Currently, the standard surgical approach for chronic lateral patellar instability with at least two documented patellar dislocations is to stabilize the patella by means of a medial patellofemoral ligament (MPFL) reconstruction.¹,² MPFL is a crucial anatomic structure that helps to prevent lateral patellar dislocation.¹,³ Consequently, MPFL reconstruction is the most frequent surgical procedure performed in patients with lateral patellar instability.

MPFL reconstructions have variable success rates, and one reason for inconsistent outcomes may be inadequate placement of the attachment points during surgery. Hence, it is recommended to perform anatomic reconstructions on the basis of normal attachment points of the MPFL.¹

Of the two attachment points, the femoral and the patellar, the most important is undoubtedly the femoral attachment point.⁴ The anatomic femoral fixation point is a relatively easy and reproducible way to obtain optimal length change behavior of the graft for satisfactory long-term clinical results.⁴

The aim of this chapter is to assess which reference points delineate the optimal attachment points in MPFL reconstruction surgery.

Several authors have reported that femoral tunnel placement tends to be nonanatomic, and malpositioning has been documented in 31% to 64% of MPFL reconstructions.⁵,⁶ As a consequence, medial patellofemoral contact pressure may be increased and knee flexion diminished. Determining where to locate the femoral attachment point in MPFL reconstruction surgery is critical because it controls the length change behavior of the graft and therefore the graft tension and patellofemoral compression force at different angles of knee flexion.⁴ Poor placement of the femoral attachment point has resulted in increased patellofemoral contact pressures, increased rates of MPFL reconstruction failure, and loss of graft isometry.⁷,⁸

Several methods for identifying the proper femoral attachment point during MPFL reconstruction have been described.¹,⁹,¹⁰,¹¹,¹²,¹³,¹⁴,¹⁵,¹⁶,¹⁷,¹⁸ The existence of so many methods is an indication that the ideal method has not yet been found.

One option for locating the femoral attachment point is to use radiographic landmarks. The objective of the radiographic method is to simplify the operation and limit the incision to a very small cut (2-3 cm) on the femoral side of the knee. This method can also assist in the postoperative assessment of ligament attachment placement.

In a 2007 laboratory study, Schöttle et al¹⁴ were the first to describe reliable radiographic landmarks for an anatomic femoral attachment point during MPFL reconstruction surgery. They indicated that the radiographic point of the attachment on a true lateral radiograph is 1 mm anterior to the tangent of the posterior femoral cortex (reference line), 2.5 mm distal to a perpendicular line traced through the initial part of the medial femoral condyle, and proximal to a perpendicular line traced through the most posterior part of the Blumensaat line (Figure 4.1A). Using human cadaveric knees, Redfern et al¹² also concluded that radiographic landmarks can help to precisely locate the anatomic femoral attachment of the MPFL.

Despite the reproducible radiographic landmarks, however, the curved outline of the posterior femoral cortex varies depending on a patient’s history of weight-bearing activity. Therefore, Stephen et al¹⁶ suggested that the posterior femoral cortex may not represent a consistent anatomic landmark for reliably determining the femoral attachment location. To avoid the limitations of the previous methods, Stephen et al¹⁶ used normalized dimensions of the articular geometry and determined the anatomic femoral attachment of the MPFL in relation to the size of the medial femoral condyle: If anteroposterior size is 100%, then the MPFL attachment is 40% from the posterior, 50% from the distal, and 60% from the anterior outline (Figure 4.1B). However, Stephen et al’s method is very difficult to implement in a sterile operating room environment, which may explain why it is not used in daily clinical practice, in contrast to Schöttle et al’s method.

Radiographic landmarks could be helpful intraoperatively for anatomic graft placement. Schöttle et al¹⁴ have recommended using fluoroscopy intraoperatively to identify an anatomic femoral attachment point. They emphasized that obtaining a true lateral image (Figure 4.1) is imperative for performing an anatomic femoral attachment point. However, a true lateral view is not always easy to establish in the operating room. Interestingly, Balcarek et al¹⁹ demonstrated that minor degrees of deviation from the true lateral view significantly alter the location of the femoral attachment point. For instance, 5° of divergence may cause a 5-mm shift away from the native femoral attachment point.¹⁹ The difficulty of obtaining true lateral fluoroscopic views in the operating room may explain the high incidence of nonanatomic femoral attachment points in MPFL reconstruction surgery.¹⁹

The “Schöttle point” has become the benchmark for intraoperative radiographic confirmation of femoral attachment point.³ However, does the radiologic method permit making a real anatomic femoral attachment point?

Recently, Ziegler et al²⁰ showed that even with the use of a strict lateral view x-ray, as advised by Schöttle, the radiographic method does not accurately locate the anatomic femoral attachment of the MPFL. The authors instead found a distance of 4.1 mm from the anatomic MPFL attachment to the Schöttle point. If the lateral projection is not strict, the error is still greater. Thus, a rotation of only 5° with respect to a strict lateral projection has a significant effect on the location of the anatomic femoral attachment point (between 7.5 and 9.2 mm).

Similarly, Sanchis-Alfonso et al¹³,²¹ observed that the radiologic methods generally do not allow a proper anatomic femoral placement. The authors found a distance of 3.73 ± 1.86 mm (range, 0.37-8.04 mm) from the center of the anatomic MPFL femoral attachment to the Schöttle point using a true lateral view (unpublished data). Moreover, the radiographic method was even more prone to errors for identifying the femoral anatomic fixation point in female knees with a severe trochlear dysplasia.¹³ Therefore, the radiologic method is only an approximation and should not serve as the sole basis for performing an anatomic femoral attachment point during MPFL reconstruction surgery.

Nevertheless, fluoroscopy is an ingenious radiographic real-time method that can be helpful for surgeons who rarely perform this type of surgery, in order to avoid gross failures when determining the femoral attachment point in the MPFL reconstruction surgery. However, the medical literature seems to show that no relation exists between the femoral tunnel localization and clinical results in the short and medium term.⁴,⁶,²² When the nonanatomic location is not excessively abnormal and the ligament functions as a virgin ligament from the kinematic point of view, the clinical results are good.⁴

The question for the current chapter is not whether selecting a femoral attachment point that is not strictly anatomic is good or bad but whether the radiographic reference points permit locating the exact point of the anatomic femoral attachment of the MPFL. And the answer is no. The radiologic method is, in fact, insufficient, and therefore other options must be investigated for locating the exact anatomic point of the femoral insertion of the MPFL.

Determination of bony landmarks (Figure 4.2) is another method for identifying the appropriate location of the femoral attachment point. The femoral insertion of the MPFL is distal to the adductor tubercle (AT) and proximal-posterior from the medial femoral epicondyle (MFE). The center of the femoral attachment of the MPFL is located in a groove midway between the MFE and the AT (Figure 4.3).¹⁶

Several authors have used the MFE as an anatomic landmark to locate the femoral insertion during MPFL reconstruction surgery.²³,²⁴ However, others advocate the use of the AT as a landmark for MPFL reconstruction instead of the MFE because the distances between the AT and the femoral insertion of the MPFL vary less than those between the MFE and the femoral insertion of the MPFL.¹⁷ Moreover, the MFE is usually not well defined.¹⁷ It looks like a C-shaped ridge and has a central sulcus for the insertion of the superficial medial collateral ligament.⁵ Moreover, its wider area makes it more difficult to identify this anatomic structure accurately. 17 However, the AT is a well-defined anatomic landmark and therefore easy to identify.¹⁷