2.1 Central pivot

This extraarticular area of the knee contains both cruciate ligaments. The cruciate ligaments are the main static restrictors of AP translation of the tibia in relation to the femur. Knee dislocation must result in injury to at least one cruciate ligament unless there is an associated fracture. In most knee dislocations both cruciate ligaments are disrupted. Experimental studies [3] revealed that the anterior cruciate ligament is torn by the femoral notch, usually in hyperextension; whereas the PCL is more sensitive to forces applied parallel to the axis of its fibers. High-energy trauma with high strain applied to the PCL may cause its avulsion from the femoral notch, resulting in an injury pattern that also involves the posterior capsule, which “peels off” its femoral attachment deep to the origin of the gastrocnemius muscle. In general, knee dislocations are associated with midsubstance cruciate injuries.

2.2 Posteromedial corner

The PMC of the knee contains the superficial medial collateral ligament, the deep MCL, the posterior oblique ligament (POL), the direct insertion of semimembranosus, and the medial head of the gastrocnemius muscle ( Fig 6.7.2-2 ). The medial meniscus also helps to stabilize the knee via its meniscofemoral and meniscotibial attachments and one of these attachments is often ruptured in knee dislocation; severe rotatory forces may result in both the femoral and tibial attachments rupturing. The superficial MCL is the largest structure on the medial side of the knee. On the femoral side it attaches to a bony depression located proximal and posteriorly to the femoral epicondyle. Distally it attaches to the medial tibial crest. The POL consists of three fascial expansions of the semimembranosus tendon [5]. Repair or reconstruction of the PMC involves restoration of the MCL and the POL and the medial meniscal ligaments.

2.3 Posterolateral corner

The PLC of the knee has complex anatomy and injury is due to varus thrust on the knee, often combined with rotation or hyperextension. The main structures to be repaired or reconstructed are the lateral collateral ligament, the popliteus tendon and the popliteofibular ligament ( Fig 6.7.2-3 ). The lateral meniscus also helps to stabilize the knee via its meniscofemoral and meniscotibial attachments and one of these attachments is often ruptured in a knee dislocation; severe rotatory forces may result in both the femoral and tibial attachments rupturing. These injuries should be repaired, if possible. The meniscotibial attachment may avulse the periphery of the tibial plateau, producing a Segond fracture ( Fig 6.7.2-4 ). Three additional lateral structures frequently injured during knee dislocations are the biceps tendon, the iliotibial band, and the common peroneal nerve. In some cases, the fibular head may present with an avulsion fracture; the iliotibial band may be stripped away from Gerdy′s tubercle or the tubercle may be avulsed. Peroneal nerve injury may be present in one third of all knee dislocations and its prognosis is poor, with half of the patients unable to recover useful function [6]. In the most severe injuries, the nerve is avulsed from the sciatic nerve ( Fig 6.7.2-1c ).

2.4 Extensor mechanism

Posterior dislocations are frequently associated with disruption of the extensor mechanism of the knee and this may be associated with severe soft-tissue injury with closed degloving or open wounds. Vascular injury is a common finding. The combination of a knee dislocation with an extensor mechanism disruption is the most difficult type of knee dislocation to rehabilitate because the knee dislocation benefits from immediate motion while the extensor mechanism injury benefits from limited motion during the early rehabilitation period.

2.5 Popliteal fossa

The major concern with any knee dislocation is vascular injury ( Fig 6.7.2-5 ). A recent systematic review [7] identified 862 patients with knee dislocations, of whom 171 (25%) sustained vascular injuries. However, most contemporary literature reports an incidence of flow limiting vascular injury in the 5–15% range. Regardless of the exact incidence, surgeons must be alert and look for popliteal artery injuries. All patients must have examination of the peripheral pulses and this must be recorded in the medical notes. Any abnormality mandates immediate action. The anatomy of the popliteal artery makes it susceptible to injury with significant knee displacement. The artery is relatively tethered in two sites: proximally, at the level of its emergence from the fibrous tunnel of Hunter′s canal and, distally, at the level where it crosses deep to the soleus arch and trifurcates.

3.1 Neurovascular assessment

In all cases, neurovascular assessment is a priority.

It is important to assess the ability of the patient to perform dorsiflexion of the great toe. The possibility of compartment syndrome should always be considered. Perfusion below the knee, including palpation of the pulses of the posterior tibial artery and anterior tibial (dorsalis pedis) artery, must be checked and compared with the contralateral side. Doppler scans are recommended to document the presence and intensity of the pulses distal to the knee if there is any difficulty with palpation. If there are no pulses distal to the knee, an emergent surgical exploration of the artery is indicated. Do not delay imaging unless it can be performed in the time it takes to prepare the operating room. In general, vascular lesions with clear ischemic signs require immediate vascular intervention. The later the intervention, the higher the amputation rate and the results of revascularization after 6 hours are very poor. If the pulses are present but diminished, advanced imaging is indicated, usually with computed tomographic (CT) angiogram or an MR angiogram. The ankle brachial pressure index (ABPI) has been used to determine whether the patient should undergo an arteriography and it is recommended that patients with an ABPI less than 0.9 have urgent vascular imaging or surgery [9]. If vascular repair is required, a temporary arterial shunt is helpful and reduces ischemic time. A provisional external fixator may be required to stabilize the joint.

Patients with no vascular symptoms or signs still require close observation and should be admitted to hospital. A detailed vascular clinical examination is recommended at admission, after 4–6 hours and at 24 and 48 hours. This must be clearly documented in the medical records [8]. Late popliteal artery thrombosis, usually associated with an asymptomatic intimal tear, is a recognized and devastating complication [10].