From the Guidelines
Bone remodeling under stress occurs through a complex process involving increased osteoclastic activity that exceeds the rate of osteoblastic new bone formation, resulting in bone weakening and microtrabecular disruption. This process is described in the 2024 update of the ACR Appropriateness Criteria for stress fractures, which highlights the two varieties of stress fractures: fatigue fractures and insufficiency fractures 1.
Key Points
- Repetitive overloading leads to increased osteoclastic activity, exceeding the rate of osteoblastic new bone formation, resulting in bone weakening and microtrabecular disruption 1.
- This process can eventually lead to a cortical break, resulting in a stress fracture, which accounts for up to 20% of all injuries seen in sports medicine clinics 1.
- Certain medical interventions, such as radiation therapy and long-term osteoporosis treatment with bisphosphonates, predispose patients to the insufficiency variation of stress fractures 1.
Bone Remodeling Process
The bone remodeling process under stress involves the coordinated response of osteocytes, osteoblasts, and osteoclasts. Osteocytes detect mechanical signals and initiate a response, activating osteoblasts to deposit new bone tissue and osteoclasts to remove bone from areas experiencing less stress.
Clinical Implications
Understanding the bone remodeling process under stress is essential for preventing and managing stress fractures, particularly in athletes and individuals with certain medical conditions. Regular weight-bearing exercise can stimulate the bone remodeling process, helping to build and maintain bone density throughout life. However, excessive stress on the bone can lead to fatigue fractures, highlighting the importance of proper training and injury prevention strategies.
From the Research
Bone Remodeling Under Stress
- Bone remodeling is a continuous process that ensures the mechanical integrity of the skeleton and plays an important role in calcium homeostasis 2.
- This process involves the activation of several different stem cell populations and the regulation of two contrasting processes: bone resorption and bone formation 2.
- Mechanical forces are indispensable for bone homeostasis, and skeletal formation, resorption, and adaptation are dependent on mechanical signals 3.
- The exact mechanisms by which the body senses and transduces mechanical forces to regulate bone remodeling have long been an active area of study among researchers and clinicians 3.
Mechanisms of Bone Remodeling
- The bone remodeling cycle replaces old and damaged bone and is a highly regulated, lifelong process essential for preserving bone integrity and maintaining mineral homeostasis 4.
- The remodelling cycle occurs within the basic multicellular unit and comprises five co-ordinated steps: activation, resorption, reversal, formation, and termination 4.
- The key signalling pathways controlling osteoclastic bone resorption and osteoblastic bone formation are receptor activator of nuclear factor-κB (RANK)/RANK ligand/osteoprotegerin and canonical Wnt signalling 4.
- Cytokines, growth factors, and prostaglandins act as paracrine regulators of the cycle, whereas endocrine regulators include parathyroid hormone, vitamin D, calcitonin, growth hormone, glucocorticoids, sex hormones, and thyroid hormone 4.
Response to Stress
- Mechanical forces can alter bone mass in response to changing conditions, and loss of mechanical stimulation can significantly weaken the bone structure, causing disuse osteoporosis and increasing the risk of fracture 3.
- Calcium and vitamin D are essential for maintaining bone health, and deficiencies in these nutrients can lead to compromised bone repair and post-traumatic bone loss 5.
- The skeleton represents the main source of calcium, which is increasingly required during fracture-callus mineralisation, and post-traumatic calcium mobilisation might occur under conditions of insufficient calcium and vitamin D status 5.