The initial step in evaluating wrist radiographs involves ensuring adequate image quality. Proper positioning for the PA projection includes the shoulder abducted 90 degrees and the elbow flexed at 90 degrees, with parallel alignment of the radius and ulna. A correctly positioned PA view reveals the extensor carpi ulnaris groove.[img]1[img]

For the lateral projection, the elbow is flexed to 90 degrees and adducted against the trunk, with the distal forearm and hand resting on the ulnar side. A true lateral view is confirmed by the palmar surface of the pisiform projecting at the middle third between the palmar aspect of the capitate and the palmar aspect of the distal scaphoid pole, assessing pronation or supination.[img]1[img]

The oblique view is obtained by elevating the radial side of the wrist 30 degrees from the table. An adequate oblique view shows the trapezio-trapezoidal interval and waist of the scaphoid. [img]1[img]

1. Evaluation of carpal joints-Arch

Assessing joint alignment and spaces is crucial for detecting carpal instability, dislocation, and fractures. Carpal alignment is commonly evaluated by drawing three smooth, curvilinear arcs along the radiocarpal and midcarpal joints. Disruption in these arcs indicates fractures, ligamentous abnormalities, subluxation, or dislocation.

Midcarpal alignment can be assessed using vertically oriented parallel lines drawn across the distal surfaces of the trapezoid, capitate, hamate, and the bases of the 2nd through 5th metacarpals.[img]2[img]

1. Assess the lunate position on frontal radiograph

Checking clear spaces at the capitolunate, scapholunate, and lunotriquetral joints on frontal radiographs is vital. Symmetric joint spaces measuring 1-2 mm suggest normalcy. [img]3[img] ( Asymmetry may indicate ligamentous abnormalities. Additionally, evaluating the lunate's shape in the frontal projection and identifying the "piece of pie" sign can reveal lunate or perilunate dislocation.

Mayfield et al. categorized ligamentous injuries affecting the lunate into four stages of carpal instability: Stage I: Scapholunate dissociation, Stage II: Perilunate dislocation, Stage III: Midcarpal dislocation, Stage IV: Lunate dislocation. [img]3[img]

1. Assess Capitolunate line (CL) and scaphoid lunate (SL) angle on lateral radiograph.

The SL angle and CL angle on lateral radiographs help identify dorsal intercalated segment instability (DISI) and volar intercalated segment instability (VISI). Normal alignment shows SL angle within 30° to 60°, and CL angle at 0°. DISI exhibits increased SL and CL angles, while VISI shows decreased SL angle and increased CL angle. [img]4[img]

1. MRI Assessment of extrinsic alignment

Extrinsic ligaments connecting forearm bones to carpal bones are classified as palmar and dorsal. Noteworthy palmar ligaments include radioscaphocapitate (RSC), long radiolunate (LRL), and ulnocapitate (UC). Dorsal ligaments, particularly dorsal radiotriquetral (DRT), should be considered. [img]5[img] [img]6[img]

1. MRI Assessment of intrinsic ligament

Intrinsic ligaments, with superior yield strength, include scapholunate interosseous ligament (SL), lunotriquetral interosseous ligament (IL), midcarpal ligaments, and distal carpal row interosseous ligaments. Differentiating CIA from extrinsic Midcarpal Instability (MCI) is crucial, as CIA involves adaptive changes without substantial intracarpal ligament injury. [img]7[img]

7. Mayo Classification: Decoding Carpal Instability[img]8[img]

The Mayo classification system classifies carpal instability into four primary types:

1) Carpal Instability Dissociative (CID): CID involves disruption within or between bones of the same carpal row, seen in conditions like scapholunate dissociation (SLD), lunotriquetral dissociation, and distal dissociative carpal instability. SLD, often caused by wrist hyperextension and ulnar deviation, results in rotatory subluxation of the scaphoid. Key indicators include an increased scapholunate joint width (>4 mm), rotation of the distal scaphoid pole, and dorsal intercalated segment instability (DISI). Untreated SLD can lead to scapholunate advanced collapse (SLAC) wrist, necessitating surgical repair). [img]9[img]

2) Carpal Instability Nondissociative (CIND): CIND involves symptomatic dysfunction between the radius and carpal rows without internal disruptions. Radiocarpal CIND exhibits insufficiency of extrinsic radiocarpal ligaments, leading to ulnar sliding. Midcarpal Instability Nondissociative (MCI) affects both radiocarpal and midcarpal joints, with THC and RSC ligaments playing crucial roles. MCI types include palmar, dorsal, combined, and extrinsic. Surgical intervention may be required based on the specific instability type.

3) Carpal Instability Complex (CIC): CIC results from carpal derangement affecting bones within the same carpal row (CID features) and between proximal and distal carpal rows (CIND features). Three CIC groups include dorsal perilunate dislocation (lesser arc injury), dorsal perilunate fracture-dislocation (greater arc injury), and palmar perilunate dislocation. These injuries involve ligamentous and osseous components, requiring careful evaluation and often surgical intervention. [img]12[img] [img]13[img]

4) Carpal Instability Adaptive (CIA): CIA occurs due to postural adjustments in response to external factors. Examples include post-malunion of distal radial fractures and Madelung’s deformity. Distinguishing CIA from extrinsic Midcarpal Instability (MCI) is crucial, considering shared extracarpal pathology. Accurate diagnosis guides appropriate management for optimal reconstruction and restoration of wrist function. [img]14[img] [img]15[img] [img]16[img] [img]17[img]