Introduction
At the Orthopaedic Research Laboratory (ORL) an anatomical shaped permanent medial meniscus implant, named Trammpolin, was developed. The Trammpolin implant was developed to reduce pain in the knee by restoring physiological cartilage stresses after a meniscectomy. Current treatments are pain medication and knee arthroplasty. With a limited life time of knee arthroplasties this isn’t a suitable solution for patient younger than 60. Using a minimally invasive, low impact procedure, the Trammpolin implant can be implanted, and reduce pain and restore the functionality of the knee. In a clinical trial the first patients have recently received the Trammpolin implant (Figure 1).
For optimal functioning, the Trammpolin implant needs to be positioned correctly. Therefore, within the BioMechMeniscus project pre-planner software was developed to select the optimal size and position. Furthermore, a patient specific surgical guide was developed to be able to accurately place the implant.
Pre-Planner software
Pre-Planner software was developed in which knee geometry files can be loaded based on MRI scans. Based on these geometry files the optimal size and location of the implant are determined based on the shape of the tibia, as can be seen in Figure 2. If necessary, in the Pre-Planner software the surgeon can make adjustments to the position of the implant, and choose a different size. When finalized, the implant, in combination with the tibia can be exported. This serves two purposes, first, for visualization in preparation and during the surgery; and second as an input for the design of a patient specific surgical guide.
The accuracy of the Pre-Planner tool was tested by comparing the automated size and location determination with the size and location determined by an orthopedic surgeon. For this test an existing database with 19 MRI scans of knees was used. These knees were previously segmented and converted into 3D models. Each knee was then run through the Pre-Planner for a size and location estimation. The Orthopedic surgeon then determined if the predictions were correct, or if (small) adjustments had to be made. The size of the implant was predicted correctly in 18 out of 19 cases. In one case the implant size predicted was one size too large. In 16 out of 19 cases the correct location was predicted. In the remaining 3 the position had to be moved more posterior for an optimal position.
Patient specific 3d printed surgical guide
For accurate placement of the Trammpolin meniscus implant a patient specific 3d printed surgical guide was developed (Figure 3). Based on the position determined by the Pre-Planner and after finetuning by an orthopedic surgeon, a guide was made, that will fit in only one location on the tibia (Figure 4). Currently used surgical tools can be attached to the patient specific guide for drilling holes and placing the screws in the tibia (Figure 5).
The patient specific 3d printed surgical guide was tested on a cadaver after each design iteration. In all of the cadaveric experiments the patient specific 3d printed surgical guide was capable of positioning the implant in a suitable location. The final design of the surgical guide resulted in the implant being placed in the desired location as was planned in the Pre-Planner.
Socioeconomic impact
The Pre-Planner provides the surgeon with the optimal size and location of the implant before the surgery. During the surgery this is also available and can be used to ensure the implant is positioned in the correct location. The Pre-Planner makes the surgery more time efficient, and reduces the risk of placing the implant in a less optimal location, and could therefor reduce the cost of surgery.
The 3d printed patient specific surgical guide furthermore simplifies the surgical procedure, ensuring the implant is placed at the desired position. This could reduce the surgical time, but more importantly the optimal placement of the implant could increase the patient satisfaction and function of the knee joint.
Conclusions
First patients were successfully implanted with the Trammpolin implant in a clinical trial.
In this study Pre-Planner software was developed in which the optimal size and location of the Trammpolin meniscus implant could be determined. In addition, a patient specific 3d printed surgical guide was developed. Both the Pre-Planner and the patient specific guide optimize the surgical procedure possibly resulting in a decrease in surgical time, and a better patient satisfaction, and knee function.
