Sports Medicine Research: In the Lab & In the Field: What is the Role of the Long Head of the Bicep Tendon? Part II (Sports Med Res)
Thursday, October 13, 2011

What is the Role of the Long Head of the Bicep Tendon? Part II

The Long Head of the Biceps Tendon Has Minimal Effect on In Vivo Glenohumeral Kinematics: A Biplane Fluoroscopy Study

Giphart JE, Elser F, Dewing CB, Torry MR, Millett PJ. Am J Sports Med. 2011 Sep 30. [Epub ahead of print]
http://www.ncbi.nlm.nih.gov/pubmed/21965188


The role of the long head of the biceps tendon at the shoulder is not clearly understood. Some feel that it serves as a humeral head depressor, similar to the supraspinatus. Others feel that the effect of the biceps on shoulder stability is limited. Recently, there was a SMR post examining the role of the biceps in the presence of rotator cuff tears. However that study used cadavers to determine the amount of humeral head translation in response to simulated muscle forces. Therefore, in vivo testing is required to determine the true role of the biceps tendon on shoulder stability. Giphart et al. examined glenohumeral arthrokinematics (e.g., translation, gliding) with biplanar fluoroscopy in 5 patients that had a unilateral biceps tenodesis. Assessments were performed bilaterally during glenohumeral abduction, the late cocking phase of a throw, and a simulated lifting motion (similar to a Speeds Test). Glenohumeral arthrokinematics were determined every 10° for shoulder abduction and the simulated lift. The late cocking position was divided into three phases (90°/90° phase, max external rotation, and final internal rotation) which represented the positions of the throwing motion. Muscle activity of the biceps was also recorded during each task. The uninjured contralateral control shoulder was used as an internal control. They found that the tenodesed shoulder had significantly greater anterior translation during abduction and the final internal rotation phase of the late cocking position compared to the control arm. However, these translations positioned the humeral head in a more centered position on the glenoid and the increases in translation between shoulders were less than 1.0mm.

This study is a very interesting in vivo that suggests the biceps tendon has minimal effects on the arthrokinematics of the shoulder. In vivo testing allows the effects of actual muscle activity and forces to be examined instead of being simulated. Simulated muscle forces in cadaver studies are limited to a small number of muscles at the shoulder which don’t accurately predict the in vivo setting. The results of the current study suggest that after an isolated tenodesis of the biceps tendon only small translations occur at the shoulder. This information suggests that the biceps has minimal effects on shoulder stability. However, biceps tenodesis are commonly performed in conjunction with rotator cuff repairs. It is thought that the biceps compensates for the torn rotator cuff and therefore develops degenerative changes. This study did not examine the effect of a biceps tenodesis in rotator cuff tear patients. Therefore, it may suggest that the biceps has minor effects on shoulder stability in a healthy shoulder, however when a rotator cuff tendon is torn the biceps may become a major dynamic restraint. It would be interesting if this group continues there studies to determine the effect of the biceps among patients with rotator cuff tears. This information will help surgeons determine if performing a biceps tenodesis is problematic to the rest of the shoulder joint due to increased joint translations. Furthermore, clinicians can also develop preventive strategies to minimize biceps tendon degeneration in patients with rotator cuff tears by identifying positions and motions that may dramatically increase strain on the biceps. Do you think the role of the biceps changes in the presence of rotator cuff tears? Do you think it’s possible to prevent biceps degeneration in the presence of rotator cuff tears? Do you think a rotator cuff repair will return proper joint kinematics?

Written by: Stephen Thomas
Reviewed by: Jeffrey Driban

5 comments:

MEShiresATC said...

"and the final internal rotation phase of the late cocking position"

I may have misread this but the late phase of cocking is maximal external rotation.

Stephen J. Thomas, PhD, ATC said...

You are correct. However for this study the researchers divided the late cocking position into three phases (90°/90° phase, max external rotation, and final internal rotation) which represented the positions of the throwing motion. Thanks for the comment.

MEShiresATC said...

I plead ignorance on the article since I cannot access the full text.

Maybe it is semantics, and sometimes I get caught up in them...

Internal rotation starts the throwing phase it should have nothing to do with cocking.

Are they trying to say follow through?

Brandon Davis, ATC said...

This was an interesting study in that I do not hear much about isolated biceps tenodesis. Studies that include biceps tenodesis usually have concomitant rotator cuff disease. I feel like this study could have been enhanced in many ways. First the number of subjects is low (n=5) making it difficult to generalize the results. It would be interesting to know the muscle activity of the rotator cuff muscles along with biceps muscle during each task. Comparing those results with the contralateral side would explain more of the biceps involvement in glenohumeral arthrokinematics. With less than a 1.0mm difference between involved and uninvolved biceps tenodesis, it appears the long head of the biceps tendon serves little purpose in shoulder stability. However, due to the biceps tendon orientation within the shoulder, not until dynamic stability is lost from rotator cuff pathology do we see the full function of the long head biceps tendon. I do believe that as rotator cuff integrity decreases, the biceps will be the next structure to deteriorate due to increased demands. Eccentric training for the biceps in the presence of rotator cuff tears can possibly aid at attenuating greater force and torque at the shoulder.

Stephen J. Thomas, PhD, ATC said...

Brandon thanks for commenting. Yes, you are correct the sample size was low and makes it difficult examining the results. There may be differences with a larger sample size. Yes, muscle activity may help explain the pathomechanics of the injury. When examining both part I and this post it seems that you are correct. The biceps has a very small role in shoulder stability without rotator cuff injury but when the rotator cuff is injured the biceps tendon compensates and attempts to maintain shoulder stability. I am curious if eccentric training would be the optimal treatment to both prevent biceps injury in rotator cuff tear patients and also to help treat patients with current biceps symptoms. Again thanks for commenting.

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