Ligamentum flavum ossification (OLF) is a condition in which the ligamentum flavum bone fertilizer is enlarged and invades the human spinal canal, causing compression of the spinal cord, which is more common in the following thoracic and cervicothoracic segments. Thoracic OLF is the leading cause of thoracic spinal stenosis, accounting for more than 80% of cases, with thoracic disc herniation and posterior longitudinal ligament ossification (OPLL) accounting for 10% each. In 1912, Le Double was the first to propose the thoracic OLF phenomenon. Although only a small number of patients with OLF have clinical symptoms, the rate of paralysis is high, diagnosis is difficult, and the risk of surgery is high, so it should be paid great attention to.
The ligamentum flavum connects adjacent lamina and forms the posterior wall of the spinal canal. The anterior end of the ligament is attached to the anterior inferior border of the lamina, the caudal end is attached to the posterior superior border of the lamina, and the ligamentum flavum fuses with the interspinous ligament at the midline, but leaves a gap for the venule to penetrate. The ligamentum flavum on each side is divided into the interlaminar part and the joint capsule, which fuses with the small joint capsule. The content of elastic fibers in the ligamentum flavum is as high as 60% to 80%, which can be lengthened by 35% to 45% when the spine is in the maximum flexion position, and can be shortened by 10% in the maximum extension position, and it will not cause a protrusion into the spinal canal during extension due to the pretension.
Mechanism of ossification of the ligamentum flavum: may be related to local injury, and the local incidence of severe kyphosis can be as high as 571%, the lower thoracic segment and cervicothoracic segment of the most common sites are stress concentration areas, which also indicates that it is related to injury;Often co-exists with skeletal fluorosis, dish, and ankylosing spondylitis;Associated with metabolic diseases such as diabetes;It is also thought to be a degenerative change with age;This disease is also similar to OPLL, there are racial differences, and it is common for Asians, not only among Japanese people, but also among Chinese.
Ossification of the ligamentum flavum usually occurs at the superior edge of the lamina and the inner edge of the superior articular process, connecting with the limina margin or process. It can occur at any segment of the thoracic spine, mostly at the junction of the thoracothoracic 10 and 12 and cervicothoracic junctions, and in most cases it is multisegmental and can occur adjacent or spaced. According to the degree of ossification, the ossified mass tissue is divided into four zones: ligament zone, cartilage-like zone, calcified cartilage zone and ossified zone. A significant proportion of patients have concomitant disc herniation and OPLL.
The incidence of OLF varies from one company to another, with a Japanese statistic of 116% ~25%。Most patients are over 40 years of age, and the male-to-female ratio is about 2:1. Pain is the most common symptom of thoracic disc herniation;However, thoracic spine OLF and OPLL are chronic spinal cord compression disorders, so pain symptoms are not prominent. The onset is insidious, gradually aggravated, and in the early stage, after only feeling that after walking for a certain distance, the lower limbs are weak, stiff, heavy, inflexible, etc., and they can continue to walk after resting for a while, which is called spinal cord-derived intermittent claudication, which is significantly different from the neurogenic intermittent claudication commonly characterized by pain and numbness in lumbar spinal stenosis. As the disease progresses, there is a feeling of stepping on cotton, difficulty walking, numbness and banding of the trunk and lower limbs, difficulty in urine and urinary defecation, urinary retention or incontinence, sexual dysfunction, etc. Examination is mostly characterized by upper motor neuron lesions, i.e., sensory deficits in the trunk and lower extremitiesWeakened muscle strength and increased muscle tone in the lower extremities;Knee and Achilles tendon hyperreflexia;Positive pathological signs, etc. However, when the lesion is located in the thoracolumbar segment, it may manifest as signs of lower motor neuron damage, that is, extensive muscle atrophy of the lower limbs, decreased muscle tone, weakened or absent knee and Achilles tendon reflexes, and pathological signs cannot be elicitedor concomitant features of upper and lower motor neuron damage in the spinal cord, such as decreased muscle tone and positive pathological signs.
Clinical findings of OLF lie in raising awareness and vigilance. Numbness and weakness of the lower extremities for no apparent reason, or vertebral tract signs, should be considered if cervical and lumbar pathology has been ruled out, thoracic spinal cord compression should be considered. Clear lateral x-rays exclude other thoracic spine disorders, and spinous opacities are found in the posterior part of the foraminumMRI sagittal view shows the spinal canal and identifies the segment of the ligamentum flavum ossification and the degree of compression of the spinal cordCT scan clearly shows the occupancy of the compressed segment and can determine the presence or absence of consolidated OPLLThe absence of MRI signal indicates that the ossification is mature, and the low signal and uneven CT ossification density may continue to grow, providing doctors with the basis for estimating the prognosis.
Spinal stenosis and spinal cord damage caused by OLF should be operated as soon as possible, using "uncovered" posterior spinal wall excision and decompression, including the lamina, ligamentum flavum, and medial articular process1 2. The surgical decompression range should exceed the compression area (LCM) to avoid dural expansion after decompression and compression by the incision edge. If the OPLL is merged, the range of rear decompression should exceed one segment above and below the OPLL.