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 al^10–13 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 impingement^14–16 or an aggressive roofplasty needs to be performed.^16,17 Failure to recognize this impingement will lead to an increased risk of graft failure.

Fig. 26-2 On a lateral radiograph with the leg in full extension, Blumensaat’s line (A) (solid white arrows) represents the roof of the notch. The slope of the roof can be measured by the femoral roof angle (B) and is an important preoperative assessment for planning tibial tunnel placement. An assessment of the “trueness” of the roof of the notch (C) may also avoid intraoperative complications. Sharper inlet and outlet corners (solid white arrow) allow better application of the over-the-back femoral guides but may contribute to anterior impingement. Gently sloped or curved inlet and outlet edges (curved arrows) may make it more difficult for the tongue of an over-the-back femoral guide to lock into position but protects the graft anteriorly against impingement.

Review of the preoperative lateral radiograph should also assess the trueness of Blumensaat’s line. Is it a straight line from front to back with sharp corners or edges at the inlet and outlet of the notch, or is it rounded at the ends with bumps or curves in the middle that may affect femoral tunnel selection? The roof of the notch is rarely perfectly flat; it usually has a slight curve at the inlet (anterior aspect of the notch) and the outlet (the over-the-back) position. Anteriorly, the gentle transitioning curve or blending of the femoral groove and femoral condyles into the articular surface prevents a sharp edge or corner cutting into the anterior aspect of the ACL in full extension. Posteriorly within the notch, a change in slope occurs approximately 1 cm anterior to the true over-the-back position. This change of slope is usually located at the anterior edge of the leading aspect of the ACL insertion onto the lateral femoral condyle and has been termed the “resident’s ridge” by Clancy¹⁸ (Fig. 26-3). Preoperative or intraoperative awareness of the resident’s ridge is essential for optimal placement of the femoral tunnel and successful outcome of the reconstruction. If the change of slope is acute and mistaken for the true over-the-back position, the femoral tunnel will be placed too far anteriorly and lead to one of the most common causes of failure for ACL reconstructions. At the time of notchplasty, a prominent resident’s ridge should be taken down with a bur or osteotome to confirm optimal placement of the femoral tunnel guide and ensure proper positioning of the femoral tunnel. Finally, the true outlet of the notch or over-the-back position on the femur is frequently gently curved, making it difficult to lock in the extended tongues of the femoral guides designed to offset the tunnel position relative to the posterior cortex. This edge may need to be flattened or a preliminary concavity created at the site of the femoral tunnel to allow the guide to be properly seated.

Fig. 26-3 The “resident’s ridge” is a change in the slope of the roof and lateral wall of the notch that occurs just anterior to the femoral anterior cruciate ligament (ACL) footprint. Cross-sectional view of a cadaveric femur (A) shows the resident’s ridge’ (black arrow) to be just anterior to the ACL footprint (black triangles) and almost 10 mm anterior to the true over-the-back position represented by the posterior cortex of the femur and capsule (white arrow). The probe identifies a resident’s ridge on the arthroscopic view (B).

Indications and Potential Risks

Although some controversy exists regarding the necessity or extent of a notchplasty, a few fundamentals related to notchplasty cannot be debated. First, the space within the intercondylar notch must be adequate to avoid impingement on the ACL graft. Second sharp edges, osteophytes, spurs, or corners that could irritate the graft must be removed. Third, and probably most importantly, the femoral tunnel must be optimally positioned in the posterior quartile of the notch along the lateral femoral condyle. For most surgeons, notchplasty, at least to a minimal degree, allows for optimally arthroscopic visualization to ensure that proper tunnel placement occurs.

Historically, more aggressive notchplasties were necessary to avoid roof impingement due to the relatively anteriorly placed tibial tunnels based on the original description of reconstruction by Clancy.¹⁹ Over time, aggressive notchplasties for routine ACL reconstructions have become less commonplace in favor of tibial tunnels placed onto the posterior edge of the tibial ACL footprint, which allows for less risk of impingement and minimal notchplasty. In these cases notchplasty is performed primarily to optimize visualization of the femoral tunnel placement. Devices have been developed to base the tibial tunnel off the notch roof, virtually guaranteeing the absence of impingement in full extension and potentially obviating the need for any notchplasty at all.²⁰

In addition to primary or revision ACL reconstruction in which notchplasty is performed as an adjunct to the procedure, notchplasty may be indicated as the primary procedure itself. As noted previously, no one is currently recommending prophylactic notchplasties to reduce the risk of ACL injuries; however, in patients who have postoperative extension loss or arthrofibrosis, notchplasty may be the procedure of choice. Shelbourne and Johnson²¹ performed arthroscopic débridement of scar tissue and manipulation under anesthesia with notchplasty in this population with good success in regaining motion in selected patients. Clearly, prevention is the best treatment, and initial adequate notchplasty may help prevent future extension loss. Tonino et al and Millet et al in separate papers^22,23 agree that inadequate notchplasty or space available for the ACL graft at the time of initial surgery was a common cause of arthrofibrosis, and adequate notchplasty might have prevented the complication.

One might argue that notchplasty is a benign procedure and therefore an aggressive notchplasty is indicated in everyone. This may not be true. LaPrade et al²⁴ found that aggressive notchplasty, in a canine model, led to early degenerative changes in the patellofemoral joint. Jarvela et al²⁵ correlated their clinical findings of postoperative patellofemoral arthritis 7 years after ACL reconstruction with a large notchplasty. In contrast, Morgan et al²⁶ failed to show abnormal pressure changes (in vitro using pressure-sensitive film) on the patellofemoral joint after notchplasty. Another potential risk of aggressive notchplasty is alteration of the biomechanical effects of the ACL reconstruction itself. Markolf et al²⁷ showed increased graft forces, particularly with the knee flexed at 90 degrees after notchplasty, and surmised that this could lead to an increased risk of graft failure. Anatomically, the ACL is meant to fill the notch and lie gently on the roof of the notch in full extension. This serves as an added buttress versus anterior displacement in addition to the tension along the fibers of the ligament itself. With aggressive notchplasty, this normal relationship may not occur.

Techniques and Avoiding Complications

Preoperative planning continues to play an important role when considering the necessity and extent of notchplasty. Preoperative notch and lateral radiographs may reveal relative notch stenosis, spurs, or osteophytic overgrowth.²⁸ These can be related to gender, genetics, degeneration, or the chronicity of the ACL injury. Nonetheless, when recognized preoperatively, it allows the surgeon to be more aggressive at the time of surgery to ensure the postoperative notch will be adequate to house the new ligament without impingement. When preoperatively evaluating the lateral view, it is very important to obtain the image with the knee in full extension, which allows careful interpretation of the slope and relative anterior/posterior position of the roof of the notch. This interpretation may indicate either a more aggressive notchplasty or the need to move the tibial tunnel more posteriorly to avoid notch roof impingement.

The notchplasty itself can be performed either arthroscopically or via a mini-open incision. The two primary goals are (1) to avoid impingement and graft irritation and (2) to optimize visualization for femoral tunnel placement. With the advent of central tibial tunnel placement 7 to 10 mm anterior to the PCL, it is rarely necessary to perform an aggressive notchplasty to avoid graft impingement. Proper tibial tunnel placement obviates impingement unless secondary osteophytic overgrowth has occurred due to chronicity of injury. For nonchronic reconstructions, the most important goal is adequate visualization for placement of the femoral tunnel, avoiding mistaking the resident’s ridge for the real over-the-back position, and careful visualization of the posterior cortex of the femoral condyle. Currently, we use only a minimal notchplasty in virtually all of our primary reconstructions.

Notchplasty begins with débridement of soft tissue and remnant ACL from within the notch and on the surface of the medial wall of the lateral femoral condyle. The shaver placed on an alternating setting is effective for removing large loose fragments, and the shaver set at high speed removes tissues adherent to the medial wall of the notch. If the remnant ACL is adherent to the PCL or remnant ACL stump and if the posterior capsule is present posteriorly in the notch, an arthroscopic biter can macerate the tissue, making it easier for the shaver to be effective. Many surgeons use thermal ablation probes to accomplish this step. Special care should be used when débriding soft tissues posterior and medial to the PCL because numerous bleeders are present and one could enter the popliteal artery. In general, we avoid débriding the tissue just adjacent to the 12-o’clock position. This avoids bleeding and allows us to complete 90% of our notchplasties without a tourniquet. If bleeding is encountered, it can be controlled with arthroscopic electrocautery or by inflating the tourniquet. The ligament of Humphrey, the anterior meniscofemoral ligament, lies obliquely just anterior to the PCL and is frequently damaged at the time of soft tissue débridement or tibial tunnel reaming. There are no data that support poor outcomes secondary to the sacrifice of the ligament of Humphrey; nonetheless, it is probably best to leave it intact as a secondary rotational stabilizer if possible.

Bony notchplasty usually begins anteriorly and progresses posteriorly. Arthroscopically, a subtle pink color change can be visualized at the entrance of the femoral notch where the articular surface of the lateral femoral condyle thins and curves acutely into the surface of the wall of the notch (Fig. 26-4). This subtle change is usually about 1 to 2 mm onto the articular surface and marks our initial site of anterior notchplasty. This edge can be taken down with a small osteotome or a high-speed bur/shaver (Fig. 26-5). Once the leading edge is removed, the high-speed bur/shaver is used to flatten the remaining wall to the same depth in a front-to-back direction. The goal is to create a smooth flat surface that does not irritate the graft and allows direct visualization to the posterior outlet (over-the-back position) of the notch. In general, the extent of this minimal notchplasty is effective for visualization of the over-the-back position in most patients.

Fig. 26-4 Arthroscopic view of the inlet of the notch revealing the presence of the posterior cruciate ligament (PCL) and absence of the anterior cruciate ligament (ACL). A, The subtle pink color change is noted where the articular cartilage of the lateral condyle transitions, becoming thin and curving into the roof of the notch (identified by spinal needle) (B). Minimal notchplasty will begin by removing this 1 to 2 mm of articular surface and working posteriorly to flatten the roof and lateral wall. In acute ACL reconstructions, it is rare to require more aggressive notchplasty to provide space for the reconstruction or visualize the true over-the-back position.

Fig. 26-5 Initiation of notchplasty can be performed using a small osteotome (A, B) or simply by using mechanical arthroscopic devices such as an arthroscopic shaver set on high speed or an arthroscopic bur.

Approximately, two-thirds to three-quarters of the way back, the bur frequently becomes more erratic and is difficult to maintain on the surface of the wall of the notch. This is due to a change in slope that occurs within the notch and a change in density of the bone itself. This is the resident’s ridge.¹⁸ The change in slope occurs immediately anterior to the ACL insertion onto the femur. The erratic nature of the bur is secondary to the increased cortical thickness of the ACL insertion itself. The resident’s ridge should be carefully flattened with the bur to match the entire flat surface of the wall of the notch. This will allow excellent visualization of the true over-the-back position on the femur and allow optimal placement of the femoral over-the-back guide. Indeed, at the time of notchplasty, we will usually make a small “prehole” or concavity where we expect the tunnel placement to be. This allows the over-the-back guide to slide more securely in place over the back of the lateral femoral condyle. It should be noted that leaving the cortical edge on the most posterior aspect of the notch is important during notchplasty and guide placement. Notchplasty that is too aggressive on the posterior wall of the notch can make proper positioning of the over-the-back guide difficult.

Although notchplasties for primary reconstructions performed in a timely fashion are generally straightforward, notchplasties can be particularly challenging in cases of revisions, chronic reconstructions, and patients who suffered from postoperative loss of extension or arthrofibrosis. In revision cases, the previous surgeon may have débrided relative landmarks. In chronic cases, significant osteophytic overgrowth can virtually close off the entire entry into the notch or can leave spurs posteriorly that throw off the over-the-back guides. Ultimately the goal in these complex cases is the same: full extension, adequate space available for the ligament, and excellent visualization for reconstructions.

Technically, the surgeon must work stepwise from known to unknown and from front to back in the notch. Débridement of soft tissue is usually straightforward; however, care must be taken to avoid viable anatomical structures including previous reconstructed ligaments. If a Cyclops lesion is present (scar tissue anteriorly in the notch, frequently with an adherent fat pad), flexing and extending the knee under arthroscopic visualization may help to identify the ACL so that the surgeon can target the scar tissue itself. In some cases it may be necessary to remove even the reconstructed ligament to regain full extension. Fortunately, débridement and notchplasty in post-ACL patients with arthrofibrosis are usually successful in regaining motion and normal gait as well as returning to athletic activities.^29,30 In patients with significant bony overgrowth, the surgeon should begin by carefully taking down obvious osteophytes under direct visualization and then working posteriorly. Osteophytes are usually softer than the native bone and are removed easier by the bur/shaver. In revision cases in which osteophytes may be present posteriorly, we recommend obtaining intraoperative radiographs to confirm femoral tunnel placement prior to drilling to ensure optimal position.

In conclusion, knowledge of notch anatomy and technical pearls in performing an appropriate notchplasty when indicated are essential skills in routinely obtaining successful outcomes of ACL reconstructions. Currently, only minimal notchplasty is usually necessary to assist in optimizing visualization of femoral tunnel placement.