Alberto G. Schneeberger

Mechanical strength of repairs of the rotator cuff

We have studied the mechanical properties of several current techniques of tendon-to-bone suture employed in rotator-cuff repair. Non-absorbable braided polyester and absorbable polyglactin and polyglycolic acid sutures best combined ultimate tensile strength and stiffness. Polyglyconate and polydioxanone sutures failed only at high loads, but elongated considerably under moderate loads. We then compared the mechanical properties of nine different techniques of tendon grasping, using 159 normal infraspinatus tendons from sheep. The most commonly used simple stitch was mechanically poor: repairs with two or four such stitches failed at 184 N and 208 N respectively. A new modification of the Mason-Allen suture technique improved the ultimate tensile strength to 359 N for two stitches. Finally, we studied the mechanical properties of several methods of anchorage to bone using typically osteoporotic specimens. Single and even double transosseous sutures and suture anchor fixation both failed at low tensile loads (about 140 N). The use of a 2 mm thick, plate-like augmentation device improved the failure strength to 329 N. The mechanical properties of many current repair techniques are poor and can be greatly improved by using good materials, an improved tendon-grasping suture, and augmentation at the bone attachment.

Experimental Rotator Cuff Repair. A Preliminary Study

BACKGROUND The 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. METHODS We 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. RESULTS In 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. CONCLUSIONS The 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. CLINICAL RELEVANCE Different 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.

Mechanical strength of arthroscopic rotator cuff repair techniques: an in vitro study.

Background: Retears after rotator cuff repairs occur relatively frequently and may compromise the functional result. The goal of this study was to analyze the mechanical properties following arthroscopic techniques for rotator cuff repair and to evaluate possible alternative techniques.Methods: In the first part, five different bone anchors (the Revo screw; Mitek Rotator Cuff anchor, 5.0-mm Statak, PANALOK RC absorbable anchor, and 5.0-mm Bio-Statak) were tested in vitro under cyclic loading on five pairs of cadaveric shoulders. Then five types of arthroscopic tendon suturing instruments were tested on rotator cuff tendons. Finally, the arthroscopically performed mattress and modified Mason-Allen stitches, fixed with either the Revo screw or the Bio-Statak, were evaluated on ten pairs of human cadaveric shoulders.Results: The holding strengths of the various anchors were similar, ranging from 130 to 180 N, and approximated the holding strength of knotted number-2 suture materials. The fixation of the tested anchors yielded comparable values of stiffness except for one anchor, which showed significantly greater subsidence under cyclic load (p = 0.003). All tested, commercially available arthroscopic suturing devices were unsuitable for performing a modified Mason-Allen stitch on normal supraspinatus tendons. Modification of a commercially available suture punch with a longer needle allowed us to consistently perform a modified Mason-Allen stitch. The modified Mason-Allen stitch, which has shown favorable mechanical properties in open repairs of the rotator cuff, was not found to be stronger than the mattress stitch when performed arthroscopically and used with bone anchors. When the modified Mason-Allen stitch was fixed to one anchor, it was even weaker than a mattress stitch repaired with another anchor (168 versus 228 N). Unequal loading of the two suture branches due to the more rigid modified Mason-Allen stitch may be the reason for this difference.Conclusions: Arthroscopic techniques for rotator cuff repair with use of the mattress stitch and bone anchors allow for a relatively solid fixation. The holding strength is not improved with use of the modified Mason-Allen stitch. Although a direct comparison with previous in vitro studies is not possible, the holding strength of open fixation techniques seems to be stronger. If rotator cuffs are subjected to high postoperative loading, open repair might be preferred to reduce the risk of a retear, until stronger arthroscopic fixation techniques are developed.

Semiconstrained total elbow replacement for the treatment of post-traumatic osteoarthrosis

Forty-one consecutive patients were managed for post-traumatic osteoarthrosis or dysfunction of the elbow with use of a non-customized semiconstrained Coonrad-Morrey total elbow prosthesis. The average age at the time of the operation was fifty-seven years (range, thirty-two to eighty-two years). The patients were followed for an average of five years and eight months (range, two to twelve years). Radiographs were made at least two years postoperatively (average, five years and one month; range, two to twelve years) for thirty-nine of the forty-one patients. According to the Mayo elbow performance score, sixteen patients (39 per cent) had an excellent result, eighteen (44 per cent) had a good result, five (12 per cent) had a fair result, and two (5 per cent) had a poor result. Thirty-six (95 per cent) of the thirty-eight patients who had a functioning implant at the time of follow-up considered the outcome to be satisfactory. Preoperatively, thirty-seven patients (90 per cent) had moderate or severe pain; postoperatively, thirty (73 per cent) had no or only mild discomfort. Motion improved from an average arc of flexion of 40 to 118 degrees preoperatively to an average arc of flexion of 27 to 131 degrees postoperatively. All thirty-eight functioning implants rendered the elbow stable. Eleven patients (27 per cent) had a major complication. Nine of them (22 per cent of the series) needed an additional operation. There was no aseptic loosening, and most of the complications were primarily due to so-called mechanical failure. The ulnar component fractured in five patients (12 per cent), and the polyethylene bushings wore out in two (5 per cent). These complications were attributed principally to the performance of strenuous physical labor, such as lifting more than ten kilograms on a regular basis, against the advice of the surgeon; excessive preoperative deformity of the joint; or an unstable traumatic injury. Two patients (5 per cent) had an infection. Semiconstrained joint replacement of the elbow can be a reliable form of treatment, and frequently is the only viable option, for the difficult problems encountered with post-traumatic destruction of a joint. Restoration of function, relief of pain, and patient satisfaction can be achieved even when a patient is less than sixty years old if that patient has low demands and a low level of activity. However, the mechanical failures underscore the fact that this procedure is relatively contraindicated in patients who anticipate strenuous physical activity or who are not expected to comply with the postoperative protocol. This observation reflects the tendency for increased and excessive use of a previously functionless joint, after it has been rendered stable and pain-free, to lead to mechanical failure.

Reduction of triceps muscle force after shortening of the distal humerus: A computational model

Bone deficiency resulting in shortening of the distal humerus may occur after fractures, treatment of nonunions, or revision of total elbow arthroplasty. A biomechanical model of the triceps muscle and tendon was used to investigate the effect of distal humeral shortening on triceps force production. The analysis indicated that shortening of the distal humerus primarily influences the media head of the triceps, which contributes most to elbow extension strength in extended elbow positions. In a posture of 30 degrees elbow flexion, shortening the distal humerus by 1, 2, and 3 cm reduced the extension strength by 17%, 40%, and 63%, respectively. At 90 degrees of flexion, strength was reduced by 11%, 15%, and 21%, respectively. This result suggests that shortening the humerus by 1 cm may be well tolerated, but shortening by 2 or more cm may cause a significant reduction in triceps force. This would be particularly important in patients requiring terminal extension strength for weight bearing.

Anconeus Arthroplasty: A New Technique for Reconstruction of the Radiocapitellar and/or Proximal Radioulnar Joint

Background: Management of posttraumatic radiocapitellar and/or proximal radioulnar joint dysfunction and pain is a challenging problem, often with more than one pathological feature, and to date there are no consistently reliable solutions. The unreliability of prosthetic replacement prompted us to develop an anconeus arthroplasty wherein the anconeus muscle is rotated into the radiocapitellar and/or proximal radioulnar joint.Methods: Three interposition options were assessed in our laboratory and were employed clinically: interposition at the radiocapitellar joint (Type I), interposition at the radiocapitellar and proximal radioulnar joints (Type II), and proximal radioulnar interposition (wrap) (Type III). The clinical outcomes in fourteen patients who had been treated with one of the three types of anconeus interposition arthroplasty were reviewed at least two years (mean, 6.1 years) postoperatively.Results: Anatomic dissection of twenty-five specimens revealed that all three applications were possible. Of the fourteen patients, twelve (all six with a Type-I interposition, three of the five with a Type-II interposition, and all three with a Type-III interposition) had a satisfactory overall subjective result. The Mayo Elbow Performance Score averaged 63 points before the surgery and 89 points after it.Conclusions: Anconeus interpositional arthroplasty offers a reasonable likelihood of improved subjective and objective function in patients with the challenging problem of radiocapitellar and/or proximal radioulnar joint dysfunction and pain after trauma, even when there is Essex-Lopresti axial instability.

Anterior deltoid reeducation for irreparable rotator cuff tears revisited

BACKGROUND A previous study introduced a method of conservative treatment of irreparable rotator cuff tears (RCTs) using a rehabilitation program (anterior deltoid reeducation [ADR]). The purposes of this study were to present our experience with ADR and to compare our results with those of the previous study. METHODS Thirty consecutive elderly patients with irreparable RCTs were prospectively enrolled and taught how to perform the home-based ADR program for a period of 3 months. Clinical and radiographic evaluations were determined at the first visit. Clinical follow-up was available after 9 and 24 months. Failure of the ADR program was defined as abandonment of the ADR program because of pain and/or a patients decision to undergo surgery at any time or a less than 20-point improvement in the American Shoulder and Elbow Surgeons score at last follow-up. RESULTS Of the 30 patients, 9 did not complete the 3-month ADR program because of pain. Of the 21 patients who completed the ADR program, 3 were not satisfied with the outcome and went on to undergo surgery. Eighteen of the 30 patients completed the program and had a follow-up at 24 months. Among these 18 cases, there were significant mean improvements between pre-ADR and follow-up outcome scores among all variables (P < .005). However, 6 of these 18 patients did not have an improvement in the American Shoulder and Elbow Surgeons score by at least 20 points. Overall, the ADR program had a success rate of only 40%. CONCLUSION A 3-month ADR program had limited success to treat irreparable RCTs. We could not reproduce the high rate of satisfactory results of 82% found in a previous study.