A 38 old-man developed a DVT and was treated with lovenox. Over the next two days, he developed pain in his groin followed by numbness of the left anterior thigh with buckling of his knee. His hematocrit fell from 36 to 25. His patellar reflex was absent on the left and 2+ on the right. Ankle jerks were normal bilaterally.

Spontaneous retroperitoneal hemorrhage into the psoas muscle is often associated with coagulopathies (e.g., excessive anticoagulation, hemophilia). The hematoma places pressure on the underlying lumbar plexus, resulting in weakness of hip flexion (iliopsoas), knee extension (quadriceps) and hip adduction (thigh adductors). The knee reflex is typically depressed. Sensory loss may be present over the anterior thigh, medial thigh, and/or medial calf. Pain often interferes with assessment of muscle strength.