Knee Dislocation

Clinical and Reduction
Complications and Investigations

• Knee dislocation is a relatively rare injury but an important one to recognise because coexistent vascular injury, if missed, often leads to limb loss. 
• Knee dislocation often presents in the context of multisystem trauma or spontaneous relocation, which can make detection more difficult. 
• The Kennedy Classification (positional) and Washer Classification (anatomical) is described in the literature but from emergency perspective the management will focus on reduction and investigation and treatment of possible vascular injury. 

Clinical and Reduction 

• The affected limb has a gross deformity of the knee with swelling and immobility, but up to 50% of knee dislocations are reduced by the time of ED presentation and may not be obvious. 
• Many knee dislocations have associated fractures; thus, it is important to obtain radiographs prior to ligamentous stressing to avoid promoting fracture displacement. 
• A careful vascular examination is required. The popliteal artery may be damaged in all variants of knee dislocation/subluxation. 
• Reduction is straightforward and often easily accomplished in the ED. After adequate sedation, longitudinal traction will relocate the majority of knee dislocations. 
• Post reduction the knee should be splinted in 20 degree flexion. 

Complications and Investigations

In cases presenting with "hard signs" of arterial injury, immediate surgical revascularisation is indicated : 

1. the absence of pulses 
2. expanding or pulsatile hematomas 
3. palpable thrills or audible bruits 
4. history of pulsating haemorrhage 

In the absence of hard signs an ankle / brachial index should be performed and if it is less than 0.90 then vascular surgery should be consulted and three imaging modalities can be used : 

1. Duplex ultrasound 
2. CT Angiogram 
3. Arteriography is being replaced by these less invasive manoeuvres. 

Coexistent peroneal nerve injury occurs in 25-35% of patients and must be ruled out. This injury most commonly manifests with decreased sensation at the first web space with impaired dorsiflexion of the foot. 

All knee dislocations, regardless of emergent revascularisation needs, should be admitted for serial perfusion checks. 

References

1. Rockwood CA Jr, Green DP, Bucholz RW, eds. Rockwood and Green's Fractures in Adults. 4th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 1996:971-85. 
2. Seroyer ST, Musahl V, Harner CD. Management of the acute knee dislocation: the Pittsburgh experience. Injury. Jul 2008;39(7):710-8. 
3. Snyder WH III, Thal ER, Bridges RA, et al. The validity of normal arteriography in penetrating trauma. Archives of Surgery. 1978;113:424-426. 
4. Rose SC, Moore EE. Trauma angiography: the use of clinical findings to improve patient selection and case preparation. J Trauma. Feb 1988;28(2):240-5.