Joint Penetration (Penetrating Joint Injury)

Why an open joint is dangerous

A joint is a sealed space lined with synovium and filled with lubricating synovial fluid. When a wound breaches it, bacteria from the skin, the object or saliva enter the joint. Synovial fluid is a good growth medium and has limited immune defense, so infection (septic arthritis) can develop quickly. Bacterial enzymes and inflammation can destroy cartilage within days, leading to permanent arthritis. Infection can also spread to bone (osteomyelitis).

Common causes

• falls onto glass, metal or sharp objects
• puncture wounds from nails, needles, thorns or splinters
• human bites, particularly "fight bites" over the knuckles
• animal bites, especially cat bites, which are deep and narrow
• stab and gunshot wounds
• open fractures near a joint
• lawn mower, machinery and motor vehicle injuries

Signs of an open joint

• a wound over or near a joint, sometimes deceptively small
• leakage of clear or yellowish, slightly sticky fluid
• pain on moving the joint
• swelling of the joint
• air seen in the joint on X-ray or CT
• later, signs of infection: increasing pain, heat, redness, swelling, inability to move the joint and fever

A clenched-fist injury may look minor when the hand is open, because the wound in the tendon and capsule shifts when the fingers straighten.

Diagnosis

1. Examination of the wound, joint movement, nerves and circulation.
2. X-rays: look for air in the joint, fractures and foreign bodies such as glass or teeth fragments.
3. CT scan: very sensitive for small amounts of air inside the joint, and increasingly used, especially for the knee.
4. Saline load test: sterile fluid (sometimes with dye) is injected into the joint away from the wound. If it leaks from the wound, the joint is open.
5. Joint fluid sampling if infection is suspected.

Treatment

• IV antibiotics started promptly, chosen to cover skin bacteria, and bite organisms such as Eikenella and Pasteurella when relevant.
• Tetanus booster if not up to date. See tetanus.
• Surgical irrigation and debridement: the joint is washed out, usually by arthroscopy or open surgery, and dead tissue and debris removed.
• Wound management: closure or leaving partly open, depending on contamination.
• Repair of tendons, ligaments, cartilage or fractures as needed.
• Splinting and early physical therapy to restore movement.

Some small, clean wounds near a joint with no evidence of joint involvement on CT can be managed with washout of the wound and antibiotics, but the decision is made by a surgeon.

Complications

• septic arthritis and joint destruction
• osteomyelitis
• stiffness and loss of motion
• post-traumatic arthritis
• tendon rupture, particularly with knuckle injuries

Outlook

With early washout and antibiotics, most people recover good joint function. Delays of more than about 24 hours, high-energy injuries, bites and contaminated wounds carry a higher risk of infection and lasting problems.

Frequently asked questions

What is a penetrating joint injury?

It is a wound that goes through the skin and the joint capsule into the joint, such as a puncture into the knee or a bite over a knuckle. It exposes the joint to bacteria and can cause a serious joint infection.

How do I know if a cut has gone into a joint?

Warning signs include clear, slightly sticky fluid leaking from a wound over a joint, pain on moving the joint and swelling. Often you cannot tell from the outside, so any deep or puncture wound near a joint should be checked by a doctor the same day.

Why are fight bites so dangerous?

When a fist hits teeth, the tooth can pierce the knuckle joint and inject mouth bacteria. The wound looks small and seals over, but infection can develop quickly. Fight bites need emergency assessment, antibiotics and often surgical washout.

Do all open joint injuries need surgery?

Most confirmed open joints are washed out surgically to prevent infection. Very small wounds where tests show the joint is not involved may be managed with cleaning and antibiotics. An orthopedic surgeon makes this decision.

What is septic arthritis after a joint injury?

It is infection inside the joint, causing severe pain, swelling, redness, warmth and fever, usually within a few days of the injury. It is an emergency because it can destroy joint cartilage quickly and needs drainage and antibiotics.