However, when the weight was removed in these trials, both ligatures markedly lost tension. Veterinary surgeons use them when tying off the uterine pedicle both ligatures tighten easily and clamp down through surrounding fatty tissue to compress an artery. The strangle knot and modified miller’s knot are essentially identical except for the location of the crossing strand ( Fig 1). The constrictor knot’s performance was consistent with its reputation, it being commonly used without any additional locking knots to secure sacks or prevent a rope’s end fraying. The SDOS knot and the modified surgeon’s knot were intermediate, and the surgeon’s knot, strangle knot and modified miller’s knot retained very little tension. The constrictor knot was the only ligature that retained tension well. This may be attributed partly to the friction in the additional throw and partly to the awkward ‘D’ shape that such knots adopt during tightening, the ideal being more circular. The results indicate that the double overhand also works to prevent tightening. The three that did not (the surgeon’s knot, the modified surgeon’s knot and the SDOS knot) all incorporate a double overhand intended to prevent slipping. The strangle knot, modified miller’s knot and constrictor knot all tightened readily. The ligature was then retied using a fresh section of suture material, and the sequence was repeated several times for each combination of ligature and suture material. Again, the peak force was recorded and the load cell reset to zero. After at least 30 seconds, recording was restarted and the handle was rotated. The load distributing frame was then raised and supported, releasing all tension on the suture material. This peak force was recorded and the load cell was reset to zero. The measured force increased steadily until the ligature slipped. The load cell was set to record and the vice handle was rotated to lower the jaw at a rate of about 0.05mm/sec. The prepared weight was then suspended from the frame, taking care to avoid any shock load or pendulum movement. With the knot in place and no load on the suture material, the tare weight for the load cell was set to zero. After each test, this loop was rotated slightly around the four pulleys to test a fresh portion of the suture material. Each end hung down and was knotted securely to the cord of the load distributing frame, creating a circular loop of suture material and cord. The selected suture material was threaded over one small pulley, knotted around the rod below the washer using the test ligature and then threaded over the other small pulley. To test the properties of a constrictor knot, he designed a horizontal test bench to measure the force required to pull a rod through a ligature, using friction as an indirect measure of tension. This study evaluated the constrictor knot for use in surgery and compared it with other ligature knots.īefore this study was initiated, one of the authors (HT) tested the constrictor knot’s ability to restrict flow in plastic tubing and also used it as a ligature for such procedures as pedicle ligation in canine ovariohysterectomy. We found no study that examined either the constrictor knot or the stability of the critical first part of a ligature knot. However, these studies all considered the completed knot. Leitch et al bench tested several knots for their ability to attenuate flow through a plastic tube. In the knotting world, the constrictor knot is the pre-eminent binding knot. This critical risk was the subject of this study. Despite this, slipping may occur prior to the addition of the lock, particularly during an instrument tie. ![]() In practice, ligatures are locked with additional overhand knots. This study examined the ability of a ligature to be tightened and then remain tight. Ligature failures are reported, sometimes with critical consequences (eg after pulmonary resection and laparoscopic cholecystectomy in humans, or following pedicle ligation in canine or equine hysterectomy).
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