- See:
- Rheumatoid Boutonniere
- Thumb Boutonnere Injuries
- Mechanism of Injury:
- rupture of central slip directly from its bony insertion commonly results from closed blunt trauma (w/ or w/o fracture);
- rheumatoid Arthritis
- volar PIP dislocation
- Pathology:
- lesion results from disruption of extensor central slip along w/ disrupiton of triangluar ligament (the later of which can occur either at the time of injury, or can occur w/ chronic attenuation;)
- w/ central slip disruption, PIP joint may initially be capable of weak finger extension if the triangular ligament remains intact;
- active extension is possible, since the triangular ligment holds holds the lateral bands in an anatomic position;
- Disrupted Triangular Ligament:
- patients will not be able to actively extend PIP joint, but will be able to actively hold the PIP in extension, if it is first passively extended;
- this occurs because the lateral bands will relocate into their native position w/ PIP extension, allowing pt to hold finger in extension;
- if it is unclear whether the central slip is disrupted, then test PIP joint extension w/ the wrist and MP joints held in flexion;
- this should relax the lateral bands;
- Triangular Ligament Intact:
- the intrinsic contributions to the central slip are disrupted, and therefore the intrinsics transmit their actions to the DIP, causing hyper-extension;
- later on, the triangular ligament will slowly attenuate, allowing the deforming forces of the volarly positioned intrinsics and transverse retinacular ligament, to pull the lateral bands into a volar direction, below axis of PIP joint;
- subsequently, the lateral bands will act as flexors of the PIP joint, as well as acting as extensors of the DIP joint;
- forced active extension hastens this process;
- this accenuates the PIP flexion & DIP extension deformities;
- in chronic cases, there is contrature of the transverse retinacular ligament, which converts a dynamic deformity to a fixed PIP contracture;
- MP Joint:
- may show a hyperextension deformity, since w/o the normal insertion of the extensor slip to the PIP joint, all of the force is concentrated on the MP joint