Checking for the tenodesis effect involves a simple passive maneuver of the wrist to observe the reciprocal motion of the fingers, which is crucial for assessing the integrity of the flexor and extensor tendons in the hand.
Understanding the Tenodesis Effect
The tenodesis effect, also known as tenodesis action, is a natural biomechanical phenomenon in the hand where passive wrist movement causes a reciprocal movement in the fingers. This effect is a result of the length-tension relationship of the extrinsic finger tendons as they cross both the wrist and finger joints. It's a fundamental principle used in hand rehabilitation and for assessing tendon function.
Purpose of Checking Tenodesis
Evaluating the tenodesis effect is a quick and effective way to:
- Assess Tendon Continuity: It helps determine if the extrinsic flexor and extensor tendons are intact.
- Screen for Injuries: Useful in screening for potential tendon lacerations or ruptures, particularly in the forearm or wrist.
- Evaluate Surgical Outcomes: After tendon repair or transfer, it helps confirm the restoration of function.
- Guide Rehabilitation: Understanding the presence or absence of this effect can guide therapeutic interventions.
How to Perform the Tenodesis Test
To properly check for the tenodesis effect, the subject's hand must be relaxed, ensuring no active muscle contraction interferes with the passive movement.
Here are the step-by-step instructions for the assessment:
- Positioning: Ask the subject to maintain complete laxity (relaxation) in their hand. The examiner will passively move the wrist.
- Wrist Flexion:
- Gently and passively bend the subject's wrist forward (into flexion).
- Expected Result: With normal tendon integrity, all digits (fingers) should passively extend.
- Wrist Extension:
- Gently and passively bend the subject's wrist backward (into extension).
- Expected Result: With normal tendon integrity, all digits (fingers) should passively flex.
Summary of Tenodesis Test Movements:
| Wrist Movement | Expected Finger Response |
|---|---|
| Passive Flexion | Passive Extension |
| Passive Extension | Passive Flexion |
Interpreting the Results
- Normal Tenodesis: The digits respond as described above (extension with wrist flexion, flexion with wrist extension). This indicates that the extrinsic tendons are likely intact and functioning properly.
- Abnormal or Absent Tenodesis:
- If digits do not extend with passive wrist flexion, it may suggest a problem with the flexor tendons (e.g., laceration, adhesion).
- If digits do not flex with passive wrist extension, it may suggest a problem with the extensor tendons (e.g., laceration, adhesion).
Further Assessment and Localization
While the tenodesis test is an excellent screening tool, a comprehensive evaluation often involves further steps:
- Active Motion Testing: If an abnormality is noted during the tenodesis test, assessing the active range of motion at each individual joint of the affected finger can help to localize the specific tendon or tendons involved. For instance, testing active flexion and extension at the metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints can pinpoint the affected area more precisely.
- Sensory and Vascular Checks: In cases of suspected injury, it's also crucial to assess sensation and blood supply to the digits.
Understanding and correctly performing the tenodesis test provides valuable insight into the functional integrity of the hand's extrinsic tendons, guiding further diagnostic and therapeutic decisions. For more detailed information on hand assessment, consult reliable medical resources.
