Thoracic spinal stenosis is the narrowing of the lumen of the thoracic spinal canal due to a variety of pathological factors, resulting in compression of the spinal cord or nerves inside the spinal canal and the subsequent development of a series of symptoms. Compared to lumbar spinal stenosis, thoracic spinal stenosis is rare in clinical practice. There are many pathological factors causing thoracic spinal stenosis, the most common being the following two conditions: first, hypertrophy and ossification of the ligamentum flavum, which is involved in the posterior wall of the thoracic spinal canal, and the posterior longitudinal ligament, which is involved in the anterior wall of the thoracic spinal canal; second, herniated thoracic intervertebral disc and ossification of the fibrous ring at the site of the herniation, or the combined presence of osteophytes at the posterior edge of the vertebral body (commonly known as bone spurs), with the herniated part of the disc or bone spurs The herniated part of the disc or spur “encroaches” on the space of the spinal canal and compresses the spinal cord or nerve roots. The second cause is easier to understand, while for the first cause, we need to understand what “ossification” is. Ligaments, in common parlance, are what people call “tendons”, which are soft and flexible. Ligament ossification, on the other hand, refers to the complex evolution of the soft ligament into hard bone under specific pathological conditions. This change is not simply a change in hardness, but a change in nature. Externally, the ligament becomes thicker and harder; from the internal structure, the ligament cells become bone cells, and osteoblasts, Haver’s system, and other tissue structures unique to bone appear, which means that the ligament really changes into a piece of bone. When the ossified ligament thickens and enlarges to a certain degree, it will locally protrude into the spinal canal and compress the thoracic spinal cord, causing lower limb dysfunction or abnormal urinary and fecal functions, which is called thoracic spinal stenosis. So, is ossification and calcification the same concept? The answer is no. Osteosclerosis means that the ligament becomes bone, and pathological examination reveals bony tissue structure, which is a qualitative change; whereas pathological examination of calcification shows that its essence is the deposition of calcium salts, and there are no osteoblasts in its internal structure, while its ligament remains a ligament, and there is no essential change. How can ligament ossification and calcification be distinguished? Preoperatively, the most important differential diagnosis is computer-aided tomography, which is known as CT. CT is an imaging technique to differentiate the density of the lesion, the higher the density, the whiter and brighter the CT film; the lower the density, the darker the CT film. When calcification occurs in the ligament, its calcium salt deposits are sometimes very dense and sometimes more sparse. When its density is high, it can sometimes look very similar to ossification on CT films, and experienced physicians can mostly identify whether it is calcification or ossification, but the most definitive way to identify it is to perform a postoperative pathological examination. In fact, ossification of the ligamentum flavum and ossification of the posterior longitudinal ligament are the most common of the pathogenic factors leading to thoracic spinal stenosis. The ligamentum flavum is located posterior to the spinal cord; the posterior longitudinal ligament is located anterior to the spinal cord. Ossification of the ligamentum flavum accounts for approximately 80% of cases and ossification of the posterior longitudinal ligament for approximately 10% of cases. In the most serious case, ossification of the ligamentum flavum and ossification of the posterior longitudinal ligament exist at the same time, which puts the spinal cord in a dangerous situation of “front and back attack and back-breaking”.