Background
Fluoride is an important element for bone mineralization. It causes an increase in bone mass by stimulation of the osteogenetic process [
1]. However, over intake of fluoride may cause fluoride intoxication, so-called fluorosis [
2‐
10]. Its typical clinical features include dental fluorosis, diffuse densification of bone, calcifications of bony insertions of many ligaments, discs, and interosseous membranes,
i.e. interosseous of the ribs, forearm, and leg, posterior longitudinal ligament, transverse atlantal ligament, ligamentum flavum, and membrana obturatoria [
8‐
10]. Thoracic spinal stenosis caused by ossification of ligamentum flavum (OLF) is a rare disease [
11‐
20]. However, thoracic OLF caused by skeletal fluorosis is rather rare. Only 6 cases have been reported in the English literature [
3,
13]. The authors' purpose is to evaluate the clinical feature, operative method, and prognosis of thoracic OLF caused by skeletal fluorosis.
Materials and methods
All the patients with thoracic OLF, who underwent surgical management in the authors' hospital from 1993–2003, were retrospectively studied. The cases accorded with the following criteria were included. Diagnostic criteria for fluorosis: epidemic history including a long history living in a high fluorosis area; dental fluorosis; typical X-ray findings including diffuse densification of bone, calcifications of bony insertions of many ligaments, discs, and interosseous membranes, i.e. interosseous of ribs, forearm, and leg; urinalysis of fluoride may increase. Diagnostic criteria for thoracic ossification of ligamentum flavum: typical clinical symptoms and findings which included numbness in the lower limbs and below the relative segment of trunk, motor weakness in the lower extremities and difficulty in walking; physical examination showed increased lower limbs muscle tension, increased in deep tendon reflexes and appearance of pathological reflex, i.e. Babinski sign. X ray, CT scan, and MRI were used to confirm the diagnosis.
For each the patient, A-P view and lateral view X-ray of the thoracic spine were taken. Then thoracic MRI was taken to ensure the diagnosis and identify the involved segments. CT scan was performed for the involved segments. A-P view, lateral view X-ray of forearms and legs and A-P view of the chest were also taken.
Indication of surgery: symptoms and signs of thoracic myelopathy; CT scan and MRI demonstrated significant thoracic canal stenosis; the symptoms and signs correlation with the imaging findings.
En bloc decompression was performed on each patient. In one patient combined with cervical ossification of posterior longitudinal ligament, cervical open door decompression was performed additionally. In one patient combined with lumbar stenosis, lumbar laminectomy decompression was performed additionally.
Preoperative radiographic localization with a Kirschner wire was used to confirm the operative level on the morning of operation day. After induction of general anesthesia, the patient was placed prone with an indwelling bladder catheter. The abdomen was decompressed to avoid excessive epidural bleeding. According to the X-ray localization result, a midline incision was made at the appropriate level and extended to the fascia. Subperiosteal dissection of the paraspinal muscles was performed using electrocautery cutting. The spinous processes were shortened using rongeurs (not totally removed). The laminectomy was performed with high-speed drill. The width of the laminectomy was approximately one third the size of the inside of the facet. After the laminae were totally floated, it was taken off en bloc by holding the residues spinous processes (Fig
4).
The ossified ligamentum flavum often adhered to the dura mater. So, much care should be paid to avoid rupture of the dura mater. Occasionally, the dura mater also ossified. In those cases, we did not take away the ossified dura mater totally, just floated it. When coexistent lesions were present at noncontinuous thoracic levels, clinical symptoms and neuro-imaging findings were examined. The level considered to be the likely cause of clinical symptoms was then surgically treated. When coexistent lesions were present at the cervical or lumbar region, the depression of the relevant region was performed.
The neurological statuses were evaluated with the JOA scoring system of myelopathy preoperatively and at the end point of follow up (table
2). The recovery rate, described by Hirabayashi et al [
21], indicating the degree of recovery of normal function postoperatively, was calculated as follows: (postoperative JOA score – preoperative JOA score)/(11- preoperative JOA score) ×100.
Table 1
Summary of clinical features observed in 23 patients with OLF
numbness and sensory deficit | 22 |
lower-limb weakness and gait disturbance | 21 |
Low-back pain | 8 |
"squeezing tight band" around chest or abdomen | 6 |
neurological claudication | 4 |
leg pain | 12 |
fecal & urinary incontinence | 18 |
knee and ankle hyperreflexia | 18 |
positive patellar and ankle clonus | 14 |
positive Babinski sign | 15 |
Table 2
summary of the JOA scoring system for the assessment of myelopathy
lower-limb motor dysfunction | |
unable to walk | 0 |
Able to walk on flat floor with walking aid | 1 |
Able to walk up/downstairs w/handrail | 2 |
Lack of stability & smooth reciprocation of gait | 3 |
no dysfunction | 4 |
lower-limb sensory deficit | |
severe sensory loss or pain | 0 |
Mild sensory deficit | 1 |
no deficit | 2 |
trunk sensory deficit | |
severe sensory loss or pain | 0 |
Mild sensory deficit | 1 |
no deficit | 2 |
sphincter dysfunction | |
unable to void | 0 |
marked difficulty in micturition | 1 |
minor difficulty in micturition | 2 |
no dysfunction | 3 |
X-ray and CT scan were performed 3 days after the operation to conform the decompression levels and decompression area. X-ray was performed at the end of the follow up to identify whether there was spinal instability.
Statistical analysis
Paired t test was used to analyze the differences between the results before operation and at end of follow up. Multiple linear regression was conducted to determine the quantitative variables best correlating to surgical outcome. ANOVA was used to analyse differences among the three groups according to the duration of preoperative symptom. When the results of ANOVA indicated < 0.05, further statistical analysis was followed to determine whether there was any significance difference between any two groups. The statistical results were analyzed using the Statistical Analysis System (SAS). Significance was accepted for P-values of < 0.05 in all of the above analyses.