Patients and study design
This retrospective case-control study assessed patients who underwent primary THA at a single institution from 2008 to 2016. During the study period, our institution performed 661 primary THAs. All data for this study were obtained from the hospital archive system.
We sent postal questionnaires to 38 patients (50 hips) who underwent primary THA for high hip dislocation (Crowe type III and IV dysplasia) to evaluate postoperative satisfaction. Among the questionnaire respondents, 23 patients (32 hips), excluding cases with a follow-up period of less than 1 year after THA, were enrolled as part of the high hip dislocation group (H group). For the control group, we included 46 patients (64 hips) who underwent primary THA for Crowe type Ⅰ dysplasia (Figure 1). The control group was formed by recruiting data-matched controls per patient in the H group. Data matching involved matching for age (±10 years), sex, body mass index (±5 kg/m²), and surgical approach (posterior approach). To investigate the influence of femoral shortening osteotomy, the H group was divided according to whether femoral shortening osteotomy was performed or not. Ten patients (15 hips) underwent THA with femoral shortening osteotomy (FO group), while 12 patients (15 hips) underwent THA without femoral shortening osteotomy (N-FO group). One patient (2 hips) who underwent THA with femoral shortening osteotomy on one side and without on the other side was excluded when considering the influence of femoral shortening osteotomy.
Surgical information
All operations were performed by a single senior surgeon using a posterior approach in a lateral decubitus position under general anesthesia. For cases with acute limb lengthening greater than 40 mm at preoperative planning, THA with femoral shortening osteotomy (double chevron osteotomy) was performed (Figure 2). Femoral shortening osteotomy was performed below the level of the lesser trochanter. The longitudinally split fragments from the resected femur were placed around the osteotomy site as a structural allograft. Morselized cancellous bone, which was obtained from the resected femoral head, was grafted to accelerate bone union at the osteotomy site.
Preoperative planning was performed for all THAs in both groups with the use of a computed tomography (CT)-based 3-D templating and navigation software (CT-based Hip, version 1.0 or 1.1; Stryker Navigation, Freiburg, Germany). The cup was implanted with press-fit fixation with the assistance of the navigation system. The cup was basically implanted at the level of the true acetabulum. The main target of cup orientation angle was at an anatomical inclination of 40 degrees and anteversion of 20 degrees. In both groups, all femoral components were implanted without the navigation system.
Clinical evaluations
Clinical evaluations were performed using the patient demographics, the Japanese Orthopaedic Association hip score (JOA score) [Imura S, 1995], the 36-item short-form health survey (SF-36), the visual analogue scale (VAS), and the results of the unique questionnaire that was developed for the evaluation of patient-reported outcomes. The JOA score was evaluated prior to THA and at the time of the final follow-up. The SF-36 and VAS were only evaluated at the time of the final follow-up and were enclosed in the questionnaires sent to the patients. The JOA score consists of four items: pain, ROM, gait, and activities of daily living (ADL), which are filled out by doctors. The total score is 100 points, with a higher score indicating higher hip function.
Leg length discrepancy (LLD) was measured from pre- and postoperative CT images (LightSpeed VCT; GE Medical Systems, Milwaukee, WI, USA) using the CT-based 3-D templating software (ZedHip; Lexi, Co., Ltd., Tokyo, Japan). In this study, LLD was defined as the difference in distance from the anterior superior iliac spine to the midpoint of the femoral condyle.
We obtained CT images 4 weeks prior to surgery and about 1 week after surgery.
CT images were acquired for 3-D templating preoperatively and for confirming cup position postoperatively in other studies [Ueno T et al., 2018; Ueoka K et al., 2019].
Questionnaire
The questionnaire consisted of 13 questions, which we developed for this study (Figure 3). The contents included the reason for deciding to undergo the operation, the degree of satisfaction with the surgery (with 100 full marks, for the patient to fill out themselves), positive or negative points about the surgery, social troubles, walking level, and VAS. The last question was “Do you still feel that surgery was the best choice for you?” Missing data on the questionnaire were completed, where possible, via telephone interviews.
Statistics
Based on a previous report [Sonohata M et al., 2018], we suggested that the minimal clinically important difference in the JOA score was 10 points and the standard deviation (SD) was approximately 15 points. Power analysis suggested that a total of 82 hips would be required to detect a clinically significant difference in the JOA score, with 80% power and 5% α error.
Statistical analyses were performed using a statistical software program (SPSS software for Windows, version 24.0; SPSS, Inc., Chicago, IL, USA). Group comparisons for quantitative data (e.g., patient demographics, SF-36, VAS) were performed using the unpaired t-tests, whereas categorical data (e.g., results of the questionnaire) were compared using the chi-square test or Fisher’s exact test. A p-value less than 0.05 was considered statistically significant.