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SICOT e-Newsletter

Issue No. 42 - March 2012

Training & Education

Total Knee Arthroplasty: Patient Specific Instrumentation (PSI)

Mahmoud A. Hafez
Professor & SICOT Full Member - Cairo, Egypt

The technique of patient specific instruments (PSI) is revolutionary as it provides an alternative to conventional instrumentation systems that have been in use since the 1970s. This new concept is a midway between conventional jigs and the complex computer-assisted technologies such as robotics and navigation. When we talk about technology in surgery, we have to consider cost, complexity, operative time and potential hazards. These factors have made navigation more popular than robotics and again they will pave the road for PSI to be much more popular than navigation. Robotics was clinically used in orthopaedics in the early 1990s but was not exploited by implant companies and it was used only by developing surgeons. A decade later, navigation was introduced and over the years it has been employed by the industry and slowly by surgeons. However, PSI has been adopted by 9 industrial companies and many surgeons only in the last couple of years. It is all about simplicity, especially when combined with accuracy, making some new technologies more accepted than others.

The concept of this technique was first reported by Hafez et al in 2004 followed by experimental application¹ on 45 knee specimens (17 cadaveric and 28 plastic) showing successful performance of TKA in all cases without resorting to conventional jigs. The accuracy was accepted and the operative time was almost half compared to conventional techniques. The technique was later validated and showed no significant inter- or intra-observer variations. The clinical application of this technique was reported late² and it was preceded by the work of Howell et al³ and later on by several other authors using similar techniques from other implant companies.

Figure 1 illustrates the technical steps of this technique. Preoperative CT or MRI images are acquired and imported to a special software system that has 3D data of the TKA implant to be used. Planning includes sizing, alignment, bone cutting and verification of optimal implantation and positioning. Two virtual templates (femoral and tibial cutting guides) are designed and then transformed into physical guides using rapid prototyping technology (a printing machine). The guides have built-in information of the preoperative planning that can be transferred to the patient’s knee when the guides are positioned on the matching surfaces of the distal femur and the proximal tibia. Then, surgeons can use these guides to make all necessary cuts or to guide the position of the conventional cutting blocks without using intra- or extra-medullary guides.


Figure 1

The PSI technique can be used for complex cases of extra-articular deformities, medically unfit patients, bilateral TKA and severe articular deformities. It eliminates medullary guides, reduces operative time, and provides more accurate planning. Nevertheless, the broad based application of the PSI technique should be delayed until a Level I clinical study is published.

References:

  1. Hafez MA, Chelule KL, Seedhom BB, Sherman KP (2006) Computer-assisted Total Knee Arthroplasty Using Patient-Specific Templating. Clin Orthop Relat Res:444:184-192.
  2. Hafez MA (2011) Custom made cutting guides for TKA (2011). In Surgery of the Knee (5th Ed.), Install JN, Scott N (Eds). Churchill Livingston.
  3. Howell SM, Kuznik K, Hull ML, Siston RA (2008) Results of an initial experience with custom-fit positioning total knee arthroplasty in a series of 48 patients. Orthopedics: 31(9):857-63.

Is custom fit instrumentation the future of total knee arthroplasty? A young surgeon’s perspective

Kamal Bali
Young Surgeons Committee Member - Panchkula, India

Restoration of mechanical axis to within 3 degrees of neutral has been identified as one of the major factors influencing the longevity of implants in TKA [1-5]. In an attempt to achieve this, computer-assisted TKA has evolved over years as a well accepted surgical technique. Although the technique provides more accurate alignment in all planes than conventional techniques [6-9], potential limitations include the need for accurate landmark registration, increased surgical time and cost of equipment, pin loosening and bone fracture, and substantial learning curve [10]. As such, recent studies have begun to assess the use of custom-fit guided TKA using preoperative MRI or CT scans or long leg radiographs, or a combination of these to determine component placement and allow for a normal mechanical alignment [10-18]. However, the technique is still in its early stages and there are limited studies on the subject to advocate its widespread use.

Technique:

Various companies (Signature, Biomet; Visionaire, Smith & Nephew; Trumatch, Depuy; OtisMed, Stryker; Prophecy, Wright; PSI, Zimmer) are now coming up with different systems that utilize the custom fit technique. Most of these systems can be used with both cruciate retaining and cruciate sacrificing implants. While some of these systems use only customised drill guides for pin placement, others use patient specific disposable cutting blocks for the same. Although a few of the available systems (e.g. OtisMed, OtisKnee) target restoring the anatomical axis (tibiofemoral angle) within normal limits (4 degree valgus to 10 degree valgus), most of the current systems customise the implants with an aim to restore the mechanical axis to neutral.

When using customised knee arthroplasty systems, a detailed preoperative MRI or CT scan of the full leg or just the knee joint is usually obtained. Some systems additionally get full length weight bearing radiographs of the involved limb. The images obtained preoperatively are processed and planning carried out using different proprietary softwares. Virtual models of the distal femur and proximal tibia are created from which rapid protype positioning guides or customised cutting blocks are produced. Most of these systems also consider intra-operative flexibility in the design of the customised blocks or the drill guides. As such, standard instrumentation can be utilised in the event that bone resection modifications are needed, such as additional distal resection to accommodate for a flexion contracture.

CT or MRI?:

The generation of customised guides or blocks is based primarily on preoperative CT scans [11-16] or MRI of the arthritic limb [10,17-19]. While CT scans are presumed to be more accurate than MRI [20], the excessive amount of radiation exposure involved might be a hindrance in its widespread use for custom fit TKA. However, MRI has an additional disadvantage of not being able to be used in patients with prior surgeries having metallic implants in situ. This might actually be an important limitation of MRI-based customised knees. The custom fit TKA holds a lot of promise in patients with deformed femur/tibia due to prior fractures and many of these have some residual implants in situ. As such, MRI-based technology might not be feasible in these patients.

White et al [20] compared the accuracy of MRI and CT imaging for the manufacture of patient-specific templates for TKA in 10 bovine knees. The authors found that the bone models generated from MRI scans were dimensionally less accurate and visibly inferior than those generated from CT scans. They, thus, concluded that current MRI scans do not offer a viable alternative to CT. Their findings were supported by Klatt et al [19] who reported malalignment in all 4 cases operated by custom fit technique TKA based on preoperative MRI. Nevertheless, subsequent studies have shown encouraging results with the use of MRI-based custom fit TKA.

Potential Advantages:

Custom fit technique is now emerging as an alternative to navigation assisted TKA. Just like computer navigated TKA, it offers the potential advantages of accurate restoration of alignment, decreased blood loss and lesser chances of fat embolism due to decreased invasiveness involved in the technique. Additionally, the procedure is less complex and saves time. This is because the alignment is not based on any fixed anatomical landmarks such as the centre of the hip or ankle. Instead, the cutting guides or blocks allow for measured resection so that the implant returns the knee to what is determined to be the original alignment and ligament balance that existed before the arthritic changes. As the cutting blocks and guides are designed on the basis of preoperative work-up, it is supposed to reduce the need for intraoperative evaluation of alignment and hence save time [17-18].

There is also a decreased requirement of instruments in the operating room (and hence decreased need of cleaning and sterilising the instruments). This can be particularly beneficial in hospitals with limited sterilization equipment and can allow more cases to be accomplished in the same time period. Another potential advantage of the system is the generation of a fairly well-balanced knee after the cuts in the majority of the cases and decreased need of knee balancing [17-18]. This might be potentially very beneficial not only for inexperienced surgeons but also for experienced surgeons when dealing with difficult cases requiring TKA.

Cost Effectiveness:

The biggest concern regarding the technology is its cost effectiveness. It is estimated that the basic cost of the surgical procedure may increase by around 20% and it is the patient who has to ultimately bear this cost. However, barring this initial increased cost the technology is actually supposed to reduce potential accessory expenditures. For instance the procedure actually shortens the operating room time by around 10-20 minutes [17,18]. This in turn means a reduced anaesthesia and post-anaesthesia related costs. Use of fewer instruments and operating trays actually reduces the room turn-over and non operating time. Due to the decreased blood loss involved in the procedure as compared to conventional technique, there is a potential reduction in the need for blood transfusions. Furthermore, many patients report fast rehabilitation and reduced length of stay in hospital.

All these "indirect" expense reductions may ultimately neutralise the increased basic cost of the procedure. However, there are limited studies on the subject as to justify for now the cost effectiveness of this procedure.

Surgeon Perceptions:

Mont et al [20] conducted a study in 2010 to assess how commonly the custom fit technique was being used by surgeons and whether they perceived any benefits to their patients and/or their practices. Out of the 50 surgeons who responded to the survey, 10 reported using custom fit positioning technology while 29 of the remaining 40 indicated that they were interested in trying out the new technique. The two most common reported benefits by surgeons using this technology were a more natural feel of the knee in the operated patients (7 out of 10) and earlier walking after the surgery (4 out of 10). The two reasons that were most frequently cited by the surgeons who were not interested in custom fit technology were cost and insufficient clinical outcomes.

The results of this study suggested that, if additional clinical studies at longer follow up support the use of this technology, more surgeons might be willing to adopt this technique.

Conclusion:

Custom fit technology has the potential to revolutionise the techniques of TKA. Apart from achieving the main goal of restoration of coronal alignment and rotation of components during TKA, it offers many additional advantages. However, at present, cost constraints and limited clinical studies on the subject are major blocks in the universal acceptance of this technology. Nevertheless, the technology holds promise and as the custom fit systems evolve, the technology is likely to become more cost effective. Most of the surgeons seem willing to adopt this technology if longer term studies show positive outcomes with this technology. Probably some multicentric randomised control trials are needed to fully establish this innovative technology before it can be fully incorporated into the mainstream of orthopaedic practice.

References:

  1. Jeffery RS, Morris RW, Denham RA. Coronal alignment after total knee replacement. J Bone Joint Surg Br. 1991;73(5):709-14.
  2. Bolognesi M, Hofmann A. Computer navigation versus standard instrumentation for TKA: a single-surgeon experience. Clin Orthop Relat Res. 2005;440:162-9.
  3. Perillo-Marcone A, Barrett DS, Taylor M. The importance of tibial alignment: finite element analysis of tibial malalignment. J Arthroplasty. 2000;15(8):1020-7.
  4. Bankes MJ, Back DL, Cannon SR, Briggs TW. The effect of component malalignment on the clinical and radiological outcome of the Kinemax total knee replacement. Knee. 2003;10(1):55-60.
  5. Mahaluxmivala J, Bankes MJ, Nicolai P, Aldam CH, Allen PW. The effect of surgeon experience on component positioning in 673 Press Fit Condylar posterior cruciate-sacrificing total knee arthroplasties. J Arthroplasty. 2001;16(5):635-40.
  6. Chauhan SK, Clark GW, Lloyd S, Scott RG, Breidahl W, Sikorski JM. Computer-assisted total knee replacement. A controlled cadaver study using a multi-parameter quantitative CT assessment of alignment (the Perth CT Protocol). J Bone Joint Surg Br. 2004;86(6):818-23.
  7. Anderson KC, Buehler KC, Markel DC. Computer assisted navigation in total knee arthroplasty: comparison with conventional methods. J Arthroplasty. 2005;20(7 Suppl 3):132-8.
  8. Chin PL, Yang KY, Yeo SJ, Lo NN. Randomized control trial comparing radiographic total knee arthroplasty implant placement using computer navigation versus conventional technique. J Arthroplasty. 2005;20(5):618-26.
  9. Decking R, Markmann Y, Fuchs J, Puhl W, Scharf HP. Leg axis after computer-navigated total knee arthroplasty: a prospective randomized trial comparing computer-navigated and manual implantation. J Arthroplasty. 2005;20(3):282-8.
  10. Lombardi AV Jr, Berend KR, Adams JB. Patient-specific approach in total knee arthroplasty. Orthopedics. 2008 Sep;31(9):927-30.
  11. Grafinger RW, Datz L, Hitzl W, Dorn U. CT scans increase rotational accuracy in total knee arthroplasty. Z Orthop Unfall. 2008;146(6):782-7.
  12. Hafez MA, Chelule KL, Seedhom BB, Sherman KP. Computer-assisted total knee arthroplasty using patient-specific templating. Clin Orthop Relat Res. 2006;444:184-92.
  13. Michaut M, Beaufils P, Galaud B, Abadie P, Boisrenoult P, Fallet L. Rotational alignment of femoral component with computed-assisted surgery (CAS) during total knee arthroplasty. Rev Chir Orthop Reparatrice Appar Mot. 2008;94(6):580-4.
  14. Mizu-uchi H, Matsuda S, Miura H, Okazaki K, Akasaki Y, Iwamoto Y. The evaluation of post-operative alignment in total knee replacement using a CT-based navigation system. J Bone Joint Surg Br. 2008;90(8):1025-31.
  15. Nabeyama R, Matsuda S, Miura H, Mawatari T, Kawano T, Iwamoto Y. The accuracy of image-guided knee replacement based on computed tomography. J Bone Joint Surg Br. 2004;86(3):366-71.
  16. Uslu M, Ozsar B, Kendi T, Kara S, Tekdemir I, Atik OS. The use of computed tomography to determine femoral component size: a study of cadaver femora. Bull Hosp Jt Dis. 2005;63:49-53.
  17. Spencer BA, Mont MA, McGrath MS, Boyd B, Mitrick MF. Initial experience with custom-fit total knee replacement: intra-operative events and long-leg coronal alignment. Int Orthop. 2009;33(6):1571-5.
  18. Howell SM, Kuznik K, Hull ML, Siston RA. Results of an initial experience with custom-fit positioning total knee arthroplasty in a series of 48 patients. Orthopedics. 2008;31(9):857-63.
  19. Klatt BA, Goyal N, Austin MS, Hozack WJ. Custom-fit total knee arthroplasty (OtisKnee) results in malalignment. J Arthroplasty. 2008;23(1):26-9.
  20. Mont MA, Johnson AJ, Zywiel MG, Bonutti PM. Surgeon Perceptions Regarding Custom-fit Positioning Technology for Total Knee Arthroplasty. Surg Technol Int. 2010;20:348-51.
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