ボタン穴様変形を呈した稀な指PIP関節側副靭帯断裂の 1 例

An 18-year-old male, suffered a sprain injury of the right small finger during a basketball game. He visited our hospital because of pain and inability to move the small finger.<br>On inspection, the injured finger showed a boutonniere-like deformity, making the patient unable to extend the PIP joint passively against resistance.<br>X-ray examination demonstrated no fracture, but an ulnar stress view showed gross instability of the joint. Therefore, we suspected an injury of the radial collateral ligament combined with central slip rupture at the PIP joint of the right finger, and performed surgery immediately.<br>The operative findings revealed that the central slip was not torn, but the radial collateral ligament was avulsed from its attachment at the middle phalanx, and the stump of the avulsed ligament was caught between the radial lateral band and the central slip of the extensor tendon.<br>We pulled back the entrapped ligament stump, allowing free extension of the PIP joint.<br>We then repaired the torn radial collateral ligament, returning it to its original attachment to the middle phalanx, using a small bone anchor. We started range of motion exercises of the small finger actively on the day after the operation. A buddy tape was also attached between the small finger and the ring finger up until the 7th week, and this remained in place at all times except during motion exercise.<br>At the final evaluation, the patient had recovered a full ROM with no pain, regaining all of his original activities, including basketball.<br>This was a very rare case, because most of the collateral ligaments of the PIP joints are severed at their proximal attachment. We consider that a boutonniere-like deformity, as we seen here, may occur in the following manner. If the PIP joint receives stress force from a lateral direction when in a slightly flexed position, the distal attachment of the collateral ligament will be torn and the ipsilateral condyle will protrude temporarily between the lateral band and the central slip of the extensor tendon. Then, on repositioning of the PIP joint, the torn stump of the ligament will be left between the lateral band and the central slip of the extensor tendon.