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Homer Stryker Center

Primary Knee Symposium: Biomechanical Considerations in the Knee

Knee Alignment: Are We Getting What We’re Aiming For? - Mark Kester, PhD

Slides

Mark Kester, PhD

Standard radiographs do not necessarily show whether there is a problem with component alignment after TKA because they are two dimensional. With all the alignment considerations on both the femoral and tibial sides—flexion-extension, varus-valgus, internal-external, proximal-distal, anterior-posterior, lateral-medial—there are many ways to malalign components.

Dr. Kester reviewed the results of 398 modern TKA performed at the Mayo clinic between 1984 and 1989. The knees were classified according to whether they were within 3 degrees of the coronal plane. At 15 years (±4.7 yrs), survival rates were actually slightly better for those outside of the ±3º window. PSlide A The study conclusion was that survivorship depends upon more than simple coronal alignment.1

Dr. Kester then reviewed the results of a study that compared knees implanted via computer-assisted techniques to those implanted via regular jig-based techniques. Cumulative errors were greater overall for the jig-based cohort.2 PSlide B

In further analyzing knees implanted via a jig-based technique, Dr. Kester looked at a published article that reviewed CT scans for 159 CR knees, categorized them based on adherence to alignment goals, determined cumulative error and then compared their functional scores.3 Results showed that functional scores were better in femurs that better met alignment goals in the sagittal and transverse plane and tibias that better adhered to alignment goals in the sagittal and coronal planes.3 PSlide C

Another article review showed that computer assisted knees were more accurate than conventional instruments at attaining ±3° coronal alignment, and that knees with coronal alignment within this window had superior IKS and SF12 scores.4 PSlide D

In conclusion, Dr. Kester asserted that although coronal alignment is important, we cannot forget the other 5 degrees of freedom for the tibial and femoral components. PSlide E

References

  1. Parratte, S. et. al. Reproducing the Mechanical Axis did not improve the 15-Year Survival of 398 Modern TKA.
  2. Chauhan, S. et. al. Computer-assisted knee arthroplasty versus a conventional jig-based technique. JBJS [Br]. 2004; 86-B:373-7.
  3. Longstaff, L. et. al. Good Alignment After Total Knee Arthroplasty Leads to Faster Rehabilitation and Better Function. JOA. 2009; Vol. 24 No. 4.
  4. Choong, P. et. al. Does Accurate Anatomical Alignment Result in Better Function and Quality of Life? Comparing Conventional and Computer-Assisted Total Knee Arthroplasty. JOA. 2009; Vol. 24, No. 4.