Acetabular Dysplasia

DefinitionLateral Subluxation Hip

 

Abnormal development of acetabulum with decreased femoral head coverage

 

Aetiology

 

DDH 

Perthes

SUFE

NMD e.g. cerebral palsy

Skeletal Dysplasia (MED etc)

 

Plus

- trauma

- infection 

 

Epidemiology

 

Females > Males

- keeping with DDH

- males usually with other diagnosis

- considerable number are asymptomatic diagnosis on X-ray

 

Problem of late teens / early twenties

 

NHx 

 

3 important factors

 

1.  Degree of lateral subluxation

- CE < 20° = 80% OA

- unknown if covering head decreases OA

- 20 - 50% so called primary OA due to dysplasia

 

2.  Young age

- acetabulum can remodel to age 5

- dysplasia improves only with concentric reduction

- most rapidly in first 6 months

 

3.  Symptomatic 

- natural history of asymptomatic subluxation is unknown

- likely to be much more benign

- it is known that early symptomatic acetabular dysplasia has a much poorer prognosis

- i.e. the twenty year old with a symptomatic hip will likely have severe arthritis in ten years

- untreated DDH said to lead to OA by age 50 in 50%

 

Weinstein JBJS July 2000

 

1.  Subluxation 

- all get severe OA & clinical disability

- age of symptoms depends on severity

 

2.  Dysplasia 

- NHx difficult to predict

- strong association between women & degenerative joint disease

 

3.  Dislocated hips (untreated) 

- may have no disability

- if have well developed false acetabulum may develop severe DJD

 

Clinical

 

3 peaks of patient presentation

- depends on degree of subluxation

 

1.  Severe subluxation - patient in teens

2.  Moderate subluxation - patient in 20 & 30's

3.  Minimal subluxation - postmenopausal patients

 

Acetabular Rim Syndrome Ganz JBJS Br 1991 

- patients with acetabular dysplasia found to have 20% incidence of labral tear

- complain of sharp knife like pain in groin and giving way or locking

- elicited by flexion and IR

- brings proximal & anterior femoral neck into contact with rim of acetabulum

- this is where labrum is likely to be damaged -> superolateral quadrant

 

X-ray Measurements

 

1.  Shenton's Line

- Cooperman found it to be best prognostic sign

 

2.  Acetabular Index 

- paediatric

- triradiate cartilage to lateral edge of acetabulum

- birth 30°

- at 2 years - 20°

- N = < 30°

- DDH > 35°

 

3.  Sharp's Acetabular Angle 1961

- adult 

- inferior tip tear drop to lateral edge acetabulum

- > 42° Abnormal

 

Sharp's Acetabular Angle /> 40

 

4.  Centre Edge Angle of Wiberg 1939

- Perkin's line and line to centre femoral head

- < 20° abnormal / dysplasia

- > 40° Protrusio

- demonstrated increased increased of OA smaller the CE angle

 

Centre Edge < 20 degrees

 

5.  Sourcil angle

- line of angle of sourcil (sclerotic weight bearing area of femoral head)

- horizontal line

- normal     < 10°

- dysplasia  > 10° 

 

Sourcil Angle /> 10 degrees

 

6.  Weinstein Extrusion Index

- Head Covered / Total Width

- < 75% head covered abnormal

 

7.  Lateral Subluxation 

 

Teardrop to femoral head

 

Ganz Group I   13+/- 4mm

        Group II    6+/- 2mm

 

8.  Peak to Edge Distance

 

Ganz group I    3+/- 5mm

         group II 16+/- 4mm

 

CT Reconstruction

 

Probably best anatomical view of hip prior to deciding on osteotomy

 

Management

 

Aim is to decrease cartilage stress below stress threshold

- by increasing joint surface area  & decrease joint reaction force

- decreasing later OA & providing a painless functional joint

 

Controversy regarding treatment painless hip  with CE < 20o

 

Options 

 

1. Femoral osteotomy

- varising ostetomy

 

2. Acetabular osteotomy

- Reconstructive - Salter / Ganz

- Salvage - Chiari / Shelf

 

3. Both

 

4.  Hip Arthroscopy

- debridement labral tear