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The Impact Of Dividing The Flexor Tendon Pulleys On Tendon Excursion And Work Of Flexion In A Cadaveric Model
Hatcher G. Cox, M.D.1,2, Bradford Hill, M.D.2, Pooyan Abbasi, M.Sc.3, Aviram Giladi, M.D.2, Ryan Katz, M.D.2.
1Department of Plastic Surgery, Medstar Georgetown University Hospital, Washington, DC, USA, 2The Curtis National Hand Center, MedStar Union Memorial Hospital, Baltimore, MD, USA, 3MedStar Health Research Institute, Hyattsville, MD, USA.

PURPOSE
The A2 and A4 pulleys of the flexor tendon system have traditionally been considered critical components of efficient digital flexion. This dogma has recently been challenged. The practical implications of understanding true pulley function are most apparent when deciding to sacrifice pulleys to achieve a high-quality flexor tendon repair, especially in Zone 2. Using fresh cadaveric hands and a novel model to measure force and excursion, we sought to clarify the clinical significance of releasing different pulleys.
METHODS
Combinations of A1, A2, and A4 pulleys were released on the index through small fingers of fresh, never frozen cadaveric hands. Excursion was measured as the distance the tendon was pulled by the motor to achieve palm touchdown. The force applied by the motor was constant (25 Newtons); work was derived from the product of force and excursion (distance). The change in excursion and work needed to achieve palm touchdown before and after pulley compromise was measured. Excursion varies amongst digits and specimens at baseline; therefore, the percent change from the intact state was used to compare groups. The following comparisons were made: A2 versus A1, A4 versus A1, A4 versus A2, A1+A2 versus A2, A1+A4 versus A4.
RESULTS
Table 1 shows the change in excursion after isolated or combination pulley release. Isolated A2 or A4 release had the greatest individual impact on excursion. When A1 was released with A2, the additional impact was significant; however, when A1 was released with A4, the impact was marginal (Table 2). No clinically or statistically significant change in the work of flexion was detected.
Table 1: Change in excursion

Pulley(s) ReleasedNPercent change excursion
(mean ±SD)
Change Excursion in mm (mean ±SD)
A1110.69 ±1.221.46 ±0.68
A2154.77 ±1.522.40 ±0.85
A483.88 ±1.932.05 ±0.78
(A1+A2)119.90 ±2.526.04 ±1.77
(A1+A4)82.63 ±2.812.25 ±0.70

Table 2: Comparing change in excursion
GroupsPercent Difference in Excursion (mean ±SD)p – value
A2 vs. A14.07 ±0.79<0.001*
A4 vs. A13.19 ±0.930.001*
A4 vs. A2-0.89 ±0.880.314
(A1+A2) vs. A25.13 ±0.79<0.001*
(A1+A4) vs. A4-1.24 ±1.000.220
Difference = (µgroup1group2)
* significant at Bonferroni-corrected α = 0.01

CONCLUSIONS
Sacrifice of the A2 and A4 pulleys made a statistically significant difference in flexor tendon excursion. The addition of A1 release was significant when added to A2 release, but not when added to A4 release, which is likely because of the interposed intact A2 pulley. We did not find a significant difference in the percent work between groups. We found the absolute change in excursion in millimeters after pulley release to be statistically significant, although clinically negligible. Because the absolute change is not likely clinically significant, we argue that A2 or A4 sacrifice to achieve an excellent tendon repair is justified. A1 may play a larger role than previously believed if other proximal pulleys are sacrificed.


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