This study with mean follow-up period more than 5 years revealed that postoperative satisfaction, JOA scores and SF-36 of primary THA for Crowe type III and IV dysplasia were comparable to those of Crowe type I. The height of the H group was significantly shorter than that of the control group due to the effect of high hip dislocation. In the H and FO group, intraoperative blood loss and surgery time were increased compared with the control and N-FO group. No difference was detected in perioperative complications, but results may change as the number of cases increases.
PROMs
The postoperative JOA score was favorable without any significant difference between the H and control group, and between the FO and N-FO group. The JOA score in patients with high hip dislocation was not much different from previous reports [Kawai T et al., 2014]. Although no significant difference was detected, the JOA score tended to be poor in the cases with femoral osteotomy (FO group).
The SF-36, including the subscale, at the final follow-up showed no significant difference between the H and control group, and between the FO and N-FO group. Each subscale score was as good as, or even better than, previous reports [Nilsdotter AK et al., 2010; Fernandez-Fairen M et al., 2011]. As described in Limitations later, the reasons for this result were considered that there may be a selection bias in this study. In other words, in this study, only the cases that responded to the postal questionnaire were enrolled, and it is possible that cases with good postoperative outcomes were selectively analyzed. However, no significant difference was detected in postoperative SF-36 between the H group and control group, which suggesting that there is no difference in postoperative PROMs depending on the degree of preoperative pelvic deformity.
Additionally, each group has the NPS of over 50 and is considered a good outcome. Hamilton et al. reported the NPS for joint replacement was 60, individual scores for total hip replacement (THR) and total knee replacement (TKR) were 71 and 49 respectively [Hamilton DF et al., 2014]. From the above, we considered that patients in the FO group with the lowest NPS (=60) in this study were also satisfied with THA.
Questionnaire
In this study, patients chose one of five options (very satisfied, satisfied, neither, dissatisfied, and very dissatisfied) at questionnaire to measure postoperative satisfaction. Then, the cases who selected "very satisfied" or "satisfied" were considered satisfied. The method of selecting one of the five options is called a five-point Likert scale and the method has good measurement properties, validity, and reliability [Dawson J et al., 1996]. Additionally, that is simple and available in many languages [Rolfson O et al., 2016]. In this study, the patient satisfaction was measured with two methods, NPS and Likert scale. Therefore, we believed that the results of patient satisfaction had high reliability.
In the H group, the VAS scores at the final follow-up were significantly higher than those in the control group, and more patients felt that postoperative rehabilitation was serious. When the H group was divided into the FO and N-FO groups, the VAS scores and number of patients who felt “serious rehabilitation” in the FO group were significantly higher. These results suggest that the FO group might have an adverse effect on the clinical outcomes in the H group. All patients in the FO groups had Crowe type IV dysplasia and had very severe cases with acute limb lengthening greater than 40 mm. There are some reports that the intensity of early postoperative pain increases the risk of chronic postsurgical pain [Puolakka PA et al., 2010; Fletcher D et al., 2015]. THA with femoral shortening osteotomy is an effective and reliable technique [Thorup B et al., 2009; Wang D et al., 2017; Necas L et al., 2019]. However, based on this study, for patients who will undergo THA with femoral shortening osteotomy, it is desirable to explain before surgery that the postoperative rehabilitation will be more serious and there may be the possibility of persisting pain compared to normal cases.
Patients sometimes had low back pain before THA [Staibano P et al., 2014; Chimenti PC et al., 2016], which was improved after THA [Parvizi J et al., 2010; Weng W et al., 2016]. In this study, low back pain improved after surgery in all cases. It was found that THA easily improved preoperative back pain even in patients with high hip dislocation. The chief complaint of patients with high hip dislocation in the gluteal muscle is often low back and buttock pain. Therefore, low back pain caused by malalignment due to pelvic deformity or LLD should be considered as an important factor in determining the surgical indication of THA for Crowe type III and IV dysplasia.
Leg length discrepancy
There are many past reports indicating that a postoperative LLD >10 mm decreases postoperative function and satisfaction of THA [O’Brien S et al., 2010; Meermans G et al., 2011]. In the H group, patients strongly wanted to correct LLD, probably due to the large difference in preoperative LLD. However, when one-sided THA with femoral shortening osteotomy for the high hip dislocation was performed, there was a limitation to the amount of LLD correction, and postoperative LLD was often greater than 10 mm. In this study, postoperative LLD of one-sided THA with femoral shortening osteotomy was 18.7 ± 7.9 mm. Although a significant difference was not detected, it may have led to declined satisfaction in the FO group.
Limitations
This study had several limitations. First, the number of cases was small due to the rarity of high hip dislocation. In particular, there were only a few cases available for the investigation of the effects of femoral shortening osteotomy. If the number of hips is increased, there is a possibility that the results of the questionnaire will show a significant difference. However, considering that high hip dislocation was extremely rare and that the study was performed at a single institution, this study had an adequate number of hips for analysis. Second, there is a possibility that selection bias had occurred because the only patients who answered the questionnaire were enrolled in this study. This fact could artificially inflate the proportion of satisfied or unsatisfied patients. The response rates of this study were not very high at 61% (23/38 cases), however those were almost the same as the previous survey studies [Meyer R et al., 2018; Sieja A et al., 2019]. Third, the validity evaluation of the questionnaire itself in this study had not been performed in the past, and the knee condition at the time of the evaluation had not been confirmed. However, the questionnaire included the NPS, Likert scale, and VAS that have been evaluated for their effectiveness in past reports [Hamilton DF et al., 2014; Rolfson O et al., 2016], and we considered that the questionnaire had a certain validity and reliability. Finally, preoperative PROMs, especially SF-36, had not been acquired, so the degree of improvement in surgery could not be investigated. However, the PROMs at the final follow-up were comparable between the H and control groups. Future studies that consist of more cases of high hip dislocation with a longer follow-up period are warranted in order to confirm the results of this study.