Rehabilitation of Distal Radius Fractures: A Biomechanical Guide
Section snippets
Basic fracture healing
The major factors determining the mechanical environment of a healing fracture include the rigidity of the selected fixation device, the fracture configuration, the accuracy of fracture reduction, and the amount and type of loading at the fracture gap [2]. The fracture site stability may be enhanced artificially by a variety of external or internal means that includes cast treatment, pins, external fixation, and plates. Fracture healing under unstable or flexible fixation typically occurs by
Fracture site forces
Movement of the bone fragments depends on the amount of external loading, stiffness of the fixation device, and stiffness of the tissue bridging the fracture. The initial mechanical stability of the bone fixation should be considered an important factor in clinical fracture treatment [7].
The physiologic forces with wrist motion have been estimated to lie between 88–135 Newtons (N) [8], [9]. Eighty-two percent of the loads across the wrist are transmitted through the distal radius [10]. Cadaver
Biochemical response to injury
The basic response to injury at the tissue level is well known. It consists of overlapping stages, including an inflammatory phase (1–5 days), a fibroblastic phase (2–6 weeks), and a maturation phase (6–24 months) [16]. Following a fracture there is bleeding from disrupted vessels, which leads to hematoma formation. Several chemical mediators, including histamine, prostaglandins, and various cytokines are released from damaged cells at the injury site, inciting the inflammatory cascade [17],
Tendon gliding
Much of the work on tendon gliding has been applied to tendon repairs. The information gleaned from this work, however, has therapeutic implications with regard to distal radius fractures (Box 2). The dorsal connective tissue of the thumb and phalanges forms a peritendinous system of collagen lamellae that provides gliding spaces for the extensor apparatus [24], [25], [26]. The extensor retinaculum is divided into six to eight separate osteofibrous gliding compartments. Within the tunnels and
Cast treatment
Cast treatment is nonrigid fixation: it reduces fracture site mobility but does not abolish it because of the intervening soft tissue. A cast relies on three-point fixation to maintain the fracture position. If the wrist is casted in a flexed and ulnar deviated position, a component of ligamentotaxis is also in play. The initial focus of therapy is directed toward reestablishing finger motion. Active finger motion should be gentle and not pushed early on, because the flexed and ulnar deviated
Causes of treatment failures
There are a large number of extrinsic tendons crossing the fracture site. Dorsal angulation of >30° and radial angulation >10° greatly affects the moment arms and subsequently the excursion and strength of these tendons [73].
If joint malalignment is the etiology of loss of forearm rotation, then continued therapy is of no benefit (Fig. 8A,B). Biomechanical studies have demonstrated that radial shortening ≥10 mm caused a 47% pronation loss and a 27% supination loss [74]. More than 10° of dorsal
Summary
Fracture healing and surgical decision making are not always predictable. The suggested protocols are intended to be flexible rather than rigid to be responsive to patient progress and the fracture site stability. A methodologic approach to the rehabilitation following a distal radius fracture, based on a knowledge of the biology of fracture healing and biomechanics of fixation, may preempt some of the pitfalls associated with distal radius fracture healing.
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