Moment arms of the muscles crossing the anatomical shoulder

The objective of the present study was to determine the instantaneous moment arms of 18 major muscle sub‐regions crossing the glenohumeral joint during coronal‐plane abduction and sagittal‐plane flexion. Muscle moment‐arm data for sub‐regions of the shoulder musculature during humeral elevation are currently not available. The tendon‐excursion method was used to measure instantaneous muscle moment arms in eight entire upper‐extremity cadaver specimens. Significant differences in moment arms were reported across sub‐regions of the deltoid, pectoralis major, latissimus dorsi, subscapularis, infraspinatus and supraspinatus (P < 0.01). The most effective abductors were the middle and anterior deltoid, whereas the most effective adductors were the teres major, middle and inferior latissimus dorsi (lumbar vertebrae and iliac crest fibers, respectively), and middle and inferior pectoralis major (sternal and lower‐costal fibers, respectively). In flexion, the superior pectoralis major (clavicular fibers), anterior and posterior supraspinatus, and anterior deltoid were the most effective flexors, whereas the teres major and posterior deltoid had the largest extensor moment arms. Division of multi‐pennate shoulder muscles of broad origins into sub‐regions highlighted distinct functional differences across those sub‐regions. Most significantly, we found that the superior sub‐region of the pectoralis major had the capacity to exert substantial torque in flexion, whereas the middle and inferior sub‐regions tended to behave as a stabilizer and extensor, respectively. Knowledge of moment arm differences between muscle sub‐regions may assist in identifying the functional effects of muscle sub‐region tears, assist surgeons in planning tendon reconstructive surgery, and aid in the development and validation of biomechanical computer models used in implant design.

[1]  E. Crelin Atlas of Human Anatomy , 1965, The Yale Journal of Biology and Medicine.

[2]  G R Johnson,et al.  Application of spherical and cylindrical wrapping algorithms in a musculoskeletal model of the upper limb. , 2001, Journal of biomechanics.

[3]  D R Pichora,et al.  Glenohumeral contact forces , 2000, Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine.

[4]  P. Herberts,et al.  Intramuscular pressure and electromyography in four shoulder muscles , 1991, Journal of orthopaedic research : official publication of the Orthopaedic Research Society.

[5]  A Farron,et al.  Isolated rupture of the subscapularis tendon. , 1996, The Journal of bone and joint surgery. American volume.

[6]  M Vitti,et al.  Simultaneous EMG of latissimus dorsi and sternocostal portion of pectoralis major muscles during butterfly natatory stroke. , 1984, Electromyography and clinical neurophysiology.

[7]  N. Poppen,et al.  Normal and abnormal motion of the shoulder. , 1976, The Journal of bone and joint surgery. American volume.

[8]  Craig Cunningham,et al.  The Upper Limb , 2009 .

[9]  M G Pandy,et al.  Musculoskeletal Model of the Upper Limb Based on the Visible Human Male Dataset , 2001, Computer methods in biomechanics and biomedical engineering.

[10]  T. Santner,et al.  Changes in the moment arms of the rotator cuff and deltoid muscles with abduction and rotation. , 1994, The Journal of bone and joint surgery. American volume.

[11]  Alain Farron,et al.  Isolated Rupture of the Subscapularis Tendon. Results of Operative Repair* , 1996, The Journal of bone and joint surgery. American volume.

[12]  F. Netter Atlas of Human Anatomy , 1967 .

[13]  D. Palma,et al.  Surgery of the Shoulder , 1951, The Indian Medical Gazette.

[14]  F. V. D. van der Helm Analysis of the kinematic and dynamic behavior of the shoulder mechanism. , 1994, Journal of biomechanics.

[15]  J. Insall,et al.  Chondromalacia Patellae. A prospective study. , 1976, The Journal of bone and joint surgery. American volume.

[16]  K. An,et al.  Comparison of two methods for computing abduction moment arms of the rotator cuff. , 1997, Journal of biomechanics.

[17]  F. C. T. Helm,et al.  Analysis of the kinematic and dynamic behavior of the shoulder mechanism , 1994 .

[18]  F. V. D. van der Helm,et al.  Modelling the mechanical effect of muscles with large attachment sites: application to the shoulder mechanism. , 1991, Journal of biomechanics.

[19]  S. Howell,et al.  Clarification of the role of the supraspinatus muscle in shoulder function. , 1986, The Journal of bone and joint surgery. American volume.

[20]  K. An,et al.  Shoulder muscle moment arms during horizontal flexion and elevation. , 1997, Journal of shoulder and elbow surgery.

[21]  G. Johnson,et al.  Modelling the muscles of the scapula morphometric and coordinate data and functional implications. , 1996, Journal of biomechanics.

[22]  N. Poppen,et al.  Forces at the glenohumeral joint in abduction. , 1978, Clinical orthopaedics and related research.

[23]  James A. Johnson,et al.  The effect of muscle loading on the kinematics of in vitro glenohumeral abduction. , 2007, Journal of biomechanics.

[24]  M. Pandy 4 Moment A r m of a Muscle Force , 1999 .

[25]  K N An,et al.  Determination of muscle orientations and moment arms. , 1984, Journal of biomechanical engineering.

[26]  A. Flatt THE UPPER LIMB. , 1964, Physical therapy.

[27]  D Karlsson,et al.  Towards a model for force predictions in the human shoulder. , 1992, Journal of biomechanics.

[28]  Poppen Nk,et al.  Forces at the glenohumeral joint in abduction. , 1978 .

[29]  Freddie H. Fu,et al.  Shoulder muscle forces and tendon excursions during glenohumeral abduction in the scapular plane. , 1995, Journal of shoulder and elbow surgery.

[30]  M. Pandy Moment arm of a muscle force. , 1999, Exercise and sport sciences reviews.

[31]  Freddie H. Fu,et al.  A Dynamic Analysis of Glenohumeral Motion after Simulated Capsulolabral Injury. A Cadaver Model* , 1998, The Journal of bone and joint surgery. American volume.

[32]  Marcus G Pandy,et al.  Contributions of the individual muscles of the shoulder to glenohumeral joint stability during abduction. , 2008, Journal of biomechanical engineering.

[33]  G Németh,et al.  Muscle activity and coordination in the normal shoulder. An electromyographic study. , 1990, Clinical orthopaedics and related research.

[34]  J. Saunders,et al.  Observations of the Function of the Shoulder Joint , 1996, Clinical orthopaedics and related research.

[35]  G L Niebur,et al.  The relevance of the moment arm of shoulder muscles with respect to axial rotation of the glenohumeral joint in four positions. , 2000, Clinical biomechanics.

[36]  G Sjøgaard,et al.  A model predicting individual shoulder muscle forces based on relationship between electromyographic and 3D external forces in static position. , 1998, Journal of biomechanics.