Bone-like cracking noises are usually gas bubbles in joint fluid or tendons snapping over bone. A sharp crack with pain after injury can mean a fracture.
Common causes of cracking noises
- Gas bubbles popping in the joint fluid (cavitation).
- Tendons or ligaments snapping over bone.
- Rough cartilage.
Harmless
Painless cracking is usually fine.
Concerning
A loud crack with pain, swelling or inability to bear weight can mean a fracture.
Care
Rest, ice and see a doctor if there is injury.
Prevention
Strengthen the muscles around joints.
Source of the sounds
Cracking sounds in joints (crepitus) typically come from gas bubbles in synovial fluid, tendons snapping over bone or rough cartilage surfaces. Bones themselves do not crack unless fractured. A fracture can cause a crack or snap at the time of injury, followed by pain, swelling, deformity and difficulty using the limb.
- Synovial fluid contains dissolved gases like carbon dioxide and nitrogen that form bubbles when pressure in the joint changes.
- The neck, back, knees and ankles often make popping noises with movement.
- Humans have 206 bones in adulthood and about 300 at birth, which fuse as growth continues.
When it is a concern
Cracking with pain, swelling, locking or reduced motion needs a medical check. Osteoporosis affects about 10 million Americans over 50, according to the Bone Health and Osteoporosis Foundation, and makes fractures more likely. Weight-bearing exercise, calcium (1,000 to 1,200 mg daily for adults, depending on age and sex) and vitamin D help bone strength. Avoid forcing joints to crack since repeated forced manipulation of the neck carries risks.
Source of the sounds
Joint cracking comes from gas bubbles in synovial fluid, tendons snapping over bone or ligaments shifting. Most noises without pain are harmless.
When it is a concern
Sounds with pain, swelling or restricted movement should be checked, especially after an injury.
Joint noise research
Studies using ultrasound show snapping can result from tendons sliding over bony prominences, such as the biceps femoris or iliotibial band. Crepitus is reported by up to 90 percent of adults at some time. One 2015 study using real time MRI recorded that the cavity forms with knuckle cracking. Noise without pain does not predict arthritis.
Evaluation and care
Pain, swelling or locking after injury suggests tears. Physical therapists teach strengthening and motion control. In osteoarthritis, crepitus often accompanies cartilage thinning, which is confirmed on X rays. Weight loss, exercise and anti inflammatory medicines help symptoms.
Based on data from the Arthritis Foundation and the American Academy of Orthopaedic Surgeons
