Background: Rehabilitation methods that generate
increased tendon force and motion have been advocated to improve
results following intrasynovial flexor tendon repair. However, the
effects of rehabilitation force and motion on tendon-healing may
be masked by the high stiffness produced by newer suture methods.
Our objective was to determine whether the biomechanical properties
of tendons repaired by one of two multistrand suture methods were
sensitive to an increased level of applied rehabilitation force.
Methods: Two hundred and fourteen flexor digitorum
profundus tendons from 107 adult dogs were transected and repaired.
Dogs were assigned to one of four groups based on the rehabilitation
method (low force [<5 N] or high force [17
N]) and the repair technique (four-strand or eight-strand
core suture) and were killed between five and forty-two days after
the procedure. Repair-site structural properties were determined
by tensile testing, and digital range of motion was assessed with
use of a motion-analysis system.
Results: Tensile properties did not differ between
the low and high-force rehabilitation groups, regardless of the
repair technique (p > 0.05). In contrast, tensile properties
were strongly affected by the repair technique, with tendons in
the eight-strand group having an approximately 35% increase
in ultimate force and rigidity compared with those in the four-strand
group (p < 0.05). Ultimate force did not change significantly
with time during the first twenty-one days (p > 0.05);
there was no evidence of softening in either of the repair or rehabilitation groups.
Force increased significantly from twenty-one to forty-two days,
while rigidity increased throughout the forty-two-day period (p < 0.05).
Conclusions: Increasing the level of force applied
during postoperative rehabilitation from 5 to 17 N did not accelerate
the time-dependent accrual of stiffness or strength. Suture technique
was of primary importance in providing a stiff and strong repair
throughout the early healing interval.
Clinical Relevance: Our findings suggest that there
be a reexamination of the concept that increases in force produced
by more vigorous mobilization protocols are beneficial to tendon-healing.
While more vigorous rehabilitation may help to improve hand function,
we found no evidence that it enhances tissue-healing or strength
in the context of a modern suture repair.