Pathology – injury to an artery with subsequent reduced blood supply to the leg. Typically occurs during dislocation of the knee joint.
Presentation – history of injury. Pulsating bleed in an open wound, expanding haematoma in a closed wound. Probable pain, pins and needles, muscle weakness.
Diagnosis – hard clinical signs: pulsating bleed, expanding haematoma, audible bruit, palpable thrill, diminished or absent pulses. Soft clinical signs -altered sensation, pale appearance or coldness of the extremity. Investigations – ankle brachial index (ABI), angiography.
Normal values – ABI > 0.9.
Treatment – surgical repair or bypass grafting. Amputation of the leg in 12% of surgical cases.
Where to refer – accident and emergency department.
Arteries are muscular tubes that carry oxygen-rich blood from the heart to the body. The popliteal artery is located at the back of the knee and is firmly anchored above and below the joint. The anterior and posterior tibial arteries branch off the popliteal artery, supplying blood to the lower leg and foot; the dorsalis pedis and posterior tibial pulses represent blood flow through these arteries respectively.
Haemorrhaging of blood from an artery, or obstruction of blood flow within the artery (e.g. occlusion), interferes with the delivery of essential nutrients to the extremities (ischaemia), potentially leading to further tissue injury, infection or amputation.
The popliteal artery may be injured by a penetrating object, but is particularly susceptible to injury if the shin bone (tibia) dislocates relative to the thigh bone (femur). Knee (tibiofemoral) dislocations typically occur with high velocity (e.g. road traffic accident), low velocity (e.g. sports) or ultra-low velocity (e.g. fall from body height in obese individuals) trauma. Vascular injury occurs in 18% of knee dislocations, therefore clinicians should have a high index of suspicion in confirmed or suspected cases of tibiofemoral dislocation.
Arterial injury may present as a pulsating bleed through an open wound, or an expanding collection of blood within the body (expanding haematoma) if the skin remains intact. An abnormal sound (audible bruit) or vibration (palpable thrill) at the site of injury indicates turbulent blood flow through an artery secondary to vascular damage. A pale appearance of the limb (pallor) or coldness of the extremity (poikilothermia) is suggestive of reduced blood flow to the leg, but these signs can also be present in other conditions (e.g. systemic shock, hypothermia).
Individuals may describe severe pain that is inadequately controlled with appropriate medication. Altered sensation within a specific distribution of skin (paraesthesia) and muscle weakness (paresis) indicate potential reduced oxygen supply to nerve tissue. Acute extremity compartment syndrome (AECS) may present with similar symptoms and it is important to differentiate these two conditions.
Vascular injury can be diagnosed using a combination of clinical findings, non-invasive and invasive studies. For details on the diagnostic accuracy of individual tests, please visit the statistics section.
The posterior tibial and dorsalis pedis pulses (video 1) should be compared with the unaffected side and the findings documented. In addition to the clinical presentation described above (pulsating bleed, expanding haematoma, audible bruit or palpable thrill), a diminished or absent pulse (pulseless-ness) on the injured leg is considered a hard sign of vascular injury.
Video 1: assessment of dorsalis pedis and posterior tibial pulses.
The ankle brachial index (ABI) is a non-invasive test that uses Doppler ultrasound and a blood pressure cuff to determine the systolic blood pressure (blood pressure when the heart contracts) at the ankle and the arm. The pressure at the ankle is divided by the pressure of the arm to determine the ABI; an ABI below 0.9 is considered abnormal. A number of studies have shown that vascular injury is unlikely to be present following knee dislocation if pulses are normal and the ABI is greater than 0.9.
Arteriography (also called angiography) is an invasive technique that is considered the best method for ruling in a vascular injury. This procedure carries greater risks compared with non-invasive modalities (e.g. contrast induced kidney problems) and may delay surgery. The routine or selective use of arteriography is typically based on its availability and the preferred guidelines of the treating department.
Based on the above factors, and in the absence of hard signs, the following recommendations have been proposed for suspected arterial injury following knee dislocation:
1. Assess pulses and measure ABI
2. If pulses are normal AND ABI >0.9, continue vascular monitoring for 48 hours.
3. If pulses are abnormal OR ABI <0.9, order CT angiography (figure 1)
4. If pulses are abnormal AND ABI <0.9, proceed to surgery with intra-operative angiogram.
Figure 1: CT arteriography showing occlusion of the popliteal artery (left image). From Gray & Cindric (2015).
Surgical treatment (repair or bypass grafting) is performed in 80% of patients diagnosed with vascular injury. Associated injuries (e.g. knee dislocation or fracture) should be managed appropriately.
The risk of amputation significantly increases if blood supply is not sufficiently restored within eight hours of vascular injury; the amputation rate following surgical repair is 12%. Patients with a multi-ligament knee injury and associated popliteal artery injury that requires bypass grafting have significantly lower functional scores than those without vascular involvement.
Individuals with suspected vascular injury should be referred for assessment on an emergency basis (i.e. Accident & Emergency).
Written by: Richard Norris & Daniel Massey, The Knee Resource
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Inaba K, Potzman J, Munera F, McKenney M, Munoz R, Rivas L, et al. Multi-slice CT angiography for arterial evaluation in the injured lower extremity. J Trauma. 2006;60(3):502-6; discussion 6-7.
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