Types of Instability

• Carpal instability dissociative refers to instability within a carpal row—scapholunate or lunotriquetral ligament tear, and perilunate instability. This generally involves an intrinsic ligament injury, and leads to counter rotation between the radial and ulnar components of the carpal row.
• Carpal instability nondissociative (CIND) occurs when the bones within each carpal row are normally constrained but support has been lost either between the rows or between a row and its neighboring structure (ie, midcarpal instability). Extrinsic ligaments are most likely injured in this case.
• Carpal instability complex incorporates each of the above-said elements and denotes marked loss of ligamentous support (ie, perilunate dislocation).

Lunate Posture

• Dorsal Intercalated Segment Instability refers to abnormal lunate extension seen on lateral radiographs. This most commonly is associated with scapholunate ligament tears, which unlink the lunate from the flexion moment that the scaphoid imparts.
• Volar intercalated segmental instability (VISI) describes abnormal flexion of the lunate on lateral radiographs. This most commonly occurs with disruption of the lunotriquetral ligament, which releases the lunate to flex with the scaphoid, and can also occur with generalized ligamentous laxity leading to a CIND pattern.
• Ulnar translocation and dorsal translocation of the carpus involve displacement of the carpus as a unit with the lunate moving in the direction specified.

Force Transmission

• Greater arc injuries involve an arc of injury that is transmitted through, and fractures, the involved carpal bone (trans-scaphoid perilunate dislocation).
• Scaphoid most commonly fractured bone and typically through middle third
• Capitate, hamate, radial styloid, lunate all have been reported
• Lesser arc injuries involved purely soft tissue injury and can disrupt multiple ligamentous structures without fracture.

Chronicity

• Acute (<1 week)
• Subacute (1–6 weeks)
• Chronic (>6 weeks): Primary ligament healing unlikely

Perilunate Dislocation

• Occur from forceful wrist extension, ulnar deviation, and intercarpal supination.
• Mayfield et al described the accepted sequence of perilunar instability
• Injury occurs from radial to ulnar –> disruption of scapholunate ligament or scaphoid fracture (Stage 1) à disruption of lunocapitate articulation (stage II)–> lunotriquetral ligament injury (Stage 3)–> disassociation of carpus from lunate > dislocation of lunate from its fossa into carpal tunnel (usually still attached by short radiolunate ligament) (Stage 4)
• Defining characteristic is dislocation of capitate head from the lunate concavity (usually dislocates dorsally)
• Herzberg: Stage I (lunate still in fossa), IIA out of fossa but rotated less than 90 IIB rotated more than 90
• Diagnosis
• History (usually high energy)
• Physical examination: will note wrist deformity, pain, may often see median nerve paresthesias

Imaging:

• Posteroanterior and lateral radiographs of the wrist (appropriate with third metacarpal collinear to longitudinal axis of radius)
• Should see disruption of Gilula lines-, defined as the normally continuous arches created by connecting the images of the subchondral lines of the proximal surfaces of the proximal carpal row, the distal surfaces of the proximal carpal row, and the proximal surface of the distal carpal row.
• Scaphoid Ring sign- flexion of the scaphoid 
• Traction Imaging important
• Assessment of reduction including assessment of ulnar carpal translation is important- normal lunate uncovering is 40-49% in both neutral and radial deviation. 

Treatment:

(urgent closed reduction followed by definitive fixation)

• Closed Reduction: Initial treatment consists of closed reduction. Maneuver combines axial traction, wrist extension, and a thumb stabilizing the volar lunate before flexing the hand back over the lunate to reduce the dorsal perilunate dislocation. Patients should be examined for signs of acute carpal tunnel syndrome.
• Surgery: should generally be performed within the first week
• Approach: dorsal volar or combined; combined approach more concerning for wound issues and used in cases of median nerve injury or volar access
• Timing of surgery- 25% of PLD/FD are missed initially, studies show worse outcomes >45 days. 
• Consider salvage procedures after 6-8 weeks (PRC if capitate and lunate fossa preserved)
• Acute injuries: dorsal or combined dorsal and volar approaches with K-wires placed across the scapholunate, scaphocapitate, and lunotriquetral joints (otherwise known as box pinning)
• Capsular-ligamentous ruptures and the scapholunate/lunotriquetral ligaments may be repaired. Fixation is generally maintained for 10–12 weeks.
• Greater arc injuries including the trans-scaphoid perilunate dislocation are ideally treated with ORIF of the fractured carpal bone in conjunction with necessary K-wire fixation of ruptured ligaments. However, when comminuted, contaminated by open wounds, or when occurring in older individuals, proximal row carpectomy or wrist arthrodesis may best serve the patient.
• Transcaphoid injuries do not typically have ruptured SL –> compression screw and LT repair using bone anchor or pinning LT
• Results- post traumatic arthritis present in 60-70% of patients (in-service question), but this does not necessarily correlate with outcomes; moderate disability;
• Scaphoid Fractures
• Most commonly fractured carpal bone and accounts for 70% of all carpal bone fractures. Often occurs after FOOSH (hyperextension) or axial load
• Waist fractures (65%), proximal third (25%), distal third (10%)
• Incidence of AVN is highest with proximal pole fracture because the dorsal carpal branch (which is a branch of the radial artery) supplies the proximal 80% of the scaphoid via retrograde flow
• Herbert Classification
• Type A- stable, acute fracture
• Type B- unstable acute fracture such as with a distal oblique fracture, a complete waist fracture, a proximal pole fracture, or a perilunate associated fracture
• Type C- delayed union
• Type D- nonunion
• Physical Exam- anatomic snuffbox tenderness, positive scaphoid compression test
• Imaging- scaphoid view is 30 degrees wrist extension and 20 degrees of ulnar deviation 
• Non-op can be considered for stable, nondisplaced fractures
• Percutaneous screw fixation for proximal pole fracture, > 1mm displacement
• Nondisplaced waist fractures have decreased time to union and faster return to work with percutaneous fixation
• ORIF- comminuted fractures or those with associated perilunate dislocation, or DISI (radiolunate angle > 35 degrees)
• Complications- malunion (humpback deformity due to flexion of the distal pole and extension of the proximal pole) nonunion, AVN, and SNAC wrist