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Introduction
Total Knee arthroplasty (TKA) is a common and successful surgical procedure. However, surgeons, engineers and scientists are trying to employ the new technologies of robotics, navigation and 3D printing to improve the outcome and patient’s satisfaction of TKA. As with any new healthcare technology, there are issues related to safety, cost effectiveness, and medicolegal aspects that could affect the ability to obtain FDA or CE certification. Patient-specific instruments (PSI) involve five different steps: imaging, planning, 3D production, packing/sterilization and finally the surgery. PSI are currently produced by the implant companies, but some of these steps are outsourced. This raises the medicolegal question: who is responsible for its failure?
De facto necessity of new technologies use
Since the emergence of 3D printers in the 80s, their use has been incorporated into many fields, including medical applications where conventional complicated tools and kits were replaced by PSI. They have been important and necessary for use in many complicated cases where conventional instruments were impossible to use, such as cases of dwarfism (achondroplasia), excessive femoral and tibial bowing, or even in cases of bleeding tendency such as haemophilia. They have been essential for use with cases of severe bone loss, such as revision total hip arthroplasty surgeries with custom-made implants, to the extent that they have become the de facto go-to-treatment for complicated cases such as cervical pedicle screw placement, revision total shoulder arthroplasty and complicated cases of bone osteotomy. With more technological advancements, other more sophisticated techniques, such as computer aided navigation (CAN) have been incorporated and this offers more accuracy and versatility with complicated cases. It should be noted that the term is used interchangeably with Computer-assisted orthopedic surgery (CAOS). It is expected that ascost of machinery decreases, CAN will become an essential part of day-to-day use¹. For example, the use of CAN in comparison to traditional 2D fluoroscopy has shown that lesser operative and insertion time is needed with CAN. Also, blood loss and incidence of complications were lower with CAN².
PSI prologue and scanning perplexities between MRI and CT scans
PSI is a technique that is used in bone surgeries and dental implant placements. The input generally consists of a scan of the region of interest, in addition to a model of the implant to be used, whether it is a pedicle screw, a dental prosthesis or a femoral and tibial implant in TKA surgeries. Once the input data are obtained, preoperative planning is performed to specify the location of the implant and accordingly match it with the PSI, which may have cutting slots to guide saw blades in bone resection, or drill holes to guide the drilling of dental implant, or a pedicle screw. The PSI is aligned to the patient anatomy using CAN software, so that in surgery, theoretically, the implant is placed in the exact position of its preoperative planning. The use of these techniques calls for the availability of a 3D model of the region of interest, which is obtained by the means of computed tomography (CT) or magnetic resonance imaging (MRI). Choosing a CT scan will give certain benefits for planning the case and increasing the accuracy, because the rate of changing bone in arthritis is much slower than the degradation of cartilage. Designing PSI for such a case is much easier than with MRI, which requires the presence of an experienced technician who will be able to make out the details of the already degrading cartilage from the rest of the soft tissue, especially in patients with obesity. Although a CT scan is cheaper than MRI, it also entails the risk of radiation exposure from X-rays. On the other hand, MRI may not be feasible for patients that have implants such as a pacemaker. Similar Computer aided techniques are employed during the use of robotics and computer navigation in TKA surgeries, which offer superior accuracy. Ironically, one of the methods for obtaining data in computer navigation is based on a CT scan, which is then coupled with the use of reflection pins that are used for referencing the position of the bone with respect to the robot.
Accuracy appraisal: TKA case study
The accuracy of PSI in TKA in comparison to conventional methods is generally comparable. According to a retrospective study that evaluated primary TKA in 150 cases, PSI offered better outcomes in the restoration of the kinematic axis, where the conventional instruments group had more valgus outliers than the PSI group³. On the other hand, Victor et al. stated that PSI doesn’t offer much improvement in TKA⁴. Regarding tibial and femoral component rotation, it was noticed that surgeons may not be able to recognize a 10-degree flexion secondary to flexed femoral and tibia components5. Thus the femoral component may be rotated internally. In PSI, the stem, keel in tibial implant and the pegs in the femoral implant are incorporated into the design of the guide and are thus predetermined and can be performed correctly. The final alignment of the PSI is of paramount importance. It is then preferred that a hospital-based system where the surgeon is more engaged in the positioning of the implant in preoperative planning (and thus the PSI) is used5, which is preferred than a having a technician perform the planning of the case to reduce legal liability.
Surgical challenges with navigation techniques, PSI and conventional instruments
In TKA surgery (and many other similar arthroplasty surgeries), the operating time is very important for many considerations, such as hospital capacity and possibility of infections in prolonged surgeries. The operating time consists of two parts, a fixed part and a variable part. The fixed part generally consists of time that is the same across all surgeries such as anaesthesia time, sterilizing operating site, tourniquet application and wound closure. The variable part is where the main operations of surgery occur and that is where PSI, CAN and conventional technique competes in time reduction. It was concluded that the use of PSI have yielded similar outcomes as with conventional surgeries. However, there some caveats to this, for example in TKA, the tibial PSI is said to have the highest percentage of inaccuracies, it is thus recommended that tibial PSIs are used very carefully along with verifying planned cut by means of CAN for a specific number of cases to help the learning curve⁵. However, it has been reported that in many cases, PSI had errors in them that rendered them unusable and, in such cases, switching to a conventional tool will prolong the time of surgery. In some cases, duplicate PSI for one part were delivered, which may affect surgery schedule⁶. Furthermore, CAN offers more options with regard to soft tissue release in case of a wrong planned cut, where trial implant can be used and the amount of soft tissue release is planned.
Outcome of each technique
In terms of each technique being compared, CAN offers the most accurate surgical performance, however, its cost is relatively a lot higher in comparison to PSI or conventional tools. Additionally, CAN-employed robots required very special calibration measures and may cause serious legal liability for both the manufacturing companies and the using surgeon.
Conclusion
The PSI technique is a promising toolkit and considered to be a middle ground alternative in knee surgery. It is user friendly and more cost- effective than robotics and navigation. From the medicolegal aspect, the responsibility toward its failure is divided between all parties involved in PSI production, and the source of errors should be identified and attributed to whoever was performing each step. Implant companies should not produce PSI without obtaining an approval of the planning from the surgeon. Recently, the author (MAH) has implemented a hospital-based PSI technique, where all five steps of PSI (imaging, planning, 3D production, packing/sterilization and finally the surgery) are done in one location⁷. This could eliminate the divided responsibility and the difficulty in identifying the source of errors.
References
[1] Desai, A. S., Dramis, A., Kendoff, D., & Board, T. N. (2011). Critical review of the current practice for computer-assisted navigation in total knee replacement surgery: cost-effectiveness and clinical outcome. Current reviews in musculoskeletal medicine, 4(1), 11–15. https://doi.org/10.1007/s12178-011-9071-1
[2] Meng, X. T., Guan, X. F., Zhang, H. L., & He, S. S. (2016). Computer navigation versus fluoroscopy-guided navigation for thoracic pedicle screw placement: a meta-analysis.Neurosurgical review, 39(3), 385–391. https://doi.org/10.1007/s10143-015-0679-2
[3] Nunley, R. M., Ellison, B. S., Zhu, J., Ruh, E. L., Howell, S. M., & Barrack, R. L. (2012). Do patient-specific guides improve coronal alignment in total knee arthroplasty? Clinical orthopaedics and related research, 470(3), 895–902. https://doi.org/10.1007/s11999-011-2222-2
[4] Victor, J., Dujardin, J., Vandenneucker, H., Arnout, N., & Bellemans, J. (2014). Patient-specific guides do not improve accuracy in total knee arthroplasty: a prospective randomized controlled trial. Clinical orthopaedics and related research, 472(1), 263–271. https://doi.org/10.1007/s11999-013-2997-4
[5] Hafez, M. A., & Moholkar, K. (2017). Patient-specific instruments: advantages and pitfalls. SICOT-J, 3, 66. https://doi. org/10.1051/sicotj/2017054
[6] https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfres/res.cfm?id=131198
[7] Hafez MA, Hamza H, Nabil A. Hospital-based patient Specific Templates for Total Knee Arthroplasty: A proof of concept clinical study. Techniques in Orthopaedics. 2018; 33 (4). 258-263
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