Experimental Study Of The Biomechanical Properties Of Scaphoid And The Effect Of Radial Styloidectomy On It

Objectives: Through the study of the biomechanical properties of scaphoid and the effect of radial styloidectomy on it, provide a theoretical basis for clinical of scaphoid fracture. Scaphoid fracture is the most common type in wrist fracture, accounted for 80% or more. The special blood supply and the particular anatomical position of scaphoid led to the fracture heal in scaphoid is more difficult then others in wrist. Adding to there is no uniform standards and principles about the diagnosis, treatment of scaphoid fracture, the missed diagnosis of fresh fracture of scaphoid and nonunion often happens, and it leads to the difficult of clinical treatment and delays the time of treatment, even leads the traumatic arthritis. In clinical work, with the old fracture of sacphoid, we often use the radial styloidectomy to reduce the creation of activity of the wrist joint to scaphoid and use the bone grafting and internal fixation to promote fracture healing. This technique has been generally recognized by us, but after radial styloid cut, there is almost no study about what the change of biomechanical properties of scaphoid happens. In view of the status quo, we consider it having certain guiding significance for clinical to research the biomechanical properties of scaphoid and the effect of radial styloidectomy on it.Methods: Eight cases of voluntary donation fresh adult upper limbs were used and they were all cut from lower 1/3 of forearm. Take X-ray photo of forearm and wrist, proofing the anantomy of them normal. The specimens were fixed in the experimental bench. The outer side of the protruding part of the distal radius is determined as the styloid process of the radius area, connected the proximal and distal point, partitioned the styloid process of radius into 3 parts, cut 1/3, 2/3 of the styloid process of radius in turn. Do an operation incision in Lister tuberosity, on the back side of the wrist joint. On the premise of not destroying the integrity of the wrist joint ligament, position the pressure sensitive film on the five articular surface of scaphoid, according to the BOSE-3500 biomechanical test machine, the wrist were drived by the strength of 100 N with the speed of 5 mm/s, to take the movement of flexion, extension, radial deviation and ulnar deviation. And then test the change of the five articular surface of scaphoid, in the normal wrist and after styloid process of radius cut 1/3, 2/3 in turn.Results: In the normal wrist joint, the pressure of each articular surface of the scaphoid are uniform, the average value of them is(0.357±0.021) MPa; but they are different in other positions of wrist joint: when wrist joint in flexion position, the max pressure is(0.381±0.024) MPa, between scaphoid and capitate bone; when wrist joint in extension position; the max pressure is 0.427±0.027 MPa,between scaphoid and capitate bone; when wrist joint in radial deviation position, the max pressure is(0.421±0.023) MPa, between scaphoid and trapezium; when wrist joint in ulnar deviation position, the max pressure is(0.339±0.024) MPa, between scaphoid and small multangular bone. When styloid process of radius cut 1/3, the pressure between scaphoid and radius turn smaller, especially when wrist joint in radial deviation and ulnar deviation, they are(0.302±0.021) MPa and(0.327±0.023) MPa respectively. There is statistically significant difference compared with normal wrist(P<0.05). But there is no statistically significant difference compared with normal wrist(P>0.05) in the other four articular surface of scaphoid. When styloid process of radius cut 2/3, there is no statistically significant difference compared with styloid process of radius cut 1/3(P>0.05), but the pressures of other articular surface of scaphoid turn uneven: when wrist joint in radial deviation position and neutral position, the pressure between scaphoid and lunar bone increases significantly, they are(0.471±0.029) Mpa, and(0.425±0.025) Mpa respectively, having statistically significant difference(P<0.05).Conclusion: The pressure of every articular surface of scaphoid in normal wrist joint is basically equal, this is the complex and efficient reflect of the wrist. When styloid process of radius cut 1/3, the pressure between scaphoid and radius becomes smaller, especially when wrist joint in radial deviation and ulnar deviatio,so the effect of radial styloidectomy in reducing the stimulation to scaphoid in wrist joint activity is obviou. When styloid process of radius cut 2/3, the pressures of other articular surface of scaphoid turn uneven: when wrist joint in radial deviation position and neutral position, the pressure between scaphoid and lunar bone increases significantly. And this is the important inducement of lunar bone necrosis and triangular cartilage rupture. when wrist joint in ulnar deviation position and extension position, the pressures of all articular surface of scaphoid become smaller, and it just is the reflect of instable of wrist joint. So in order to keep the stable of wrist joint, properly keeping some styloid process of radius is necessary, and the range is about 2/3 of styloid process of radius. The radial styloidectomy isn’t suit for the fracture of scaphoid near-end, for that needs to cut a large range of styloid process of radius.