The Case Against Shape Matching & Patient-specific Instruments for Total Knee Arthroplasty

David Backstein M.D., MEd, FRCSC
University of Toronto
Toronto, ON

Prior to making a change to clinical practice as significant as replacing the conventional TKA instruments which are the current standard of practice, we must ask ourselves: what would be the motivation? It is acknowledged that while standard instruments have been used to great success for many years, approximately 10-20% of TKA patients are less than satisfied with their outcome1,2,3.


Patient-Specific Guides (PSGs) require CT- or MRI-imaging to produce customized, disposable cutting guides which are commercially manufactured preoperatively and used to guide the bone cuts made by the surgeon, intra-operatively. Advocates of patient-specific guides (PSG) articulate two primary advantages over conventional techniques: 1) improved component alignment and reduced mal-positioning, 2) improved operating room efficiency and reduced overall cost of the procedure. A third objective of some PSG advocates is the ability to restore the "kinematic" axis. This axis differs from the neutral, hip-knee-ankle mechanical axis which has been the goal of TKA surgery for decades. Instead, the kinematic aligned knee utilizes a transverse axis in the femur around which the tibia and patella flex and extend. Determining which axis is most appropriate is a separate and even more controversial issue than that of PSGs and beyond this brief discussion.

In theory, these PSGs prevent surgeons' technical errors which result in coronal malalignment while at the same time eliminating the need for costly instruments and sterilization procedures. However, in reality, TKA performed with patient-specific instrumentation (aimed to restore the mechanical axis) have a similar number of outliers as conventional instrumentation. This has been well demonstrated by Nunley et al.4 in a study which used CT-scans to compare postoperative alignment of 50 TKA performed with conventional instruments to 50 which used PSGs and found no benefit in terms of frequency of outliers.

Furthermore, the argument which proposes cost savings and efficiency with PSGs is similarly flawed. The feasibility of obtaining a preoperative MRI or CT-scan for every primary TKA performed is simply not possible in the current Canadian health care environment. The poor availability of such imaging has the potential to worsen already long surgical wait times, particularly when one considers that the demand for TKA is expected to double by 20175. In addition to the time and financial cost of imaging, the occasional need to abort the use of PSGs mid-case and revert to standard instruments has been documented. Therefore hospitals must still have standard instruments available and ready, thus potentially duplicating costs and actually making PSG more expensive than conventional techniques. These findings have been studied by Nunley et al.6 who have stated that routine use of this new technology is not cost-effective in its current form.

In summary, the case in favour of PSG has yet to be made and the increased cost yet to be justified. Infection and aseptic loosening are two of the most pressing issues facing TKA surgery and there is no evidence that this new technology will be of any benefit in reducing the incidence of these complications. Similar to the routine use of computer navigation, which has resulted in improved alignment but has not eliminated outliers and has not improved the clinical outcomes, PSG cannot be justified for routine use at this time7,8.


  1. Wylde V, Learmonth I, Potter A, Bettinson K, Lingard E. Patientreported outcomes after fixed- versus mobile-bearing total knee replacement: a multi-centre randomised controlled trial using the Kinemax total knee replacement. J Bone Joint Surg Br. 2008;90:1172-1179
  2. Robertsson O., Dunbar M., Pehrsson T., Knutson K., Lidgren L. Patient satisfaction after knee arthroplasty: a report on 27,372 knees operated on between 1981 and 1995 in Sweden. Acta Orthop Scand. 2000;71:262-267.
  3. Bourne R., Chesworth B., Davis A., Mahomed N., Charron K. Patient Satisfaction after Total Knee Arthroplasty Who is Satisfied and Who is Not? Clin Orthop Relat Res (2010) 468:57-63
  4. Nunley R., Ellison B.,  Zhu J., Ruh E., Howell S., Barrack R. Do Patient-specific Guides Improve Coronal Alignment in Total Knee Arthroplasty? Clin Orthop Relat Res (2012) 470:895-902.
  5. Iorio R., Robb W.J., Healy W.L., Berry D.J., Hozack W.J., Kyle R.F., Lewallen D.G., Trousdale R.T., Jiranek W.A., Stamos V.P., Parsley B.S. Orthopaedic surgeon workforce and volume assessment for total hip and knee replacement in the United States: preparing for an epidemic. J Bone Joint Surg Am. 2008;90:1598-1605.
  6. Nunley R.M., Ellison B.S., Ruh E.L., Williams B.M., Foreman K., Ford A.D., Barrack R.L. Are patient-specific cutting blocks cost-effective for total knee arthroplasty? Clin Orthop Relat Res. 2012 Mar;470(3):889-94. Epub 2011 Dec 20.
  7. Blakeney W.G., Khan R.J., Wall S.J. Computer-assisted techniques versus conventional guides for component alignment in total knee arthroplasty: a randomized controlled trial. J Bone Joint Surg Am. 2011;93:1377-1384.
  8. Brin Y.S., Nikolaou V.S., Joseph L., Zukor D.J., Antoniou J. Imageless computer assisted versus conventional total knee replacement: a Bayesian meta-analysis of 23 comparative studies. Int Orthop. 2011;35:331-339.