Stephan Perren

Experimental Rotator Cuff Repair. A Preliminary Study

BACKGROUNDnThe repair of chronic, massive rotator cuff tears is associated with a high rate of failure. Prospective studies comparing different repair techniques are difficult to design and carry out because of the many factors that influence structural and clinical outcomes. The objective of this study was to develop a suitable animal model for evaluation of the efficacy of different repair techniques for massive rotator cuff tears and to use this model to compare a new repair technique, tested in vitro, with the conventional technique.nnnMETHODSnWe compared two techniques of rotator cuff repair in vivo using the left shoulders of forty-seven sheep. With the conventional technique, simple stitches were used and both suture ends were passed transosseously and tied over the greater tuberosity of the humerus. With the other technique, the modified Mason-Allen stitch was used and both suture ends were passed transosseously and tied over a cortical-bone-augmentation device. This device consisted of a poly(L/D-lactide) plate that was fifteen millimeters long, ten millimeters wide, and two millimeters thick. Number-3 braided polyester suture material was used in all of the experiments.nnnRESULTSnIn pilot studies (without prevention of full weight-bearing), most repairs failed regardless of the technique that was used. The simple stitch always failed by the suture pulling through the tendon or the bone; the suture material did not break or tear. The modified Mason-Allen stitch failed in only two of seventeen shoulders. In ten shoulders, the suture material failed even though the stitches were intact. Thus, we concluded that the modified Mason-Allen stitch is a more secure method of achieving suture purchase in the tendon. In eight of sixteen shoulders, the nonaugmented double transosseous bone-fixation technique failed by the suture pulling through the bone. The cortical-bone-augmentation technique never failed. In definite studies, prevention of full weight-bearing was achieved by fixation of a ten-centimeter-diameter ball under the hoof of the sheep. This led to healing in eight of ten shoulders repaired with the modified Mason-Allen stitch and cortical-bone augmentation. On histological analysis, both the simple-stitch and the modified Mason-Allen technique caused similar degrees of transient localized tissue damage. Mechanical pullout tests of repairs with the new technique showed a failure strength that was approximately 30 percent of that of an intact infraspinatus tendon at six weeks, 52 percent of that of an intact tendon at three months, and 81 percent of that of an intact tendon at six months.nnnCONCLUSIONSnThe repair technique with a modified Mason-Allen stitch with number-3 braided polyester suture material and cortical-bone augmentation was superior to the conventional repair technique. Use of the modified Mason-Allen stitch and the cortical-bone-augmentation device transferred the weakest point of the repair to the suture material rather than to the bone or the tendon. Failure to protect the rotator cuff post-operatively was associated with an exceedingly high rate of failure, even if optimum repair technique was used.nnnCLINICAL RELEVANCEnDifferent techniques for rotator cuff repair substantially influence the rate of failure. A modified Mason-Allen stitch does not cause tendon necrosis, and use of this stitch with cortical-bone augmentation yields a repair that is biologically well tolerated and stronger in vivo than a repair with the conventional technique. Unprotected repairs, however, have an exceedingly high rate of failure even if optimum repair technique is used. Postoperative protection from tension overload, such as with an abduction splint, may be necessary for successful healing of massive rotator cuff tears.

Xylenol orange, a fluorochrome useful in polychrome sequential labeling of calcifying tissues.

Xylenol orange is fixed in newly formed calcified tissues where it remains until removal of the bone mineral. It may be visualized in undecalcified histological sections in a similar way to the tetracyclines by means of its fluorescence. The fluorescence contrasts to that of known fluorescent dyes. Intravital bone labeling by Xylenol orange is achieved by parenteral administration of the dye. A dose of 90 mg/kg given as a 3% aqueous solution was found suitable. The general toxicity, local effect on calcification and resistance of the fluorescence to histological chemicals and long term excitation were assessed. It is noteworthy that the fluorescence of Xylenol orange is found exactly at the same site as that of tetracyclines, fluoresceins and Calcein blue. Xylenol orange is thus suitable for single or for polychrome sequential labeling.

The effect of fracture on femoral head blood flow: Osteonecrosis and revascularization studied in miniature swine

Miniature swine were used to study the effect of cervical fracture on femoral head blood flow. Laser Doppler flowmetry was used to evaluate femoral head blood flow before and after the fracture, after internal fixation with or without compression, and 8 weeks post-fracture. Fluorescent bone-labeling was performed at 2, 4 and 6 weeks post-fracture. Femoral head blood flow decreased to 40 percent of baseline following fracture, partly from the disruption of venous drainage. Histologically, all femoral heads showed some degree of trabecular thinning, microfracture, and neovascularization when compared with controls. Analyses of the laser Doppler flowmetry data, fluorescent label histology, microradiography and bone densitometry indicated that late (4-6 weeks) revascularization produces severe trabecular mechanical weakening and resultant femoral head collapse. Femoral head ischemia following fracture probably falls along a continuum, with only the more severe cases proceeding to mechanical collapse. Femoral neck fractures in the minipig produce femoral head necrosis of a severity and incidence which closely parallels that of the human population; thus, the minipig is a useful model for further study of complications following femoral neck fracture in humans.

Scientific and Technical Background

The Association for the Study of Internal Fixation (ASIF) was founded in 1958 in Switzerland under its original German name “Arbeitsgemeinschaft fur Osteosynthesefragen (AO),” a working group to deal with questions on internal fixation of fractures. This group in the meantime has become an international organization dedicated to improving the care of patients with musculoskeletal injuries and their sequelae through research and education in the principles, practice, and quality control of the results of treatment. In 1984 this study group was transformed into a nonprofit foundation providing an umbrella structure for its activities in the fields of research, development, education, and documentation. New technologies and products developing from ideas and from research and development activities are licensed to the three Synthes producers, Mathys AG Bettlach, Stratec Medical Oberdorf, both in Switzerland, and Synthes USA, Paoli. The royalties which they pay finance the activities of the AO/ASIF Foundation.