No abstract

The time course of muscle contractile and cellular properties was studied in rabbit ankle flexor muscles after injury produced by eccentric exercise. Cyclic eccentric exercise was produced by increasing the tibiotarsal angle of the rabbit while activating the peroneal nerve by use of transcutaneous electrodes. Muscle properties were measured 1, 2, 3, 7, 14, and 28 days after exercise to define the time course of muscle changes after injury. A control group receiving only isometric contraction was used to study the effect of cyclic activation itself. The magnitude of the torque decline after 1 day was the same with use of isometric or eccentric exercise, but eccentric exercise resulted in a further decrease in torque after 2 days, at which time isometrically exercised muscles had fully recovered. The most prominent morphological changes in the injured muscle fibers were the loss of antibody staining for the desmin cytoskeletal protein and deposition of intracellular fibronectin, even when the injured muscle fibers retained their normal complement of contractile and enzymatic proteins. The presence of fibronectin inside the myofibers indicated a loss of cellular integrity. Invasion by inflammatory cells was apparent on the basis of localization of embryonic myosin. Thus eccentric exercise initiates a series of events that results in disruption of the cytoskeletal network and an inflammatory response that could be the mechanism for further deterioration of the contractile response.

It has been postulated that some arthroscopic shoulder stabilization failures may be due to knot slippage. In an effort to improve arthroscopic technique, we performed tensile testing on four arthroscopically tied knots with two commonly used suture materials. Handtied square knots served as controls. Sutures of No. 1 Maxon and No. 1 Ticron were used. Four types of sliding knot configurations were tested: the overhand loop, the Duncan loop, the Roeder knot, and the Snyder knot. Knots were tied via a knot pusher, and testing was performed in a normal saline-filled thermoplastic chamber. Knots were tied around two rings connected to a Bionix 858 materials testing apparatus. The knots were tested under conditions of cyclic loading and loading to failure. Results of the testing revealed that the most important factor in knot security was the type of suture material, although there were differences with the type of knot. With the Maxon suture, there was significantly decreased ultimate failure load of all of the arthroscopically tied knots compared with handtied square knots. Knots tied with Ticron were similar in strength for both arthroscopically and handtied groups. The surgeon who chooses a monofilament absorbable suture should be aware that a high percentage of knots fail under low load cyclic testing, and that all of these knots were inferior to handtied square knot controls in testing to failure.

Isometric positioning of the ACL graft or prosthesis is an important consideration in successful reconstruction of the ACL-deficient knee. This study documented the relationship between graft placement and intraarticular graft length changes and graft tension changes during knee passive range of motion. Fifteen fresh cadaveric knees were mounted in stabilizing rigs. The ACL was identified and cut in each specimen. Intraarticular reconstruction was then performed using a 6 mm polypropylene braid (3M LAD, St. Paul, MN). The following graft placements were evaluated: 1) over-the-top, 2) modified over-the-top with a femoral bone trough, 3) femoral drill hole positions, and 4) tibial drill hole positions. The proximal end of the graft was fixed to the lateral aspect of the femur with a screw and spiked washer. The distal end of the graft was attached to a turnbuckle attached to a load cell on the anterior aspect of the tibia. The knee was then extended passively from 90 degrees to 0 degrees. Two experiments were performed. In Experiment A, the turnbuckle was adjusted to keep graft tension constant and the graft length changes were recorded. In Experiment B, the graft fixation sites were not altered and tension changes with range of motion were recorded. A change in the graft distance between attachment sites with knee range of motion can be monitored either by ligament length or by tension change. With the over-the-top technique, in Experiment A, the graft distance between attachment sites increased as the knee was extended (means = 4.9 mm); in Experiment B, large tension increases were recorded with knee extension.(ABSTRACT TRUNCATED AT 250 WORDS)