Volar plates positioned at, or distal to, the watershed line have been shown to have a higher incidence of attritional rupture of the flexor pollicis longus (FPL). In this study, we aimed to evaluate the effect of wrist extension and volar tilt on the contact between the plate and the FPL tendon in a cadaver model. We hypothesized that, following volar plate application, loss of native volar tilt increases the contact between the FPL and the plate at lower degrees of wrist extension.
A volar locking plate was applied on 6 fresh-frozen cadavers. To determine the contact between the plate and the FPL tendon, both structures were wrapped with copper wire and circuit conductivity was monitored throughout wrist motion. A lateral wrist radiograph was obtained at each circuit closure, indicating tendon-plate contact. Baseline measurements were obtained with plate positioned at Soong grades 0, 1, and 2. An extra-articular osteotomy was made and contact was recorded at various volar tilt angles (+5°, 0°, –5°, –10°, –15°, and –20°) in 3 different plate positions. A blinded observer measured the degree of wrist extension on all lateral radiographs. Data were analyzed using linear mixed-effects regression model.
Plates placed distal to the watershed line had the most contact throughout wrist range of motion. Significantly, less wrist extension was required for contact in wrists with neutral or dorsal tilt and in distally placed volar plates. Volar tilt, wrist extension, and plate position were 3 independent risk factors determining contact between plate and tendon.
Loss of volar tilt, increased wrist extension, and higher Soong grade plate position result in greater contact between wire-wrapped FPL tendon and plate.
The FPL/plate contact chart generated in this study may be used to assess the risk of rupture in the clinical setting.
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Published online: September 16, 2017
Accepted: August 4, 2017
Received: January 10, 2017
This study was funded in part by the American Foundation for Surgery of the Hand, Resident Fast Track Grant.
© 2017 by the American Society for Surgery of the Hand. All rights reserved.
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