Joint Instability

How joints stay stable

Stability comes from three layers:

1. bony shape: the hip is a deep socket, the shoulder a shallow one
2. passive restraints: ligaments, the joint capsule and cartilage rims such as the shoulder labrum and knee menisci
3. active restraints: muscles and tendons, coordinated by the nervous system (proprioception, the sense of joint position)

Instability develops when one or more of these layers is damaged or weak.

Causes

Traumatic instability

An injury tears or stretches ligaments or the joint capsule:

• shoulder: a dislocation tears the labrum and capsule; young athletes have a high risk of recurrent dislocation
• knee: an ACL tear causes the knee to buckle with pivoting; patellar dislocation causes kneecap instability
• ankle: repeated sprains lead to chronic ankle instability
• thumb: "skier's thumb" (ulnar collateral ligament tear)
• elbow: after a fall on an outstretched hand

Atraumatic instability and hypermobility

Some people have naturally loose ligaments. Many are fine, and flexibility can be an asset in dance or gymnastics. Others develop pain and instability. Conditions include:

• hypermobility spectrum disorders
• Ehlers-Danlos syndrome, especially the hypermobile type
• Marfan syndrome
• Down syndrome

Multidirectional shoulder instability, often in both shoulders, is typical.

Muscle weakness and nerve problems

Weak or poorly coordinated muscles, after injury, stroke or nerve damage, can allow a joint to slip. Shoulder subluxation after a stroke is an example.

Symptoms

• a feeling that the joint is loose, slipping or shifting
• the joint "giving way" or buckling
• partial dislocations (subluxations) that pop back in
• full dislocations
• pain, swelling and clicking
• apprehension or fear of certain positions, such as raising the arm overhead
• reduced confidence in sport or daily activities

Diagnosis

• history: how instability started, direction of slipping, number of episodes
• examination: specific stability tests for each joint, such as the apprehension test for the shoulder and the Lachman test for the ACL; a hypermobility assessment (Beighton score)
• X-rays: fractures and bone loss from repeated dislocation
• MRI or MR arthrogram: ligament, labrum, cartilage and meniscus damage
• CT to measure bone loss in recurrent shoulder dislocation

Treatment

Non-surgical

• physical therapy: the cornerstone. Strengthening the muscles around the joint, balance and proprioception training, and sport-specific retraining
• bracing, taping or splints during recovery or sport
• activity modification while healing
• pain relief with ice and acetaminophen (paracetamol) or ibuprofen, following the label

Most people with atraumatic instability and many with first-time sprains do well with rehabilitation alone.

Surgery

Considered for:

• recurrent dislocations despite rehab, especially in young athletes with shoulder instability
• ACL tears in people who want to return to pivoting sports or whose knee keeps giving way
• chronic ankle instability not improved after 3 to 6 months of rehab
• significant bone loss or associated injuries

Procedures include arthroscopic labral repair (Bankart repair), bone block procedures (Latarjet), ACL reconstruction, medial patellofemoral ligament reconstruction and ankle ligament repair (Broström). Rehabilitation after surgery takes months.

Complications

• recurrent dislocations
• cartilage and meniscus damage
• early osteoarthritis
• nerve or blood vessel injury during dislocation

Frequently asked questions

What causes joint instability?

The most common cause is ligament damage from an injury such as a sprain, dislocation or ACL tear. Other causes include naturally loose joints (hypermobility), connective tissue disorders such as Ehlers-Danlos syndrome, and muscle weakness.

What does joint instability feel like?

People describe the joint feeling loose, slipping, shifting or giving way, sometimes with pain, clicking or swelling. Some avoid certain movements because they fear the joint will dislocate.

Can joint instability be fixed without surgery?

Often, yes. Targeted physical therapy that strengthens surrounding muscles and improves balance and joint position sense helps many people, especially with hypermobility or after first-time sprains. Surgery is reserved for recurrent or severe instability.

Is joint instability serious?

It can be. Repeated dislocations and giving-way episodes can damage cartilage and lead to early arthritis. A dislocation with numbness or a cold limb is an emergency. Early assessment and rehab reduce long-term problems.