The trochlear isometric point is different in patients with recurrent patellar instability compared to controls: a
Tulio Campos1, Akash Soogumbur2, Iain R McNamara2
1Department of Orthopaedics, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
Summary
The trochlear groove in patellar instability is not circular, unlike in healthy knees. This difference impacts the medial patellofemoral ligament (MPFL) tension, potentially leading to poor outcomes in reconstruction surgery.
Area of Science:
- Orthopedic surgery
- Biomechanical analysis
- Radiographic imaging
Background:
- The medial patellofemoral ligament (MPFL) is crucial for patellar stability.
- Accurate MPFL tunnel placement is vital for successful reconstruction.
- Understanding the trochlear groove's geometry is key to optimizing MPFL function.
Purpose of the Study:
- To investigate the theoretical isometric point of the femoral groove's curve.
- To relate this point to the origin of the MPFL femoral tunnel on lateral radiographs.
- To compare patellar instability and control cohorts.
Main Methods:
- Radiographic analysis of 40 patellar instability patients and 20 controls.
- Definition of Schöttle's point and the trochlear groove's arc.
- Measurement of distances from Schöttle's point to the groove in extension and flexion.
Main Results:
- Trochlear dysplasia was present in the patellar instability cohort; controls had circular trochleae.
- The change in length from Schöttle's point to the trochlea was significantly greater in the patellar instability cohort (+6.0 mm) versus controls (-2.0 mm).
- The center of the best-fit circle for the trochlear groove did not correlate with Schöttle's point in either cohort.
Conclusions:
- Dysplastic trochleae are non-circular, and their best-fit circle centers differ from controls.
- MPFL does not behave isometrically in normal knees.
- The increased MPFL length change in patellar instability patients, due to trochlear dysplasia, explains why isolated MPFL reconstruction may fail.
