Robotic-arm Assisted Total Knee Arthroplasty: the Relationship between Bone Resection, Gap Balancing and Resultant Implant Alignment

Document Type : RESEARCH PAPER


1 Royal Infirmary of Edinburgh, Edinburgh, UK

2 Newcastle upon Tyne Hospitals NHS Foundation Trust, UK


Objectives: The primary aim was to assess the association between bone resection and the resultant 
flexion and extension gaps in the medial and lateral compartments of the knee when performing robotic -
arm assisted total knee arthroplasty (rTKA). The secondary aims were to compare medial and lateral 
bone resections and the influence on limb alignment, and whether the amount of bone resection that 
resulted in equal gaps was predictable.
Methods: A prospective study of 22 consecutive patients with a mean age of 66 years undergoing rTKA was 
conducted. The femoral component was mechanically aligned, and the alignment of the tibial component was 
adjusted (+/-3degrees of the mechanical axis) to obtain equal extension and flexion gaps. All knees underwent soft 
tissue balancing using sensor-guided technology. The final compartmental bone resection, gaps, and implant 
alignment were obtained from the robot data archive.
Results: There was a correlation between bone resection and the resultant gap in the medial (r=0.433, p=0.044) 
and lateral (r=0.724, p<0.001) compartments of the knee. There were no differences in bone resection from the 
distal femur and posterior condyles in the medial (p=0.941) or lateral compartments (p=0.604) or for the resultant 
gaps (p=0.341 and p=0.542, respectively). There was more bone removed from the medial compartment compared 
to the lateral aspect: 0.9mm (p=0.005) in extension and 1.2mm (p=0.026) flexion. The differential bone resection 
changed the knee alignment by one degree of varus. There were no significant differences between the actual and 
predicted medial (difference 0.05, p=0.893) or lateral (difference 0.00, p=0.992) tibial bone resection. 
Conclusion: There was a direct association between bone resection and resultant compartment joint gap when 
using rTKA, which was predictable. Gap balancing was achieved when less bone was resected from the lateral 
compartment which resulted in an estimated one-degree varus alignment of the knee. 
 Level of evidence: II


Main Subjects

Volume 11, Issue 4
April 2023
Pages 278-284
  • Receive Date: 16 February 2022
  • Revise Date: 17 January 2023
  • Accept Date: 29 January 2023
  • First Publish Date: 29 January 2023