The long head biceps - a shoulder stabilizer.

The Role of the Long Head of the Biceps Tendon in Posterior Shoulder Stabilization during Forward Flexion

These authors used a cadaver model to help understand role the long head of the biceps tendon (LHBT) in glenohumeral stability.

They found that loading the biceps tendon at 30 and 60 degrees of forward flexion increased glenohumeral stability when posteriorly directed loads were applied. 

Comment: The stabilizing effect of the biceps tendon is demonstrated by one of the common mechanisms for a SLAP injury in which posterior force applied to the joint avulses the origin of the long head from the glenoid.

We find it helpful to consider the analogy of a monorail in which the train is stabilized by sliding along a fixed track

The biceps "rail" is secured to the superior glenoid rim.

The humerus is secured on the rail by the biceps sheath and the transverse humeral ligament as shown in this arthroscopic view

and in this illustration from our late colleagues John Clark and Doug Harryman's classic "Tendons, ligaments, and capsule of the rotator cuff. Gross and microscopic anatomy"

The biceps sheath and the transverse humeral ligament keep the humerus riding along the rail of the biceps tendon - the stabilizing effect of which becomes greater as the shoulder is elevated, bringing the transverse humeral ligament closer to the supraglenoid tubercle.

The role of the biceps tendon in stabilizing the shoulder is not only important for understanding the SLAP tear, but also in glenohumeral arthroplasty. For this reason, we preserve the long head tendon of the biceps in performing the ream and run (see this link  or anatomic total shoulder (see this link)  unless it is severely frayed or dislocated. While some surgeons (self-declared "biceps killers") routinely sacrifice the tendon at arthroplasty, in our experience the incidence of problems with a preserved biceps post arthroplasty is very low.

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How you can support research in shoulder surgery Click on this link.

Here are some videos that are of shoulder interest

Shoulder arthritis - what you need to know (see this link)

Shoulder arthritis - x-ray appearance (see this link)

The smooth and move for irreparable cuff tears (see this link)

The total shoulder arthroplasty (see this link).

The ream and run technique is shown in this link.

The cuff tear arthropathy arthroplasty (see this link).

The reverse total shoulder arthroplasty (see this link).

The normal shoulder, aTSA, and RSA are stabilized by concavity compression

The glenohumeral joint.

>The humeral head is precisely centered on the glenoid as the hand carries out precision activities, such as painting or surgery.

>The humeral head is precisely centered in the glenoid as the arm carries out forceful activities, such as the throwing a baseball over 100 miles per hour or bench-pressing over 700 pounds.

>The glenohumeral joint allows a greater range of motion than any other articulation in the body while enabling these activities.

These remarkable features could not be achieved by a joint constrained by a deep socket as is found in the hip

or by a joint constrained by isometric ligaments as are found in the knee

How, then, is the precise centering of the glenohumeral joint accomplished? 

In the early 1990’s, the mechanism for this robust centering of the large humeral ball on the small glenoid socket was given the name “concavity compression” [1][2][3][4].  As the name implies, centering is achieved by a force pressing the humeral head into the glenoid concavity.

Note that the rotator cuff muscles act as humeral head “compressors” (not "humeral head depressors")

Even when a displacing force is applied, as long as the net vector of the forces acting on the humeral head is contained within the glenoid, the shoulder is stable

The maximal angle between the glenoid centerline and the net force vector that can be stabilized is referred to as the balance stability angle

If the net force vector does not lie within the balance stability angle, the shoulder is unstable

The balance stability angle is reduced by loss of the glenoid labrum and by glenoid rim fractures

 When the symmetry of glenoid concavity is compromised by osteoarthritis, the forces across the joint cause the arthritic humeral head to sit in the posterior concavity

The superior articulation.

While the foregoing presents the concept of concavity compression at the glenohumeral joint, the same mechanism also provides stability at the articulation between the proximal humeral convexity and the coracoacromial arch

This articulation is particularly effective in centering the humeral head when superiorly directed loads are applied, such as when pushing up out of an armchair or when leaning on crutches. The effectiveness of the coracoacromial concavity is compromised by acromioplasty and by sectioning of the coracoacromial ligament, potentially leading to anterosuperior escape and pseudoparalysis

Concavity compression and shoulder arthroplasty

Just as in the normal shoulder, the concavity of the anatomic prosthetic glenoid stabilizes the prosthetic humeral head when a compressive load is applied. Many component designs provide a small degree of glenohumeral mismatch, sacrificing a bit of the centering effect to allow some translation of the humeral component

before rim loading and deformity of the plastic glenoid occurs

Just as in the normal shoulder, as long as the net force on the humeral head is contained within the balance stability angle, the articulation is stable. This explains how an anatomic shoulder arthroplasty can be stable, even if the glenoid component is placed in retroversion

 If the glenoid is worn, the effectiveness of its concavity is compromised

In the case of the reverse total shoulder, the humeral concavity is stabilized on the glenosphere by concavity compression. As long as the force across the joint lies within the humeral cup, the joint remains stable.

 If, however, the net force lies outside the humeral cup concavity, the joint dislocates

Loss of the concavity of the humeral cup can contribute to instability of the reverse total shoulder

In conclusion, the glenohumeral joint will remain centered as long as there is a concavity that captures the net force across the joint.

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[1] "Mechanics of glenohumeral instability." Clin Sports Med 10(4): 783-788, 1991

[2] "Mechanisms of glenohumeral joint stability." Clin Orthop Relat Res(291): 20-28, 1993

[3] "Glenohumeral stability from concavity-compression: A quantitative analysis." J Shoulder Elbow Surg 2(1): 27-35, 1993

[4] Practical Evaluation and Management of the Shoulder. Saunders, Philadelphia. 1994. Now in the public domain. Click here for a copy.

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To see a YouTube video on how the ream and run is done, click on this link.

To see a YouTube of our technique for total shoulder arthroplasty, click on this link.
To see a YouTube of our technique for a reverse total shoulder arthroplasty, click on this link.
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How you can support research in shoulder surgery Click on this link.

We have a new set of shoulder youtubes about the shoulder, check them out at this link.

Be sure to visit "Ream and Run - the state of the art" regarding this radically conservative approach to shoulder arthritis at this link and this link

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages  arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

How the shoulder works, videos by the late Doug Harryman

Our late fellow, Doug Harryman, produced many wonderfully educational videos.
In recognition of him and his many critical contributions to our understanding of the shoulder, we present a two part video that he produced and narrated on the mechanics of the shoulder.
Part I
Part II
Sit back watch, learn, and remember him.

More about Doug Harryman can be found at this link and at this link.

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Healing through joint replacement

Supporting progress in shoulder surgery

Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book

Click here to see the new Rotator Cuff Book

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

See the countries from which our readers come on this post.

Use the "Search" box to the right to find other topics of interest to you.