X-ray of knee prosthesis

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Author: Mikael Häggström [notes 1]

Post-operative evaluation

Overhang (arrow) does not seem to have any detrimental effect.[1] It is therefore not necessary to measure or report.

Knee replacement is evaluated by the following measures:

  • HKA: Hip-knee-ankle angle, which is ideally between 3° varum to 3° valgum from a right angle.[2]

  • - FFC: frontal femoral component angle. It is typically regarded as optimal when being 2–7° in valgus.[3]
    - FTC: frontal tibial component angle, which is regarded as optimal when being at a right angle. A varus position of more than 3° has generally been found to increase the failure rate of the prosthesis.[3]

  • - Anterior femoral notching (the femoral component causing reduced thickness of the distal femur anteriorly), seems to cause an increased risk of fractures when exceeding about 3 mm.[4]
    - LTC: lateral (or sagittal) tibial component angle, which is ideally positioned so that the tibia is 0–7° flexed compared to at a right angle with the tibial plate.[3]

Report

In Swedish healthcare[5], the numbers of the angles are not reported if being within normal limits. Example of an normal case:

  • Postoperative images of knee implant in unremarkable position.

Also, unless you know the referring physician is familiar with the same angle terminology, preferably report any deviating angles as varus/valgus deviation or ventral/dorsal angulation, such as:

  • An abnormally increased valgus angulation of __° of the femur component in relation to femoral diaphysis.
  • An abnormally increased dorsal angulation of __° of the tibial diaphysis in relation to the tibial component.
See also: General notes on reporting

Follow-up

Potential complications that need to be evaluated on follow-up are as follows.

Radiolucent lines

Radiolucent lines may indicate loosening of the implant. A radiolucent line thinner than than 2 mm can be tolerated at the cement-bone interface (for cemented implants) or implant-bone interface (for cementless implants) if it remains stable and appears within the first 6 months (cemented implants) or the first 2 years (cementless implants) after surgery.[6]

Displacement

A change in position is indicated by a significant change in either of the angles listed in the post-operative evaluation section above.[6]

Infection

Signs of infection include:[6]

  • Rapidly progressing radiolucency and/or osteolysis
  • Periosteal reaction
  • Bubbles of air within soft tissue or fluid collection.

Other complications

  • Fractures of prosthesis components.
  • Wear of the polyethylene insert, which is the case when progressive thinning occurs over time.
  • Dissociation of the polyethylene insert from the patellar component or tibial baseplate.

Reporting

In Swedish healthcare[7], an example report of a normal case may be:

  • No changes since previous images on <date>.
See also: General notes on reporting

Notes

  1. ↑ For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Radlines:Authorship for details.

References

  1. ↑ S.G.F. Abram, A.G Marsh, F. Nicol, A.S. Brydone, A. Mohammed, S.J. Spencer (2018-02-21). "The Impact Of Tibial Component Overhang On Outcome Scores And Pain In Total Knee Replacement ". Orthopaedic Proceedings. 
  2. ↑ Inui, Hiroshi; Taketomi, Shuji; Nakamura, Kensuke; Takei, Seira; Takeda, Hideki; Tanaka, Sakae; Nakagawa, Takumi (2013). "Influence of navigation system updates on total knee arthroplasty ". Sports Medicine, Arthroscopy, Rehabilitation, Therapy & Technology 5 (1): 10. doi:10.1186/2052-1847-5-10. ISSN 1758-2555. PMID 23638774.  (CC-BY-2.0)
  3. ↑ 3.0 3.1 3.2 Gromov, Kirill; Korchi, Mounim; Thomsen, Morten G; Husted, Henrik; Troelsen, Anders (2014). "What is the optimal alignment of the tibial and femoral components in knee arthroplasty? ". Acta Orthopaedica 85 (5): 480–487. doi:10.3109/17453674.2014.940573. ISSN 1745-3674. PMID 25036719. 
  4. ↑ Lee, Ju Hong; Wang, Seong-Il (2015). "Risk of Anterior Femoral Notching in Navigated Total Knee Arthroplasty ". Clinics in Orthopedic Surgery 7 (2): 217. doi:10.4055/cios.2015.7.2.217. ISSN 2005-291X. 
  5. ↑ NU Hospital Group, Sweden, Sep 2018
  6. ↑ 6.0 6.1 6.2 Cyteval, C. (2016). "Imaging of knee implants and related complications ". Diagnostic and Interventional Imaging 97 (7-8): 809–821. doi:10.1016/j.diii.2016.02.015. ISSN 22115684. 
  7. ↑ NU Hospital Group, Sweden, Oct 2018
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