The Schöttle Point Is Consistently Located Distal to the Medial Femoral Physis in Pediatric Patients: A Digitally Reconstructed Radiographic Study

Abstract

Background: Significant controversy surrounds ideal tunnel position for medial patellofemoral ligament (MPFL) reconstruction (MPFLR) in the pediatric setting. The start point for femoral tunnel positioning (the Schöttle point) relative to the distal medial femoral physis is not well defined. Previous studies provide conflicting data regarding position of the MPFL origin and the Schöttle point relative to the distal femoral physis. Hypothesis: The Schöttle point would be consistently distal to the distal medial femoral physis. Study Design: Descriptive laboratory study. Methods: The institutional picture archiving and communication system was queried for computed tomography (CT) imaging studies of pediatric knees. Data were imported to an open-source image computing platform. True lateral digitally reconstructed radiographs and 3-dimensional (3D) renderings were generated, and the Schöttle point was registered in 3D space. Then, 3D distance measurements were obtained from the Schöttle point to the distal medial femoral physis. Results: A total of 49 pediatric knee CT scans were included. Mean age was 13.0 ± 2.3 years. Mean minimum distance from the medial physis to the Schöttle point was 9.9 ± 3.0 mm (range, 3.4-16.1 mm). In 49 of 49 cases (100%), the Schöttle point was distal to the physis. Using a 6-mm reaming diameter would result in 3 of 49 (6%) femurs having violation of the distal medial femoral physis. Moving the start point 3 mm distally would result in 0 of 49 (0%) sustaining physeal injury. Conclusion/Clinical Relevance: The Schöttle point is consistently distal to the distal medial femoral physis. The mean minimum distance from the Schöttle point to the physis on the medial cortex is 9.9 mm. The Schöttle point provides a safe and reliable radiographic landmark for pediatric MPFLR, although reaming diameter should be considered.

Comparison of Failure Rates at Long-term Follow-up Between MPFL Repair and Reconstruction for Recurrent Lateral Patellar Instability

“…The knee was then placed at 90° of flexion, and the Schöttle point was identified on the medial aspect of the knee on true lateral fluoroscopic views. 14 , 29 A small secondary incision was then made, and a guide pin was placed on the Schöttle point with fluoroscopic guidance. The graft was shuttled between layers 2 and 3 of the medial incision.…”

Physeal Location on the Distal Femoral Cortical Surface Is Consistently Proximal to Apparent Location on the Perfect Lateral Radiograph: A 3-Dimensional Digitally Reconstructed Radiograph Study

“…Perfect lateral views were reconstructed by aligning the posterior and distal aspects of the femoral condyles. 2,8 The coordinate system of the image was transformed such that the perfect lateral view was centered in the projection field.…”

“…This underscores the incomplete understanding of the 2-dimensional projection of the physis seen on the lateral radiograph and highlights the challenges of using the lateral radiograph intraoperatively to evaluate the physis. 8 To our knowledge, no studies exist that investigate the relationship between the location of the physis at the cortex and its projection on the perfect lateral radiograph.…”

Arthroscopically Assisted Double-Bundle Medial Patellofemoral Ligament Augmentation With Physeal-Sparing Suture Fixation for Recurrent Patellar Dislocation in Skeletally Immature Patients

“… 9 , 10 Growing attention has been drawn to fluoroscopy-guided MPFL-R with autograft, which has demonstrated satisfactory efficiency for adolescents. 2 , 11 , 12 Nevertheless, the main concern arises from the risk of physeal injury. The distance from the MPFL origin to the distal femoral physis varies from 3.7 mm proximal to 10.0 mm distal in skeletally immature specimens.…”