1 Magnetic Resonance Imaging Assessment of Abductor Muscles Shortly After Curved Periacetabular Osteotomy
Taiki Matsunaga, MD, Yuki Kamachi, MD, Koichi Kinoshita, MD, PhD, Tetsuya Sakamoto, MD, PhD, Takuaki Yamamoto, MD, PhD
Department of Orthopaedic Surgery, Fukuoka University School of Medicine, 7-45-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan
Address correspondence to: Takuaki Yamamoto, MD, PhD, Department of Orthopedic Surgery, Fukuoka University Faculty of Medicine, 7-45-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan
Telephone number: + 81-92-801-1011 Fax: +81-92-864-9055
E-mail: [email protected]
Approval: This prospective study was approved by the Institutional Review Board of Fukuoka University Hospital (No. 2017M078).
Source: The Journal of Arthroplasty https://doi.org/10.1016/j.arth.2020.08.04
2 Abstract
Background: Curved periacetabular osteotomy (CPO) is performed via an anterior approach without detachment of the hip abductor muscles. This study aimed to evaluate the abductor muscle status shortly after CPO on magnetic resonance imaging (MRI).
Methods: We prospectively evaluated 38 hips in 38 patients 1 week and 3 months after CPO between October 2017 and July 2019. The status of the abductor muscles was assessed on MRI using the following criteria: grade 0, normal; grade I, strain/edema;
grade II, partial tear; and grade III, complete tear. We also evaluated associations between muscle status and patients’ characteristics.
Results: One week after CPO, the gluteus maximus was classified as grade 0 in all patients. The gluteus medius was grade 0 in 84.2% of patients and grade I in 15.8%.
The gluteus minimus was grade I in 55.3% of patients and grade II in 44.7%. Three months after CPO, both the gluteus maximus and gluteus medius were grade 0 in all patients, while the gluteus minimus was still grade I in 47.4%. There were no significant differences between patients with a grade 0 and grade I gluteus minimus at 3 months after CPO in patients’ characteristics (age and body mass index) or clinical scores (Harris Hip Score and Japanese Orthopedics Association score).
Conclusion: Both the gluteus minimus and medius showed abnormal appearances on MRI 1 week after CPO, whereas only the gluteus minimus showed abnormalities 3 months after CPO. This abductor muscle status did not affect the postoperative Harris Hip Score or Japanese Orthopedics Association score.
3 Keywords
periacetabular osteotomy; abductor muscles; magnetic resonance imaging; anterior approach; minimal impact
4 Acetabular dysplasia of the hip is a known cause of hip osteoarthritis [1]. Several types of periacetabular osteotomy (PAO) have been developed to treat symptomatic acetabular dysplasia, including the Bernese PAO, curved periacetabular osteotomy (CPO), University of Colorado PAO, rotational acetabular osteotomy (RAO), and transposition osteotomy of the acetabulum (TOA). The success rates of these procedures have been reported to range from 60.5% to 82% in Bernese PAO [2-4], 94.3% to 96.8% in CPO [5-8], 98.5% in University of Colorado PAO [9], 78% to 96%
in RAO [10,11], and 94.1% to 94.2% in TOA [12,13].
Among those osteotomies, both RAO and TOA are performed using the lateral approach, which requires detachment of the gluteal muscles from the pelvis to enable iliac osteotomy [10-13]. The lateral approach provides a good view of the osteotomy site, which enables the correct rotation of the bone fragment [14]. However, this step raises concerns about the direct damage caused to the abductor muscles [15,16].
Conversely, CPO and Bernese PAO are performed via an anterior approach [15,17], in which the direct effect on the abductor muscles is minimal because the gluteal muscles are not detached from the pelvis [16,18]. Early recovery of the abductor muscle function has been reported at 3 months after CPO and Bernese PAO [5,18]. However, the status of the abductor muscles shortly after PAO using an anterior approach has not been fully evaluated.
The purpose of this study is to use magnetic resonance imaging (MRI) to evaluate the status of the abductor muscles shortly after CPO (at 1 week and 3 months
postoperatively) and to assess the clinical impact using the Harris Hip Score (HHS) [19]
and Japanese Orthopedics Association (JOA) score [20]. Our hypothesis was that PAO via an anterior approach has a minimal impact on the abductor muscles.
5 Patients and Methods
This study included 40 hips in 39 consecutive patients who underwent CPO
performed by one senior surgeon at our hospital from October 2017 to July 2019. One hip in 1 patient was excluded because of claustrophobia. One of the 2 hips in 1 patient was excluded because of pregnancy; however, the contralateral hip was included. Thus, 38 hips in 38 patients were evaluated in this study. None of the patients performed preoperative strength training of the abductor muscles. All patients underwent MRI examination at 1 week and 3 months after CPO. The 1-week postoperative MRI
evaluation was performed to exclude the effects of weight-bearing on the muscle status, while the 3-month postoperative MRI evaluation was performed to evaluate the
sequential changes caused by CPO after excluding the effects of confounding factors, such as working status or sports activity. The mean age of the patients at the time of surgery was 38.6 ± 13.9 years (range 14-56). The mean body mass index (BMI) was 23.0 ± 3.6 kg/m2 (range 16.7-33.8). The mean period to the 1-week postoperative MRI was 7.2 ± 0.9 days (range 5-10). The mean period to the 3-month postoperative MRI was 96.7 ± 13.7 days (range 84-151) (Table 1).
In our institution, indications for CPO include acetabular dysplasia with symptoms, such as pain that is tolerable but uncomfortable and has caused some limitations in daily activities for more than 5 months; a lateral center edge angle (LCEA) [21] of <25 on anteroposterior pelvic radiographs in the supine position; improvement in joint
congruency on an anteroposterior pelvic radiograph with the hip in abduction; and age after closure of the triradiate cartilage under 65 years at the time of surgery [15]. The Tönnis grade is used to classify the severity of osteoarthritis [22]. As previous studies
6 have shown a poor clinical outcome of CPO for patients with Tönnis grade 2 or 3
osteoarthritis [2,23-25], CPO was only indicated for patients with Tönnis grade 0 or 1 osteoarthritis.
Surgical Technique and Postoperative Rehabilitation
First, hip arthroscopy was performed with both lower limbs in traction using a Hana table (Mizuho OSI, Union City, CA), which is a radiolucent traction table. Bilateral traction was performed to avoid pelvic rotation due to uncountered unilateral traction and to stabilize the patient’s body on the operating table [26,27]. The state of the labrum and cartilage in the femoral head and acetabulum was determined. No patient received arthroscopic repair of the hip labrum or cartilage. After removal of the traction, an anterior incision was made from the distal border of the anterior superior iliac spine (ASIS) and extended distally for approximately 8 cm along the tensor fasciae latae muscle. The ASIS was then osteotomized and retracted medially with the inguinal ligament and sartorius muscle. The iliopsoas muscle was then partially detached around the iliac osteotomy site and retracted medially along with the femoral artery, vein, and nerve. When the chisel had contacted the innominate groove, the ischium was
osteotomized under image intensifier guidance. The superior ramus of the pubis was then osteotomized. Finally, iliac osteotomy was performed from inside to outside of the pelvis with a chisel. The acetabular fragment was rotated laterally and fixed with 3 poly-L-lactic acid screws. The osteotomized ASIS was then repositioned and fixed with 2 titanium cannulated cancellous screws.
Active motion exercises were begun on the first postoperative day. As the first timepoint of weight-bearing, 20 kg partial weight- bearing with the use of 2 crutches or
7 a walker was allowed at 2 weeks postoperatively, followed by an increase of 10 kg in weight every 2 weeks. Full weight-bearing without a crutch, cane, or walker was allowed at 3 months postoperatively. Return to work and sports activities were allowed from 3 months postoperatively.
Clinical Evaluation
Age, BMI, HHS, and JOA score (preoperatively and 3 months after CPO) were evaluated. The HHS includes 4 categories assessed using a 100-point scale: pain, function, range of motion, and absence of deformity. The JOA score includes 4
categories assessed using a 100-point scale: pain, range of motion, gait, and activities of daily living. Each category of the HHS and JOA score was also investigated.
Radiographic Evaluation
MRI scans were performed using a 1.5 T unit (Achieva 1.5T Nova Dual; Philips Healthcare, the Netherlands). For axial T2 turbo spin echo scans, the following pulse parameters were used: repetition time/echo time/flip angle = 3146/100 ms/90, slice thickness = 5 mm, field of view = 350×350 mm2, dot matrix = 512×410, band width
= 219 Hz/Px, image solution = 0.8×1.6×5.0 mm3, echo train length = 24, and number of sections = 30.
Intramuscular intensity changes in the abductor muscles were assessed on axial T2-weighted MRI. The gluteus maximus, gluteus medius, and gluteus minimus muscles were assessed at the level of 20 mm above the superior margin of the acetabulum (Fig.
1); this level was selected to minimize the effects of arthroscopy, such as traction and
8 fluid extravasation or edema/bleeding. The images were examined to assess the target muscle status using the following grading system proposed by Chan et al [28]: grade 0 (normal), no abnormality; grade I (strain/edema), less than 5% of muscle fiber
disruption and feathery edema-like pattern; grade II (partial tear), disorganization of muscle fibers; and grade III (complete tear), complete discontinuity of muscle fibers.
There is reportedly minimal impairment of strength and function in muscles with grade I damage (strain/edema), generally weakened muscle strength and activities in grade II (partial tear), and loss of muscle function in grade III (complete tear) [28]. MRI findings were evaluated independently by 2 orthopedic surgeons to determine the presence or absence of edema and tearing in the muscle. The kappa coefficients were 0.88-1.00 (intraobserver variance) and 0.89-1.00 (interobserver variance).
The LCEA and acetabular roof obliquity (ARO) [29] were measured on anteroposterior radiographs preoperatively and 1 week postoperatively.
Statistical Analysis
The Mann-Whitney U-test was used to compare patients’ characteristics, clinical scores, and radiographic data between 2 groups (grade 0 and grade I status for the gluteus medius 1 week postoperatively and the gluteus minimus 3 months
postoperatively). Statistical analyses were performed using SPSS version 20.0 (IBM, Armonk, NY). P < .05 was defined as denoting statistical significance.
Results
One week after CPO, the gluteus maximus showed no abnormal findings in any of the patients. The gluteus medius showed no abnormality in 84.2% (32/38 hips) and
9 grade I changes in 15.8% (6/38 hips). There were no significant differences between patients with a gluteus medius status of grade 0 and grade I at 1 week postoperatively in any of the assessed patients’ characteristics (age, BMI) or radiographic data
(preoperative and postoperative LCEA, correction of LCEA, preoperative and postoperative ARO, correction of ARO). Five of the 6 hips with a grade I gluteus medius also had a grade II gluteus minimus (Fig. 2). The gluteus minimus was
classified as grade I in 55.3% (21/38 hips) and grade II in 44.7% (17/38 hips) (Table 2).
Three months after CPO, both the gluteus maximus and gluteus medius showed no abnormality in all patients, whereas the gluteus minimus still had grade I changes in 47.4% (18/38 hips) (Table 3). There were no significant differences between patients with a grade 0 and grade I gluteus minimus at 3 months postoperatively in any of the assessed patients’ characteristics (age, BMI) or clinical scores (HHS and JOA score) (Table 4); there were also no significant differences between these 2 groups in each category of the HHS and JOA score.
Discussion
In this study, at 1 week after CPO, no abnormality was seen in the gluteus maximus, whereas the status of the gluteus minimus was grade I or II in all cases. When
performing an osteotomy of the ilium via an anterior approach, a chisel needs to be inserted from inside to outside of the ilium [2,10]. One possible explanation for the lack of changes in the gluteus maximus after CPO may be its anatomical location, in that the gluteus maximus is located furthest from the iliac osteotomy line. In contrast, the gluteus minimus is located close to the ilium; thus, chisel positioning probably caused the changes to the gluteus minimus.
10 At 1 week after CPO, the gluteus medius was grade I in 6 cases (15.8%); among these hips, the gluteus minimus was grade II in 5 hips and grade I in 1 hip. As the gluteus medius is located just above the outer layer of the gluteus minimus, the effects of CPO on the gluteus medius may have been prevented in cases where there was no excessive insertion of the chisel.
Grade I change in the gluteus minimus was still present in 47.4% of patients 3 months after surgery. There were no significant differences between those with a gluteus minimus status of grade I and grade 0 in patients’ characteristics (age, BMI) or clinical scores (HHS, JOA score). Both the gluteus minimus and gluteus medius have been reported to contribute significantly to the stability of the pelvis [30,31]. Ralston et al [32] have reported that hip abduction force correlates with the muscular mass of the abductor muscles and that the mass ratio of the gluteus medius, gluteus minimus, and tensor fasciae latae is 4:2:1. Because the gluteus medius may be the main muscle responsible for abductor muscle strength, these 47.4% of patients with only grade I changes in the gluteus minimus may have had good clinical scores, including both the HHS and JOA score.
Our study was a single-surgeon case series. Parcells et al [33] reported that the analysis of a series of consecutive cases operated on by a single surgeon using a standardized intraoperative and postoperative protocol minimizes many clinical variables. Therefore, we believe that the single-surgeon case series design is not necessarily a weakness of our study.
Our study had several limitations. First, we did not identify any direct correlations between MRI findings and abductor muscle function itself. Second, the timing of the required 3-month postoperative MRI evaluation ranged from 84 to 151 days
11 postoperatively. Third, preoperative MRI evaluation was not performed, and it is
possible that underlying hip deformity and mechanical changes had caused MRI changes preoperatively. Fourth, although the evaluated point was 20 mm above the superior margin of the acetabulum, the effects of hip arthroscopy could not be
completely ruled out. Finally, only 1 MRI slice at the level of 20 mm above the superior margin of the acetabulum was evaluated.
Conclusion
Abductor muscle abnormality was observed in both the gluteus minimus and medius at 1 week after CPO, whereas at 3 months after CPO only the gluteus minimus showed abnormality in 47.4% of patients. This abductor muscle status did not affect the
postoperative clinical outcomes. These results suggest that PAO via the anterior approach has a minimal impact on the abductor muscles and optimizes postoperative return to adequate function.
Acknowledgments
We thank Dr Trish Reynolds, MBBS, FRACP, from Edanz Group
(www.edanzediting.com/ac), Daisuke Setoguchi, MD, PhD, and Nobunao Doi, MD, PhD, for editing drafts of this manuscript.
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16 Table 1. Patients’ Characteristics.
n = 38
Age at surgery (y) 38.6 13.9 (14-56)
Gender (male:female) 2:36
Body mass index (kg/m2) 23.0 3.6 (16.7-33.8)
Period to MRI 1 wk after surgery (d) 7.2 0.9 (5-10)
Period to MRI 3 mo after surgery (d) 96.7 13.7 (84-151)
All data are expressed as the mean standard deviation (range).
MRI, magnetic resonance imaging.
17 Table 2. Distribution of Gluteal Muscle Status 1 wk Postoperatively.
Gluteal Muscle
Muscle Status G Mini (n = 38) G Med (n = 38) G Max (n = 38)
Grade 0 0 (0%) 32 (84.2%) 38 (100%)
Grade I 21 (55.3%) 6 (15.8%) 0 (0%)
Grade II 17 (44.7%) 0 (0%) 0 (0%)
Grade III 0 (0%) 0 (0%) 0 (0%)
G mini, gluteus minimus; G med, gluteus medius; G max, gluteus maximus; Grade 0 (normal), no abnormality; Grade I (strain/edema), less than 5% of muscle fiber disruption and feathery edema-like pattern; Grade II (partial tear), disorganization of muscle fibers; Grade III (complete tear), complete discontinuity of muscle fibers.
18 Table 3. Distribution of Gluteal Muscle Status 3 mo Postoperatively.
Gluteal Muscle
Muscle Status G Mini (n = 38) G Med (n = 38) G Max (n = 38)
Grade 0 20 (52.6%) 38 (100%) 38 (100%)
Grade I 18 (47.4%) 0 (0%) 0 (0%)
Grade II 0 (0%) 0 (0%) 0 (0%)
Grade III 0 (0%) 0 (0%) 0 (0%)
G mini, gluteus minimus; G med, gluteus medius; G max, gluteus maximus; Grade 0 (normal), no abnormality; Grade I (strain/edema), less than 5% of muscle fiber disruption and feathery edema-like pattern; Grade II (partial tear), disorganization of muscle fibers; Grade III (complete tear), complete discontinuity of muscle fibers.
19 Table 4. Patients Characteristics and Clinical Scores 3 mo Postoperatively in Patients With a Grade 0 and Grade I Status of the Gluteus Minimus.
Grade 0 (n = 20) Grade I (n = 18) P-Value
Age at surgery (y) 35.4 ± 15.1 42.3 ± 12.2 .13
Body mass index (kg/m2) 22.3 ± 3.3 23.8 ± 4.0 .22
Harris Hip Scores (points)
Preoperative HHS (max 100) 73.5 ± 12.5 72.5 ± 12.3 .82 Postoperative HHS (max 100) 84.2 ± 13.1 81.0 ± 14.5 .48
Change in HHS 11.2 ± 15.9 7.7 ± 17.0 .52
JOA scores (points)
Preoperative JOA (max 100) 70.6 ± 13.4 64.7 ± 10.8 .15 Postoperative JOA (max 100) 75.4 ± 17.5 76.2 ± 12.9 .87
Change in JOA 4.9 ± 20.3 10.5 ± 16.0 .37
These data are expressed as the mean standard deviation. HHS, Harris Hip Score; JOA, Japanese Orthopedics Association.
20 Fig. 1.
(A) Muscle status was assessed using T2-weighted MRI. (B) The gluteus minimus, gluteus medius, and gluteus maximus were assessed at the level of 20 mm above the superior margin of the acetabulum.
G max, gluteus maximus; G med, gluteus medius; G mini, gluteus minimus; MRI, magnetic resonance imaging.
21 Fig. 2.
MRI findings of a 16-year-old girl 1 week after CPO. The status of the gluteus maximus is grade 0 (no abnormality), that of the gluteus medius is grade I (strain or edema), and that of the gluteus minimus is grade II (partial tear). CPO, curved periacetabular osteotomy.