Headless compressions screws are cannulated tapered titanium screws with variable thread pitch angle, allowing a fully threaded screw to apply compression along its entire length. These screws have been most commonly used for scaphoid fractures1 but have also been studied in fractures of small bones, such as capitellum, midfoot, and talar neck,2-4 and arthrodesis in the foot, ankle, and hand.5-7 Headless compression screws have been found to produce equivalent fragment compression to partially threaded cancellous screws while allowing less fragment displacement.8,9 The lack of a head may decrease soft tissue irritation compared with the partially threaded cancellous screws. Finally, headless compression screws are independent of cortical integrity, as the entire length of the screw features a wide thread diameter to capture cancellous bone in the proximal fragment, unlike partially threaded cancellous screws, which only possess a thread purchase in the distal fragment and depend on an intact cortex.
Vertical shear fractures of the medial malleolus occur through the supination-adduction of the talus exerted onto the articular surface of the medial malleolus.10 Optimal fixation of these fractures must be sufficient to maintain stable anatomic reduction of the ankle joint articular surface, allowing early range of motion, maintaining congruency of the ankle joint, and decreasing the risk of future post-traumatic arthritis to maximize functional outcome.11
A wide variety of techniques are available for fixation of these fractures, including various configurations of cortical screws, cancellous screws, tension bands, and antiglide plates. Clinically, 2 parallel 4.0-mm partially threaded cancellous screws are most often used. Limited evidence indicates that headless compression screws may be a viable option for fixation of medial malleolus fractures. One case reports the use of a headless compression screw for a horizontal medial malleolar fracture,12 and a small retrospective case series that used headless compression screws for all medial malleolar fractures showed satisfactory outcomes, a high union rate, and low patient-reported pain.13
We evaluate the stiffness, force to 2-mm displacement of the joint surface, and elastic properties of these 2 different constructs in vertical medial malleolar fractures in synthetic distal tibiae. We hypothesize that the parallel headless compression screw fixation will be stiffer and require more force to 2-mm displacement than parallel unicortical cancellous screw fixation.
MATERIALS AND METHODS
Identical vertical osteotomies (17.5 mm) were made from the medial border of the medial malleolus using a custom jig in 20 left 4th-generation composite synthetic distal tibiae (Sawbones, Pacific Research Labs; Model No. 3401) to simulate an Orthopaedic Trauma Association type 44-A2.3 fracture. The tibiae were then cut 18 cm from the tibial plafond and randomized to 2 fixation groups (n = 10 specimens for each group): parallel unicortical screw fixation or parallel unicortical headless compression screw fixation (Figures 1A-1D). Custom polymethylmethacrylate jigs were used to reproducibly drill identical holes with a 3.2-mm drill for the parallel unicortical screw construct and the drill bits provided by the Acutrak 2 Headless Compression Screw System (Acumed). The parallel unicortical screw construct consisted of 2 parallel 4.0-mm-diameter, 40-mm partially threaded cancellous screws (Depuy Synthes), and the headless compression fixation construct consisted of 2 parallel 4.7-mm-diameter, 45-mm titanium Acutrak 2 screws parallel to each other in the transverse plane. The Acutrak screws were placed per manufacturer instructions by first drilling with the Acutrak 2-4.7 Long Drill bit (Acumed), followed by the Acutrak 2-4.7 Profile Drill bit for the near cortex.
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