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Salter innominate osteotomy (SIO) has been successfully used in the treatment of Legg–Calvé–Perthes disease (LCPD). Recent studies that have raised concerns about acetabular retroversion after SIO have been based on plain radiographs. In order to assess the true acetabular orientation, the present study uses a specific magnetic resonance imaging (MRI) technique. In addition, the association between acetabular morphology and clinical function as well as health-related quality of life was assessed. Twenty-three patients with 24 operated hips who underwent SIO for LCPD between January 2004 and November 2014 were included. Mean age was 8.5 ± 2.2 years at surgery and 18.5 ± 2.9 years at follow-up. MRIs were conducted at 1.5 T using radial sequences. The analysis included the acetabular version, acetabular sector angles (ASAs) and alpha angles. Plain radiographs were used in order to obtain the Stulberg classification. Patient-related outcome measures included the international Hip Outcome Tool and Euroqol-5 dimensions scores. In comparison to the non-operated side, the MRI of previously operated hips showed no difference of version at the center of the femoral head but significantly decreased version just below the roof level. As a marker for posterior acetabular coverage, the ASAs between 9 and 11 o’clock were significantly decreased when compared with non-operated hips. In hips with a mild acetabular retroversion (<15°), the function was significantly decreased when compared with non-retroverted hips. The SIO is an effective tool in order to restore acetabular containment in LCPD. When compared with the non-operated hips, our collective displays only moderate changes of acetabular orientation and coverage.
INTRODUCTIONLegg–Calvé–Perthes disease (LCPD) is a common hip pathology during early childhood that affects mainly boys and leads to hip pain and limitation of the range of motion. The impaired circulation of the femoral head is followed by a collapse of the bone structure of the proximal femoral epiphysis with potential secondary deformation and degenerative changes [1].
The primary treatment goal in LCPD patients is to restore containment of the hip joint [2]. This can be achieved by conservative as well as surgical measures. Among other osteotomies, the Salter innominate osteotomy (SIO) [3, 4] is an established procedure in the treatment of LCPD patients [4–8]. If adequate containment of the hip is achieved, a remodeling to a congruent shape is possible even in the face of collapse and deformation [5, 9].
Several studies have reported on the results of former SIO [8–13]. While these studies have mostly displayed good long-term results, concerns have been raised about potential acetabular retroversion due to overcorrection. Acetabular retroversion might lead to femoroacetabular impingement [14], which is a recognized risk factor for secondary hip osteoarthritis (OA) [15].
Studies on this topic have mainly used conventional radiographs in order to determine the acetabular version. The findings on radiographs, however, may be highly biased by pelvic tilt and other inherent limitations of conventional radiographs [16–19].
Magnetic resonance imaging (MRI) has the capacity of providing accurate measurements without radiation exposure [20]. In our literature review, we found two studies that assessed the sequelae of LCPD by using three-dimensional imaging [21, 22], while the respective patients underwent different types of treatment. However, we found no study that investigated the effects of the SIO by using MRI during the follow-up (FU).
Therefore, our aim was to determine the three-dimensional acetabular morphology by MRI in skeletally mature LCPD patients who had undergone SIO during childhood. Furthermore, MRI-based coverage and version were compared with standard radiographic signs, while these parameters were also related to functional scores.
MATERIALS AND METHODS Study populationSixty-two consecutive patients had undergone SIO with and without intertrochanteric varisation osteotomy due to LCPD in our University Center between January 2004 and November 2014. Exclusion criteria for this retrospective cohort study (Level 3) were any neuromuscular disorder, an open triradiate cartilage, an age below 14 years at FU and an inability to undergo MRI or to follow the physician’s instructions due to cognitive impairment. As 27 patients were too young to have a closed triradiate cartilage and the others did not fulfill any exclusion criteria, 35 patients were eligible for FU. Two of them had already undergone total hip replacement and 10 patients could not be investigated due to missing contact data (n = 4) or refusal to participate (n = 6). Finally, 23 patients were available for the final FU and MRI investigation (Fig. 1). Approval was obtained by the local Ethics Committee.
Fig. 1.
Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) diagram of operated hips (flowchart of patient inclusion) FU, follow-up; SIO, Salter Innominate Osteotomy; THA, total hip arthroplasty.
Fig. 1.
Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) diagram of operated hips (flowchart of patient inclusion) FU, follow-up; SIO, Salter Innominate Osteotomy; THA, total hip arthroplasty.
All surgeries were performed by F.T. and K-P.G. Twenty-two patients received surgery on one hip while one patient received bilateral surgery. As each hip was treated as an independent data point, data from 24 operated hips and 22 non-operated hips were pooled together, and the respective mean values were compared against each other. All non-operated hips were once again reviewed at FU and were found to be free of LCPD and of pain.
Follow-up (clinical)FU clinical examination included the assessment of the anterior and posterior impingement sign.
Regarding patient-related outcome measures (PROMs), we chose the international Hip Outcome Tool (iHOT) [23] as a score especially developed for joint preserving surgery. Furthermore, the Euroqol-5 dimensions (EQ-5D) [24] score was obtained as a measure for health-related quality of life.
Follow-up (conventional radiographs)Conventional radiographic evaluation consisted of a standard antero-posterior (AP) pelvic radiograph in the supine position as well as a frog-leg lateral hip radiograph on the operated side. On AP radiographs, lateral center-edge (LCE) angles [25] and acetabular indices (AIs) [26] were measured for both the operated and the non-operated hips. Furthermore, the crossover sign as well as the ischial spine sign were determined [16]. On frog-leg lateral radiographs, alpha angles were determined [27].
All operated hips were classified according to the Stulberg (SB) classification [28] using conventional AP radiographs.
SB classes I and II were pooled into one group (spherical head type = SHT), as were SB classes III, IV and V (deformed head type = DHT).
Furthermore, hips were graded according to the Kellgren and Lawrence (KL) classification for OA [29].
Follow-up (MRI)Non-contrast MRI was performed and measured solely for study purposes using a specified technique with a high inter- and intraobserver reliability by one observer (J.G.) [20]. In order to compensate for pelvic obliquity and rotation, the centers of the reformation axis were aligned with the centers of the femoral heads in both the transverse and coronal planes. MRI-based comparison of operated and non-operated hips could be performed in 20 out of 24 hips. In four hips, an analysis was not possible due to metal artifacts of remaining osteosynthesis devices (n = 2) and bilateral previous surgery (n = 2).
Modified acetabular sector angles (ASAs) were measured in a clockwise manner from 9 to 3 o’clock (9/10/11/12/1/2/3 o’clock) (Fig. 2). Furthermore, the cartilage covered area angle (CCAA) between the acetabular edge and the acetabular fossa as well as the alpha angles were measured accordingly. The latter was measured using the most approximated circle based on the femoral head morphology. The acetabular version was measured in the transverse plane passing through the center of the femoral head [30] as well as just below the roof level when the most cranial contour of the femoral head became visible for the first time.
Fig. 2.
Magnetic resonance imaging (MRI) pelvic alignment and performed measurements: MRI alignment in the (A) axial, (B) coronal and (C) sagittal planes presenting the measured clockwise plains; (D) measurement of the anteversion at the femoral head center, (E) the anteversion at the acetabulum roof, (F) the anterior (*; 3 o’clock) and posterior (#; 9 o’clock) Acetabular Sector Angles (ASA) and (G) the Cartilage Covered Area Angles (CCAA) anteriorly (*; 3 o’clock) and posteriorly (#; 9 o’clock).
Fig. 2.
Magnetic resonance imaging (MRI) pelvic alignment and performed measurements: MRI alignment in the (A) axial, (B) coronal and (C) sagittal planes presenting the measured clockwise plains; (D) measurement of the anteversion at the femoral head center, (E) the anteversion at the acetabulum roof, (F) the anterior (*; 3 o’clock) and posterior (#; 9 o’clock) Acetabular Sector Angles (ASA) and (G) the Cartilage Covered Area Angles (CCAA) anteriorly (*; 3 o’clock) and posteriorly (#; 9 o’clock).
Statistical analysisStatistical analysis was performed using SPSS (IBM, V. 25, Chicago, IL, USA).
The first comparisons were drawn between the overall collective of operated and non-operated hips. Furthermore, the subgroup analyses included a comparison between (i) the SHT and DHT hips on the operated side, (ii) the SHT hips and non-operated hips and (iii) the DHT hips and non-operated hips. In order to preclude anatomical differences within the control group, non-operated hips in the SHT and DHT groups were compared, and no significant differences were found. Continuous variables were presented as the mean with standard deviation (SD) and the range, and categorical variables were presented as counts and percentages. Between-group comparisons were performed using paired t-tests, Mann–Whitney U tests or Wilcoxon signed rank tests (when applicable). The significance level was set at P < 0.05.
RESULTSEight patients had surgery on their right hip and 14 on their left hip. Twenty patients were male (87.0%) and three were female. Further baseline data are displayed in Table I.
Table I.Baseline characteristics of patients in the different groupsa
. Total . SHT . DHT . Age at surgery 8.5 ± 2.2 (4.6–13.7) 7.7 ± 1.3 (5.5–9.7) 9.0 ± 2.5 (4.6–13.7) Femoral osteotomy 20/24 (83.3%) 9/9 (100%) 11/15 (73.3%) Age at follow-up 18.5 ± 2.9 (14.3–24.1) 17.3 ± 3.3 (14.3–24.0) 19.2 ± 2.6 (15.2–24.2) SB classification I 6 (25.0%) 6 (66.7%) II 3 (12.5%) 3 (33.3%) III 11 (45.8%) 11 (73.3%) IV 3 (12.5%) 3 (20.0%) V 1 (4.2%) 1 (6.7%) . Total . SHT . DHT . Age at surgery 8.5 ± 2.2 (4.6–13.7) 7.7 ± 1.3 (5.5–9.7) 9.0 ± 2.5 (4.6–13.7) Femoral osteotomy 20/24 (83.3%) 9/9 (100%) 11/15 (73.3%) Age at follow-up 18.5 ± 2.9 (14.3–24.1) 17.3 ± 3.3 (14.3–24.0) 19.2 ± 2.6 (15.2–24.2) SB classification I 6 (25.0%) 6 (66.7%) II 3 (12.5%) 3 (33.3%) III 11 (45.8%) 11 (73.3%) IV 3 (12.5%) 3 (20.0%) V 1 (4.2%) 1 (6.7%) Table I.Baseline characteristics of patients in the different groupsa
. Total . SHT . DHT . Age at surgery 8.5 ± 2.2 (4.6–13.7) 7.7 ± 1.3 (5.5–9.7) 9.0 ± 2.5 (4.6–13.7) Femoral osteotomy 20/24 (83.3%) 9/9 (100%) 11/15 (73.3%) Age at follow-up 18.5 ± 2.9 (14.3–24.1) 17.3 ± 3.3 (14.3–24.0) 19.2 ± 2.6 (15.2–24.2) SB classification I 6 (25.0%) 6 (66.7%) II 3 (12.5%) 3 (33.3%) III 11 (45.8%) 11 (73.3%) IV 3 (12.5%) 3 (20.0%) V 1 (4.2%) 1 (6.7%) . Total . SHT . DHT . Age at surgery 8.5 ± 2.2 (4.6–13.7) 7.7 ± 1.3 (5.5–9.7) 9.0 ± 2.5 (4.6–13.7) Femoral osteotomy 20/24 (83.3%) 9/9 (100%) 11/15 (73.3%) Age at follow-up 18.5 ± 2.9 (14.3–24.1) 17.3 ± 3.3 (14.3–24.0) 19.2 ± 2.6 (15.2–24.2) SB classification I 6 (25.0%) 6 (66.7%) II 3 (12.5%) 3 (33.3%) III 11 (45.8%) 11 (73.3%) IV 3 (12.5%) 3 (20.0%) V 1 (4.2%) 1 (6.7%)There were no differences between the SHT and DHT subgroups both concerning age at surgery and at FU (P = 0.558 and P = 0.064, respectively).
A positive anterior as well as posterior impingement sign occurred more often on the operated side than on the non-operated side (P = 0.003 and P = 0.02, respectively). Differences between the subgroups are shown in Table II. iHOT and EQ-5D score values were similar among the subgroups (P = 0.123 and P = 0.73, respectively).
Table II.Outcome scores and clinical examination at follow-up in all operated hips and contralateral non-operated hipsa
. Total . SHT . DHT . Non-operated . iHOT 80.7 ± 16.3Outcome scores and clinical examination at follow-up in all operated hips and contralateral non-operated hipsa
. Total . SHT . DHT . Non-operated . iHOT 80.7 ± 16.3Pelvic radiographs at FU showed a decreased lateral coverage, as the LCE angle of all operated hips was lower than that of non-operated hips (P = 0.009). The AI was similar between the two (P = 0.545). Subgroup differences are presented in Table III.
Table III.Radiographic measurements at follow-up in all operated hips and contralateral non-operated hipsa
. Total . SHT . DHT . Non-operated . LCE angle 25.8 ± 8.1Radiographic measurements at follow-up in all operated hips and contralateral non-operated hipsa
. Total . SHT . DHT . Non-operated . LCE angle 25.8 ± 8.1Nearly all hips showed no or doubtful signs of OA (KL grades 0 and 1), and only one hip was classified as KL grade 2 (Table I).
The version just below the acetabular roof was negative on average (<0°) for both the operated and non-operated hips and was significantly lower for the operated hips (P = 0.006). Especially, SHT hips were shown to have a decreased version both in comparison with DHT hips and with the control group.
Hips with SIO had significantly lower ASAs in the 9, 10, 11 as well as 3 o’clock positions in comparison with the non-operated hips (P = 0.001, P < 0.001, P = 0.011 and P = 0.004, respectively). The subgroup differences as well as the assessment of CCAA angles are displayed in Table IV.
Table IV.MRI measurements at follow-up in all operated hips and contralateral non-operated hipsa
. Total . SHT . DHT . Non-operated . Anteversion acetabulum roof −6.8 ± 6.7
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