Biomechanics of the Shoulder Since the time of Leonardo di Vinci's pioneering exploration of the human anatomy, man has recognized the perfect union of form and function found in the shoulder joint. Providing a fortuitous combination of mobility and stability, the shoulder joint complex permits a wide range of motion that differentiates human arm movement from that of lower animals. Examined from the unique perspective offered by modern biomechanical research, the shoulder joint is considered to have played a pivotal role in the human evolutionary process, enabling man to better utilize projectile weapons by developing accurate throwing techniques, among other advantageous adaptive qualities. Today, the study of shoulder biomechanics is an essential component of clinical orthopedic care, sports medicine, mechanical injury rehabilitation and a wide array of other fields. By conducting a thorough review of the prevailing research on shoulder biomechanics, the splendidly simple yet efficiently effective structural composition of this foundational joint can be more fully revealed. The following literature review is intended to demonstrate the biomechanical perfection of the human shoulder, synthesizing clinical research published during the last two decades in an attempt to assess the important part played by this joint in facilitating efficient, painless and powerful movements.

Foundations of Biomechanical Study

Although the various forms of human movement have been studied for centuries on an individual basis -- with skeletal, muscular, neurological and sensory aspects of movement forming the basis of entire fields of empirical medical inquiry -- the concept of biomechanics has only recently emerged to describe the intricately complex synergy of activities which occurs in concert whenever people throw a ball or sketch a portrait. As a relatively recent contribution to anatomical research, biomechanics was devised largely to combine elements of several branches within modern movement science while forming an integrated model. When the totality of automatic internal processes which dictate even the most imperceptible of movements is fully considered, with "the neuromuscular system acting to control the release of metabolic energy for the purpose of generating controlled patterns of tension at the tendon ... (and) that waveform serving as a function of the physiological characteristics of the muscle" (Winter, 2009), it is quite evident that biomechanical research is essential to furthering knowledge within a number of fields. As a founding member of the Canadian Society for Biomechanics, and the author of scholarly research on the subject which spans several decades, David A. Winters is one of the world's foremost authorities on the biomechanical nature of human locomotion, and he has observed of "the relationship between the sensory system, the neurological pathways, the muscles, the skeletal system ... (that) the essential characteristic of this total system is that it is converging in nature" (Winter, 2009). This concept of convergence is a crucial to the modern comprehension of biomechanics, because a rapid acceleration in the rate of technological advancement has enabled scientists, doctors, surgeons and other specialists to more fully explore the collaborative way in which bodily movement is initiated, directed and controlled.

Structure of the Shoulder

The human shoulder is an especially effective assemblage comprised of just three bones -- the clavicle or collarbone, the scapula or shoulder blade, and the humerus or upper arm bone -- as well as the network of connected tendons, ligaments, and muscles in the neck and arm. The colloquial term "shoulder joint" is generally used in reference to the glenohumeral and acromioclavicular joints, which are the primary joints located within the shoulder structure. In humans, the point where the humerus connects to the scapula, with the head of the bone fitting into the glenoid fossa, is considered to be the shoulder joint. In biomechanical terms, this unique arrangement is an extension of optimal evolutionary design, as "the development of a more laterally directed glenoid cavity of the scapula and a longer and more laterally twisted clavicle allowed for a freer mobility to raise the arm and facilitated vertical climbing" (Veeger & Van Der Helm, 2007). Several muscles actively contribute to the process of internal rotation within the shoulder, including the anterior ?bers of the deltoid, the latissimus dorsi, the teres major, the pectoralis major, and the subscapularis (Patel, Gustafson & Jastifer, 2012). The presence of the fibrocartilaginous labrum, as well as the inclusion of both a constrained capsule and glenohumeral ligaments, serves to increase the shoulder's stability during movement. However, this static stabilizing structures is provided with an extended level of support by the musculature structure surrounding the shoulder girdle, a design which optimizes dynamic stability. A specialized muscle known as the rotator cuff not also works as a dynamic stabilizer, while contributing to the shoulder's passive stability in light of its proximity to and positioning around the...

This combination of static and dynamic stabilizers is reactive to various forms of force applied by the glenohumeral joint, ensuring stability during different positions throughout the shoulder's biomechanical motion arc (Lugo, King & Ma, 2008).
Research on Shoulder Biomechanics

Biomechanical measurement of shoulder movement and range of motion is typically expressed as flexion and extension (movement elevating the humerus away from the anterior thorax within the sagittal plane), abduction (elevation within the coronal plane), and internal-external rotation (axial rotation of the humerus when the arm is held in an adducted position) (Nordin & Frankel, 2001). Due to the shoulder's fundamental importance to many movements which are crucial to everyday life -- such as driving, writing, throwing, lifting, pulling and climbing -- a substantial portion of biomechanical research has focused on this area of the body. Sports medicine specialists publish comprehensive analyses of the impact of pitching baseballs and passing footballs, and orthopedic surgeons continually improve shoulder reconstruction surgeries to restore range of movement during recovery from serious injuries, and biomechanics forms the foundation of these advancements. Our growing understanding of the biomechanical nature of human movement has enabled doctors to anatomical experts to discover that "during normal motion, the scapula will upwardly rotate and posteriorly tilt on the thorax during elevation of the arm in flexion, abduction, scapular plane abduction, or unrestricted overhead reaching & #8230; (while) scapulothoracic internal or external rotation is less consistent during arm elevation" (Ludewig & Braman, 2011). Insights such as these are extremely informative in terms of orthopedic diagnostics, post-surgery rehabilitation, and preventative medicine, because the precise calibration of several interconnected variables is necessary to facilitate proper range of motion and joint movement in the shoulder. By expanding the base of biomechanical knowledge pertaining to the shoulder's unique muscular, skeletal and structural construction, the scientific and medical research community has provided an invaluable resource for the improvement of diagnostic and treatment methods with a wide range of specializations.

Medical Diagnostic Implications of Shoulder Biomechanics

The degradation of rotator cuff capability and shoulder flexibility can occur whenever this delicate arrangement of muscles, bones, ligaments and tendons is subjected to an inordinate amount of pressure, stress or fatigue. Rotator cuff disease, shoulder impingement, clavicle malunion and localized soreness are just a few of the dozens of afflictions which can restrict range of motion in the shoulder, causing severe physical distress for patients suffering from these maladies. Research on the biomechanical properties of the shoulder has spawned a host of advances within the realm of diagnostic medicine, because "any quantitative assessment of human movement must be preceded by a measurement and description phase, and if more meaningful diagnostics are needed, a biomechanical analysis is usually necessary" (Winter, 2009). For example, computational studies on the effect of clavicle injury on shoulder movement have consistently indicated that "with progressive clavicular shortening, there is a resulting functional change in the biomechanics of the shoulder including a clinically signi-can't change in the moment generating capacity about the glenohumeral joint" (Patel, Gustafson & Jastifer, 2012). Findings such as this are crucial from a biomechanical perspective, because the interconnected nature of the total system containing the shoulder and its surrounding components has wide ranging implications for future advances in the treatment of neck, arm, and chest injuries. Professional athletes and those who pursue an active personal lifestyle are especially concerned with advances in shoulder biomechanics, because torn ligaments and rotator cuffs can adversely affect one's ability to pick a ball up off of the ground, let alone throw or catch one during the heat of athletic competition. Proper biomechanical technique when moving the shoulder is perhaps the most effective step in preventing traumatic stresses from occurring within this crucial region of the body.

Conclusion

Incorporating the emerging science of biomechanics into the wide array of medical and therapeutic fields involving anatomical care of the shoulder has provided immediate dividends for physicians, physical therapists, orthopedists, and patients. For example, research on the biomechanics of the shoulder has revealed that "disruption of stabilizing structures can cause clinical manifestations of pain or instability & #8230; (while) injuries and pathologic processes can potentially cause similar clinical presentations," which is why it is crucial to "understand the etiology of these different causative factors so that we can offer effective treatment for patients suffering from shoulder instability" (Lugo, Kung & Ma, 2008). Biomechanics is simply the latest advancement in…