Given the vignette and radiographic findings, the diagnosis is straightforward. This is a polytrauma patient with multiple extremity fractures including a right closed humerus fracture with a nerve deficit, a closed right femur fracture, an open right tibia fracture, and possibly a left knee injury.

The most likely etiology of the patient’s neurologic deficit is stretch or entrapment of the radial nerve due to the humeral shaft fracture. The radial nerve descends down the medial aspect of the humerus until a third of the way down, where it dives more posteriorly. At this level, the radial nerve runs in the spiral groove and remains in contact with the posterior surface of the humerus. Consequently, radial nerve injury is more common with middle and distal third humerus fractures where it can be stretched from bony disconnection or become entrapped between bone ends at the fracture site. The radial nerve gives off the branches that innervate the triceps in the axilla proximal to the lesion so triceps function remains intact. Patients will experience distal loss of function including wristdrop (weakness in extension), loss of metacarpophalangeal (MP) joint extension, and sensory loss over the dorsum of the hand.

After the primary survey is completed and all life-threatening injuries are addressed, the extremities should be evaluated to assess the four functional components (nerves, vessels, bones, and soft tissues). Injury to three of these four elements constitutes a “mangled extremity.”

Open fractures are those with a conduit of communication between the fracture and the environment due to the disruption of the intervening soft tissue and skin. Because of the open communication, there exists a higher risk for infection. Bone healing is also slowed in open fractures and more often results in nonhealing known as a nonunion.

Fat embolism syndrome occurs in up to 15 % of polytrauma patients, particularly in association with long bone fractures like the femur. It typically presents between 24–72 hours following the trauma. The classic triad consists of respiratory symptoms, neurological changes, and a reddish-brown petechial rash. Respiratory findings such as hypoxemia, dyspnea, and tachypnea are the earliest manifestations. A chest x-ray may demonstrate Acute Respiratory Distress Syndrome (ARDS). Neurologic abnormalities develop afterwards, most often manifested by confusion, drowsiness or altered level of consciousness, and, in severe cases, seizure or paralysis. Lastly, the classic petechial rash develops, but in only 50–60 % of cases. The petechial rash results from extravasation of erythrocytes secondary to the occlusion of dermal capillaries by fat emboli. The rash, in the proper clinical context, is pathognomonic for fat embolism syndrome.

Compartment syndrome. Don’t forget the 6 Ps: pain out of proportion to injury with gentle passive stretch of the involved muscles, pressure (swollen and tense compartments), paresthesia, pulselessness, poikilothermia, and paralysis. This is a surgical emergency.

A concomitant femoral neck fracture. A missed femoral neck fracture may lead to avascular necrosis (AVN) if not treated. AVN is largely irreversible and leads to end-stage dysfunction of the hip joint.

Approximately 1 mm per day, though factors like age and nutritional status may affect the rate.

Not with neuropraxia. Yes for axonotmesis and neurotmesis.

Endoneurium, perineurium, and epineurium. Sunderland has further divided neurotmesis into three grades depending on whether the endoneurium alone is affected, the endoneurium and the perineurium are both affected, or all three layers including the epineurium (i.e., complete transection or avulsion) are affected.

Embolization of fat and marrow from the fracture (or from surgical intramedullary rodding) into the bloodstream. There are both mechanical and metabolic theories as to how this embolization occurs after injury.

The joint above and below any long bone fracture must always be evaluated radiographically.

This is a term for the knee when an ipsilateral femur and tibia fracture are present. A floating knee tends to flail or float between bony disconnections above and below the injury.