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]
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