In this MRI-based study of moderate and severe ankle sprains, bone bruises were observed in as many as 81.4% of patients. The bruises were widespread, often on weight-bearing areas as well as the midfoot. Low-intensity findings on T1-weighted imaging and high-intensity findings on T2-weighted imaging usually imply bone marrow edema or hemorrhage. These results are not specific to bone fractures, although Yao and Lee have described that occult or microfractures can be detected on T2-weighted imaging . Karthiga et al. reported that MRI was helpful to identify bone marrow edema as a sign of recent fracture at the injury site . Guermazi et al. recently reviewed that MRI signal changes (i.e., bone bruises) in joints sometimes suggested a microfracture, which could be a cause of OA . In this study, bone bruises were frequently observed, and might be similar to the microfractures witnessed in OA.
Pure ligament injuries do not usually cause joint pain by weight bearing if rigid fixation of the ankle, such as casting, is performed properly. In this study, 38 of 70 patients (54.0%) complained of ankle joint pain at weight bearing even following external solid fixation. Univariate analysis revealed a significant association between bone bruises of the talocrural joint surface and use of the crutches after fixation (P = 0.041). Furthermore, multiple regression analysis uncovered that the OR (95% CI) of having bone bruises of the talocrural joint of the talus in relation to the use of the crutches was 3.03 (1.03–8.94). Therefore, in the treatment of ankle sprain, if the patient complains of joint pain even after solid fixation, it may be necessary to avoid weight bearing by means of crutches to ensure bone damage recovery. Furman et al. reported that post-traumatic arthritis (PTA) was one of the most frequent causes of ankle joint OA in America and suggested the major mechanism in PTA development to be cartilage fracture . In the present study, bone bruises of the weight-bearing surface of the talus were significantly associated with crutch use due to pain during weight bearing (P = 0.041). Although it is not possible to judge cartilage damage using MRI, it is feasible that micro-fractures of joint surfaces have cartilage fractures. Therefore, crutches may be advised to prevent PTA in patients with pain at weight bearing even after solid fixation of the ankle.
Various fixation periods have been proposed for the external fixation of ankle sprains, ranging from short- to long-term. A short period of immobilization was shown to be advantageous even for severe ankle sprains [20, 21]. A meta-analysis by Kerkhoffs et al. found that functional treatment appeared to be a favorable strategy for treating acute ankle sprains when compared with long-term immobilization . Conversely, other reports described that fixation of over 6 weeks was needed for proper ligament healing [23, 24, 25], and Hubbard and Cordova observed that ankle laxity did not significantly decrease during 8 weeks . Such evidence indicated the need for more stringent and long-term immobilization for ligament healing and restoration of joint stability after an ankle sprain. In this study, the period of external fixation required to reduce pain varied from 8 days to 72 days (average: 29.5 days). Considering the wide range in degrees of bone and ligament damage, a large variation in the fixation period is expected. As this period should be adjusted depending on the case, recommending a strictly set fixation period may be suboptimal.
The current study revealed that the incidence of bone bruises detected by MRI in the midfoot associated with ankle sprain was 34.3%. Since MRI could not evaluate ligament damage in the midfoot, we considered that damage to the midfoot may have been more prevalent if ligament damage was assessed and included. Lohrer et al. suggested that midtarsal sprains should be treated differently to ankle sprains, with more aggressive and longer immobilization . Although various external fixation methods have been proposed for ankle sprains, fixing the midfoot is often overlooked. Fixation is often performed by limiting the range of immobilization to the ankle joint, restricting the lateral movement of the ankle joint, and preserving some ankle dorsiflexion and plantarflexion. In moderate or severe cases of ankle sprain, external fixation for not only the ankle, but also the midfoot, should be performed in consideration of the possibility of midfoot injury.
Lastly, as 57 of 70 patients (81.4%) in our cohort had bone bruises around the ankle joint, examination using MRI might be helpful for more accurate evaluation of ankle joint sprains. From the viewpoint of treatment, however, it appears important to presume the presence of both bone bruise and ligament injury in the ankle and midfoot and perform detailed visual inspection and palpation to pinpoint the area of the injured site. The affected area should then be fixed for an appropriate period. If pain develops with walking after fixation, crutches should be provided to reduce weight-bearing stress. Ultimately, MRI may not be necessary if such a treatment course is followed.