Is the biceps long head a pain generator? How would we know? Are we keepers or killers?

The long head tendon  of the biceps (LHTB) is a component of normal shoulder structure and function. There are billions of people walking the earth with intact biceps tendons who are not in pain, so it cannot be called a "pain generator". 

In the normal shoulder the (LHTB) provides a secure anchor for half of the biceps and stability for the shoulder - both through its contribution to concavity compression and also by the "monorail" mechanism in which the transverse humeral ligament and intertuberular groove glide along the biceps monorail providing increasing stability against anterior and posterior translation as the humerus is elevated as shown in this nice diagram by Steve Lippitt.

While Speed-s and Yergason's tests are often used to detect pathology of the LHTB, we have found that the saw test is more sensitive and specific. In this test the elbow is held at 90 degrees of flexion holding a weight as shown in the video below.

Out of respect for the stabilizing function of the long head tendon of the biceps we are biceps keepers rather than biceps killers when we perform shoulder arthroplasty.  We will only sacrifice the biceps if it is seriously frayed or unstable in the groove.

In 50 years of doing shoulder arthroplasty, we've never had to take a patient back to the OR for postoperative biceps issues. There is one patient who had biceps symptoms when she played golf and a positive saw test. Her symptoms responded to a single injection of her biceps sheath.

We always appreciate feedback and commentary on the blog. Jed Kuhn, immediate past president of the American Shoulder and Elbow Surgeons and consummate educator, after reading the post gave us a 'biceps reading list', which is included here:

Throwing, the Shoulder, and Human Evolution

Adaptive pathology: new insights into the physical examination and imaging of the thrower’s shoulder and elbow

Evidence of sympathetic innervation and a1-adrenergic receptors of the long head of the biceps brachii tendon

Sympathetic and Sensory Neural Elements in the Tendon of the Long Head of the Biceps

You can support cutting edge shoulder research that is leading to better care for patients with shoulder problems, click on this link

Follow on twitter/X: https://x.com/RickMatsen
Follow on facebook: https://www.facebook.com/shoulder.arthritis
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/

Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link). 

Shoulder instability

Glenohumeral instability is one of the most common disabling conditions of the shoulder. Yet given the great flexibility of the joint and the small, shallow socket provided by the glenoid

it is a wonder that the shoulder remains as stable as it does with everything we ask it to do

In order to understand, evaluate and manage shoulder instability, one needs to understand how the joint is normally stabilized. Our late fellow, Doug Harryman, did a great job explaining shoulder stability in these two videos: Shoulder Mechanics 1 and Shoulder Mechanics 2.  

The principles of shoulder stability are detailed in Chapter 3 of the freely available Practical Evaluation and Management of the Shoulder (see this link.). 

While the knee is stabilized by ligaments that remain isometric through its range of flexion and extension, the shoulder has no isometric structures that limit its range of motion. The surrounding soft tissues remain lax in most functional positions of the shoulder, except those performed at the extremes of shoulder motion (such as in the baseball pitch shown above).

 (N.B.: laxity is not the same thing as instability (see Laxity of the normal glenohumeral ioint: A quantitative in vivo assessment)

While the hip is stabilized by a deep acetabular socket (which limits hip range of motion when its rim is contacted by the femur), the shoulder's socket is shallow, allowing it a great range of impingement-free motion.

The essential mechanism stabilizing the shoulder is concavity compression, a mechanism that functions throughout the range of shoulder motion. Just as the compressive effect of gravity stabilizes the golf ball in the small, shallow concavity of the tee

the glenohumeral joint is stabilized when the net force on the humeral head compresses it into the small, shallow glenoid concavity of the glenoid

As long as the net force acting on the humeral head passes within the glenoid concavity, the joint is stable. The glenoid arc provides a range of positions in which this condition can be met.

The glenoid bone, cartilage and labrum each contribute to the concavity.

The concavity is less in the anteroposterior direction than in the superiorinferior direction.

As a result, the joint's stability from front to back is less than its stability from top to bottom.

If the concavity is compromised, the range of stable positions is reduced.

As pointed out in A Prospective Analysis of Patients With Anterior Versus Posterior Shoulder Instability, while anterior instability is often traumatic, posterior instability more commonly arises from repeated overloading and wear of the posterior supporting structures from pushing and lifting activities that differentially load the back of the joint. 

Recurrent posterior instability may be accompanied by progressive loss of the supportive posterior glenoid cartilage and bone (see Prospective Evaluation of Posterior Glenoid Bone Loss After First-time and Recurrent Posterior Glenohumeral Instability Events).

 

Stability is also compromised if the net force is not directed within the glenoid concavity.

Fortunately, the scapula can usually be positioned so that the concavity is aligned with the compressive force.

For example, if the hand pushes forward while the scapula is retracted, the force on the humerus is not aligned with the glenoid socket and stability is threatened.

However, if the hand pushes forward while the scapula is protracted, the force on the humerus is closely aligned with the glenoid socket, so stability is optimized.

Functional instability has been defined as instability from pathological muscle activation patterns resulting in malalignment of the net humeral force with the glenoid (see Characteristics of functional shoulder instability). 

Often functional instability can be managed by patient education and physical training to strengthen the cuff muscles that provide compression of the humeral head into the glenoid concavity while avoiding positions that risk force malalignment (such as press ups without scapular protraction as shown earlier).  In refractory cases, muscular retraining may be enhanced by using electrical stimulation (see Shoulder-Pacemaker Treatment Concept for Posterior Positional Functional Shoulder Instability: A Prospective Clinical Trial).

The specifics of surgical treatment for glenohumeral instability are beyond the scope of this post. However, understanding the concavity compression mechanism of shoulder stability can help guide practice: 

(1) when instability results from deficiencies in the labrum, cartilaginous lip, or glenoid bone, consider restoring the glenoid concavity through Bankart repair or bony procedures

(2) when instability results from malalignment of the net humeral force with the glenoid, consider restoring the constraints to excessive motion, using capsular repair/shift, rotator interval plication and/or remplissage.  

You can support cutting edge shoulder research that is leading to better care for patients with shoulder problems, click on this link.

Follow on twitter: https://twitter.com/shoulderarth
Follow on facebook: click on this link
Follow on facebook: https://www.facebook.com/frederick.matsen
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/

Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).

How does the glenohumeral joint maintain stability while allowing such a great range of motion?

As pointed out three decades ago in Mechanics of Shoulder Stability, the function of the glenohumeral joint depends on some unique stabilizing mechanisms (illustrations below are by Steve Lippitt in Practical Evaluation and Management of the Shoulder).

While the hip is stabilized by a deep socket, the glenohumeral joint has a shallow socket that allows a wide range of motion without the ball abutting against the rim of the socket.

While the knee is stabilized by isometric ligaments, the glenohumeral joint's ligaments and capsule are lax in its functionally important mid range positions

As pointed out in In vivo quantification of the laxity of normal and unstable glenohumeral joints laxity is not the same as instability; healthy subjects without symptoms may have as much laxity as patients needing surgical repair for symptomatic shoulder instability.

We must, therefore, ask how can the relatively large humeral head be stabilized in the small glenoid socket while still allowing a greater range of motion than any other joint and amazing feats of strength as shown in these classic videos by our late partner Douglas Harryman (see Shoulder Stability 1 and Shoulder Stability 2)

One of the special mechanisms of glenohumeral stability is concavity compression as first described in Mechanisms of Glenohumeral Stability. In concavity compression, the direction of the sum of the forces applied to the humeral head is contained within the glenoid socket.

Concavity compression is enhanced by increasing the force compressing the head into the glenoid and by the deepening of the glenoid concavity by the concave cartilage and the labrum.

One of the other contributions of the glenoid labrum is the creation of the glenohumeral suction cup effect.

The compliant labrum allows the socket to seal to the humeral head much as the compliant edges of a suction cup allow it adhere to a man's forehead

See Doug Harryman's video on suction cup effect; while the quality of the video is not great, the message is clear.


The suction cup is not only important in the normal shoulder: in performing a ream and run procedure for arthritis, stability is enhanced by preserving the glenoid labrum. When a healthy labrum can be preserved, the stabilizing effect of the suction cup can be observed at the time of surgery. Turn your volume up, so you can hear the 'kiss' sound as the suction is broken by applying a strong posteriorly directed force on the humerus.

Recently, our colleagues at the University of Utah and Japan revisited A stabilizing role of the glenoid labrum: the suction cup effect

Using a cadaver model, they sought to quantify the effect of the anteroinferior and posterosuperior labrum to glenohumeral stability.

They measured the peak force required to translate the humeral head in the anterior, anteroinferior, posterior, and posteroinferior directions was measured under 5 conditions:
intact labrum,
an anteroinferior labral tear,
a posterosuperior labral tear,
combined labral tear, and
no labrum.


The stability ratio was defined as the peak translational force divided by the compressive force. Within force-translation curves, they defined the suction cup effect as the force required to release the negative pressure created by an intact labrum.

They found that the suction cup effect was usually present with the intact labrum and disappeared after removal of the labrum for anterior and posterior translations. After creation of an anteroinferior labral tear, the stability ratio for posterior direction decreased and the suction cup effect disappeared. After creation of a posterosuperior labral tear, stability ratios in the anterior and anteroinferior directions decreased and the suction cup effect disappeared. The stability ratio for anterior and anteroinferior testing was more diminished by posterosuperior labral tears than anteroinferior labral tears, and the stability ratio for posterior testing was more diminished by anteroinferior labral tears than posterosuperior labral tears.

They concluded that anteroinferior labral tears decreased posterior stability and posterosuperior labral tears decreased anterior and anteroinferior stability, largely because of loss of the suction cup effect.

Comment: In order to achieve its amazing mobility and stability, the shoulder requires some specialized stabilizing mechanisms - such as concavity compression and the suction cup effect - that are not as important in other articulations. Understanding these special mechanisms provides insight into the functioning of the normal shoulder and the management of shoulder instability.

You can support cutting edge shoulder research that is leading to better care for patients with shoulder problems, click on this link.

Follow on twitter: https://twitter.com/shoulderarth
Follow on facebook: click on this link
Follow on facebook: https://www.facebook.com/frederick.matsen
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/

Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).