Anatomy

The subtle anatomy of the intercondylar notch in three dimensions plays an important role in the incidence of ACL injuries as well as in optimizing surgical techniques of notchplasty and the ultimate outcome of reconstructions. Several investigators ¹^–⁵ have shown that a small notch width or a small notch width index (notch width divided by condylar width) is directly correlated to increased risk of ACL injuries, especially in women (Fig. 26-1). A debate has surfaced that it is not a small notch width alone that leads to an increased risk of injury but rather a smaller ligament within the notch that may play a role. Shelbourne et al⁶ showed when reconstruction is performed with the same size of graft, regardless of notch width or gender, the success rates were similar. Anderson et al⁷ compared magnetic resonance imaging (MRI) of groups of male and female basketball players and found smaller ligaments in the female athletes as well as differences in notch width. Charlton et al⁸ found gender variations in both notch width and ACL volume in the groups they compared. Regardless of the debate, it is clear that radiographic findings of a small notch is predictive of ACL injury. In addition, the shape of the notch on an anteroposterior (AP) notch view may also play a role regarding ACL injury risk, with an A-framed notch being relatively more stenotic and leading to increased risk of injury compared with a wider and forgiving inverted U-shaped notch. It should be emphasized that no one is currently promoting prophylactic notchplasty in athletes with an intact ACL who incidentally have been found to have a small notch.

Fig. 26-1 The notch width index can be measured on radiographic tunnel views or magnetic resonance imaging scans and represents the ratio of the width of the notch (dotted arrows) to the intercondylar width at the level of the popliteus indentation (large bold arrows).

While the AP perspective is clearly important when evaluating the intercondylar notch, the lateral perspective may be as or more important for preoperative planning. On a lateral radiograph, Blumensaat’s line represents the roof of the intercondylar notch. The slope (angular orientation relative to the femur), position (anterior/posterior translational position relative to the central axis of the femur), and trueness (absolutely straight or curved at the ends) are highly variable among patients (Fig. 26-2). Numerous authors have demonstrated an increased risk of ACL reconstruction failure or postoperative extension loss if graft roof impingement is apparent on the lateral perspective.^9,¹⁰ Howell et al¹⁰^–¹³ have been instrumental in increasing the surgical community’s awareness of the importance of identifying potential graft roof impingement preoperatively to guide either tunnel placement or the extent of notchplasty intraoperatively. A preoperative lateral radiograph should be routinely obtained in full extension. If the slope of the roof of the notch is acute or its relative position is too posterior, either the tibial tunnel should be placed more posteriorly to avoid impingement¹⁴^–¹⁶ or an aggressive roofplasty needs to be performed.^16,¹⁷ Failure to recognize this impingement will lead to an increased risk of graft failure.