Electromyographic activity of selected scapular stabilizers during glenohumeral internal and external rotation contractions.

HYPOTHESIS: An important synergistic relationship exists between the scapular stabilizers and the glenohumeral rotators. Information on the relative contribution of the scapular stabilizers to glenohumeral rotation would be useful for exercise prescription for overhead athletes and for patients with shoulder pathology. We hypothesized that the scapular stabilizers would be highly active during both maximal and submaximal internal and external rotation. MATERIALS AND METHODS: Eight healthy male volunteers (16 shoulders) performed internal and external glenohumeral rotation testing at maximal and submaximal intensities. They also performed a scapular retraction rowing exercise at maximal and submaximal levels. Electromyographic (EMG) signals were recorded from the infraspinatus, pectoralis major, serratus anterior, and middle trapezius. Values were compared among muscle groups, among individual muscles at different intensity levels, and among individual muscles at different points in the arc of motion. RESULTS: For submaximal glenohumeral internal rotation, activity in the scapular stabilizers was not different (P = .1-.83) from activity in the internal rotator throughout the range of motion. For the initial two-thirds of maximal internal rotation, middle trapezius activity and pectoralis major activity were higher (P < .05) than serratus anterior activity. For submaximal external rotation, activity in the scapular stabilizers during the middle phase of the motion was higher (P < .05) than activity in the external rotators. For maximal external rotation these differences were present throughout the motion with middle trapezius activity exceeding 100% maximal voluntary contraction. CONCLUSIONS: The scapular stabilizers functioned at a similar or higher intensity than the glenohumeral rotators during internal and external rotation. This highlights the importance of training the scapular stabilizers in upper extremity athletes and in patients with shoulder pathology.

Biomechanical comparison of a knotless suture anchor with standard suture anchor in the repair of type II SLAP tears.

PURPOSE: To compare the biomechanical strength of knotless suture anchors and standard suture anchors in the repair of type II SLAP tears. METHODS: Five pairs of cadaveric shoulders (10 shoulders) were dissected free of soft tissue except for the glenoid labrum and long head of the biceps tendon. Type II SLAP tears were created and repaired with 1 of 2 anchors: the Mitek Lupine suture anchor or the Mitek Bioknotless suture anchor (DePuy Mitek, Raynham, MA). All specimens were preloaded to 10 N, and loaded for 25 cycles in 10 N increments to a maximum of 200 N. If specimens were still intact after 200 N, they were loaded to ultimate failure. The load at which 2 mm of gapping occurred, load to ultimate failure, mode of failure, and the number of cycles to failure were compared using the Wilcoxon signed-rank test. RESULTS: Load to 2-mm gapping was lower (P = .042) for knotless anchors (70 N) versus knotted anchors (104 N), with similar differences for ultimate failure (74 N v 132 N; P = .043), cycles to 2-mm gapping (133 v 219 cycles; P = .042), and cycles to failure (143 v 297; P = .043). Eight of 10 specimens failed at the soft tissue interface (4 knotless, 4 knotted) and 2 failed by anchor pullout (1 knotted, 1 knotless). CONCLUSIONS: The results of this study suggest that repair of a type II SLAP with a Mitek knotted suture anchor and mattress suture configuration through the biceps anchor is stronger than repair with a Mitek knotless suture anchor. The most likely method of repair failure was at the suture-soft tissue interface regardless of the type of anchor used. The application of a suture anchor that requires arthroscopic knot tying may be preferable to a knotless anchor for the surgical repair of type II SLAP tears. CLINICAL RELEVANCE: Repair of type II SLAP tears with knotless suture anchors may allow for the avoidance of arthroscopic knot tying but is weaker than repair with standard suture anchors.

Cyclic loading of 3 Achilles tendon repairs simulating early postoperative forces.

BACKGROUND: The abstract goes here and covers two columns. Accelerated rehabilitation has been advocated after Achilles tendon repair, but it produces significant forces at the repair site. The abstract goes here and covers two columns. HYPOTHESIS: Stresses applied to the repaired Achilles tendon simulating postoperative forces may exceed the strength of some repairs. STUDY DESIGN: Controlled laboratory study. METHODS: Fifteen Achilles tendons were incised 4 cm proximal to the calcaneal insertion, then were repaired using either a percutaneous, 4-strand Krackow, or an epitendinous augmented 4-strand Krackow technique. Tendons were cyclically loaded to 1000 cycles each at 100, 190, and 369 N. The number of cycles to initial gapping, 5-mm gapping, and total failure were compared using Mann-Whitney U tests with adjustments for multiple comparisons. RESULTS: Gap resistance was significantly greater for augmented Krackow repairs (2208 cycles to initial gapping) versus nonaugmented repairs (502 cycles, P = .024) and for nonaugmented Krackow repairs versus percutaneous repairs (5 cycles, P = .024). All percutaneous repairs failed during the 100-N cycling (102 +/- 135 cycles). All nonaugmented Krackow repairs failed during the 190-N cycles (total cycles to failure: 1268 +/- 345). All augmented Krackow repairs were intact (no gapping) after the 190-N cycles. Four failed during 369-N cycling (total cycles to failure, 2017 +/- 11), and 1 remained intact for 3000 cycles. CONCLUSION: Epitendinous cross-stitch weave augmentation of Achilles tendon repairs significantly increased repair strength and gap resistance. CLINICAL RELEVANCE: Epitendinous cross-stitch weave augmentation of Achilles tendon repairs may better allow for early stretching and ambulation after Achilles tendon repair.

Cyclical loading of coracoclavicular ligament reconstructions: a comparative biomechanical study.

BACKGROUND: Reconstruction for injuries to the acromioclavicular joint remains controversial. HYPOTHESIS: A coracoclavicular ligament reconstruction with a semitendinosus tendon would have superior performance to the classic coracoacromial ligament transfer with or without augmentation. STUDY DESIGN: Controlled laboratory study. METHODS: Five cadaveric shoulders were used to reconstruct the coracoclavicular ligaments with 3 methods: coracoacromial ligament transfer without augmentation, coracoacromial ligament transfer augmented with No. 5 Ethibond suture, and a semitendinosus tendon. Each reconstruction was cyclically loaded at 40 N to 80 N for 2500 cycles, then from 40 N to 210 N for 2500 cycles, followed by loading to failure. The number of cycles to 50% and 100% loss of acromioclavicular joint reduction were recorded. RESULTS: During the 40 N to 80 N-loading cycle, the coracoacromial transfer without augmentation failed (15 +/- 16 cycles). The augmented coracoacromial ligament transfer and the semitendinosus reconstruction did not fail (P = .008). During the 40 N to 210 N-loading cycle, the augmented coracoacromial ligament transfer failed (207 +/- 399 cycles). The semitendinosus reconstruction survived through both loading cycles (P < .01). CONCLUSION: Coracoclavicular ligament reconstruction with a semitendinosus graft is a biomechanically superior construct in a cyclically loaded setting to a coracoacromial ligament transfer augmented with a No. 5 Ethibond suture. CLINICAL RELEVANCE: The semitendinosus graft is a strong, biologic option for reconstruction of the coracoclavicular ligaments.

Optimizing Achilles tendon repair: effect of epitendinous suture augmentation on the strength of achilles tendon repairs.

BACKGROUND: Epitendinous suture augmentation has been shown to increase gap resistance and overall strength in flexor tendon repairs of the hand. The purpose of this study was to evaluate the effect of various suture augmentation techniques in Achilles tendon repair. MATERIALS AND METHODS: Eighteen fresh-frozen cadaveric Achilles tendons were transected and repaired with a 4-strand Krackow core stitch. Suture augmentation was performed with 3 figure-of-eight stitches in 6 specimens and a running cross-stitch weave in 6 specimens. The other 6 specimens were not augmented. Each tendon was loaded to failure on an MTS. Force to failure (defined as peak force or force at 5 mm gapping), gapping resistance, stiffness, and elongation were compared. RESULTS: Force to failure (p < 0.001), stiffness (p < 0.01) and gapping resistance (p < 0.05) were increased by suture augmentation. Additionally failure force and gapping resistance for the cross-stitch augmentation was higher than the figure-of-eight augmentation (p < 0.05). CONCLUSION: Cross-stitch augmentation of Achilles tendon repair yields a stronger and stiffer repair with greater resistance to gapping. CLINICAL RELEVANCE: Achilles tendon repairs augmented with a cross stitch weave will be able to withstand substantially higher forces than non-augmented repairs.

Reconstruction of the coracoclavicular ligaments with tendon grafts: a comparative biomechanical study.

BACKGROUND: Numerous surgical techniques have been described to address injuries to the coracoclavicular ligaments. PURPOSE: To compare the biomechanical properties of tendon graft reconstructions with those of the native coracoclavicular ligaments and various other repair methods. STUDY DESIGN: Controlled laboratory study. METHODS: Eleven fresh-frozen human cadaveric shoulders were tensile tested to failure to compare the biomechanical properties of the native coracoclavicular ligaments, coracoacromial ligament transfer, No. 5 Mersilene suture repair, 5-mm Mersilene tape repair, and tendon graft reconstructions with gracilis, semitendinosus, and long toe extensor tendons. RESULTS: Reconstructions with semitendinosus, gracilis, or long toe extensor tendon grafts were found to have superior initial biomechanical properties compared with coracoacromial ligament transfer; failure strengths were as strong as those of the native coracoclavicular ligaments. Failure of the tendon grafts occurred through the midsubstance of the tendon graft, not at the fixation site. CONCLUSIONS: Tendon graft reconstruction may be an alternative to coracoacromial ligament transfer and may provide a permanent biologic reconstruction with superior initial biomechanical properties, including that of tensile strength. CLINICAL RELEVANCE: Use of tendon graft reconstruction may limit the need for postoperative immobilization and lead to an accelerated rehabilitation program.