You may know the 5 P’s, but it’s easy to be fooled
A 28-year-old male presents to the emergency department at 4 pm with months of worsening bilateral lower extremity pain. He has experienced this pain multiple times in the past, usually while running. He states that he is an avid runner, and the pain usually starts around 20 minutes into his run. “The pain is always in my lower shins, and after I stop, the pain goes away after 15 minutes. I just thought it was shin splints, which I’ve had in the past. This time the pain hasn’t gone away. I ran this morning around 8 am, and instead of the pain getting better, it just stayed there. I’ve tried ibuprofen, acetaminophen, ice…Nothing seems to be working. Could it be something else?”
One major orthopedic emergency is compartment syndrome. Most physicians can rapidly cite the 5 p’s of compartment syndrome: pain out of proportion to exam or injury, paresthesias, pallor, pulselessness, and paralysis. Pain with passive stretch of muscles in the affected compartment is also strongly supportive.
However, it’s easy to be fooled. The exam is only useful in alert patients who can cooperate with exam. Pallor, pulselessness, and paralysis are late findings, and motor weakness can be limited due to pain.
While acute compartment syndrome is most often suspected in association with extremity fracture, Mavor in 1956 first described chronic compartment syndrome due to exertion in young athletes. This condition is commonly misdiagnosed in the ED and primary care visits.
Who does this affect?
This condition is due to overuse and usually affects young endurance athletes, particularly runners (or sports like soccer, lacrosse, etc.). Men and women are equally affected. The prevalence is unknown, as many of those affected do not seek medical treatment. Several observational studies have demonstrated it is more common than many realize. One retrospective study of 4100 military personnel found an incidence of 0.49 per 1000 person-years, with age over 40 years as a significant risk factor. One study of patients evaluated for lower leg pain of unknown cause found 34% of patients to have elevated compartment pressures. Another cohort of 80 patients found increased pressures in 28% of patients with recurrent exercise-induced pain.
Most studies and case reports include athletes and runners with difficult training regimens. It most commonly affects the anterior compartment of the lower leg. However, this condition affects many other populations and can include compartments in the foot, thigh, forearm (gymnasts and climbers), and hand.
Why does this occur?
Compartment syndrome due to exertion is associated with several mechanisms, meaning the pathophysiology is not well understood. Suspected mechanisms include inability to clear metabolic waste products due to decreased vascular flow. Exercise leads to increased vascular flow, causing muscular expansion and increased pressure. This pressure elevation reduces blood flow within the specific compartment, causing ischemia. Interestingly, affected patients may have reduced capillary flow at baseline. Fascial defects are also more common in these patients, as 40% of patients with exertional compartment syndrome suffer from a fascial hernia near the intramuscular septum between the anterior and lateral compartments of the lower extremity.
What are the features?
The differential for lower leg pain is extensive, shown in Table 1 above. Most patients with exertional compartment syndrome are athletes, and they typically describe gradually worsening pain with exertion in a specific anatomical region. Pain can be aching, squeezing, cramping, or sharp. Patients usually can pinpoint the specific time of onset. Symptoms can be bilateral and usually stop with rest, as the muscle edema and vascular flow improve, allowing tissue oxygenation. Paresthesias and weakness can occur with severe ischemia. Anterior compartment involvement will cause weak ankle dorsiflexion with dorsal foot numbness, deep compartment weak toe flexion and plantar foot numbness, and lateral compartment weak ankle eversion. Several findings increase likelihood of exertional compartment syndrome, particularly in the anterior compartment of the lower leg:
- Pain induced by athletic activity only.
- Pain limited to the anterior compartment of the lower leg.
- Pain requiring the athlete to stop exertion/running.
- Tenderness to palpation only in the involved compartment.
Examination is commonly normal at rest, creating difficulty in diagnosis. If the patient has recently exercised, the involved compartment may still be tender to palpation. Weakness or absent pulses on exam suggest late stage disease, acute compartment syndrome, or another condition such as claudication or vascular disease. Similar to many other conditions, the history provides the keys to diagnosis, as unfortunately the exam is not reliable.
What about stress fractures?
Stress fractures and medial tibial stress syndrome have localized bony tenderness, with minimal soft tissue tenderness. They also have pain at rest and with impact, contrary to exertional compartment syndrome.
The patient’s vital signs are normal, but he demonstrates significant pain to palpation over the anterior compartments of his lower extremities. He has some mild weakness with objective neurologic testing in the lower extremity, though his pulses are normal.
What are the red flags that indicate you need to do more?
One condition that cannot be missed is acute on chronic compartment syndrome. A patient may have chronic pain with running that resolves with rest. The keys that require consideration of the acute on chronic disorder include pain that does not resolve, pain out of proportion to the examination, pain with passive stretching, paresthesias, and decreased or absent capillary blood flow or distal pulses in the involved extremity. Pain that resolves could be exertional; however, if the pain continues or does not abate, acute compartment syndrome should be assumed. Any objective neurologic finding, specifically weakness in the affected distribution, is also a major red flag.
Other limb and life-threatening conditions include arterial occlusion (embolus or thrombus), phlegmasia cerulean dolens and alba dolens, spinal cord disease, and infectious etiology. These conditions will be suggested by abnormalities on your exam and history.
Our patient possesses several red flags. First, he is an avid runner. Despite stopping his workout seven hours ago, his pain has not abated. He has significant tenderness to palpation with weakness of the involved compartments. Even though his vascular status is normal, you begin to suspect acute compartment syndrome.
How do you diagnose this condition?
Lab studies won’t help you with this one…unless muscle necrosis has occurred in which case the serum creatinine kinase (CK) level will be elevated. Rhabdomyolysis with elevated CK, acidosis, and myoglobinuria may be found.
The diagnosis depends on the history and exam clinical findings. If acute compartment syndrome is suspected, orthopedic consultation is required. Compartment pressures are a vital adjunct for diagnosis. This may not be necessary if the disease is clinically apparent, but more than likely, the consulting surgeon will desire a pressure measurement. A normal pressure may allow observation of the patient, though this should be up to the orthopedist managing the patient during admission. Elevated pressures are defined by absolute compartment pressure > 30 mm Hg, delta pressure < 20 to 30 mm Hg (delta pressure = diastolic blood pressure – measured compartment pressure). Ultimately, measuring a pressure has little risk, while not measuring can lead to missed diagnosis and permanent deformity and dysfunction.
For other patient populations such as young children, those with altered mental status or critical illness, and uncooperative patients, it is difficult to obtain a history and obtain a reliable exam. Compartment pressure managements may be the only means of diagnosis.
What about exertional compartment syndrome?
For patients with exertional compartment syndrome where the pain has resolved but you consider the diagnosis, compartment pressure measurement is needed for definitive diagnosis. Consult an orthopedic surgeon. Exertional compartment syndrome is not as easy to diagnose as the acute form. Measurement techniques and timing differs among experts, though the most widely used criteria includes timed measurements: preexercise pressure > 15 mm Hg, 1 minute postexercise pressure > 30 mm Hg, and 5 minute postexercise pressure > 20 mm Hg. These criteria are associated with a 5% false positive rate. Measurement during exercise has failed repeatedly due to feasibility issues.
What about imaging?
Near infrared spectroscopy and magnetic resonance imaging (MRI) have been advocated, with variable results. Plus, neither of these are required on an emergent basis, but rather they can be completed on an outpatient basis for exertional compartment syndrome diagnosis.
What’s the management?
Chronic exertional compartment syndrome management first includes rest with no inciting activity with non-steroidal medications, orthotics, stretching, and ice. This targets any anatomical anomaly and inflammation. If symptoms resolve, the athlete can gradually return to full activity. Unfortunately, conservative treatment is often ineffective. If compartment syndrome is confirmed by pressures, surgical intervention including subcutaneous fasciotomy may be needed. This entails one or two small incisions, which has success rates of 80% to 90%. Patients with involvement of the deep posterior compartments or with diabetes have decreased success rates and often require fasciectomy (full excision of fascial bands).
Acute on chronic compartment syndrome requires emergent orthopedic surgery consultation. If any red flags are present, don’t wait: talk with your orthopedic immediately. Place the extremity at the level of the heart and relieve any external pressure on the limb. Provide analgesia while ensuring the patient has normal blood pressure, as hypotension can reduce perfusion to the affected tissue. The definitive treatment, fasciotomy, may be needed.
Your 28-year-old male displays signs and symptoms concerning for acute on chronic compartment syndrome. He has paresthesias, and his pain is continuing. Foot dorsiflexion is also weak. You immediately call your orthopedic surgeon on call, who states compartment pressure measurement will be needed. He is there 5 minutes later and obtains pressures of 40 mm Hg in both anterior compartments. The patient is taken to the OR emergently for compartment release.
Exertional compartment syndrome may occur most commonly in patients 20-40 years of age with overexertion, particularly running. This condition is often missed due to lack of knowledge and pain attribution to other conditions. Pain usually starts at a definitive time point in activity and resolves with rest. Pain that does not resolve is suggestive of acute on chronic compartment syndrome. Definitive diagnosis requires compartment pressure management. If any concern for acute compartment syndrome is present, consult orthopedic surgery immediately.