Final answer:
A fully extended arm during a fall commonly results in a Colles fracture, while a somewhat flexed elbow may lead to a less severe injury. Direct impact primarily leads to distal humerus fractures, and varus or valgus shear forces impact the elbows ligaments, with valgus forces sometimes necessitating Tommy John surgery.
Step-by-step explanation:
The type of elbow injury associated with biomechanical stress can be matched to the position and type of force applied during the incident of an outstretched hand colliding with the ground. A fall onto an outstretched hand often leads to a Colles fracture, which is a complete transverse fracture of the distal radius. The displacement of the fragment causes a posterior and superior movement, resulting in a deformity that resembles a 'dinner fork' appearance of the forearm. This injury corresponds to an elbow that is fully extended at the time of impact.For instance, when the elbow is somewhat flexed, a potential injury may be less severe due to the reduced force transmitted directly through the extended limb. In comparison, a direct impact to the elbow frequently leads to a distal humerus fracture, especially in children. The olecranon of the ulna is driven upward, causing a separation at the distal humerus. Lastly, varus or valgus shear forces can cause damage to the elbow's collateral ligaments, with varus stress affecting the lateral structures and valgus stress often resulting in the injury known as Tommy John surgery, especially prevalent among baseball pitchers.