Ossification of the posterior longitudinal ligament (OPLL) in the cervical spine and related neurological complications are not uncommon in East Asian countries. The estimated prevalence of cervical OPLL-related hospitalization is 7.7 per 100,000 person-years in Taiwan, and higher incidence rates have been observed in elderly and male patients 3).
Genetic factors are considered to play an important role in the etiology of OPLL based on nationwide pedigree surveys, twins surveys, and human leukocyte antigen (HLA) haplotype analysis 4).
The relationship between single-nucleotide polymorphisms (SNPs) in various genes and OPLL has been studied. A case-control association and sib-pair linkage studies have shown that several genes are related to the suscepti- bility to OPLL. These include genes for collagen, type VI, alpha 1 (COL6A1), collagen, type XI, alpha 2 (COL11A2), bone morphogenetic protein 2 (BMP2), ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), estrogen receptor 1 (ESR1), interleukin-1 beta (IL1B), leptin receptor, and transforming growth factor beta 1 (TGFB1) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14).
The progression of cervical ossification of the posterior longitudinal ligament (OPLL) can lead to increase in the size of the OPLL mass and aggravation of neurological symptoms.
The most characteristic symptom of OPLL is myelopathy resulting from the compression of the spinal cord; other signs and symptoms include sensory dysfunction of the upper and the lower extremities, motor weakness, an in- creased deep tendon reflex, and neurogenic bladder and bowel 15). 16) 17).
OPLL is not a two-dimensional (2D) disease, but rather a three-dimensional (3D) disease. Therefore, conventional measurement of parameters using radiography may not be suitable for evaluating OPLL.
3D method of measurement is superior to the conventional method in terms of evaluating the clinical state of symptomatic OPLL patients. Higher 3D OPLL ratio has an adverse effect on the spinal cord 18).
There are multiple options for managing cervical OPLL, ranging from observation to many kinds of surgical procedures, including posterior laminoplasty, laminectomy with or without fusion, anterior corpectomy with or without instrumentation, and circumferential decompression and fusion. None of these surgical approaches is free of complications. However, to date, there is still a lack of consensus regarding the choice of the surgical approach and the timing of surgical intervention. Cervical SCI and related neurological disabilities are more likely to occur in OPLL patients, who should therefore be cautioned regarding the possibility of a subsequent SCI if treated without surgery 19).
Anterior cervical spine decompression and reconstruction is a safe and appropriate treatment for cervical myelopathy in the setting of single or two level OPLL. Cervical laminectomy or laminoplasty is indicated in patients with preserved cervical lordosis having three or more levels of involvement. Younger patients with good pre operative functional status and less than 2 levels of involvement have better outcome following anterior surgery 20).
Progression of cervical OPLL is associated with younger age, involvement of multiple levels, and mixed-type morphology. OPLL masses that are contiguous with the vertebral body and have trabecular formation are useful findings for identifying masses that are less likely to progress 21).
Although posterior decompressive surgery is widely used to treat patients with cervical myelopathy and multilevel ossification of the posterior longitudinal ligament (OPLL), a poor outcome is anticipated if the sagittal alignment is kyphotic (or K line negative).
Sixty patients with cervical OPLL were included. All underwent an initial CT examination and had at least 24 months' follow-up with CT. The mean duration of follow-up was 29.6 months. Fourteen patients (Group A) had CT evidence of OPLL progression, and 46 (Group B) did not show evidence of progression on CT. The 2 groups were compared with respect to the following variables: sex, age, number of involved segments, type of OPLL, and treatment methods. The CT findings, such as the connection of an OPLL mass with the vertebral body and formation of trabeculation in the mass, were evaluated.
Sex and treatment modality were not associated with OPLL progression. The mean age of the patients in Group A was significantly lower than that in Group B (p = 0.03). The mean number of involved segments was 5.3 in Group A and 3.6 in Group B (p = 0.002). Group A had a higher proportion of cases with the mixed type of OPLL, whereas Group B had a higher proportion of cases with the segmental type (p = 0.02). A connection between the vertebral body and OPLL mass and trabeculation formation were more common in Group B (p < 0.01).
Progression of cervical OPLL is associated with younger age, involvement of multiple levels, and mixed-type morphology. OPLL masses that are contiguous with the vertebral body and have trabecular formation are useful findings for identifying masses that are less likely to progress 22).