The sagittal bands are paired radial and ulnar fibrous bands at the MCP joint that wrap around from the palmar plate and deep transverse metacarpal ligament to encircle the extensor digitorum tendon dorsally. They keep the extensor tendon centred over the metacarpal head and transmit its pull to the proximal phalanx base to extend the MCP joint.
| Origin | Palmar plate of the MCP joint and the deep transverse metacarpal ligament on each side |
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| Insertion | Extensor digitorum tendon over the dorsum of the MCP joint |
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Keep the extensor digitorum tendon centred over the metacarpal head during MCP flexion and transmit extensor force to extend the MCP joint.
Rupture of the sagittal bands, most often the radial band of the middle finger, lets the extensor tendon dislocate ulnarly into the groove between metacarpal heads, a condition known as boxer's knuckle when caused by a punch. Patients cannot actively extend the MCP joint from flexion but can hold it extended once it is passively straightened. Acute injuries are usually treated with a relative motion or MCP extension splint, and chronic or failed cases are repaired or reconstructed. Attritional sagittal band failure also contributes to ulnar tendon drift in rheumatoid arthritis.
Tear of the sagittal band, typically radial, from a punch or forced flexion, causing painful extensor tendon subluxation or dislocation and an extensor lag at the MCP joint.
Stretching of the radial sagittal band by MCP synovitis lets the extensor tendons slip ulnarly, contributing to ulnar drift of the fingers.
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