The tension required at repair to reappose the supraspinatus tendon to bone rapidly increases after injury

Rotator cuff tears occur frequently and can cause significant pain and reduced shoulder function. A high percentage of patients are satisfied after surgical repair of rotator cuff tears, but a smaller percentage of patients with chronic tears continue to have pain and poor shoulder function. This may be partly attributable to an increase in the repair tension, the force required at repair to reappose the tendon to its original insertion site on the humerus. Increases in repair tension have been shown to occur for long-standing ruptures of the supraspinatus tendon, but the precise tension at various times after injury are unknown. Therefore, the objective of the current study was to determine the repair tension at various times after a rotator cuff tear. This was achieved by creating a full-thickness supraspinatus tendon tear in a rat model and measuring the mechanical characteristics of the musculotendinous unit at 0, 2, 4, 9, and 16 weeks after injury. The repair tension rapidly increased initially after injury followed by a progressive, but less dramatic, increase with additional time. These findings suggest that rotator cuff tears should be repaired early in the clinical setting. Future studies will investigate the effect of repair tension on tendon to bone healing after repair.     

Biomechanical effect of patch graft for large rotator cuff tears: a cadaver study

It is not possible for some rotator cuff tears to be repaired because of a large defect associated with muscle retraction. The purpose of the current study was to investigate the use of a synthetic patch graft to restore abduction force transmission in the glenohumeral joint with a rotator cuff defect. Shoulders from cadavers (n = 10) were fixed in the hanging arm and in neutral rotation, and loading was applied to the rotator cuff tendons and middle deltoid. After a simulated supraspinatus tendon defect and retraction, a patch graft was inserted into the defect and the effects of reattachment to the greater tuberosity, narrowing of the defect by using a smaller graft, and anterior graft attachment (rotator interval tissue versus subscapularis) were investigated. Abduction torque generation was measured and normalized to the intact condition. Compared with torque generation after creation of a supraspinatus defect (61% of normal torque), abduction torque increased with a graft between the infraspinatus and either the rotator interval (68% of normal) or subscapularis (80% of normal). The optimum grafting technique for abduction torque restoration occurred with a reduced size patch connected anteriorly to the subscapularis and sutured to the greater tuberosity (107% of normal). The patch graft acts to redirect force transmission, thereby providing a potential treatment option for otherwise irreparable defects. These same principles can be applied when tendon transfers are used to reconstruct large or massive cuff tears.     

In-vitro reconstruction of massive rotator cuff ruptures with triceps tendon or coracoacromial ligament

The possibility of reconstructing a massive rotator cuff rupture with a free graft of the triceps tendon or the coracoacromial ligament was tested experimentally in an anatomical and biophysical cadaver investigation. After dissection of the rotator cuff, a section of the supraspinatus tendon was removed to simulate a defect in the cuff. In dissection of the grafts, a bony squama was incorporated by osteotomy. The rotator cuff was reconstructed by suturing the free grafts into the defect. In addition, the bony squama was refixed in a prepared bone groove in the greater tuberosity of the humerus. The tensile strength and the elasticity of the grafts were compared with that of the supraspinatus tendon in rupture tests. The mean value of the maximum load determined (FRm) was greatest for the triceps tendon (706.451 N), while very much lower values were found for the coracoacromial ligament (395.836 N) and the supraspinatus tendon (496.792 N). The mean value of the maximum elasticity (LAm) was lowest for the coracoacromial ligament (4.701%); the supraspinatus tendon (7.047%) and the triceps tendon (8.250%) showed very much greater elasticity. Received: 6 November 1999     

Variation in external rotation moment arms among subregions of supraspinatus, infraspinatus, and teres minor muscles.

A rotator cuff tear causes morphologic changes in rotator cuff muscles and tendons and reduced shoulder strength. The mechanisms by which these changes affect joint strength are not understood. This study's purpose was to empirically determine rotation moment arms for subregions of supraspinatus, infraspinatus, and for teres minor, and to test the hypothesis that subregions of the cuff tendons increase their effective moment arms through connections to other subregions. Tendon excursions were measured for full ranges of rotation on 10 independent glenohumeral specimens with the humerus abducted in the scapular plane at 10 and 60 degrees . Supraspinatus and infraspinatus tendons were divided into equal width subregions. Two conditions were tested: tendon divided to the musculotendinous junction, and tendon divided to the insertion on the humerus. Moment arms were determined from tendon excursion via the principle of virtual work. Moment arms for the infraspinatus (p < 0.001) and supraspinatus (p < 0.001) were significantly greater when the tendon was only divided to the musculotendinous junction versus division to the humeral head. Moment arms across subregions of infraspinatus (p < 0.001) and supraspinatus (p < 0.001) were significantly different. A difference in teres minor moment arm was not found for the two cuff tendon conditions. Moment arm differences between muscle subregions and for tendon division conditions have clinical implications. Interaction between cuff regions could explain why some subjects retain strength after a small cuff tear. This finding helps explain why a partial cuff repair may be beneficial when a complete repair is not possible. Data presented here can help differentiate between cuff tear cases that would benefit from cuff repair and cases for which cuff repair might not be as favorable.     

Restoration of anterior–posterior rotator cuff force balance improves shoulder function in a rat model of chronic massive tears

The rotator cuff musculature imparts dynamic stability to the glenohumeral joint. In particular, the balance between the subscapularis anteriorly and the infraspinatus posteriorly, often referred to as the rotator cuff “force couple,” is critical for concavity compression and concentric rotation of the humeral head. Restoration of this anterior–posterior force balance after chronic, massive rotator cuff tears may allow for deltoid compensation, but no in vivo studies have quantitatively demonstrated an improvement in shoulder function. Our goal was to determine if restoring this balance of forces improves shoulder function after two‐tendon rotator cuff tears in a rat model. Forty‐eight rats underwent detachment of the supraspinatus and infraspinatus. After four weeks, rats were randomly assigned to three groups: no repair, infraspinatus repair, and two‐tendon repair. Quantitative ambulatory measures including medial/lateral forces, braking, propulsion, and step width were significantly different between the infraspinatus and no repair group and similar between the infraspinatus and two‐tendon repair groups at almost all time points. These results suggest that repairing the infraspinatus back to its insertion site without repair of the supraspinatus can improve shoulder function to a level similar to repairing both the infraspinatus and supraspinatus tendons. Clinically, a partial repair of the posterior cuff after a two‐tendon tear may be sufficient to restore adequate function. An in vivo model system for two‐tendon repair of massive rotator cuff tears is presented. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29: 1028–1033, 2011     

Function of the supraspinatus muscle: Abduction of the humerus studied in cadavers

We evaluated the function of the supraspinatus tendon with a dynamic shoulder model. Active glenohumeral joint motion was simulated in 10 cadaveric shoulder specimens with hydrodynamic cylinder forces at the deltoid muscle and at the rotator cuff. Computerized regulation initiated standardized cycles of glenohumeral joint motion, where the isolated effect of the supraspinatus muscle could be studied. The efficacy of the supraspinatus muscle on elevation of the glenohumeral joint was measured with an ultrasonic sensor system. Pressures underneath the coracoa-cromial vault were recorded with capacitive sensors, as an indicator of the impingement at the shoulder. Elimination of force of the supraspinatus muscle led to a 6 percent decrease in elevation of the glenohumeral joint. The deltoid muscle was able to reverse this loss of elevation by a force increase of one third of the lost supraspinatus force. If no force was applied to the supraspinatus muscle, average pressures underneath the coracoacromial vault decreased 8 percent. It was concluded that the supraspinatus produces less torque and more glenohumeral joint compression than the deltoid. However, the supraspinatus has no effect on depression of the humeral head during elevation.

The clinical consequence of our observations is that operative closure of supraspinatus tendon defects is not mandatory.     

Direct biceps tendon and supraspinatus contact as an indicator of rotator cuff tear during shoulder arthroscopy in the lateral decubitus position

The purpose of this study was to evaluate consecutive shoulder arthroscopies for the presence or absence of a space between the biceps tendon and the supraspinatus as an indicator of a full-thickness rotator cuff tear. We performed 588 consecutive shoulder arthroscopies in the lateral decubitus position, and the presence or absence of a space between the rotator cuff (supraspinatus) and the biceps tendon was recorded immediately upon entering and insufflating the joint. Of the 588 patients, 174 (30%) were found to have full-thickness rotator cuff tears. Of these 174 patients, 171 had absence of the space between the biceps and the supraspinatus, for a sensitivity of 98%. Of the 414 patients in whom no full-thickness tear was present, 4 had absence of the space, for a specificity of 99%. The 4 patients with a false-negative result had adhesive capsulitis. During shoulder arthroscopy, a normal interval exists between the supraspinatus and biceps tendons as a result of joint insufflation. Loss of this interval is both highly sensitive (98%) and specific (99%) for a full-thickness rotator cuff tear. The space between the rotator cuff and the biceps tendon can be a reliable adjunct for verification of a full-thickness rotator cuff tear immediately upon entering the shoulder joint but should not be used in place of a full arthroscopic evaluation of the cuff.     

Rat supraspinatus muscle atrophy after tendon detachment.

Rotator cuff tears are one of the most common tendon disorders found in the healthy population. Tendon tears not only affect the biomechanical properties of the tendon, but can also lead to debilitation of the muscles attached to the damaged tendons. The changes that occur in the muscle after tendon detachment are not well understood. A rat rotator cuff model was utilized to determine the time course of changes that occur in the supraspinatus muscle after tendon detachment. It was hypothesized that the lack of load on the supraspinatus muscle would cause a significant decrease in muscle mass and a conversion of muscle fiber properties toward those of fast fiber types. Tendons were detached at the insertion on the humerus without repair. Muscle mass, morphology and fiber properties were measured at one, two, four, eight, and 16 weeks after detachment. Tendon detachment resulted in a rapid loss of muscle mass, an increase in the proportion of fast muscle fibers, and an increase in the fibrotic content of the muscle bed, concomitant with the appearance of adhesions of the tendon to surrounding surfaces. At 16 weeks post-detachment, muscle mass and the fiber properties in the deep muscle layers returned to normal levels. However, the fiber shifts observed in the superficial layers persisted throughout the experiment. These results suggest that load returned to the muscle via adhesions to surrounding surfaces, which may be sufficient to reverse changes in muscle mass.     

A biodegradable button to augment suture attachment in rotator cuff repair

Recent experimental studies suggest that the use of suture anchors for rotator cuff tear (RCT) repair transfers the "weak link" to the suture-tendon interface where failure occurs as the sutures cut through the tendon. The purpose of this study was to evaluate the effect of using a suture augmentation button on the fixation strength of rotator cuff tendon repair. A 1.5 cm by 2 cm defect was created in the supraspinatus tendon of seven cadaveric shoulder pairs and two suture anchors inserted in each humerus for suture attachment. For one of each pair, the defect was repaired with sutures placed in a horizontal mattress configuration. The other side was repaired with the sutures being passed through low profile, bioabsorbable buttons placed on the bursal tendon surface prior to knot tying. The supraspinatus tendon was cyclically loaded at a physiologic rate and load (33 mm/sec and 180 N, respectively). The number of loading cycles was recorded when the specimens developed 0.75 cm and 1.5 cm gaps at the repair site. The specimens were then tested to failure. Specimens in the unaugmented group developed 0.75 cm and 1.5 cm gaps at an average of 135 cycles and 362 cycles, respectively. The button augmented group developed these gaps at average of 420 cycles and 708 cycles, respectively. These differences were statistically significant (p < 0.05). The gaps progressively increased in all specimens, which eventually failed by suture cutting through tendon in all specimens. This study demonstrates that in vitro, suture augmentation with a low profile, bioabsorbable button provides significantly enhanced fixation when using suture anchors to repair torn rotator cuff tendon. This device may be a useful adjunct to current methods of rotator cuff repair.     

Begutachtung des Rotatorenschadens

The key to analyzing defects and tears in the rotator cuff is a profound knowledge of the anatomical structures and the resulting biomechanics. Defects of the rotator cuff are very frequent shoulder pathologies in the older population. Due to insurance requirements expert opinions have to differentiate between defects as a result of degenerative processes and tears caused through trauma. This article gives some advice for this decision. The rotator cuff is a tendon plate of four muscles inserting on the humeral head that works as a twin force coupling. The tendons of the supraspinatus and the infraspinatus muscles act as a cable system with two anchor points, comparable to a suspension bridge. The function of the delta muscle is particularly supported by the supraspinatus. Therefore, injuries of the central rotator cuff will affect the rotator cable system and the delta muscle. If this cannot be shown, there has to be substantial doubt about any trauma or primary injury. The medical assessment of rotator cuff injuries requires an accurate clinical and radiological diagnosis.     

肱骨外展动作中肩袖生物力学的有限元分析

目的构建肩关节有限元模型，用于分析肩袖生物力学。 方法采集1名26岁健康男性志愿者右肩CT、MRI数据，构建肩关节有限元模型，包含肩胛骨、肱骨、锁骨，以及肩袖肌群（冈上肌、冈下肌、小圆肌、肩胛下肌）。模拟肱骨在肩胛骨平面外展，分析肩袖肌肉应力变化。 结果肱骨在肩胛骨平面外展0°~30°过程中，各组肌腱与肱骨头连接处的应力均增大。冈上肌腱应力变化速率较快；肩胛骨前方的肩胛下肌对比肩胛骨后方的冈下肌-小圆肌，两组肌腱的应力变化较为同步。当肱骨在肩胛骨平面外展30°时，冈上肌腱、肩胛下肌腱及冈下肌腱-小圆肌腱与肱骨头连接面的平均应力分别为7.894 8、4.721 7、3.768 8 Mpa，冈上肌腱关节面与滑囊面结点平均应力分别为7.931 4、4.099 0 Mpa。冈上肌腱的关节面与滑囊面应力有明显差异，应力差值随肱骨在肩胛骨平面外展而增大，造成的剪切力可造成冈上肌腱撕裂。 结论肩袖对肩关节的活动与稳定性有重要作用，其受力特点易引起肩袖损伤。     

Subscapularis tendon tears

Pathology of the subscapularis tendon is both infrequently identified and not commonly considered as a major source of shoulder pain and dysfunction. Subscapularis tendon pathology can present as isolated tears; partial-thickness tears; anterosuperior tears, also involving the supraspinatus tendon; complete rotator cuff avulsion; and rotator interval lesions, in which instability of the long head of the biceps tendon may dominate the clinical presentation. Although an accurate physical examination is paramount, modalities such as arthroscopy, magnetic resonance imaging, and ultrasound have advanced knowledge of the spectrum of abnormalities involving the subscapularis tendon. Nonsurgical management may be effective for most partial tears. Surgically, open repair is more frequent than use of arthroscopic techniques. Tears of the subscapularis tendon portend a different prognosis than do supraspinatus tendon tears, especially when the injury is acute and diagnosis is delayed.     

Reconstruction of large rotator cuff tendon defects with porcine small intestinal submucosa in an animal model

Large rotator cuff tears represent a challenging problem. The purpose of our study was to evaluate the small intestinal submucosa (SIS) extracellular matrix in reconstruction of such defects in an animal model. Forty rats were equally divided into an SIS group (reconstruction of a large supraspinatus tendon defect by use of the SIS) and a defect group (no repair). The operative and contralateral normal shoulders underwent histologic evaluation and biomechanical testing at 6 and 16 weeks. Neovascularization and fibroblastic ingrowth were present in SIS-regenerated tendons, which had an ultimate force to failure that was 78% of normal at 16 weeks. This was higher than in the defect group, which demonstrated an ultimate force to failure that was 34% of normal (P = .008). The ultimate force to failure of the SIS-regenerated tendons approached that of the normal tendon at 16 weeks. The SIS extracellular matrix served as a scaffold promoting host tissue ingrowth and appears promising in the management of large rotator cuff defects in a rat model. However, human beings sustain tears at the bone-tendon interface and demonstrate decreased healing potential relative to rats. Therefore, the findings of this preliminary study should not be extrapolated to human beings without further investigation.     

Margin convergence of the posterior rotator cuff to the biceps tendon

Massive rotator cuff tears can often be repaired arthroscopically with satisfactory results. Tear pattern recognition, knot security, and loop security are essential in the repair of large and massive rotator cuff tears. In the case of a massive U-shaped tear, with a contracted immobile supraspinatus and a deficient rotator interval, a type of margin convergence technique can be used. This technique allows for the partial closure of the rotator cuff defect along with the proximal advancement of the posterior cuff by securing the posterior leaf of the cuff tendon to the tendon of the long head of the biceps brachii. Because of the mechanical effect of strain reduction in margin convergence, this procedure decreases the strain at the margin of the posterior cuff, thereby protecting its repair to bone. Our goal with this procedure is not to obtain healing of the cuff to the biceps, but to optimize the conditions for healing of the rotator cuff to bone.     

Glenohumeral joint motion after medial shift of the attachment site of the supraspinatus tendon: a cadaveric study

During a rotator cuff repair, it is ideal to reattach the torn edge of the cuff tendon back to the greater tuberosity. However, with massive tears where the torn edges are too retracted to be reattached to the greater tuberosity, they may have to be reattached somewhere more medial. It is clinically important to know how far medially one can shift the reattachment site without sacrificing function of the shoulder. Ten fresh, previously-frozen cadaveric shoulders were used. Medial shift of the supraspinatus tendon was simulated by placing the suture anchors along lines 3, 10, or 17 mm medial to the cuff attachment site. The ranges of glenohumeral motion were measured using a goniometer with a constant torque applied to the humerus. All motions, except for internal rotation at 60 degrees of abduction, were significantly restricted by medial shift of 10 mm or more compared with that of the intact shoulder. We conclude that significant restriction of joint motion occurs when a bony trough is created more than 10 mm medial to the cuff attachment site.     

Suprascapular nerve neuropathy leads to supraspinatus tendon degeneration

BackgroundNowadays most of attention regarding rotator cuff is payed to how to reduce the failure after rotator cuff surgical repair rather than how to prevent the rotator cuff tear before surgery. The etiologies of rotator cuff tear are still unclear. As we all know, the nerve system include brain, spinal cord, sensory organs and all the neurons allover our body coordinates the homoeostasis of our body. We hypothesis that the nerve injury proximal to suprascapular nerve can leads to rotator cuff degeneration even tear.MethodsThirty-six SD rats were used. A defect on the suprascapular nerve was made on the right side and a sham surgery on the nerve (expose nerve only) at the left side. The insertion of supraspinatus tendon and supraspinatus muscle were harvested for testing. Twelve rats were sacrificed for biomechanical (six rats) and histological (six rats) properties were evaluated at 3, 6, and 9 weeks after surgery, respectively.ResultsSignificant inferior biomechanical properties of rotator cuff were found in nerve injured side compared to the nerve intact side at 6–9 weeks. Significant muscle atrophy was found at nerve injured side from 3 to 9 weeks. The enthesis of nerve injured side showed significant excessive cell maturity, reduced cellularity, smaller metachromasia area and more type-III collagen especially at 9 weeks after surgery.ConclusionsThe neuropathy proximal to suprascapular nerve can leads to rotator cuff degeneration even tear. The nerve dysfunction maybe an important etiology for rotator cuff tear.     

An anatomic study of the supraspinatus muscle and tendon

The gross and histologic anatomy of the myotendinous portion of the supraspinatus muscle was investigated with coronal and sagittal sections from 20 anatomic specimen shoulders. The anterior lateral portion of the supraspinatus contained more tendon than the posterior portion of the muscle in all 20 specimens. In seven specimens there were separate muscle fibers that originated from the most anteromedial area of the supraspinatus fossa. Knowledge of this anatomy aids in magnetic resonance image interpretation and open or arthroscopic evaluation of the supraspinatus. This consistent tendinous portion may be useful in rotator cuff repair and may provide a firm area for suture closure of the rotator interval. This prominent anterior tendinous area may serve to protect the supraspinatus during anterior forward flexion motion through the impingement arc.     

Clinical and structural results of open repair of an isolated one-tendon tear of the rotator cuff

BACKGROUND: The clinical outcomes of open rotator cuff repair are well established, but the structural results and their effect on clinical outcome are poorly known. We assessed the structural changes in the musculotendinous units after open rotator cuff repair and correlated these findings with the clinical outcome to establish a benchmark for future series. METHODS: Thirty-two consecutive standardized open repairs of a single tendon tear of the rotator cuff were analyzed in twenty-one men and eleven women with an average age of 59.0 years. The supraspinatus tendon was involved in twenty-two patients and the subscapularis tendon, in ten. The clinical outcome, including the Constant score, was assessed prospectively for all patients at an average of thirty-eight months postoperatively. The structural outcome was assessed on standardized magnetic resonance imaging scans. RESULTS: The mean overall subjective shoulder value was 82.8% of the value for a normal shoulder. On the average, the age and gender-adjusted Constant score increased from 63.9% preoperatively to 94.5% postoperatively (p < 0.0001); the score for pain, from 6.8 points to 13.2 points (p < 0.0001); and the score for activities of daily living, from 11.2 points to 17.9 points (p < 0.0001). The overall rerupture rate was 13% (four of the thirty-two shoulders). All reruptures were distinctly smaller than the original tear. Muscular atrophy or fatty infiltration did not significantly decrease after the tendon repair. In fact, fatty infiltration in the supraspinatus (p < 0.0053) and infraspinatus (p < 0.003) muscles increased significantly. CONCLUSIONS: Direct open repair of a complete, isolated tear of one tendon of the rotator cuff resulted in significant subjective and objective improvement and very high patient satisfaction. Successful direct repair was not associated with a decrease in preoperative muscular atrophy and was associated with increased fatty infiltration of the muscle.     

Botulinum toxin is detrimental to repair of a chronic rotator cuff tear in a rabbit model

Re‐tear continues to be a problem after rotator cuff repair. Intramuscular botulinum toxin (Botox) injection can help optimize tension at the repair site to promote healing but could have an adverse effect on the degenerated muscle in a chronic tear. We hypothesized that Botox injection would improve repair characteristics without adverse effect on the muscle in a chronic rotator cuff tear model. The supraspinatus tendon of both shoulders in 14 rabbits underwent delayed repair 12 weeks after transection. One shoulder was treated with intramuscular Botox injection and the other with a saline control injection. Six weeks after repair, outcomes were based on biomechanics, histology, and magnetic resonance imaging. Botox‐treated repairs were significantly weaker (2.64 N) than control repairs (5.51 N, p = 0.03). Eighty percent of Botox‐treated repairs and 40% of control repairs healed with some partial defect. Fatty infiltration of the supraspinatus was present in all shoulders (Goutallier Grade 3 or 4) but was increased in the setting of Botox. This study provides additional support for the rabbit supraspinatus model of chronic cuff tear, showing consistent fatty infiltration. Contrary to our hypothesis, Botox had a negative effect on repair strength and might increase fatty infiltration. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1152–1157, 2015.     

Partial Articular Supraspinatus Tendon Avulsion Repair and Patch: A Technical Note for Augmenting the Supraspinatus Reinsertion with the Long Head of the Biceps Tendon

Background

There is no clear consensus on the treatment of partial articular-sided supraspinatus tendon avulsions. Debridement alone might not be sufficient to prevent further tendon degradation or alleviate patient complaints. Direct repair using a suture anchor without treating the concomitant conditions of the long head of the biceps tendon might come with residual anterior shoulder pain or even further loss of function in cases of failed repair. The purpose of the present study is to describe an arthroscopic technique by which the long head of the biceps tendon can be included in the partial articular-sided supraspinatus tendon avulsion repair.

Technique Presentation with video

In this technical note we describe the arthroscopic repair and augmentation with tenotomized biceps of partial supraspinatus tendon tears to address three main concepts for successful rotator cuff repairs, namely rotator cuff biologic augmentation, tendon to bone healing and postoperative pain prevention.

Conclusion

The biceps tendon is a mechanically robust, locally available autograft that can be used in borderline partial articular-sided supraspinatus tendon avulsions in order to biologically augment healing at the tendon-bone interface without any immunogenic reactions or morbidity following harvesting.