Thurs., 10/14/10 Basic Science, Paper #32, 4:05 pm OTA-2010
Immediate Weight Bearing after Fixation of Humeral Shaft Fractures with Small-Fragment Hybrid Plating: A Clinical and Biomechanical Study
Lisa K. Cannada, MD1; J. Tracy Watson, MD1; Courtney B. Farnhorst, BA2;
Sean Owen, MD1; James Bucheit, MS2; J. Gary Bledsoe, PhD 2;
1St. Louis University Hospital, St. Louis, Missouri, USA;
2St. Louis University Medical School, St. Louis, Missouri, USA
Purpose: For polytrauma patients with humeral shaft fractures, weight bearing on the upper extremity is advantageous to assist with mobilization and rehabilitation. Previous studies evaluated weight bearing after humerus fixation with nonlocking large-fragment and small-fragment locking plates. We sought to correlate a biomechanical study with a clinical series of humeral shaft fractures in multiple trauma patients. All patients were treated with small-fragment low-contact dynamic compression combination plates (LCP) in hybrid mode. Immediate weight bearing on the involved extremity was allowed.
Methods: Mechanical testing was performed on 16 fourth-generation humeral Sawbones. Initial axial and torsional stiffness was determined for each specimen. A 3.5-mm locking compression plate or a 4.5-mm nonlocking compression plate was applied on each specimen. Each sample then had a 5-mm segment removed. Specimens were then cyclically loaded to –333 N and 1.0 N-m for 90,000 cycles to simulate 90 days of crutch usage. Samples then underwent load to failure. Failure was defined as bone fracture, screw cutout, gap closure, or axial rotation >13°. Statistical analysis was performed using analysis of variance (P < 0.05.) We retrospectively reviewed all patients with lower extremity, pelvic, and/or acetabular trauma with an associated humeral shaft fracture treated with a 3.5-mm small-fragment LCP plate configured in hybrid mode. To be included in the study group, the patients were required to have initiated immediate weight bearing on the extremity. Clinical and radiographic follow-up was completed.
Results: The 3.5-mm plate specimens had average axial stiffness of 980.56 ± 143.10 N with an initial unplated average axial stiffness of 1938.51 ± 386.79 N. The 4.5-mm plated specimens had an average axial stiffness of 1220.37 ± 276.02 N with an initial unplated average stiffness of 1829.90 ± 628.97 N. Torsional stiffness for the 3.5-mm and 4.5-mm constructs was 1.53 ± 0.19 N-m and 2.04 ± 0.40 N-m, respectively. Failure loads for 3.5-mm plates averaged 1870 N and 4.5-mm plates averaged 2366 N. The 3.5-mm plated bones failed due to incidental torsion during axial loading, whereas 4.5-mm constructs all failed as a result of gap closure. Clinical evaluation revealed 13 patients with an average age of 36 years (range, 15-65). There were 5 OTA 12-A, 5 12-B, and 3 12-C fracture types. All fractures were treated with at least an 8-hole 3.5-mm plate. There was 1 nonunion requiring revision at 6 months that healed. There were no failures of fixation.
Conclusion: Successful fracture fixation requires matching the correct plate to fit the bone. Humeral fixation has classically required a 4.5-mm broad LCP. Biomechanical comparison by analysis of variance reveals a significant difference between the average axial stiffness and torsional stiffness of 4.5-mm compression plates versus 3.5-mm locking compression plates. These results followed expectations due to differences in plate dimensions. However, 3.5-mm plates provided 92% of the axial stiffness and 75% of the torsional stiffness of 4.5-mm plates. Failure loads and mode of failure were significantly different between plates. No construct failed by bone fracture or screw cutout, and cyclic loading was not a contributing factor. Our model includes a significant fracture gap, which required the plate to carry the entire load, and is the worst-case scenario for constructs in a clinical setting. While the plates performed differently, both appear to support loads that are anticipated in the clinical setting. This was confirmed, as no hardware failures occurred in our patients stabilized with 3.5-mm hybrid plating techniques who were allowed immediate weight bearing. This study supports the use of small-fragment plates for humeral shaft fractures if anatomically appropriate. Immediate loading can be initiated without fear of construct failure.
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• The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an “off label” use). ◆FDA information not available at time of printing. Δ OTA Grant.