Arthroscopic treatment of intraarticular malunions of the distal radius

Relevant biomechanics and natural history

The development of osteoarthritis (OA) following displaced intraarticular fractures has been attributed to a variety of factors, including the initial trauma to cartilage, elevated contact stresses, and joint instability. Early cadaveric studies of simulated intraarticular fractures have demonstrated increased contact stresses using pressure-sensitive film inserted into the radiocarpal joint space. With a 1-mm scaphoid fossa depression, lunate fossa pressures increased in neutral position and in radial deviation. Lunate fossa contact area increased in ulnar deviation and radial deviation with 1-mm scaphoid fossa depressions, and in all loading positions with 3-mm scaphoid fossa depression. As the magnitude of the fracture displacement increased, there was a shift in the focus of the maximum stresses toward the fracture line as well as altered kinematics. A deepened articular cavity of the distal radius due to a metaphyseal comminution zone is associated with early OA and reduced joint motion. One study of 6 freshly frozen cadaver forearms showed that wrist motion decreased significantly to between 54% and 69%, and that there was a significant decrease in the contact area in maximum extension for all locations by approximately 50%. In maximum flexion and neutral position, contact area decrease was significant for the scaphoid fossa by 51% to 54% and the total radial joint surface by 47% to 50%. Contact pressure showed a significant increase in maximum extension in the scaphoid fossa by 129%.

In a now classic paper, Knirk and Jupiter retrospectively reviewed 43 intraarticular fractures in 40 young adults (mean age, 27.6 yr), with a mean follow-up of 6.7 years. Because most of the fractures (38/43) were treated with older, nonrigid fixation methods that were popular at that time (including cast or pins and plaster), there was a high incidence of residual intraarticular incongruity. Jupiter noted that radiographic evidence of arthritis was present in all of the fractures (8) whose articular incongruity was 2 mm or more, in contrast to only 2 out of 19 of the fractures that healed with a congruous joint. OA was found in 22 out of 24 of the patients that had any step-off whatsoever.

Catalano et al. studied 21 patients under the age of 45 who had undergone internal fixation of displaced intraarticular fractures. At an average of 7.1 years, osteoarthrosis of the radiocarpal joint was radiographically apparent in 16 wrists (76%). A strong association was found between the development of osteoarthrosis of the radiocarpal joint and residual displacement of articular fragments at the time of bony union (p <0.01). They revisited 16 of these patients at 15 years postoperatively. Arthrosis was present in 13 out of 16 of the wrists and there was an additional 67% reduction of the joint space. The predictive value of these studies is that articular incongruity following a distal radius fracture (DRF) is the most significant factor in the development of radiocarpal osteoarthritis.

Diagnosis

The diagnosis is made radiographically because clinical examination cannot distinguish an extraarticular fracture from an intraarticular fracture. These include standard AP lateral and oblique radiographs including comparison views of the opposite wrist for preoperative planning. A CT scan with 3-D reconstruction is useful for determining the fracture configuration, degree of articular incongruity (including the sigmoid notch), and the amount of angular correction needed.