Introduction Carpus is a complex unit of bony articulations that transfers the forces of the hand to the supporting forearm and upper extremity Allows wide range of motion in 2 planes Carpal bones are 8 in number arranged in 2 rows Main motions Extension Flexion Radial and ulnar deviation The primary axis of motion resides within the head of carpitate.
General, surgical and applied anatomy Bones and joints Composed of 8 bones in 2 rows The 8 bones are influenced by Shape of distal radius The distal ulnar Triangular fibrocartilage complex
Anatomy of the Wrist Carpal bones tightly linked by capsular and interosseous ligaments. Capsular (extrinsic) ligaments originate from the radius and insert onto the carpus. Interosseous (intrinsic) ligaments traverse the carpal bones. The lunate is the key to carpal stability.
Extrinsic ligaments Extrinsic ligaments link the carpal bones to the radius, ulna, and metacarpals.
Lunate Connected to both scaphoid and triquetrum by strong interosseous ligaments. Injury to the scapholunate or lunotriquetral ligaments leads to asynchronous motion of the lunate and leads to dissociative carpal instability.
Intercarpal Ligaments Injury to these ligaments leads to abnormal motion between the two rows, and non-dissociative wrist instability patterns.
Neurovascular anatomy Circulation of the wrist is obtained through the radial, ulnar, and anterior interosseous arteries and the deep palmar arch
Neurovascular anatomy The scaphoid, capitate, and about 20% of all lunates are supplied by a single vessel and thus are at risk for avascular necrosis. The trapezium, triquetrum, pisiform, and 80% of lunates receive nutrient arteries through two nonarticular surfaces and have consistent intraosseous anastomoses. AVN is therefore rare. The trapezoid and hamate lack an intraosseous anastomosis and, after fracture, can have avascular fragments.
Mechanism of injury Most common is an axial compression force applied with the wrist in hyperextension Most common injury is a fall on the outstretched hand Other mechanisms Palmer flexion,twisting injuries
Mechanism of injury High energy forces Results in carpal bone fractures or ligamentous disruption of both extrinsic and extrinsic ligaments and perilunate dislocation Low energy forces results in minor injuries such as sprains
Imaging Plain radiographs: multiple views necessary: Anteroposterior Lateral Oblique Clenched-fist AP Radial and ulnar deviation
Imaging Gilula's lines. A. AP views show three smooth Gilula arcs in a normal wrist. These arcs outline proximal and distal surfaces of the proximal carpal row and the proximal cortical margins of capitate and hamate. B. Arc I is broken, which indicates an abnormal lunotriquetral joint due to a perilunate dislocation..
Imaging Standard scaphoid views detect most carpal injuries PA x-ray with wrist neutral and in ulnar deviation elongates scaphoid to better visualize MRI scans are useful in detecting occult fractures, AVN of the carpal bones, and ligamentous injuries. Perilunate dislocations are easily missed if the continuity of Gilula's line is not assessed.
General Principles of Treatment Carefully evaluate x-rays for subtle fractures and/or evidence of carpal instability. Reduce and immobilize scaphoid fractures or perilunate injuries pending definitive treatment. Diagnose and appropriately treat ligament and bony injuries.
Lunate fractures Rare <1% of all carpal fractures Isolated fractures of lunate often missed
Lunate anatomy Sits like a keystone in the proximal row Well protected in concavity of the lunate fossa of the radius Vascular supply-proximal carpal arcade dorsally,palmarly 7-26% of lunates have single volar or dorsal blood supply
Mechanism of injury Hyperextension injury Others: repetitive stresses of the wrist Strenuous push Avulsion of the dorsal pole( S-L tension)
Classification of lunate fractures Acute fractures are classified in 5 groups: Frontal fracture of palmer pole Osteochondral fractures of the proximal articular surface Frontal fracture of the dorsal pole Transverse fracture of the body Trans articular fracture of the body
Management of lunate fractures Undisplaced-cast immobilization for 4wks ORIF Displaced fractures Associated carpal instability Non-union
Perilunate dislocation Triquetral and scaphoid malrotation Result of a fall on an outstretched, hyperextended hand Relatively rare Occurs when the lunate maintains normal position with respect to the distal radius while all other carpal bones are dislocated posteriorly
Perilunate dislocation Very commonly associated with a scaphoid waist fracture Sometimes ulnar styloid as well Lunate appears triangular in shape on PA view Lunate rotates forward slightly on lateral view In lateral view, all other carpal bones are dislocated posterior with respect to lunate
Represents 2 nd of the 4 stages of ligamentous injury around lunate bone resulting from forced hyperextension They are referred to as lesser arc injuries The 4 stages of injury are: Scapholunate dissociation(stage I) Perilunate dislocation(II) Midcarpal dislocation(III) Lunate dislocation(IV) With increasing hyperextension perilunate dislocation may become a lunate dislocation
Mechanism of Injury Load applied to hand forcing the wrist into extension and ulnar deviation Severe ligament injury necessary to tear the distal row from the lunate to produce perilunate dislocation
Physical Exam Dorsal displacement of the carpus may be seen Significant swelling common Evaluate for compartment syndrome If lunate is dislocated, median nerve symptoms may be present
Note lack of “colinearity” among the radius, lunate, and capitate on the lateral x-ray.
Imaging Note loss of normal carpal “arcs” and abnormal widening of the scapholunate interval. Look for associated fractures “trans-scaphoid” injuries
X-ray usually Obvious
X-ray may be subtle
Initial Treatment Closed reduction is performed with adequate sedation. Early surgical reconstruction if swelling allows. Immediate surgery needed if there are signs of median nerve compromise. Delayed reconstruction if early intervention is not necessary.
Technique of Closed Reduction Longitudinal traction for minutes For dorsal perilunate injuries: apply dorsal directed pressure to the lunate volarly while a reduction maneuver is applied to the hand and distal carpal row Palmar flexion then reduces the capitate into the concavity of the lunate.
Closed Reduction and Pinning Poor results with closed reduction and pinning alone Very difficult to reduce adequately wrist needs to be ulnarly deviated to correct scaphoid flexion radial deviation needed to close S-L gap
ORIF with volar and dorsal approaches Procedure of Choice
Dorsal Approach Repair S-L ligament
Reduce lunate first- may need to temporary pin to radius
Pin Carpus: S-L, L-T and mid- carpal joints
Trans-scaphoid Perilunate Injuries Require reduction and fixation of the fractured scaphoid. Most of these injuries best treated ORIF with volar and dorsal approaches repair of injured structures. Open repair supplemented by pin and screw fixation.
Fix scaphoid first: dorsal approach
Pin L-T and Mid-carpal joints
Make sure Radius-Lunate- Capitate are colinear and S-L angle restored
Perilunate Injuries Conclusion Perilunate fracture dislocations are high-energy injuries Must recognize different injury patterns transcaphoid pure ligamentous trans radial-styloid Early open and anatomic fixation with volar and dorsal approaches provides the best chance at a reasonable functional result
Perilunate dislocation conclusion Median nerve dysfunction- 16% of the patients 16-25% of perilunate dislocations are missed initially
Lunate dislocation Most severe of carpal instabilities Most frequently dislocated carpal bone Most commonly associated with a trans-scaphoid fracture Involves all the intercarpal joints and disruption of most of the major carpal ligaments Produces volar dislocation and forward rotation of lunate Concave distal surface of lunate comes to face anteriorly
Lunate dislocation Capitate drops into space vacated by lunate Results in dislocation of other carpal bones Capitate and all other carpal bones lie posterior to lunate on lateral radiograph Triangular appearance of lunate on frontal projection (piece of pie sign) Spilled tea cup sign (lateral view)
Dislocated Lunate s/s tenderness Swelling ROM painful & limited May compress median nerve
Lunate dislocation Dislocation usually occurs in two steps – 1 st the ligaments are torn and then the bone dislocates + Murphy’s sign Murphy’s Sign – pt makes a fist. Indication – lunate dislocation
Other imaging modalities CT scan MRI
Treatment Closed reduction at A/E ORIF
Complications Wrist arthritis Persistent pain Joint instability Recovery takes at least 6months