Distal radius malunion—an intra-articular or extra-articular distal radius fracture healed in nonanatomic alignment, resulting in wrist pain, degenerative changes, decreased range of motion, altered wrist mechanics, instability, or a combination of these.
The biomechanical effects of malunion were first described by Rouen in 1919; Campbell detailed treatment with biplanar osteotomies in the 1930s.
The distal radius may normally bear loads of up to 4000 N, with 80% normally borne by the radius.
Recent studies showed that increasing ulnar positivity by only 2.5 mm raises the load across the ulna to 42% of the total borne by the wrist.
Deformity does not correlate well with symptom severity.
Key measurements—radial inclination, radial length/height, ulnar variance, and radial/volar tilt (Figure 27.1 and Table 27.1)
Most common deformity is loss of palmar/volar tilt in the sagittal plane and loss of radial length relative to the ulna.
Malunion is the most common complication of distal radius fracture, with an overall rate as high as 17%.
Frequently occurs in distal radius fractures managed nonoperatively and in elderly, osteoporotic bone.
Other causes—inadequate reduction, neglect or delayed presentation, and inadequate fixation or immobilization after operative intervention
Ulnar-sided wrist pain is the most common complaint and may be a consequence of altered ulnar variance, incongruity, or malalignment of the sigmoid notch.
Greater severity or duration of deformity may lead to radiocarpal/midcarpal/distal radioulnar instability, wrist deformity, numbness/tingling/weakness in the median nerve distribution, or arthritic/degenerative changes.
Correlated with a lower DASH (Disabilities of Arm, Shoulder, and Hand) score
Detailed neurovascular examination
Include careful testing of median nerve for carpal tunnel syndrome.
Allen test for perfusion, presence of intact deep palmar arch
Decreased range of motion—shifted flexion/extension arc, decreased pronosupination
Dinner fork deformity (Figure 27.2)
Prominence of the ulnar head with pronosupination
Decreased grip strength (↓50%)
Prior surgical incisions
Focused examination—radiocarpal, ulnocarpal, and distal radioulnar joints (DRUJ). Check for pain, crepitus, and instability.
Posteroanterior (PA) and lateral wrist radiographs to measure criteria of malunion (Table 27.1)
Degenerative changes at the radiocarpal joint, midcarpal joint, and DRUJ should be noted.
Advanced imaging is not routinely used in initial evaluation. However, it can be useful to evaluate complex and/or intra-articular deformity.
Computerized tomography (CT)—shows bony detail of articular incongruity, status of fracture healing, as well as rotational and translational deformities
MRI—shows gradient of soft tissue injury at the DRUJ, extrinsic or intrinsic carpal ligaments, and articular cartilage
No widely adopted system.
Malunions may be described using radiographic parameters (Table 27.1). Alternatively, they may be described using the eponymous fracture pattern from the original injury (Colles fracture, Smith fracture, Barton fracture, etc.).
TABLE 27.1 Radiographic Assessment of Distal Radius Malunions: Normal Values and Acceptable limits of Deformity14,17
FIGURE 27.2 Dinner fork deformity resulting from loss of radial length, inclination, and palmar tilt.
FIGURE 27.3 Posteroanterior and lateral radiographs of a distal radius malunion demonstrating loss of radial inclination and length, increased ulnar variance, and dorsal angulation.
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