Bone Bruises: Do They Go Away?
Abstract & Commentary
Synopsis: Patients with MRI-confirmed bone bruises associated with ACL tears were re-evaluated with repeat MRI 2-5 years after their original injury. Most nonfocal bone bruises completely resolved; however, focal lesions (type III lesions) were still present on follow-up scans.
Source: Costa-Paz, M. Magnetic resonance imaging follow-up study of bone bruises associated with anterior cruciate ligament ruptures. Arthroscopy. 2001;17(5):445-449.
Bone bruises, or trabecular microfractures, are highly associated with ACL injuries and are said to be present in about two-thirds to three-quarters of MRIs in patients with acute ACL tears. They were originally described and classified by Vellet and associates in 1991.1 They recognized the importance of characterizing the bruises as either focal (geographic) or diffuse. The present study by Costa-Paz and associates highlights this important point. A cohort of 21 patients with isolated ACL injuries with MRI-detected bone bruises and no cartilaginous injury at the time of arthroscopy were studied. MRIs were repeated 24-64 months (average, 34) following the original injury and compared with the original MRI. Bone bruises were characterized as diffuse (type I), focal (type II), or with associated disruption or depression of the normal contour of the cortical surface (type III). On follow-up MRI, all type I lesions and 10/11 type II lesions completely resolved. However, all 5 patients with type III lesions had ". . .evidence of persistent abnormality on MRI scans. . ." The clinical outcome of the ACL reconstruction had no correlation with the type of bone bruise or the results of the follow-up MRIs. Costa-Paz et al conclude: "Although long-term clinical implications of these findings are uncertain, a severe occult osteochondral lesion sustained at the time of ACL rupture seems to be persistent on MRI, even after a successful outcome."
Comment by Mark D. Miller, MD
Although this study is limited by the relatively small number of patients evaluated (21 patients and only 5 with type III bone bruises), it does provide some helpful information. The bone bruise is the result of an impaction injury involving the middle third of the lateral femoral condyle on the back of the tibia. When the ACL tears, the knee actually subluxes or dislocates anteriorly and, much like a Hill-Sach lesion in the shoulder, has an impaction injury. Johnson and colleagues have shown us that focal bone bruises are severe and result in local chondrocyte death!2 Fortunately, nonfocal, diffuse bone bruises do not have adverse outcomes. In fact, in a study published 3 years ago, we noted that these lesions completely resolved as a result of gradual diffusion over a period of 2-4 months.3 What is interesting, and certainly merits additional study, is the type III bone bruise. Perhaps this is a sentinel lesion and may represent a knee that is at risk for adverse sequelae down the line. Only additional study and research will provide this answer.
References
1. Vellet AD, et al. Occult post-traumatic osteochondral lesions of the knee: Prevalence, classification and short-term sequelae evaluated with MR imaging. Radiology. 1991;178:271-276.
2. Johnson DL, et al. Articular cartilage changes seen with magnetic resonance imaging-detected bone bruise associated with acute anterior cruciate ligament rupture. Am J Sports Med. 1998;26:409-414.
3. Miller MD, et al. The natural history of bone bruises. A prospective study of magnetic resonance imaging-detected trabecular microfractures in patients with isolated medial collateral ligament injuries. Am J Sports Med. 1998;26:15-19.
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