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Editorial   |    
The Lateral Intercondylar Ridge—A Key to Anatomic Anterior Cruciate Ligament Reconstruction
Freddie H. Fu, MD, DSc, DPs(Hon)1; Susan S. Jordan, MD1
1 Center for Sports Medicine, University of Pittsburgh Medical Center, 3200 South Water Street, Pittsburgh, PA 15203. E-mail address for F.H. Fu: ffu@upmc.edu. E-mail address for S.S. Jordan: jordanss@upmc.edu
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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2007 Oct 01;89(10):2103-2104. doi: 10.2106/JBJS.G.00851
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As our techniques for anterior cruciate ligament reconstruction have evolved, our focus has drifted from anatomy. We believe that it is important to hearken back to anatomy and to fully understand normal anatomy so that we can try to restore it with anterior cruciate ligament reconstruction surgery. The results associated with current anterior cruciate ligament reconstruction techniques are adequate but not exceptional. A recent meta-analysis of the outcomes of anterior cruciate ligament reconstruction indicated that only 33% of patients who had reconstruction with hamstring tendon graft and 41% of those who had reconstruction with bone-patellar tendon-bone graft had normal outcomes according to the final International Knee Documentation Committee score1. There is clearly room for improvement, and we think that the keys to improvement will be based on anatomical anterior cruciate ligament reconstruction.
In their paper entitled "Morphology of the Femoral Intercondylar Notch," Farrow et al. evaluate the anatomy of the lateral intercondylar notch in 200 cadaveric specimens. The authors' goal—namely, to perform a detailed study of the area where the anterior cruciate ligament attaches in order to provide more reliable guidance for femoral tunnel placement—is admirable. The authors note that the osseous ridge that Dr. Clancy termed the "resident's ridge" was present in 194 of the 200 specimens. They suggest renaming it the "lateral intercondylar ridge" on the basis of its anatomic location. In their discussion, Farrow et al. state that "it is likely that the lateral intercondylar ridge represents the anterior border of the femoral attachment of the anterior cruciate ligament," concurring with Hutchinson and Ash, who performed an earlier study of the lateral intercondylar wall anatomy2. Farrow et al. also describe an osseous ridge along the medial aspect of the intercondylar notch, which marks the posterior aspect of the posterior cruciate ligament attachment.
We applaud the authors for the clinical relevance of their paper. Improper femoral tunnel placement is a common error in anterior cruciate ligament surgery, and the identification of consistent anatomic landmarks to assist in more accurate tunnel placement is critical. The authors draw attention to the clinically relevant point that most surgeons usually remove the "lateral intercondylar ridge" during notchplasty prior to placing the femoral tunnel. Unfortunately, notchplasty has become a routine step in anterior cruciate ligament surgery, obliterating the osseous and soft-tissue landmarks that outline the femoral attachment of the anterior cruciate ligament. We have found that placing the arthroscope in the anteromedial portal allows full visualization of the anterior cruciate ligament attachment site and makes notchplasty unnecessary in about 95% of cases. If, after identification of the soft-tissue and osseous landmarks of the insertion site and tunnel-marking, visualization is still limited by a narrow notch, notchplasty can then be performed. Initially, however, notchplasty should be avoided to allow preservation of these important landmarks that guide accurate tunnel placement.
In our center, we have also performed detailed anatomic studies of the lateral intercondylar notch over the past two years. In addition to cadaveric dissection and fetal histologic analysis, we performed sixty arthroscopic dissections at the time of anterior cruciate ligament reconstruction to identify the osseous ridges and soft-tissue attachments of the anterior cruciate ligament bundles. Our findings support Farrow et al.'s conclusion that the "lateral intercondylar ridge" consistently marks the border of the anterior cruciate ligament attachment (the anterior border with the knee in extension and the superior border with the knee in 90° of flexion). We also discovered the existence of another ridge, the "lateral bifurcate ridge," which separates the anteromedial and posterolateral bundles of the anterior cruciate ligament at the femoral attachment. This ridge is prominent in many knees undergoing anterior cruciate ligament reconstruction, and we now use it as an anatomic landmark to guide the placement of individual anteromedial and posterolateral bundles during anterior cruciate ligament reconstruction. In addition to our cadaveric and arthroscopic dissections, we performed three-dimensional laser digitization of our specimens to study the topography of the anterior cruciate ligament attachment. We found that the topography is different when the anteromedial bundle attachment is compared with the posterolateral bundle attachment and that the two ridges described above are easily visible (Fig. 1). We also studied the anatomy of the medial aspect of the intercondylar notch and found the consistent presence of a ridge marking the posterior border of the posterior cruciate ligament attachment, which Farrow et al. also described. These ridges and changes in osseous topography may prove to be useful during navigation-assisted ligament reconstruction.
 
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+Fig. 1A three-dimensional laser digitization of the lateral intercondylar notch of a human cadaveric specimen in 90° of flexion. The large arrowheads point to the "lateral intercondylar ridge," which marks the superior border of the anterior cruciate ligament attachment with the knee in 90° of flexion. The small arrowheads point to the "lateral bifurcate ridge," which separates the anteromedial (AM) and posterolateral (PL) bundle femoral attachments.
We have even observed the presence of prominent osseous ridges along the lateral intercondylar notch of the femur in many animals. For both humans and animals, we suspect that the ridges and variation in slope of the anterior cruciate ligament attachment exist because of osseous remodeling in response to stress from the ligament fibers, in accordance with Wolff's law.
In summary, we congratulate Farrow et al. on the tremendous clinical relevance of their anatomic study. Our studies in Pittsburgh confirm the importance of the lateral intercondylar ridge as a landmark to guide accurate femoral tunnel placement during anterior cruciate ligament reconstruction. When treating fractures, reduction must come before fixation. Similarly, with anterior cruciate ligament reconstruction surgery, we believe that it is most important to restore the anatomy first and to consider graft choice and fixation methods later. ?
Biau DJ, Tournoux C, Katsahian S, Schranz P, Nizard R. ACL reconstruction: a meta-analysis of functional scores. Clin Orthop Relat Res.2007;458: 180-7.458180  2007  [PubMed]
 
Hutchinson MR, Ash SA. Resident's ridge: assessing the cortical thickness of the lateral wall and roof of the intercondylar notch. Arthroscopy.2003;19: 931-5.19931  2003  [PubMed][CrossRef]
 

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+Fig. 1A three-dimensional laser digitization of the lateral intercondylar notch of a human cadaveric specimen in 90° of flexion. The large arrowheads point to the "lateral intercondylar ridge," which marks the superior border of the anterior cruciate ligament attachment with the knee in 90° of flexion. The small arrowheads point to the "lateral bifurcate ridge," which separates the anteromedial (AM) and posterolateral (PL) bundle femoral attachments.

References

Biau DJ, Tournoux C, Katsahian S, Schranz P, Nizard R. ACL reconstruction: a meta-analysis of functional scores. Clin Orthop Relat Res.2007;458: 180-7.458180  2007  [PubMed]
 
Hutchinson MR, Ash SA. Resident's ridge: assessing the cortical thickness of the lateral wall and roof of the intercondylar notch. Arthroscopy.2003;19: 931-5.19931  2003  [PubMed][CrossRef]
 
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