Background A 58-year-old man was referred to a private physical therapy centre in Madrid (Spain), by an orthopaedic surgeon four weeks after an arthroscopy procedure for a posterior horn medial meniscus tear.

During physical examination, the presence of a stiff calf muscle, intense calf pain, blushing leg and oedema raised the concern of the physical therapist.

Venous Thromboembolism is a consequence of Deep Venous Thrombosis (DVT), blood clots in the pelvic, leg or major upper-extremity veins that can move out from them, causing potentially deadly pulmonary embolisms.

The incidence of DVT after knee arthroscopy is rare, ranging from 0.2% to 0.4% in the six weeks following surgery.

Methods Dorsiflexion Homans´ test was carried out by the physical therapist during the assessment of the patient. The finding was negative, but based in the clinical examination, the physiotherapist decided to perform an ultrasound examination according to the other signs and symptoms detected, as recommended in Wells Clinical Decision Rules for DVT risk detection.

With the patient in a prone position, sonography was performed with Esaote My Lab 25 Gold ultrasound with a linear transductor, with a frequency of 12 MHz, Gain 44 and double focus over a popliteal vein cross-sectional probe above the popliteal fossa.

Results A widened popliteal vein that did not react to transductor compression, and the presence of a hyper-echogenicity structure in the lumen was found. The patient was rerouted to emergency service and later hospitalised due to deep venous thrombosis confirmed with Doppler ultrasound examination.

Conclusions Arthroscopic knee surgery is considered as a moderate risk factor for developing DVT, and the recommendation is to take care of signs and symptoms classified as red flags for physiotherapy treatment. In the differential diagnosis of the DVT, the Homans´ test is commonly used. However, a false negative Homans’ test is possible when the blood clot is in the popliteal fossa.

This case report illustrates how, despite a physical examination, high-risk diseases occasionally go unnoticed or are confused with other pathologies by the physical therapist or physician. Applying physiotherapy treatment in this cases would result in lethal consequences.

With the right formation and experience, a physiotherapist using sonography can detect red flags or alarm signs showing that treatment by a physical therapist is contraindicated.