Late breakage of orthopaedic staple causing peroneal nerve palsy

Comparative evaluation of different anchoring techniques for synthetic cruciate ligaments. A biomechanical and animal investigation

Under certain well-defined indications alloplastic material may be used in cruciate ligament surgery. The stability and survival of such a synthetic ligament is to a great extent dependent on the anchorage with which it is fastened to the bone. Most fixation methods have proved to be too weak or have revealed other essential drawbacks, resulting in clinical and experimental failure. A new ligament fixation device (LFD) was developed and tested biomechanically and in animal experiments. In the biomechanic investigation the new LFD was compared to single staples, double staples in the belt-buckle technique, and ligament guidance through additional bone tunnels (Z-technique). The tests were carried out on human cadaver knees, plastic bones, and dog stifle joints. The evaluated parameters were linear and maximum load, stiffness, and elongation. In addition, hysteresis tests were performed to assay the long-term resistance of the fixation. The tests showed a significant superiority of the LFD in all measured variables compared to the other anchorages. The pull-out strength, at 1866 +/- 43 N (cadaver knee), was about four times that for the single staple, and about twice as high as that for the double staple and Z-technique. The animal experiments were performed on German shepherd cross-breed dogs. In six animals the anterior cruciate ligaments were excised bilaterally and replaced by a 6-mm Trevira ligament, on one side anchored with staples in the Z-technique, on the other with the LFD. Postoperatively the dogs were allowed to move freely; no additional protection was employed. After 6 months the animals were sacrificed and the knees examined macroscopically, radiologically, microscopically, and by biomechanical testing. After half a year of implantation, the pull-out strength of the alloplastic ligament was 662 +/- 62 N for the LFD and 531 +/- 67 N for the staples. Three ligaments in the staple group and one in the LFD group had ruptured completely, and two ligaments partially, one in each group. The average anterior drawer in the LFD group was 2.8 mm, in the staple group 4.0 mm. In all cases the alloplastic ligament was separated from the bone by a fibrous interface. None of the fixation devices showed signs of loosening. There was no foreign body reaction around the anchorages. Major cartilage degeneration was observed in two stifle joints of each group, mainly associated with instability.

[Experimental evaluation of various anchoring techniques for synthetic ligaments]

One of the weak points of augmentation or replacement of cruciate ligaments by synthetic material is the fixation of these artificial ligaments to the bone. The present investigation examines the mechanical properties of a newly developed anchoring technique (ligament fixation device = LFD) in regard to linear and maximum load, stiffness, creep, and long-term durability compared to single staples, double staples in belt buckle technique, and passing the ligament through an additional bone tunnel. The tests are carried out on cadaver knees and plastic bones under standardized conditions with the same artificial ligament in all experiments (Trevira hochfest). The LFD shows a linear load of 1866 N in cadaver knees and 1874 N in plastic bones. The stiffness is 68.3 N/mm respectively 51.9 N/mm, the elongation at 500 N load 12.7 mm respectively 10.9 mm. In the hysteresis tests with submaximum loads the ligament/LFD-unit lasts 8515 cycles in the plastic bone and 4431 cycles in the cadaver knee. These results are significantly superior to all other fixation techniques concerning linear load, stiffness and long-term durability. They permit aggressive functional treatment and immediate postoperative weight bearing of the operated knee.