# Traumatic Knee Dislocation > Traumatic knee dislocation for NEET-PG Orthopaedics: popliteal artery injury, ankle-brachial index, Schenck classification and staged ligament reconstruction. - Canonical URL: https://prepelephant.com/topics/neet-pg/orthopaedics/traumatic-knee-dislocation - Exam / course: NEET-PG · Subject: Orthopaedics - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-14 - Last updated: 2026-10-14 - Reference basis: Apley's System of Orthopaedics and Fractures; Campbell's Operative Orthopaedics; Rockwood and Green's Fractures in Adults - How to cite: "Traumatic Knee Dislocation", PrepElephant, https://prepelephant.com/topics/neet-pg/orthopaedics/traumatic-knee-dislocation ## Direct answer A traumatic knee dislocation is a displacement of the tibia relative to the femur that usually tears at least two major knee ligaments and carries a high risk of popliteal artery injury. Vascular assessment with an ankle-brachial index or angiography comes before ligament repair, and the Schenck classification grades the injury by which ligaments are torn. ## What you must remember - **Definition:** the tibia displaces relative to the femur, and the knee may reduce spontaneously before arrival, so the joint can look normal. - **Vascular risk:** popliteal artery injury is the critical complication, and it can be missed when the knee has reduced spontaneously. - **Ankle-brachial index:** a value below 0.9 suggests arterial injury and calls for urgent vascular imaging, usually CT angiography. - **Schenck classification:** KD I is a single cruciate tear, KD II is both cruciates with collaterals intact, KD III is both cruciates with one collateral side, KD IV is all four major stabilisers torn, and KD V is a dislocation with a periarticular fracture. - **Wascher suffixes:** a C suffix denotes vascular injury and an N suffix denotes nerve injury. - **Peroneal nerve:** the common peroneal nerve is often injured, and foot drop after knee dislocation signals this injury. - **Staged treatment:** ligament reconstruction is done once the soft tissues settle, often in stages, rather than immediately in a swollen knee. ## A pathway from arrival to ligament reconstruction A 35-year-old man is hit in a road crash, and his knee looks reduced on arrival with a cold, pale foot. The steps set out the order in which the injury is assessed and treated, because the vascular check comes before any ligament work. 1. **Check vascular status.** Examine the foot pulses and colour and compare them with the other limb, because a knee that looks reduced can still hide a popliteal injury. 2. **Measure the ankle-brachial index.** A value below 0.9 suggests arterial injury and calls for urgent vascular imaging, usually CT angiography. 3. **Reduce and splint.** If the knee remains dislocated, reduce it, splint it in extension and recheck the pulses after reduction. 4. **Grade the injury.** Record the Schenck grade and any Wascher suffixes, which set out the ligaments and the vascular or nerve involvement. 5. **Examine nerves and soft tissues.** Test the common peroneal nerve and examine the skin, because open wounds and compartment risk change the management. 6. **Plan staged reconstruction.** Repair or reconstruct the ligaments once the soft tissues settle, then rehabilitate to restore stability and motion. ## Where the exam tries to catch you Knee dislocation questions test whether the candidate protects the limb before reconstructing the knee. - **Trap:** assuming a reduced knee has no vascular injury. **Correct:** spontaneous reduction is common, so the popliteal artery must be assessed with the ankle-brachial index or angiography. - **Trap:** repairing ligaments immediately in a swollen knee. **Correct:** surgery is staged after the soft tissues settle, which lowers the risk of wound problems and stiffness. - **Trap:** missing a common peroneal nerve injury. **Correct:** foot drop after knee dislocation signals a peroneal nerve injury, which must be documented before surgery. ## Frequently asked questions ### What is the most dangerous complication of traumatic knee dislocation? The most dangerous complication of traumatic knee dislocation is popliteal artery injury, which can threaten the limb if it is missed. It is assessed with pulses, the ankle-brachial index and angiography, even when the knee has reduced spontaneously. ### What does an ankle-brachial index below 0.9 indicate after knee dislocation? An ankle-brachial index below 0.9 after knee dislocation suggests possible arterial injury and calls for urgent vascular imaging. It is a screening tool, so a reassuring value does not fully exclude vascular injury. ### What is the Schenck classification of knee dislocation? The Schenck classification grades knee dislocation by the ligaments torn, from KD I with a single cruciate tear to KD IV with all four major stabilisers torn. KD V describes a dislocation with a periarticular fracture, and suffixes record vascular or nerve injury. ### When is ligament reconstruction done after traumatic knee dislocation? Ligament reconstruction after traumatic knee dislocation is done in stages, once the soft tissues and any vascular repair have settled. Early surgery in a swollen knee raises the risk of wound complications and stiffness.