With this protocol, we were able to assess the mechanical properties of a flexor tendon repair. Novel developments, such as linear tension strength, can be reliably evaluated this way. Even slight differences can be detected.
To begin, place a fresh cadaveric upper limb on the dissecting table, with the ventral palmar side facing the surgeon. Using a number 15 scalpel, place a median longitudinal incision at the index finger on the palmar side, beginning from the distal phalanx, distally toward the A1 pulley over the metacarpophalangeal joint. Sever the A1 and A2 pulleys longitudinally without injuring the flexor tendons, and then sever the flexor digitorum profundus at the level of the distal interphalangeal joint using a scalpel.
Use a tendon retractor to set the tendon under traction and retrieve the flexor digitorum profundus at the level of the A1 pulley. Then, make a six centimeter transversal incision on the rasceta crease, using a number 15 scalpel. Make another transversal incision 10 centimeters proximal to the rasceta.
Next, make a longitudinal incision at the median of the palmar side of the forearm, connecting the two transversal incisions. Develop two opposing skin flaps at the level of the forearm fascia to expose the flexor tendons. The flexor tendons are readily identifiable under the skin.
Again, use a tendon retractor to place the flexor digitorum tendon under traction, and retract the tendon proximal to the wrist. Sever the tendon at the musculotendinous junction for maximal tendon length with a number 11 scalpel, and place the tendon specimen into 500 milliliters of 0.9%saline solution. Repeat these steps for the third to fifth fingers.
Fix the tendon specimen on an expanded polystyrene plate with pins or 18-gauge cannulas, and transect the tendon in the middle, using a scalpel with a number 11 blade. Next, for the Adelaide"cross lock 4-strand core repair, insert the needle into the left stump of the transected tendon, and follow the path of the tendon on the surgeon's side for 1.5 centimeters, and exit at the surface of the tendon. Insert the needle three millimeters to the left and take a bite of three millimeters, exiting toward the surgeon.
Then, insert the needle three millimeters to the right, next to the exit point of the first path, and follow the tendon to the very side until the left stump. Insert the needle into the right stump in a path at the very outer part of the tendon, and exit approximately 1.5 centimeters to the right of the stump. Then, insert the needle again at three millimeters to the right.
Take a grasp, and exit at the side of the tendon. Insert the needle back toward the right stump, entering approximately three millimeters to the left. Exit at the right stump, and enter again into the left stump for 1.5 centimeters.
Grasp a portion of the tendon of three millimeters with the suture, and exit near the midline. Reinsert the needle three millimeters nearer to the stump, and follow the direction of the tendon to the right, making sure to exit at the stump. Insert the needle into the right stump, and follow the tendon fibers approximately 1.5 centimeters to the right.
Exit at the surface. Re-enter the tendon further to the right and take a grasp, aiming to the far side. Insert the needle three millimeters to the left, and follow the tendon, exiting at the stump.
Now, tie a surgical knot with eight throws, alternating the direction manually. For M-Tang 6-strand core repair, insert the needle of the loop approximately 1.5 centimeters from the right stump of the tendon, and grasp a portion of the tendon of approximately three millimeters in size. Then, pass the needle through the loop and insert the needle into the surface of the tendon.
Follow the path of the tendon and exit between the stumps. Re-insert the needle into the opposite stump and follow the tendon in the deep plane for 1.8 centimeters. Exit at the surface of the tendon.
Next, enter three millimeters near the stump. Follow a transversal path to the far side of the tendon and exit there. Insert the needle bearing the loop three millimeters to the left, further away from the stumps.
Follow the path of the tendon and exit between the stumps. Re-enter at the opposite stump and exit 1.5 centimeters to the right at the surface of the tendon. Cut one of the two strands arming the needle with scissors.
Then, insert the needle and grasp a three millimeter portion of the tendon. Manually tie a surgical knot with eight throws, alternating the direction. Take another loop suture and perform a Tsuge suture by grasping a portion of the tendon of approximately three millimeters at 1.5 centimeters to the right.
Re-insert the needle and follow the path of the tendon to the left. Exit between the stumps. Re-enter into the left stump and follow the path of the tendon for 1.5 centimeters.
Exit at the surface of the tendon. Cut one of the two strands arming the needle with a pair of scissors, and re-insert the needle, grasping three millimeters of the tendon. Finally, tie a surgical knot manually with eight throws, alternating the direction.
The linear tensile strength of polypropylene and polytetrafluoroethylene, when using the Kirchmayr-Kessler technique, is shown here. There was no difference between the two materials in terms of linear tensile strength, although polytetrafluoroethylene was somewhat weaker due to slippage. When an epitendinous running suture was used, slippage was less of a problem for the polypropylene repairs, but the repair broke down at approximately 50 Newton.
On the contrary, repairs with polytetrafluoroethylene failed at around 70 Newton due to slippage. With the combination of a stronger repair, such as 4-strand Adelaide"or 6-strand M-Tang, and a stronger suture material, such as polytetrafluoroethylene or multistrand, a linear tension strength of 75 Newton or more could be achieved. No significant advantage of the 4-strand versus the 6-strand technique was observed.
A summary of the results from the flexor tendon repairs is shown here. Repairs with polytetrafluoroethylene displayed a peak tensile strength comparable to multistrand. Both the repairs were significantly stronger than those with polypropylene.
The repairs should be performed symmetrically at both stumps of the severed tendon. The multistrand suture should be rinsed in order for the suture to slip evenly through the fibers of the tendon. The knots of the repair poses some problems.
Maybe in the future, some knotless kind of repair can be developed.
