Magnification of Digital Hip Radiographs in Hip Arthroplasties: a Study in the Real Practice

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Noppadol Wangjiraphan
Ukrit Songpaiboon
Tharanas Jantharagsarangsee


Background: Preoperative templating of total hip arthroplasty (THA) by placing a plastic template over the digital radiograph on a computer screen has high accuracy in size estimations. Some researchers have found that most radiographs have relatively constant magnifications of 15% or 20%, and templating with these constant magnifying factors without calibration may be acceptable in the real practice.

Objective: To determine the magnification of digital hip radiographs of Thai patients and comparing with the acceptable range for the estimation of the acetabular cup size (±4% or 2 mm)

Materials and methods: A retrospective-analytical study was conducted among hip radiographs of 119 patients who underwent unilateral THAs at Lampang Hospital from May 2015 to July 2019. We measured the diameter of femoral head prostheses in the PACS program and compared with the actual sizes from the medical records to calculate the magnification. The percentages of radiographs with magnification in the range of 15±4% and 20±4% were analyzed. The clinical data was compared between the two magnification groups, within versus outside the range. Logistic regression analysis was utilized to identify the factors that influenced the magnification.

Results: The mean age was 58.6±12.2 years; 51.3% were female; and the mean body mass index (BMI) was 22.3±3.9 kg/m2. The average magnification was 14.1±4.1%. There were 115 radiographic images (57.8%) with magnification in the range of 15±4%; and 82 images (41.2%) with magnification in the range
of 20±4%. No differences in age, gender, BMI were found between groups with magnification within or outside the range of 15±4% (p=0.848, 0.347 and 0.158, respectively). The magnification group in the range of 20 ± 4 % was older than the magnification group of <16% (60.5±11.6 vs 56.0±12.6 years, p=0.009). Age was a factor that affect the magnification for being within or outside the range of 20±4% (OR 0.97, 95%CI 0.95-0.99, p=0.022).

Conclusion: The digital hip radiographs had an average magnification of 14%. Three-fifths of the radiographs had a magnification in the range of 15±4 %, and only two-fifths had a magnification in the range of 20±4%. Hip radiograph should be calibrated with known-diameter metal marker before templating
on the computer-screen images. Otherwise, templates with 15% magnification could be used and more appropriately than the 20% magnifying templates.


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Wangjiraphan, N., Songpaiboon, U., & Jantharagsarangsee, T. . (2020). Magnification of Digital Hip Radiographs in Hip Arthroplasties: a Study in the Real Practice. Lampang Medical Journal, 41(1), 30–38. Retrieved from
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