Radiographic Landmarks for the Femoral Attachment of the Medial Patellofemoral Complex: A Cadaveric Study

Editorial Commentary: Proper Femoral Tunnel Placement for Medial Patellofemoral Ligament Reconstruction Requires Optimal Radiographic Technique

Femoral tunnel malposition has been shown to be a risk factor for medial patellofemoral ligament reconstruction failure. Palpation of the "saddle point" between the adductor tubercle and medial epicondyle can be an effective strategy; however, compared to using fluoroscopy, tunnel placement using palpation alone may result in significantly more frequent malposition. Accordingly, use of radiographic landmarks has gained in popularity. However, the technique is not without its pitfalls. The first issue lies with obtaining an adequate x-ray. Deviation from a true lateral x-ray by as little as 5° can result in significant tunnel malposition. Including sufficient visible femoral shaft is also required; a minimum requirement is 4 cm. The literature widely varies as to the anatomic, fluoroscopic position. Schottle's point (1.3 mm anterior to the posterior cortical extension line) is the most well studied.

Radiographic Landmark Measurements for the Femoral Footprint of the Medial Patellofemoral Complex May Be Affected by Visible Femoral Shaft Length on Lateral Knee Radiographs

PURPOSE

To assess the effect of visible femoral shaft length on the accuracy of radiographic landmarks of the medial patellofemoral complex (MPFC).

METHODS

In 9 cadaveric knees, the MPFC footprint was exposed on the medial femur, and its proximal and distal boundaries were marked. Lateral fluoroscopic images of the knee were assessed in 1-cm length increments, beginning 1 cm proximal to the medial condyle and continuing proximally to 8 cm. The MPFC midpoint was described on each image relative to the posterior cortical line of the femur and a line perpendicular to this line through the proximal margin of the medial condyle. In addition, the MPFC midpoint was assessed relative to a line from the proximal posterior cortex to the midpoint of Blumensaat line.

RESULTS

Using the posterior cortical line as a reference, the MPFC radiographic landmark moved anteriorly with decreasing visible femoral shaft on radiographs, particularly at 4 cm and less. However, no proximal-distal change was noted. Linear regression analysis demonstrated a relationship between visible femoral shaft and MPFC position on radiographs (R = 0.461, R2 = 0.212, B = -0.636, P < .001). For every centimeter decrease in the visible femoral shaft, the radiographic MPFC footprint moved anteriorly by 0.636 mm. Receiver operating characteristic curve analysis revealed that a minimum of 4 cm of femoral shaft on lateral radiographs is required for accurate MPFC footprint localization (area under the curve = 0.80; sensitivity = 76.7%; specificity = 69.0%; P < .001). In contrast, no anterior-posterior change was seen when referencing a line from the proximal posterior cortex to the midpoint of Blumensaat line.

CONCLUSIONS

When using the posterior cortical line to identify the midpoint of the MPFC, at least 4 cm of femoral shaft should be visible for accurate assessment. If less than 4 cm of shaft is visible, a line through the midpoint of Blumensaat line and the proximal posterior cortex can be used as an alternative method to estimate the position of the femoral footprint.

CLINICAL RELEVANCE

As fluoroscopy is frequently used intraoperatively for MPFC reconstruction, our findings may serve as a guide when assessing femoral tunnel placement on fluoroscopy.

Femoral neck-shaft angle can predict the anterior capsular thickness in patients with femoracetabular impingement syndrome

PURPOSE

To measure the femoral neck-shaft angle (NSA) on computed tomography (CT) images in femoracetabular impingement syndrome (FAIS) patients and explore its relationship with the anterior capsular thickness (ACT).

METHODS

A retrospective review of prospectively collected data from 2022 was performed. Inclusion criteria included: primary hip surgery, 18 to 55 years of age, and CT imaging of the hips. Exclusion criteria included: revision hip surgery, mild or borderline hip dysplasia, hip synovitis, and incomplete radiographs and medical records. NSA was measured on CT imaging. ACT was measured using magnetic resonance imaging (MRI). Multiple linear regression was performed to assess the association between ACT and related variables, including age, sex, body mass index (BMI), lateral center-edge angle (LCEA), alpha angle, Beighton test score (BTS), and NSA.

RESULTS

A total of 150 patients were included. The mean age, BMI, and NSA were 35.8 ± 11.2 years, 22.8 ± 3.5, and 129.4° ± 7.7°, respectively. Eighty-five (56.7%) patients were females. Multivariable regression analysis revealed that NSA (P = 0.002) and sex (P = 0.001) were significantly negatively correlated with ACT. Age, BMI, LCEA angle, alpha angle, and BTS were not correlated with ACT.

CONCLUSIONS

This study confirmed that NSA significantly predicts ACT. A decrease in the NSA by 1° increases the ACT by 0.24 mm.

LEVEL OF EVIDENCE

Level III.

Editorial Commentary: The Medial Patellofemoral Complex Is Composed of the Medial Patellofemoral Ligament and the Medial Quadriceps Tendon-Femoral Ligament: Do We Need to Reconstruct Both?

The medial patellofemoral ligament (MPFL) has been known as the primary soft-tissue restraint to lateral patellar translation. More recent anatomic studies have identified additional fibers that extend to the quadriceps tendon (medial quadriceps tendon-femoral ligament [MQTFL]), leading to the use of the term "medial patellofemoral complex" (MPFC) to describe the broad and variable attachment of this complex on the patella and quadriceps tendon. Whereas many techniques and outcomes of traditional MPFL reconstruction have been described, fewer reports exist on anatomic MPFC reconstruction to recreate both bundles of this complex. To date, the specific biomechanical roles of, and indications for, reconstruction of the MPFL versus MQTFL fibers have not been defined. One primary benefit of MQTFL reconstruction has been to avoid the risk of patella fracture, which is not obviated in the setting of concurrent patellar fixation when reconstructing both components of the MPFC. The risks and benefits comparing fixation on the patella, quadriceps tendon, or both with anatomic double-bundle reconstruction remain to be determined. Additional studies are needed to understand the differences between reconstructing the proximal and distal fibers of the MPFC with regard to graft length changes and femoral attachment sites, in order to optimally recreate the function of each graft bundle in the surgical treatment of patellar instability.