Based on the preoperative CT or MRI image reconstruction of the lower extremity, the osteotomy angle and thickness are determined with the aid of computer-aided design (CAD), and the patient-specific instrumentation (PSI) is constructed using 3D printing technology to perform Total Knee Arthroplasty (TKA). The technique of TKA has been used in the clinic for many years. The theoretical goal is to reduce operative time and increase the accuracy of prosthesis placement to improve clinical outcomes for patients. However, the results of the most recent study (JAAOS 2013) suggest that there is no valid evidence that PSI offers these advantages over conventional TKA. Of course, the article does point out that for specific, complex TKA, PSI can provide useful assistance. The authors report a case of TKA with extra-articular deformity completed using PSI to explore the value of PSI in this type of procedure.
1. Medical history and diagnosis.
The patient was a female, 69 years old, with a history of 7 years. She presented with progressively increasing right knee pain and limitation of motion, which appeared after weight-bearing and exertion, and was worse after going up and down stairs, and could be relieved after initial rest, and was treated conservatively with oral glucosamine sulfate, non-steroidal anti-inflammatory drugs, and “small acupuncture” and intra-articular injection of sodium vitrate. He was injured in a car accident 23 years ago, resulting in a comminuted fracture of the right lower middle femur, and underwent an incision and internal fixation. He had a history of hypertension, which was well controlled by regular antihypertensive drugs. The patient was 153 cm tall, weighed 85 kg, and had a BMI of 36 kg/m2. 25 cm of postoperative scar on the right knee, 10-90 degrees of right knee mobility, pressure pain on both the medial and lateral knees, and positive patellar grinding. Preoperative full-length x-ray and weight-bearing ortho-lateral radiograph of the knee suggested severe osteoarthritis of the right knee and angular deformity of the right lower and middle femoral segments.
Preoperative diagnosis: severe osteoarthritis of the right knee, postoperative right femoral stem fracture (angular deformity), hypertensive disease.
2. Preoperative plan.
(1), severe osteoarthritis of the knee, pain, affecting the patient’s life, consistent with the indications for total knee replacement.
(2), The deformity occurred in the coronal position, extra-articular middle and lower femur; measured in full-length lower extremity film, the middle and lower femur was angulated medially, and the femoral valgus angle was about 14 degrees.
(3), Full-length CT scan of the right lower extremity was taken, and the DICOM format file was input into Materialise Mimics 17.0 for 3D reconstruction to determine the center of rotation of the femoral head, the center of the knee joint and the center of the ankle joint, to mark the mechanical axis of the femur and tibia, to determine the osteotomy direction of the femur and tibia in coronal position perpendicular to the mechanical axis, and to determine the osteotomy thickness with the initial replacement criteria.
(4), select the surface of the bony structure that can be determined to be revealed during surgery, and reverse the reverse model. The STL file of the guide plate was designed and generated, and the osteotomy guide plate was 3D printed in the EOS FORMIGA110 device using medical plastic PA2200, sterilized and ready for use.
3.Surgical operation points.
(1).Conventional access to reveal the joint, but preserve the femoral condyle and tibial plateau edge bone.
(2) The bone surfaces in contact with the osteotomy guide should be fully exposed, such as the anterior femoral cortex and the medial part of the tibial tuberosity, and the meniscus and other residual structures should be removed; the platform and the cartilage of the femoral condylar surface in contact with the osteotomy guide should be scraped off with special tools.
(3) The osteotomy module is closely fitted to the bone surface and then fixed with a fixed nail. After reconfirming that the osteotomy angle and thickness are consistent with the preoperative plan, the osteotomy of the distal femur and proximal tibia is completed; the thickness of the osteotomy block is measured to determine whether it is consistent with the preoperative plan.
(4).Use the through condylar line and Whiteside line to determine the external rotation of the femur, and complete the osteotomy of the anterior and posterior femoral condyles with conventional tools.
(5), Use a gap gauge to measure the flexion-extension gap with a medial-lateral balance in the flexion position and a tight medial gap of approximately 5 mm in the extension position.
(6), Use Pie-Crusting technique to release the posterior half of the superficial medial collateral ligament to balance in the extension position.
(7).Finish the prosthesis installation according to the routine.
4.Post-operative treatment Routine anticoagulation, infection prevention, analgesia treatment after surgery, 24 hours after drainage removal joint extension and flexion functional exercise, and support crutches for weight bearing on the ground. Post-operative X-rays were taken, and the force line of the lower limb was restored and the prosthesis was placed accurately.
Total knee replacement for extra-articular deformity usually requires a thorough evaluation of the site of deformity, the angle of the deformity, and the impact of the deformity on the surgical operation to determine whether the deformity should be corrected intra-articularly or extra-articularly; whether the deformity should be corrected and replaced in one phase, or staged. Typically, deformities that are distant from the articular surface, single-plane, and relatively small in angle can be corrected intra-articularly.
Extra-articular deformities may cause difficulty in determining lower extremity force lines, interfere with the use of intramedullary positioning rods, and cause new soft tissue imbalances through intra-articular osteotomy correction. Computerized navigation can help determine lower extremity force lines without the need for intramedullary positioning, and navigation with a soft tissue balance design can also aid surgical manipulation and is appropriate for use in joint replacement for extra-articular deformities. However, computerized navigation is not commonly performed due to expensive equipment, long learning curve, and increased operative time. The use of 3D printing to create personalized osteotomy guides saves surgical operation time through detailed preoperative design, special software and equipment can be purchased by the manufacturer, and the guide operation process is simple and easy to master. The disadvantages are that it requires additional cost for CT or MRI scan of the lower extremity; the design and production of the guide requires special operators and doctors, which requires a certain amount of preparation time; and once the surgical plan is changed, the guide cannot be reused; the accuracy of the surgery depends on the accuracy of the design and the precision of the guide. Because the difficulty in this case was the determination of the femoral force line and osteotomy, only the distal femoral and proximal tibial osteotomy guides were used. With regard to the design of the guide plate, it was relatively easy to determine the force line of the lower extremity with high accuracy. In contrast, the determination of external rotation of the femur depends on the accurate judgment of the through-condylar line, so it is prone to deviation.
In this case, although the femoral deformity was slightly near the level of the joint, it was only in the coronal plane and the angle was not large (the valgus angle was 14 degrees and the angular deformity was about 10 degrees). With preoperative measurements, the deformity could be corrected by reducing the distal osteotomy of the medial femoral condyle and appropriately increasing the distal osteotomy of the lateral femoral condyle. However, a non-rectangular extension gap is subsequently created, due to a medial-lateral ligament imbalance due to degeneration on the one hand, and a soft tissue imbalance due to intra-articular orthosis on the other. The former is balanced by deep medial collateral ligament release and medial bone removal; the latter is released by the author using the medial collateral ligament Pie-Crusting technique, which has the advantages of not increasing the damage of excessive stripping of the medial structures, not affecting the joint line level, and operating in a straightforward and controlled manner.
Therefore, the use of 3D printing technology to design personalized osteotomy guides can provide an effective solution for total knee replacement with extra-articular deformities.