PMC5121176_01
Post-operative anterior-posterior plain film radiograph of the patient's left hip. No cause of the patient's mechanical symptoms was detected
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Fig1
Anterior-posterior and lateral X-rays of the patient's hip were acquired (Figs. 1, 2).
Post-operative lateral plain film radiograph of the patient's left hip. No cause of the patient's mechanical symptoms was detected
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Fig2
Anterior-posterior and lateral X-rays of the patient's hip were acquired (Figs. 1, 2).
A 2D CT coronal slice of the patient with the mismatched left hip resurfacing (right) and the patient's previous right hip resurfacing (left) in view. The femoral head of the mismatched component is not sitting centrally in the acetabular component with B being 1.5 times greater than A. On the previous right hip resurfacing, with correctly paired components, the femoral head is centrally placed (C to D)
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Fig3
Consequently, a low-dose CT scan (1.4 mSv) of the patient's hip was obtained (Fig. 3).
Three-dimensional model of the patient's metal-on-metal (MoM) resurfacing. The acetabular (A) and femoral head (B) centres of rotation have been marked and the red arrow demonstrates that the two points are not overlapping, which indicated component size mismatch (CSM)
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Fig4
The centre of rotation of each component was compared (Fig. 4) and the distance between the edge of the acetabular cup and femoral head surface was measured (Fig. 5). This method works on the premise that a fully engaged head should be equally spaced from the outer surface of the acetabular cup and that the centre of rotation of spheres fitted to the outer surface of the acetabular and femoral head components should overlap, provided that an offset-bore acetabular component has not been used.     Three-dimensional analyses of the CT scan indicated a potential CSM (Figs. 4, 5).
Lateral (left) and true anterior-posterior of the acetabular cup (right) views of a three-dimensional model of the patient's MoM resurfacing. A is the acetabular centre of rotation and B is the femoral head centre of rotation. The red arrows indicate that the femoral head is not centred in the acetabulum, which suggests CSM
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Fig5
Three-dimensional analyses of the CT scan indicated a potential CSM (Figs. 4, 5).
Photo of the revised Adept hip resurfacing removed from the 53-year-old gentleman. Manufacturer labels in the surgical notes record the components as being a 56-mm cup designed for a 48-mm head and a 48-mm head. Engravings (red arrows) and coordinate measuring machine measurements confirm the CSM, as the cup is actually a 56-mm cup designed for a 50-mm head
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Fig6
On visual inspection, implant labelling pointed to a bearing size mismatch (Fig. 6).