Biceps Crease Interval
The Biceps Crease Interval (BCI) is a reliable clinical measurement tool used by orthopedic specialists to assess and diagnose distal biceps tendon ruptures.
When a distal biceps tendon ruptures, the muscle belly retracts proximally toward the shoulder. The BCI quantifies this physical displacement by measuring the distance between the main elbow crease and the distal edge of the biceps muscle belly.
What is the Biceps Crease Interval Used For?
The primary clinical purpose of the Biceps Crease Interval is to identify full-thickness distal biceps tendon tears. It provides an objective, measurable distance that complements traditional manual physical examination tests—such as the Hook Test or Biceps Squeeze Test—helping clinicians confirm tendon retraction without relying solely on immediate imaging like MRI.
How to Perform the Biceps Crease Interval Measurement
Follow these clinical steps to measure the BCI accurately:
- Patient Position: Have the patient sit comfortably facing the examiner.
- Arm Placement: Begin with the patient’s unaffected arm relaxed in flexion, then gently and fully extend the elbow.
- Mark the Crease: Draw a straight transverse line directly across the main flexion crease of the antecubital fossa.
- Locate the Biceps Apex: Lightly stroke the distal biceps contour back and forth along its central longitudinal axis. Identify the exact point where the muscle begins to turn most sharply toward the antecubital fossa (the distal cusp of the biceps muscle belly).
- Mark the Biceps Line: Draw a second transverse line across this distal cusp.
- Measure the Distance: Use a flexible measuring tape to measure the distance in centimeters between the antecubital crease line and the biceps cusp line.
- Bilateral Comparison: Repeat the exact measurement on the affected arm and calculate the difference between sides.
Diagnostic Criteria & Positive Results
Understanding normative values versus diagnostic thresholds is essential when interpreting BCI results:
| Measurement Metric | Normal Range | Diagnostic Threshold (Positive Result) |
| Biceps Crease Interval (Absolute) | 4.8 cm ± 0.6 cm (Dominant & Non-Dominant) | > 6.0 cm |
| Biceps Crease Ratio (Side-to-Side) | ~1.0 (Symmetrical) | > 1.2 (Affected vs. Unaffected Side) |
Interpreting the Findings
- Positive for Rupture: A BCI greater than 6.0 cm or a side-to-side BCI ratio greater than 1.2 indicates significant proximal muscle retraction, strongly confirming a distal biceps tendon rupture.
- Negative/Normal: A distance within the normal range of 4.8 cm ± 0.6 cm (or equal to the contralateral side) suggests an intact tendon, though partial tears should still be evaluated if clinical suspicion remains high.