10 The Terminology of Dislocation
10 The Terminology of Dislocation 62
Dislocation is the “permanent separation” of articular surfaces. The term subluxation “a little bit dislocated” is a clinico-radiological term and does not relate to anatomy. It should not there- fore be used in sonographic classification. Sono- graphically, a distinction is made between cen- tred and decentred joints.
Centred joints are type I and type II joints.
Decentred joints are type D, type IIIa and b and type IV.
The treatment and the prognosis of these hip types is different. The terms dislocation or sub- luxation should not be used. They are not spe- cific enough. They signal a “bad” hip, but the exact pathology and therefore its consequences cannot be determined (“bad weather” gives no indication as to what type of weather to expect!)
Key Points:
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The alpha value determines the hip type, the beta value is responsible for the precise differentiation within the type. NB. The exceptions: type IIc, type D.
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Type D hip is the first stage of decentring.
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A subdivision of type IIc into type IIc sta- ble and IIc unstable.
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The classification of premature infants is made according to the calendar age, the management is according to the gesta- tional age.
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The distinction between elasticity and in- stability.
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