X-ray of hip prostheses

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Main components of a hip prosthesis[1]

Author: Mikael Häggström [notes 1]
For X-ray of the hip joint in the presence of a prosthesis, this article first deals with the first postoperative image which is more focused at prosthesis configuration, and separately describes subsequent follow-ups which are more focused at complications.

Quality checking

  • The referral or complementary information needs to specify the type of prosthesis and when it was inserted.[2]
  • Images that need to be available include the first postoperative ones, as well as the most recent previous exam.[2]

First postoperative image: Configuration

Post-operative projectional radiography ("X-ray") is routinely performed to ensure proper configuration of hip prostheses.

The direction of the acetabular cup influences the range of motion of the leg, and also affects the risk of dislocation.[3] For this purpose, the acetabular inclination and the acetabular anteversion are measurements of cup angulation in the coronal plane and the sagittal plane, respectively.

  • Acetabular inclination.[4] This parameter is calculated on an anteroposterior radiograph as the angle between a line through the lateral and medial margins of the acetabular cup and the transischial line which is tangential to the inferior margins of the ischium bones.[4]

  • Acetabular inclination is normally between 30 and 50°.[4] A larger angle increases the risk of dislocation.[3]

  • Acetabular anteversion.[5] This parameter is calculated on a lateral radiograph as the angle between the transverse plane and a line going through the (anterior and posterior) margins of the acetabular cup.[5]

  • Acetabular anteversion is normally between 5 and 25°.[3] An anteversion below or above this range increases the risk of dislocation.[3] There is an intra-individual variability in this method because the pelvis may be tilted in various degrees in relation to the transverse plane.[3]

  • Leg length discrepancy after hip replacement is calculated as the vertical distance between the middle of the minor trochanters, using the acetabular tear drops[4] or the transischial line[3] as references for the horizontal plane. A discrepancy of up to 1 cm is generally tolerated.[4][3]

  • Center of rotation: The horizontal center of rotation is calculated as the distance between the acetabular teardrop and the center of the head (or caput) of the prosthesis and/or the native femoral head on the contralateral side.[4] The vertical center of rotation instead uses the transischial line for reference.[4] The parameter should be equal on both sides.[4]

Hip prosthesis zones according to DeLee and Charnley,[6] and Gruen.[7] These are used to describe the location of for example areas of loosening.

Cement coverage is regarded as acceptable when there are no translucent zones on an anteroposterior image in at least 6 of 7 Gruen-zones.[2] Absence of cement in zone 7 (medially-proximally) needs to be noted. On a lateral image, the distal tip of the prosthesis should be centered, and not be in contact with the cortex.[2] The cup should not have translucent zones in zone 1 and 2. It is acceptable to have translucent zones in parts of zone 3.[2]

Report

The postoperative report should include:[2]

  • Prosthesis configuration. If the report is likely to undergo double reading, the parameters need to be given in numbers even if within normal limits.
  • Cement coverage.
See also: General notes on reporting

Further follow-ups: Complications

Further follow-ups after the initial postoperative image are focused on various complications.

Dislocation

  • Dislocated artificial hip

  • Liner wear, particularly when over 2 mm, increases the risk of dislocation.[8] Liner creep, on the other hand, is normal remoulding.[3]

Fracture

Post-operative femoral fractures are graded by the Vancouver classification:

Type Description
A Fracture in the trochanteric region
B1 Fracture around stem or just below, with well fixed stem
B2 Fracture around stem or just below, with loose stem but good proximal bone
B3 Fracture around stem or just below, with poor quality or severely comminuted proximal bone
C Fracture below theprosthesis

Loosening

Hip prosthesis displaying aseptic loosening (arrows)

On radiography, it is normal to see thin radiolucent areas of less than 2 mm around hip prosthesis components, or between a cement mantle and bone. However, these may still indicate loosening of the prosthesis if they are new or changing, and areas greater than 2 mm may be harmless if they are stable.[9] The most important prognostic factors of cemented cups are absence of radiolucent lines in DeLee and Charnley zone I, as well as adequate cement mantle thickness.[10] In the first year after insertion of uncemented femoral stems, it is normal to have mild subsidence (less than 10 mm).[9]

Report

Further follow-up reports should include at least:

  • Dates of the images used for comparison
  • Absence of change in position, or a description of any change.[2]
  • Absence or of loosening, or a description of it.[2]
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. ↑ Andrew Still (2002-11-02). Total Hip Replacement. University of Southern California. Retrieved on 2017-01-05.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Radiologists: Torsten Boegård, Mats Geijer, Marianne Petrén-Mallmin. Orthopedic surgeons: Lennart Sanzén, Christer Strömberg, Torbjörn Ahl. Hip - Radiologic evaluation of prosthetic surgery (Swedish title: HÖFT - Radiologisk undersökning vid proteskirurgi). Swedish Orthopaedic Association (SOA). Publication #18, 2006
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Iain Watt, Susanne Boldrik, Evert van Langelaan and Robin Smithuis. Hip - Arthroplasty -Normal and abnormal imaging findings. Radiology Assistant. Retrieved on 2017-05-21.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 Vanrusselt, Jan; Vansevenant, Milan; Vanderschueren, Geert; Vanhoenacker, Filip (2015). "Postoperative radiograph of the hip arthroplasty: what the radiologist should know ". Insights into Imaging 6 (6): 591–600. doi:10.1007/s13244-015-0438-5. ISSN 1869-4101. PMID 26487647. 
  5. ↑ 5.0 5.1 Shin, W. C.; Lee, S. M.; Lee, K. W.; Cho, H. J.; Lee, J. S.; Suh, K. T. (2015). "The reliability and accuracy of measuring anteversion of the acetabular component on plain anteroposterior and lateral radiographs after total hip arthroplasty ". The Bone & Joint Journal 97-B (5): 611–616. doi:10.1302/0301-620X.97B5.34735. ISSN 2049-4394. 
  6. ↑ John J. Callaghan, Aaron G. Rosenberg, Harry E. Rubash (2007). The Adult Hip, Volume 1 . Lippincott Williams & Wilkins. p. 958. ISBN 978-0-7817-5092-9. 
  7. ↑ Neumann, Daniel R.P.; Thaler, Christoph; Hitzl, Wolfgang; Huber, Monika; Hofstädter, Thomas; Dorn, Ulrich (2010). "Long-Term Results of a Contemporary Metal-on-Metal Total Hip Arthroplasty ". The Journal of Arthroplasty 25 (5): 700–708. doi:10.1016/j.arth.2009.05.018. ISSN 0883-5403. 
  8. ↑ Daniel J. Berry, Jay Lieberman (2012). Surgery of the Hip . Elsevier Health Sciences. p. 1035. ISBN 9781455727056. 
  9. ↑ 9.0 9.1 Roth, Trenton D.; Maertz, Nathan A.; Parr, J. Andrew; Buckwalter, Kenneth A.; Choplin, Robert H. (2012). "CT of the Hip Prosthesis: Appearance of Components, Fixation, and Complications ". RadioGraphics 32 (4): 1089–1107. doi:10.1148/rg.324115183. ISSN 0271-5333. 
  10. ↑ Steffen Breusch, Henrik Malchau (2005). The Well-Cemented Total Hip Arthroplasty: Theory and Practice . Springer Science & Business Media. p. 336. ISBN 978-3-540-24197-3. 
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