DISTAL INTERPHALANGEAL JOINT ARTHRODESIS COMPARING TENSION-BAND WIRE AND HERBERT SCREW - A BIOMECHANICAL AND DIMENSIONAL ANALYSIS

Thirty cadaveric distal interphalangeal joints (15 male and 15 female joints) were prepared with either a Herbert screw or a tension-band wi re technique to simulate an arthrodesis. To elucidate mechanical diffe rences between these constructs, the strength of the specimens was det ermined for three-point anteroposterior and lateral bending and for ax ial torsion. The Herbert screw demonstrated significantly greater ante roposterior bending strength and greater torsional rigidity when compa red to the tension-band wire technique. For dimensional analysis, the height and width of each distal phalanx was measured prior to fixation , 4 mm from the distal tip of the bone (the region that must accommoda te the large-diameter threads of the Herbert screw). Results indicated that the mean height of the distal phalanx (3.55 mm) is smaller than the diameter of the screw (3.90 mm). Fracture or thread penetration at the tip of the distal phalanx during screw placement occurred in 25 o f the specimens overall and in all the female phalanges, often resulti ng in stretching or violation of the nail bed. Despite fracture or scr ew penetration, the Herbert screw appears to offer additional strength that may be clinically important for joint arthrodesis.