Aaron Sciascia

The Role of Core Stability in Athletic Function

The importance of function of the central core of the body for stabilisation and force generation in all sports activities is being increasingly recognised. ‘Core stability’ is seen as being pivotal for efficient biomechanical function to maximise force generation and minimise joint loads in all types of activities ranging from running to throwing. However, there is less clarity about what exactly constitutes ‘the core’, either anatomically or physiologically, and physical evaluation of core function is also variable.‘Core stability’ is defined as the ability to control the position and motion of the trunk over the pelvis to allow optimum production, transfer and control of force and motion to the terminal segment in integrated athletic activities. Core muscle activity is best understood as the pre-programmed integration of local, single-joint muscles and multi-joint muscles to provide stability and produce motion. This results in proximal stability for distal mobility, a proximal to distal patterning of generation of force, and the creation of interactive moments that move and protect distal joints. Evaluation of the core should be dynamic, and include evaluation of the specific functions (trunk control over the planted leg) and directions of motions (three-planar activity). Rehabilitation should include the restoring of the core itself, but also include the core as the base for extremity function.

Current concepts: scapular dyskinesis

The scapula serves many roles in order for proper shoulder function to occur. These roles include providing synchronous scapular rotation during humeral motion, serving as a stable base for rotator cuff activation and functioning as a link in the kinetic chain. Each role is vital to proper arm function and can only occur when the anatomy around the shoulder is uncompromised. The presence of bony and soft tissue injury as well as muscle weakness and inflexibility can alter the roles of the scapula and alter scapular resting position and/or dynamic motion. This altered scapular position/movement has been termed ‘scapular dyskinesis’. Although it occurs in a large number of shoulder injuries, it appears that scapular dyskinesis is a non-specific response to a painful condition in the shoulder rather than a specific response to certain glenohumeral pathology. The presence or absence of scapular dyskinesis needs to be determined during the clinical examination. An examination consisting of visual inspection of the scapular position at rest and during dynamic humeral movements, along with the performance of objective posture measurements and scapular corrective maneuvers, will help the clinician ascertain the extent to which the scapula is involved in the shoulder injury. Treatment of scapular dyskinesis should begin with optimised anatomy and then progress to the restoration of dynamic scapular stability by strengthening of the scapular stabilisers utilising kinetic chain-based rehabilitation protocols.

Clinical implications of scapular dyskinesis in shoulder injury: the 2013 consensus statement from the ‘scapular summit’

The second international consensus conference on the scapula was held in Lexington Kentucky. The purpose of the conference was to update, present and discuss the accumulated knowledge regarding scapular involvement in various shoulder injuries and highlight the clinical implications for the evaluation and treatment of shoulder injuries. The areas covered included the scapula and shoulder injury, the scapula and sports participation, clinical evaluation and interventions and known outcomes. Major conclusions were (1) scapular dyskinesis is present in a high percentage of most shoulder injuries; (2) the exact role of the dyskinesis in creating or exacerbating shoulder dysfunction is not clearly defined; (3) shoulder impingement symptoms are particularly affected by scapular dyskinesis; (4) scapular dyskinesis is most aptly viewed as a potential impairment to shoulder function; (5) treatment strategies for shoulder injury can be more effectively implemented by evaluation of the dyskinesis; (6) a reliable observational clinical evaluation method for dyskinesis is available and (7) rehabilitation programmes to restore scapular position and motion can be effective within a more comprehensive shoulder rehabilitation programme.

Electromyographic Analysis of Specific Exercises for Scapular Control in Early Phases of Shoulder Rehabilitation

Background Restoration of control of dynamic scapular motion by specific activation of the serratus anterior and lower trapezius muscles is an important part of functional rehabilitation. This study evaluated activation of those muscles in specific exercises. Hypothesis Specific exercises will activate key scapular-stabilizing muscles in clinically significant amplitudes and patterns. Study Design Controlled laboratory study. Methods Muscle activation amplitudes and patterns were evaluated in the serratus anterior, upper trapezius, lower trapezius, anterior deltoid, and posterior deltoid muscles with electromyography in symptomatic (n = 18) and asymptomatic (n = 21) subjects as they executed the low row, inferior glide, lawnmower, and robbery exercises. Results There were no significant differences in muscle activation amplitude between groups. Muscle activation was moderate across all of the exercises and varied slightly with the specific exercise. The serratus anterior and lower trapezius were activated between 15% and 30% in all exercises. Upper trapezius activation was high (21%-36%) in the dynamic exercises (lawnmower and robbery). Serratus anterior was activated first in the low row and last in the lawnmower and robbery. The upper trapezius and lower trapezius were activated first in the lawnmower and robbery. Conclusion These specific exercises activate key scapular-stabilizing muscles at amplitudes that are known to increase muscle strength. Clinical Relevance These exercises can be used as part of a comprehensive rehabilitation program for restoration of shoulder function. They activate the serratus anterior and lower trapezius—key muscles in dynamic shoulder control—while variably activating the upper trapezius. Activation patterns depended on scapular position resulting in variability of amplitude and activation sequencing between exercises. Inferior glide and low row can be performed early in rehabilitation because of their limited range of motion, while lawnmower and robbery, which require larger movements, can be instituted later in the sequence.

Evaluation of Apparent and Absolute Supraspinatus Strength in Patients With Shoulder Injury Using the Scapular Retraction Test

Background Physical examination of patients with shoulder injury not involving actual rotator cuff tears frequently demonstrates decreased rotator cuff strength on manual muscle testing. This decrease has been attributed to supraspinatus muscle weakness, but it may be owing to alterations in scapular position. Hypothesis The position of stabilized scapular retraction, by minimizing proximal kinetic chain factors and providing a stable base of muscle origin, positively influences demonstrated supraspinatus strength. Study Design Controlled laboratory study. Methods Supraspinatus strength was tested in 20 injured patients and 10 healthy controls in both the empty-can arm position and a position of scapular retraction using a handheld dynamometer. Pain in both maneuvers was measured by use of a visual analog scale. Results Paired t tests indicated the scapular retraction position resulted in statistically significantly (P =. 001) higher supraspinatus strength values within both groups. There was no significant difference between the 2 positions in visual analog scale scores. Conclusion This study shows that demonstrated apparent supraspinatus weakness on clinical examination in symptomatic patients may be dependent on scapular position. The weakness may be owing to other factors besides supraspinatus muscle weakness, such as a lack of a stable base in the kinetic chain or scapula. Clinical Relevance The clinical examination that addresses scapular posture and includes scapular retraction will allow more accurate determination of absolute supraspinatus muscle strength and allow efficacious rehabilitation protocols to address the source of the demonstrated weakness.

Scapular Summit 2009, July 16, 2009, Lexington, Kentucky

This was the third research meeting focused on scapular function and dysfunction, following similar meetings in 2003 and 2006. The purpose of this meeting, hosted by the Shoulder Center of Kentucky, was to continue to examine the biomechanical and clinical factors thought to be associated with the role of the scapula in shoulder function and dysfunction. Since the last Summit, much more information has been created in this area, and it was thought that enough progress had been made that an organized overview of current knowledge could provide some consensus statements to guide further research and provide assessment and treatment guidelines. A call for abstracts was extended to researchers with proven interest and published research on the scapula. The meeting was organized around 3 primary categories of information: scapular kinematics and dysfunction, clinical evaluation of the scapula, and interventions. The last session of the meeting involved development of consensus statements for each category. This document represents the current state of knowledge concerning the aspects of scapular function and dysfunction discussed at the Summit. It is expected that, as more knowledge is developed, the gaps will be filled in and a clearer understanding of the roles of the scapula in shoulder function will emerge. This issue includes the consensus statements and abstracts from the Summit.

Glenohumeral Internal Rotation Deficit: Pathogenesis and Response to Acute Throwing

Overhand throwing places high loads and stresses on the joints and tissues of the shoulder and arm. As a result, throwing athletes regularly demonstrate altered shoulder internal and external ranges of motion where internal rotation (IR) is decreased and external rotation is increased in the dominant arm when compared with the nondominant arm. This alteration can exist as a result of alterations to the bones (humeral retroversion), capsule (posterior thickening), or muscle (passive stiffness known as thixotropy). When the amount of IR or total arc of motion difference reaches a certain threshold (typically 20 or more degrees of IR or 8 degrees total arc difference), it is known as glenohumeral internal rotation deficit or total arc of motion deficit. Glenohumeral internal rotation deficit and total arc of motion deficit can cause alterations in biomechanics such as scapular “wind-up” or alteration of glenohumeral joint kinematics, which can in turn lead to clinical findings of impingement and labral pathology. This study will review the causes of motion alteration, effects of altered motion on the throwing motion, provide definitions for the various types of rotation deficits, and how to evaluate and treat rotational deficits.

The Pediatric Overhead Athlete: What is the Real Problem?

Objective: The purposes of this article are to examine shoulder and elbow injuries in pediatric athletes, to evaluate the pathophysiology and pathomechanics that may be associated with the pathoanatomy, and to present suggestions for the prevention of those injuries. Data Sources: This article will review the published sports medicine literature on these topics in baseball and tennis injuries and present a kinetic chain-based perspective on the possible causative factors that are present in the young thrower. Results: The published literature shows that there are multiple intrinsic and extrinsic factors that contribute to the risk of injury in young throwing athletes. These factors appear to develop over time; if not recognized or addressed early, they have undesirable outcomes. Conclusions: A multitude of factors, including anatomical, biomechanical, and environmental concerns, can contribute to the dysfunction of the shoulder and elbow in young overhead athletes. Understanding the force-generating and load-absorbing processes of the body will help clinicians, coaches, and others prevent or limit the deleterious effects of such occurrences.

Mechanics and pathomechanics in the overhead athlete.

Optimal performance of the overhead throwing task requires precise mechanics that involve coordinated kinetic and kinematic chains to develop, transfer, and regulate the forces the body needs to withstand the inherent demands of the task and to allow optimal performance. These chains have been evaluated and the basic components, called nodes, have been identified. Impaired performance and/or injury, the DTS, is associated with alterations in the mechanics that are called pathomechanics. They can occur at multiple locations throughout the kinetic chain. They must be evaluated and treated as part of the overall problem. Observational analysis of the mechanics and pathomechanics using the node analysis method can be useful in highlighting areas of alteration that can be evaluated for anatomic injury or altered physiology. The comprehensive kinetic chain examination can evaluate sites of kinetic chain breakage, and a detailed shoulder examination can assess joint internal derangement of altered physiology that may contribute to the pathomechanics. Treatment of the DTS should be comprehensive, directed toward restoring physiology and mechanics and optimizing anatomy. This maximizes the body’s ability to develop normal mechanics to accomplish the overhead throwing task.

Kinetic Chain Abnormalities in the Athletic Shoulder

Overhead activities require the shoulder to be exposed to and sustain repetitive loads. The segmental activation of the body’s links, known as the kinetic chain, allows this to occur effectively. Proper muscle activation is achieved through generation of energy from the central segment or core, which then transfers the energy to the terminal links of the shoulder, elbow, and hand. The kinetic chain is best characterized by 3 components: optimized anatomy, reproducible efficient motor patterns, and the sequential generation of forces. However, tissue injury and anatomic deficits such as weakness and/or tightness in the leg, pelvic core, or scapular musculature can lead to overuse shoulder injuries. These injuries can be prevented and maladaptations can be detected with a thorough understanding of biomechanics of the kinetic chain as it relates to overhead activity.