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Functional knee phenotypes: a novel classification for phenotyping the coronal lower limb alignment based on the native alignment in young non-osteoarthritic patients

  • Michael T. HirschmannEmail author
  • Lukas B. Moser
  • Felix Amsler
  • Henrik Behrend
  • Vincent Leclerq
  • Silvan Hess
KNEE

Abstract

Purpose

The currently used system to classify the lower limb alignment (neutral, varus, valgus) does not consider the orientation of the joint line or its relationship to the overall lower limb alignment. Similarly, current total knee arthroplasty (TKA) alignment concepts do not sufficiently consider the variability of the native coronal alignment. Therefore, the purpose of this study was (1) to introduce a new classification system for the lower limb alignment, based on phenotypes, and (2) to compare the alignment targets of different TKA alignment concepts with the native alignment of non-osteoarthritic patients.

Methods

Two recent articles phenotyped the lower limb, the femur and tibia of 308 non-osteoarthritic knees of 160 patients [male to female ratio = 102:58, mean age ± standard deviation 30 ± 7 years (16–44 years)]. The present study introduces functional knee phenotypes, which are a combination of all previously introduced phenotypes. The functional knee phenotypes therefore enable an evaluation of all parameters in relation to each other and thus a comprehensive analysis of the coronal alignment. The existing functional knee phenotypes in the female and male population were investigated. In addition, how many non-osteoarthritic knees had an alignment within the range of current TKA alignment targets (mechanical, anatomical and restricted kinematic alignment) was investigated. Therefore, it was defined which functional knee phenotypes represented a target of the TKA alignment concepts and which percentage of the population had such a phenotype.

Results

Out of 125 possible functional knee phenotypes, 43 were found (35 male, 26 and 18 mutual). The most common functional knee phenotype in males was NEUHKA0° + NEUFMA0° + NEUTMA0° (19%), followed by VARHKA3° + NEUFMA0° + VARTMA0° (8.2%). The most common functional knee phenotype in females was NEUHKA0° + NEUFMA0° + NEUTMA0° (17.7%), closely followed by NEUHKA0° + NEUFMA0° + VALTMA0° (16.6%). The functional knee phenotype representing a mechanical alignment target was found in 5.6% of the males and 3.6% of the females. The phenotype representing an anatomical alignment target was found in 18% of the males and 17% in females. Five of the nine phenotypes representing a restricted kinematic alignment target were found in this population (male 5, female 4, mutual 4). They represented 31.3% of all males and 45.1% of all females.

Conclusion

A more individualized approach to TKA alignment is needed. The functional knee phenotypes enable a simple, but detailed assessment of a patient’s individual anatomy and thereby could be a helpful tool to individualize the approach to TKA.

Level of clinical evidence

III, retrospective cohort study.

Keywords

Knee Native Alignment Classification Phenotype CT HKA FMA TMA TKA concepts Mechanical alignment Anatomical alignment Restricted kinematic alignment 

Abbreviations

CT

Computed tomography

FMA

Femoral mechanical angle

HKA

Hip–knee–ankle angle

HDP

Hydroxymethane diphosphonate

NEU

Neutral

OA

Osteoarthritis

SD

Standard deviation

SPECT

Single-photon emission computed tomography

TMA

Tibial mechanical angle

TKA

Total knee arthroplasty

VAL

Valgus

VAR

Varus

Notes

Funding

The statistical analysis was funded by Symbios, Yverdon les Bains, Switzerland.

Compliance with Ethical Standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

All investigations were conducted in conformity with ethical principles of research and that institutional approval of the human protocol for this investigation was obtained.

Informed consent

Informed consent for participation in the study was obtained.

Supplementary material

167_2019_5509_MOESM1_ESM.xlsx (20 kb)
Supplementary material 1 (XLSX 20 kb)

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Copyright information

© European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2019

Authors and Affiliations

  • Michael T. Hirschmann
    • 1
    • 2
    Email author
  • Lukas B. Moser
    • 1
    • 2
  • Felix Amsler
    • 4
  • Henrik Behrend
    • 5
  • Vincent Leclerq
    • 3
  • Silvan Hess
    • 1
    • 2
  1. 1.Department of Orthopaedic Surgery and TraumatologyKantonsspital Baselland (Bruderholz, Liestal, Laufen)BruderholzSwitzerland
  2. 2.University of BaselBaselSwitzerland
  3. 3.SymbiosYverdon les BainsSwitzerland
  4. 4.Amsler ConsultingBaselSwitzerland
  5. 5.Department of Orthopaedic SurgeryKantonsspital St. GallenSt. GallenSwitzerland

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