Magnetic resonance imaging of bone bruising in the acutely injured knee--short-term outcome.

AIM: To investigate the short-term outcome and associated injuries of bone bruising in the acutely injured knee.

METHOD AND MATERIALS: Thirty patients (age range 17-39 years, mean 28 years) with bone bruising identified on magnetic resonance imaging (MRI) after an acute knee injury were rescanned 12-14 weeks post-injury. The volume of bone bruising was measured on coronal STIR (short TI inversion recovery) images and correlation made with the presence and type of ligamentous and osteochondral injuries.

RESULTS: All bone bruises were present on repeat MRI. Twenty of the 30 patients (67%) had associated anterior cruciate ligament (ACL) injuries, seven of the 30 (23%) had collateral ligament injuries and three of the 30 (10%) had no associated ligamentous injuries. Greater than 50% reduction in bone bruise volume was demonstrated at repeat scanning in 24 of the 30 patients (80%) and less than 50% in five of the 30 patients (17%). One patient showed an increase in volume of bone bruising at follow-up. There was no correlation between initial size or size reduction of bone bruising and the presence/absence or type of associated injuries. In 21 patients the bone bruises resolved from the periphery, whilst eight patients showed bone bruises that resolved towards the joint margin, all of whom had associated osteochondral injuries. Of the 30 patients, 17 showed bone bruising that extended to the joint margin, 10 of whom had associated osteochondral injuries on MRI. On clinical review some degree of knee pain was still present in all but one of the patients reviewed. The single patient who reported complete resolution of symptoms was one of the three patients with isolated bone bruising.

CONCLUSION: Bone bruises persist for at least 12-14 weeks, which is longer than previously quoted. Two discrete patterns of bone bruise resolution have been demonstrated. The size and persistence of bone bruising is not related to the presence or absence or type of associated ligamentous injuries.