1. The Proximal Biceps Tendon Anatomy and Biomechanics Geoff Wilkin, PGY-2 Upper Extremity Rounds June 24, 2011

2. Anatomy

3. Biceps Brachii Two-heads - Short & Long Innervation: Musculocutaneous nerve Major forearm supinator and elbow flexor Two joint muscle (shoulder & elbow)

4. Origin Supraglenoid tubercle ~40-60% Glenoid Labrum ~50% Variable Fibre location/orientation 22% 33%37%8% B G L

5. Intra-articular portion Glides up to 18mm Relatively avascular zone (more later)

6. Rotator Interval Borders Coracoid Process Supraspinatus tendon Subscapularis tendon Transverse lig. humerus Contents LHB tendon Coracohumeral lig. Superior Glenohumeral lig.

7. Biceps Reflection Pulley Entrance to bicipital groove Confluence of CHL, SGHL & Subscap. 30° turn of LHB tendon

9. Bicipital Groove Opening angle ~101-120° Large variability (18-172°) Very acute and very flat angles assoc. with biceps pathology Transverse humeral ligament Anchors tendon in groove

10. Blood Supply Two Distinct Patterns: 2-sourceMusculotendinous (Brachial a.) Oseotendinous (Thoracoacromial a.)

11. Blood Supply Two Distinct Patterns: 3-sourceMusculotendinousOseotendinousMesotenon (Ant. Humeral circumflex a.)

12. Watershed Areas In both patterns: ~1.2 - 3cm from origin If mesotendon present: ~9 - 10cm from origin Common sites of rupture

13. Histology Distal: “Traction” tendon - parallel collagen, tenocytes Proximal: Capsular surface - “Traction” tendon Humeral surface - “Gliding” tendon Irregular/interwoven collagen, Tenocytes more similar to chondrocytes Avascular

14. Biomechanics & Function

15. “The proximal biceps has been likened to the uninvited guest who never leaves the party.” “Pain generator” “Vestigial structure” “Vital structure”

16. Glenohumeral Stability A secondary stabilizer Pagnani et al., 1996 55N load reduced translation in all directions

17. Glenohumeral Stability A secondary stabilizer in cuff pathology Su et al., (Arthroscopy, 2010) Simulated cuff tears 55N LHB force decreased superior & anterosuperior translation May be cause of biceps hypertrophy & “hour-glass” finding

18. Glenohumeral Stability Stabilizer during elbow motion Kumar et al. (CORR 1989) Simulated elbow flexion & supination Upward migration of humeral head with LHB cut, none when intact

19. Glenohumeral Stability Dynamic stabilizer throughout ROM A “Centring” effect at extremes of range Youm et al., 2009 (J Shoulder Elbow Surg)

20. EMG Studies Physiologic force in LHB not known Estimates made based on cross-sectional area How active really is the LHB with shoulder motion?

21. EMG Studies Levy et al, 2001 (J Shoulder Elbow Surg) Elbow locked in brace Almost zero EMG activity with shoulder motion

22. In vivo Studies Warner & McMahon, (JBJS-Am 1995) Superior migration of humeral head on Xray in proximal biceps rupture Kido et al., Humeral head depression on Xray when biceps contracted assoc. with rotator cuff tear

23. Conclusions Avascular area vulnerable to degeneration/rupture Static stabilizer Probably humeral head depressor Probably a dynamic “centring” force Maybe only with concomitant elbow motion