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Letters to the Editor to:

Scientific Articles:
Richard W. Nyffeler, Clément M.L. Werner, Atul Sukthankar, Marius R. Schmid, and Christian Gerber
Association of a Large Lateral Extension of the Acromion with Rotator Cuff Tears
J Bone Joint Surg Am 2006; 88: 800-805 [Abstract] [Full text] [PDF]
*Letters to the Editor: Submit a response to this article

Electronic letters published:

[Read Letter to the Editor] Dr. Nyffeler et al. respond to Dr. Jobe.
Richard W. Nyffeler, M.D., Clement M.L. Werner, M.D, Atul Sukthankar, M.D., Marius R. Schmid, M.D., and Christian Gerber, M.D.   (29 June 2006)
[Read Letter to the Editor] Mechanism of Humeral Head Depression
Christopher M. Jobe, M.D.   (1 June 2006)
[Read Letter to the Editor] Bilaterality of Large Lateral Extension of the Acromion?
Jibanananda Satpathy   (15 May 2006)
[Read Letter to the Editor] Dr. Nyffeler, et al, respond to Dr. Bhatia, et al.
Richard W. Nyffeler, M.D., Dipl. Eng. ETH, Clement M.L. Werner, M.D., Atul Sukthankar, M.D., Marius R. Schmid, M.D., and Christian Gerber, M.D.   (19 April 2006)
[Read Letter to the Editor] Humeral head medialization in massive cuff tears can influence the "Acromion index".
Deepak N. Bhatia, Joe F. deBeer (Cape Shoulder Institute), Prof. Donald F. du Toit ( University of Stellenbosch, Cape Town, South Africa)   (13 April 2006)

Dr. Nyffeler et al. respond to Dr. Jobe. 29 June 2006
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Richard W. Nyffeler, M.D.
Dept. Orthopaedic Surgery, University of Berne, Inselspital, 3010 Berne, SWITZERLAND,
Clement M.L. Werner, M.D, Atul Sukthankar, M.D., Marius R. Schmid, M.D., and Christian Gerber, M.D.

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Re: Dr. Nyffeler et al. respond to Dr. Jobe.

richard.nyffeler{at}bluewin.ch Richard W. Nyffeler, M.D., et al.

To The Editor:

Dr. Jobe, who is an acknowledged contributor to Gagey and Hue's publication(1), correctly states that these authors previously described a humeral head depression effect of the deltoid muscle. In fact, Gagey and Hue recognized that the deltoid muscle wraps around the humeral head. They calculated the forces acting on the proximal humerus and found that the resultant force vector of the middle deltoid was oriented downward. We are convinced, as are others as well(2,3), that this is not true.

In our model(4) the resultant force vector of the middle deltoid is always oriented upwards. In the case of an acromion with a wide lateral extension, which completely covers the humeral head (acromion index = 1.0) the action line of the middle deltoid is a straight line between the origin and the insertion of this muscle. The resultant force vector is parallel to the action line and oriented upwards. If the acromion is smaller and does not completely cover the humeral head, then the muscle fibers of the middle deltoid wrap around the proximal humerus and exert an additional compressive force on the humeral head (pulley effect). However, the main force component is still oriented upwards and the resultant force vector is in line with the muscle fibers at their origin on the acromion (see Fig. 4 and Fig. 5a and 5b of our article). This can easily be shown by replacing the middle deltoid by a cord which inserts at the tubercle of the deltoid and passes through an eye-hook on the acromion. Pulling on the free end of the cord results in an ascension and abduction of the humerus.

Similar results have been found in a 3D finite element model of the shoulder, including scapula, humerus, cartilage, the three portions of the deltoid and the rotator cuff muscles(5). This study confirmed that the humeral head translates superiorly during active arm elevation. The amount of superior translation was influenced by the lateral extension of the acromion and was larger for acromions with a large lateral extension.

We agree with Dr. Jobe that the above described mechanism could also be applied to the anterior aspect of the acromion. However, the anterior extension of the acromion was not investigated in our study and should be examined on lateral radiographs.

References:

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

2. Blasier RB, Hughes RE, Carpenter JE, Kuhn JE: Letter to the Editor. Clinical Orthopaedics & Related Research, 388:258, 2001.

3. Kölbel R., Bergmann G. Letter to the Editor. Clinical Orthopaedics & Related Research, 389:251, 2001.

4. 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.

5. Terrier A, Reist A, Nyffeler RW. Influence of the shape of the acromion on joint reaction force and humeral head translation during abduction in the scapular plane. Proceedings of the 5th World Congress of Biomechanics, Munich, 29 July – 4 August 2006
Mechanism of Humeral Head Depression 1 June 2006
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Christopher M. Jobe, M.D.,
Orthopaedic Surgeon, Professor & Chair
Loma Linda University Medical Center, Loma Linda, CA 92354

Send letter to journal:
Re: Mechanism of Humeral Head Depression

lkent{at}llu.edu Christopher M. Jobe, M.D.

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.
Bilaterality of Large Lateral Extension of the Acromion? 15 May 2006
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Jibanananda Satpathy,
SHO Orthopaedics
Horton General Hospital

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Re: Bilaterality of Large Lateral Extension of the Acromion?

jibnapgi{at}hotmail.com Jibanananda Satpathy

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.
Dr. Nyffeler, et al, respond to Dr. Bhatia, et al. 19 April 2006
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Richard W. Nyffeler, M.D., Dipl. Eng. ETH
Dept. Orthopaedic Surgery, University of Bern, SWITZERLAND,
Clement M.L. Werner, M.D., Atul Sukthankar, M.D., Marius R. Schmid, M.D., and Christian Gerber, M.D.

Send letter to journal:
Re: Dr. Nyffeler, et al, respond to Dr. Bhatia, et al.

richard.nyffeler{at}bluewin.ch Richard W. Nyffeler, M.D., Dipl. Eng. ETH, et al.

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
Humeral head medialization in massive cuff tears can influence the "Acromion index". 13 April 2006
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Deepak N. Bhatia,
Shoulder Fellow
Cape Shoulder Institute, Cape Town, South Africa.,
Joe F. deBeer (Cape Shoulder Institute), Prof. Donald F. du Toit ( University of Stellenbosch, Cape Town, South Africa)

Send letter to journal:
Re: Humeral head medialization in massive cuff tears can influence the "Acromion index".

thebonesmith{at}gmail.com Deepak N. Bhatia, et al.

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.