June 14, 2021 8 min read
Answer a fun quick question about wrist instability, learn more about what defines this particular condition, and find some helpful tips on the best hand therapy treatment.
Answer this Quick Question
What does DISI stand for?
Answer: a) Dorsal Intercalated Segment Instability
This sounds complicated and scary, but it’s really not – I am going to try and simplify it through a few basic principles. Normal wrist kinematics are this: the proximal carpal row consists of the scaphoid, lunate and triquetrum, which are connected to each other by the scapholunate and lunotriquetral ligaments respectively.
The scaphoid has a tendency to want to flex (move volarly), whereas the triquetrum has a tendency to want to extend (move dorsally). In a stable normal wrist the lunate sits in the middle, “balanced” by the forces tending to act on the adjacent bones.
I’m not sure who came up with the idea of the “promiscuous lunate” but I first heard it described by Sarah Mee at a Hand Therapy conference in Napier, New Zealand. It is a great concept, as it makes this easy to understand. Basically the lunate will go with whoever it’s attached to.
So, if the scapholunate ligament is disrupted, the lunate will displace dorsally with the triquetrum, i.e. DISI. If the lunotriquetral ligament is disrupted, the lunate will displace volarly with the scaphoid, i.e. VISI. A DISI may also be the result of an unstable scaphoid fracture.
If your client is referred to you with the diagnosis of DISI already made, chances are he / she has a scapholunate ligament disruption. If you are the first person to see the client or make the diagnosis, look out for the following:
In the case of a static injury, where the SLL is completed disrupted, the Terry Thomas sign may be evident on a non-stressed view too. On a lateral view you will also see an increase scapholunate angle (normal is 30-60deg, whereas >60deg indicates DISI). The ring sign is also an important diagnostic finding indicating DISI, where the scaphoid is flexed volarly but the lunate is extended dorsally.
It may take up to 12 months before dynamic instability develops and dissociation becomes evident on x-ray.
Watson’s shift test: Client’s wrist is in ulnar deviation and slight extension. Therapist puts thumb on client’s scaphoid tubercle and IF on the anatomical snuffbox (i.e. holding the scaphoid). Therapist’s thumb blocks the scaphoid from flexing, as you radially deviate the client’s wrist. Instability will cause the scaphoid to sublux dorsally. When pressure is removed, there will be a painful clunk in a positive test.
Not all scapholunate ligament injuries result in DISI. Management depends on the severity of the tear, time since injury, and presence of arthritis. Severity increases from partial tears to dynamic instability to static instability to SLAC (scapho-lunate advanced collapse) wrist arthritis.
With a Grade 1 tear, there will not be instability, thus this is not a DISI. Some Grade 2 tears do result in instability over time, but can be managed conservatively if diagnosed early. The goal of hand therapy for these clients is stability rather than mobility.
If there is dynamic or static instability, Grade 3 tear / complete disruption, they will require surgery. This will correct / improve the mechanics of the wrist, and prevent it from developing into a SLAC wrist. Goals of surgery are to reduce pain, increase function and improve wrist alignment. The ligament may be repaired in some cases, or reconstructed. Surgery may include a capsulodesis, bone-ligament-bone graft, tendon weave, or RASL.
Hand therapy should focus on strength, dexterity, proprioception and stability. Post op management depends on your surgeon’s preference, or their specific protocols. However, most commonly the client would be immobilised in a cast for 6-8 weeks, and thereafter in a removable thermoplastic splint, which is worn for a further 4 weeks between exercise sessions.
AROM can usually commence in the DTM arc around 6-8 weeks post-op. PROM is delayed as to avoid destabilising the repair. Isometric strengthening in dart throwers motion positions may be commenced around 8+ weeks. Again be careful with grip strengthening, as firm grip stresses the repaired SLL.
Many can return to normal activity by ~4 month post op, while others may take 6-12 months to reach full capacity.
We have an excellent range of wrist supports that may be suitable for your clients.
This blog is a discussion format. We have listed our views above but would love to know what you think, what your comments are or how you best treat DISI deformity in your practice. Feel free to email us at email@example.com
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