Radiological evaluation of patellofemoral instability and possible causes of assessment errors

Table 1 Anatomical factors used in the evaluation of patellofemoral instability, their normal of value and range values

Anatomic factor	Normal value	Range
Patellar height
Insall-Salvati[33]	1	(0.8-1.2)
Mod. Insall-Salvati[30]	Patella alta > 2
Blackburne-Peel[22]	0.8	(0.5-1)
Caton-Deschamps[141]	< 1.2	(0.6-1.2)
PI[142]	0.49	0.18-0.80
Trochlear morphologic finding
Trochlear depth[19]	≥ 5 mm
Sulcus depth[15]	≥ 3 mm
Sulcus angle[2,92,93]	< 144°
LTI[54]	> 11°
Patellar position
LPFA[15]	≥ 8°
Patellar tilt[17]	< 12°
Patellar lateralization[15]	< 2 mm
Patellar translation
TT-TG distance[75,76]	≤ 10 mm

PI: Patellotrochlear index; LTI: Lateral trochlear index; LPFA: Lateral patellofemoral index; TT-TG: Tibial tuberosity–trochlear groove.