The Use of Mixed Reality in Custom-Made Revision Hip Arthroplasty: A First Case Report

Summary

A complex revision hip arthroplasty was performed using a custom-made implant and mixed reality technology. According to the authors' knowledge, this is the first report of such procedure described in the literature.

Abstract

The technology of 3D printing and visualization of anatomical structures is rapidly growing in various fields of medicine. A custom-made implant and mixed reality were used to perform complex revision hip arthroplasty in January 2019. The use of mixed reality allowed for a very good visualization of the structures and resulted in precise implant fixation. According to the authors' knowledge, this is the first described case report of the combined use of these two innovations. The diagnosis preceding the qualification for the procedure was the loosening of the left hip's acetabular component. Mixed reality headset and holograms prepared by engineers were used during the surgery. The operation was successful, and it was followed by early verticalization and patient rehabilitation. The team sees opportunities for technology development in joint arthroplasty, trauma, and orthopedic oncology.

Introduction

The technology of three-dimensional (3D) printing and visualization of complex structures is rapidly growing in various fields of medicine. These include cardiovascular surgery, otorhinolaryngology, maxillofacial surgery, and, above all, orthopedic surgery^1,2,3,4,5. Currently, this technology is used in orthopedic surgery not only in the direct implementation of 3D printed elements, but also in surgical training, preoperative planning, or intraoperative navigation^6,7,8.

Total hip arthroplasty (THA) and total knee arthroplasty (TKA) are one of the most frequently performed orthopedic surgical procedures worldwide. Due to the significant improvement in the patient's quality of life, THA had been described in a previous publication as the "surgery of the century"⁹. In Poland, 49.937 THA and 30.615 TKA were performed in 2019¹⁰. As life expectancy increases, there is an upward trend in the projected number of hip and knee arthroplasty surgeries. Great efforts have been made to improve implant design, surgical technique, and postoperative care. These advances led to a better chance of restoring patient function and reducing the risk of complications^11,12,13,14.

However, the big challenge currently faced by orthopedic surgeons worldwide is working with non-standard patients whose anatomical defects in the hip joint make it very difficult or even impossible to implement an off-the-shelf implant¹⁵. Bone loss may be due to significant trauma, progressive degenerative osteoarthritis with an acetabular protrusion, developmental hip dysplasia, primary bone cancer, or metastasis^{16,17,18,19,20}. The problem of implant selection specifically concerns patients who are at risk of multiple revisions, sometimes also requiring unconventional treatment. In such cases, a very promising solution is an additive-made 3D printed implant created for a specific patient and bone defect, allowing for a very precise anatomical fit²⁰.

In the field of arthroplasty, precise implant and its sustainable fixation are crucial. Progress in preoperative and intraoperative 3D visualization has resulted in excellent solutions as augmented and mixed reality^21,22,23,24. Intraoperative use of bone and implant computed tomography (CT) holograms may allow better prosthesis placement than conventional radiography images. This emerging technology may increase the chances of therapy effectiveness and reduce the risk of neurovascular complications^21,25.

This case report concerns a patient subjected to hip revision surgery due to aseptic loosening. To address significant bone loss caused by multiple implant failures, the custom-made 3D printed acetabular implant was used. During the procedure, we used mixed reality to visualize the implant position to avoid damaging the at-risk neurovascular structures. Application implemented to mixed reality headset allows giving voice and gesture commands, making it possible to use it in sterile conditions during the surgical procedure.

A 57-year-old woman was admitted to the department with a preliminary diagnosis: loosening of the left hip's acetabular component. The patient's disease history was extensive. Throughout her life, she underwent numerous surgical procedures of the hip joint. The first treatment was hip resurfacing due to osteoarthritis caused by hip dysplasia (1977-15 years old), the second was a total hip arthroplasty due to implant loosening (1983-21 years old), and other two revision surgeries (1998, 2000-37 and 39 years old). Moreover, the patient was suffering from spastic left-sided hemiplegia caused by childhood cerebral palsy, and she was repeatedly operated due to left clubfoot deformity. She was also burdened with osteoarthritis of the thoracolumbar spine, carpal tunnel syndrome, and well-controlled arterial hypertension. The final diagnosis preceding the qualification for the next procedure was the pain and increasing function limitation caused by loosening of the left hip's acetabular component. The patient was highly motivated, physically active, and coping with disability.

Protocol

The protocol follows guidelines of the Human Research Ethics Committee of the Medical University of Warsaw. The patient gave informed consent to the procedure and acknowledged the fact that it will be recorded. The patient agreed to that prior to the procedure.

NOTE: The basic criterion for including the patient in the surgery project was the necessity to intervene because of the anatomical dysfunction, which made it impossible to use a standard implant. Mixed reality was aimed at better placement of the prosthesis, increasing the chances of successful surgery.

1. Preparation

1. Prepare a custom-made acetabular implant and plan the surgical procedure before the patient's hospitalization.
   NOTE: In this case study, persons skilled in the art of medical image diagnostics prepared the custom-made acetabular implant.
   1. Before the planned admission to the hospital, perform an x-ray in the diagnostic imaging unit.
   2. Perform a pelvic X-ray in an anterior-posterior projection.
   3. Assess the current condition of the patient's pelvis based on the X-ray.
   4. Compare the image obtained with the earlier X-ray images.
2. Take a pelvic CT scan and acquire DICOM (Digital Imaging and Communications in Medicine) files according to the protocol.
   1. Place the patient on the moveable CT scan platform.
   2. Click on the thickness button and select 512 x 512 px thickness for the scans.
   3. Click on the parameter that determines the thickness of the 1 mm layer.
   4. Start the procedure by clicking, wait for the test result.
3. Ask an engineer to design an implant proposal that can be sent digitally as a technical scheme, or a 3D printed model prototype (Figure 1).
   1. Visualize the computed tomography result in the DICOM viewer.
   2. Determine the needs for the implementation of the implant, taking into account the current anatomical conditions of the patient, biomechanics, and the function of the joint.
   3. Consult the engineer for suggestions on implants, including fixation.
   4. Approve the project and wait for shipment.
      NOTE: The final shape of the implant involves combining 3D data from a patient's CT scan with the input of a design engineer and a surgeon.
4. Print the custom-made 3D implant from the titanium alloy powder (TiAl6V4) using electron beam technology^26,27. Inside a chamber containing small amounts of TiAl6V4 powder, each time the electron beam is fired, there is selective melting and accumulation of material (plasma coating).
5. Check whether the implant was sterilized. Sterilization of implant trials and the final implant was guaranteed by the manufacturer.

2. Pre-surgery checkups

1. Perform a standard of care laboratory tests and specialist consultations.
   1. Exclude patients with potential periprosthetic joint infection (no radiological features, normal c-reactive protein (<10 mg/L), and erythrocyte sedimentation rate of 1-10 mm/h for women, 3-15 mm/h for men).
2. Check for the clinical signs of infection such as fever (systemic), pain, swelling, redness (local), and reduced joint function²⁸.
   1. Exclude patients having signs of local inflammation during the clinical examinations (redness, temperature increase, pain, swelling and loss of function indicate local inflammation). The patient gave complete informed consent to the operation.

3. Mixed reality model

NOTE: The process is performed to achieve proper implant and pelvis visualization, which will be used intraoperatively.

1. Process the pelvic CT DICOM file into a holographic representation using dedicated application.
   1. Load the CT image into mixed reality headset from acquired CT DICOM files.
      1. Open holographic DICOM Viewer.
      2. Select the folder containing CT DICOM files.
      3. Check the IP that is displayed when the headset is switched on and enter it in a designated place in the holographic DICOM Viewer.
      4. Click on the Connect button to be able to see the visualization in the mixed reality headset.
   2. Segment the pelvis bone tissue structures. This is performed manually by using the Scissors option. When the option is enabled, the user clicks the left mouse button and moves the mouse around to remove the structures that are selected with this tool.
      1. End the selection with another click of the left mouse button, which creates a pop-up for the user to confirm that he/she wants to cut out the structures that are selected.
         NOTE: The user can choose areas to be cut out from the visualization in both 3D and 2D views. It is possible to remove the structures from within or outside the selection. This is repeated until only the necessary parts of the CT image are visible.
   3. Choose a predefined transfer function (color visualization parameters) dedicated to orthopedic procedures from the list of available functions by clicking on its name: CT Bone Endoprosthesis. If needed, adjust the visualization by changing the window and level using the right mouse button connected with mouse movement in the 3D visualization window.
   4. Connect to the headset to see the prepared visualization in the 3D holographic space. Adjust the image using voice commands: Rotate, Zoom, Cut Smart, and Hand Gestures.
   5. Use the Cut Smart command to use and adjust a cutting plane that is perpendicular to user's line of sight. The closer the user moves the head into the hologram, the deeper the plane goes.
   6. Perform these movements to see the inner parts of the visualization because structures that are located anteriorly to the plane are not visualized.
      NOTE: This view is important to assess the geometrical relations between structures (pelvis, femur, and implant) (Figure 2 and Figure 3).

4. Surgery

1. Perform the surgical procedure of revision hip arthroplasty due to aseptic loosening of the acetabular component with the use of a custom-made acetabular implant and mixed reality device^14,16,29. Use a scalpel, an electrosurgical knife with a coagulator, a Luer tool and cutters for the operation.
   1. Give 1.5 g of ceftriaxone intravenously 30 min prior to the skin incision, and two subsequent doses are to be given on the day of the surgery to prevent infection. Initiate thromboprophylaxis on the day before the surgery with low molecular weight heparin (LMWH). Continue the single daily dose of 40 mg enoxaparin for 30 days after the procedure.
   2. Place and secure the patient under general anesthesia, lying down on the operating table.
   3. Release the connective tissue adhesions using the Hardinge access to the hip joint and remove the loose acetabular implant.
   4. Perform the operation in the same way as other revision procedures of the hip joint, but use a wider access.
   5. Remove all soft tissues from the surface of the acetabulum so that the shape is exactly the same as in the model provided. The implant model must perfectly adhere to the surface of the acetabular bone.
   6. Fix the new uncemented implant using specially designed screws that stabilize the implant.
   7. Perform a femoral nerve block after surgery.
2. Intraoperative holographic visualization of processed images
   1. Load the visualization of the DICOM CT scan prepared in the pre-procedural planning to the mixed reality application.
   2. Connect the mixed reality headset to the mixed reality application to see the prepared visualization in the 3D holographic space.
   3. Use intraoperative holographic visualization of the processed images to achieve adequate and precise pelvic bone surface preparation as well as for removal of the excess of connective tissue that developed as a response to loosening of the acetabular component.
   4. Ensure that the operator looks at the holographic visualization as a reference image.
   5. Use a scalpel, an electrosurgical knife with a coagulator, a luer tool, and cutters for the operation. Visualization of the 3D pelvis model should minimize the risk of damaging neurovascular structures and mistakes in implant placement.
   6. Ensure that the head-mounted display is connected to the workstation through a WiFi network. The processing of the images and the rendering is performed on the workstation and the results are displayed on the headset as holograms. Use gestures and voice commands. If necessary, get help from an engineer with POV preview.

5. Postoperative care

1. Make the patient undergo a standard rehabilitation and recovery protocol, including rehabilitation and mobilization on the first day after surgery^30,31,32.
   NOTE: Rehabilitation was implemented by a dedicated team experienced in the hip and knee arthroplasty.
2. Implement pharmacological thromboprophylaxis. Thromboprophylaxis was initiated on the day before the surgery with low molecular weight heparin (LMWH). The single daily dose of 40 mg enoxaparin was continued for 30 days after the procedure.

Results

Image preprocessing
Binary masks of the pelvic bone, femur, and endoprosthesis were semi-automatically segmented from CT DICOM images by experienced radiologic technologists using thresholding and region growing algorithms with available software³³. The prepared label maps were also manually corrected by a radiologist. Label maps were used to enhance the visualization by adding them to the CT scan in the next step. This approach made it possible to merge the volumetric rende...

Discussion

Primary and revision hip arthroplasty may require personalization to ensure effectiveness of treatment. However, the use of custom implants requires longer preparation for surgery compared to standard procedures. Custom-made 3D printed implants are the solution that gives a chance to restore function in non-typical patients whose disease has caused significant bone destruction²⁹. Standard prostheses are insufficient due to advanced degenerative disease developing rapidly, bone defects caused by pr...

Materials

Name	Company	Catalog Number	Comments
CarnaLifeHolo v. 1.5.2	MedApp S.A.
Custom-Made implant type Triflanged Acetabular Component	BIOMET	REF PM0001779
Head Constrained Modular Head + 9mm Neck for cone 12/14, Co-Cr-Mo, size 36mm	BIOMET	REF 14-107021
Polyethylene insert Freedom Ringloc-X Costrained Linear Ringloc-X 58mm for head 36mm / 10 *	BIOMET	REF 11-263658