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Fixation Constructs for Thumb Ulnar Collateral Ligament Avulsion Fractures: A Biomechanical Study
Emily Shin, MD1; Matthew Drake, MD1; Brent Parks, MD2; Kenneth R. Means, MD3
1Walter Reed National Military Medical Center, Bethesda, MD; 2Curtis National Hand Center, Baltimore, MD; 3Curtis Hand Center, Union Memorial Hospital, Baltimore, MD

Background: Thumb UCL fracture avulsions are often treated operatively in the active population. Fixation of thumb UCL fracture avulsions or reconstituting the UCL in such injuries has been shown to have more predictable results than nonoperative treatment 1. The purpose of this study was to determine if hook plate construct described by Kang et al2 for fixation of thumb ulnar collateral ligament fracture avulsion injuries (Figure 1) is at least as biomechanically strong of a construct as a suture anchor with two drill holes.
Methods: The thumb UCL was exposed via a standard approach in 7 matched pairs of cadaver hands. An osteotomy was made parallel to the shaft of the proximal phalanx along the entire insertion of the UCL. The osteotomy was fixed with either suture anchor (Mini Biocoposite SutureTak with 2-0 FiberWire, Arthrex) through two drill holes in the avulsion fragment and tied, or hook plate (1.5 mm titanium plate/screws, Synthes) construct. Specimens were then mounted on an MTS device (Figure 2), and loaded to failure. Measurement of movement across the construct was accomplished by a 3 mm differential variable reluctance transducer device (Microstrain), which was implanted to detect movement perpendicular to the fracture. Differences in load to failure and construct stiffness were compared and analyzed using a t-test.
Results: The hook plate construct failed at significantly higher loads than suture fixation. There were no differences in load to failure of the unfixed specimens. Load to failure in the hook plate construct 57.9 N (20.2 N) compared to 27 N (18.6 N) in the suture anchor construct (P0.006). The difference in construct stiffness was 48.8 N/mm (17.3 N/mm) compared to 6.6 N/mm (12.7 N/mm) (P0.000). The mechanism of failure for the hook plate group was screw pullout or bending versus anchor pullout in the suture anchor group.
Conclusions: Based on this model, the hook plate construct for fixation of thumb metacarpophalangeal joint ulnar collateral ligament fracture avulsions is biomechanically superior to the suture anchor construct. The lack of cortical apposition for the suture anchor and its placement into softer metaphyseal bone appears to contribute to suture anchor pullout and this construct should be used with caution when applied to this clinical situation.
1. Dinowitz et al. Failure of cast immobilization for thumb ulnar collateral ligament avulsion fractures. YJHSU. 1997;22(6):10571063.
2. Kang et al. The Hook Plate Technique for Fixation of Phalangeal Avulsion Fractures. J Bone Joint Surg Am. 2012;94(11).

Figure 1

Figure 2

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