Dejour et al. compared radiographs and CT scans from 143 knees with objective patellar instability against 190 control knees. The goal was to identify and quantify the specific anatomic factors responsible for recurrent patellar dislocation. Each factor was assigned a measurable radiographic threshold to guide surgical planning.
Every patient you evaluate for patellar instability needs a systematic four-factor workup: true lateral radiograph for the crossing sign and trochlear measurements, Caton-Deschamps index for patellar height, and axial CT for TT-TG distance and patellar tilt in extension.
Each threshold directly maps to a surgical decision: Crossing sign / trochlear bump ≥3 mm / depth ≤4 mm → trochlear pathology present; severe cases may warrant trochleoplasty Patellar tilt ≥20° → quadriceps plasty is required; lateral release alone will not correct this TT-TG ≥20 mm → tibial tuberosity medialization indicated, capped at 10 mm to protect the medial facet Caton-Deschamps ≥1.2 → distal advancement of the tibial tuberosity to reduce the index toward 1
The near-universal bilaterality of these findings — crossing sign in 92.5% of asymptomatic contralateral knees. Tells you this is a constitutional morphology, not a post-dislocation adaptation.
This paper is the foundation for every patellar instability algorithm that followed, including the expanded 2002 Dejour classification (Types A–D) and the modern MPFL reconstruction era, which uses the same bony factor thresholds to determine whether soft tissue repair alone is sufficient or bony correction must come first.
Dejour et al. compared radiographs and CT scans from 143 knees with objective patellar instability against 190 control knees. The goal was to identify and quantify the specific anatomic factors responsible for recurrent patellar dislocation. Each factor was assigned a measurable radiographic threshold to guide surgical planning.
Every patient you evaluate for patellar instability needs a systematic four-factor workup: true lateral radiograph for the crossing sign and trochlear measurements, Caton-Deschamps index for patellar height, and axial CT for TT-TG distance and patellar tilt in extension.
Each threshold directly maps to a surgical decision: Crossing sign / trochlear bump ≥3 mm / depth ≤4 mm → trochlear pathology present; severe cases may warrant trochleoplasty Patellar tilt ≥20° → quadriceps plasty is required; lateral release alone will not correct this TT-TG ≥20 mm → tibial tuberosity medialization indicated, capped at 10 mm to protect the medial facet Caton-Deschamps ≥1.2 → distal advancement of the tibial tuberosity to reduce the index toward 1
The near-universal bilaterality of these findings — crossing sign in 92.5% of asymptomatic contralateral knees. Tells you this is a constitutional morphology, not a post-dislocation adaptation.
This paper is the foundation for every patellar instability algorithm that followed, including the expanded 2002 Dejour classification (Types A–D) and the modern MPFL reconstruction era, which uses the same bony factor thresholds to determine whether soft tissue repair alone is sufficient or bony correction must come first.