Crush Injury and Crush Syndrome

How a crush injury damages the body

Muscle can survive without blood flow for only a limited time. Under sustained pressure, cells are squashed and starved of oxygen. After about 1 hour of heavy compression, muscle cells begin to break down. After 4 to 6 hours, damage is often permanent.

Two problems follow:

1. Local damage: dead and swollen muscle within a closed compartment raises pressure until blood can no longer get in. This is compartment syndrome, and it extends the area of dying tissue.
2. Body-wide damage (crush syndrome): when the weight is lifted, blood reaches the damaged muscle and washes out its contents. Potassium can stop the heart. Myoglobin, the muscle's oxygen-carrying pigment, clogs and poisons the kidneys. Large volumes of fluid leak into the injured muscle, causing low blood volume and shock.

Crush syndrome is the reason a person trapped for hours can seem stable, then collapse suddenly at the moment of rescue ("rescue death").

Causes of crush injury

• Disasters: earthquakes, explosions and building collapses produce large numbers of crush injuries.
• Road traffic accidents: legs trapped under dashboards or vehicles.
• Industrial and farm accidents: presses, rollers, tractors that roll over, falling loads.
• Crowd crushes: pressure on the chest and abdomen.
• Prolonged immobility: people who lie on a hard floor for many hours after a fall, stroke, overdose or heavy intoxication can crush their own muscle under their body weight. This is a common, often missed cause.
• Tight casts or splints: less commonly, external pressure that is too tight.

Crush injury symptoms

At the site of the injury

• Pain, sometimes surprisingly mild at first if nerves are compressed
• Swelling that increases over hours, and a limb that feels tense or "woody"
• Bruising, blisters and skin marked by the shape of the object
• Numbness, pins and needles or weakness
• Fractures and open wounds

Crush syndrome symptoms

• Dark brown or cola-colored urine from myoglobin
• Passing very little urine
• Weakness, nausea and vomiting
• Fast, weak pulse, low blood pressure, cold clammy skin
• Palpitations or an irregular heartbeat from high potassium
• Confusion or drowsiness

Crush injury in the feet

The foot has nine small muscle compartments and many small bones. Crush injury of the foot typically shows as severe, deep pain out of proportion to the visible injury, marked swelling across the top of the foot, pain on gently bending the toes, and numbness between the toes. Fractures of the metatarsal bones and the midfoot (Lisfranc) joints are common. Untreated compartment syndrome in the foot can leave clawed toes, stiffness and chronic pain.

How to know if tissue is dying from a crush injury

Dying tissue (necrosis) shows several signs that worsen over hours to days:

Any of these needs emergency assessment. Tissue in compartment syndrome can often be saved if pressure is released within about 6 hours.

Diagnosis

Doctors examine the limb for tension, pulses, feeling and movement, and measure compartment pressure with a needle gauge when the diagnosis is unclear. Key tests are:

• Creatine kinase (CK): a muscle enzyme. Very high levels confirm muscle breakdown (rhabdomyolysis).
• Potassium, calcium, phosphate and acid levels.
• Kidney function (creatinine) and urine output, measured hourly in severe cases.
• Urine test showing blood on a dipstick without red cells on microscopy, a sign of myoglobin.
• ECG to detect the effects of high potassium on the heart.
• X-rays or CT for fractures.

Treatment

Before and during rescue

Paramedics aim to start IV fluids before a trapped limb is freed. Large volumes of saline dilute potassium and flush myoglobin through the kidneys. When fluids are not possible and release is prolonged, a tourniquet may sometimes be used briefly as a temporary measure on medical advice.

In hospital

• Aggressive IV fluids with careful monitoring of urine output.
• Treating high potassium: calcium to protect the heart, insulin with glucose, and other measures to shift potassium into cells.
• Fasciotomy: surgical cuts through the tight tissue layer to relieve compartment pressure. The wounds are closed or skin-grafted days later.
• Wound care: removal of dead tissue (debridement), antibiotics and tetanus protection.
• Fracture fixation.
• Dialysis for acute kidney injury or potassium that cannot be controlled. Kidney function usually recovers over weeks.
• Amputation when a limb is not survivable or threatens the person's life.

Complications and outlook

Possible complications include kidney failure, cardiac arrest from hyperkalemia, shock, infection, lasting nerve damage, muscle contracture and limb loss. With prompt fluids and kidney support, most people who survive the initial injury recover kidney function. Limb outcome depends on how long compression lasted and how quickly compartment syndrome was treated. Rehabilitation with physical therapy is often needed for months.

For the general meaning of the term and first aid for everyday crushing injuries such as crushed fingers, see crushing injury.

Frequently asked questions

What are the symptoms of crush injury syndrome?

Crush syndrome causes dark or cola-colored urine, reduced urine output, weakness, nausea, a fast or irregular heartbeat, low blood pressure and confusion. It appears after a large muscle has been compressed, usually for more than an hour, and then released. It is a medical emergency.

What causes a crush injury?

Crush injuries are caused by heavy or prolonged pressure on the body: collapsed buildings, vehicle crashes, machinery, falling loads and crowd crushes. They can also happen when someone lies motionless on a hard surface for hours after a fall, overdose or stroke.

How do I know if tissue is dying after a crush injury?

Warning signs include pain that keeps getting worse, a tight swollen limb, pale, blue, mottled or black skin, coldness, numbness and loss of movement. Dark urine suggests muscle breakdown. Get emergency care immediately, because releasing compartment pressure within hours can save the tissue.

Why is it dangerous to free someone after a long crush?

When a crushed limb is released, toxins from the dead muscle, especially potassium and myoglobin, rush into the bloodstream. This can stop the heart or damage the kidneys within minutes to hours. Rescuers give IV fluids beforehand and monitor the heart to reduce the risk.

Can you recover from crush syndrome?

Yes, many people do. Kidney damage usually recovers over weeks with fluids and, if needed, temporary dialysis. Limb recovery depends on how much muscle died. Some people regain full function after surgery and therapy, while others are left with weakness, nerve damage or an amputation.