This study with a mean follow-up period >5 years showed that postoperative satisfaction, JOA score, and SF-36 score of primary THA for Crowe type III and IV dysplasia were comparable with those for Crowe type I. The height of the H group was significantly shorter than that of the control group owing to the effect of high hip dislocation. In the H and FO groups, the intraoperative blood loss and surgery time were increased compared with the control and N-FO groups. No significant difference in perioperative complications was detected, but the 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 groups, and between the FO and N-FO groups. The JOA score in the patients with high hip dislocation was not much different from those in 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 scores, including the subscale scores, at the final follow-up showed no significant difference between the H and control groups, and between the FO and N-FO groups. Each subscale score was as good as, or even better than, those in previous reports [Nilsdotter AK et al., 2010; Fernandez-Fairen M et al., 2011]. As will be described in the Limitations section, the reasons for this result were considered the possible selection bias in this study. In other words, in this study, only the patients who 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 and control groups, which suggests no significant difference in postoperative PROMs depending on the degree of preoperative pelvic deformity.
In addition, each group had a NPS of >50 and was considered a good outcome. Hamilton et al. reported a NPS of 60 for joint replacement and individual scores of 71 and 49 for total hip replacement (THR) and total knee replacement (TKR), respectively [Hamilton DF et al., 2014]. From the above-mentioned results, we considered that the patients in the FO group with the lowest NPS (60) in this study were also satisfied with THA.
Questionnaire
Questionnaires were provided to measure the patients’ postoperative satisfactions. The patients were allowed to choose one of the following five options: very satisfied, satisfied, neither, dissatisfied, and very dissatisfied. Then, the patients who selected “very satisfied” or “satisfied” were considered satisfied. This method of rating patient satisfaction through the selection of one of the five options is called the 5-point Likert scale, which has good measurement properties, validity, and reliability [Dawson J et al., 1996]. In addition, it is simple and available in many languages [Rolfson O et al., 2016]. In this study, patient satisfaction was measured with two methods, the NPS and Likert scale. Therefore, we believe that the results on patient satisfaction were of 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 the patients in the FO group had Crowe type IV dysplasia and had severe cases with acute limb lengthening of >40 mm. Some reports indicated 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, on the basis of 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 pain may persist unlike in with 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 the cases. It was found that THA easily improved preoperative back pain even in patients with high hip dislocation. The chief complaints of patients with high hip dislocation in the gluteal muscle are often low back and buttock pains. Therefore, low back pain caused by malalignment due to pelvic deformity or LLD should be considered an important factor in determining the surgical indication for THA for Crowe type III and IV dysplasia.
Leg length discrepancy
Many past reports indicated that a postoperative LLD of >10 mm decreases the postoperative function and satisfaction of THA [O’Brien S et al., 2010; Meermans G et al., 2011]. In the H group, the patients strongly wanted to undergo LLD correction, probably because of the large difference in preoperative LLD. However, when one-sided THA with femoral shortening osteotomy for high hip dislocation was performed, the amount of LLD correction was limited, and the postoperative LLD was often >10 mm. In this study, the 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 owing to the rarity of high hip dislocation. Only a few cases were available for the investigation of the effects of femoral shortening osteotomy. If the number of hips is increased, the results of the questionnaire survey could 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, selection bias was possible because only the 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 in this study were not high enough at 61% (23/38 cases); however, this proportion was similar to those reported in previous survey studies [Meyer R et al., 2018; Sieja A et al., 2019]. Third, the validity of the questionnaire used in this study had not been determined, and the presence of concurrent knee conditions at the time of the evaluation was overlooked. However, the questionnaire included the NPS, Likert scale, and VAS, which 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 to confirm the results of this study.