American Board of Surgical Assistants (ABSA) Orthopedic Practice Test

The most likely diagnosis for an athlete who is unable to plantar flex his ankle after a football injury is a ruptured Achilles tendon. The Achilles tendon is the largest tendon in the body and connects the calf muscles to the heel bone. It plays a crucial role in allowing plantar flexion, which is the movement of pointing the toes and pushing off while walking or running.

In the case of a rupture, the athlete often experiences a sudden and severe pain in the back of the ankle or lower leg at the moment of injury, frequently describing a sensation similar to being kicked or hit in that area. The inability to plantar flex is a critical clinical sign, as this function is primarily facilitated by the intact Achilles tendon.

While other conditions such as bursitis, fasciitis, and calf muscle strains can impact the athlete's ability to perform certain movements, they do not typically result in a complete inability to plantar flex the ankle to the extent seen in a tendon rupture. The immediate loss of function and the characteristic pain profoundly align with the diagnosis of a ruptured Achilles tendon.