Supplementary Fixation Improves Stability of Intra-Articular Distal Radius Fractures Managed With a Spanning Plate.

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.

Chitranjan S. Ranawat Award: Motion During Total Knee Cementing Significantly Decreases Tibial Implant Fixation Strength.

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.

Posterior Glenoid Osteotomy With Capsulolabral Repair Improves Resistance Forces in a Critical Glenoid Bone Loss Model.

Background: There is no widespread consensus on the surgical treatment of posterior shoulder instability with critical posterior glenoid bone loss. Hypothesis: That opening posterior glenoid wedge osteotomy with soft tissue repair would improve the resistance forces of instability when compared with soft tissue repair alone in the setting of 20% critical bone lose. Study Design: Controlled laboratory study. Methods: Native glenoid retroversion was measured on 9 shoulders using computed tomography (CT) scans. The humerus was potted in 90° of forward flexion and 30° of internal rotation relative to the scapula, and a posterior dislocation was performed to create a posterior capsulolabral injury model. The specimens were each taken through a fixed sequence of testing: (1) posteroinferior capsulolabral tear, (2) no glenoid bone loss with posteroinferior capsulolabral repair, (3) 20% posterior glenoid bone loss with posteroinferior capsulolabral repair, and (4) 20% glenoid bone loss with posterior glenoid opening wedge osteotomy and posteroinferior capsulolabral repair. Bone loss was created using a sagittal saw. The resultant peak forces with 1 cm of posterior translation were measured. A 1-way repeated-measures analysis of variance was used to compare mean force values. Results: After the initial dislocation event, all shoulders had a resultant posterior capsulolabral injury. The resulting labral injury was extended from 6- to 9-o'clock in all specimens to homogenize the extent of injury. Repairing the capsulolabral complex in the 20% posterior glenoid bone loss group did not result in a statistically significant increase in resistance force compared with the labral deficient group (34.1 vs 22.2 N; P = .068). When 20% posterior bone loss was created, the posterior glenoid osteotomy with capsulolabral repair was significantly stronger (43.8 N) than the posterior repair alone both with (34.1 N) and without (31.8 N) bone loss (P = .008 and .045, respectively). Conclusion: In the setting of critical posterior glenoid bone loss, an opening wedge posterior glenoid osteotomy with capsulolabral repair improved resistance to posterior humeral translation significantly compared with capsulolabral repair alone. Clinical Relevance: The results of this biomechanical cadaveric study may aid in surgical planning for this complex patient population.

Supination Adduction Vertical Medial Malleolar Fracture Fixation with Buttress Plating vs a Novel Screw-Only Construct: A Cadaveric Biomechanical Study.

BACKGROUND: Supination adduction ankle fractures are unique among rotational ankle fractures as plate constructs are more commonly used than independent screws for medial malleolar fixation. The purpose of this study was to compare fracture displacement between plate fixation to a novel screw-only construct using a cadaveric biomechanical early-weightbearing model for the treatment of vertical medial malleolus fractures. METHODS: Six nonosteoporotic fresh-frozen cadaver shanks and feet in matched pairs underwent a vertical osteotomy of the medial malleolus to simulate the supination adduction type injury. Osteoporosis was measured using DEXA scans. One specimen from each pair was fixed with a one-third tubular buttress plate and the other with screw-only fixation. The specimens were then axially loaded for 100 000 cycles to simulate protected weightbearing, and subsequently loaded to failure in supination. Stiffness, fracture displacement, and load to failure were recorded. Statistical significance was set at P <.05. RESULTS: There were no measurable differences in displacement between the 2 constructs during axial cyclic loading after 100 000 cycles (plate, 0.74 ± 0.09 mm; screws, 0.79 ± 0.18 mm; P = .225). During supination and axial load to failure, the plate outperformed the screw construct. For load to failure (2 mm displacement) at the fracture site, the plate group failed at 716 ± 240 N, whereas the screw group failed at 567 ± 237 N (P = .015). During load to catastrophic failure, the plate group outperformed the screw group (plate, 6011 ± 1646 N; screws, 4578 ± 1837 N; P = .002). CONCLUSION: For vertical medial malleolar fractures, the screw-only construct demonstrated no statistical difference when compared to buttress plating for cyclical axial loading, simulating early weightbearing in a boot. However, buttress plating is 21% to 24% stronger than the screw-only fixation construct in overall strength and prevention of catastrophic failure when loading in a supinated position. CLINICAL RELEVANCE: The screw-only construct is biomechanically similar to a buttress plate when simulating early protected weightbearing. This suggests that early weightbearing as tolerated in a controlled ankle motion boot beginning 2 weeks postoperatively is mechanically safe for this fracture pattern and does not result in unacceptable amounts of fracture displacement. This construct may be useful as a less invasive treatment modality for the treatment of vertical medial malleolus fractures in select patients.