Compartment syndrome

Definitions & Key takeaways

Compartment syndrome is when increased pressure within a closed space in the body (a compartment) causes decreased blood flow and can result in tissue damage. It usually occurs in the limbs after traumas and fractures, which causes swelling and bleeding within the compartment. Other causes can include severe burns, plaster casts, and surgery.

Symptoms of compartment syndrome include pain, tightness or numbness, loss of pulse in the extremity, and pallor or coolness of the skin. Diagnosis is made with a physical exam and measuring the pressure within the compartment. If not treated in time, it can lead to ischemia, then permanent damage and loss of the limb.

Chapters:

Watch video only

Introduction0:00–0:22

With compartment syndrome, compartment refers to separate sections of the body that contain muscles, nerves, and blood vessels surrounded by a layer of fibrous connective tissue, called fascia.
When the pressure within these compartments rises, normal blood flow can be cut off, leading to tissue damage due to hypoxia, or the lack of oxygen.

Physiology0:22–1:21

Compartment syndrome typically happens in the limbs, usually in the lower leg or the forearm. Now, if we remove the skin and then we remove the fat tissue from the lower leg, we would uncover the fascia.
Fascia surrounds the muscles, keeping them tightly together while they contract to move the limb, and it also help attach these muscles to the bones.
Now if we look at a cross section of the lower leg, we can see that the fascia sends intermuscular septa that together with the interosseous membrane between the tibia and fibula divide the lower leg into four compartments.
The anterior, lateral, deep posterior and superficial posterior compartments all contain their own muscles, and blood vessels.
For example, the anterior compartment holds the muscles that perform dorsiflexion of the foot and also aid in it’s inversion and eversion; the deep peroneal nerve that innervates them; and its blood supply comes from the anterior tibial artery and veins.

Pathology1:21–3:49

Since the fascia is not elastic it can’t stretch much. Therefore any increase of the cellular and extracellular volume or a decrease of the volume capacity, like with some external compression, will lead to the increase of the pressure inside the compartment.
This will compress the structures within, and the first ones to feel the effect of compression are the veins, because the pressure inside their lumen is normally low.
As the pressure increases, the arteries will become compressed next and this obstructs the normal blood flow. This cuts off the oxygen supply and hypoxia develops, which causes cells to start releasing substances like histamine and nitric oxide.
These substances cause capillaries to become leaky so fluid leaks out, causing extracellular edema that further increase intra-compartment pressure.
Okay, let’s look at the muscle cells! Hypoxia prevent their mitochondria from producing adenosine triphosphate, or ATP, which is the cell’s main source of energy.
Inside the cell membrane is a sodium potassium pump that needs ATP in order to pump sodium out of the cell and potassium inside.
So without ATP, there’s an increase of intracellular sodium levels which cause water to move into the cells causing intracellular edema.
If hypoxia lasts long enough, intracellular edema can lead to cell membrane rupture, causing proteins to leak out into the extracellular space.
These proteins draw more water from the capillaries and we get a vicious cycle of increased compartment pressure, tissue hypoxia, edema and cellular death and even more pressure.
The most common cause of compartment syndrome is bleeding inside the compartment. This typically occurs with long bone fracture, like the tibia or the forearm bones, and penetrating wounds or surgical procedures that injure blood vessels.
Other causes are swelling of the tissue after severe burns, intravenous drug injection, repetitive use of the injured muscles, or a vigorous muscle contractions like in a tetany or seizures.
Any limb compression, like from a crush injury or from an inappropriately placed cast can also lead to compartment syndrome.
Another potential cause can be reperfusion injury. This occurs with the reestablishment of normal blood flow to hypoxic cells.
These cells stop producing proteins, like antioxidants. So providing them with oxygen again can lead to the formation of toxic reactive oxygen species that they can’t get rid of.

Signs and symptoms3:49–5:16

Signs and symptoms of compartment syndrome can be remembered as the six Ps, which are pain, paresthesia, pulselessness, pallor, poikilothermia and paralysis.
The most common is pain, which is usually described as sharp and deep, and worsens with passive stretching of the affected muscles.
Pain is followed by paresthesia, which is an abnormal sensation like feeling of pins and needles or numbness that can even progress to anesthesia, or loss of sensation.
Other four Ps are less common, as pulselessness appears only when the compartment pressure is so high that it makes arteries collapse.
Then a pallor of the skin can appear together with poikilothermia, which is the inability to regulate body temperature and usually presents as cold extremities.
Paralysis is rare and suggests extensive damage to both the muscles and nerves. Complications such as necrosis can occur when normal blood flow is not established in time leading to tissue death due to the lack of oxygen.
For example, necrosis of the flexor muscles of the forearm leads to their fibrosis and shortening which results in permanent flexion of the wrist and hand known as Volkmann's contracture.
Another complication is rhabdomyolysis where muscles breakdown. Muscle proteins, like creatine kinase and myoglobin, start leaking out into the bloodstream.
Myoglobin is especially toxic for the kidneys and can cause acute renal failure. Diagnosis includes physical examination, where the affected group of muscles appears stiff, firm and feels hard like wood.

Diagnosis5:16–5:56

The individual complains of pain that worsens with passive stretching of the muscles. The best diagnostic tools are the intra-compartmental pressure monitors that can be inserted directly inside the compartment.
When rhabdomyolysis develops, a laboratory workup can show elevated levels of creatine kinase and myoglobin, while urinalysis can show tea colored urine due to high levels of myoglobin.
Imaging techniques like radiography, CT, MRI and ultrasound can help locate bone, muscle and blood vessel injuries. Treatment is surgical and involves a procedure called fasciotomy where the fascia is cut open, relieving the pressure and reestablishing normal blood flow.

Treatment5:56–6:21

Fascia can be left open for a few days, until the cause of increased pressure is treated. When the compartment syndrome is caused by some external factors, like an inappropriate cast, its removal can result in the spontaneous recovery and the surgery may not be needed.

Review6:21–6:45

All right, as a quick recap. Compartment syndrome refers to the increased pressure inside the section of the limb that contains muscles, nerves and blood vessels, and results in the reduction of blood supply and tissue necrosis.
It usually develops in the lower leg and forearm after traumas like a bone fracture. If not treated in time, it can lead to permanent muscle and nerve damage.