Personalized alignment philosophies using robotic total knee arthroplasty

Personalized alignment philosophies using robotic total knee arthroplasty

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In recent years, knee phenotyping has become an important philosophy in total knee arthroplasty (TKA). Together with the different concepts around alignment and the increased technological advancements offered by robotic-assisted systems, TKA is moving towards a more personalized experience. In the first article of this series, Michael T Hirschmann, founder of the functional knee phenotype classification from Kantonsspital Baselland, Bruderholz, Switzerland, leads us through knee phenotyping personalized alignment philosophies in TKA.

Michael Hirschmann

Michael T Hirschmann

Kantonsspital Baselland, Bruderholz, Switzerland

Understanding variation: knee phenotypes

Personalized approaches to TKA are becoming commonplace. After many years of experience with TKA, the technological advancements of the last decades have instigated a shift in the beliefs around TKA, steering away from the idea that all knees are the same and the adoption of a “one-size-fits-all” approach to a much more personalized one. This is in keeping with the philosophy of personalized medicine seen across many other disciplines and is particularly valid in the case of TKA given that around 20% of patients remain dissatisfied after TKA [1, 2]. As with all personalized approaches, there are a great number of factors that must be taken into account. Two important considerations are the alignment and the phenotyping of the knee [3–5]. It is clear that an osteoarthritic knee which has undergone changes exhibits variation, particularly in coronal tibial and femoral alignment [6], yet Hirschmann et al [3] showed that there is also great variability of the overall lower limb alignment in young people with nonosteoarthritic knees. At the time of the study [3], a now somewhat oversimplified classification system was in place, which categorized knees into neutral, valgus, and varus based on the coronal knee alignment. Hirschmann et al [3] found that the varus and valgus groups represented around 40% of the study population, from which one can conclude that neutral alignment should not be viewed as “normal” given that varus and valgus groups constitute more than just a negligible part of the nonosteoarthritic population [3]. Yet not only is there variation in knee alignment, but there is also enormous variability in anatomy, laxity, and kinematics [3, 5, 7]. Hirschmann et al [4] have therefore introduced the term “phenotype” into knee surgery. In their understanding, phenotypes exist for bony alignment in three planes (coronal, lateral, and axial), laxity, kinematics, and biology. In their landmark work, they primarily proposed a novel classification system for phenotyping the coronal lower limb as a means to better denote the variability of the overall coronal lower limb alignment. This classification takes into account the orientation of the femoral and tibial joint lines; indeed, by doing so, 43 different combinations of overall alignment and tibial and femoral joint lines, the so-called functional knee phenotypes, were identified in the nonarthritic population [4]. In a later publication this was validated on several series of osteoarthritic knees [8–11].

Further to this, there is another classification termed coronal plane alignment of the knee (CPAK) which comprises nine subgroups according to joint line obliquity (JLO) and arithmetic hip-knee-ankle angle (aHKA) [12]. Where the functional phenotype classification accounts for the degree of varus or valgus deformity individually in the femur and tibia and identifies the mismatch between mechanical alignment of the tibia and femur, the CPAK provides room for individualization of preoperative alignment planning in TKA by considering the individual JLO and aHKA [13]. Furthermore, according to both classifications, gender-based differences in knee phenotype have been found [7, 8, 13]. There is a large variability in extension-flexion gap widths in varus osteoarthritic knees, with larger gap sizes being found in women compared with men [7]. In men the varus phenotype is influenced by the femoral mechanical angle, though in both men and women tibial mechanical angle values are similar [8], and CPAK Type III (apex distal/valgus) and VI (neutral/valgus) alignments are more common in women, whereas CPAK Type I (apex distal/varus ) and IV (neutral/varus) are more seen in men [14]. 

Just recently Hirschmann et al [15] extended their original coronal alignment phenotypes to 3D. The authors highlighted the importance of bony alignment for extension gap, flexion gap, and anterior compartment and introduced their 3-compartment phenotype concept. 

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  • Understanding variation: knee phenotypes

  • What are knee phenotypes?

  • Early strategies in alignment

  • Personalized alignment methods

  • Personalized alignment in robotic TKA

  • Phenotypes and robotic TKA

  • Is there a normal knee?

  • Conclusion

Accuracy and early outcomes
Part 2 | Accuracy and early outcomes
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Header 3 Mid- to long-term outcomes of robotic arm-assisted total knee arthroplasty
Part 3 | Mid- to long-term outcomes
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AO Recon resources

Contributing experts

This series of articles was created with the support of the following specialists (in alphabetical order):
Fares Haddad

Fares Haddad

University College London and University College London Hospitals, London, UK

Michael Hirschmann

Michael T Hirschmann

Kantonsspital Baselland, Bruderholz, Switzerland

Sebastien Lustig

Sébastien Lustig

Lyon North University Hospital—Hospices Civils de Lyon, Lyon, France

This article was edited by Lyndsey Kostadinov, AO Innovation Translation Center, Clinical Science, Switzerland.

References

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