Acute ankle sprain is a common injury seen by both orthopaedic surgeons and primary care physicians. The treatment of an acute ankle sprain is relatively well established, and most patients recover within three to twelve weeks after the injury. Patients who do not recover may develop chronic ankle instability, peroneal tendon pathology, anterior ankle impingement, and symptomatic osteochondral lesions of the talus1-3. Even patients who recover may develop any of these same conditions after a symptom-free interval. Therefore, an ankle sprain can have a profound impact on both the patient and society, both in the acute setting and at a later date.
The medical community has not developed an understanding of ankle sprain prevention strategies that matches its knowledge of treatment strategies. Robust prevention strategies could reduce the patient's pain and dysfunction, economic losses to the patient due to reduced work capacity, and productivity losses to society.
The development of prevention strategies requires quantifying the societal magnitude of the injury with sound epidemiological techniques. With or without the Health Insurance Portability and Accountability Act, the great concern for privacy in the United States confounds attempts to develop databases and registries of disease and injury that could enable robust epidemiological studies.
The authors of "The Epidemiology of Ankle Sprains in the United States" deserve commendation for their creativity, insight, and diligence in developing and presenting their study. They used the United States Consumer Product Safety Commission's National Electronic Injury Surveillance System (NEISS) for the database from which they sampled injury incidence data. The database itself samples the population by receiving injury data submitted by 100 hospitals in the United States. NEISS stratifies the hospitals into five groups on the basis of hospital size and whether the facility is a pediatric specialty hospital. NEISS assigns statistical weights to each of the strata that represent the proportion of all hospitals in the United States represented by a given stratum. The authors then calculated population incidences with the sample incidences from NEISS, the NEISS weights, and United States Census Bureau data. The authors calculated population subgroup incidences by age, sex, race, physical location of the injury event, the activity at the time of injury, and the sport being played if the injury occurred during athletic activity. Incidence rate ratios, resembling odds ratios, were calculated within each subgroup from the subgroup incidences.
Five principal findings emerged from the results of their methods. First, the incidence of ankle sprains that presented to a hospital emergency department in the United States between 2002 and 2006 was 2.15 per 1000 person-years. Second, more than half (53.5%) of these sprains occurred in individuals between the ages of ten and twenty-four years. Third, black males had the highest incidence rate ratio of any race-sex subgroup. Fourth, males had a higher incidence of ankle sprain than females among individuals younger than twenty-four, but females had a higher incidence among individuals older than thirty. Fifth, among athletic activities, approximately 40% of ankle sprains occurred while the individuals were playing basketball.
The authors acknowledge that an overall incidence of 2.15 per 1000 person-years is lower than previous reports. However, the reader must keep in mind that the database records only the individuals who present to an emergency room and not those who present in other ambulatory settings. Given that only about one-third of individuals ultimately diagnosed with an ankle sprain present to an emergency room, the authors’ results are consistent with prior reports of an incidence between five and seven per 1000 person-years4. The skewed distribution of ankle sprains toward younger patients is not surprising, but it is important in directing efforts toward prevention. Reducing the incidence of ankle sprain among young individuals will reduce the incidence of chronic complications of ankle sprain during their later, economically productive years.
The high risk ratio for ankle sprain among black males is a curious finding that begs for additional study. Identifying the factors responsible for this elevated risk may guide efforts to reduce this disparity. A similar investigation would be useful to explain the increased risk of ankle sprains among women more than thirty years old, which were more likely to occur in the home. Many women in this age group have had children, and they may be predisposed to an increased risk of ankle sprain because of the ligament-relaxing effects of progesterone during pregnancy. Also, it is probably safe to assume that we have all had more than one mother in our practices who sprained her ankle tripping over one of the children's toys!
It is not surprising that basketball is by far the most common sport played by those who have sprained their ankle, and this might be one of the best opportunities for injury prevention intervention. Court surfaces, shoe wear, and the technical skills of the players all contribute to the risk of ankle sprain while playing basketball. Whether bracing or neuromuscular education reduce the risk of ankle sprain remains unclear, and the authors open the door to clarification of the role of bracing, neuromuscular education, and sport-specific training in preventing a subset of ankle sprains. The authors developed a robust model with rigorous epidemiological and statistical techniques, but they acknowledge the weaknesses in their study from the database. First, the true incidence of ankle sprain in the United States is underreported in the database. However, their result is consistent with prior reports when corrected for the reported likelihood of presenting to an emergency department with an ankle sprain. Second, injuries that are not truly ankle sprains may be erroneously reported as such to the database. The authors’ reported confidence intervals seem to account for this type of error. Finally, approximately one-fourth of the racial data is missing, which could confound the significant differences in incidence rate ratios. Only a better database can reduce statistical error. Nevertheless, the study presents useful, reliable information to guide further study of acute ankle sprain, and enhance injury prevention efforts.