Introduction
In healthy and normal knee joints, the ends of the bones are covered by a protective layer called cartilage. Several factors contribute to wearing away the cartilage layer in the knee joint such as age, obesity, trauma, repetitive stress, or genetics. This results in a bone-on-bone condition of the knee joint resulting in a painful condition called arthritis. The conservative management of this condition is carried out in the initial stages however if the symptoms fail to improve or if there is a failure in previous surgeries the patients are referred for total knee arthroplasty surgery. Patient-specific instrumentation technique involves modern technology in improving the efficiency of total knee arthroplasty surgery. This article will discuss patient-specific instrumentation techniques and their benefits and drawbacks in detail.
What Is Knee Arthroplasty?
Knee arthroplasty is referred to as total knee replacement or knee replacement, it is a surgical procedure that involves the replacement of the worn-off or damaged parts of the knee joint with an artificial prosthetic device.
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This surgical procedure helps in end-stage arthritis by relieving pain and preserving or retaining some range of motion in the knee joint.
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In circumstances where the entire knee joint needs replacement, the ends of the thigh bone and shinbone are repaired and the surface of the entire joint is resurfaced.
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The ends of the artificial prosthetics are inserted into the central parts of the bone and the surgeon may insert implants to secure the knee joints when the ligaments of the knee joint are not strong enough to secure the joint.
What Is Patient-Specific Instrumentation?
Orthopedic surgery is one of the rapidly growing fields with various advancements in its treatment and surgical technique. A proper surgical plan is necessary for a good surgical outcome. One of the advancements in the surgical technique of knee arthroplasty is patient-specific instrumentation (PSI).
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This is a modern technique that uses three-dimensional imaging from magnetic resonance imaging (MRI) or computed tomography (CT) to generate pre-operative planning for surgical bone cutting.
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This technique involves a computer-assisted surgical technique for generating pre-operative planning such as sizing, alignment of the prosthesis, customization of the resection blocks, and fabrication of the templates for the accurate and proper placement of the implant prosthesis.
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This technique allows for better restoration of the mechanical axis of the knee joint than the conventional total knee replacement surgery that used mechanical guides for the replacement surgery.
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A knee replacement surgery is only successful when there is proper knee alignment, kinematics of the knee, and soft tissue balancing. Patient-specific instrumentation technique takes that all into consideration during pre-operative planning.
What Is the Pre-operative Planning of PSI Technique?
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Prior to the surgery, the PSI surgical guide is created with the help of a three-dimensional model of the knee joint obtained using radiographic techniques such as MRI, CT, and a full-leg anteroposterior X-ray.
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The manufacturing engineers turn the two-dimensional images of the MRI or CT into a three-dimensional representation of the knee using a software program.
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This helps in identifying the anatomical landmarks of the knee.
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The pre-operative planning of the surgical technique is presented to the operating surgeon. The surgeon is able to correct or modify the surgical planning.
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Once the surgical plan is authorized by the surgeon, customized cutting guides for the tibial and femoral resections are manufactured.
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During the procedure, the PSI guides are used directly as slotted cutting guides.
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The PSI cutting guides are used for primary resection of the proximal tibia bone and distal femoral bone. Standardized instrumentations are used for the subsequent cutting.
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These customized cutting guides facilitate accurate bone resection.
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The remaining procedure is performed in the same way as usual knee replacement surgery.
What Are the Benefits and Drawbacks of the PSI Technique?
1. The PSI technique necessarily requires the use of MRI or CT before the surgical planning of the procedure. This in turn affects the patient by having additional expenses including the cost of the PSI technique. However, conventional instrumentation requires sophisticated sterilization which is quite expensive, hence the technique has the advantage of low cost compared to the conventional technique.
2. Pre-operative scanning plays an important role in determining surgical guides. The accuracy of the scanning technique is directly proportional to the accuracy of the cutting guides. Both MRI and CT have their advantages and disadvantages. CT scan is more user-friendly and enables the surgeon to perform the planning and designing, unlike MRI-based PSI which requires the technician to do manual segmentation of the image for designing and is contraindicated in patients with pacemakers, obese patients, and implants.
3. In PSI, the technique requires three to four weeks maximum for the final production of the cutting guides. This could delay the procedure.
- The PSI was adopted to reduce the surgical time of the TKA procedure however the time taken for preoperative imaging, transferring the image to the manufacturers of the cutting guide, pre-operative planning of the engineers, authorization from the operating surgeon, correction or alterations made by the operating surgeons, manufacturing the surgical guide, transferring the guide to the hospital and their sterilization could delay the waiting period of the patient.
- However, recent studies conducted comparing the operative time of the conventional technique and the PSI technique showed that the operating time of PSI was 24 minutes shorter than the conventional technique.
4. The successful outcome of the surgical procedure greatly depends on the surgeon’s experience and skill. Accurate placement of the surgical guide is mandatory. If there is any slight misalignment in the positioning of the surgical guide it could result in erroneous cuts in all three planes.
5. Post-operative knee pain and patellar tracking disorder (deviation or movement in the kneecap) are generally the most common complaints after a knee replacement surgery. Malpositioning of the implant in the conventional technique has resulted in patellar instability in the knee and procedure failure. Hence in the PSI technique, it is crucial for the surgeon to properly position the tibial cutting guide since it is closely related to the patellar tendon. Making sure the tibial cutting guide is in its proper position is necessary to avoid post-operative pain and patellar tracking disorder.
Conclusion
Total knee replacement surgery is commonly advised in patients with post-traumatic or end-stage arthritis. New advancements and the use of modern technology in the technique of TKA are determined to improve the accuracy of the procedure and reduce surgical time. Patient-specific instrumentation involves computer-assisted pre-operative planning. it is not recommended as a gold standard technique of TKA and studies do not suggest improved surgical outcomes in PSI technique. However, in cases with difficulties and complications in pre-operative planning, the PSI technique is recommended.
