Final answer:
The nurse practitioner suspects cauda equina syndrome in the 39-year-old patient due to her symptoms of leg numbness, weakness, and bladder incontinence following a fall from a horse.
Step-by-step explanation:
The 39-year-old patient experiencing leg numbness, weakness, and sudden bladder incontinence following a fall off of a horse may lead the nurse practitioner to suspect cauda equina syndrome. This condition occurs when there is compression of the nerve roots within the lower spine which can cause motor and sensory loss, as well as urinary and bowel incontinence if severe enough. These symptoms are not generally associated with hip fracture, avascular necrosis, or genu recurvatum; therefore, cauda equina syndrome is the most fitting diagnosis considering the patient's symptoms and recent trauma.