SL Ligament Flashcards
What are the three anatomically distinct components of the scapholunate interosseous ligament?
The SLIL consists of
* dorsal,
* proximal (membranous), and
* volar (palmar) portions.
These form a C-shaped or horseshoe-shaped structure connecting the scaphoid and lunate bones, with each portion having unique biomechanical properties.
What are the yield strengths of all three components of the scapholunate interosseous ligament?
- Dorsal portion: approximately 260-300 N;
- Volar (palmar) portion: approximately 118 N;
- Proximal (membranous) portion: approximately 20-65 N.
This biomechanical hierarchy directly influences their relative contributions to carpal stability.
Which component of the scapholunate interosseous ligament plays the most critical role in maintaining carpal stability and why?
The dorsal component is most critical due to its superior strength (260-300 N yield strength), greater thickness (approximately 3 mm), and crucial role in preventing both translational and rotational instability. The volar and proximal components play secondary stabilizing roles.
What is considered the normal scapholunate interval on plain radiographs and what measurement suggests dissociation?
Normal interval is typically less than 2 mm. A gap greater than 3 mm is generally considered diagnostic of scapholunate dissociation (Terry Thomas sign), though early or partial tears may not manifest radiographically.
Why might a scapholunate gap less than 2 mm on acute plain radiographs fail to exclude an SLIL rupture?
Normal measurements cannot exclude SLIL injury because:
1) secondary stabilizers may temporarily maintain alignment in acute injuries,
2) pre-dynamic and dynamic instability patterns may only reveal abnormalities on stress views, and
3) partial tears may not immediately manifest as widened gaps.
What is the gold standard diagnostic method for scapholunate interosseous ligament injuries?
Wrist arthroscopy is the gold standard as it allows direct visualization and probing of the ligament.
MRI arthrography offers higher sensitivity than plain radiographs but remains secondary to arthroscopic assessment for definitive diagnosis.
Which nerve provides innervation to the scapholunate interosseous ligament and what is its functional role?
The posterior interosseous nerve (PIN) provides proprioceptive and nociceptive innervation to the SLIL, particularly its dorsal component, contributing to wrist proprioception and dynamic stability.
What is the clinical significance of the relationship between dorsal wrist ganglions and the posterior interosseous nerve?
Dorsal wrist ganglions, which typically arise from the scapholunate ligament, may cause pain through compression of posterior interosseous nerve terminal branches. This neuroanatomical relationship explains the characteristic aching wrist pain associated with these ganglions.
What classifications or staging systems are commonly used for scapholunate ligament injuries?
The Geissler arthroscopic classification and the Garcia-Elias/Andersson classification are commonly used.
Geissler focuses on arthroscopic findings (grades I-IV), while
Garcia-Elias/Andersson addresses clinical forms based on injury progression and carpal instability patterns.
How do pre-dynamic, dynamic, and static scapholunate instability patterns differ radiographically?
Pre-dynamic instability shows normal static radiographs but symptomatic laxity on examination; dynamic instability demonstrates normal static views but abnormal stress radiographs (clenched fist); static instability reveals abnormal alignment on standard radiographs with widened scapholunate gap (>3mm) and/or scapholunate angle abnormalities.
What are the typical dimensions of the dorsal component of the scapholunate interosseous ligament?
The dorsal component is approximately 2-3 mm in thickness and 2-5 mm in length. These dimensions contribute to its superior mechanical properties compared to the thinner volar and proximal components.
How does the innervation of the SLIL by the posterior interosseous nerve influence surgical approaches to the wrist?
The nerve’s role in proprioception suggests preserving it during surgery to maintain wrist stability and function. Terminal branches of the PIN provide proprioceptive feedback, and injury during surgery may result in a painful neuroma, a consideration rooted in research on SLIL innervation and surgical outcomes.
What is the pathomechanical significance of isolated injuries to different components of the scapholunate interosseous ligament?
Isolated dorsal component injuries typically result in more significant instability patterns than injuries to volar or proximal components due to the dorsal portion’s primary role in carpal stability. Progressive injury patterns often begin with the proximal component before affecting the volar and finally the critical dorsal component.
During surgical reconstruction of the scapholunate interosseous ligament, which component is typically prioritized and why?
The dorsal component is prioritized during reconstruction because it provides the primary stabilizing function. Restoration of this component is essential for reestablishing both translational and rotational stability of the scapholunate joint.
In a patient with a suspected SLIL injury but a normal scapholunate gap on plain radiographs, what diagnostic steps should be pursued?
Dynamic stress views, MRI arthrography, or arthroscopy should be considered to detect partial tears or dynamic instability, as research shows these may not appear on initial static imaging. Stress maneuvers like the Watson scaphoid shift test can help identify pre-dynamic or dynamic instability.
