Subterminal key pinch dynamometry: a new method to quantify strength deficit in ulnar nerve paralysis

Area of Science:

• Orthopedics and Rehabilitation
• Neuroscience

Background:

• Accurate assessment of ulnar nerve repair recovery is crucial.
• Manual muscle testing is being superseded by dynamometry for grip strength.
• Existing grip strength tests involve multiple nerves, complicating ulnar nerve assessment.

Purpose of the Study:

• To introduce and validate a novel 'subterminal key pinch' measurement for assessing ulnar nerve function.
• To evaluate the sensitivity of the subterminal key pinch in quantifying preoperative ulnar nerve deficits.

Main Methods:

• Utilized a commercially available pinch meter to measure hand strength.
• Instructed 17 patients undergoing ulnar nerve repair to apply pressure using the thumb's interphalangeal joint.
• Maintained thumb interphalangeal joint extension to isolate ulnar nerve contribution and exclude flexor pollicis longus influence.

Main Results:

• Preoperatively, grasping strength was 46% of normal, key pinch was 58%, and pinch-to-zoom strength was 26%.
• The novel subterminal key pinch measured only 7% of normal strength.
• The subterminal key pinch demonstrated the most significant strength deficit, exceeding 90%.

Conclusions:

• The subterminal key pinch is a highly sensitive measure for detecting ulnar nerve deficits.
• This novel pinch measurement offers a more precise assessment of ulnar nerve function compared to traditional methods.
• The findings support the utility of the subterminal key pinch in evaluating recovery after ulnar nerve repair.