CAOS TKA Provides Improved Functional Outcomes Compared to Conventional TKA

Clinical Contributor

Gérard Giordano, MD
Hôpital Joseph Ducuing
Toulouse, FR

Technical Contributors

Wen Fan
Exactech, Inc.

Yifei Dai, PhD

Exactech, Inc.


Computer-assisted orthopaedic surgery (CAOS) has been shown to offer a clear advantage regarding surgical accuracy in total knee arthroplasty (TKA) with a body of research studies demonstrating a significant reduction of alignment outliers compared to conventional TKA instrumentation.1,2 However, conflicted data exists in the literature for a consensus regarding the advantage of CAOS technology in clinical outcomes or satisfaction rates for the patient. While some studies have shown superior functional outcomes in CAOS TKA compared to its conventional counterparts,3 others reported no difference between CAOS and conventional cases.4 More studies are needed to further contribute knowledge and evidence on this topic. The objective of this study was to compare short-term clinical outcomes between TKA cases performed using a contemporary CAOS system and cases with conventional instrumentation.

Materials and Methods

With approval from the institutional review board and signed informed consents from the patients, a prospective, multicenter, consecutive TKA case series was collected by three surgeons from three different clinical sites [2 US sites, 1 EU site] using the same implant system. Seven hundred and ninety-five (795) patients were enrolled with surgery dates between November 2009 and September 2018, including 334 CAOS TKA cases and 461 conventional TKA cases. Each surgeon performed both CAOS and conventional surgeries. Patient demographics, baseline clinical measurements, and the latest minimum one-year follow-up visit were reviewed and compared between the CAOS TKA group and the conventional TKA group. The clinical measurements investigated were Range of Motion (ROM), Knee Society Score (KSS: knee, function, pain, and each sub-component measure), and patient satisfaction Visual Analog Scale (VAS 1-10, with 10 indicating the highest satisfaction). All data analyses were performed using custom scripts in R 3.6.1 (RStudio, Inc., Boston, MA, USA). Two-sample t-tests were used for continuous outcomes, and the chi-squared test was used for binary outcomes. To further assess the detected post-operative significance, a multivariate regression analysis was performed to assess the impact of region (EU vs US) and treatment type (CAOS vs conventional). Statistical significance was defined as p ≤ 0.05.


At the time of study, 215 CAOS and 350 conventional patients were available for analysis of patient reported outcomes with mean post-operative follow-up periods of approximately two to three years (Table 1A). Patients from the CAOS group were older and a had higher BMI than those from the conventional group (p values < 0.01, Table 1A). Pre-operatively, for the baseline measures, although CAOS patients had higher KSS function scores than patients in the conventional group, no significant difference was found in each sub-component measure for KSS function (“Walking”, “Stairs”, and “Walking Aid”) (Figure 1). No other differences existed between the two groups’ patient characteristics and pre-operative baseline.

Post-operatively, a significantly higher ROM was achieved in the CAOS group compared to the conventional group (p values < 0.01, Table 1B). Additionally, higher KSS function scores were found in CAOS patients compared to the conventional group (p values < 0.01, Table 1B). Differences were also seen in the sub-component measures. Compared to the conventional patients, CAOS patients scored significantly better in all sub-component measures (p values ≤ 0.05, Figure 1). No difference was found in KSS knee and KSS pain scores. Although EU patients were associated with higher post-operative ROM, geographic region was not significantly correlated with KSS function and its sub-component measures. In contrast, CAOS surgery was significantly associated with better KSS function and sub-component measures (“Walking” and “Stairs”) compared to conventional surgery (p values < 0.04). Both groups achieved a mean satisfaction rate of 9 (N.S.). Fourteen (14) conventional cases were revised due to pain (5), loosening (3), infection (2), instability (1), and patellofemoral complications (3). Four (4) knees in the CAOS group were revised due to infection.


This study demonstrated significantly better short-term functional outcomes for the patients who received CAOS TKAs compared to those who received a conventional TKA. Aligned with the reports from previous studies,3,5 the findings from this study added to the existing evidence of the benefits of CAOS in achieving improved clinical outcomes compared to conventional TKA. Furthermore, the CAOS group demonstrated excellent short-term survivorship with zero (0) cases of early failure due to causes linked to post-operative mal alignment.

This study presented only short-term outcomes. Mid- to long-term performance of the CAOS TKA of this study cohort remains to be shown. The short-term results reported by this study provide early evidence that the use of CAOS technology may provide better function and greater ROM in TKAs. Further recruitment of global study sites will provide for a more robust patient cohort moving forward.

Table 1. A) Details of demographics and characteristics of the study cohort. B) Summary of pre- and post- operative outcomes.

Figure 1. Comparisons between CAOS and conventional TKA groups regarding sub-component measures under A) pre-operative and B) post-operative KSS function. Pre-operatively, all sub-component measures were statistically equivalent between CAOS and conventional groups. In contract, all sub-component measures demonstrated better outcomes in the CAOS group compared to the conventional group. Charts for KSS knee are not shown due to no difference in findings for the post-operative comparisons.


  1. Jenny JY, et al. Consistency of implantation of a total knee arthroplasty with a non-image-based navigation system: a case-control study of 235 cases compared with 235 conven­tionally implanted prostheses. J Arthroplasty. 2005;20(7): 832-9.
  2. Sparmann M, et al. Po­sitioning of total knee arthroplasty with and without naviga­tion support: a prospective, randomised study. J Bone Joint Surg Br. 2003;85(6):830-5.
  3. Rebal BA, et al. Imageless computer navigation in total knee arthroplasty provides superior short term functional outcomes: a meta-analysis. J Arthroplasty. 2014;29(5):938-44.
  4. Johnson DR, et al. Evaluation of total knee arthroplasty performed with and without computer navigation: a bilateral total knee arthroplasty study. J Arthroplasty. 2013;28(3):455-8.
  5. Hoffart HE, et al. A prospective study comparing the functional outcome of computer-assisted and conventional total knee replacement. J Bone Joint Surg Br. 2012 Feb;94(2):194-9.