Vertebral body strengthening When the mechanical properties of the vertebral body are significantly reduced due to osteoporosis, smaller trauma, or even no trauma, can lead to vertebral fractures. In this case, certain materials can be infused into the vertebral body to enhance its strength and stiffness. This procedure is called vertebral body strengthening. In 1987, Galibert et al. were the first to use this procedure to treat vertebral hemangiomas and called it vertebroplasty. Since then, more and more people have been treated with this procedure for osteoporotic vertebral fractures. In the early 1990s, another technique called vertebral kyphoplasty was introduced in the clinic to reduce the complications of vertebroplasty and to restore the height of the fractured vertebrae. In the first decade of the 21st century, additional techniques such as intravertebral metal bracing emerged, but many of the later techniques did not reach the same level of popularity as vertebroplasty and kyphoplasty. The advent of vertebral body strengthening has had a tremendous impact on the treatment of patients with osteoporotic vertebral fractures. I. Diagnosis of osteoporotic vertebral compression fractures The diagnosis of most osteoporotic vertebral compression fractures is easy. Patients are mostly over 60 years of age, have minor trauma or no trauma, and feel pain in the low back, require bed rest, or have significant limitations in daily activities. Some patients start with mild pain and can get out of bed, but the pain gradually increases. Most patients visit the hospital 2 to 3 weeks after the onset of the disease. Having the patient prone and with muscles relaxed and obvious percussion pain at the spinous process is very useful in identifying the site of the fractured vertebra. Osteoporotic vertebral fractures tend to occur in the thoracolumbar junction region. Therefore, deep percussion pain in the thoracolumbar segment should be highly suspicious of the possibility of vertebral fracture. It should also be noted that the site of pain felt by the patient himself may not correspond to the site of the fracture. In fact, patients with fractures of the thoracolumbar segment often complain of lower back pain. Plain radiographs can diagnose most osteoporotic vertebral fractures, but it may be difficult to diagnose vertebral trabecular fractures in which there are no changes in vertebral morphology. Also, plain radiographs have difficulty in distinguishing whether the fracture is old? or a fresh fracture. At this point, magnetic resonance imaging (MRI) can play an important role. II. Indications for surgery Vertebral body strengthening is mainly used for recent osteoporotic vertebral compression fractures. The fracture is within 3 to 4 months and the patient has no significant effect on conservative treatment measures such as bracing and pain medication. The following factors should be taken into account for treatment with bracing or surgery: the duration of the fracture, the degree of pain, the degree of vertebral height loss, and the patient’s wishes. Once bracing is chosen, the brace should be worn for at least 2 months without changing the choice easily, unless the following conditions occur: unsatisfactory pain control; progressive loss of vertebral height in the first few weeks after the fracture. A CT scan is necessary if there is doubt about the integrity of the posterior wall of the vertebral body prior to vertebral strengthening surgery. Because breakage of the vertebral wall predisposes to leakage of the injected material, CT is superior to MRI in demonstrating breakage of the vertebral wall. for most patients, vertebroplasty or kyphoplasty is no longer indicated 4 months after the fracture. Unless the fracture does not heal or healing is delayed. III. Injection material The most commonly used intravertebral body injection material is a mixture of bone cement, (polymethylmethacrylate PMMA) with a small amount of contrast agent. It can also be mixed with a certain amount of hydroxyapatite. Mixing hydroxyapatite reduces the amount of cement to reduce the stiffness of the cement. Bone cement injected by vertebroplasty will form 2 round-like support blocks within the vertebral body; and bone cement from vertebroplasty will infiltrate into the vertebral trabecular space. IV. Complications The most common complication of vertebral body strengthening is leakage of bone cement through the broken bone cortex or veins. A less common complication is leakage of bone cement into the venous system, with or without pulmonary embolism. Leakage of bone cement can be classified as intradural epidural leakage, intervertebral foramen leakage, intervertebral disc leakage, paraspinal soft tissue leakage, paravertebral vein leakage, and puncture needle tract leakage depending on the site of leakage. Paraspinal leaks, disc leaks and paravertebral vein leaks usually do not cause clinical symptoms, but intradural and foraminal leaks may cause spinal cord and nerve root compression and symptoms. The cement leakage can also be classified according to the route of leakage into three categories: type B, type C, and type S. Type B leakage is the leakage of cement along the basilar vein to the posterior border of the vertebral body; type C is the leakage along the cortical defect of the vertebral body; and type S is the leakage along the intervertebral vein. The overall leakage rate was 29% for PVP and only 8.4% for PKP. The epidural leakage rate was 10.7% for PVP and only 1.2% for PKP; the intervertebral leakage rate was 8.4% for PVP and 4.0% for PKP; and the paravertebral leakage rate was 6% for PVP and 4.6% for PKP. It is generally accepted that there is no direct linear relationship between the amount of bone cement injected into the vertebral body and the pain relief effect. In 2005, Yoon et al. reported two patients with osteoporotic vertebral compression fractures who underwent vertebroplasty and underwent revision surgery because the amount of cement injected was insufficient. In one case, approximately 2-3 ml of bone cement was injected through the unilateral arch; in the other case, 4 ml of bone cement was injected through the arch on one side and 1 ml of bone cement was injected through the arch on the other side, and the injection was terminated due to leakage. We also encountered a 75-year-old female patient who was diagnosed with an osteoporotic compression fracture of the lumbar 2 vertebral body at an outside hospital and underwent retrobulbar kyphoplasty via one side of the arch, after which the pain increased and she had difficulty standing. Biopsy of the lumbar 2 vertebral body showed bone tissue resorption, granulation tissue, fibrosis and sclerosis between bone tissues, and a small amount of cartilage tissue next to the bone. We performed a strengthening plus pedicle screw fixation of the lumbar 2 vertebral body via the other side of the pedicle.