Anatomy and biomechanics of the anterior cruciate ligament
Michael Dienst, MD, Robert T. Burks, MD, Patrick E. Greis, MD *
Department of Orthopedic Surgery, University of Utah University Hospital, Salt Lake City, UT 84132 USA
During the last 25 years, the anterior cruciate ligament (ACL) has been one of the most studied structures of themusculoskeletal system. Gross and microscopic anatomy, biomechanics and function, mechanisms of failure, clinical course, and treatments have been intensively studied. This article discusses the anatomy and biomechanics of the native ACL. Defining the normal properties of the ACL provides a foundation for understanding acute ACL injury, the fate of chronic ACL deficiency, and refinement of ACL reconstructiontechnique.
Gross anatomy Femoral attachment The femoral attachment of the ACL is at the posterior part of the inner surface of the lateral femoral condyle [3,4]. This site has been described by Girgis et al  and Odensten and Gilquist . Girgis et al  described this site as a segment of a circle, with a straight anterior border and a convex posterior border. Odensten and Gilquist  andother authors who used Laser-digitizers  found the ACL to have a more oval form (Fig. 1). The bony origin is 11 mm to 24 mm in diameter . The axis of the long diameter is tilted 26° ± 6° forward from the vertical [3,5] and the posterior convexity contours the posterior articular margin of the lateral femoral condyle . On lateral radiographs the center of the femoral origin has been locatedat 24.8% of the distance defined by the intersection of Blumensaat’s line and the contour of the lateral femoral condyle. It is at 28.5% of the height of the lateral femoral condyle from Blumensaat’s line (Fig. 2A). In clinical practice, it is sufficient to divide the intercondylar fossa into quadrants. The origin of the ACL can be found just inferior to the most superoposterior quadrant (Fig.2B) . On a notch view of the knee joint, the entire femoral attachment of the ACL is lateral to the midline of the intercondylar notch and occupies the superior 66% (range 45% to 75%) of the notch . The center of the femoral tunnel for ACL reconstruction is between the 10 and 11 o’clock (right knee) or 1 and 2 o’clock (left knee) positions (Fig. 3). Tibial attachment
Embryology The kneebegins to form from a concentration of mesenchyme in the fourth week of gestation. The formation is rapid, with the appearance of a recognizable knee joint by the sixth week . The ACL itself appears as a condensation in the blastoma at about 6.5 weeks . It begins as a ventral ligament and gradually invaginates with the formation of the intercondylar space. It appears well before jointcavitation and remains extrasynovial at all times. Although it changes very little to achieve its final form, it does migrate posteriorly. The fact that the cruciate ligaments and semilunar cartilages are derived from the same blastoma tends to corroborate the thesis that these structures function in concert.
* Corresponding author. E-mail address: firstname.lastname@example.org (P. Greis).
The ACLfibers fan out as they approach their tibial insertion . The insertion site is a wide, de-
0030-5898/02/$ – see front matter D 2002, Elsevier Science (USA). All rights reserved. PII: S 0 0 3 0 - 5 8 9 8 ( 0 2 ) 0 0 0 1 0 - X
M. Dienst et al / Orthop Clin N Am 33 (2002) 605–620
Fig. 1. Femoral attachment of the ACL (after Girgis et al. , Odensten and Gilquist , and Smith et al). Fig. 3. Notch view of the knee joint. * = medial tibial spine.
pressed area approximately 11 mm (range 8 – 12 mm) in width and 17 mm (range 14 – 21 mm) in the anteroposterior direction, located in front of, and lateral to, the medial intercondylar tubercle (Fig. 4) [1,3,4]. It sends variable fibers anteriorly to pass beneath the transverse meniscal ligament. A few fibers of the ACL may...