High incidence of acetabular retroversion in gluteal muscle contracture patients based on X-ray film

doi:10.21203/rs.3.rs-1970247/v1

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High incidence of acetabular retroversion in gluteal muscle contracture patients based on X-ray film

https://doi.org/10.21203/rs.3.rs-1970247/v1

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Objective

In the clinic, gluteus muscle contracture (GMC) is found to cause pelvic structural changes, including acetabular retroversion (AR). However, its incidence has not been reported. This study aimed to explore the anteroposterior pelvic radiographs of GMC patients to identify the prevalence of AR.

Methods

The imaging characteristics of anteroposterior pelvic radiographs on 100 cases of GMC and 100 healthy people were analyzed. GMC was diagnosed by ‘iliac hyperdense line’(IHDL), while ‘prominence of the ischial spine’ (PRIS) or cross-over sign’ (COS) were used to define AR.

Results

‘iliac hyperdense line’ was only observed in GMC patients (92%). There were 80 cases that showed PRIS in the GMC group, but only 19 in the control group. Similarly, the incidence of COS was 76% in patients and 5% in normal people. All the differences between the two groups of these indicators were statistically significant (P < 0.001). Furthermore, a statistical correlation was confirmed between PRIS and COS when they were positive in GMC patients.

Conclusion

AR showed a high incidence in patients with GMC based on PRIS and COS.

gluteus muscle contracture

acetabular retroversion

anteroposterior pelvic radiographs

iliac hyperdense line

prominence of the ischial spine

crossed sign

Gluteal muscles contracture (GMC) is a clinical disease, which involves pathophysiological changes in degeneration, necrosis, and fibrosis of the gluteus muscle and its fascia [1]. Patients present clinical signs of snapping hip, out-toe gait, unable to squat with the adduction of hip and so on [2]. According to previous studies, GMC mostly occurs in the patients with a history of repeated intramuscular injection in the period of infant and preschool age [3], with an incidence rate of 0.7–10.1% [4–6]. Notably, patients with GMC are more common in China compared with other countries [7]. After muscles of buttock contracture, the elasticity and length of the muscle will decrease to form fiber contracture band. Furthermore, the biomechanical properties of contracture band are significantly changed, showing intensified tension and strength, so it will have a strong pulling effect on pelvis and femur [8]. Since most GMC can occur in childhood during which the bone is not fully developed, long-term untreated GMC will cause structural changes in the pelvis and femur. Nibin et al.[9] found that GMC in children can lead to varying degrees of pelvic tilt, hip valgus, and lower limb discrepancy. In addition, Youtian et al.[10] also found a reduced equatorial-edge angle (EE angle) in GMCs, suggesting that GMC can cause acetabular retroversion (AR). As a type of pelvic structural changes, AR leads to femoro acetabular impingement (FAI) and hip arthritis [11, 12], which will significantly affect patients’ quality of life. However, there were no studies that reported the incidence of AR in patients with GMC.

Clinically, AR can be diagnosed by anteroposterior pelvic radiographs. Reynolds et al.[13] proposed that AR showed a special feature named crossed sign (COS) on X-ray photography, which presented as the projection of anterior and posterior part of the acetabular rim intersected. In 2008, Kalberer et al.[14] proposed the concept of prominence of the ischial spine (PRIS) that protruding sciatic spines can be seen in the inner wall of the pelvis, which can also reflect the sign of AR. Therefore, this study aimed to determine the incidence of AR in GMC patients by observing PRIS and COS in anteroposterior pelvic radiographs.

A retrospective design was adopted for this study, the present study was approved by Peking University Shenzhen Hospital Ethical Review Approval .

Inclusion and exclusion criteria

From February 2020 to September 2021, 100 GMC patients treated with arthroscopic release were included. Inclusion criteria for GMC patients were: 1) all cases showed differentiated degrees of snapping hip, out-toe gait, and unable to squat with the adduction of hip when performed preoperative physical examination before surgery; 2) all patients were confirmed as GMC through arthroscopy during surgery; 3) aged from 15 to 45 years.

In the same period, 100 non-GMC patients were randomly chose from people who visited the hospital and took anteroposterior pelvic radiographs. Inclusion criteria for non-GMC patients were: 1) no symptoms or signs similar to GMC; 2) showed no pathological changes examined on anteroposterior pelvic radiographs; 3) aged from 15 to 45 years.

All participants (both GMC and control group) had no any history of trauma or surgery that affect the structure of pelvis and hip, such as lumbar spondylolisthesis, acetabular fracture, and so on. In addition, diseases that affect the structure of hip joint like FAI, ankylosing spondylitis, or congenital deformity were excluded.

Radiographic techniques

In this study, all participants received the unified imaging examination, namely anteroposterior pelvic radiographs. Specifically, subjects were maintained at supine position, and kept lower limbs straight naturally in shoulder width. The internal rotation of both lower extremities makes big toes contact with each other, with the angle of 15^o. The midpoint of vertical line between superior margin of pubic symphysis and a connecting line between bilateral anterior superior iliac spine is the "central point" of the pelvis, which is directly pointed by X-ray tube with the distance of 120 cm. Subsequently, the imaging device was used to avoid any rotation of pelvis through ensuring pubic symphysis fronted straight coccyx and bilateral obturator and ilium wing were symmetrical [15]. Under the circumstances, the distance from the midpoint of sacrococcygeal joint to the upper edge of pubic symphysis should be 40-55 mm for men and 25-40 mm for women [16].

Image analysis

Two orthopedic surgeons independently analyze all radiographic film to judge the existence of ilium high density line, prominence of the ischial spine, and crossed sign without knowing the research purpose and patient information. A third orthopedist was intervened and discussed to get a consensus when there was a disagreement.

Ilium high density line refers to longitudinal high density line shadow appears alongside sacroiliac joint [17], and GMC is diagnosed when it shows in X-ray plate (Fig.1). Sciatic spine is a osseous prominence of ischiadic body between the greater and lesser sciatic notch, and positive PRIS can be presented as the visible tip of sciatic spine on the anteroposterior pelvic radiographs (more than 1 mm) [14] (Fig.2). Acetabulum is a fossa structure at the out side of hip bone, and COS is positive when the projection of anterior and posterior part of the acetabular rim intersected using imaging analysis [13] (Fig.3). Both PRIS and COS were reported to be associated with acetabular retroversion, and there is a high correlation between them.

Statistical analyses

All the data were processed using SPSS software (version 22.0, IBM, Chicago, USA). Age and BMI were reported as mean ± standard deviation, and the independent groups t test for comparisons between the patients and the control groups was performed. The chi-square test was conducted (1) to compare the sex ratio between two groups, (2) to compare the positive rate of IHDL, PRIS, and COS between two groups, and (3) to examine the correlation between PRIS and COS in two groups. A difference was considered to be significant when the p value was ＜0.05.

A total of 200 subjects were included in this study, with 100 participants from the experimental and control groups each. As shown in Fig. 4, GMC patients tend to abduce and external rotate the hip joint when squat and could not adopt the sitting posture with crossed legs. Particularly, in some severe cases, flat atrophic buttocks with hollows were observed. The group with GMC patients aged 30.13 ± 5.91 years,BMI 21.79 ± 1.87 kg/m² and the number of males was 40, while the proportion of men was 43% in the control group with the age of 31.06 ± 4.81 and BMI 22.43 ± 2.16 kg/m². There were not statistically differences between the age, BMI, and gender (Table 1).

Table 1

The demographic characteristics and the incidence of IHDL, PRIS, and COS in GMC patients and healthy people
	GMC patients	Healthy people	X²	p
Age	30.13 ± 5.91	31.06 ± 4.81	/	0.839
BMI	21.79 ± 1.87	22.43 ± 2.16	/	0.769
Sex(Males/Females)	40/60	43/57	/	0.667
IHDL (+)	92	0	170.370	<0.001
PRIS (+)	80	19	74.427	<0.001
COS (+)	76	5	104.596	<0.001

IHDL was observed in 92% of the GMC patients (92%, Cohen’s kappa = 0.784), which was significantly higher than healthy people (Cohen’s kappa = 1) (p < 0.001). There were 80 cases showed PRIS in the GMC group (Cohen’s kappa = 0.768), but only 19 in the control group(Cohen’s kappa = 0.834). Similarly, the incidence of COS was 76% in patients (Cohen’s kappa = 0.861) and 5% in normal people (Cohen’s kappa = 0.789). The positive ratios between two groups for PRIS and COS were significantly different (p < 0.001 ) (Table 1).

In GMC patients, the incidence of COS was 95% in the positive PRIS and 0 of 20 in the negative PRIS, suggesting a statistical correlation between PRIS and COS when they are positive (p < 0.001). However, there was no correlation between PRIS and COS in non-GMC patients (p > 0.05) (Table 2).

Table 2

Numeric distribution of COS in the positive and negative PRIS group with GMC
	COS (+)	COS (-)	p
GMC patients
PRIS (+) 80	76	4	<0.001
PRIS (-) 20	0	20	<0.001

In the GMC group, there are 92%, 80%, and 76% of the patients showed IHDL, positive PRIS, and positive COS respectively. However, the number of the people who presented above-mentioned sign were 0, 19, and 5 correspondingly in normal participants. All the differences between two groups for these indicators were statistically significant (P < 0.001). In addition, a statistical correlation was presented between positive PRIS and positive COS in GMC patients.

The etiology of GMC has not yet demonstrated and it is generally believed to associate with a history of repeated injections in the buttocks [18]. Its pathologic change involved the degenerative necrosis of gluteal muscle and proliferation of fibrous tissue. As one of the biggest muscle in the buttock, gluteus maximus starts from the posterior exterior of the iliac bone, which is equivalent to the level of the sacroiliac joint, and ends at femoral gluteal tuberosity and iliotibial band. The contractured gluteus maximus can pull the posterior part of the ilium, causing local bone hyperplasia and thickening. Furthermore, this continuous pulling force may cause gradual lateral displacement of the above-mentioned bone structure, resulting in being perpendicular to the coronal plane increasingly [17]. X-ray has attributes of penetrability, which is absorbed by substance during penetration. In addition, the intensity of X-ray was attenuated by increased density and thickness of body tissues, eventually showing a more obvious high-density shadow on the X-ray plate. When the X-ray is irradiated from the sagittal plane, obviously bright dense line shadow can be observed through film in GMC patients because of the increased amount of bone to pass. However, not all GMC patients existed affected gluteus maximus, so the high density line of the ilium was not showed in some of them. In contrast, this phenomenon of imaging change does not appear in healthy people who lack the fibrotic contracture of gluteus maximus.

AR refers to the pathological anatomical variation of the acetabum on the horizontal plane, where acetabular opening directs from anterior-lateral to lateral or posterolateral [13]. Accoding the study of Kalberer et al.[14], the sensitivity and specificity of PRIS in predicting AR were 91% and of 98%. The lower hemipelvis rotates excessively retroverted when AR occurs, and then the sciatic spine adducts beyond the rim of the pelvic ring, resulting in a positive PRIS on the anteroposterior pelvic radiographs. There were no previous studies that determined the incidence of PRIS in normal people, but PRIS appeared in some normal people according to this study. We speculate that this phenomenon may be related to the anatomical variation of sciatic spine, which mainly shows longer sciatic spine, and should be confirmed by further studies. Jamali et al.[19] showed a sensitivity of 96% and 95% specificity for assessing AR by COS. After AR occurs, the anterior and posterior edges of acetabular relatively rotate. Therefore, the proximal end of the projection of acetabular anterior wall is located outside the posterior wall, which intersects the posterior wall while continuing to the distal end, showing positive COS via X-ray films. However, similar to the result of a previous study, COS can be seen in a small proportion of normal individuals. Moreover, we found a correlation between PRIS and COS, which matched the research of Kalberer et al.[14]. Because the AR in GMC patients involves the retrovertion of the inferior hemipelvis, the probability of the COS being positive is also high when the PRIS is positive (76/80).

As early as in 1999, Reynolds proposed AR as the cause of hip pain. With the change of structure, it was subsequently confirmed to be an important cause of acetabular impingement and hip osteoarthritis. The incidence of AR is 20% for osteoarthritis [20], and even as high as 31 to 60% in patients with Perthes disease [21, 22]. However, there was no study explored the incidence of AR in GMC patients, and this study showed the incidence of 80%. The mainly involved soft tissues of GMC are gluteus maximus, gluteus medius, tensor fascia lata, and even affects gluteus minimus, piriformis muscle, and surrounding hip joint capsule tissue. The contractural tissues with increased structural stiffness and strength stretch the attached pelvic structure, causing a series of skeletal structural variations.The gluteus medius is located between the anterior and posterior gluteal lines, which starts from the relatively free anterosuperior part of upper iliac bone and ends at the femoral trochanter. In GMC patients, the affected gluteus medius pull the iliac bone, resulting in its external rotation. Furthermore, this force is transmitted to the other two sections of the hipbone: sciatic bone and pubic bone. In other words, during growth and development, the continuous traction brought by this contracture band will gradually drive the acetabulum, which is the convergence of the three bones, to retroversion. In addition, the contracture of gluteus minimus can forms a contracture belt with the involved gluteus medius in patients with severe GMC, causing the opening of acetabular toward lateral or posterolateral and showing AR on the anteroposterior pelvic radiographs of GMC patients.

Arthroscopic release has become the preferred method to treat patients with GMC, which mainly by arthroscopic radiofrequency vaporization to release contractural muscle tissues [23]. However, none of the reported studies addressed the issues of adjustment for pelvic structure. In 2019, Oleas-Santillán et al.[24] found that the inelastic fibrotic contracture of GMC patients pulled the great trochanter of the femur continually, making the femoral head gradually anteversion until anterior hip dislocation. The anteverted femoral head compressed the anterior upper edge of the acetababulum, thus destroying the normal anatomical relationship between them. For GMC patients with AR, the posterior tilt of the acetabulum works against the forward warped femoral head, which jointly causes increased local pressure in the hip joint and will accelerate the degenerative changes of the hip joint. Based on our study, an early surgical intervention is needed to avoid accelerating the degeneration of the hip joint due to AR during the clinical diagnosis and treatment of GMC patients. Moreover, arthroscopic release surgery can fully release the contracture tissue, while cannot fully resolve the problem of AR. Therefore, for patients with GMC, we should not only consider the changes in the contracture muscle, but also pay attention to the effects caused by the AR, and intervene it accordingly. For example, postoperative hip muscle eccentric training is a ideal way to regulate and maintain the neutral position of pelvis.

There are several limitations need to be demonstrated in this study. First of all, it is difficult to achieve strict standard positive shooting posture, especially for patients with GMC. In the course of filming, we tried to keep symmetrical bilateral obturator and ilium wing as we could. Second, this study only selects X-ray to observe the AR because of the advantage of its simplicity, convenience, and cheap. Although this method has been confirmed to qualitative diagnosis of AR, CT is needed to quantitatively diagnose its severity.

AR showed a high incidence in patients with GMC based on PRIS and COS. Therefore, special attention should be paid to the effects of AR on the degenerative changes of the hip joint in GMC.

Ethical approval and consent to participate

Approval for the study was obtained from the ethics committee at Peking University Shenzhen Hospital. Due to the retrospective nature of this research, exemption of informed consent was granted by the ethics committee at Peking University Shenzhen Hospital. The authors confirmed that all methods were performed in accordance with the relevant guidelines and regulations.

Consent for publication

Not applicable.

Availability of data and materials

The datasets generated and analyzed during the current study are not publicly available due risk of compromising individual privacy but are available from the corresponding author on reasonable request.

Competing interests

The authors have no competing interests to declare that are relevant to the content of this article.

Funding

This study was funded by the Sanming Project of Medicine in Shenzhen, China(No. SZSM201612078).

Authors’ contributions

Conception and design: Xintao Zhang, Yikun Zhao. Searched relevant studies: Xueping Dong, Yikun Zhao, Mengdi Zhang. Collection of clinical data: Xueping Dong, Zhen Zhao. Analysis and interpretation of data: Xueping Dong, Yikun Zhao, Mengdi Zhang. Wrote the manuscript: Yikun Zhao, Xueping Dong. Reviewed submitted version of manuscript: Xintao Zhang. All authors contributed to critical revision of the work and approval of the final version.

Acknowledgements

Not applicable.

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No competing interests reported.

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High incidence of acetabular retroversion in gluteal muscle contracture patients based on X-ray film

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