and the schema (left) (B).
The left S1 nerve is compressed by the dislocated left L5 inferior articular process and bone fragment (A, white circle).
Left L5 inferior articular process dislocated ventral to left S1 superior articular process is intraoperatively confirmed (B).
We performed partial facetectomy of the left L5/S1, posterior decompression of the S1 nerve root tunnel, and removal of the bone fragment, considering there were no spinal instability on preoperative dynamic x-film and no stenosis of the left L5 intervertebral foramen and the difficulty of inserting screw to the left S1 pedicle. Intraoperative findings revealed that the left L5 inferior articular process was located ventral to the left S1 superior articular process (Fig. 2B). The left S1 nerve was compressed by the dislocated left L5 inferior articular process and bone fragment. We could not intraoperatively confirm the site from which the bone fragment originated.
Pathological examinations of the tissue at the left L5/S1 lumbosacral facet, bone fragment, and yellow ligament revealed poor accumulation of inflammatory cells and no obvious abnormal findings.
After the operation, his symptom completely disappeared with satisfactory result. Postoperative images showed decompression of the left S1 nerve on MRI CISS and partial facetectomy and removal of the bone fragment on CT (Fig. 3A, B).
Postoperative MRI CISS (A) and 3D-CT (B).
Postoperative MRI CISS shows decompression of the left S1 nerve (A).
Partial facetectomy of the left L5/S1 and removal of the bone fragment are confirmed via postoperative 3D-CT (B).
Several congenital spinal anomalies and their association with systematic anomalies have been reported.1,2) There are also reports on several types of anomalies at lumbosacral facet joints, such as congenital absence of lumbosacral facet joint3-6) and two separate facet joints on the same lumbosacral facet joint,7) but there are no reports on unilateral lumbosacral facet abnormality resembling "facet interlocking" (Fig. 4).
Schema of congenital anomalies previously reported and in the present case.
A: Absence of lumbosacral articular facet joint due to the absence of the L5 inferior articular process and S1 superior articular process.
B: Two separate facet joints on the same side.
C: Present case.
The apophyseal joints are composed of some tissues including one pair of superior and inferior articular processes. These tissues are derived from embryonic mesoderm,8) but the exact developing process how the normal facing of the superior articular process dorsally and the inferior articular process ventrally has not been well investigated. For the facet abnormality resembling facet interlocking, embryological event to form such apophyseal joint seems to play an important role.
A bone fragment at the tip of the articular process has been reported and is considered the etiological factor.9) The mechanism to form the bone fragment presenting in this case has not been clarified, but such an accessory center of ossification and reactive ossification due to the additional mechanical stress with the affection of this congenital deformity are considered as the etiological factors. As for another possibility, the bone fragment could originate from the abnormally deviated left L5 inferior articular process due to its fracture. In such a consideration, the abnormally deviated left L5 inferior articular process resembling facet interlocking is considered a congenital deformity because of no abnormal delivery, medical and traumatic history. Additionally, hypoplasia of the left S1 pedicle, which was reported as the coexistence of other facet anomaly,5) suggests this abnormality as congenital deformity.
The present case was diagnosed as left S1 radiculopathy caused by the compression of the dislocated left L5 inferior articular process ventrally to the left S1 superior articular process and bone fragment, and partial facetectomy of left L5/S1, posterior decompression of the S1 nerve root tunnel, and removal of the bone fragment were performed. Considering why his symptom appeared over 50 years in spite of congenital abnormality, the mechanical stress to the left L5/S1 facet, indicating mild spondylosis of the left L5/S1 facet and bone fragment, would cause the additional factors compressing the left S1 nerve. After the operation, decompression of the left S1 was confirmed on postoperative MRI and the symptom disappeared. We decided to perform a simple decompressive procedure, considering there were no spinal instability on preoperative dynamic X-ray films and no stenosis of the left L5 intervertebral foramen and the difficulty of inserting screw to the left S1 pedicle because of hypoplasia of the left S1 pedicle.
His symptom completely disappeared, and no recurrence has been found for the short postoperative period, but we should keep a careful follow-up because there are no reports on this congenital facet anomaly resembling facet interlocking.
We report the interesting and unique findings of a rare case presenting radiculopathy due to congenital facet abnormality resembling facet interlocking.
Informed consent was obtained from the patient for the publication of this case report and the accompanying images.
There are no conflicts of interest to declare.
