Why Computer-assisted Surgery Now?

Bernard Stulberg, MD
St. Vincent CharityMedical Center

In an era where technological developments have led to greater and simplified communications, better products and generally lower overall costs inmost activities we participate in, it remains puzzling that the use of technologically advanced tools to provide improved feedback to surgeons has not found widespread use. It is particularly puzzling that such has been the case in total knee arthroplasty (TKA) over the past decade, where the accumulated data supports substantially improved precision1 in an operation where precisionis critical to long-term success.

My experience with 503TKAs performed with CAOS techniques was a clinical failure rate of less than 2 percent, with one failure due to mal alignment, two infections and one fracture above the implant unrelated to the CAOS procedure.

Computer-assisted orthopaedic surgery (CAOS) technologies for TKA were introduced in late 1999 and 2000, and the early devices used were slowly introduced into the marketplace in 2001 and 2002. I introduced CAOS for TKA in my practice in late 2003, and began using it routinely in 2004. Throughout that period of time there was continuous but cautious evolution of the software, and its adoption by the large proportion of TKA surgeons was minimal(<1%). Despite these evolutions, my own personal experience with 503 TKAs performed with CAOS techniques was a clinical failure rate of less than 2 percent, with one failure due to malalignment, two infections and one fracture above the implant unrelated to the CAOS procedure.

My experience was a small one among a broad population of interested investigators who have continued to demonstrate improved consistency of alignment for femoral and tibial components in all planes (90-95 percent consistency versus 70-75 percent with standard mechanical instrumentation). A meta-analysis by Hetaimish et al. revealed that patients undergoing navigated TKA demonstrated a significant improvement in prosthesis alignment.2

This demonstrated improvement in alignment has led many to infer a direct causation to a reduction in revision rates for patients who have undergone navigated TKA. This reduction in revision rates is highlighted by the 2014 Australian Registry data showing a 20 percent reduction in revisions at nine-year follow-up for patients less than 65 years of age when computer-assisted surgery was used.

These improved clinical outcomes and reduction in revisions have made a direct impact on patient outcomes following navigated TKA. A 2013 meta-analysis by Rebal et al. conducted literature searches for Level 1 randomized trials that compared TKA using imageless computer navigation to those performed with conventional instruments. The results of the meta-analysis concluded TKA using imageless computer navigation provided more accurate alignment and superior functional outcomes at short-term follow-up.3

More recently, there has been great interest in patient specific instrumentation (PSI), an approach that uses three-dimensional imaging modalities (i.e., CT or MRI) to reconstruct the geometry of the knee joint and allow an engineer to design pre-formed cutting blocks or pin blocks to properly position standard instrumentation. While popular because of their marketed ease of use, PSI technology has been met with variable success due to the inconsistency of the results in the hands of experts,4 and its inability to be used in every case. It is interesting that CAOS has been used in some studies to confirm PSI’s accuracy, and there are reported studies where its improvement compared to standard instrumentation was in the 85-90 percent range, where alignment with standard instrumentation was 70-75 percent.4

Computer-assisted TKA should be the initial approach for most surgeons, as this technology is the “gold standard” of implant alignment and will be the foundation to document further improvements in precision of our procedures.

I believe that the time to become familiar with, and to routinely use, quantitative techniques to assist in implanting total knee prosthesis is NOW. Not only because the newer approaches to navigation allow us to position and evaluate kinematic performance of our implants intraoperatively, rapidly, and with no or little additional time,5 but also because they allow us to document what we have performed, and to help us form judgments about the performance of our operations to continually improve. In an era where we must demonstrate the VALUE of what wedo, such an approach is critical. I would also suggest that computer-assisted TKA should be the initial approach for most surgeons, as this technology is the “gold-standard” of implant alignment and will be the foundation to document further improvements inprecision of our procedures.

I think that the ExactechGPS® system, in particular, has merged the computational improvements in the field with innovative instrumentation to enhance user friendliness of CAOS techniques through an approach that miniaturizes the equipment, improves clarity of understandingof baseline abnormalities through its morphing technology, allows customization of the software to fit each individual surgeon’s approach, and helps decrease the cost of the intervention by improving the predictability of implant placement and balancing to enhance the recovery processand overall outcome.

ExactechGPS® Guided Personalized Surgery


Because alignment and stability data provide the baseline data upon which other 3-D technologies are based, (such as PSI technologies), these can easily be incorporated into the system. As such, PSI through this technique now allows the surgeon to provide the data, use the software to plan the size of component and position the components and position the pins for the cutting blocks — just as in PSI done remotely. But it also allows intraoperative adjustment by the surgeon, feedback that the resections are appropriate/accurate, and then kinematic feedback as to how these judgments have led to a properly balanced TKA — all in about the same time it takes to perform a primary TKA with mechanical instruments (+/- 5 minutes).5 Clearly this is moving the technology in the right direction. Further approaches, such as to address the predictability ofrevision TKA with CAOS techniques, are not far away.

These newer approaches to TKA with CAOS, and ExactechGPS in particular, are continuing to evolve rapidly to make the instrumentation and software intuitive and desirable while avoiding the major inconveniences of the more traditional CAOS systems.

I encourage you to try them, commit a certain number of TKA surgeries to them, and then assess if you have found it useful. I think you will find, as I did, that it will help you become an even better TKA surgeon. •


  1. Cheng T, Zhao S, Peng X, Zhang X. Doescomputer-assisted surgery improve post-operativeleg alignment and implant position followingtotal knee arthroplasty? A meta-analysis ofrandomized trials Knee Surg Sports TraumatolArthrosc. 2012 Jul;20(7):1307-22. doi: 10.1007/s00167-011-1588-8. Epub 2011 Jul 6.
  2. Hetaimish BM, Khan MM, Simunovic N,Al-Harbi HH, Bhandari M, Zalzal PK. Meta-analysisof navigation vs conventional total kneearthroplasty. J Arthroplasty. 2012 Jun;27(6):1177-82. doi: 10.1016/j.arth.2011.12.028. Epub 2012Feb 13.
  3. Rebal BA, Babatunde OM, Lee JH, GellerJA, Patrick DA Jr, Macaulay W. Imagelesscomputer navigation in total knee arthroplastyprovides superior short term functionaloutcomes: a meta-analysis. J Arthroplasty.2014 May;29(5):938-44. doi: 10.1016/j.arth.2013.09.018. Epub 2013 Oct 18.
  4. Nam D, Maher PA, Rebolledo BJ, NawabiDH, McLawhorn AS, Pearle AD. Patient-specificcutting guides versus an imageless, computer-assisted surgery system in total kneearthroplasty. Knee. 2013 Aug;20(4):263-7. Epub2013 Jan 21.
  5. Petrera P. Navigated Total Knee ArthroplastyIs No Slower than Conventional InstrumentedTKA. 2014 ICJR Transatlantic OrthopaedicCongress.