Final answer:
Inadequate reduction, soft tissue interposition, or entrapped fracture fragments are common reasons for incongruent radial capitellar joint after reducing a Bado Type III Monteggia fracture. Failure to properly realign the joint can lead to functional compromise and early arthritis.
Step-by-step explanation:
The most common reason for an incongruent radial capitellar joint after the reduction of a Bado Type III Monteggia fracture is most likely due to inadequate reduction or unrecognized associated fractures or ligamentous injuries. In a Bado Type III Monteggia fracture, the ulna is fractured and the radial head dislocates posteriorly. After reduction, it is essential that the radiocapitellar joint alignment is properly restored; however, interposition of soft tissue, entrapped fracture fragments, or an inadequate reduction can lead to incongruency. This discordance can result in compromised joint function, and potentially painful movements or early arthritis as rough or jagged surfaces grind against each other.