Fig 1.
Cadaver canine shoulder (right) with skin and periscapular muscles removed.
(A) Posterior bursal view: The supraspinatus (yellow), infraspinatus (pink) and teres minor muscles (blue) can be visualized. The posterior arthroscopic portal site (green) will be located between the infraspinatus and teres minor muscles. (B) Anterior bursal view: The anterior arthroscopic portal site (red) will be located between the supraspinatus and subscapularis muscles. (C)–(E) Posterior articular view (from viewing perspective of the anterior portal): Approximately 2 cm2 of the lateral joint capsule (C) under the infraspinatus will be resected from its humeral to glenoid insertions (D, dotted line), exposing the extra-articular rotator cuff muscles (E, colors as in Panel A) to the joint compartment. h = humeral head, g = glenoid, b = biceps tendon.
Fig 2.
Arthroscopic shoulder capsulectomy.
(A) The animal was placed in a dorsal recumbent position with neck extension, and a forelimb suspension system was utilized to provide forelimb traction and ensure adequate glenohumeral joint distraction. (B) Arthroscopic posterior capsulectomy was performed with instrumentation in the posterior portal and the arthroscope in the anterior portal. (C) The humeral insertion of the intact posterior capsule visualized from the anterior portal (photo taken in a cadaver shoulder for clarity). The arrow denotes the insertion of the capsule at the supraspinatus/infraspinatus transition. (D) Removal of any remaining capsular tissue from the humeral or glenoid ends of the defect was done with an arthroscopic shaver (photo taken in a cadaver shoulder for clarity). a = anterior portal, c = joint capsule, h = humeral head articular surface, g = glenoid articular surface.
Fig 3.
Creation and surveillance of a posterior joint capsule injury, representative photographs from the left shoulder.
(A) At index procedure, completion of the capsulectomy exposed the deep surface of the infraspinatus tendon and muscle, (B) At two weeks, there was negligible healing tissue present at the capsulectomy site. (C) At four weeks, the capsulectomy site appeared hemorrhagic and white, and thin fibrous tissue (arrows) was present. (B) At eight weeks, the deep surface of the infraspinatus tendon appeared yellow with fibrous tissue (arrows) originating medial to the glenoid rim and extending laterally to the deep surface of the tendon. i = infraspinatus tendon, h = humeral head articular surface, g = glenoid articular surface.
Fig 4.
Necropsy findings at 10 weeks after the index procedure, representative images from the right shoulder.
(A) Fibrovascular plaques were observed over the deep surface of the infraspinatus tendon (arrow), extending to the glenoid rim at the level of the scapular neck. (B) This material was thin, friable, and discontinuous (arrow), demonstrating that the capsular injury had remained patent. (C) The lateral infraspinatus muscle was edematous and its deep surface was covered with fibrovascular plaques laterally (arrow) and fibro-fatty tissue that encapsulated an accumulation of fluid medially (asterisk). (D) The deep surface of a non-operated normal canine infraspinatus tendon/muscle is shown for comparison. h = humeral head, g = glenoid, b = biceps tendon. Lines on C and D denote location of histologic sections of infraspinatus tendon (horizontal) and infraspinatus muscle (vertical).
Fig 5.
Biceps tendon and glenoid insertion.
Longitudinal histologic sections from non-operated normal (A-C) and operated (D-G) animals (t = tendon; b = bone). The insertion of the non-operated animal showed the characteristic fibrocartilaginous transition zone with a well-defined tidemark and aligned chondrocytes (B, where B is a higher magnification of the region denoted by the left box on A). The adjacent tendon was characterized by parallel rows of tenocytes sandwiched between highly aligned collagen fibers (C, where C is a higher magnification of the region denoted by the right box on A). Ten weeks after posterior arthroscopic joint capsule injury, the tendon and its glenoid insertion showed reactive/reparative changes (D-G). The tendon in the operated animal (D) was thicker than normal (A). The distribution of chondrocytes at the tidemark was not uniform (E, where E is a higher magnification of the region denoted by the left box on D), and some foci showed few or no chondrocytes (white arrow) while others showed clustering of chondrocytes (black arrow), suggestive of proliferation. The tendon adjacent to the insertion showed villous hyperplasia (ampersand) and foci of marked hypervascularity (asterisk) (E). The rest of the tendon showed increased numbers of cells surrounded by basophilic ground substance (F, where F is a higher magnification of the region denoted by the middle box on D). There was marked hypervascularity along the entire length of the superior aspect of the tendon (G, where G is a higher magnification of the region denoted by the right box on D). Hematoxylin and eosin stain. Scale bar = 5mm (A, D), 500 microns (B, E), 200 microns (C, F, G).
Fig 6.
Infraspinatus tendon and humeral insertion.
Longitudinal histologic sections from non-operated normal (A) and operated (B-G) animals (t = tendon; b = bone). At low magnification, the infraspinatus tendons in the operated shoulders (B) were markedly thicker than normal (A). Examination of all sections revealed a wide degree of pathologic changes at the tendinous insertion site, including irregularly distributed and clustered chondrocytes (C), marked proliferation and clustering of chondrocytes separated from the tidemark by vascular invasion (asterisk) (D), and deposition of osteoid around clusters of chondrocytes consistent with endochondral bone formation (E, where E is a higher magnification of the region denoted by the left box on B). The infraspinatus tendons adjacent to their insertion sites were markedly hypercellular consisting of stromal cells and a chronic inflammatory infiltrate with increased vascularity (F, where F is a higher magnification of the region denoted by the middle box on B). The operated tendons more medial to the insertion sites show an increased number of hypertrophied tenocytes and diffusely distributed lymphocytes (G, where G is a higher magnification of the region denoted by the right box on B). Hematoxylin and eosin stain. Scale bar = 5 mm (A, B); 200 microns (C-E); 500 microns (F, G).
Fig 7.
The muscle-tendon interface of the infraspinatus muscle ten weeks post joint capsulectomy showed reactive/reparative changes. Low magnification cross-sections of regions sampled from non-operated normal (A) and operated (B) animals (t = tendon; m = muscle). Boxes delineate regions shown at high magnification in C and D respectively. In contrast to the normal discrete muscle-tendinous interface (C), the interface in the operated animals was disorganized and characterized by a marked increase in stromal cells and capillaries, and small, rounded muscle cells (D). Hematoxylin and eosin stain. Scale bar = 2 mm (A, B); 200 microns (C, D).