CASE 40: 3D printed guides for femoral neck cut and stem version

The Story

“Zeynep first presented to my clinic with ongoing pain and stiffness in both of her hips and her lower back. This was causing her to limit her normal day to day activities. She was only 49-years old when she presented, much younger than the average age for primary hip replacement in the UK, 67-years old. For this reason, we had to position her implant with the greatest precision to try and increase the longevity of her implant.

She had complex hip anatomy. She had coxa vara of the femoral neck, acetabulae protrusio and a ring of acetabular osteophytes.

This was hugely impacting her life, as she loved hiking and running. The pain she was experiencing was preventing her from being able to do this, and she was keen to get back to sport after her operation.”

The Investigation

Plain radiographs confirmed end staged osteoarthritis.

The Evidence

Coronal CT demonstrating end stage osteoarthritis in both hips. The pre-operative scan was used to plan the procedure and design the patient specific instrumentation for Zeynep’s operation. This instrumentation guides the surgeon in the femoral neck cut and the reaming angle of the acetabulum.

EOS (standing) demonstrates Zeynep’s varus femoral necks. Biplanar low-dose EOS imaging in the standing position is used to help understand leg alignment in a functional position. Patients with varus femoral necks are at an increased risk of post-operative leg length discrepancy, so understanding their functional anatomy pre-op is vital for surgical planning.

EOS (sitting) was ordered pre-operatively to help plan the procedure. The lateral image is used to assess the spinopelvic alignment in a sitting position.

Pre-operative 3D reconstructed CT of the patient’s anatomy. Image courtesy of mediCAD®, Hectec GmbH.

The Diagnosis

Zeynep had bilateral end stage osteoarthritis at a young age requiring bilateral total hip arthroplasty.

The Plan

We planned to perform a primary total hip replacement using 3D CT planning (for planning implant sizes and positions) and patient specific instrumentation (PSI) to deliver the planned implant positions in the operation.

The preoperative CT scan was analysed and used to plan the optimum femoral stem and acetabular cup for Zeynep. Using a computer reconstructed 3D model of Zeynep’s pelvis, instrumentation specific to Zeynep’s anatomy was designed to guide the surgeon when making the femoral cut and reaming the acetabulum.

The PSI jigs are 3D printed from plastic and are sterilised before being used intraoperatively. They locate to specific bony landmarks identified on the pre-operative CT scan. The femoral jig fits over the femoral head and neck. Two pins can be used to secure the jig. It shows the surgeon the optimum position for making the femoral cut and the optimum angle to make the cut at. Provided the jig is correctly located, this helps to improve the accuracy of the cut.

We planned to replace her left hip first, followed by her right with time for post-operative recovery in between.

PSI femoral jig sat on a 3D printed model of the patient’s proximal femur. This jig is designed for the posterior surgical approach and is also complementary to the patient’s anatomy. It is used to aid in the cutting of the femoral neck, to ensure the position and the angle of the neck cut is correct. Note this is a right sided model and we are looking at the posterior aspect.

CT plan (left) - 3D plan and ‘transparent view’ of the 3D plan demonstrating the acetabular and femoral component’s position and orientation illustrating the planned restoration of the centre of rotation. Images courtesy of mediCAD, Hectec GmbH.

CT plan (right) - 3D plan and ‘transparent view’ of the 3D plan demonstrating the acetabular and femoral component’s position and orientation illustrating the planned restoration of the centre of rotation. Images courtesy of mediCAD, Hectec GmbH

The First Operation

We used a posterior approach with 4 stay sutures to protect the nerve.

• The femur was cut with the PSI jig.

• The socket was reamed to 45mm using the PSI orientation guide.

• Bone graft from the femoral head was inserted into the medial wall to help build bone stock within this protrusio hip.

• A 46mm socket was impacted with a press fit. A ceramic 28mm liner was inserted.

• A femoral stem, size 2 Short neck lateralised, was inserted with a short 28mm ceramic head.

• Length and stability were satisfactory.

The First Outcome

Anteroposterior plain radiograph demonstrating the left total hip replacement in situ. The position of the implant is good.

Lateral plain radiograph showed good position of femoral stem and cup.

The Second Operation

The second procedure was a repeat of the first, on the right-hand side. We were able to capture some intraoperative images to demonstrate the femoral jig in use.

PSI femoral jig (intraoperative image 1) - This image shows the placement of the femoral jig on the posterior aspect of the proximal femur.

PSI femoral jig (intraoperative image 2) - This image shows the jig, pinned in place, being used as a cutting guide to remove the femoral head.

PSI femoral jig (intraoperative image 3) - Image three shows the femoral head being removed with the jig attached.

The Second Outcome

The achieved femoral neck cut level has a high accuracy when using a 3D printed guide.

In cases where the internal anatomy of the patient’s femur is complex or would not allow to achieve an optimal prosthetic femoral version, the surgeon can choose cemented fixation and have greater control of the stem version.

Intra-operative anteversion guides and cemented stems help deliver the target version.

Anteroposterior plain radiograph demonstrating both hip replacements in situ. Both are in the planned position.

Lateral plain radiograph showed good position of femoral stem and cup.

Post-operative 3D CT reconstruction showed accurate reconstruction of horizontal and femoral offsets.

Post-operatively the patient was happy with her bilateral hip replacements. She is undergoing physiotherapy with the aim to return to running.

The Verdict

Zeynep’s case was a complex primary hip replacement. There were three main challenges:

1. Young patient under 50

   • It is important that this implant lasts as long as possible. This may need to last for up to 50-years. There are 3 main factors that determine how long a hip implant will last: surgical, implant and patient. Patient specific instrumentation can guide the surgeon in achieving an optimal position in complex cases.

2. Reconstructing the medial acetabular wall and the hip centre of rotation.

   • The protrusio acetabulae result in native acetabulae that are more medial than normal. Techniques include: minimal acetabular reaming, bone autograft (from the femoral head) at the base and a cup that is not too small or too medially placed.

3. Avoiding leg length discrepancy

   • All complex hip anatomy cases increase the risk. In this case, the Coxa vara increases the risk of a longer leg as most stems have a larger neck angle than this patient.

Other important operative considerations for Zeynep included:

• Ring osteophytes and protrusio acetabulae can result in a “captive” hip: this risks fracture of the femur or posterior acetabular wall if care not taken during dislocation during hip replacement. This can be avoided if the osteophytes are removed before dislocation or the neck is cut before dislocation.

• For cases of acetabular protrusio, bone graft from the femoral head (autograft) can be used (sliced) to place in the floor of the acetabulum.

• In closer detail

  Preoperative planning is key to preparing surgical procedure. It is of great importance to achieve a satisfying functional outcome through adequate component orientation and fixation, restoration of femoral offset and limb length but also for implant size prediction. Whilst plain radiograph templating is currently the standard approach for preoperative planning of THA and has become an essential aspect of preparation for elective surgery, the use of three-dimensional computed tomography (3D-CT) imaging for pre-operative planning remains limited. 3D-CT aids surgical more accurately planning and implant sizing, crucial for good functional hip reconstruction.

  3D CT planning is likely to expand as the demand increases for everlasting and “do-it-all” hip replacement.

• Evidence for this treatment

  Otomaru I, Nakamoto M, Kagiyama Y, Takao M, Sugano N, Tomiyama N, et al. Automated preoperative planning of femoral stem in total hip arthroplasty from 3D CT data: atlas-based approach and comparative study. Med Image Anal. 2012;16(2):415-26.

  Belzunce MA, Henckel J, Di Laura A, Hart A. Uncemented femoral stem orientation and position in total hip arthroplasty: A CT study. J Orthop Res. 2020.

  Moralidou, M., Di Laura, A., Henckel, J., Hothi, H., & Hart, A. J. (2022). Accuracy of a Three-Dimensional (3D)-Printed Patient-Specific (PS) Femoral Osteotomy Guide: A Computed Tomography (CT) Study. Bioengineering, 9(11), 667.

  Moralidou M, Henckel J, Di Laura A, Hart A. Guiding prosthetic femoral version using 3D-printed patient-specific instrumentation (PSI): a pilot study. 3D Printing in Medicine. 2023 Dec;9(1):1-8

  Moralidou, M., Di Laura, A., Henckel, J., Hothi, H., & Hart, A. J. (2020). Three- dimensional pre-operative planning of primary hip arthroplasty: a systematic literature review. EFFORT open reviews, 5(12), 845.

  Di Laura, A., Henckel, J., Hothi, H., & Hart, A. (2020). Can 3D surgical planning and patient specific instrumentation reduce hip implant inventory? A prospective study. 3D Printing in Medicine, 6, 1-11.

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