Session V - Knee / Tibia

Fri., 10/11/13 Knee/Tibia, PAPER #65, 3:27 pm OTA 2013

What Is a “Critical Bone Defect” in Open Tibia Shaft Fractures Definitively Treated With an Intramedullary Nail?

Nikkole Haines, MD; William Lack, MD; Rachel Seymour, PhD; Michael J. Bosse, MD;
Carolinas Medical Center, Charlotte, North Carolina, USA

Background/Purpose: Tibia fractures are the most common long bone fractures representing 2% of all fractures with 12% to 23.5% open injuries, making them the most common open long bone injuries. When focusing on patients treated with intramedullary nailing (IMN), reported nonunion rates range from 3.4% to 18%. Currently, some treatments approaches include early, staged intervention for “critical bone defects”. It is unclear when these staged treatments are indicated as the literature has yet to define the minimum threshold for bone loss requiring surgical intervention. This study aims to better define a “critical bone defect” based on clinical outcomes of union versus nonunion.

Methods: 180 patients age 18 to 65 years with open tibia diaphyseal fractures definitively treated with IMN from January 1, 2007to June 30, 2012 were retrospectively identified. 35 patients had 1 to 5 cm of bone loss on ≥50% of the cortices, at the time of definitive fixation, with a recorded outcome or at least 6 months of follow-up. Factors analyzed included: defect size, time to surgery, Gustilo-Anderson classification, number of procedures, use of additional fixation or biologic agents, deep infection requiring surgical intervention, presence of impaired vascular status, malignancy, diabetes, simultaneous injuries, autoimmune disease or immunosuppression, and total number of comorbidities. Average defect size measurements were calculated from cortical gap between bone fragments on standard AP and lateral radiographs. Analysis used a multivariate regression model to identify factors contributing to nonunion.

Results: Overall 50 of 180 patients with open tibial shaft fractures treated with IMN had defects of 1 to 5 cm on ≥50% of the cortices. 15 patients with qualifying defects were lost to follow-up. Patients achieving union averaged a defect size of 1.9 ± 0.5 cm/cortex, while those with nonunion averaged 3.0 ± 1.1 cm/cortex (P <0.01). No other covariates predicted healing outcomes. To further elucidate the definition of a critical bone defect, patients were group by bone defect size. Comparing patients with average cortical defects of 1 to 3 versus ≥3 cm revealed union rates of 61.5% and 0%, respectively (P = 0.018). Receiver operating characteristic curve analysis produced an area under the curve of 0.80, defining a 3-cm average defect as a good prognostic threshold for predicting union without intervention (P = 0.0001).

Conclusion: Determining initial injury factors that predict patient outcomes provide surgeons useful information for operative planning. Knowing the chances a patient will likely go on to nonunion at the time of initial fixation provides an opportunity to set both patient and surgeon treatment expectations. This study demonstrates that patients with a 1 to 3-cm average cortical defect have a high probability of achieving union. In patients with an average defect of ≥3 cm, nonunion was universal, thus increasing the value of early planned intervention. Diaphyseal bone grafting research addressing clinically significant differences should employ a conservative threshold for a “critical bone defect.” An average cortical defect of ≥3 cm appears to be a reasonable threshold defect size. Limitations of this study include the retrospective nature and small cohort size. Further studies, including multicenter retrospective and prospective observational studies, are necessary to further characterize critical bone defects.

Alphabetical Disclosure Listing

• 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.