Introduction. Following tear of its tendon, the muscle undergoes retraction, atrophy and fatty infiltration. These changes are inevitable and considered irreversible and limit the potential of successful repair of musculotendinous units. It was the purpose of this study to test the hypothesis that administration of anabolic steroids can prevent these muscular changes following experimental supraspinatus tendon release in the rabbit. Methods. The supraspinatus tendon was experimentally released in 20 New Zealand rabbits. Musculotendinous retraction was monitored over a period of 6 weeks. The seven animals in group I had no additional intervention, six animals in group II had local and seven animals in group III had systemic administration of nandrolone deconate during six weeks of retraction. At the time of sacrifice, in-vivo muscle performance as well as radiologic and histologic muscle changes were investigated. Results. Supraspinatus retraction was significantly higher in group I (1.8 ± 0.2cm) than in group II (1.5 ± 0.3cm, p = 0.044) or III (1.2 ± 0.3cm, p = 0.001). The reduction in radiological cross sectional area, as a measure for atrophy, was significant in groups I (p = 0.013) and II (p = 0.030) and insignificant in group III (p = 0.149). Histologically, there was no fatty infiltration in the treated groups II (p = 1.000) and III (p = 0.812), but in the untreated group I (p = 0.0312). The work of the respective muscle during one standardized contraction with supramaximal stimulation decreased markedly in groups I (p = 0.056) and II (p = 0.0528), and also but less in group III (p = 0.23). Conclusion. This is the first documentation of prevention of important muscle alterations after chronic retraction of the musculotendinous unit caused by rotator cuff tear. Nandrolone deconate administration in the post tendon release phase prevented fatty infiltration of the supraspinatus muscle and reduced functional muscle impairment caused by myo-tendinous retraction

Purpose of this study is to create an experimental model of electrophysologic evaluation of the supraspinatus muscle on rats, after traumatic rupture of its tendon. The population of this study consisted of 10 male Sprague Dawley rats weighting 300–400g. Under general anaesthesia we proceeded with traumatic rupture of the supraspinatus tendon and exposure of the muscle. The scapula was immobilized, and the supraspinatus tendon was attached to a force transducer using a 3–0 silk thread. A dissection was performed in order to identify the suprascapular nerve, which was then stimulated with a silver electrode. Stimulations were produced by a stimulator (Digitimer Stimulator DS9A) and were controlled by a programmer (Digitimer D4030). Fiber length was adjusted until a single stimulus pulse elicited maximum force during a twitch under isometric conditions. Rectangular pulses of 0.5 ms duration were applied to elicit twitch contractions. During the recordings, muscles were rinsed with Krebs solution of approximately 37 8C (pH 7.2–7.4) and aerated with a mixture of 95% O2 and 5% CO2. The output from the transducer was amplified and recorded on a digital interface (CED). The following parameters were measured at room temperature (20–21 8C): single twitch tension; time to peak; half relaxation time; tetanic tensions at 10, 20, 40, 80 and 100 Hz; and fatigue index, which was evaluated using a protocol of low frequency (40 Hz) tetanic contraction, during 250 ms in a cycle of 1 s, for a total time of 180 s. The fatigue index value was then calculated by the formula [fatigue index=(initial tetanic tension − end tetanic tension) ∗ 100/(initial tetanic tension)]. In the end, the transducer was calibrated with standard weights and tensions were converted to grams. The mean single twitch was 8.2, the time to peak 0.034 msec and the half relaxation time 0.028 msec. The strength of titanic muscle contractures was 5.7 msec at 10Hz and 17.7 at 100Hz. Finally, the fatigue index was calculated at 48.4. We believe that electrophysiologic evaluation of the supraspinatus muscle in rats will help us understanding the pathology of muscle atrophy after rotator cuff tears and possibly the functional restoration after cuff repair

Introduction. Many literatures regarding more specific tests to diagnose the supraspinatus tendon injuries and the best rehabilitation methods to strengthen the supraspinatus have been published. However, conflicting results have been reported. 2-deoxy-2-[18F] fluoro-D-glucose (FDG) positron emission tomography (PET) has been recently used to assess skeletal muscle activities in various fields. Purpose. To evaluate & compare the metabolic activities of deltoid & rotator cuff muscles after the full-can & empty-can exercises using PET-CT. Materials and Methods. Ten healthy volunteers (age 27–34/mean 29.8 ± 2.7) with no history of shoulder pain and diabetes mellitus participated in this study. After FDG injection, both arms were maintained in the position of empty can and full can for ten minutes respectively. PET-CT was performed at forty minutes after the injection. The maximum standardized uptake value (SUV) was measured in the anterior, middle and posterior deltoid, supraspinatus, subacapularis and infraspinauts on the entire axial images. Results. The middle deltoid and subscapularis showed significantly greater activity during the empty-can exercise than during the full-can exercise (P=.006 and P=.003 respectively). The muscular activity of the supraspinatus also increased during the empty-can exercise than during the full-can exercise, although no statistical difference existed between two exercises. Six cases of eight cases who had increased activity of the subscapularis had increased activity in superior one half of the subscapularis than in lower one half of it, although there is no significant difference between two portions. Conclusion. The Empty-can exercise requires more strength of the middle deltoid, subscapularis and supraspinatus to keep the arm in internal rotation. The increased activity of the middle deltoid and subscapularis muscles after the empty-can exercise can make the empty-can test less specific to the supraspinatus muscle. The empty-can test can induce pain and weakness due to the subscapularis pathology. The full-can test can be used to test the function of the supraspinatus with the least amount of surrounding middle deltoid and subacapularis muslce activity

Summary. Strong mechanical fixation is critical to the success of rotator cuff repairs. In this comparative study in cadaveric shoulders, single-tendon full-thickness supraspinatus tears were repaired using two different types of PEEK knotless suture anchors-ReelX STT (Stryker) and Opus Magnum PI (Arthrocare)-using a single-row technique in both instances. Cyclic testing was performed followed by loading until mechanical failure. No significant difference was observed in gap formation, measured as the distance between the supraspinatus tendon and bone at the repair site, during cyclic loading. However, the maximum load was statistically higher for repairs with the ReelX anchor. Purpose. The objective of this study was to compare the gap formation during cyclic loading and maximum repair strength of single-row full thickness supraspinatus repairs performed using two different types of PEEK knotless suture anchors in a cadaveric model. Methods. Nine matched pairs of cadaveric shoulders were used in this study. All soft tissue was removed except for the supraspinatus, and a full thickness tear was formed. Single-row repairs were performed with two anchors per repair using either the Opus Magnum PI (Arthrocare) or the ReelX STT (Stryker). The specimens were mounted to an Instron at 45° to simulate an anatomic direction of load, and fiducial markers were placed on the repair in anterior and posterior positions. A 10 N preload was applied and held for 60 seconds, and then the tendon was cycled from 10 N to 90 N at 0.25 Hz for 500 cycles, followed by load to failure at 1 mm/s. A video digitizing system was used to track the markers and measure gap formation during loading. Gap formation was calculated by subtracting the distance between the markers at 10 N preload from the maximum displacement at 5 and 500 cycles. Paired t-tests were used to compare the cyclic displacement and max load. Results. One specimen from each of two matched pairs (one from each anchor group) failed during cyclic loading, leaving seven matched pairs for analysis. No significant difference was found in cyclic displacement between the two groups in either anterior or posterior positions at 5 and 500 cycles. However, maximum load to failure was significantly greater for repairs performed with the ReelX STT anchors (289N ± 57N) as compared to the OPUS anchors (178N ± 36N), with a p=0.009. Conclusions. These results suggest that the anchor type chosen for cuff repairs may affect the overall stability of the repair. Achieving stable fixation is critical for promoting healing of the tendon back to bone and to the long-term success of the repair, and using anchors that provide stronger fixation may decrease the occurrence of post-surgical tears and instability. The ReelX STT anchor outperformed the Opus Magnum PI anchor in terms of supporting significantly higher loads before failure, potentially leading to stronger repairs clinically

Antegrade nailing of proximal humeral fractures using a straight nail can damage the bony insertion of the supraspinatus tendon and may lead to varus failure of the construct. In order to establish the ideal anatomical landmarks for insertion of the nail and their clinical relevance we analysed CT scans of bilateral proximal humeri in 200 patients (mean age 45.1 years (sd 19.6; 18 to 97) without humeral fractures. The entry point of the nail was defined by the point of intersection of the anteroposterior and lateral vertical axes with the cortex of the humeral head. The critical point was defined as the intersection of the sagittal axis with the medial limit of the insertion of the supraspinatus tendon on the greater tuberosity. The region of interest, i.e. the biggest entry hole that would not encroach on the insertion of the supraspinatus tendon, was calculated setting a 3 mm minimal distance from the critical point. This identified that 38.5% of the humeral heads were categorised as ‘critical types’, due to morphology in which the predicted offset of the entry point would encroach on the insertion of the supraspinatus tendon that may damage the tendon and reduce the stability of fixation.

We therefore emphasise the need for ‘fastidious’ pre-operative planning to minimise this risk.

Cite this article: Bone Joint J 2014;96-B:249–53.

We used an inverted shoulder arthroplasty in 43 consecutive patients with a mean age of 78 years (65 to 97) who had sustained a three- or four-part fracture of the upper humerus. All except two were reviewed with a mean follow-up of 22 months (6 to 58).

The clinical outcome was satisfactory with a mean active anterior elevation of 97° (35° to 160°) and a mean active external rotation in abduction of 30° (0° to 80°). The mean Constant and the mean modified Constant scores were respectively 44 (16 to 69) and 66% (25% to 97%). Complications included three patients with reflex sympathetic dystrophy, five with neurological complications, most of which resolved, and one with an anterior dislocation. Radiography showed peri-prosthetic calcification in 36 patients (90%), displacement of the tuberosities in 19 (53%) and a scapular notch in ten (25%). Compared with conventional hemiarthroplasty, satisfactory mobility was obtained despite frequent migration of the tuberosities. However, long-term results are required before reverse shoulder arthroplasty can be recommended as a routine procedure in complex fractures of the upper humerus in the elderly.