Size of ischial fibro-ostosis is associated with heterotopic ossification after total hip arthroplasty
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The hypothesis of the present study was that degenerative fibro-ostosis (FO) of the ischial hamstring tendon insertion is a risk factor for heterotopic ossification (HO) following THA.
We followed 103 consecutive patients (43 males, 60 females, mean age 61 years) who underwent unilateral cementless THA for primary hip osteoarthritis and investigated the incidence of HO within the first 12 months after surgery. On pre-operative radiographs, a standardized evaluation for FO of the ischial hamstring tendon insertion concerning horizontal, vertical, and square dimensions was performed. HO was classified according to Brooker on radiographs at 12 months post-operatively.
At follow-up, 56 patients (54%) had no radiographic evidence of HO, 23 (22%) were classified as Brooker I, 17 (17%) as II, 6 (6%) as III, and 1 (1%) as IV, respectively. Patients with post-operative HO had significantly greater vertical (3.0 mm vs. 2.3 mm, p = 0.001) and horizontal (47.9 mm vs. 39.1 mm, p = 0.025) dimensions of FO than patients without HO. Patients with FO and a vertical dimension of ≥ 2.5 mm were more likely to develop HO (55.6%) than patients with a vertical FO dimension of less than 2.5 mm (34.7%, OR = 2.35 p = 0.047). A weak correlation between the vertical and horizontal size of FO and the severity of HO was observed.
Radiographic evidence of asymptomatic FO is a potential risk factor for the development of HO following THA and may be used as a simple diagnostic tool to pre-operatively identify patients at risk for post-operative HO. This association has not been previously described and further research to confirm the present findings and to justify additional prophylactic treatment in these patients is warranted.
KeywordsHeterotopic ossification Total hip arthroplasty Ischial fibroostosis Risk factor
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All study procedures involving human participants were in accordance with the ethical standards of the institutional research committee of the University of Heidelberg and with the 1964 Helsinki declaration and its later amendments or comparable ethical standard.
Informed consent was obtained from all individual participants included in the study.
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