Investigation

AP / Long Leg Views

 

Quantify Valgus Malalignment

 

 

Lateral Xray

 

1.  Assess Patella Alta

 

30^o flexion

 

A.  Blumensaat's line / Inaccurate

 

Knee flexed to 30^o

- line should just touch inferior pole of patella

- pole above line - alta

- pole below line - baja

 

 

B.  Blackburn-Peele ratio / Best and Most accurate

 

Distance between tibial and patella articular surface

- divided by patella articular surface

- patella alta > 1

 

 

C.  Insall ratio

- less accurate, probably because more difficult to measure

- ratios also difficult to remember and calculate

- length of patella tendon v length patella

- patella alta LT : LP 1.2

- patella baja LT : LP <1

 

 

2.  Assess Trochlea Dysplasia

 

Dejour Crossover Sign

- lateral x-ray at 30^o with condyles superimposed

- identify base of trochlea

 

Normal

- clearly defined trochlea groove

 

 

Abnormal / Crossover

- line of floor of trochlea crosses lateral lip of condyle

- indicates trochlea is deficient proximally

 

 

Trochlea depth

- < 8 mm shallow

 

Dejour grading system 1 - IV

 

Patellofemoral view

 

1.  Skyline view

 

Technique

- 45^o

- shoot throught film

 

Look for

- OCD

- bony avulsion MPFL

 

 

2.  Laurin view / patella tilt

 

Technique

- knee 20^o, camera at bottom

 

Assessment patella tilt

- first line anterior aspect both condyles

- line lateral facet

- should diverge laterally

 

Patella tilt

- lines parallel or open medially

 

 

3.  Merchant view / patella subluxation

 

Technique

- 40^o flexion, beam from top

- patella should be well engaged

- central ridge should lie at or medial to bisector of the trochlea groove

 

Congruence angle

- draw sulcus angle

- bisector of sulcus angle

- line to central ridge of patella

- should be - 10^o (i.e. medial)

- lateral direction is positive

 

Normal

 

 

Subluxed

 

 

4.  Trochlea dysplasia

 

Normal

 

 

Sulcus angle

- > 140^o flattened

 

 

5. Excessive Lateral Pressure Syndrome

 

Ficat and Hungerford

 

A.  Indirect signs of excessive lateral pressure

- thickened subchondral plate

- increased density lateral facet

- lateralisation of trochlea

- medial facet osteoporosis

- hypoplasia lateral condyle

 

 

B.  Indirect signs of excessive lateral ligament tension

- fibrosis lateral retinaculum

- calcification lateral retinaculum

- lateral osteophyte

- bipartite patella

- lateral facet hypoplasia

- medial compartment hypoplasia

 

 

CT

 

1.  Skyline View

 

Assess for

- lateral tilt

- subluxation

- trochlea dysplasia

 

 

2.  Lateralisation of tibial tuberosity

 

 

Jones et al Skeletal Radiology

 

Superimpose 2 axial slices

 

A.  Axial slice of trochlea

- line of posterior condyles

- line perpendicular through trochlea

 

 

B.  Slice through tibial tuberosity

- perpendicular line through TT

 

 

Calculate Distance between two points / TTTG

 

10 - 15 mm normal, > 15 abnormal

 

Pandit et al Int Orthop 2011

- normal 10 +/-1 on MRI

 

MRI

 

Articular Cartilage Damage

MPFL integrity

OCD

Loose Bodies

 

 

Arthroscopy

 

Assess chondral surfaces

Removal of Loose Bodies

Tracking

- not particularly valid

- patient is relaxed / knee filled with fluid