JBJS | Biomechanical Effect of Medial Advancement of the Supraspinatus Tendon. A Study in Cadavera*

The Journal of Bone & Joint Surgery, Volume 80, Issue 6

Articles | June 01, 1998

Biomechanical Effect of Medial Advancement of the Supraspinatus Tendon. A Study in Cadavera*

JAIN LIU, M.D.†; RICHARD E. HUGHES, PH.D.‡; SHAWN W. O'DRISCOLL, M.D., PH.D.‡; KAI-NAN AN, PH.D.‡, ROCHESTER, MINNESOTA

View Disclosures and Other Information

Investigation performed at the Division of Orthopedic Research, Mayo Clinic and Mayo Foundation, Rochester

The Journal of Bone & Joint Surgery. 1998; 80:853-9

5 Recommendations (Recommend) | 3 Comments | Saved by 3 Users Save Case

text A A A

Abstract

During the repair of some rotator-cuff tears, the torn tendon cannot be freed up adequately to permit reattachment at its original anatomical site of insertion. An option is to advance the site of insertion medially and reattach the tendon to a trough in the sulcus or to the humeral head. The biomechanical effects of such medial advancement on the moment arm of the supraspinatus muscle during glenohumeral elevation were studied in ten fresh-frozen shoulders from cadavera. Medial advancement of the site of insertion of the supraspinatus tendon was simulated by the placement of suture anchors in the sulcus of the proximal part of the humerus at points three, ten, and seventeen millimeters medial to the junction of the supraspinatus tendon and the bone. These distances were chosen not because they represent clinical options but because the large range allowed biomechanical study of medial advancement. Nylon lines were attached to the suture anchors and were passed back through an eyehook at the midpoint of the supraspinatus muscle. The excursion of each line was measured as the humerus was elevated, and the moment arm was estimated from the joint angle and excursion data with use of the principle of virtual work. Three and ten millimeters of medial advancement of the tendon (attachment in the sulcus) had a minimum (non-significant) effect on the moment arm during elevation compared with the value determined for the intact condition. However, seventeen millimeters of medial advancement was found to reduce the moment arm significantly (p < 0.05).CLINICAL RELEVANCE: Our study of cadavera indicates that a limited amount of medial advancement (as much as ten millimeters) is acceptable from a biomechanical point of view, although the clinical maximum is dictated by other clinical factors.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

For sixty years after Codman's report on what is believed to be the first operative repair of a tear of the rotator cuff, orthopaedic surgeons have attempted not only to repair the torn tendons but also to close the defect in the rotator cuff as much as possible. Many authors have emphasized the importance of a watertight closure^9,16,17,20, with some considering such closure necessary to prevent arthropathy secondary to the tear¹⁸. When a tear is small or medium-sized, watertight closure can be easily achieved with direct repair. For most medium-to-large tears, a tendon-to-bone repair is performed after a bone trough has been made (the McLaughlin method). To permit healing, undue tension at the site of the repair should be avoided by adequate mobilization of the retracted tendon^6,8,14,23. However, when the tear is large or massive and it is not possible to reattach the tendon to its original site of insertion, alternatives for repair include muscle advancement^7,11, tendon transfer^3,6, tendon-grafting^19,23, or medial advancement of the tendon and insertion to a bone trough^12,13,21.

Although reattachment at the original anatomical site of insertion on the greater tuberosity is ideal, medial insertion at the groove of the anatomical neck^3,12,14 or on the humeral head has been recommended when this is not possible^8,9. McLaughlin even recommended a much more medial position on the humeral cartilage for the closure of massive tears of the rotator cuff, but this has been thought by others¹⁹ to be an unsatisfactory technique because leverage and power in abduction are lost. Although most massive tears are not repaired with the McLaughlin technique, medial advancement of the supraspinatus tendon may be useful when the tendon cannot be reattached to the site of insertion because of scarring and retraction from a previous operation. It also may be useful when the infraspinatus and the other tendons, except for the supraspinatus, can be reattached to their original sites of insertion.

Such medial advancement undoubtedly affects the biomechanics of the shoulder, notably the moment arm of the supraspinatus. The moment arm of a muscle is an important determinant of the muscle's function because the torque produced by the muscle is the product of its force and its moment arm. A muscle with a larger moment arm can generate greater torque with the same amount of force; alteration of the site of insertion of a muscle may affect its moment arm and thereby reduce its capacity to generate torque. Therefore, the change in the moment arm after medial advancement can be used as an indicator of the functional capacity of the muscle to move the joint. We performed the present study to test the hypothesis that medial advancement of the site of insertion of the supraspinatus changes its moment arm during glenohumeral elevation.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Funds were received in total or partial support of the research or clinical study presented in this article. The funding sources were National Institutes of Health Grant AR41171, the Rotary Foundation (J. L.), the Li Foundation (J. L.), and the National Science Council, Taiwan (J. L.).

†Deceased.

‡Biomechanics Laboratory, Department of Orthopedics, Mayo Clinic, 200 First Street S.W., Rochester, Minnesota 55905. E-mail address for Dr. An: an.kainan@mayo.edu.

†Deceased.

‡Biomechanics Laboratory, Department of Orthopedics, Mayo Clinic, 200 First Street S.W., Rochester, Minnesota 55905. E-mail address for Dr. An: an.kainan@mayo.edu.

View Large | Download Slide(.ppt)
Add to My JBJS

Fig. 1 Drawing of the shoulder. The supraspinatus and the nylon lines are shown relative to the osseous structures. The three rows of pseudoinsertion points correspond to medial advancement of three millimeters (1), ten millimeters (2), and seventeen millimeters (3). The supraspinatus muscle is shown here for anatomical reference, but that muscle was replaced by a nylon line in the actual experiment.

View Large | Download Slide(.ppt)
Add to My JBJS

Fig. 2 Drawing showing the locations of the pseudoinsertion points in the humeral head. The points were separated by seven millimeters in the medial-lateral and anterior-posterior directions. Row 1 is most lateral and row 3 is most medial.

View Large | Download Slide(.ppt)
Add to My JBJS

Fig. 3 Drawing of the testing apparatus. The medial edge of the scapula is fixed to the Plexiglas fixture with use of plastic bolts, so that the angle of the arm is the glenohumeral angle. The testing fixture is made of Plexiglas, so as not to interfere with the electromagnetic tracking device (3Space source). The potentiometers (not shown) were located approximately one meter behind the tracking device.

View Large | Download Slide(.ppt)
Add to My JBJS

Fig. 4 Graph depicting the measured and fitted excursions for one trial.

View Large | Download Slide(.ppt)
Add to My JBJS

Fig. 5 Free-body diagram of a planar analysis of an elevated upper extremity, used to estimate the maximum strength of the extremity. g = acceleration due to gravity, marm = mass of the upper extremity, lcm = distance from the center of the glenohumeral rotation to the center of the mass of the upper extremity, ? = angle (from vertical) of the extremity, Fhand = magnitude of the downward vertical force applied to the hand, fx and fy = horizontal and vertical joint reaction forces, and M = net intersegmental reaction moment required for moment equilibrium. The muscle force vectors are denoted by muscle name.

View Large | Download Slide(.ppt)
Add to My JBJS

Fig. 6 Graph showing the normalized moment arms during elevation (as measured by the glenohumeral angle) according to the amount of medial advancement (three, ten, or seventeen millimeters). The data for each specimen were normalized to the moment arm of the supraspinatus that was measured for the intact condition of the same specimen.

View Large | Download Slide(.ppt)
Add to My JBJS

Fig. 7 Graph showing the mean moment arms (and standard deviation) of the supraspinatus during elevation (as measured by the glenohumeral angle) for intact specimens.

View Larger

TABLE I ABSOLUTE MOMENT ARM ACCORDING TO GLENOHUMERAL ELEVATION ANGLE

*The values are given as the mean and standard deviation. †Refers to the amount of medial advancement.

Glenohumeral Elevation Angle (degrees)	Absolute Moment Arm* (degrees)
Intact	3 mm†	10 mm†	17 mm†
10	24.6 ± 8.1	20.2 ± 3.8	22.4 ± 3.4	21.8 ± 4.1
20	28.0 ± 4.0	23.1 ± 2.8	23.6 ± 4.3	21.0 ± 5.8
30	29.5 ± 4.8	24.7 ± 3.3	22.9 ± 5.4	17.4 ± 7.7
40	29.0 ± 5.7	24.9 ± 4.1	20.6 ± 6.0	12.5 ± 9.2
50	26.8 ± 6.3	23.7 ± 4.7	16.9 ± 6.7	7.1 ± 10.4
60	23.0 ± 7.1	21.1 ± 5.6	12.0 ± 8.0	1.9 ± 11.3

Add to My JBJS

TABLE I ABSOLUTE MOMENT ARM ACCORDING TO GLENOHUMERAL ELEVATION ANGLE

*The values are given as the mean and standard deviation. †Refers to the amount of medial advancement.

Glenohumeral Elevation Angle (degrees)	Absolute Moment Arm* (degrees)
Intact	3 mm†	10 mm†	17 mm†
10	24.6 ± 8.1	20.2 ± 3.8	22.4 ± 3.4	21.8 ± 4.1
20	28.0 ± 4.0	23.1 ± 2.8	23.6 ± 4.3	21.0 ± 5.8
30	29.5 ± 4.8	24.7 ± 3.3	22.9 ± 5.4	17.4 ± 7.7
40	29.0 ± 5.7	24.9 ± 4.1	20.6 ± 6.0	12.5 ± 9.2
50	26.8 ± 6.3	23.7 ± 4.7	16.9 ± 6.7	7.1 ± 10.4
60	23.0 ± 7.1	21.1 ± 5.6	12.0 ± 8.0	1.9 ± 11.3

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

The study was performed on ten fresh-frozen shoulders from cadavera. There were five right shoulders and five left shoulders from four men and five women who had been a mean of sixty-seven years old (range, forty to eighty-nine years old) at the time of death. All of the shoulders had full motion and no evidence of a tear of the rotator cuff, arthritis, or an osseous deformity. With the elbow in 90 degrees of flexion, a Steinmann pin was drilled through the humerus just distal to the deltoid tuberosity. The pin was oriented parallel to the ulnar axis for reference. The humerus was transected just distal to the site of insertion of the deltoid. The skin and all muscles except the deltoid and the rotator cuff were dissected and removed.

The deltoid was detached from its origin and its muscle belly was excised, leaving only the insertion of the tendon. Similarly, the supraspinatus, subscapularis, infraspinatus, and teres minor muscles were elevated from their origins on the scapula, and each muscle was transected one centimeter proximal to the musculotendinous junction, leaving all of the tendons and the capsule intact. The coracoacromial ligament was preserved. Fifty-pound (22.7-kilogram) test nylon lines were sutured, with use of the modified Mason-Allen (Gerber) method¹⁰, to the anterior, middle, and posterior portions of the deltoid tendon and the midpoints of the musculotendinous junctions of the infraspinatus, supraspinatus, and subscapularis tendons.

The superior portion of the capsule was cut open from the superior labral margin to expose the humeral head. Pseudoinsertion points were chosen to simulate altered sites of insertion of the supraspinatus (Fig. 1). A thirty-pound (13.6-kilogram) test nylon line was attached from the pin at each pseudoinsertion point to a custom-made tapered acrylic suture anchor (3.25 millimeters in diameter at the larger end and ten millimeters long) inserted into the humeral head through a hole that had been predrilled with a 2.5-millimeter drill-bit. Three rows of three pins each were arranged seven millimeters apart, for a total of nine pseudoinsertion points (Fig. 2). The rows were three, ten, and seventeen millimeters medial to the site of insertion of the supraspinatus tendon. There were three points in each row to allow estimation of the moment arm in the anterior, middle, and posterior portions of the supraspinatus. A model of an intact supraspinatus was created by attaching a nylon line from the supraspinatus tendon to its anatomical site of insertion.

A fiberglass rod was inserted into the humeral intramedullary canal and was fixed with acrylic pins and cement. The referencing Steinmann pin then was replaced by a thinner fiberglass pin. The scapula was mounted to a Plexiglas table with bolts and cement (Fig. 3). The plane of the scapula was kept perpendicular to the ground during mounting. A Plexiglas guide-plane was affixed to the test table such that it was coplanar to the scapular plane, which was defined as the plane containing the center of the glenoid and the superior and inferior angles of the scapula. The orientation of the scapula was determined relative to reference marks on the test fixture, so that a glenohumeral angle of 0 degrees could easily be reproduced for each specimen. A sliding guide was fastened to the distal end of the intramedullary rod, and it was used to ensure that elevation of the arm occurred in the scapular plane and no internal or external rotation occurred during elevation. The sliding guide was set so that the anterior aspect of the humerus, which was marked by the fiberglass pin, was orthogonal to the Plexiglas guide-plane.

Eyehooks were fixed to the scapula, and the nylon line from each muscle was passed through a corresponding eyehook to simulate the line of action of the respective muscle. An eyehook was placed in the medial portion of the supraspinous fossa (to simulate the supraspinatus muscle), midway between the inferior angle and the spine of the scapula along the medial border of the infraspinous fossa (to simulate the infraspinatus muscle), midway between the inferior and superior angles along the medial border of the subscapular fossa (to simulate the subscapularis muscle), in the middle of the spine of the scapula (to simulate the posterior portion of the deltoid), on the lateral aspect of the acromion (to simulate the middle portion of the deltoid), and at the anterior tip of the acromion (to simulate the anterior portion of the deltoid). The line attached to the pin at each pseudoinsertion point was passed through the eyehook in the supraspinous fossa. All of the nylon lines were passed through holes in a Plexiglas panel to potentiometers (model 3500S-2-103; Bourns, Riverside, California) with a resistance tolerance of ±3 per cent and a linearity tolerance of ±0.2 per cent. Each line was wound around a cylinder on the shaft of the potentiometer, and a 2.5-newton weight was hung on the end of each line to remove slack.

A magnetic tracking device (3Space Isotrak; Polhemus, McDonnell Douglas Electronics, Colchester, Vermont) was used to measure the glenohumeral angle. It also was used to digitize landmarks at the completion of the experiment. The absolute error of this system has been reported to be less than one millimeter of displacement, and the angular error has been reported to be less than 0.5 degree¹. The signal source of the tracking device was attached to the Plexiglas table, which would not interfere with the magnetic tracking, and the position-sensor was attached to the humeral shaft. Data were collected at thirty hertz. A second position-sensor was used for digitization.

The humerus was elevated from 0 degrees (the hanging position) to maximum elevation in the scapular plane. The weights on the ends of the nylon lines were small, so their tensions were not enough to elevate the humerus. The humerus was elevated by the experimenter raising the intramedullary fiberglass rod. Weights were placed on the nylon lines at the beginning of the experiment; each trial consisted of the experimenter elevating the humerus slowly and smoothly within a ten-second period. Three trials were performed for each test to provide information on intertrial variability. After testing, the joint was disarticulated. The locations of the pseudoinsertion points were digitized with use of the position-sensor of the tracking device.

Excursion of the tendon was measured by the rotation of the potentiometers, and the angle of glenohumeral elevation was determined from the data obtained with the tracking device. Polynomial regression was used to model the relationship between the excursion (in millimeters) and the glenohumeral angle (in radians). A limit on the order of the polynomial was used (sixth order) to avoid overfitting of the data. The lowest-order polynomial satisfying the requirement that the root mean square error be less than 0.5 millimeter was selected for each muscle in each specimen. The polynomial regression fit was analytically differentiated to give the instantaneous moment arm² (Fig. 4). The moment arms were calculated at 1-degree intervals by numerically evaluating the differentiated polynomials. The sign convention was defined such that a positive moment arm indicated agonist function and a negative value represented antagonist function with respect to elevation. All trials were examined to identify non-physiological measurements, which occurred when a nylon line caught on tissue and was suddenly released. Data obtained during the initial 10 degrees of elevation are not presented because experimental factors (such as inertia and friction) introduce errors in the estimates of the moment arm during the first few degrees of movement.

The elevation moment arm of force applied to the pseudoinsertion point was normalized to the moment arm of the supraspinatus itself. A two-factor analysis-of-variance model (SAS; SAS Institute, Cary, North Carolina) was used to test whether the angle of glenohumeral elevation (in 10-degree increments), the amount of medial advancement (none and three, ten, and seventeen millimeters), and the interaction of the two had a significant effect on the normalized moment arm during elevation (the specimen was used as a blocking variable). Duncan multiple-range tests were used for post hoc analyses. Type-I errors were controlled at the p < 0.05 level of significance. The sample size was sufficient to have an 80 per cent chance of detecting a 20 per cent difference in the magnitude of the normalized moment arm. The moment arms measured at the three anterior-to-posterior pseudoinsertion points were averaged to obtain estimates for each amount of medial advancement. Means were used to make it easier to present the data.

A static, planar biomechanical model of elevation of the upper extremity was used to analyze the effect of medial advancement of the supraspinatus tendon on the maximum isometric strength of the limb (Fig. 5). The model was based on a hypothetical 1.67-meter-tall individual who weighs 617 newtons and holds the upper extremity in 60 degrees of elevation in the scapular plane. The mass and the location of the center of the mass of the upper extremity were scaled from stature and body mass, respectively⁴. The moment arms for the supraspinatus, infraspinatus, subscapularis, and anterior and middle portions of the deltoid at a glenohumeral angle of 40 degrees were used in the model because a shoulder rhythm of 2 degrees of glenohumeral elevation for each degree of scapulothoracic movement was assumed¹⁵. The posterior portion of the deltoid muscle was not included because it had an adduction moment arm. The maximum force that each muscle could produce was modeled as the product of the physiological cross-sectional area and a muscle-specific tension of 63.0 newtons per square centimeter. The maximum mass that could be applied to the hand while static equilibrium was maintained at the glenohumeral joint was determined to be the maximum strength of the upper limb.

Results

Introduction | Materials and Methods | Results | Discussion | References

The mean moment arm of the intact supraspinatus muscle reached a maximum of 29.5 millimeters at 33 degrees of glenohumeral elevation (Fig. 6). The mean moment arms were determined for the intact condition and the three conditions of medial advancement (Table I).

The angle of glenohumeral elevation (p < 0.0001) and the amount of medial advancement (p = 0.005) affected the normalized moment arm. Post hoc tests showed that the mean normalized moment arm with three or ten millimeters of medial advancement did not differ from that for the intact condition or from each other (Fig. 7). However, seventeen millimeters of medial advancement dramatically decreased the magnitude of the moment arm compared with that for the intact condition (p < 0.05) and that with three and ten millimeters of medial advancement (p < 0.05).

In fact, the normalized moment arm with seventeen millimeters of medial advancement was less than zero at 57 degrees of glenohumeral elevation, at which point the tendon restricted elevation. The mean absolute moment arm was 1.9 millimeters at 60 degrees of glenohumeral elevation. The specimens that had a negative moment arm with seventeen millimeters of medial advancement also tended to have a smaller moment arm for the intact condition. This finding explains why the mean normalized moment arm (Fig. 7) with seventeen millimeters of advancement was a negative value when the angle of elevation was more than 57 degrees while the mean absolute moment arm was positive (Table I).

The biomechanical model predicted maximum lifting strengths of sixty-seven, sixty-five, sixty-four, and fifty-nine newtons for the intact condition and three, ten, and seventeen millimeters of medial advancement, respectively.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

The results of the present study demonstrate that only a more extreme amount (seventeen millimeters) of medial advancement of the supraspinatus tendon has a negative effect on the moment arm during glenohumeral elevation. As much as ten millimeters of medial advancement was not found to have a substantial biomechanical effect. Thus, ten millimeters of medial advancement probably is biomechanically acceptable. A simple model of elevation strength of the upper extremity indicated that the strength deficit was most pronounced with seventeen millimeters of medial advancement. Although medial advancement of the supraspinatus tendon is an important option for the repair of a tear of the rotator cuff^13,20, clinical factors may limit the acceptable amount of medial advancement to less than ten millimeters.

For optimum healing, undue tension at the site of a repair should be avoided. Large or massive tears (tears that are greater than three centimeters) can be repaired only after adequate mobilization of the cuff^3,6,8,14,23. Even so, rotator cuffs with larger tears retear more frequently than those with small tears do^12,16. Even after extensive mobilization, some torn tendons cannot be reattached to their original site of insertion. Recommendations for dealing with such situations have included making a trough in the groove between the greater tuberosity and the humeral head^3,14 or in the humeral head itself^8,9. Our data suggest that reattachment of the tendon within ten millimeters of its original site of insertion should be biomechanically acceptable.

Advancement of the supraspinatus tendon may also impair strength in elevation by shortening the musculotendinous unit: the length-tension effect of muscle would reduce the maximum force generated by the supraspinatus. However, we cannot predict the effect of medial advancement of the tendon on length-tension because there usually is loss of tissue and scarring of the tendon in such circumstances.

There are some limitations of the present study. First, the cadavera that we tested may not be representative of the clinically relevant population; specifically, the age at the time of death was greater than the age of many patients who have a tear of the rotator cuff. In addition, a relatively small number of specimens were studied and in vitro kinematics may differ from in vivo kinematics. Also, the simple static planar biomechanical model of elevation of the upper extremity that was used did not include the effect of changes in the length of the muscle on the maximum production of isometric force by the supraspinatus muscle.

A potential concern about the results presented here is that humeral rotation was controlled by forces applied to the intramedullary rod by the experimenter's finger rather than by loading of the tendons. However, our results are similar to those of Otis et al., who controlled humeral orientation by altering the tension applied to the tendons; this suggests that the method that we used had no effect on our results. Poppen and Walker also reported a moment arm of the supraspinatus of approximately twenty millimeters, on the basis of geometric measurements on radiographs.

In conclusion, the supraspinatus tendon may be reattached with as much as ten millimeters of medial advancement from the original site of insertion without negative biomechanical consequences.

NOTE: Dr. Jain Liu was primarily responsible for conceiving the idea for this study, conducting the research, and writing this paper. Tragically, he was struck and killed by lightning soon after completing this manuscript. The coauthors wish to recognize his enthusiasm, intelligence, wit, and hard work.

References

Introduction | Materials and Methods | Results | Discussion | References

An, K. N.; Jacobsen, M. C.; Berglund, L. J.; and Chao, E. Y.: Application of a magnetic tracking device to kinesiologic studies. J. Biomech.,21: 613-620, 1988.21613 1988 [PubMed]

An, K. N.; Takahashi, K.; Harrigan, T. P.; and Chao, E. Y.: Determination of muscle orientations and moment arms. J. Biomech. Eng.,106: 280-282, 1984.106280 1984 [PubMed]

Bigliani, L. U.; Cordasco, F. A.; McIlveen, S. J.; and Musso, E. S.: Operative repairs of massive rotator cuff tears: long-term results. J. Shoulder and Elbow Surg.,1: 120-130, 1992.1120 1992

Chaffin, D. B., and Andersson, G. B. J.: Occupational Biomechanics, pp. 62-69. New York, Wiley, 1984.

Codman, E. A.: Complete rupture of the supraspinatus tendon. Operative treatment with report of two successful cases. Boston Med. and Surg. J.,164: 708-710, 1911.164708 1911

Cofield, R. H.: Current concepts review. Rotator cuff disease of the shoulder. J. Bone and Joint Surg.,67-A: 974-979, July 1985.67-A974 1985

Debeyre, J.; Patte, D.; and Elmelik, E.: Repair of ruptures of the rotator cuff of the shoulder with a note on advancement of the supraspinatus muscle. J. Bone and Joint Surg.,47-B(1): 36-42, 1965.47-B(1)36 1965

DeOrio, J. K., and Cofield, R. H.: Results of a second attempt at surgical repair of a failed initial rotator-cuff repair. J. Bone and Joint Surg.,66-A: 563-567, April 1984.66-A563 1984

Ellman, H.; Hanker, G.; and Bayer, M.: Repair of the rotator cuff. End-result study of factors influencing reconstruction. J. Bone and Joint Surg.,68-A: 1136-1144, Oct. 1986.68-A1136 1986

Gerber, C.; Schneeberger, A. G.; Beck, M.; and Schlegel, U.: Mechanical strength of repairs of the rotator cuff. J. Bone and Joint Surg.,76-B(3): 371-380, 1994.76-B(3)371 1994

Ha'Eri, G. B., and Wiley, A. M.: Advancement of the supraspinatus muscle in the repair of ruptures of the rotator cuff. J. Bone and Joint Surg.,63-A: 232-238, Feb. 1981.63-A232 1981

Harryman, D. T., II; Mack, L. A.; Wang, K. Y.; Jackins, S. E.; Richardson, M. L.; and Matsen, F. A., III: Repairs of the rotator cuff. Correlation of functional results with integrity of the cuff. J. Bone and Joint Surg.,73-A: 982-989, Aug. 1991.73-A982 1991

Hawkins, R. J.: The rotator cuff and biceps tendon. In Surgery of the Musculoskeletal System, edited by C. McC. Evarts. Ed. 2, vol. 2, p. 1412. New York, Churchill Livingstone, 1990.

Hawkins, R. J.; Misamore, G. W.; and Hobeika, P. E.: Surgery for full-thickness rotator-cuff tears. J. Bone and Joint Surg.,67-A: 1349-1355, Dec. 1985.67-A1349 1985

Liu, J.; Hughes, R. E.; Smutz, W. P.; Niebur, G.; and An, K. N.: Roles of deltoid and rotator cuff in shoulder elevation. Clin. Biomech.,12: 32-38, 1997.1232 1997

Liu, S. H., and Baker, C. L.: Arthroscopically assisted rotator cuff repair: correlation of functional results with integrity of the cuff. Arthroscopy,10: 54-60, 1994.1054 1994 [PubMed]

McLaughlin, H. L.: Lesions of the musculotendinous cuff of the shoulder. I. The exposure and treatment of tears with retraction. J. Bone and Joint Surg.,26: 31-51, Jan. 1944.2631 1944

Neer, C. S., II; Craig, E. V.; and Fukuda, H.: Cuff-tear arthropathy. J. Bone and Joint Surg.,65-A: 1232-1244, Dec. 1983.65-A1232 1983

Neviaser, J. S.; Neviaser, R. J.; and Neviaser, T. J.: The repair of chronic massive ruptures of the rotator cuff of the shoulder by use of a freeze-dried rotator cuff. J. Bone and Joint Surg.,60-A: 681-684, July 1978.60-A681 1978

Neviaser, R. J.: Tears of the rotator cuff. Orthop. Clin. North America,11: 295-306, 1980.11295 1980

Nobuhara, K.; Hata, Y.; and Komai, M.: Surgical procedure and results of repair of massive tears of the rotator cuff. Clin. Orthop.,304: 54-59, 1994.30454 1994 [PubMed]

Otis, J. C.; Jiang, C.-C.; Wickiewicz, T. L.; Peterson, M. G. E.; Warren, R. F.; and Santner, T. J.: Changes in the moment arms of the rotator cuff and deltoid muscles with abduction and rotation. J. Bone and Joint Surg.,76-A: 667-676, May 1994.76-A667 1994

Packer, N. P.; Calvert, P. T.; Bayley, J. I. L.; and Kessel, L.: Operative treatment of chronic ruptures of the rotator cuff of the shoulder. J. Bone and Joint Surg.,65-B(2): 171-175, 1983.65-B(2)171 1983

Poppen, N. K., and Walker, P. S.: Forces at the glenohumeral joint in abduction. Clin. Orthop.,135: 165-170, 1978.135165 1978 [PubMed]

Topics

View Large | Download Slide(.ppt)
Add to My JBJS

Fig. 4 Graph depicting the measured and fitted excursions for one trial.

View Large | Download Slide(.ppt)
Add to My JBJS

Fig. 7 Graph showing the mean moment arms (and standard deviation) of the supraspinatus during elevation (as measured by the glenohumeral angle) for intact specimens.

View Larger

TABLE I ABSOLUTE MOMENT ARM ACCORDING TO GLENOHUMERAL ELEVATION ANGLE

*The values are given as the mean and standard deviation. †Refers to the amount of medial advancement.

Glenohumeral Elevation Angle (degrees)	Absolute Moment Arm* (degrees)
Intact	3 mm†	10 mm†	17 mm†
10	24.6 ± 8.1	20.2 ± 3.8	22.4 ± 3.4	21.8 ± 4.1
20	28.0 ± 4.0	23.1 ± 2.8	23.6 ± 4.3	21.0 ± 5.8
30	29.5 ± 4.8	24.7 ± 3.3	22.9 ± 5.4	17.4 ± 7.7
40	29.0 ± 5.7	24.9 ± 4.1	20.6 ± 6.0	12.5 ± 9.2
50	26.8 ± 6.3	23.7 ± 4.7	16.9 ± 6.7	7.1 ± 10.4
60	23.0 ± 7.1	21.1 ± 5.6	12.0 ± 8.0	1.9 ± 11.3

Add to My JBJS

TABLE I ABSOLUTE MOMENT ARM ACCORDING TO GLENOHUMERAL ELEVATION ANGLE

*The values are given as the mean and standard deviation. †Refers to the amount of medial advancement.

Glenohumeral Elevation Angle (degrees)	Absolute Moment Arm* (degrees)
Intact	3 mm†	10 mm†	17 mm†
10	24.6 ± 8.1	20.2 ± 3.8	22.4 ± 3.4	21.8 ± 4.1
20	28.0 ± 4.0	23.1 ± 2.8	23.6 ± 4.3	21.0 ± 5.8
30	29.5 ± 4.8	24.7 ± 3.3	22.9 ± 5.4	17.4 ± 7.7
40	29.0 ± 5.7	24.9 ± 4.1	20.6 ± 6.0	12.5 ± 9.2
50	26.8 ± 6.3	23.7 ± 4.7	16.9 ± 6.7	7.1 ± 10.4
60	23.0 ± 7.1	21.1 ± 5.6	12.0 ± 8.0	1.9 ± 11.3