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Radiological factors associated with posterior dislocation after total hip arthroplasty for osteonecrosis of the femoral head – A retrospective study
, Goro Motomura, Satoshi Hamai, Shinya Kawahara, Taishi Sato, Ryosuke Yamaguchi, Takeshi Utsunomiya, Yasuharu Nakashima
∗Corresponding author: Goro Motomura. motomura.goro.014@m.kyushu-u.ac.jp
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Received: ,
Accepted: ,
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
The dislocation rate after total hip arthroplasty for osteonecrosis of the femoral head is higher than that after total hip arthroplasty for osteoarthritis. However, few reports have investigated the factors contributing to dislocation after total hip arthroplasty for osteonecrosis of the femoral head. The aim of this study was to assess radiological factors associated with posterior dislocation after total hip arthroplasty for osteonecrosis of the femoral head.
We retrospectively reviewed 179 cementless total hip arthroplasties for osteonecrosis of the femoral head using a posterolateral approach between 2002 and 2020 with a minimum follow-up period of 24 months. The following radiological factors were examined for a possible association with posterior dislocation after total hip arthroplasty: cup anteversion angle, cup inclination angle, femoral offset, and stem anteversion angle.
Posterior dislocation occurred in seven hips (3.9 %). Compared to hips without posterior dislocation, those with posterior dislocation exhibited a significantly smaller cup anteversion angle (p = 0.045) and a nonsignificantly greater decrease in femoral offset (p = 0.089). Based on receiver operating characteristic curve analyses, the cutoff values for predicting posterior dislocation were 9.9° for the cup anteversion angle and 8.1 mm for the decrease in femoral offset. Logistic regression analysis showed a significantly higher risk of posterior dislocation among hips with a cup anteversion angle less than 9.9° (odds ratio = 7.1, p = 0.022) or with a decrease in femoral offset over 8.1 mm (odds ratio = 5.0, p = 0.040).
A small cup anteversion angle and a decreased femoral offset are suggested to be associated with posterior dislocation after total hip arthroplasty in patients with osteonecrosis of the femoral head.
Keywords
Cup anteversion
Dislocation
Femoral offset
Osteonecrosis of the femoral head
Total hip arthroplasty
1 Introduction
Total hip arthroplasty (THA) is recognized as an optimal treatment for osteonecrosis of the femoral head (ONFH),1 although poor outcomes of THA for ONFH were reported,2–4 particularly dislocation. Itokawa et al. reported that patients with ONFH had a higher risk for dislocation (9.09 %) than those with osteoarthritis (1.17 %).5
Although many studies have analyzed dislocation after THA, only one examined the risk factors for posterior dislocation (PD) in ONFH patients, and found an association with age (≤40 or ≥62 years), body weight (≥54 kg), posterolateral approach, and femoral head diameter (<32 mm).6 No studies have assessed the radiological factors associated with PD after THA for ONFH; therefore, the present study investigated this issue.
2 Material and methods
2.1 Patients
The institutional review board of our hospital approved this study. We retrospectively reviewed 224 consecutive cementless THAs for ONFH in 183 patients at our institution between April 2002 and April 2020 whose follow-up period were longer than 24 months. Clinical data, including those on PD, were retrieved from medical records. The diagnosis of ONFH was based on plain radiographs and magnetic resonance images.7 In 41 patients with bilateral THA, we selected only the side with longer follow-up or a history of PD. Four patients with a history of anterior dislocation were excluded from the study. We therefore retrospectively reviewed 179 THAs for ONFH.
The percentage of patients followed up for 24 months was 87.2 %. The mean age at THA was 54.2 (range, 18–82) years, and the mean body mass index (BMI) was 23.3 (range, 15.0–38.3) kg/m2. Etiologically, ONFH was associated with steroids in 112 patients and with alcohol in 67 patients. According to the staging system of the Japanese Investigation Committee of Health and Welfare (JIC),7 20 hips were classified as stage 3A, 42 as stage 3B, and 117 as stage 4. Forty-eight hips had a history of femoral osteotomy for ONFH.
2.2 Surgery
In all cases, cementless THA was performed through the posterolateral approach by experienced hip surgeons at our institution. Posterior soft tissues were repaired as much as possible. Cementless stems were implanted in all THA procedures; the fit-and-fill type in 118 hips, the tapered-wedge type in 52 hips, and others in 9 hips. Cementless acetabular cups were implanted in all cases. The head size was 26 mm in 3 hips, 28 mm in 53 hips, 32 mm in 120 hips, and 36 mm in 3 hips; it was determined by the cup size, and differed according to the duration of surgery.
2.3 Radiological assessments
Throughout the study period, a standardized protocol was used for plain radiographs of the hip joints. Postoperative anteroposterior and cross-table lateral radiographs were taken in the supine position in the operating room in order to assess component positions. Regarding the anteroposterior radiographs, surgeons kept each patient in the supine position with both hips in neutral abduction and adduction, and the X-ray beam was centered on the symphysis pubis at the vertical midline. The tube-to-film distance was 110 cm in all cases. Cross-table lateral radiographs were also obtained, with the patella of the operated side manually fixed in a neutral position and the contralateral hip fixed to 90° by a surgeon. The X-ray beam was then delivered perpendicularly to the film cassette, which was rotated 45° relative to the long axis of the body. One author independently and blindly evaluated each of the radiological factors listed below using a SYNAPSE PACS system (Fujifilm Medical, Tokyo, Japan). With reference to the past reports, the cup inclination angle (Fig. 1a) was measured8 and the cup anteversion angle (Fig. 1a) was calculated.9 The cup version (positive for anteversion and negative for retroversion) was determined from lateral radiographs. The femoral offset was assessed pre- and postoperatively, and was defined as the distance from the femoral head center to the femoral axis (Fig. 1a).10 The decrease in femoral offset was calculated by subtracting the postoperative femoral offset from the preoperative femoral offset. The stem anteversion angle was measured using cross-table lateral radiographs (Fig. 1b).11
2.4 Statistical analysis
All statistical analyses were performed using the JMP software program (version 16.0; SAS Institute, Cary, NC, USA), and differences were considered significant when the p value was <0.05. Data are expressed as means ± SD (range). Clinical characteristics were compared between the PD group and the non-PD group using Wilcoxon's test and Fisher's exact test. Radiological values were compared between these groups using Wilcoxon's test. Sensitivity, specificity, and receiver operating characteristic (ROC) curves were used to evaluate the effect of radiological factors on PD. Simple logistic regression analysis was performed to calculate the relation between PD and both the cup anteversion angle and the decrease in femoral offset.
3 Results
During the follow-up period, PD occurred in seven hips (3.9 %). Patient characteristics are shown in Table 1. The mean age at THA was significantly older in the PD group than in the non-PD group (p = 0.043). There was no difference between the two groups in gender, BMI, steroid history, JIC stage, history of previous osteotomy, or usage of the greater diameter of the femoral head (≥32 mm).
| PD group: 7 hips | Non-PD group: 172 hips | P value | |
| Age at THA (y) | 62.6 ± 6.6 | 53.8 ± 12.6 | 0.043* |
| Gender (n) | |||
| Male/Female | 3/4 | 90/82 | 0.71 |
| BMI (kg/m 2 ) | 22.1 ± 3.2 | 23.3 ± 3.8 | 0.38 |
| Steroid therapy (n) | |||
| +/− | 4/3 | 108/64 | 1.0 |
| JIC stage (n) | |||
| Stage 3/Stage 4 | 3/4 | 59/113 | 0.69 |
| Previous osteotomy (n) | |||
| +/− | 2/5 | 46/126 | 1.0 |
| Femoral head size (n) | |||
| ≤28 mm/≥32 mm | 4/3 | 52/120 | 0.21 |
| Stem type (n) | |||
| Fit and fill/tapered wedge or others | 6/1 | 112/60 | 0.43 |
Radiological assessment showed that the cup anteversion angle was significantly smaller in the PD group (9.8 ± 8.2°) than in the non-PD group (15.7 ± 7.6°, p = 0.045) (Table 2). ROC curve analysis demonstrated that the cutoff value of the cup anteversion angle for predicting PD was 9.9° (sensitivity 71 %, specificity 74 %). On the other hand, there was no difference in the cup inclination angle between the two groups.
| PD group: 7 hips | Non-PD group: 172 hips | P value | |
| Cup anteversion angle (°) | 9.8 ± 8.2 | 15.7 ± 7.6 | 0.045* |
| Cup inclination angle (°) | 39.7 ± 10.2 | 38.4 ± 6.0 | 0.94 |
| Decrease in femoral offset (mm) | 6.7 ± 6.5 | 3.2 ± 6.5 | 0.089 |
| Stem anteversion angle (°) | 13.5 ± 6.5 | 13.6 ± 6.5 | 0.87 |
The decrease in femoral offset was nonsignificantly larger in the PD group (6.7 ± 6.5 mm) than in the non-PD group (3.2 ± 6.5 mm, p = 0.089). ROC curve analysis demonstrated that the cutoff value of decreased femoral offset for predicting PD was 8.1 mm (sensitivity 71 %, specificity 79 %). On the other hand, the stem anteversion angle did not differ between the two groups.
Simple logistic regression analysis showed a significantly higher risk of PD among hips with a cup anteversion angle less than the cutoff value (9.9°) (odds ratio = 7.1, p = 0.022). Similarly, this analysis showed a significantly higher risk of PD among hips with a decreased femoral offset over the cutoff value (8.1 mm) (odds ratio = 5.0, p = 0.040) (Fig. 2).
4 Discussion
This study assessed the radiological factors associated with PD after THA for ONFH. A small cup anteversion angle and a decreased femoral offset are known to affect PD after THA irrespective of underlying hip diseases. We found that a cup anteversion angle less than 9.9° or a decrease in femoral offset over 8.1 mm were associated with PD in patients with ONFH. Since both parameters can be easily assessed during preoperative planning or intraoperative X-ray examination, we believe that they can be useful indicators for surgeons.
A cup anteversion angle of 5–25° is widely recognized as a safe zone that minimizes dislocation risk after primary THA for osteoarthritis, ONFH, rheumatoid arthritis, and so on.9 In the current series, hips with a cup anteversion angle less than 9.9° had higher risk of PD in patients with ONFH. Since soft tissue in hips with ONFH is less constrained than in hips with osteoarthritis,12 hip prostheses achieve a higher range of motion in cases of ONFH, resulting in implant impingement. Therefore, the safe zone for hips with ONFH might be narrower than for hips with osteoarthritis.
A decrease in femoral offset over 8.1 mm was also associated with PD in this study. A high-offset stem was reported to be useful for preventing dislocation after THA for osteoarthritis, ONFH, developmental dysplasia of the hip, and rheumatoid arthritis,13,14 and greater femoral offset might stabilize hip prostheses by stretching the quadratus femoris.10 For the same reason that less-constrained soft tissue leads to a narrower safe zone for cup angles in ONFH, a decrease in femoral offset results in excessive joint laxity, which in turn leads to dislocation after THA. Therefore, proper assessment of femoral offset could help reduce the rate of PD after THA for ONFH.
This retrospective study has several limitations. First, the sample size was relatively small due to the small number of PDs; therefore, we were unable to examine the additive effects of the two factors. Further studies are needed to determine whether the combination of a small cup anteversion angle and a large decrease in femoral offset is more effective than either factor alone for reducing PD after THA for ONFH. Second, in this study we used only plain X-ray radiography, not CT, for radiological evaluation. When measuring very small distances, ideally CT should be used instead of X-rays because X-ray-based calculations may not be as accurate as those based on CT images. However, all of the radiological factors assessed in this study have been previously validated in X-ray evaluations.8–10 Furthermore, to minimize between-patient variations in plain radiograph assessments as much as possible, we used a standardized protocol to evaluate component positions in the operating room after THA. In addition, since radiation exposure in CT examinations is not negligible, plain X-ray evaluation, which can be performed easily and with lower radiation exposure compared to CT, was employed in this study.
5 Conclusion
In this retrospective study, a small cup anteversion angle and a decreased femoral offset are suggested to be associated with posterior dislocation after total hip arthroplasty in patients with osteonecrosis of the femoral head. The cutoff values for predicting posterior dislocation were 9.9° for the cup anteversion angle and 8.1 mm for the decrease in femoral offset. Further research is needed to determine whether the combination of a small cup anteversion angle and a large decrease in femoral offset is more effective than either factor alone for reducing posterior dislocation after total hip arthroplasty for osteonecrosis of the femoral head.
Ethical statement
This study was approved by our institutional review board.
Funding statement
This study was supported by the Ministry of Health Labour and Welfare, Japan, Research Program on Rare and Intractable Diseases Grant (JPMH20FC1010).
Guardian/patient's consent
Informed consent was waived due to the retrospective and anonymous study design.
CRediT authorship contribution statement
Kosei Sakamoto: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing - original draft, Writing - review & editing. Goro Motomura: Conceptualization, Funding acquisition, Methodology, Writing - original draft, Writing - review & editing. Ryosuke Yamaguchi: Conceptualization, Methodology, Writing - review & editing. Takeshi Utsunomiya: Conceptualization, Methodology, Writing - original draft, Writing - review & editing. Yasuharu Nakashima: Conceptualization, Project administration, Supervision, Writing - review & editing.
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