Key-words:
Achondroplasia - ossification of ligamentum flavum - ossified ligamentum flavum -
spinal canal stenosis
Introduction
Achondroplasia is an autosomal dominant genetic disease that affects the fibroblast
growth factor receptor 3 (FGFR3) gene but also can be found as a new mutation in certain
populations.[[1]] The effect on intracartilaginous ossification during the development of the spine
can result in an unusual anatomy such as thoracolumbar kyphosis, short pedicles, and
a progressive decrease in the interpedicular distance in a craniocaudal direction,
resulting in a narrow spinal canal.[[2]],[[3]] Other findings include an underdeveloped and narrow sacrum. The iliac wings are
also located relatively higher, and the L5 vertebra is deeply sunk below the iliac
wings.[[4]],[[5]]
This abnormal anatomy could make an achondroplastic patient tend to have spinal stenosis
so that the symptoms would present earlier than the normal population at the third
to fourth decade of life.[[6]] Patients with spinal canal stenosis will have symptoms such as intermittent claudication,
nerve root compression, and paraplegia, depending on the level of stenosis. Although
canal stenosis at the lumbar region is commonly found in the normal population, the
imaging of the whole spine is recommended to screen the other regions for pathology
in the achondroplasia patient, as cervical, thoracic, and thoracolumbar spinal stenosis
are also commonly found in these patients.[[7]]
There are multiple causes of spinal stenosis such as degenerative discs, posterior
osteophytes, facet hypertrophy, and hypertrophic ligamentum flavum. The ossified ligamentum
flavum (OLF) is a rare condition that is reported in the Asian and Caucasian populations.[[8]] The developmental mode of OLF was confirmed to be mainly endochondral ossification,
which is also controlled by the FGFR3 gene.[[9]],[[10]] The frequency of intraoperative dural tear is accompanied by dural ossification,
which makes the surgical decompression more technically demanding.[[10]],[[11]]
The gold standard of treatment of spinal canal stenosis is to address the level of
pathology and early decompression of the neural elements; this includes avoiding complications
such as incidental durotomy and spinal cord injury during decompression. Surgical
planning, instrumentation, and patient counseling about complications are important
prior to performing the operation.
This article reports an achondroplasia patient with thoracolumbar and lumbar spinal
canal stenosis caused by abnormal anatomy and OLF.
Case Report
A 52-year-old Thai male with achondroplasia presented with 2 years of leg pain and
intermittent claudication of both legs [[Figure 1]]. A year after, he was unable to walk due to progressive weakness and numbness of
both legs. Physical examination revealed a significantly decreased range of motion
on his back. Manual muscle testing revealed bilateral generalized muscle weakness
on both lower extremities. Manual muscle testing revealed motor muscle power grade
3 of the hip flexors and knee extensors, and grade 4 for ankle dorsiflexion, big toe
extension and ankle plantar flexion. Bilateral paresthesia was found below the L1
level; both legs had hyperreflexia with Babinski and clonus signs which were positive
In addition, there are no muscle weakness and sensory abnormalities on both the upper
extremities. Scapulohumeral reflex (Shimizu), Tromner reflex, and Hoffmann reflex
were negative. These findings indicated that the pathology level of spinal canal stenosis
is cephalad level of L1–L2.
Figure 1: Preoperative image of the patient with typical appearance of achondroplasia with
the stooped posture
A plain radiograph of the lumbosacral spine in the posteroanterior view of the thoracolumbar
spine showed a large pedicle cortex outline and a progressive decrease of the interpedicular
distance from the cephalad to the caudate [[Figure 2]] and [[Figure 3]]. A plain radiograph of the lumbosacral spine in the lateral view also showed large
pedicles that were short in length, and the canal was measured to be <13 mm. We also
found a minimal wedge deformity of the L1 and L2 vertebra. The OLF was seen in the
intervertebral foramen of L3 and L4. Computer tomography (CT) showed OLF varying in
size located at the T10/11 and L1–L5 levels [[Figure 4]], and CT screening of the whole spine including the cervical spine and thoracic
spine revealed no OLF [[Figure 5]]. Sagittal and axial T2-weighted magnetic resonance imaging of the lumbar spine
showed that the thecal sac was severely compressed at T11 posterolaterally by the
OLF and severely compressed at L1–L5 by both the degenerative disc anteriorly and
the OLF posteriorly [[Figure 6]].
Figure 2: Plain radiograph of the lumbosacral spine in the lateral view revealed short pedicles
and ossified ligamentum flavum in the intervertebral foramen of L3 and L4
Figure 3: Plain radiograph of the lumbosacral spine in the posteroanterior view revealed a
progressive narrowing of the interpedicular distance
Figure 4: Preoperative computer tomography parasagittal view revealed an ossified ligamentum
flavum at T10/11 through L5 varying in size. The axial view revealed ossified ligamentum
flavum at the sublamina and facets, causing central and lateral recess stenosis of
T10 and L1-L5
Figure 5: Preoperative computer tomography screening of the whole spine including cervical
spine and thoracic spine revealed no ossified ligamentum flavum
Figure 6: Preoperative magnetic resonance imaging revealed markedly spinal canal stenosis from
T10/11 and L1-L2 to L5/S1. The sagittal view showed multiple lumbar disc degeneration
from L1/2 to L5/S1 with mild posterior bulging. The axial view revealed severe central
and lateral recess stenosis
The operation was performed after proper surgical preparation, which included the
patient and family education regarding a higher than usual chance of perioperative
complications. The patient was in the prone position on a Jackson spinal table. Hypotensive
anesthesia was used during the operation. Pedicular screws were inserted by the freehand
technique with fluoroscope guidance from T10 to S1. Laminectomy and removal of the
OLF were performed at T11 and L1–L5 using a high-speed burr and a Kerrison rongeur
[[Figure 7]]. During surgical decompression, there was an incidental durotomy at L1/2. The dura
mater was repaired with nonabsorbable sutures, fibrin sealant, and a fat pad graft
which were taken from subcutaneous fat. After all pathologies were addressed, the
surgeon rechecked the repaired dura and small-size tear by direct visualization with
the Valsalva maneuver with assistance from the anesthesiologist.
Figure 7: Intraoperative picture after decompression
After initial postoperative care, the plain radiograph of the lumbosacral spine was
taken which revealed a good instrument position [[Figure 8]]. The patient was able to sit and stand with gait aid by the day 7. Bilateral leg
pain dramatically improved immediately after the operation. At 6 months postoperatively,
the patient's motor power gradually improved to Grades 3–4 at L2–L3 bilaterally and
Grades 4–5 at L4–S1. The patient also had a decrease of numbness in both the legs.
He was independently walking with a gait aid.
Figure 8: Postoperative plain radiograph of the lumbosacral spine after decompression and posterior
spinal fusion and instrumentation from T10 to S1
Discussion
In spinal canal stenosis in an achondroplastic patient, the causes to compromise the
canal are not different from the normal population. These causes include degenerative
discs, posterior osteophytes, facet hypertrophy, or ligamentum flavum, and another
contributing cause is thoracolumbar kyphosis from wedge-shaped vertebra. However,
these patients are more susceptible to spinal canal stenosis because of their abnormal
anatomy of the spine, despite having such subtle pathology.[[12]],[[13]]
In an achondroplastic patient, there are abnormalities of intracartilaginous ossification,
resulting from the mutation of the FGFR3 gene. Ossification of the ligamentum flavum
also occurs through intracartilaginous ossification. This may have some correlation,
but the mechanism is still unknown. Previously, in the literature, there have only
been eight achondroplastic cases presenting with spinal stenosis and OLF reported,
with the age ranging from 18 to 58 years, and all patients were the Japanese.[[14]],[[15]],[[16]],[[17]],[[18]],[[19]] The levels of pathology were mostly reported to be thoracic and thoracolumbar,
and only one study reported pathology at the lumbar region. To the best of our knowledge,
this is the first study that reported OLF at the thoracolumbar and lumbar regions.
Myelopathy at the thoracic and thoracolumbar level was commonly found in achondroplastic
patients in contrast to lumbar spinal stenosis in the normal population. Early surgical
decompression is the key to gain better neurologic recovery and pain improvement in
achondroplastic patients with spinal canal stenosis, especially with thoracic or thoracolumbar
stenosis [[Table 1]].
Table 1: Previous case report and this study
Length of fusion and the lowest instrumented level after decompression must also be
considered differently in the achondroplastic patient because of the anatomically
deep sinking of L5 below the intercristal line that makes the lumbosacral junction
quite stable after the fusion.[[21]] The S2 and iliac instrumentation might not be needed in these patients, and this
would result in a smaller surgical wound and less instrumented complications.
The incidence of incidental durotomy during lumbar decompression varies widely among
different authors (1%–17%) depending on many factors such as surgeon experience, type,
and complexity of the surgery, particularly for revision surgery.[[22]] Dural ossification is a common finding in OLF (40%)[[8]] and could lead to iatrogenic tears of the dura during decompression in achondroplastic
patients with spinal stenosis. According to Sun et al., the incidence of dural tears
and cerebrospinal fluid leakage in OLF patients was 32%.[[23]] Therefore, a CT evaluation to identify an OLF and dural ossification is recommended.
In the surgical technique aspect, it is recommended to use a high-speed burr to gradually
thin the lamina before using the Kerrison rongeur to remove the bone, then to recheck
the small size dural penetration and promptly repair the dura tear. These steps are
necessary, and the skill of the surgeon must be considered. Patient and family education
in case of severe perioperative complications such as spinal cord injury, dural tears,
and worsened motor function after surgery is also very important.
Written informed consent was obtained from the patient for publication of this case
report and any accompanying images.
Conclusion
In this report, we described a rare case of achondroplasia with OLF presenting with
progressive myelopathy and claudication symptoms from multiple levels of spinal canal
stenosis. Laminectomy, removal of the ossified ligament, and fusion with instrumentation
resulted in the improvement of the patient's neurological symptoms and function.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form, the patient has given his consent for his images and other clinical information
to be reported in the journal. The patient understands that name and initials will
not be published and due efforts will be made to conceal identity, but anonymity cannot
be guaranteed.
