Oblique axial MR imaging of the normal anterior cruciate ligament bundles

Abstract

The anterior cruciate ligament (ACL) is composed of the anteromedial and posterolateral bundles [1, 2]. Although these two bundles are closely aligned anatomically, they do have distinct biomechanical functions with the anteromedial bundle stabilizing the knee in flexion and the posterolateral bundle stabilizing the knee in extension [1–5]. Most ACL tears are complete with the tear extending across both bundles. Partial tears of the ACL are less frequently encountered and may involve both bundles to a similar degree or one bundle predominantly. Although complete ACL tears do not have the capacity to heal, a limited blood supply to the ACL via the medial geniculate artery does allow healing of partial tears [6, 7]. Correct assessment regarding the presence, severity, and location of partial tears is relevant since delayed recognition of a partial tear can result in progression to complete tear [6]. Also, if only one bundle is predominantly torn, isolated single bundle reconstruction rather than full ACL graft reconstruction may be undertaken [8, 9]. Early evaluation of partial ACL tears could possibly improve clinical and surgical management [10]. A prerequisite to diagnosing ACL bundle injury on MR imaging is clear delineation of both bundles and awareness of their normal appearance. Orthogonal planes can delineate the normal ACL bundle structure in only 42% of knees [11]. In this study, we describe a new oblique axial plane for imaging the normal ACL bundles on MR imaging; evaluate how well the normal ACL bundles can be evaluated on this plane compared to the standard sagittal, coronal, and axial planes [12–15]; and describe the normal MR appearances.