Osteoporosis increases the risk of vertebral fractures primarily because it causes bones, including the vertebrae in the spine, to become weak, porous, and fragile. This fragility makes the vertebrae much more susceptible to breaking under stresses that healthy bones would normally withstand without injury.
At the core of osteoporosis is an imbalance in the bone remodeling process. Normally, bone tissue is constantly broken down by cells called osteoclasts and rebuilt by osteoblasts, maintaining a healthy, strong bone structure. In osteoporosis, this balance is disrupted: osteoclasts break down bone faster than osteoblasts can rebuild it. This leads to a loss of bone mass and deterioration of the bone’s internal microarchitecture. The bones become less dense and more porous, losing their strength and resilience.
The vertebrae are particularly vulnerable because they bear much of the body’s weight and are involved in many movements like bending, twisting, and lifting. When osteoporosis weakens the vertebrae, even normal daily activities or minor stresses—such as bending forward, coughing, or sneezing—can cause the front part of a vertebra to crack and collapse. This type of injury is called a vertebral compression fracture.
These fractures often occur through a mechanism called flexion-compression. This means that when the spine bends forward (flexion) and pressure is applied (compression), the weakened vertebral body can collapse, often forming a wedge shape. This collapse reduces the height of the vertebra and can cause the spine to curve abnormally, leading to a hunched posture known as kyphosis.
The structural deterioration in osteoporosis involves both the loss of bone mass and the breakdown of the internal lattice-like framework of the bone. This micro-architectural damage means that the vertebrae lose their ability to distribute mechanical loads evenly. Instead, stress becomes concentrated in weaker areas, increasing the likelihood of fractures.
Hormonal changes, especially the decrease in estrogen levels after menopause, play a significant role in accelerating bone loss. Estrogen normally helps regulate bone remodeling by inhibiting excessive bone resorption. When estrogen levels drop, osteoclast activity increases, leading to faster bone breakdown. Additionally, deficiencies in calcium and vitamin D impair the bone’s ability to rebuild, further weakening the vertebrae.
At the cellular level, the RANK/RANKL/OPG signaling pathway is crucial in controlling osteoclast formation and activity. In osteoporosis, this pathway becomes dysregulated, often with increased RANKL or decreased osteoprotegerin (OPG), tipping the balance toward more bone resorption. Inflammatory cytokines like interleukin-1, interleukin-6, and tumor necrosis factor-alpha also enhance osteoclast activity, contributing to bone loss.
Once a vertebral fracture occurs, it can destabilize the spine and alter its biomechanics. The fractured vertebra loses height and strength, which can increase the load on adjacent vertebrae, making them more prone to subsequent fractures. This cascade effect can lead to multiple vertebral fractures over time, worsening spinal deformity and pain.
Vertebral fractures caused by osteoporosis are often painful, especially in the acute phase, and can cause chronic back pain, reduced mobility, and loss of height. The deformity from multiple fractures can compress internal organs and impair lung function, significantly affecting quality of life.
In some cases, vertebral fractures can be unstable, involving not just the front part of the vertebra but also the middle and posterior columns of the spine. These more severe fractures may involve rotational or shear forces and can disrupt ligaments and joints, potentially leading to neurological complications.
Because osteoporosis-related vertebral fractures can occur with minimal trauma, prevention and treatment focus on strengthening bone through medications that inhibit bone resorption or stimulate bone formation, ensuring adequate calcium and vitamin D intake, and lifestyle measures like weight-bearing exercis
