To The Editor:

The authors(1) point out a correlation between lateral acromial extension and rotator cuff tears and hypothesize a head depression mechanism for the deltoid. This mechanism of head depression has previously been hypothesized by Gagey and Hue in 2000(2).

Discussion of the mechanism proposed by Gagey and Hue (2) would have been a helpful addition to this paper because it is three-dimensional. This 3-D concept would tie in the findings by Zuckerman, et al,(3) of an association of a larger anterior extension of the acromion with cuff disease. As proposed by Gagey and Hue(2), the head depression mechanism of the deltoid involves a curved array of deltoid vectors. Therefore, an extension of the acromion in either the lateral or anterior direction would contribute to a decrease in head compression and thereby produce an increased incidence of rotator cuff pathology.

References:

1. Nyffeler RW, Werner CML, Sukthankar A, Schmid MR, Gerber C. Association of a Large Lateral Extension of the Acromion With Rotator Cuff Tears. J Bone Joint Surgery, 88A(4):800-805, April, 2006.

2. Gagey O, Hue E. Mechanics of the Deltoid Muscle. Clinical Orthopaedics & Related Research, 375:250-257, 2000.

3. Zuckerman JD, Kummer FJ, Cuomo F, Simon J, Rosenblum S, Katz N. The Influence of the Coraco-Acromial Arch Anatomy on Rotator Cuff Tears. J Shoulder Elbow Surg., 1:4-14, 1992.

To the Editor,

I read the article by Nyffeler, et al, “Association Of A Large Lateral Extension Of The Acromion With Rotator Cuff Tears"(1) with great interest. I am curious whether the authors found a large lateral extension of the acromion in the contra-lateral shoulder of some of these patients. If so, it is interesting to speculate that the other shoulder might be predisposed to rotator cuff tears. This would also answer the question about whether a lateral extension of the acromion is the result or cause of rotator cuff tears.

References:

1. Nyffeler RW, Werner CML, Sukthankar A, Schmid MR, Gerber C. Association of a large lateral extension of the acromion with rotator cuff tears. J Bone Joint Surg Am. 2006;88:800-5.

We thank Drs. Bhatia, deBeer and du Toit for their interest in our article(1). They remarked that humeral head medialization in massive cuff tears can influence the "acromion index" and suggested that a large lateral extension of the acromion may, therefore, be relative rather than absolute and its association with rotator cuff tears be a consequence rather than a cause.

We agree with the authors that medialization of the humeral head secondary to degeneration of the articular cartilage, flattening of the humeral head and glenoid erosion decreases the distance from the glenoid plane to the lateral aspect of the proximal humerus and therefore increases the acromion index. These morphological changes were typically present in the group of patients with primary osteoarthritis and an intact cuff, treated with an anatomical total shoulder prosthesis (group 2 of our study). The patients with a full-thickness rotator cuff tear involving at least the supraspinatus tendon (group 1) had no or only mild degenerative changes of the joint surfaces. No patient included in our study had a cuff tear arthropathy requiring the insertion of an extended humeral head prosthesis or a reverse total shoulder prosthesis. The patients of group 1 were treated with a cuff repair and in some cases with an additional latissimus dorsi tendon transfer. The acromion index of the rotator cuff tear group was significantly higher than the acromion index of the osteoarthritis group with a medialized humeral head.

The degenerative changes of the greater tuberosity encountered in cuff tear arthropathy (sclerosis, subchondral cysts, osteophytes or osteolysis) are typically seen at the insertion of the rotator cuff tendons, that means at the superior or postero-superior part of the greater tuberosity. These changes do not influence the acromion index, which takes as reference the most lateral aspect of the proximal humerus (Fig. 1 on page 801 and Fig. 3 on page 802).

The patients with primary osteoarthritis and more than 15 degrees of retroversion were excluded because the preliminary study with cadaver shoulders showed that internal or external rotation of the scapula affected the acromion index. This can be explained by the fact that true antero-posterior radiographs of shoulders with excessive retroversion do not show the most lateral aspect of the acromion but the postero-lateral part of the acromion. The reason why we did not differentiate between concentric shoulders and non-concentric shoulders due to a massive rotator cuff tear is explained in the discussion of our article. Superior subluxation of the humeral head decreases the acromion index, unless it is associated with superior glenoid erosion, as in cases of rheumatoid arthritis, but such cases were not included in this investigation.

As stated in the last sentence of our article, we actually do not know, if a large lateral extension of the acromion is a cause or a consequence of rotator cuff pathology.

References:

1. Nyffeler RW, Werner CML, Sukthankar A, Schmid MR, Gerber C. Association of a large lateral extension of the acromion with rotator cuff tears. J Bone Joint Surg Am. 2006;88:800-5

To The Editor:

We read with interest the article by Nyffeler, et al, “Association of a large lateral extension of the acromion with rotator cuff tears(1).” We would like to draw attention to the fact that during the natural progression of rotator cuff tears and cuff tear arthropathy, osseous changes in the glenoid and greater tuberosity can modify the radiological “acromion index” described by the authors. Medialization of the humeral head secondary to glenoid erosion can be present with or without superior migration of the head(2). This would result in a higher acromion index as a result of increase in the glenoid plane-acromion distance, thereby erroneously suggesting a larger lateral extension of the acromion. Similarly, osteolysis, cysts, and erosion of the greater tuberosity can influence the “acromion index”(3).

The authors state that patients with >15 degrees of retroversion were excluded from the study; however, they did not differentiate between concentric shoulders and non-concentric shoulders due to a massive rotator cuff tear.

The large lateral extension of the acromion may, therefore, be relative rather than absolute, and its association with rotator cuff tears is likely to be a consequence rather than a cause.

References:

1. Nyffeler RW, Werner CML, Sukthankar A, Schmid MR, Gerber C. Association of a large lateral extension of the acromion with rotator cuff tears. J Bone Joint Surg Am. 2006;88:800-5.

2. Visotsky JL, Basamania C, Seebauer L, Rockwood CA, Jensen KL. Cuff Tear Arthropathy: Pathogenesis, Classification, and Algorithm for treatment. J Bone Joint Surg Am. 2004; 86:35-40.

3. Pearsall AW 4th, Bonsell S, Heitman RJ, Helms CA, Osbahr D, Speer KP. Radiographic findings associated with symptomatic rotator cuff tears. J Shoulder Elbow Surg.2003; 12:122-7.