Orthopedics

Computer-assisted TKA: Greater Precision, Doubtful Clinical Efficacy: Affirms

Michael E. Berend, MD

Abstract

Component and limb alignment are essential surgical variables that influence the long-term performance of a total knee arthroplasty (TKA). Total knee arthroplasty failure remains multifactorial, and computer-assisted surgical techniques may address only part of the failure pathophysiology. Despite attempting to use computer-assisted surgical techniques to improve TKA alignment, recent evidence has reported that the entire nature of the computer-assisted experience is not particularly forgiving, as significant increases in time and complications remain problematic. It appears computer-assisted surgical techniques are not yet “ready for primetime” with reproducible and proven long-term benefits for patients. Further studies are needed to better determine the precise target toward which to aim computer-assisted surgery efforts.

Prosthetic component and limb alignment are essential surgical variables that influence the long-term performance of a total knee arthroplasty (TKA). Our institution has previously reported that >3° of varus alignment of the tibial component is associated with decreased survival.1 Furthermore, the risk of failure was markedly increased in patients with a body mass index >33 kg/m2 and a varus tibial component (hazard ratio=168).

The effects of varus alignment of the tibial component have also been studied in a laboratory model that examined tibial cortical strains under varus loading conditions.2 An area of markedly increased strain was observed in the posteromedial aspect of the tibia in knees with a tibial component aligned in 5° of varus (Figure A). We hypothesize that these strains may correlate with a medial bone overload pathophysiology that results in component subsidence and loosening (Figures B, C).

Figure 1: Posterior medial "hotspot" measured with full-field photoelastic strain analysis hypothesized to represent one of the mechanisms involved in medial tibial overload and collapse leading to aseptic loosening (A). AP radiograph at 1 year demonstrates early bone resorption and subsequent implant subsidence (B). Significant medial tibial remodeling is seen 2 to 3 cm below the joint line in the medial tibial plateau with increased bone density (C).

It is important to ask if all knees implanted with a varus tibial component fail. Fortunately, no. An often-overlooked finding from our work on alignment-based failure leading to bony collapse beneath the implant is that it is an uncommon occurrence representing only 0.6% of all patients.1 This is a strong indication that TKA failure is multifactorial. We found 12% of the knees had tibial component alignment >3° of varus.1 The question then becomes: Are computer-assisted TKAs achieving <12% outliers? Series comparing conventional instrumentation to computer-assisted surgical techniques demonstrate mixed results.3-6

Despite attempting to use computer-assisted surgical techniques to improve TKA alignment, recent evidence has reported that the entire nature of the computer-assisted experience is not particularly forgiving. Bonutti et al7 reported on 81 unselected knees from 2 cohorts: 1 with minimally invasive TKAs and the other with navigated TKAs. They found that postoperative alignment in these groups was similar, and not better in the navigated knees. The navigated knees took an extra 60 minutes, which is considerably longer than has been previously reported. The complication rate was alarming at 14%, including 2 femur fractures, 1 early revision, 4 reoperations for stiffness, and 4 pin-site bleeding problems. With no clearly demonstrated radiographic benefits and a high complication rate, including an early revision rate of 8.6%, navigation did not begin to improve on a 0.6% long-term loosening rate in knees possibly associated with an underlying alignment problem.

Current concerns associated with the workflow of existing computer-assisted surgical techniques include data acquisition and analysis. Can we reliably acquire the data during the operation, interpret it, and know which portions of the data are helpful and which are safe to ignore? Certainly additional problems are encountered during…

Abstract

Component and limb alignment are essential surgical variables that influence the long-term performance of a total knee arthroplasty (TKA). Total knee arthroplasty failure remains multifactorial, and computer-assisted surgical techniques may address only part of the failure pathophysiology. Despite attempting to use computer-assisted surgical techniques to improve TKA alignment, recent evidence has reported that the entire nature of the computer-assisted experience is not particularly forgiving, as significant increases in time and complications remain problematic. It appears computer-assisted surgical techniques are not yet “ready for primetime” with reproducible and proven long-term benefits for patients. Further studies are needed to better determine the precise target toward which to aim computer-assisted surgery efforts.

Prosthetic component and limb alignment are essential surgical variables that influence the long-term performance of a total knee arthroplasty (TKA). Our institution has previously reported that >3° of varus alignment of the tibial component is associated with decreased survival.1 Furthermore, the risk of failure was markedly increased in patients with a body mass index >33 kg/m2 and a varus tibial component (hazard ratio=168).

The effects of varus alignment of the tibial component have also been studied in a laboratory model that examined tibial cortical strains under varus loading conditions.2 An area of markedly increased strain was observed in the posteromedial aspect of the tibia in knees with a tibial component aligned in 5° of varus (Figure A). We hypothesize that these strains may correlate with a medial bone overload pathophysiology that results in component subsidence and loosening (Figures B, C).

Figure 1A: Posterior medial “hotspot” measured with full-field photoelastic strain analysis Figure 1B: Early bone resorption and subsequent implant subsidence Figure 1C: Significant medial tibial remodeling

Figure 1: Posterior medial "hotspot" measured with full-field photoelastic strain analysis hypothesized to represent one of the mechanisms involved in medial tibial overload and collapse leading to aseptic loosening (A). AP radiograph at 1 year demonstrates early bone resorption and subsequent implant subsidence (B). Significant medial tibial remodeling is seen 2 to 3 cm below the joint line in the medial tibial plateau with increased bone density (C).

It is important to ask if all knees implanted with a varus tibial component fail. Fortunately, no. An often-overlooked finding from our work on alignment-based failure leading to bony collapse beneath the implant is that it is an uncommon occurrence representing only 0.6% of all patients.1 This is a strong indication that TKA failure is multifactorial. We found 12% of the knees had tibial component alignment >3° of varus.1 The question then becomes: Are computer-assisted TKAs achieving <12% outliers? Series comparing conventional instrumentation to computer-assisted surgical techniques demonstrate mixed results.3-6

Despite attempting to use computer-assisted surgical techniques to improve TKA alignment, recent evidence has reported that the entire nature of the computer-assisted experience is not particularly forgiving. Bonutti et al7 reported on 81 unselected knees from 2 cohorts: 1 with minimally invasive TKAs and the other with navigated TKAs. They found that postoperative alignment in these groups was similar, and not better in the navigated knees. The navigated knees took an extra 60 minutes, which is considerably longer than has been previously reported. The complication rate was alarming at 14%, including 2 femur fractures, 1 early revision, 4 reoperations for stiffness, and 4 pin-site bleeding problems. With no clearly demonstrated radiographic benefits and a high complication rate, including an early revision rate of 8.6%, navigation did not begin to improve on a 0.6% long-term loosening rate in knees possibly associated with an underlying alignment problem.

Current concerns associated with the workflow of existing computer-assisted surgical techniques include data acquisition and analysis. Can we reliably acquire the data during the operation, interpret it, and know which portions of the data are helpful and which are safe to ignore? Certainly additional problems are encountered during TKA, such as saw-blade deflection and cementation errors, that are not directly addressed by computer-assisted techniques.8 It is exciting to hypothesize that the next generation of computer-assisted techniques in which the data acquisition and planning portion of a computer-assisted TKA is done preoperatively, based on an imaging protocol, has potential to solve some of the problems associated with current computer-assisted techniques.9

Alignment in TKA is certainly important. Failure continues to be multifactorial. Further studies are needed to better determine a more precise target toward which to aim computer-assisted surgery efforts. We cannot take an extra 60 minutes per case and accept a 14% complication rate with today’s technology. Hopefully there will be further proven and safe developments in this area in the future.

References

  1. Berend ME, Ritter MA, Meding JB, et al. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res. 2004; (428):26-34.
  2. Green GV, Berend KR, Berend ME, Glisson RR, Vail TP. The effects of varus tibial alignment on proximal tibial surface strain in total knee arthroplasty: The posteromedial hot spot. J Arthroplasty. 2002; 17(8):1033-1039.
  3. Saragaglia D, Picard F, Chaussard C, Montbarbon E, Leitner F, Cinquin P. Computer-assisted knee arthroplasty: comparison with a conventional procedure. Results of 50 cases in a prospective randomized study [in French]. Rev Chir Orthop Reparatrice Appar Mot. 2001; 87(1):18-28.
  4. Mielke RK, Clemens U, Jens JH, Kershally S. Navigation in knee endoprosthesis implantation—preliminary experiences and prospective comparative study with conventional implantation technique [in German]. Z Orthop Ihre Grenzgeb. 2001; 139(2):109-116.
  5. Jenny JY, Boeri C. Navigated implantation of total knee endoprostheses—a comparative study with conventional instrumentation [in German]. Z Orthop Ihre Grenzgeb. 2001; 139(2):117-119.
  6. Victor J, Hoste D. Image-based computer-assisted total knee arthroplasty leads to lower variability in coronal alignment. Clin Orthop Relat Res. 2004; (428):131-139.
  7. Bonutti PM, Dethmers D, Ulrich SD, Seyler TM, Mont MA. Computer navigation-assisted versus minimally invasive TKA: benefits and drawbacks. Clin Orthop Relat Res. 2008; 466(11):2756-2762.
  8. Catani F, Biasca N, Ensini A, et al. Alignment deviation between bone resection and final implant positioning in computer-navigated total knee arthroplasty. J Bone Joint Surg Am. 2008; 90(4):765-771.
  9. Lombardi AV Jr, Berend KR, Adams JB. Patient-specific approach in total knee arthroplasty. Orthopedics. 2008; 31(9):927-930.

Author

Dr Berend is from the Center for Hip & Knee Surgery and the Joint Replacement Surgeons of Indiana Research Foundation, Mooresville, and Rose-Hulman Biomedical Engineering Laboratory, Terre Haute, Indiana.

Dr Berend receives royalties for intellectual property from and is a consultant for Biomet, and is a member of the Joint Replacement Surgeons of Indiana Research Foundation, which receives research support from Biomet, MCS, Javelin Pharmaceuticals, St Francis Hospital, and ERMI.

Presented at Current Concepts in Joint Replacement 2008 Winter Meeting; December 10-13, 2008; Orlando, Florida.

“Orthopaedic Crossfire” is a registered trademark of A. Seth Greenwald, DPhil(Oxon).

Correspondence should be addressed to: Michael E. Berend, MD, Center for Hip & Knee Surgery, 1199 Hadley Rd, Mooresville, IN 46158.

DOI: 10.3928/01477447-20090728-24

10.3928/01477447-20090728-24

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