Weight-bearing radiography depends on limb loading

  • Robert Karl Zahn
  • Lisa Renner
  • Carsten Perka
  • Hagen Hommel



The mechanical axis of the lower limb has shown to vary between different weight-bearing conditions and change after total knee arthroplasty (TKA). The purpose of this study was to investigate the correlation between mechanical axis alignment in standing long-leg radiographs and limb loading after TKA.


Mechanical axis of the lower limb and limb loading have been prospectively evaluated in 115 patients 10 days and 3 months after TKA. By the moment of standing long-leg radiography for analysis of the mechanical leg axis, two digital scales separately captured the load of each limb.


Mechanical axis changed from an initial − 1° ± 2° valgus alignment to a varus axis of + 1° ± 2° (p < 0.01). This change in alignment was associated with an increase of limb loading from 89.9 ± 10.7 to 93.0 ± 7.0% (p < 0.01). The mechanical axis strongly correlated with relative limb loading at the first and second measurements (r = 0.804, p < 0.001, respectively, r = 0.562, p < 0.001). A significant change in the rate of outliers was registered within the observation period. These alterations and distinctions were much more pronounced in patients with postoperative incomplete extension (n = 15).


The postoperative mechanical axis correlates with limb loading. A clinical relevant change in frontal alignment of the lower limb is associated with increased limb loading after TKA. The actual mechanical axis can only be assessed at physiological limb loading in long-leg radiographs with complete extension at full weight bearing.

Level of evidence

Diagnostic study, Level II.


Total knee arthroplasty Total knee replacement Mechanical axis Limb loading Standing long-leg radiographs 



Body mass index


Total knee arthroplasty


Numerical rating scale



No funding hase been received for this study.

Compliance with ethical standards

Conflict of interest

The authors have no conflicts of interest.

Ethical approval

This study was approved by the competent ethical committee (AS 17 (bB)/2015).

Informed consent

A written informed consent was obtained from all patients.


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Copyright information

© European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2018

Authors and Affiliations

  • Robert Karl Zahn
    • 1
    • 4
  • Lisa Renner
    • 1
  • Carsten Perka
    • 1
  • Hagen Hommel
    • 2
    • 3
  1. 1.Center for Musculoskeletal Surgery, CharitéUniversity Medicine BerlinBerlinGermany
  2. 2.Clinic for Orthopaedics, Sports Medicine, and RehabilitationKH-MOL GmBHWriezenGermany
  3. 3.Academic Teaching Hospital of the Medical School of Brandenburg Theodor FontaneNeuruppinGermany
  4. 4.Center for Musculoskeletal Surgery, CharitéUniversity Medicine BerlinBerlinGermany

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