Scapholunate advanced collapse: a pictorial review
- 4.5k Downloads
Scapholunate advanced collapse (SLAC) is the most common cause of osteoarthritis involving the wrist. Along with clinical investigation, radiological studies play a vital role in the diagnosis of SLAC wrist. Given that the osteoarthritic changes that are seen with SLAC occur in a predictable progressive pattern, it is important to understand the pathological evolution of SLAC to be able to recognise the associated progressive imaging findings seen with this disease process. Focusing on radiological findings, this article provides a pictorial review of the anatomy of the scapholunate interosseous ligament as well as the common terminology and biomechanical alterations seen in the pathway leading to the development of SLAC arthropathy. We will then discuss two additional common causes of SLAC wrist and their imaging findings, namely scaphoid non-union advanced collapse and calcium pyrophosphate dehydrate disease. In addition, we will provide a brief overview of the current treatment options of these pathological entities.
• SLAC is the most common cause of osteoarthritis involving the wrist.
• Arthritic changes of SLAC occur in a predictable progressive pathological and radiographic pattern.
• Imaging is key for diagnosing, monitoring progression and assessing post-treatment changes of SLAC.
KeywordsScapholunate advanced collapse Arthritis Wrist Radiography Review
Osteoarthritis of the wrist is a painful disease process, which can lead to decreased function and disability of the upper extremity. Scapholunate advanced collapse (SLAC) is a frequently encountered progressive form of wrist osteoarthritis that most often occurs secondary to traumatic injury of the scapholunate ligament . Other causes of SLAC include calcium pyrophosphate dehydrate (CPPD) crystal deposition disease , scapholunate non-union advanced collapse (SNAC), idiopathic avascular necrosis of the scaphoid (Preiser disease), midcarpal instability, intra-articular fractures involving the radioscaphoid or capitolunate joint, perilunate dislocation and Kienbock’s disease [3, 4]. Imaging, including radiography, computed tomography (CT) and magnetic resonance imaging (MRI), is frequently utilised to diagnose SLAC, monitor its progression and to assess post-treatment changes. This article will provide a pictorial review of the relevant anatomy, terminology, pathological processes, common causes and treatment options pertinent to the understanding of SLAC wrist.
Scapholunate interosseous ligament
Terminology in the pathway to the development of SLAC wrist
Key radiological measurements of the SLAC wrist pathological terms
Scapholunate diastasis (PA radiograph)
Rotary subluxation of the scaphoid (lateral radiograph)
Dorsal intercalated segment instability (DISI) (lateral radiograph)
1. Scapholunate interval >4 mm (2–4 mm is suspected scapholunate diastasis)
1. Scapholunate angle >60–80° (scaphoid tilted volarly)
1. Scapholunate angle >80° (60–80° is suspected DISI; lunate tilted dorsally)
2. Radioscaphoid angle >60°
2. Radiolunate angle >10°
3. Capitolunate angle >30°
Scapholunate dissociation is the loss of synchronous motion or normal alignment between the scaphoid and lunate bones usually from ligamentous injury [7, 8]. The mechanism of injury in scapholunate dissociation is most commonly trauma causing wrist extension, ulnar deviation and intercarpal supination . Eventually scapholunate dissociation leads to misalignment of other scaphoid joints and ultimately to osteoarthritis (SLAC wrist) .
Scapholunate diastasis is the term used to describe an abnormal increase in the scapholunate interval. Scapholunate diastasis occurs when there is a functionally complete tear of the scapholunate ligament. Scapholunate diastasis can be seen in the setting of scapholunate dissociation. However, scapholunate dissociation and scapholunate diastasis are not truly synonyms as one may have dissociation with a preserved width of the scapholunate interval .
It is controversial whether scapholunate dissociation and rotary subluxation of the scaphoid (as well as often concomitantly occurring DISI) are the same terms, or if one of these is a subset of the other. However, it seems that there are subtle but definite differences between these terms as rotary subluxation of the scaphoid and DISI focus on the individual orientation of the scaphoid and lunate, respectively, while scapholunate dissociation focuses on the relationship between the scaphoid and lunate .
SLAC wrist pathogenesis
Osteoarthritis of the wrist occurs almost exclusively (95 %) as a periscaphoid problem. There are three different patterns of arthropathy seen about the wrist which include SLAC, triscaphe arthritis (between the trapezium, trapezoid and distal scaphoid) and a combination pattern. SLAC wrist is the most common type of wrist arthritis and accounts for approximately 55 % of all wrist arthritis .
SLAC is an osteoarthropathy of the carpus secondary to altered stress around an unstable scaphoid. In SLAC, there is ligamentous instability of the wrist including disruption of the scapholunate ligament, which causes scapholunate dissociation, scapholunate diastasis, rotary subluxation of the scaphoid and DISI. Changes in alignment of the carpus, particularly changes in position of the scaphoid, result in inordinate stress and load to be placed predominantly on the radioscaphoid and capitolunate joints.
The most common cause of SLAC is rotary subluxation of the scaphoid, which can be attributed to the elliptical configuration of the radioscaphoid joint. Even with advanced cases of SLAC, the articulation between the lunate and radius is grossly preserved due to the spherical nature of this joint, as opposed to the elliptical nature of the radioscaphoid joint [4, 16, 17].
Scaphoid non-union advanced collapse (SNAC)
SNAC is due to a non-united fracture of the scaphoid and is a common cause of wrist arthropathy, with a pattern of osteoarthritic change which is very similar to the pattern seen with SLAC wrist. Although SNAC and SLAC are in fact two different derangements, they have a similar pathophysiology and therefore SNAC wrist can be thought of as a variant of SLAC wrist. The difference between these two entities is that as opposed to SLAC where the scapholunate ligament is interrupted with resultant scapholunate diastasis, with SNAC the scaphoid is fractured and the scapholunate ligament and joint are usually preserved. The proximal pole of the fractured scaphoid behaves similar to a small lunate because the fragment is a small spheroid shaped bone which is situated within the spheroidal portion of the scaphoid fossa. This configuration of the non-united scaphoid causes osteoarthritic changes to occur between the radius and the distal scaphoid fracture fragment, progressing proximally but only up to the non-union site [3, 8].
Calcium pyrophosphate dehydrate (CPPD) crystal deposition disease
SLAC and SNAC treatment options
SLAC is a frequently encountered wrist arthropathy, with consistent, predictable and progressive imaging features. Along with clinical findings, radiological studies play a vital role in the diagnosis, monitoring and follow-up after treatment of this entity. It is, therefore, crucial to understand the anatomy and function of the scapholunate interosseous ligament, predictable progressive nature of this arthritic disease process, as well as the common causes and treatment options of SLAC wrist.
- 4.Patel N, Russo G, Rodner C (2012) Osteoarthritis of the wrist. In: Chen Q (ed) Osteoarthritis—diagnosis, treatment and surgery. InTech, Rijeka, pp 173–175Google Scholar
Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.