Time to Return to Running After Tibial Stress Fracture in Female Division I Collegiate Track and Field

Marissa Jamieson, MD; Allison Schroeder, MD; Jason Campbell, BS; Courtney Seigel, MS, ATC; Sonsecharae Everson, ATC, MS; Timothy L. Miller, MD


Curr Orthop Pract. 2017;28(4):393-397. 

In This Article


The K-M classification system was designed with the goal of producing a system that is easily reproducible and clinically relevant and, thus, in combination with injury location, can help guide treatment and prognosis.[7] The unique aspect of this classification system is that it takes into account symptomatology and allows the use of any imaging modality. Previous classification systems are limited by the fact that that they require MRI, which is not easily accessible for all athletes. No previous studies have looked at the relationship between the injury severity grade on the K-M system and time to return to sport.

Although the relationship between time to return to sport and K-M classification was not significant, there was a positive correlation between these two variables, indicating that a higher K-M grade correlates with a longer time to recovery. The average time to return to running for the grade V injuries was 4–5 wk longer than the grades II and III injuries.

A study by Beck et al.[9] reported similar findings. They compared radiographs, bone scans, CT, and MRI grades of tibial stress injuries to clinical severity and length of recovery and found no significant relationship between time to healing and imaging grade, although a positive trend existed for MRI. They used a system devised by Fredericson et al.[10] to determine MRI grade which uses periosteal and marrow edema and the presence of a fracture line to differentiate between grades. The K-M classification differs from Fredericson because higher-grade stress injuries are further separated into groups based on displacement of the fracture and nonunion, which is not included in any of the classification systems used in other studies.

Nattiv et al.[11] performed a 5-year prospective evaluation of stress fractures in collegiate track and field athletes. They had a larger cohort with 61 injuries in 34 athletes; however, they included all locations and not just the tibia. Based on the MRI system from Fredericson et al.[10] they found that higher MRI grade as well as lower bone mineral density were associated with a significant delayed recovery of bone stress injuries in track and field athletes. Additionally, they found that skeletal sites of predominant trabecular bone structures, sacrum, pubic bone, and femoral neck all had a significantly delayed recovery.

A similar study by Arendt et al.[3] also demonstrated a significant correlation between imaging grade of stress injury and return to full activity. Their cohort included 74 collegiate athletes from various sports, with the tibia being the most common site of injury. Their grading system included both radiographs and MRI and, similar to the system by Fredericson et al.,[10] the highest grade was differentiated from lower grades by the presence of a fracture line, and displacement was not taken into account.

Several aspects of our study could help explain the nonsignificant findings. First, none of the athletes in our study had an injury classified as a grade IV, indicating a displaced fracture, and there were only two grade V injuries, nonunions. With the majority being grades II and III injuries, either no fracture line or nondisplaced fracture, it may be difficult to detect differences in recovery time between these groups. Additionally, when a fracture line is identified (grade III), the injury is typically treated more aggressively with protected weightbearing, immobilization, and complete rest. This, in turn, may lead to near equal recovery times to grade II fractures, which are treated with relative rest and less likely with protected limited weightbearing.

Kijowski et al.[12] performed a study to validate Fredericson et al.'s[10] MRI classification system. They retrospectively reviewed 142 tibial stress injuries and found that grades 2, 3, and 4a had similar degrees of periosteal and bone marrow edema with no significant difference in return to play. Only grade 4b injuries, linear areas of intracortical signal abnormality, had a significantly increased time to recovery. They concluded that grades 2, 3, and 4a could be combined into a single category in an abbreviated Fredericson classification system. The K-M classification system accomplishes this by combining injuries without a fracture line into grade II. Based on this study and previous studies, a higher K-M grade would be expected to have longer times to recovery. If our study had a larger number of grades IV and V injuries, our data may have shown a significant difference in recovery time.

BMI and time to recovery also were evaluated independent of K-M grade. There was no statistically significant relationship between BMI and time to return to sport, but our data did show an inverse relationship between these two variables, implying that the athletes with a larger BMI actually may heal from their injuries more quickly compared to those who have a lower BMI. The lack of statistical significance may be attributed to the fact that BMI is relatively homogenous at the lower end of the normal spectrum in this population of elite young female athletes. Previous studies have shown that a lower BMI is a significant risk factor for stress fractures in female runners,[4,5,13,14] especially in the context of the female athlete triad, but none have evaluated the relationship of BMI with return to sport. A lower BMI in athletes may be indicative of poor nutritional status, which could account for longer recovery time.

The main weakness of our study is its limited sample size. Further studies with larger numbers are needed to elucidate the relationship between the K-M grading system and expected time to return to running after tibial stress fracture in female track and field athletes. Although this study focused only on tibial stress injuries in female athletes to eliminate multiple variables, future studies could incorporate stress injuries of variable locations into the analysis.

Previous literature has shown that it is difficult to predict which athletes will develop stress fractures or stress reactions and who will recover expeditiously. The overall goal of treatment in these athletes is to return them to their sport as quickly and safely as possible and to prevent future injuries. A standardized classification system with prognostic value for return to sport affects management of these injuries and may give athletes, coaches, and teams a more appropriate expectation of time away from sport. Data from this study suggest that higher K-M grade injuries correlate with longer time to recovery, but larger studies are needed to determine if this relationship is significant.