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The Proximal Biceps Tendon Anatomy and Biomechanics Geoff Wilkin, PGY-2 Upper Extremity Rounds June 24, 2011
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Anatomy
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Biceps Brachii Two-heads - Short & Long Innervation: Musculocutaneous nerve Major forearm supinator and elbow flexor Two joint muscle (shoulder & elbow)
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Origin Supraglenoid tubercle ~40-60% Glenoid Labrum ~50% Variable Fibre location/orientation 22% 33%37%8% B G L
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Intra-articular portion Glides up to 18mm Relatively avascular zone (more later)
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Rotator Interval Borders Coracoid Process Supraspinatus tendon Subscapularis tendon Transverse lig. humerus Contents LHB tendon Coracohumeral lig. Superior Glenohumeral lig.
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Biceps Reflection Pulley Entrance to bicipital groove Confluence of CHL, SGHL & Subscap. 30° turn of LHB tendon
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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
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Blood Supply Two Distinct Patterns: 2-sourceMusculotendinous (Brachial a.) Oseotendinous (Thoracoacromial a.)
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Blood Supply Two Distinct Patterns: 3-sourceMusculotendinousOseotendinousMesotenon (Ant. Humeral circumflex a.)
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Watershed Areas In both patterns: ~1.2 - 3cm from origin If mesotendon present: ~9 - 10cm from origin Common sites of rupture
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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
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Biomechanics & Function
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“The proximal biceps has been likened to the uninvited guest who never leaves the party.” “Pain generator” “Vestigial structure” “Vital structure”
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Glenohumeral Stability A secondary stabilizer Pagnani et al., 1996 55N load reduced translation in all directions
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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
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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
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Glenohumeral Stability Dynamic stabilizer throughout ROM A “Centring” effect at extremes of range Youm et al., 2009 (J Shoulder Elbow Surg)
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EMG Studies Physiologic force in LHB not known Estimates made based on cross-sectional area How active really is the LHB with shoulder motion?
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EMG Studies Levy et al, 2001 (J Shoulder Elbow Surg) Elbow locked in brace Almost zero EMG activity with shoulder motion
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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
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Conclusions Avascular area vulnerable to degeneration/rupture Static stabilizer Probably humeral head depressor Probably a dynamic “centring” force Maybe only with concomitant elbow motion
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