Normal Width Between Lunate and Pisotriquetral
The normal width of the pisotriquetral space averages 1.5 mm in the neutral wrist position, decreasing to 1 mm in extension, and increasing to 3-3.5 mm in flexion. 1
Anatomical Considerations
The pisotriquetral (PT) joint is a synovial joint formed between the pisiform and triquetrum bones in the wrist. Understanding its normal dimensions is important for diagnosing pathology in this region.
Research has established specific measurements for this joint:
- In neutral wrist position: 1.5 mm average width 1
- In wrist extension: 1 mm average width 1
- In active flexion: 3.5 mm average width 1
- In passive flexion: 3 mm average width 1
Dynamic Changes in the Pisotriquetral Joint
The PT joint space is not static but changes with wrist position. Fluoroscopic and radiographic studies have demonstrated that:
- The pisiform exhibits distal excursion (2.5 mm) during wrist extension 1
- The pisiform moves proximally during active (3 mm) and passive (2 mm) flexion 1
- The PT angle opens proximally (15°) in extension and distally with active (10°) and passive (5°) flexion 1
Clinical Significance
Understanding normal PT joint measurements is crucial when evaluating:
- Pisotriquetral arthritis
- Pisiform fractures or instability
- Distal radius fractures with associated carpal malalignment
Pisiform malalignment can be categorized as:
- Wide type: joint space ≥4.0 mm (abnormally increased) 2
- Non-parallel type: loss of parallelism of the joint surface ≥20° 2
- Overriding type: proximal or distal overriding of the PT joint ≥2.0 mm 2
Imaging Considerations
For optimal visualization of the PT joint and pisiform motion, specific radiographic views are recommended:
- Wrist neutral/30° forearm supination
- Wrist extension/30° forearm supination
- Active and passive wrist flexion/45° forearm supination with thumb abduction 1
Related Carpal Measurements
When evaluating carpal relationships, other important measurements include:
- Scapholunate dissociation: gap ≥4 mm between scaphoid and lunate bones 3
- Pisohamate distance: averages 7.5 mm in neutral, increases to 8 mm in extension, and decreases to 2 mm with active flexion and 0 mm with passive flexion 1
Understanding these normal measurements helps in diagnosing carpal instability patterns and ensuring appropriate treatment of wrist pathologies.