Knee Dislocation
Can you describe the radiographs and tell me what your immediate concerns would be?
These are AP and lateral radiographs of a left knee showing an anterior knee dislo- cation. My immediate concern for this patient would be that this injury may be part of a high-energy injury. I would manage them in line with ATLS guidelines in order to ensure that all life- and limb-threatening injuries are identified and prioritised. My immediate concern for the affected limb would be the neurovascular status. An arterial injury, although less common than a nerve injury, may require surgi- cal intervention with disastrous complications (including amputation) if missed. Approximately 25% have a common peroneal nerve injury.
How would you assess and manage this patient initially?
As already mentioned, if this is a high-energy injury, I would manage the patient according to ATLS guidelines. Prior to reduction, I would assess and document the neurovascular status of the limb and assess for a ‘dimple’ sign, which is indicative of an irreducible reduction; the medial femoral condyle has buttonholed through the medial capsule. Delayed reduction risks skin necrosis. I would then attempt closed reduction under sedation as an emergency before repeating my neurovascu- lar assessment and confirming a satisfactory reduction with repeat radiographs.
There is no universally agreed management protocol for suspected arterial inju- ries. Signs of an arterial injury include reduced pulse volume or frank absence of pulses, cool toes with a slow capillary refill, an expanding haematoma around the knee, or an ankle-brachial pressure index (ABPI) <0.9, all of which warrant an urgent vascular review. Patients with these findings require urgent vascular surgical advice which may include angiography. Numerous case series have shown angiog- raphy to be superfluous in the context of an entirely normal clinical examination as above.
Even in the presence of a normal vascular examination, the patient will require serial examinations on the ward as an intimal injury may progress to critical ischaemia.
How would you proceed if this patient had a confirmed arterial injury?
Patients who sustain vascular injuries associated with a knee dislocation require urgent transfer to a trauma hospital and urgent revascularisation. I would apply a spanning external fixator to maintain a secure reduction prior to the vascular sur- geons performing a vascular repair. The vascular surgeons may wish to perform a vascular shunt prior to application of the external fixator.
Why is the popliteal artery at particular risk of injury with knee dislocations? The popliteal artery is strongly tethered in the region of the popliteal fossa, proxi- mally by the fibrous tunnel at the adductor hiatus, and distally at the fibrous tunnel at the soleus arch.
How are knee dislocations classified?
These injuries can be classified as above (where the dislocation is described in the context of the direction of tibial movement in relation to the femur) or using the knee dislocation (KD) classification proposed by Schenck:
KD I – Multiligamentous knee injury with only one cruciate ligament involved KD II – Both cruciates ruptured, but no other ligamentous injury (rare)
Knee Dislocation
KD III – Both cruciates ruptured, plus either the medial collateral ligament (MCL) or lateral collateral ligament (LCL) (three ligaments injured)
KD IV – Both cruciates and both collateral ligaments ruptured (four ligaments injured)
KD V – Multiligamentous injury with periarticular fracture
How would you investigate and manage this definitively?
I would arrange for this patient to have a preoperative MRI in order to confirm the nature of the ligamentous injury as well as rule out associated meniscal or osteo- chondral pathology. I would arrange a CT scan if there was suspicion of fracture on the plain radiographs.
Non-operative management results in a high incidence of recurrent instability, arthrofibrosis and pain, with low outcome scores. In the absence of any contraindi- cations, I would advise repair/reconstruction of the ligamentous injuries performed by a soft tissue knee surgeon with experience in this area.
The most recent evidence is in the form of the largest case series to date with a 10-year follow-up: The group performed early surgical intervention in 40 patients and followed them up to determine outcomes. The algorithm used in this study required reconstruction of the posterolateral corner by means of an open approach followed by an arthroscopically assisted reconstruction of the ACL and PCL. There is an increased risk of compartment syndrome resulting from the high-energy nature of injury together with prolonged surgery and the potential for extravasa- tion of fluid during the arthroscopically assisted reconstruction of the cruciate liga- ments. The skin wounds remained open during the arthroscopy to allow controlled drainage of the saline and a tourniquet break for reperfusion was used as required.
If the patient had a common peroneal nerve injury at the time of presentation, how would you manage this and what would you tell the patient?
Unfortunately, these injuries have a poor prognosis. Managed expectantly, one- third will return to normal, one-third will undergo partial recovery, and one-third will display no recovery. I would explain this to the patient, as well as future man- agement options, which may include nerve grafting, functional orthoses or tendon transfers.