ABSTRACT
PURPOSE: Previous studies evaluating weight bearing of distal radius fractures treated through dorsal spanning bridge plates used extra-articular fracture models, and have not evaluated the role of supplementary fixation. We hypothesized that supplementary fixation with a spanning dorsal bridge plate for an intra-articular wrist fracture would decrease the displacement of individual articular pieces with cyclic axial loading and allow for walker or crutch weight bearing. METHODS: Thirty cadaveric forearms were matched into 3 cohorts, controlling for age, sex, and bone mineral density. An intra-articular fracture model was fixed with the following 3 techniques: (1) cohort A with a dorsal bridge plate, (2) cohort B with a dorsal bridge plate and two 1.6-mm k-wires, and (3) cohort C with a dorsal bridge plate and a radial pin plate. Specimens were axially loaded cyclically with escalating weights consistent with walker and crutch weight-bearing with failure defined as 2-mm displacement. RESULTS: No specimens failed at 2- or 5-kg weights, but cohort A had significantly more displacement at these weights compared with cohort B. Cohort A had significantly more failure than cohort C. Both cohort A and cohort B had significantly more displacement at crutch weight bearing compared with cohort C. The supplementary fixation group had significantly lower displacement at crutch weight-bearing compared with cohort A in all gaps. Survival curves demonstrated the fixation cohort to survive higher loads than the nonfixation group. CONCLUSION: There was significantly less displacement and less failure of intra-articular distal radius fractures treated with a spanning dorsal bridge plate and supplementary fixation. Our model showed that either type of fixation was superior to the nonfixation group. CLINICAL SIGNIFICANCE: When considering early weight-bearing for intra-articular distal radius fractures treated with a spanning dorsal bridge plate, supplementary fixation may be considered as an augmentation to prevent fracture displacement.
ABSTRACT
BACKGROUND: Aseptic tibial loosening following primary total knee arthroplasty persists despite technique and device-related advancements. The mechanisms for this mode of failure are not well understood. We hypothesized that knee movement while the cement was curing dispersed lipids at the implant-cement interface and would result in decreased tibial fixation strength. METHODS: A cadaveric study was performed utilizing 32 torso-to-toe specimens (64 knees). Four contemporary total knee arthroplasty designs were evaluated. Each implant design was randomly assigned to a cadaveric specimen pair with side-to-side randomization. Specimen densitometry was recorded. Each tibial implant was cemented using a standard technique. On one side, the tibial component was held without motion following impaction until complete cement polymerization. The contralateral knee tibial implant was taken through gentle range of motion and stability assessment 7 minutes after cement mixing. Axial tibial pull-out strength and interface failure examination was performed on each specimen. RESULTS: The average pull-out strength for the no motion cohort (5,462 N) exceeded the motion cohort (4,473 N) (P = .001). The mean pull-out strength between implant designs in the no motion cohort varied significantly (implant A: 7,230 N, B: 5,806 N, C: 5,325 N, D 3,486 N; P = .007). Similarly, the motion cohort inter-implant variance was significant (P ≤ .001). Intra-implant pull-out strength was significantly higher in implant A than D. The average pull-out strength was significantly lower in specimens that failed at the implant-cement interface vs bone failures (4,089 ± 2,158 N vs 5,960 ± 2,010 N, P < .0025). CONCLUSION: Knee motion during cement polymerization is associated with significant decreases in tibial implant fixational strength. Reduction in implant pull-out strength was identified with each implant design with motion and varied between designs. Across all tested designs, we recommend limiting motion while cementing the tibial implant to improve fixation strength.
