Chronic subacromial impingement leads to supraspinatus muscle functional and morphological changes: Evaluation in a murine model

Abstract

Muscle atrophy and fatty infiltration have been directly correlated with higher rates of incomplete or failed healing following surgical repair of the rotator cuff. The purpose of this study was to evaluate clinically relevant functional and morphological changes in the supraspinatus muscle at various time points in this model of rotator cuff tendinopathy. Subacromial impingement was induced in 47, male C57BL/6 mice (total 94 limbs) by implantation of a metal clip in the subacromial space. Specimens were evaluated at 4, 6, and 12 weeks postoperatively. Gait analysis was used to measure various kinematic parameters. Supraspinatus muscle wet weight, histology, and quantitative reverse-transcription polymerase chain reaction analysis of genes related to muscle atrophy and adipogenesis were performed to characterize the structural, cellular, and molecular changes. Muscle atrophy and fatty infiltration was evident beginning at 6 weeks, with progression out to 12 weeks. Gait analysis identified significant functional changes in many aspects of gait and abnormal stance tracing as early as 4 weeks, verifying alterations in upper extremity function. We have demonstrated that clinically relevant changes to the supraspinatus muscle are seen starting 6 weeks after induction of subacromial impingement. Furthermore, the gait analysis provides key functional outcome measurements that may be useful for future evaluation of new therapeutic strategies.

Three-Dimensional Software- and MR-Imaging-Based Muscle Volumetry Reveals Overestimation of Supraspinatus Muscle Atrophy Using Occupation Ratios in Full-Thickness Tendon Tears

“…Our data demonstrate that 3D muscle volumetry should be preferred in patients with full-thickness SSP tendon tears when the muscle volume needs to be quantified preoperatively in order to estimate the postoperative success rate after tendon repair procedures. This is in accordance with previous studies [ 17 ] and is important since various previous experimental and clinical studies have shown that significant SSP muscle atrophy is an important adverse prognostic factor affecting patients’ outcomes in addition to other conditions, e.g., fatty infiltration or severe tear size [ 8 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ].…”

A Dual‐Network Nerve Adhesive with Enhanced Adhesion Strength Promotes Transected Peripheral Nerve Repair

“…A rat‐walking apparatus system was used to evaluate the recovery of locomotor functions by comparing the experimental foot (left hind in the system, LH) with the contralateral healthy foot (right hind in the system, RH) at week 10. [ 45,46 ] The footprint intensity and foot pressure of transected nerve rats were significantly lower than those of sham group, and no statistical difference was noticed among nerve anastomosis groups for the foot pressure (Figure 6C). Rat body wobble was reflected by stance trace (Figure 6D).…”

The Role of Indian Hedgehog Signaling in Tendon Response to Subacromial Impingement: Evaluation Using a Mouse Model

“…Recent advancements in the development and use of a mouse rotator cuff impingement model using a consistent titanium microvascular surgical clip have simplified the study of the molecular mechanisms underlying rotator cuff injury and healing due to extrinsic impingement. 9,10,12,41,42 Titanium has similar qualities to bone, and the titanium clips in our model are easy to insert and remove, which make the mouse model easy to replicate. In the current study, we used the same model to induce supraspinatus tendinopathy, then removed the clip under the acromion to simulate acromioplasty and initiate recovery.…”

“…To ensure consistent joint loading during postoperative daily cage activity, all animals underwent bilateral surgery as per the design of previous studies. 9,10,12,41,42 All animals were returned to normal cage activity immediately after surgery in specific pathogen-free cages with standardized cage amenities (feed, bedding, and water). High-resolution radiographs were obtained at the 4-week time point to confirm the subacromial position of the implanted surgical clip.…”

“…By surgically inserting a titanium microvascular clip into the subacromial space, it is possible to induce SST tendinopathy, evidenced by decreased biomechanical strength, histologic changes, and increased expression of genes involved in inflammation, matrix remodeling, and tendon development. 9,10,12,41,42 Removal of the microvascular clip after a period of impingement is analogous to the acromioplasty procedure in humans and simulates the recovery of supraspinatus tendinopathy after subacromial decompression. Our previous work demonstrated that there was a 60% decrease in SST load to failure after 4 weeks of clip impingement compared with the intact SST, followed by a gradual increase in the failure force at 2 and 4 weeks after clip removal.…”