Achondroplasia is an autosomal dominant disorder that results from a characteristic mutation in the gene encoding fibroblast growth factor receptor 3 [
4]. Achondroplasia is characterized by rhizomelic shortness of the limbs due to abnormalities of endochondral ossification. Spinal stenosis, which was classified as congenital developmental stenosis by Arnoldi
et al. [
5], is commonly identified. The achondroplastic spinal canal is one-third to one-half the size of a normal spine, secondary to decreased interpedicular distance caudally as well as shortened, thickened pedicles and laminae [
2,
6]. Nelson found that approximately 50% of patients with achondroplasia had neurological complications and that the onset of symptoms was common in patients from 30 to 50 years of age [
7]. The neurological impairment was reported to be caused by several factors, including disc degeneration, kyphosis of the lumbar vertebrae, hypertrophy of the ligamentum flavum, bony spurs and thickened laminae and facet joints [
8]. However, OLF has been reported as a cause of symptomatic spinal stenosis caused by achondroplasia in the thoracic spine in only one case [
3]. Suzuki
et al. [
3] reported a case of spinal stenosis caused by achondroplasia with OLF observed at T4/5 and T9 to T12 compressing the thecal sac. OLF is a well-known cause of progressive thoracic myelopathy reported mainly in Asian patients [
9,
10]. The most common site of OLF requiring surgery is the thoracic spine [
11]. The incidence of OLF at the lumbar spine has been reported to range from 8.6% to 11.3% [
12,
13]. A search of the literature identified no reports of OLF in the lumbar spine associated with achondroplasia. To the best of our knowledge, our present case is the first documented report of symptomatic OLF at the site of congenital lumbar spinal stenosis in achondroplasia.
The age at onset in the present case seemed to be older than that in common achondroplasia. The symptoms of lumbar spinal stenosis with achondroplasia usually occur earlier than those without achondroplasia. Although onset depends on the severity of developmental stenosis, age-related degeneration is also involved. In this regard, in our patient, the underlying developmental stenosis was likely not the sole cause of her symptoms, as it was not critical when she was young. Thus, the development of OLF with aging accelerated the severity of spinal canal stenosis, resulting in progressive symptoms requiring surgery at an older age.
Concerning treatment after diagnosis, it is important to decide the optimal timing of surgical intervention for achondroplastic patients with spinal stenosis. In the present case, decompressive wide laminectomy and resection of OLF were performed. Although a wide laminectomy was needed for resection of the adherent OLF, it was technically difficult to obtain a laminectomy that was wide enough because of the congenital narrowing of the spinal canal and the thickened laminae due to achondroplasia. Perioperative complications such as a dural tear are common during multilevel laminectomies in patients with achondroplasia [
14]. Furthermore, decompressive surgery for ossification of the ligament carries an increased risk of dural injury [
15]. In the present case, laminectomy for the severely stenotic spinal canal with adhesions of ossified ligamentum flavum was successfully completed with careful attention to avoid dural damage.