2015 ISAKOS Biennial Congress ePoster #1213

Anterior Cruciate Ligament Inclination Angle in Population of Normal Controls and in a Population of Anterior Cruciate Ligament Injured Patients

Jonathan Reid, BA, Minneapolis, MN UNITED STATES
Bret Yonke, MD, Minneapolis, MN UNITED STATES
Marc Tompkins, MD, Minneapolis, MN UNITED STATES

University of Minnesota/TRIA Orthopaedic Center, Minneapolis, MN, USA

FDA Status Not Applicable

Summary: Baseline ACL inclination angle of normal subjects, evaluated by sex and skeletal maturity, and a comparison to ACL injured patients




In anterior cruciate ligament (ACL) reconstruction, there is a renewed emphasis on placing the ACL in an anatomic based position. One method of post-operative evaluation of graft placement is the graft inclination angle. Several studies have been published on the topic, but a consensus does not exist as to the inclination angle of the ACL in the native knee.


The purpose of this study was to evaluate the angle of inclination of the native ACL in both the sagittal and coronal planes, and to compare these findings based on sex and skeletal maturity. A secondary purpose was to evaluate the ACL inclination angle of patients with a history of ACL rupture.

Material And Methods

In the first phase of the study, patients undergoing routine magnetic resonance imaging (MRI) of the knee at our MRI center over the course of 2 weeks who had an intact ACL on MRI, were included. Patients were excluded if they had significant cartilage, meniscal or ligamentous damage. Using established methods, measurements of the angle of inclination were made using MRIs in both the sagittal and coronal planes. Patients were then compared based on sex and skeletal maturity. In the second phase of the study, the inclination angle of intact ACLs in patients with a subsequent history of ACL rupture was compared to the normal ACL inclination angle. These patients were identified through our database of patients that have undergone ACL reconstruction at our institution; any patient with an intact ACL on a pre-ACL tear MRI was included.


In the first phase, 188 patients were included (36 skeletally immature/152 skeletally mature; 97 male/90 female). The overall angle of inclination was 74.28º±4.75º in the coronal plane and 46.88º±4.89º in the sagittal plane. With regard to sex, there was no difference in the angle of inclination in either the coronal (M: 74.15º±4.84º; F: 75.21º±5.46º; (P=0.16)) or sagittal plane (M: 46.02º±4.88º; F: 46.77º±4.99º; (P=0.83)). Skeletally immature patients (coronal: 71.82º±6.06º; sagittal: 44.67º±5.49º) were different in both coronal and sagittal planes (P=0.044 and 0.009, respectively) from skeletally mature patients (coronal: 75.32º±4.71º; sagittal: 47.4º±4.65º). In the second phase, no difference was found between patients with subsequent ACL rupture (n=30; coronal: 47.53º±5.16º, sagittal: 70.44º±4.87º) and the normal ACL inclination angle (P=0.74 and P=0.59, respectively).


This study adds to the current body of literature on the native ACL angle of inclination and suggests three key findings. First, while the previously suggested inclination angle of the native ACL in the coronal plane is consistent with our findings, our data suggests that the angle in the sagittal plane may be less vertical than previously cited. Secondly, when using the inclination angle for post-operative evaluation, variation based on skeletal maturity must be taken into account. Thirdly, the lack of a difference between patients with and without a history of ACL rupture suggests the absence of a predisposition for such injuries with regard to the angle of the ligament itself.