The Association Between the Extent of Sagittal Band Disruption and Extensor Tendon Subluxation in Different Flexion...

We aimed to quantitatively assess the relationship between the extent of sagittal band damage and tendon stability across different fingers and positions while also examining the effects of proximal versus distal damage.

This was a cadaveric study conducted on the index, middle, ring, and little fingers of nine cadavers. Damage was induced through stepwise sectioning either from the proximal or distal end. Sectioning was performed in increments of 10%, 25%, 50%, 75%, 90%, and 100%. Photographs were taken to measure subluxation at metacarpophalangeal joint positions of 0°, 45° flexion, and 90° flexion. Data from the index, middle, and ring fingers were pooled, whereas data on the little finger were analyzed separately.

Subluxation was greater with proximal to distal sectioning at 25%, 75%, and 90% damage thresholds. Ten percent sectioning resulted in a mean subluxation of 5.1% (95% confidence interval [CI], 2.5-7.7); 25% sectioning led to a mean subluxation of 13.6% (95% CI, 7.9-19.3); 50% sectioning resulted in a mean subluxation of 15.3% (95% CI, 9.2-21.3); 75% sectioning resulted in a mean subluxation of 18.1% (95% CI, 12.2-23.9); 90% sectioning led to a mean subluxation of 24.1% (95% CI, 17.5-30.7); and 100% sectioning resulted in a mean subluxation of 41.6% (95% CI, 33.7-49.5). Regarding the little finger, complete dislocation occurred in only one of the nine fingers.

Even minimal sagittal band damage results in measurable subluxation, but the presence of even 10% intact fibers confers some stability against subluxation. As the extent of sagittal band disruption increases, the extensor tendon progressively deviates from its native position. Damage to the proximal fibers has a more detrimental impact on tendon stability.

The relationship between sagittal band integrity and tendon stability extends beyond a simple dislocation threshold. Both the extent of damage and location of the disrupted fibers are associated with the degree of subluxation.