Final answer:
The demonstration of the posterior fat pad on the lateral elbow x-ray usually indicates trauma or other pathology, such as a fracture or effusion. While elbow positioning during imaging can affect visibility, the fat pad sign commonly suggests an underlying problem.
Step-by-step explanation:
The demonstration of the posterior fat pad on the lateral projection of the adult elbow can be indicative of underlying issues, such as trauma or other pathologies. When an individual sustains a trauma to the elbow, such as a fracture, it can lead to a hematoma and an effusion within the joint. This accumulation of fluid can cause the posterior fat pad to be pushed outward and become visible on a lateral x-ray of the elbow, which is not typically seen in a normal joint. Greater than 90 degree flexion of the elbow during x-ray imaging might also cause the fat pad sign due to the mechanical displacement of the fat pad by the proximal forearm.
Regarding the ulnar collateral ligament, described above, it provides medial support to resist the valgus forces at the elbow joint. An injury to this ligament is often associated with the overuse injuries common in throwing athletes, such as baseball pitchers. In severe cases, this might necessitate surgical intervention, commonly known as Tommy John surgery.
Ultimately, while both greater than 90 degree flexion or less than 90 degree flexion might influence the visibility of the fat pad due to the positioning of the elbow during imaging, the occurrence of a posterior fat pad on an elbow x-ray typically suggests an underlying pathology, such as a fracture, rather than being solely attributable to the degree of elbow flexion.