What is ulnar deviation?

Ulnar Deviation

Ulnar deviation is the movement of the hand toward the ulnar side (little finger side) of the forearm, representing one of the fundamental motions of the wrist joint. 1

Anatomical Definition and Mechanics

Ulnar deviation occurs at the wrist joint when the hand moves toward the ulnar side (medial side) of the forearm. This movement is one of the primary motions of the wrist, along with:

• Flexion (bending the palm toward the inner forearm)
• Extension (bending the back of the hand toward the outer forearm)
• Radial deviation (movement of the hand toward the thumb side)

The ulnar artery supplies the medial part of the anterior compartment of the forearm, wrist and hand, including the superficial structures of the central palm and most of the palmar and distal dorsal aspects of the fingers. The ulnar pulse can be palpated on the flexor surface of the wrist medially. 1

Biomechanics and Range of Motion

Ulnar deviation has several important biomechanical characteristics:

• Normal range of motion for ulnar deviation is approximately 30-45 degrees from neutral position
• During activities of daily living (ADLs), ulnar deviation can reach up to 32.5° ± 8.3° (observed during tasks like picking up a smartphone) 2
• Ulnar deviation is naturally coupled with wrist flexion - as the wrist moves into ulnar deviation, it tends to also move into flexion 3

Research shows that the majority of ADLs (54.9%) are performed in ulnar extension (combined ulnar deviation with wrist extension), with 16 out of 22 common ADLs occurring in this quadrant. 2 This demonstrates the functional importance of ulnar deviation in everyday hand activities.

Clinical Significance

Ulnar deviation has important clinical implications:

1. Radiographic Assessment: Standard radiographic examination of the wrist consists of posterior-anterior and lateral views in neutral position, often supplemented by oblique views. Radiographs are necessary for accurate measurement of ulnar variance. 1

2. Pathological Conditions:

   • Rheumatoid Arthritis: Ulnar deviation of the fingers is a common deformity that can markedly compromise hand function and aesthetics. Preoperative ulnar deviation in rheumatoid arthritis patients can average around 62 degrees. 4
   • Obstetric Brachial Plexus Palsy: Some children with this condition develop ulnarly deviated wrists, associated with impaired active and passive pronosupination and variations in ulnar variance. 5

3. Functional Wrist Kinematics: During carpal radioulnar deviation, the greatest scaphoid and lunate movement occurs in the middle of the arc—slight ulnar deviation—which the wrist frequently adopts to accomplish major hand actions. 6

4. Imaging Considerations: When evaluating ulnar-sided wrist pain, MRI is highly accurate for diagnosing lesions of the triangular fibrocartilage complex (TFCC), which can be a source of pain with ulnar deviation. 1

Clinical Evaluation

When assessing ulnar deviation clinically:

• Measure the angle between the long axis of the forearm and the third metacarpal
• Compare with the contralateral side for asymmetry
• Evaluate for pain or restriction during the movement
• Assess coupling with other wrist movements (particularly flexion)

Pitfalls and Caveats

1. Measurement Errors: Conventional wrist goniometry that evaluates range of motion in isolated directions may not accurately capture the natural coupling between ulnar deviation and flexion. 3

2. Functional Limitations: Restricted ulnar deviation can significantly impact daily activities, as most ADLs require some degree of ulnar deviation combined with extension. 2

3. Diagnostic Challenges: When evaluating ulnar-sided wrist pain, radiographs alone may be insufficient, and advanced imaging like MRI may be needed to diagnose soft tissue injuries affecting ulnar deviation. 1