Basics and Beyond ® Anatomy of the Upper Extremity

At the MCP joints:

1.  The proper collateral ligament loosens when the MCP joints are extended, and they tighten in flexion

2.  The accessory collateral ligament loosens when the MCP joints are flexed, and they tighten in extension

At the IP joints:

• The proper collateral ligament (PCL) and accessory collateral ligament (ACL) are primary stabilizers of the PIP
• The proper collateral ligaments are taut in flexion and the accessory collateral ligament attaches to the volar plate and the accessory ligaments are taught in full extension
• When the IP joints are flexed, the collateral ligaments are in a more relaxed position  but if the PIP is immobilized in excessive flexion the position allows the ligaments to become stout and stiff.
• Therefore it is recommended a small amount of tension (orthotic at 0-15 degrees of flexion) will maintain the ligament length and help preserve joint motion and prevent joint stiffness as the proper collateral ligament is still tight and will  help the PIPJ to be stable.
• As the PIP joint flexes, the tension on the proper collateral ligament increases because it stretches over the wide area of the proximal phalanx
• As the PIP joint flexes, the accessory collateral ligament folds and the VP migrates proximally allowing joint flexion

When the PIP joint is in full extension, the ACL are taut and because of the VP attachment, hyper-extension is not permitted.

Extensor Mechanism

Extensor hood