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One of the joys of life is being able to move fluidly without stiffness or hindered motion. It’s something that is easy to take for granted until your mobility is diminished.

Ease of movement is facilitated by proper functioning of the joints. When the function of any joint is hindered, your ability to carry on normally is greatly reduced. Understanding something about your joints — how they work and how they can be compromised — can help to keep you moving easily through life.

Your body has several different types of joints that define certain ranges of motion. The more obvious joints that concern us are those at the knee, elbow, shoulder, hip, wrist, and neck. We also depend on joints in our hands and feet; throughout the spinal column; where the spine adjoins the hip bones; the collar bones; the jaw — even in the skull.

When you decide to take a drink, nerve impulses instruct your muscles to contract, enabling you to grasp a glass and move it toward your mouth. The function of the joints in this example is to limit the range of motion of your fingers, wrist, elbow, and shoulder to successfully complete the required task. If any of your joints are stiff or in a locked position — or in some cases too loose — it becomes more difficult or impossible to complete the sequence of motions.

What can interfere with joint function?

Lack of use can lead to a joint locking up. If the proper spacing between two joint surfaces is not maintained, function is altered. The ligaments — bands of strong, flexible, white tissue that connect and support the joints — must be firm enough, pliable and properly supportive or the joint performance will suffer. A muscle contraction can pull the joint out of alignment. If a muscle gets a partial signal from a nerve, it may tense rather than completely contracting. This tension can prevent the joint from proper function.

As you can see from the above examples, many factors can contribute to limited range of motion, joint pain, stiffness, etc. Fortunately, your regular massages can help your joints to perform at a more optimum level.

For instance, each massage can help to increase the circulation to the joint area so each joint will receive the raw materials and nourishment it requires. This increased circulation can help to remove any cellular waste as well.

Your joints are affected by the ligaments, muscles, and tendons that surround them. So when your muscle function is improved, it can positively affect the neighboring joints. The proper attention to a joint area can help to improve the range of motion, reduce painful conditions, and restore its performance.  

Proper exercise can help as well. Joint movement encourages lubrication of the joint. The ligaments, tendons and joint capsule are warmed from the movement, which helps to keep these tissues pliable.

It’s important to avoid undue stress to your joints. Besides inviting injury, trying to do too much, too soon when working with a stressed, weakened or injured joint can prevent recovery. Be sure to stay within each joint’s limitations when exercising, stretching, or in normal activity. It’s better to go slowly than to risk injury.

Your regular massages help to return proper balance to your body’s many systems — your muscles, joints, tendons, etc. The conditions that tend to cause a muscle to remain too tense or a joint to be stiff and limited in its motions in many cases can be normalized.

Each day brings new challenges to your body’s functions — many which manifest as tensions, aches, pains, and limited ranges of motion. Making sure you get regular bodywork sessions can help your body to overcome many of these challenges and maintain a happier balance, as well as helping to head off some potential problems before they adversely affect you. So contribute to that freedom of movement by maintaining a regular massage schedule! Make your future a healthier one.

Mosby ’s Fundamentals of Therapeutic Massage © 1995

Biomechanical Factors That Contribute To Rotator Cuff Function and Injury

By Richard J. Vahl, D.C.,
and James B. Vahl, CPT

Chronic shoulder problems are the most common upper extremity problem in the general population and in sports. These injuries can occur at any age but are especially more common in the over 40 age group and among men. However, gender is making less of a difference. Therefore, women are no longer exempt. Rotator cuff impingement, tendonitis/tendonosis, capsular tears and structural injuries are all common in athletes male or female. Especially, overhead motion and contact sport athletes are venerable to these injuries. Injuries causing damage to the small delicate rotator cuff muscles are common, often debilitating and very often can easily become chronic.

Synchronous and unimpeded joint motion are both necessary for proper shoulder function. Raising the arm overhead requires a fine combination of shoulder mobility and dynamic stability. Because of its structural mechanics, the shoulder joint relies heavily on support from the group of relatively small muscles collectively known as the “rotator cuff complex.” The rotator cuff complex enables the shoulder joint to produce its numerous characteristic movements while still maintaining a balance between shoulder mobility and stability. This structural arrangement of the glenohumeral joint contributes to its highly mobile but somewhat unstable status. This synchronous and unimpeded motion is a byproduct of:

• proper scapular motion along the thorax
• balanced muscle strength and function
• efficient neurological timing of synergistic muscle contractions
• sensorimotor integration.

Biomechanical Structure

The primary role of the shoulder joint complex is to place the upper extremities in positions that allow the hand and arm to function. The upper extremities can assume an infinite number of positions in a three-dimensional perspective in space. Therefore, the shoulder joint complex is a semi or modified ball and socket type of joint which is capable of movement in all three cardinal and oblique planes of motion. The shoulder joint complex does sacrifice some of its stability as compared to the hip joint for the sake of extra mobility. Therefore, it lacks a deep, fuller socket and broader socket surface area as compared to the hip joint and socket. So, instead of a fairly closed ball and socket joint like the hip joint, it is more of a “golf ball on a tee” joint. The humeral head articulates with a smaller open and shallow saucer- type of articulation, the glenoid fossa, which is located on the anterolateral surface of the scapula. Therefore, the glenohumeral joint stability is classified as being more dynamically stable than statically stable. The major function of the four rotator cuff muscles is to work in concert with each other to allow the arm to move relatively free in numerous positions. They do all this while pulling the humeral head downward and inward within the glenoid fossa.

Biomechanical Function

Since the humeral head is three to four times larger than the glenoid fossa, only approximately 25 percent of the humeral head is in contact with the glenoid fossa at any point in time. One of the main functions of the rotator cuff muscles is to compress and depress the humeral head within the glenoid fossa, to prevent it from spinning, sliding and rolling off the top of the glenoid fossa and striking up against the undersurface of the acromion process. Under normal circumstances, the rotator cuff muscles enable the humeral head to be constrained within a couple millimeters of the center of the glenoid fossa throughout most of the arc of shoulder motion.

The four rotator cuff muscles include:

• the supraspinatus
• infraspinatus
• teres minor
• subscapularis

These muscles all work synergistically. However, they each have an individual function as well:

The supraspinatus arises from the supraspinous fossa of the scapula and attaches to the greater tuberosity on the humeral head. Its function is to work closely with the deltoid muscle to raise the arm in flexion and abduction. The supraspinatus fibers maintain a horizontal line of pull, much like guide wires, which resolves or modifies the deltoid’s vertical line of pull. Weakness or extensive damage to the supraspinatus allows the vertical pull of the deltoid to drive the humeral head directly against the undersurface of the acromion process. When this happens it is called a sub-acromial impingement.

The subscapularis is an internal rotator. It has a diagonal arrangement of its fibers and therefore, a diagonal line of pull as well. It occupies the subscapular fossa on the anterior surface of the scapula, and inserts on the lesser tubercle of the humeral head.

The infraspinatus occupies the infraspinatus fossa on the posterior surface of the scapula, below the spine of the scapula. The infraspanatus also has diagonal fibers. The diagonal orientation of the infraspinatus fibers and their line of pull create external rotation of the arm and shoulder. The teres minor attaches to the greater tubercle of the humeral head.

The teres minor occupies the upper two-thirds of the axillary border of the scapula. The infraspinatus like the teres minor attaches to the greater tubercle of the humeral head and create external rotation of the arm and shoulder. The humeral head rolls up the glenoid during abduction and flexion of the arm and shoulder.

Force couples of the subscapularis, infraspinatus, teres minor and long head of the biceps brachi muscles create a concavity compression mechanism which pulls the humeral head into the glenoid fossa.

Balanced Strength And Function:

Balanced rotator cuff strength and function are necessary to prevent upward migration of the humeral head and subacromial impingement of the rotator cuff tendons. The supraspinatus and teres minor are considered the most efficient abductors and humeral head depressors in the rotator cuff group respectively. As a group, the rotator cuff directs and stabilizes the humeral head within the glenoid while the larger extrinsic muscles like the latissimus dorsi, pectoralis major and deltoid produce the forces necessary for gross arm and shoulder movements.

Injury Mechanism:

The most common injuries to the rotator cuff include:

• primary impingement
• secondary impingement
• degenerative anatomical changes
• tendonitis
• rotator cuff tears

Rotator cuff tears are generally classified by the extent and depth of the fiber damage as either partial or full thickness tears. Encroachment of the humeral head beneath the acromion process can reduce the shoulder space. This space, between the top of the humeral head and the inferior surface of the acromion process is normally only five to ten millimeters deep. It enables the rotator cuff tendons and their lubricating bursa to glide unscathed beneath the acromion. A reduction in this space can cause impingement or abrasion of the rotator cuff and can cause impingement or abrasion of the rotator cuff and long head of the biceps tendons. On the average, up to 40 percent of rotator cuff tears are considered full thickness tears and the majority of them are considered asymptomatic. Scapular instability is found in two-thirds of individuals with rotator cuff problems. Poor scapular kinetics can lead to “reverse scapulohumeral rhythm” or hiking motion during humeral elevation can lead to impingement as the humeral head is driven upward into the acromion. During shoulder flexion and abduction, both upward rotation and posterior scapular tilt move the acromiom process away from the greater tubercle on the humeral head, allowing the humeral head and rotor cuff muscles and tendons. Factors leading to sub-acromial impingements and rotator cuff tears include the following:

• acute sudden trauma
• repetitive or cumulative trauma
• anatomical variants in acromion process shape
• capsuloligamentous levity
• excessive tension or tightness of posterior and inferior joint capsule
• impaired sensorimotor function
• improper exercise selection and technique.

Other causes of injury and rotator cuff dysfunction include kyphotic posture with rounded shoulders and abducted scapulae, and periscapular and rotator cuff muscle fatigue and weakness.

Injury Prevention:

Exercises to isolate and strengthen the rotator cuff muscles are important components of an injury prevention and/or rehabilitation program. Exercise, strengthening and conditioning, sensorimotor training, and postural awareness are all essential components of either a rehabilitation or injury prevention program.
The periscapular muscles are:

• seratus anterior
• pectoralis minor
• levator scapula
• rhomboids minor and major
• trapezius

These should be the initial focus of a proximal shoulder stability program. The rotator cuff muscles are generally included in conjunction with the periscapular muscles. Gentle stretching of the posterior joint capsule is indicated for tight shoulders. Excessive capsular tension has long been associated with upward migration of the humeral head during shoulder abduction, i.e. frozen shoulder or causing adhesive capsulitis. Proximal stability from periscapular balanced rotator cuff muscle strength and adequate flexibility help to maintain normal, healthy shoulder function. The intrinsic rotator cuff muscles are important and offset some of the potentially destabilizing forces created by the larger extrinsic muscles.

The rotator cuff muscles oblique line of pull elevation creates downward, inward compression forces. The rotator cuff and periscapular muscles force maintains the humeral head center of rotation. The glenoid labrum, a fibrocartilagenous ring, attaches around the rim of the glenoid fossa and increases the depth of the articular surface area. It augments the rotator cuff’s stabilizing effects. Even experimental removal of the glenoid labrum has led to a 20 percent reduction in shoulder stability in cadavers. Specific scapular motions against the thorax provide the stable, yet mobile supporting base from which the rotator cuff muscles work. The scapula must move with the humeral head in order to maintain a supportive surface. This in turn, enhances glenohumeral stability and maintains optimal height and length tension of the rotator cuff and deltoid muscles. Failure of the periscapular muscles to stabilize and guide the scapula during glenohumeral motion can lead to scapular “dyskinesia.”

Conclusion

Rotator cuff injuries to the shoulder are common, painful and debilitating. Many arm and shoulder movements especially including overhead activities are made possible by the collective actions of four small muscles in the rotator cuff group and structure of the shoulder joint. Understanding the biomechanics, anatomic structure and function of the shoulder and rotator cuff group of muscles can only assist healthcare professionals in establishing a better rationale and understanding for selecting specific technique and exercises for the patient and clients in both rehabilitation and injury prevention.


Dr. Richard J. Vahl is a former Professor and Department Chairman at the Palmer College of Chiropractic in Davenport, Iowa. He is an Adjunct Emeritus Professor on the ICA: Council of Fitness and Sports Health Science. In addition to his D.C. Degree he has a Ph.D. in health, physical education and sports science. He is a diplomat of the American Academy of Pain Management and a fellow in Applied Spinal Biomechanical Engineering. Vahl is a Certified Master of Fitness Science and Sports Science by the International Sports Science Association (ISSA). He has published and lectured both nationally and internationally and is a member of the National Association of Sport and Physical Education (NASPE) and the National Academy of Sports Medicine (NASM). He has been a team doctor for many state, national and international sporting and martial events and has been the team doctor and medical advisor for the USA Kendo Team and Team Miletich Fighting Arts.

James B. Vahl is a graduate of San Diego State University (SDSU) in pre-professional healthcare, molecular biology and Japanese, and is currently a student at Palmer College of Chiropractic. He is a Certified Physical Trainer by the American Council on Exercise (ACE) and a Health/Fitness Instructor, Certified by the American College of Sports Medicine (ACSM). James is also a member of the National Academy of Sports Medicine (NASM) and is the director of gobodyfitness.com.

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~ Personal column ~

This is a good time of year to be aware of stressful situations slipping into your life. In these hectic times, try to find the proper pace for yourself that brings balance and happiness. Give yourself enough time to enjoy some of life’s special offerings. 

In the news ...

Studies such as this are confirming the benefits of massage for many conditions. Be sure to reap the rewards of regular massage yourself! See you at our next appointment.

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Discovery consists of seeing what everybody has seen and thinking what nobody has thought.”            

—Albert von Szent-Gyorgyi