CASE 35: Revision for infection and malalignment using a CT planned femoral stem
The Story
“Iain limped into my office with crutches and constant right hip pain. At the age of 45, his life was a mess because of a right hip operation done 9-months previously. When he had his primary hip replacement, the surgeon had failed to recognise the significance of a bone island in his proximal femur just below the lesser trochanter (and with a similar appearance to the lesser trochanter it is easy to mistake on follow up films as the lesser trochanter).
He had sustained an intra-operative fracture at the time of his primary replacement. The surgeon used a plate and cables and changed the stem to a longer and modular-taper fluted design. This operation took 12-hours and he woke up in intensive care at a different hospital due to blood loss.”
The Investigation
Iain’s blood CRP was raised > 10mg /L so he underwent right hip aspiration which grew staphylococcus epidermidis. Serial plain radiographs showed a loose femoral stem.
The Evidence
Anteroposterior plain radiograph demonstrated a loose stem (it had moved compared to the previous radiograph). His femur was rotated and shortened by 2 centimetres. On first glance at this radiograph the leg length discrepancy doesn’t make sense as it appears as if the lesser trochanters are at the same level, however this is not the case. See the image to the right.
Anteroposterior plain radiograph with arrows. The blue arrows are pointing to the greater trochanters, with the right being about 3-4cm higher than the left. The red arrows are pointing to the true lesser trochanters, which once again are not sitting at the same height. The white arrow is pointing to a bone island on the right trochanter. This bone island is easily mistaken for the lesser trochanter.
The Diagnosis
Iain had a loose and infected right femoral stem. After discussion with the microbiologists, we planned a 2-stage revision for Iain.
The Operation - Stage one
For the first stage of Iain’s treatment, we planned to remove all of his current metal work on the left side, including the plate and cables, so we could then implant a spacer. This approach was used to manage the underlying infection.
We used Iain’s existing posterior approach scar to access his right hip. After releasing the surrounding musculature and dislocating his existing implant, it was clear just how loose the construct was.
Intraoperative stills demonstrating the excessive movement within the femoral stem. Here you can see the stem medialised and then lateralised within the femur showing how the stem is far too small for the femur.
The Plan - Stage Two
After the first stage, Iain underwent a CT scan with the spacer in situ. Taking the CT scan after the first stage of his treatment allowed for a reduction in the metal artefact in the CT images, making the subsequent 3D reconstruction of the bony anatomy more accurate. We used the 3D reconstruction of the CT scan to plan the revision procedure; to size the implants; to assess the peri-prosthetic fracture and to reduce the operative time.
CT scanning for pre-operative planning is invaluable in cases with such complex anatomy secondary to a complicated primary procedure.
3D reconstruction from CT demonstrating Iain’s bony anatomy with the spacer in situ. One cable was retained after the first stage procedure. This bony anatomy was then used to size the modular taper fluted stem.
Planning images produced from the 3D reconstruction CT above. Here the replacement implant has been superimposed into the bony anatomy to demonstrate the plan for the final implant position.
The Second Operation - Stage Two
We used the same approach as the first stage. The spacer was removed. We then implanted a new acetabular shell and the CT planned modular taper fluted stem without any complications.
The Outcome
Anteroposterior plain radiograph of the pelvis pre-op for comparison to the post-operative radiograph. White arrow = Bone island. Red arrow = Lesser trochanters. Blue arrow = Greater trochanters.
Anteroposterior plain radiograph of the right hip demonstrates the larger modular taper fluted stem in situ with evidence of healing of the previous peri-prosthetic fracture. Note how the cables and plate have been removed. This image shows a good position of the stem.
3D reconstruction of post-operative CT scan demonstrated that the CT plan was achieved.
Anteroposterior plain radiograph of the pelvis post-op labelled with arrows. Here you can see that both the greater and lesser trochanters are sitting at the same levels bilaterally and the bony island has been shifted caudally.
Lateral plain radiograph of the right hip shows the healed peri-prosthetic fracture.
Planning image produced from the pre-operative CT scan for comparison to the post-operative 3D reconstruction.
The Verdict
Iain’s initial operation could have been planned much better if CT planning had been used first time around. The CT plan for the revision operation reduced uncertainty over the healing of the peri-prosthetic fracture and shortened operative time. It ensured optimal biomechanical reconstruction through the use of the planned sizes of implant.
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3D planning is an essential step in the preparation for elective hip surgery. Its technical goals include optimal implant sizing and position as well the restoration of femoral offsets, leg length and the centre of rotation.
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For our other cases on non-CT planned modular taper fluted stems, please see Case 10 and
http://www.complexhipsurgery.com/discussion-case-five
