Are Clicking or Cracking Joints Harmful?

A Very Common Question

Almost everyone's joints make sounds at some point — knuckles crack, knees click, ankles pop, spines produce audible responses to manipulation. For most people this occasions no more than mild curiosity; for others, it is a source of genuine anxiety — particularly when the clicking is associated with pain, occurs in a joint that has been injured, or is pointed out by a concerned practitioner or family member. The clinical question is straightforward: are clicking or cracking joints a sign of something harmful, and should they be investigated or avoided? The answer, in most cases, is no — but with important and specific exceptions.

Cavitation — The Crack Explained

The sharp crack produced by knuckle-cracking and by spinal manipulation is caused by cavitation — the rapid formation of a gas bubble within the synovial fluid of a joint. Synovial fluid contains dissolved gases (nitrogen, oxygen, carbon dioxide); when the joint is rapidly distracted or the intracapsular pressure is abruptly lowered by a specific movement, the dissolved gases rapidly come out of solution, forming a bubble that produces the audible crack. The process is analogous to the pop of a vacuum seal. Radiological imaging, including real-time MRI, has confirmed this mechanism directly, showing the appearance of an intra-articular gas bubble coincident with the cracking sound. The bubble dissipates over 15–30 minutes, which explains why a joint cannot be immediately cracked a second time.

Cavitation itself is not harmful to the joint. The bubble formation does not damage articular cartilage, degenerate the joint, or cause arthritis. The pressure change involved, while rapid, is within the mechanical tolerance of healthy synovial joint structures.

Synovial Fold Snapping

A second common source of joint clicking is the snapping of synovial folds or plica — folds of synovial membrane within the joint capsule — over bony prominences or across joint surfaces during movement. This mechanism is particularly common at the knee (medial plica syndrome) and the hip. The sound produced is typically a soft click rather than a sharp crack, and it is reproducible with a specific movement rather than requiring the distraction technique needed for cavitation. Synovial fold snapping is usually benign and asymptomatic; when a plica becomes thickened, inflamed, or fibrotic (as in plica syndrome), it may produce pain and require clinical assessment and, occasionally, arthroscopic management.

Tendon Snapping

Tendons passing over bony prominences can produce snapping sounds when they briefly displace during movement and then return to their resting position. Snapping hip syndrome (coxa saltans) — the audible snap produced by the iliotibial band over the greater trochanter or the iliopsoas tendon over the iliopectineal eminence — is one of the most common clinical examples. Snapping of the peroneal tendons over the fibular malleolus and the extensor tendons of the hand over the metacarpal heads are other well-recognised examples. These sounds are typically benign, but when associated with pain or progressive instability they warrant clinical assessment to determine whether tendon subluxation or fraying is contributing.

When Sounds Are Clinically Significant

Certain joint sounds do carry clinical significance and warrant assessment. Crepitus — a coarse, grinding, or grating sensation and sound with movement — is distinct from the sharp crack of cavitation and the soft click of tendon snapping. It reflects the movement of irregular surfaces against each other, most commonly in the context of articular cartilage irregularity, degenerative changes, or intra-articular loose bodies. Crepitus is common in osteoarthritis and in joints with prior cartilage injury. While crepitus alone does not indicate the severity of the underlying pathology, it should be assessed in the context of the full clinical picture. A click accompanied by instability or giving way — particularly in the knee — suggests meniscal or ligamentous involvement and warrants orthopaedic assessment. A new click following injury, particularly to the shoulder, knee, or ankle, should similarly be evaluated.

The Knuckle-Cracking Evidence

The popular belief that habitual knuckle-cracking causes arthritis has been investigated in multiple studies and is not supported by the evidence. Radiological comparison of habitual knuckle-crackers with matched non-crackers finds no difference in the prevalence or severity of metacarpophalangeal joint osteoarthritis. One memorable self-report — a physician who cracked the knuckles of one hand but not the other for sixty years and found no difference in arthritis between the two hands — provides a compelling anecdotal demonstration consistent with the formal evidence. Knuckle-cracking may cause very mild transient soft tissue oedema with habitual forceful practice, but there is no evidence of any clinically meaningful harm from the practice.

Summary and Practical Guidance

The large majority of joint clicking and cracking is either cavitation, synovial fold snapping, or benign tendon snapping — none of which cause joint damage or require clinical investigation in the absence of associated symptoms. The presence of pain, swelling, instability, progressive limitation of movement, or new sounds following injury elevates the clinical significance and warrants assessment. Crepitus with pain should be evaluated in the context of the full clinical presentation. For the overwhelming majority of people who simply notice their joints making sounds — continue your normal activities with confidence.