X-ray of knee prosthesis
Author:
Mikael Häggström [notes 1]
Contents
Post-operative evaluation
Knee replacement is routinely evaluated by projectional radiography ("X-ray"), including the following measures:
- HKA: Hip-knee-ankle angle, which is ideally between 3° varum to 3° valgum from a right angle.[1]
- FFC: frontal femoral component angle. It is typically regarded as optimal when being 2–7° in valgus.[2]
- 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.[2]
- 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.[2]
LFC is the lateral (or sagittal) femoral component angle,[1] but its use is not necessary as long as there are no established clinically relevant reference ranges for it.
Report
In Swedish healthcare[3], 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 deviating angles as varus/valgus deviation or volar/dorsal angulation of either:
- The femur component in relation to femoral diaphysis
- 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.[4]
Displacement
A change in position is indicated by a significant change in either of the angles listed in the post-operative evaluation section above.[4]
Infection
Signs of infection include:[4]
- 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[5], an example report of a normal case may be:
- No changes since previous images on <date>.
- See also: General notes on reporting
Notes
- ↑ 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
- ↑ 1.0 1.1 1.2 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). doi:. ISSN 1758-2555. (CC-BY-2.0)
- ↑ 2.0 2.1 2.2 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:. ISSN 1745-3674.
- ↑ NU Hospital Group, Sweden, Sep 2018
- ↑ 4.0 4.1 4.2 Cyteval, C. (2016). "Imaging of knee implants and related complications ". Diagnostic and Interventional Imaging 97 (7-8): 809–821. doi:. ISSN 22115684.
- ↑ NU Hospital Group, Sweden, Oct 2018
