Distal Biceps Tendon Ruptures: The Hook Test and Endobutton Rehab Protocols
In short
A ruptured distal biceps snaps under unexpected eccentric loads; the Hook test provides 100% diagnostic sensitivity, guiding immediate surgical anatomical re-anchoring.
In this guide (4 sections)
The Mechanism of Distal Biceps Rupture
The biceps brachii has two proximal heads in the shoulder but converges distally into a single, stout tendon that inserts onto the radial tuberosity of the radius. Because of its insertion on the radius, the biceps is not merely an elbow flexor; it is the premier, most powerful supinator of the human forearm.
Rupture of the distal biceps tendon almost universally occurs when an unexpected, heavy eccentric load is applied to a flexed elbow (for example, catching a falling heavy box, deadlifting with an alternated underhand grip, or wrestling). The eccentric deceleration force overpowers the tendon fibers, snapping the tendon clean off the radial tuberosity with an audible pop.
Diagnostic Clinical Testing: The Hook Test and Biceps Squeeze
| Diagnostic Test | Testing Procedure | Positive Finding | Diagnostic Sensitivity & Specificity | |
|---|---|---|---|---|
| O'Driscoll Hook Test | Patient flexes elbow 90° with forearm fully supinated; examiner attempts to hook index finger under lateral cord-like tendon | Absence of cord-like tendon; examiner's finger sweeps through empty antecubital space | 100% sensitivity, 100% specificity; gold standard physical exam test | |
| Biceps Squeeze Test | Patient rests elbow 60° on table with forearm pronated; examiner firmly squeezes biceps muscle belly | Absence of involuntary forearm supination | Confirms loss of anatomical continuity between muscle belly and radial tuberosity | |
| Supination Strength Deficit | Resisted forearm supination tested with dynamometer or manual resistance | Severe weakness (40% to 60% loss of supination strength) | Supination strength is significantly more impaired than flexion strength |
Rehabilitation Following Cortical Endobutton Repair
- Hinged Elbow Brace with Extension Stop (Weeks 1 to 6): Lock brace initially at 90 degrees; expand extension by 10 degrees each week so full 0-degree extension is achieved at week 6, preventing contracture while protecting the intramedullary cortical button.
- Strict Resisted Supination Ban (Weeks 0 to 8): Passive supination and active flexion are permitted early, but active resisted supination (such as turning a screwdriver or opening door knobs) is strictly forbidden for 8 weeks.
- Return to Heavy Pulling and Lifting (Months 4 to 6): Begin progressive pulling exercises (cable rows, lat pulldowns) at month 4; full uninhibited heavy deadlifting and manual labor is cleared at month 6.
Frequently Asked Questions
What is the Hook test for a torn biceps tendon?
The Hook test is where a clinician attempts to hook their index finger underneath the thick biceps tendon in the crease of your elbow. If the tendon has snapped and retracted up into your arm, there is nothing to hook and the finger sweeps through empty space.
Can I live normally without surgery if my distal biceps tears?
If you do not have surgery, your arm will still bend using other muscles, but you will permanently lose 40% to 50% of your forearm twisting strength (supination). Turning screwdrivers, opening jars, or lifting heavy objects will be permanently compromised.
Why do bodybuilders tear their biceps when doing deadlifts?
When using an alternated grip (one palm facing forward and one facing backward), the arm with the palm facing forward places the distal biceps tendon under immense direct tensile strain. If the lifter jerks the bar, the tendon snaps off the bone.
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