Reliability of radiographic landmarks in medial patello-femoral ligament reconstruction in relation to the anatomical femoral torsion

Lateral to medial fluoroscopic view improves the accuracy of identifying the MPFL femoral footprint using Schottle's technique

PURPOSE

This study investigated the effect of different fluoroscopy settings on the accuracy of locating Schottle's point during medial patellofemoral ligament (MPFL) reconstruction.

METHODS

The centre of the MPFL femoral footprint was identified and marked on 44 dry femurs. Two standard true lateral knee fluoroscopic images were obtained: (1) medial to lateral (ML) and (2) lateral to medial (LM). The deviation between the anatomically determined MPFL femoral footprint and the fluoroscopically identified point was measured on both fluoroscopic images. An 'acceptable tunnel location' was defined as within a 5- or 7-mm margin of error from the anatomic MPFL footprint. Distal femoral morphometric dimensions were also measured using digital calipers. Statistical analysis determined discrepancies between techniques and their relation to femoral morphometry.

RESULTS

The LM view yielded a significantly smaller distance between the anatomical MPFL footprint and Schottle's point compared to the ML view (3.2 ± 1.5 vs. 4.5 ± 2.1 mm, p < 0.001). The LM view achieved acceptable tunnel locations, meeting the 5-mm error criterion in 90.9% of cases, while the ML view achieved 65.9% (p < 0.001). Both views yielded acceptable tunnel locations at similar rates using the 7-mm error criterion (n.s.). The anatomic MPFL footprint was displaced towards the anterior and proximal location in the ML view in reference to the Schottle point. No correlation was observed between any of the morphometric measurements and the deviations.

CONCLUSIONS

This study demonstrated that using the LM fluoroscopic view improves the accuracy of femoral tunnel placement when identifying the MPFL footprint via the Schottle technique. Adopting the LM view in surgical practice will help surgeons locate the anatomical femoral footprint accurately, replicating the native MPFL and enhancing clinical outcomes.

LEVEL OF EVIDENCE

Level 4, cadaveric study.

Comparison of five different fluoroscopic methods for identifying the MPFL femoral footprint

PURPOSE

The success of medial patellofemoral ligament (MPFL) reconstruction is closely linked to the precise positioning of the femoral tunnel. Intraoperative fluoroscopy is commonly utilized to identify the MPFL footprint. This study aimed to ascertain the most accurate fluoroscopic method among the five previously described methods used to determine the MPFL femoral footprint.

MATERIALS AND METHODS

Using 44 well-preserved dry femur bones, the MPFL femoral insertion site was demarcated using anatomical bony landmarks, namely the center of the saddle sulcus between the medial epicondyle, adductor tubercle and gastrocnemius tubercle. Fluoroscopic true lateral knee images were acquired and measurements taken, referencing established methods by Schottle et al., Redfern et al., Wijdicks et al., Barnett et al., and Kaipel et al. The distance between anatomic and fluoroscopic MPFL footprints was then measured on digital fluoroscopic images. The accuracy of the locations was compared using a margin of error of 5 and 7 mm.

RESULTS

The Schottle method consistently emerged superior, showcasing the smallest mean distance (3.2 ± 1.2 mm) between the anatomic and radiographic MPFL footprints and a high in-point detection rate of 90.9% under 5 mm criteria. While the Redfern method displayed perfect accuracy (100%) within the 7 mm criteria, the Schottle method also performed 97.7% accuracy.

CONCLUSIONS

For intraoperative identification of the MPFL footprint using fluoroscopy, the Schottle method is the most consistent and accurate among the assessed methods. Thus, its accuracy in detecting the MPFL footprint makes it recommended for MPFLR to ensure optimal outcomes.

LEVEL OF EVIDENCE

Level IV, cadaveric study.

Analysis of Graft Length Change Patterns in Medial Patellofemoral Ligament Reconstruction via a Fluoroscopic Guidance Method

BACKGROUND

A fluoroscopic guidance method for medial patellofemoral ligament (MPFL) reconstruction has been widely used to determine the anatomic femoral attachment site.

PURPOSE

To examine the graft length change patterns in MPFL reconstruction with a fluoroscopic guidance method.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Forty-four knees of 42 patients who underwent MPFL reconstruction for the treatment of recurrent patellar dislocation were examined prospectively. During surgery, suture anchors were inserted into the proximal one-third and center of the patella. A guide pin for the femoral tunnel was inserted into the position reported by Schöttle et al based on the true lateral view of the knee under fluoroscopic control. Changes in graft length patterns of the proximal and center anchors were examined through 0° to 120° of knee flexion. Favorable changes in length patterns were defined as meeting 2 of 3 criteria: (1) not long during flexion (≤3 mm between 30° and 120° of flexion) and either (2) nearly isometric during flexion between 0° and 90° or (3) slightly long during maximum extension (≤3 mm). Other patterns were considered unfavorable. If the change in length pattern was unfavorable, then the pin for the femoral tunnel was moved to different positions until it was favorable. Knees were separated into the favorable group and the unfavorable group. Differences between the groups regarding radiographic parameters were assessed. Student t test or chi-square test was used for statistical analysis.

RESULTS

Of the 44 knees, 31 (70.5%) showed favorable patterns. However, 13 knees (29.5%) showed unfavorable patterns; therefore, the position of the pin was changed. The mean ± SD distance from the original position to the final position was 5.3 ± 1.1 mm distal for 7 patients and 5.2 ± 0.4 mm posterodistal for 6 patients. Technical errors, including a nontrue lateral view and the tip of the wire not being in the determined area, were found for 4 of 13 knees in the unfavorable group. There was no statistical difference in radiographic parameters between the groups.

CONCLUSION

The graft length change pattern could be nonphysiologic at the position determined through the fluoroscopic guidance method; thus, caution may be necessary. The change in length pattern should be checked before graft fixation. If the length change pattern is unfavorable, then it is advisable to move it approximately 5 to 7 mm distally or posterodistally from the first position.

The trochlear isometric point is different in patients with recurrent patellar instability compared to controls: a radiographical study

PURPOSE

The purpose of the study was to investigate the theoretical isometric point based of the curve of the femoral groove and relating it to the origin of the MPFL femoral tunnel on lateral radiograph by comparing a patellar instability cohort with a control cohort.

METHODS

From a Patellar Instability database the radiographs of 40 consecutive patients were analysed to define Schöttle's point, and the arc of the circle of the trochlear groove. A comparison population of 20 radiographs from comparable patients with tibiofemoral joint disorders was used as a control. The distance from Schöttle's point to the most anterior part of the groove (extension) was also compared to the distance to the distal end of the roof of the notch (flexion).

RESULTS

The trochlea was circular in the controls but not the Patellofemoral Instability cohort where trochlear dysplasia is usually present. The difference between the extension and flexion length was a mean of - 2.0 ± 0.5 mm in the controls and + 6.0 ± 0.5 mm in the patellofemoral cohort. In neither cohort did the centre of the circle correspond to Schöttle's point. The extension distance correlated with the boss height.

CONCLUSIONS

The dysplastic trochlea is not circular and the centre of the best matched circle was different to the control trochleae which were circular. The circle centres did not correlate with Schöttle's point for either cohort, and was more proximal in the Patellofemoral Instability cohort.

CLINICAL RELEVANCE

For the MPFL to have equal tension throughout flexion within the groove, the length should not change. In normal knees the MPFL does not behave isometrically. The change in length, as measured from Schöttle's point to the trochlea, was greater for patellofemoral instability patients explaining why an isolated MPFL reconstruction in the presence of severe trochlear dysplasia risks poor outcomes. Level of evidence III.

Visual-palpatory versus fluoroscopic intraoperative determination of the femoral entry point in medial patellofemoral ligament reconstruction

PURPOSE

Malpositioning of the femoral entry point in reconstruction of the medial patellofemoral ligament (MPFL) can lead to abnormal and painful patellar kinematics and loss of flexion. Determination of this point is usually performed by palpation of anatomic landmarks. Accuracy of this method has not yet been investigated. The hypotheses were: 1. palpatory method is not as accurate as fluoroscopically guided method using established radiological criteria; 2. accuracy correlates with surgical experience.

METHODS

Three surgeons of varying experience defined the femoral entry point for the MPFL by palpation in ten cadaveric legs. The blinded procedures were repeated three times, and subjective difficulty of the determination was recorded. Results were documented by fluoroscopy on a true lateral radiograph. The accuracy was assessed using established radiological criteria. Surgical experience was correlated with the results, and confounding or interacting variables were assessed.

RESULTS

Mean deviation from the correct zone for the femoral entry point was 3.5 mm (range 0-18 mm). Twenty-nine percent of all palpatory determinations were inside the correct zone, 47 % were within 5 mm distance from the correct zone, and 23 % were further than 5 mm apart from the correct zone ("outliers"). No significant difference was found between surgeons of varying experience. No correlation was observed between subjective difficulty of the procedure and accuracy of determination.

CONCLUSIONS

The validity of the isolated palpatory determination of the femoral entry point in MPFL reconstruction seems to be insufficient, regardless of surgical experience. Derived from this study, fluoroscopic guidance is used in our clinic by default.

Femoral insertion site in medial patellofemoral ligament reconstruction

BACKGROUND

The optimal femoral insertion point in MPFL (medial patellofemoral ligament)-reconstruction still remains ambiguous. Three-dimensional knee simulations based on computerized tomography (CT) images acquired under physiological loading conditions give further insights to predict the optimal femoral insertion site of the MPFL. The hypothesis of the present study is that the optimal insertion point is not as reliable as thought and is dependent on subject-specific anatomical factors.

METHODS

High-resolution 3D images of the knee were acquired in ten weight-bearing knees of healthy subjects in five flexion angles (0 to 120°). The distance between different femoral insertion points and two defined patellar points was computed in each position to quantify length of respective bundles and isometry of the femoral insertion site.

RESULTS

The median length of both bundles was maximal in full extension (proximal bundle: 62.2mm and distal bundle: 59.9mm). The shortest ligament length was obtained in the flexion position 90° for bundle I (57.3mm) and 30° for bundle II (85.3mm). The calculated most isometric femoral attachment point showed a non-uniform distribution pattern related to anatomic landmarks. The radiographic landmark showed the worst isometric score value compared to virtually defined spots by surgeons and the computed most isometric point.

CONCLUSIONS

This study provides results on the MPFL path length under physiological loading conditions using high-resolution bone geometry. The most important finding of this study was that the computed, best isometric femoral insertion point showed a variable anatomical distribution. This suggests that the optimal position for femoral MPFL-graft fixation is patient specific.