Clinical History, Examination and Blood Test Results

  • Step 7 case 1 is a 61-year-old man who presented with a painful, dislocating right hip replacement.  His rheumatoid arthritis destroyed many of his joints. He had a right hip replacement in 1995 which functioned well until 2006. He then experienced increasing pain until he developed recurrent dislocation and inability to walk in 2016.  

  • Examination revealed an inability to walk, a leg length discrepancy of 8cm, no neurological deficit and no skin ulcers.

  • Blood inflammatory markers were normal.


Imaging Results

PRE-OP RADIOGRAPH

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Anteroposterior (AP) radiograph showed massive acetabular bone loss, proximal migration of the cup, erosion of the ilium by the femoral head and suspected loosening of the femoral stem. 

 

3D RECONSTRUCTION OF RIGHT HEMIPELVIS

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This image shows a 3D reconstruction of the acetabular defect of this patient. Software was used to generate this model from his pre-operative CT scan. The 3D model makes it easier to visualise the extent of this patients large Paprosky 3B defect.

 

PRE-OP CT SCAN

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This is a computed tomography scan of the same patient, demonstrating the remaining acetabular bone stock. As you scroll through the images you can see the size of the defect. This scan was used to design a custom implant, made from trabecular titanium, to fit this large Paprosky 3B defect.

 

3D MODEL OF RIGHT HEMIPELVIS 

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This is an image of the patients hemipelvis, showing the scale of the acetabular defect. It has been 3D printed and sterilised for intraoperative use.


Diagnosis

  • Severe acetabular defect classified as a Paprosky 3B.

  • Requires a custom acetabular implant because all other steps on the ladder of reconstruction are unlikely to work.


Treatment

IMPLANT DESIGN

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TRABECULAR TITANIUM

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This series of four images shows the design of the custom made implant for this patient. It is designed using the 3D reconstruction of the patient's pelvis to be complementary to the patient's own defect. The areas in green highlight regions produced from trabecular titanium to encourage bone growth for implant fixation.

This image shows the Trabecular Titanium used with these implants. In order to manufacture this structure, rapid prototyping, better known as 3D printing is utilised. This is made using electron beam sintering, which means the structure is continuous. The pores within the material have been shown to encourage bony ingrowth. 

 

IMPLANT AND PELVIC MODEL

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The first image demonstrated a 3D printed model of the implant placed within the 3D printed hemipelvic model (pictured above). The second image demonstrates the 3D printed drill guides, used intraoperatively, to guide the trajectory of the screws. All of these models are sterilised and used in the operation.

 

Key surgical steps

  • Posterior approach to allow extensile exposure of acetabulum and femur.

  • Release of psoas and gluteus maximus from the femur, and abductors from the ilium.

  • Bone preparation with reamers according to 3D computer plan and checking using sterilised plastic 3D-printed models of the acetabular pre and post bony preparation.

  • 3D printed trabecular titanium implant secured with at least 3 good screws.

  • Dual mobility bearings 44mm.

  • Cement-in-cement, small sized stem to allow for adjustment of offset and leg length.

  • Wash.


Imaging Outcomes

POST-OP RADIOGRAPH

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This post-operative AP radiograph shows the custom made Trabecular Titanium implant in situ within the pelvis, held in with three screws achieving a good initial fixation. The new stem has been cemented into the existing cement mantle. Note that only three of the seven planned screws were used.

 

POST-OP CT SCAN

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This is a computer tomography scan from the same patient. This gives you a better understanding of how the new implant is sitting against the existing acetabular bone stock. The idea is to get the trabecular metal in contact with the bone stock to encourage bony in growth. Scroll through the images.

 

3D RECONSTRUCTION OF IMPLANT IN PELVIS

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This is a 3D reconstruction produced from the post-operative CT scan above. The opacity of the pelvis has been reduced to highlight the custom implant and femoral stem

 

Clinical Outcomes

  • Outcome at 1 year post operative revealed the patient was very pleased with the outcome of the surgery. He walks with a crutch.

  • Hip movements are painless. He is able to flex up to 40 degrees (passively to 80), abduct 20 degrees.

  • He mobilises with one stick and has no mechanical symptoms or instability


Learning Points

  • Meticulous pre-operative planning required.

  • Extensive surgical exposure required.

  • Close post operative monitioring.