JunctureTendinum and Sagittal Band Relationship
The juncturae tendinum and sagittal bands transmit precise forces through the dorsum of the hand. Both structures are integral in the mechanics of normal digital extension and in stabilization of the metacarpophalangeal (MCP) joints. These two structures have an intricate relationship with each other and therefore these structures are constantly producing a balancing act during finger motion. Upon rupture of a sagittal band the EDC tendon slips in an ulnar valley producing an extensor lag. A classic test to diagnose sagittal band rupture is to passively extend the finger and asking the patient to hold this position and then flex the fingers again. Inability to extend the finger back again is suggestive of Sagittal Band rupture.
Chinchalkar SJ, Barker CA, Owsley B: J Hand Microsurg (January-June 2015) 7(1);96-101
When digits are passively placed into extension, patients are able to actively hold them in place
However, a sagittal band rupture is evident if patients are unable to actively extend their digits from a flexed position.