Sagittal Band Rupture and Extensor Tendon Displacement
In sagittal band rupture, the extensor tendon displaces toward the ulnar side when the radial sagittal band is torn, which is the most common pattern of injury. 1
Direction of Tendon Displacement
The radial sagittal band functions as a "check-rein" that prevents ulnar subluxation of the extensor digitorum communis tendon at the metacarpophalangeal (MCP) joint. 2, 1 When this radial band ruptures—either from direct trauma or spontaneous mechanisms—the extensor tendon subluxates or dislocates in the ulnar direction. 1, 3
Key Anatomic Principles
Radial band injury = ulnar tendon displacement: The majority of sagittal band ruptures involve disruption of the radial sagittal band, resulting in ulnar subluxation of the extensor tendon. 1, 3
Partial tears can still cause dislocation: Cadaveric studies demonstrate that the extensor tendon can dislocate even when the radial sagittal band is only partially divided, particularly in the middle and ring fingers. 4
Ulnar band tears behave differently: When the ulnar sagittal band tears (less common), recent cadaveric evidence suggests this may be spared of extensor instability, and the tendon may not subluxate to the radial side. 2
Clinical Presentation
Patients with radial sagittal band rupture and ulnar tendon subluxation typically present with:
MCP joint pain and edema that may be accompanied by snapping, catching, or locking sensations. 1, 5
Visible or palpable ulnar displacement of the extensor tendon during active finger extension or MCP joint flexion. 1
Associated injuries including collateral ligament sprains, capsular injury, and osteochondral fractures should be evaluated. 1
Important Clinical Caveat
Not all sagittal band tears present with extensor instability. A surgically confirmed case demonstrated that chronic ulnar sagittal band tears with fibrosis may stabilize the central band, preventing tendon subluxation despite complete band disruption. 2 Therefore, in patients with MCP pain without visible tendon subluxation or limitation of motion, sagittal band tear should still be considered in the differential diagnosis. 2
Finger-Specific Variations
Little finger: Complete section of sagittal bands caused ulnar dislocation in only one out of seven cadaveric hands, suggesting anatomic variations may prevent consistent dislocation patterns. 4
Middle and ring fingers: These digits show no significant correlation between extensor tendon excursion and sagittal band angle changes during MCP flexion, which may explain why conservative treatment is more feasible in these digits. 4