Open reduction and internal fixation often are used to treat acetabular fractures to restore joint congruency. The operations on acetabular fractures, however, are associated with heterotopic ossification (HO). The relation with the surgical approach, which can be ilioinguinal, extended iliofemoral, or dorsal, is unclear [1, 35], although some authors state the more extensile the approach, the higher the incidence of HO [8, 20]. Disabling ossification occurs in approximately 5% of nonoperatively treated patients [32], but after operative treatment, the incidence increases substantially [21, 41]. The reported incidence of HO varies from 18% to 90% [3, 22]. In a meta-analysis [11], the incidence of HO after operative repair of acetabular fractures was determined to be 25.6%. To prevent HO, two primary approaches have been used: radiation therapy [2, 7] and indomethacin [22, 23, 28]. Although both methods are effective [3, 30], both have disadvantages. For radiation therapy, patients must be transported from the ward to the radiation department, and radiation personnel must be available to perform the procedure. Especially in severely injured patients, this may not be feasible. Moreover, radiation is known to induce malignancy and oligospermia and influence fertility in women, although the dosage in pelvic radiation used for acetabular fractures is in a safe range regarding potential risk of cancer and infertility [31]. Finally, radiation therapy is relatively expensive. When using indomethacin, prolonged bleeding time, gastromucosal irritation, and an increase in nonunions of associated fractures can be observed [5].

Burd et al. reported no major difference between indomethacin and radiation therapy in preventing HO in acetabular fractures [6]. In a Letter to the Editor in 2002, Michalak [25] raised concerns regarding this study, pointing to the possibility of a Type II error, ie, not finding a difference when a difference does exist.

We therefore performed a systematic review of the existing literature with the intent of performing a meta-analysis of pooled data to ascertain whether indomethacin or radiation therapy was superior in preventing clinically important HO (Grade 3 or 4 according to Brooker et al. [4] and the studies of Johnson et al. [15] and Oertel et al. [31]) in patients with operatively treated acetabular fractures.

We performed searches of PubMed^®, MEDLINE^®, EMBASE™, and the Cochrane Controlled Trial Register. Search terms included indometacin, indomethacin, Indocid, acetabular fracture, clinical trial, heterotopic ossification, and Brooker Grade 3 or 4. We also screened the references of the obtained articles, and relevant references were retrieved. To obtain data from unpublished trials, we performed a search through the conference proceedings of the British Library. We examined references of all articles and relevant articles were read. In case of gray literature, efforts were made to retrieve the conclusions. If necessary, authors were contacted directly.

Searching these databases using the above-mentioned search terms yielded 28 results, and five more relevant studies were found in the references of the retrieved articles, leading to a total of 33 publications (Fig. 1) [1, 5–7, 9, 10, 12, 13, 15–22, 24, 26–34, 36–42]. Exclusion criteria included retrospective studies, observational studies, and case reports. The abstracts were screened for these exclusion criteria by both authors independently (TJB, JPF), leaving nine studies in our analysis [6, 7, 13, 17, 22, 26, 29, 33, 37]. After reading the full articles, two studies were excluded as they were based on retrospective data [33, 37]. One prospective study was classified as an observational study and therefore was excluded from our analysis [26]. Two studies were designed as randomized trials comparing indomethacin and radiation therapy [6, 29]. In these trials, identical treatment regimens (25 mg indomethacin three times per day versus 800 cGy radiation therapy) were used, and the end points—Brooker Grades 3 and 4—were identified. Both studies were performed by the same institution, and the study by Burd et al. [6] included the data described by Moore et al. [29]. The latter study therefore was excluded. Data of the remaining five studies were analyzed.

Fig. 1 A flowchart illustrates the method of retrieval of articles and the decision making regarding acceptance or rejection of articles. Search terms are given in the text.

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If studies involved a third treatment strategy (placebo control or various radiation regimens), we examined the possibility of data extraction from the study. This was the case in four studies. In the prospective study performed by Childs et al. [7], different radiation regimens, consisting of 700 cGy starting at different times, were compared. The aim of their study was to investigate whether logistic difficulties in radiation therapy could influence the final outcome, being the rate of Brooker Grades 3 and 4 ossification. This study concluded no differences in effectiveness were induced by different starting points of radiation therapy until 4 days postoperatively. Several patients in their study received indomethacin in addition to radiation therapy, and the data of these patients were not included in the current analysis. The other three studies randomized indomethacin versus placebo [17] or versus no prophylaxis [13, 22].

Randomization methods were documented, and in case of discussion regarding the method of randomization, consensus between the investigators decided whether a study was included. The start of the treatment regimen (preoperatively or postoperatively) and dosage were documented.

A lower percentage (p = 0.034) of patients treated with radiation had HO develop than patients treated with indomethacin (five of 60 versus 20 of 224, respectively). We found no difference in treatment regimens or followup. The validity score of the studies according to the scale of Jadad et al. [14] varied between 0 (two studies) and 3 (one study) (Table 2).

Operations on acetabular fractures, needed for restoration of joint congruency, are associated with HO. Disabling ossifications occur substantially more often after operative treatment, with a reported incidence between 18% and 90% [3, 22]. In a meta-analysis [11], the incidence of HO after operative repair of acetabular fractures was determined to be 25.6%. Two primary prophylactic approaches are well known: radiation therapy [2, 7] and indomethacin [22, 23, 28]. Several studies have been done to investigate whether indomethacin or radiation therapy is more effective in prevention of HO after surgical treatment of acetabular fractures. These studies were not able to show a difference, and as pointed out by Michalak [25], this may be the result of a Type II error. We therefore performed a systematic review of the literature to compare the effectiveness of these two approaches to prevent HO.

Pooling data of various studies increases the power and reduces the risk of a Type II error. The retrieved prospective studies in our systematic review were selected using rather strict criteria. However, the poor validity of the included studies, some of which were not randomized, made a meta-analysis inappropriate. Along with the poor validity, there was an uneven distribution of the patients among the studies, and although statistical corrections for an uneven distribution could have been applied, this was an additional argument against the performance of a meta-analysis. A large randomized clinical trial would be appropriate to confirm the findings in our systematic review. Based on the data in our systematic review, a sample size calculation using α = 0.05 and 1 – β = 0.80 indicates a sample size of 265 patients per arm, without dropout correction. Until such a demanding trial has been performed, new smaller trials could make a proper meta-analysis feasible.

We believe the studies we identified contain the best available evidence at this time regarding the prophylactic regimen for HO after surgical treatment of acetabular fractures. The incidence of HO seems lower in patients treated with radiation therapy, and therefore, despite the shortcomings of the gathered literature, when practical we advocate the use of radiation therapy for this indication rather than indomethacin.