Basics and Beyond ® Anatomy of the Upper Extremity

Digital Dorsal Mechanism

• The common extensor tendon is sustained in a central position at the MP joint level by radial and ulnar attachments to the sagittal bands
• Sagittal bands are transverse fibers coming off of the common extensor tendon
• The common extensor tendon trifurcates over the dorsum of the proximal phalanx
• The central portion of the tendon is termed the central slip
• The central slip crosses the PIPJ and attaches to the dorsal base of the middle phalanx
• The radial and ulnar slips past palmar to join the intrinsic tendons from the interroseous and lumbrical muscles to form the lateral bands
• The lateral bands are very important for balance in the hand/fingers
• The lateral bands cross the lateral aspect of the finger proximal to PIP joint and are joined to form the triangular aponeurosis (triangular ligament)
• The fibers from the triangular aponeurosis will then form the extensor terminal tendon at the distal phalanx
• Which then forms the terminal tendon
• The triangular aponeurosis holds the lateral bands in place and prevents volar slippage
• And then it crosses the dorsal surface of the DIP joint to attach to the dorsal base of the distal phalanx