Name: Ankle & knee injury — bulletproof documentation — ER Toolkit
Creator: Kim Trinh, MD

Most ankle and knee injuries are sprains the Ottawa rules can clear without an x-ray — but a few are limb emergencies. The defensible chart documents the decision rule, the neurovascular exam, and that the can't-miss injuries — knee dislocation with a popliteal injury, compartment syndrome, a septic joint, and extensor-mechanism rupture — were considered.

01What's at stake

A knee dislocation can spontaneously reduce and look deceptively normal while the popliteal artery is injured — and a present distal pulse does not exclude it. Compartment syndrome announces itself as pain out of proportion, not a lost pulse. And a septic joint or a missed extensor-mechanism rupture costs function. The Ottawa rules safely cut imaging, but they don't replace the vascular/neuro exam.

02Can't-miss diagnoses

Knee dislocation / popliteal artery injury — high-energy or ultra-low-velocity (obese); may self-reduce; assess perfusion (ABI) and image vessels even with a palpable pulse.
Compartment syndrome — pain out of proportion, pain on passive stretch, tense compartment.
Septic arthritis — hot, exquisitely painful joint; arthrocentesis.
Extensor-mechanism rupture (quadriceps/patellar tendon, patella fracture) — can't extend / straight-leg-raise.
Achilles rupture (positive Thompson test), open fracture, and DVT as a mimic.

03Decision rules & exam

Ottawa Ankle Rules — x-ray the ankle if bone tenderness at the posterior edge/tip of either malleolus, or inability to bear weight 4 steps; x-ray the foot for tenderness at the base of the 5th metatarsal or the navicular, or inability to bear weight. → near-100% sensitive
Ottawa Knee Rule — x-ray for age ≥55, isolated patellar tenderness, fibular head tenderness, inability to flex to 90°, or inability to bear weight 4 steps.
Neurovascular exam — distal pulses, capillary refill, sensation, and soft compartments; extensor-mechanism testing (can the patient extend the knee?).

Skip the typing

Work the case in the Ankle & Knee Injury Workup — it records the Ottawa ankle/knee rules and the neurovascular exam, and assembles an MDM that documents the decision rule and the can't-miss injuries considered.

04Workup & management

Imaging by the Ottawa rules; ED knee films are non-weight-bearing and low-yield in atraumatic pain — arrange outpatient weight-bearing/MRI when needed.
Knee dislocation: reduce, reassess perfusion, measure ABI (<0.9 → CT angiography), serial vascular exams, and vascular/orthopedic involvement — even after a normal-looking reduction.
Compartment syndrome: high suspicion on pain out of proportion → urgent fasciotomy/orthopedics; don't wait for a lost pulse.
Septic joint: arthrocentesis (synovial WBC, cultures before antibiotics) and orthopedics.
Extensor-mechanism/Achilles rupture: immobilize and refer; sprains → RICE, supportive care, follow-up.

05What to document

▼ weak

"Twisted knee, swollen, x-ray negative. Sprain, knee immobilizer, crutches."

▲ defensible

"Knee injury, acute effusion; Ottawa Knee Rule applied (no criteria → no x-ray, or x-ray obtained and negative). Distal pulses 2+, capillary refill brisk, sensation intact, compartments soft. Able to fully extend the knee (extensor mechanism intact); joint not hot/septic. Felt stable on exam — no concern for (self-reduced) dislocation; noted that a normal pulse would not exclude popliteal injury if dislocation were suspected. RICE, follow-up arranged; return precautions for severe pain, numbness, or a cold/pulseless limb."

06Where charts fail

Missing a self-reduced knee dislocation / popliteal injury — relying on a palpable pulse.
Attributing compartment-syndrome pain to the injury and not acting on pain out of proportion.
Not documenting the Ottawa rule or the neurovascular exam.
Missing an extensor-mechanism rupture (didn't test extension) or a septic joint.
Over-using a knee immobilizer (reserved for extensor-mechanism injury, patellar dislocation, tibial plateau fracture).

07Sources

Guignard V, Kiel J, Riveros D. Emergency department management of knee pain. Emergency Medicine Practice (EB Medicine). 2025;27(3).
Stiell IG, Greenberg GH, McKnight RD, et al. Decision rules for the use of radiography in acute ankle injuries (Ottawa Ankle Rules). JAMA. 1994;271(11):827-832.
Stiell IG, Greenberg GH, Wells GA, et al. Derivation of a decision rule for the use of radiography in acute knee injuries. Acad Emerg Med. 1995;2(11):966-973.
Mills WJ, Barei DP, McNair P. The value of the ankle-brachial index for diagnosing arterial injury after knee dislocation. J Trauma. 2004;56(6):1261-1265.

Ankle & knee injury: documentation that holds up