What is the difference between the flat surface and point surface of the triangle (neurological) tendon hammer?

Differences Between the Flat Surface and Point Surface of the Triangle Tendon Hammer

The flat surface of the triangle tendon hammer is designed for eliciting deep tendon reflexes over broader areas like the patellar tendon, while the pointed tip is used for more precise stimulation of smaller tendons and for testing superficial reflexes.

Functional Differences

Flat Surface

• Primary use: Testing larger tendons and broader areas
• Common applications:
  • Patellar tendon reflex (knee jerk)
  • Achilles tendon reflex (ankle jerk)
  • Quadriceps reflex
• Mechanism: Distributes the force over a wider area, creating more uniform stimulation
• Advantage: Provides more consistent stimulation for larger tendons where precision is less critical

Pointed Tip

• Primary use: Testing smaller tendons and specific points
• Common applications:
  • Biceps and triceps reflexes
  • Brachioradialis reflex
  • Superficial abdominal reflexes
  • Plantar reflexes (Babinski sign)
• Mechanism: Concentrates force on a smaller area for more precise stimulation
• Advantage: Allows targeting of specific motor points where accuracy is essential

Technical Considerations

Force Distribution

• The flat surface distributes the tapping force over a larger area (approximately 1-2 cm²), which is ideal for the patellar tendon where a broader stimulus is needed 1
• The pointed tip concentrates the force on a smaller area (approximately 0.25-0.5 cm²), allowing for more precise targeting of smaller tendons 2

Clinical Applications

• When testing reflexes like the patellar tendon reflex, the flat surface provides more consistent results with less variability in the stimulus-response relationship 3
• For reflexes requiring precise localization of motor points, such as the triceps reflex (which was absent in 27% of limbs in one study), the pointed tip offers better accuracy 3

Measurement Considerations

• Studies using instrumented reflex hammers show that the choice between flat and pointed surfaces affects the stimulus-response relationship in tendon reflexes 4
• The flat surface typically produces more consistent reflex responses with less variability between trials 1

Clinical Pearls

• When using the flat surface for the patellar tendon reflex, position it perpendicular to the tendon for optimal force transmission
• When using the pointed tip for smaller tendons, locate the motor points first for maximum effectiveness 5
• The pointed tip is particularly useful when testing reflexes in patients with excessive subcutaneous tissue or muscle mass where more focused pressure is needed
• For quantitative assessment of reflexes, the flat surface provides more reproducible results across multiple trials 1

Common Pitfalls

• Using the pointed tip on larger tendons may result in inconsistent or diminished reflexes due to insufficient area of stimulation
• Using the flat surface on smaller tendons may fail to provide adequate focal stimulation to elicit the reflex
• Improper technique with either surface can lead to false negative results, particularly with the triceps reflex which is technically more difficult to elicit 3

The choice between the flat surface and pointed tip should be based on the specific reflex being tested and the anatomical characteristics of the patient. Proper technique with the appropriate surface is essential for accurate neurological assessment.