In 1934, Ernest Amory Codman described partial-thickness, articular-surface rotator cuff tears involving the supraspinatus tendon as “rim rents” and expressed his confidence that “these rim rents account for the great majority of sore shoulders.” He also accurately predicted that “these lesions never heal.”^1,2 Stephen Snyder later called these defects partial-thickness articular-surface supraspinatus tendon avulsions and coined the term PASTA lesion (Fig. 10-1). Since their original description, considerable attention has been placed on recognizing, understanding, and treating incomplete thickness rotator cuff tears. However, much controversy still exists and simply put, these tears vary widely in presentation. Although the significance of pattern and pathomechanics are now well recognized, the best methods for diagnosis and treatment are yet to be determined.

Several useful classifications for these tears are available. Ellman classified incomplete rotator cuff tears, based on location, as articular surface, bursal surface, or intratendinous and graded these lesions with measurements of both the depth and the area of the defect³ (Table 10-1). The grade classification was later revised to consider the depth of the tear as a percentage of the tendon.⁴ Snyder proposed a similar classification that assigned a letter for each location and a number for grade in an effort to simplify the description of the lesion. In this system, the grade principally reflects the width of the defect, but also considers the presence of intratendinous delamination (“flap formation”) and retraction.^5,6 Unfortunately, these classification systems are best suited to describe tears isolated to the supraspinatus tendon and consider neither the pathomechanics involved nor the significance of anterior/posterior location of the tear as important elements. Several pathomechanisms have been recently proposed for anteriorly located partial thickness tears that involve the upper subscapularis tendon^7,8 and Habermeyer et al.⁷ have proposed a classification system that considers associated pathology. Similarly, the relatively posterior and intratendinous tear pattern commonly reported in young overhead throwing athletes has been recently graded for severity based on depth, width, and delamination in an attempt to provide prognosis and direction for treatment.⁹

A complete discussion of the pathomechanics of rotator cuff disease would exceed the scope of this article; however, there are several factors contributing to the articular-surface location of some incomplete tears that warrant description.^{8,10,11,12,13,14,15,16,17,18} The articular surface of the rotator cuff has fewer arterioles and overall less vascularity than the bursa surface. The articular surface has a higher modulus of elasticity and therefore greater stiffness than the bursa surface. Eccentric forces tend to be concentrated more in the articular surface. Bursal surface contact of the rotator cuff against the margin of the acromion may produce tensile undersurface fiber failure. And finally, the articular surface has a less favorable stress strain curve than the bursal surface. The pathomechanics explaining associated intratendinous tears are less clear but probably involve shear within the five-layered architecture of the rotator cuff tendon.^{15,16,17,19,20,21,22,23}

Débridement of the torn rotator cuff tendon has been recommended in order to stimulate a healing response,²⁴ and some authors have suggested that acromioplasty without tendon repair would provide good surgical outcomes.^6,25,26 However, Weber²⁷ reported that, on second-look arthroscopy
following arthroscopic rotator cuff tear débridement, “healing… was never observed.” Fukuda et al.²¹ also reported that “apparent evidence of spontaneous repair” of joint sided partial rotator cuff tears “was absent.” It is probable that the continued separation of the torn tendon edges, the poor vascularity of the involved tissues,^3,28 and the formation of a synovial covering, both on the visibly exposed segment of the tear and within the intratendinous segment of the tear,^23,28,29 precludes any potential for spontaneous healing or healing following simple arthroscopic débridement.^23,27

Progression of both the depth of the articular-surface tear and the extent of the intratendinous tear is of considerable concern, and rotator cuff repair may be advisable for the long-term function of the shoulder in some patients.^{5,27,29,30,31,32,33,34,35} However, the percentage of depth, width, and delamination of the tear that calls for repair, using either open or arthroscopic methods, is controversial.^{25,27,29,33,36} Because of the risk for both tear progression and less satisfactory surgical outcomes, some authors have suggested that partial thickness rotator cuff tears >50% of the thickness of the tendon should be repaired.^{3,25,27,30,37,38} Conversely, others have argued that in some patients, particularly overhead athletes, repair potentially increases the morbidity of the procedure and that 75% was a more reasonable depth mitigating for repair.^9,39 Finally, while many have suggested that tear completion and bursal side repair are reasonable for small full thickness tears, controversy still exists regarding the efficacy of such treatment for incomplete tears.