Notch Anatomy and Notchplasty

The intercondylar notch is the open space that lies between the medial and lateral femoral condyles of the distal femur and houses the substance of both the anterior and posterior cruciate ligaments. The anterior medial wall serves as the insertion point of the posterior cruciate ligament (PCL), and the posterior lateral wall serves as the insertion point of the anterior cruciate ligament (ACL). The intercondylar notch represents an important facet that plays a role in the incidence of ACL injuries and can be an important technical factor to consider when optimizing the surgical technique of anterior cruciate ligament reconstructions (ACLRs). The purpose of this chapter is to review the fundamental anatomy of the intercondylar notch, to understand its impact on both the risk of ACL injuries and the optimization of ACLRs, to develop a better understanding regarding when a notchplasty is indicated and to what extent it should be performed, to review techniques and pearls in performing notchplasty, and to recognize potential complications or risks associated with notchplasty so that they can be avoided.

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 have shown that a small notch width or a small notch width index (NWI) (notch width divided by condylar width) is directly correlated with increased risk of ACL injuries, especially in women ( Fig. 56.1 ). A smaller intercondylar notch may stretch the ACL over the medial edge of the lateral femoral condyle, lead to impingement upon the ligament itself via the roof, or lead to impingement at the anteromedial bone ridge in the femoral notch. A key question is whether the core problem is that a small notch leads to impingement or that the small notch simply represents a smaller ligament within the notch. Shelbourne et al. showed when reconstruction is performed with the same size of graft, regardless of notch width or gender, the success rates were similar. Anderson et al. 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 al. found gender variations in both notch width and ACL volume in the groups they compared. The smaller size of the ACL housed within a smaller notch represents less total collagen volume, which may make it more vulnerable to shearing and rotational forces during valgus loading of the extended knee (i.e., cutting or side-stepping). Regardless of the debate, it has been redemonstrated in a recent meta-analysis by Zeng et al. that individuals with a decreased NWI and narrowed notch width demonstrate a higher predisposition toward 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, more forgiving, inverted U -shaped notch. It should be emphasized that no one is currently promoting prophylactic notchplasty in athletes with intact ACLs who incidentally have been found to have a small notch.

Traditional two-dimensional measurements of the intercondylar notch have been performed via plain radiographs, computed tomography/MRI scans, or even direct measurements with a probe-measuring device at the time of arthroscopy. Measurements include notch width, notch height, cross-sectional area, bicondylar width, and NWI. Unfortunately, these measurements may be sensitive to positioning, angulation, and rotation. While significant attention has been placed upon the entrance of the notch secondary to concerns regarding impingement on the graft or lack of space needed for the graft (especially double bundle) during ACLR, it is unclear how the notch entry cross-sectional area correlates to the actual three-dimensional notch volume. Cadaveric models have shown that arthroscopic measurements of notch entry size may provide a poor approximation of actual notch volume, with a small notch entry size not necessarily predictive of a correspondingly small notch volume. It is currently unknown whether two-dimensional or three-dimensional measurement of notch dimensions provides a better correlation with respect to the incidence of ACL rupture. Schickendantz and Weiker found no significant differences in two-dimensional notch measurements between subjects with unilateral ACL injuries, bilateral ACL injuries, and noninjured subjects, suggesting that current parameters used to measure notch dimensions may not be reliable predictors of ACL injury. Al-Saeed et al. and Lombardo et al. also found no significant relationship between smaller notch dimensions and increased risk of ACL injury. The lack of correlation between notch entry size and true notch volume could explain the conflicting reports that exist in clinical and cadaveric studies comparing notch dimensions to ACL injury.

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 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. 56.2 ). Numerous authors have demonstrated an increased risk of ACLR failure or postoperative extension loss if graft roof impingement is apparent from the lateral perspective. Howell et al. 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 to be performed 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 or an aggressive roofplasty needs to be performed. Failure to recognize this impingement will lead to an increased risk of graft failure.

Review of the preoperative lateral radiograph should also assess the trueness of Blumensaat 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 posterior 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 Hutchinson and Ash ( Fig. 56.3 ). 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 ACLRs. At the time of notchplasty, a prominent resident’s ridge can 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. Modern guide systems (particularly those with outside-in or retro reaming) may allow retention of the ridge as an anatomic landmark for tunnel placement. Finally, the true posterior 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 femoral guides designed to offset the tunnel position relative to the posterior cortex. This curved 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.

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 and anatomically 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 optimal arthroscopic visualization to ensure that proper tunnel placement occurs. Visualization is absolutely imperative in ensuring anatomic placement of the femoral tunnel.

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 et al. Over time, aggressive notchplasties for single-bundle ACLRs have become less commonplace in favor of tibial tunnels placed more posteriorly in the tibial ACL footprint. This posterior position creates less risk of roof impingement and reduced need to expand the notch volume. With modern, single-bundle tunnel positioning, notchplasty is performed primarily to optimize visualization of the over-the-back position on the femur and femoral tunnel placement. With double-bundle techniques, the surgeon should be especially observant of the potential for notch roof impingement related to the anterior reconstructed bundle. In an effort to ensure the absence of notch roof impingement and in hopes of obviating the need for any notchplasty, devices have been developed to guide the tibial tunnel placement off the notch roof. While use of these devices may introduce some technical challenges, the concept of protecting the graft from impingement should be foundational to all reconstructions.

In addition to primary or revision ACLR, 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 Johnson 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, agree that inadequate notchplasty or space available for the ACL graft at the time of initial surgery was a common cause of arthrofibrosis and that adequate notchplasty might have prevented the complication. In contrast, Koga et al. reported that in some cases notchplasty may have a deleterious effect. In their report they noted that the use of notchplasty in anatomic double-bundle ACLR led to an overconstrained knee with loss of knee extension and subjective feelings of limited extension. An additional synovectomy was needed in 9.4% (6/64) of patients. They hypothesized that this was likely due to infrapatellar fat pad fibrosis secondary to bleeding from the notchplasty. Patients who did not receive notchplasty exhibited no increase in the incidence of loss of extension or graft failure. Interestingly, objective stability measurements such as KT-1000 were found to be significantly higher (more stable) in the notchplasty group, with no deleterious effects on the patellofemoral joint based on clinical and subjective measures (pain, crepitus).

One might argue that notchplasty is a benign procedure, and an aggressive notchplasty is indicated in all patients. This is not true. LaPrade et al. found that aggressive notchplasty, in a canine model, led to early degenerative changes in the patellofemoral joint. Jarvela et al. correlated their clinical findings of postoperative patellofemoral arthritis 7 years after ACLR with a large notchplasty. In contrast, Morgan et al. 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 ACLR itself. Markolf et al. showed increased graft forces, particularly with the knee flexed at 90 degrees after formal notchplasty, and surmised that this could lead to an increased risk of graft failure. In a porcine model, notchplasty has been associated with widening of the intra-articular orifice of the femoral tunnel after uniaxial cyclical loading in ACL grafts with suspensory fixation, leading to a discrepancy between the graft and tunnel at the aperture. This may be due to the removal of the more superficial, stronger, and more resistant cortical bone during notchplasty. With regard to knee biomechanics and graft laxity, anterior tibial translation was significantly increased at 30 and 60 degrees of flexion in the knee post-notchplasty. There were also significantly lower in situ forces placed on the graft during anterior tibial loading at all degrees of knee flexion post-notchplasty.

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. Joining the debate and choosing not to perform notchplasty due to the risks discussed previously, Wolf et al. showed no correlation between smaller intercondylar notch dimensions and higher rates of graft failure in their patient population undergoing individualized primary single- or double-bundle anatomic ACLR with a minimum 2-year follow-up. Ultimately, the choice of aggressive, minimal, or avoiding notchplasty will remain a surgeon preference; nonetheless, it is essential to stay true to the fundamentals of anatomy and to avoid unnecessary graft impingement to optimize outcomes of ACLRs.

Techniques and Avoiding Complications

Preoperative planning plays 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. These can be related to gender, genetics, degeneration, or the chronicity of the ACL injury. Nonetheless, when recognized preoperatively, this 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 chronicity of ACL incompetency and its effect on the femoral–tibial relationship should be carefully evaluated, as it can magnify the pathologic relationship between the notch roof and the anatomic tibial tunnel. Patients with chronic or failed ACLR demonstrated a nearly 5 times greater mean anterior tibial translation of the lateral plateau compared with acute ACL disruptions. This anterior tibial subluxation leads to an apparent/relative posteriorization of the roof slope (Blumensaat line) on lateral imaging, which in turn reduces the total notch volume available for reconstruction. In these cases when considering how to intervene with a notchplasty, the surgeon must also recognize whether the subluxation is reducible. In cases involving an abnormal relationship between the tibia and femur in an ACL-deficient state (especially in chronic and failed ACLR), placing the tibial tunnel more posterior in conjunction with a more extended roofplasty may be necessary to allow a nonimpinged ACL through a full range of motion. If the subluxation is reducible, then routine approaches are appropriate.

The notchplasty itself can be performed either arthroscopically or via a mini-open incision. Since the two primary goals are (1) to avoid impingement and graft irritation and (2) to optimize visualization for femoral tunnel placement, the specific technique does not matter, and many surgeons will have their own personal preference regarding the amount of notchplasty and the use of an osteotome, a burr, or a high-speed shaver. Osteophytic overgrowth is usually softer than subchondral bone, allowing straightforward removal with a simple shaver. Addressing an A-framed notch or one with a significantly reduced NWI may require a more aggressive approach using an osteotome or burr. It is important to be complete and recognize that you must address the entire volume and depth of the notch and not simply the anterior aperture. Currently, we use only a minimal notchplasty in virtually all of our primary reconstructions to allow for visualization of the over-the-back position, unless preoperative screening indicated a more aggressive approach.

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 soft tissue and 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. Caution should be used to not damage normal PCL tissue or the ligament of Humphrey. 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 tissue deep in the notch just adjacent to the 12-o’clock position. This allows adequate visualization of the medial wall and avoids bleeding, which in turn allows us to complete 90% of our minimal 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, is an important secondary stabilizer, and is retained if possible.

Some surgeons prefer to retain the resident’s ridge as an anatomic landmark and use soft tissue remnants as guides to placement of the femoral tunnel. This is a personal surgical preference. Adjunctive imaging, non–over the back, point-to-shoot guides, or retro-reaming techniques have been shown to be successful at creating appropriate femoral tunnels. When bony notchplasty is performed, we usually begin anteriorly and progress 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. 56.4 ). 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. 56.5 ). 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.