Acetabular posterior wall morphology in slipped capital femoral epiphysis: A three-dimensional and true axial computed tomography matched-cohort study

doi:10.21203/rs.3.rs-3905334/v1

Aims

Comparative assessment of both hip joints in patients with slipped capital femoral epiphysis (SCFE) was performed relative to the control group.

Methods

We created 3D CT reconstructions of the acetabulum in 27 hips with SCFE, 21 unaffected contralateral hips, and 108 hips of the age- and sex-matched non-SCFE control group. Following measurements performed using true axial CT scans were assessed: acetabular version angle (AVA°), posterior sector acetabular angle (PASA°), posterior wall angle (PWA°), and acetabular roofing percentage.

Results

Based on the morphology of the posterior acetabular wall, we found three type I (closed) and 24 type II (open) hips in the SCFE group. We noticed a flattening of the posterosuperior quadrant of the acetabulum in 66.66% (18 out of 27 hips) of the hips affected by SCFE. For both SCFE (p = 0.004) and unaffected hips (p = 0.009), the AVA at the proximal hip level was significantly lower than in the control group. We observed no significant between-group differences in PASA (p > 0.05). The mean values of the PWA for the SCFE group were significantly higher than in the contralateral hip (p = 0.025) and control group (p = 0.018).

Conclusions

Hips with SCFE tend to be flattened at the posterosuperior quadrant and have higher PWA values. PWA better defines the morphology of the posterior wall than the PASA. As the PWA angle increases, the mechanical shearing forces at the femoral physis may increase; however, this requires further research.

Health sciences/Anatomy/Musculoskeletal system

Health sciences/Health care/Paediatrics

slipped capital femoral epiphysis (SCFE)

children

acetabulum

acetabular anteversion

acetabular posterior wall

Slipped capital femoral epiphysis (SCFE) is a common condition of the proximal femoral physis most commonly seen in obese adolescent males [1, 2, 3]. Although there is still a lack of agreement on the pathogenesis of SCFE, the condition is known to be multifactorial, with biochemical and mechanical factors involved. Anatomical characteristics associated with a higher risk of SCFE include acetabular and femoral retroversion and greater acetabular coverage of the femoral head, which increase the mechanical shearing forces at the physis [4, 5]. The epiphyseal tubercle, a structure located on the inferior surface of the femoral epiphysis that appears to be a major epiphyseal stabilizer, can provide a rotational pivot point for slippage [6, 7].

There is no consensus in the literature regarding the direct relationship between acetabular retroversion and SCFE, or the connection between the morphology of the contralateral hip in patients with unilateral SCFE and the risk of its slippage [8, 9]. Both the acetabular version and posterior wall are known to be associated with impingement syndrome and the development of hip osteoarthritis [10].

The purpose of this study was to investigate whether differences in acetabular posterior wall morphology can be observed in patients with SCFE on 3D computed tomography (CT) reconstructions, and whether there are marked differences between the angles defining the posterior wall on the axial CT scans.

After obtaining institutional bioethics board approval we identified 24 patients with SCFE who underwent pelvic CT between January 2020 and September 2023 (a total of 27 hips because we diagnosed bilateral SCFE in three patients). We established three groups: affected hips in patients with SCFE; unaffected hips (contralateral hips without SCFE signs, a total of 21 hips) in patients with SCFE; and the age- and sex-matched non-SCFE control group (54 patients, a total of 108 hips). The mean slippage angle measured on axial CT scans in patients with SCFE was 53.12° (SD 16.83). Of the 24 patients, only two were diagnosed with acute slippage with persisting symptoms for less than three weeks. The remaining patients had symptoms for an average of 3.5 months (SD 1.9) before making the correct diagnosis.

The control group, which was identified in the hospital imaging database, comprised 54 CT scans performed in the same period for non-orthopedic reasons (diagnostics of abdominal pain or urinary disorders). The control group was selected to match the SCFE cohort based on sex and age. Medical records for each control subject were reviewed to ensure no history of hip pain or previous hip surgery. All CTs were performed using Siemens Somatom Definition AS+, Germany. Image slices were 3mm, with secondary reconstruction at 1mm. A 3D reconstruction was performed using the Siemens syngo.via imaging software. To assess the acetabular morphology, we used an exact lateral view of a 3D reconstruction assembled from the right and left iliac wings, anterior superior iliac spines, obturator foramina, and the greater sciatic notches were superimposed, Figure 1. Then, after the removal of the proximal femur based on the appearance of the posterior wall, we divided the acetabulum into two types: Type I (closed), defined as invisible posterior acetabular joint surface; and Type II (open), with visible posterior acetabular joint surface [11]. Rotational misalignment and pelvic tilt were corrected by reformatting the CT scans, defining the planes using standard anatomical references using RadiAnt DICOM Viewer software (Medixant, Poland). All measurements were performed in the reoriented true axial CT scans by two researchers (orthopaedic surgeon - Ł.W and radiologist - P.F) at two levels: 1) corresponding to the proximal 1/4 of the line joining the acetabular roof to the inferior pelvic teardrop, following Dandachli et al.[12]; and 2) corresponding to the center of the femoral head, Figure 2 [13]. Quantitative measurement procedures were done using the same standardized technique by two researchers to reduce the standard errors of measurements. An acetabular version (AVA°) was measured as the angle between a line perpendicular to a horizontal intercapital center line and a line connecting the anterior and posterior acetabular lip. The posterior sector acetabular angle (PASA°) was defined by measuring the angle between the horizontal intercapital center line and a line from the femoral head center to the posterior margin of the acetabular rim [14]. A posterior wall angle (PWA °) was measured using the angle between the line orthogonal to the horizontal intercapital center line and the tangent to the posterior articular surface area [11]. Acetabular roofing percentage was defined as a quotient of the covered part of the femoral head and the whole femoral head diameter (femoral head divided by a line between the anterior and posterior acetabular rim). A description of CT-based axial measurements is presented in Figure 3.

All procedures in the study were in accordance with the ethical standards of the institutional and /or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Statistical analysis

For statistical analysis, one-way ANOVA was used. If a second differentiating factor was considered, i.e., gender or age, a two-factor ANOVA was used. All statistical tests were calculated at the level of statistical significance p=0.05. To assess whether the control group was correctly selected, two-way ANOVA analysis was used: group × gender and group × age. Significance levels of p <0.05 were obtained for all variables, confirming the lack of statistical differences between the groups. The Mann–Whitney U test was used to determine whether there were differences between the three study groups.

We included 27 affected hips in 24 patients with SCFE — 14 boys and 10 girls, with a mean age of 12.12 years (SD 1.32). Furthermore, we analyzed a total of 21 unaffected hips in patients with SCFE. The non-SCFE control group comprised 108 hips in 54 patients—35 boys and 19 girls, with a mean age of 12.79 years (SD 1.84). Analysis of the morphology of the posterior acetabular wall in the group of slipped hips revealed three type I and 24 type II hips. In the contralateral hips without SCFE signs and in the non-SCFE control group, we observed only type II of the posterior wall. Assessing the hip morphology on 3D reconstructions in the vast majority of patients in the SCFE group, we observed flattening of the posterosuperior quadrant of the acetabulum (18 out of 27 hips), Figure 4. In the contralateral hips without SCFE, similar flattening was observed in only in two of 21 patients. In the non-SCFE control group, we observed posterosuperior quadrant flattening in only seven out of 108 hips. In this group, we found flattening of the acetabular roof (25 hips) much more often.

For measurements conducted at the level of the femoral head center, the mean acetabular version was similar in the SCFE group (12.86°) and unaffected contralateral hips (12.85°) and lower than in the non-SCFE control group (13.17°). Following is the mean posterior acetabular sector angle for individual groups: SCFE (95.91°), unaffected contralateral hips (96.49°), and non-SCFE control group (95.53°). Following is the mean posterior wall angle: SCFE (66.86°), unaffected contralateral hips (66.54°), and non-SCFE control group (67.43°). Details are presented in Table 1. Comparing the results between the study groups, we found no statistically significant differences, Table 2 and Figure 5. Analyzing measurements at the level of the proximal 1/4 hip line, we found lower values of the mean acetabular version in all study groups: SCFE (1.93°), unaffected contralateral hips (2.10°), and non-SCFE control group (7.06°). The mean posterior acetabular sector angle was higher and determined as SCFE (101.17°), unaffected contralateral hips (101.86°), and non-SCFE control group (100.95°). The mean posterior wall angle was also greater: SCFE (76.63°), unaffected contralateral hips (71.52°), and non-SCFE control group (70.52°). Details are presented in Table 3. Results from the Mann–Whitney U analysis indicate that in the SCFE and unaffected contralateral hips, the acetabular version was significantly lower than in the control group (p=0.004 and p=0.009, respectively). We observed no significant differences between groups for the PASA angle. The PWA angle in the SCFE group was significantly greater than in unaffected contralateral hips (p=0.025) and more significant than in the control group (p=0.018). Interestingly, no significant differences exist between unaffected hips and the control group, Table 4 and Figure 6.

Table. 1. Measurements at the level of the femoral head center

Groups		Roofing	AVA	PASA	PWA
SCFE	Mean	38,65	12,86	95,91	66,86
	N	27	27	27	27
	Standard deviation	7,22	3,59	7,52	4,51
unaffected contralateral hips	Mean	39,25	12,85	96,49	66,54
	N	21	21	21	21
	Standard deviation	8,50	3,36	6,63	4,96
non-SCFE control group	Mean	36,91	13,17	95,53	67,43
	N	108	108	108	108
	Standard deviation	5,74	4,15	6,75	6,87

Table. 2. Mann–Whitney U test of differences between the three study groups for measurements at the level of the femoral head center

		Roofing	AVA	PASA	PWA
SCFE vs contralateral hips	Z	−0,53	−0,083	−0,322	−0,52
SCFE vs contralateral hips	p-value	0,596	0,934	0,747	0,603
SCFE vs non-SCFE control group	Z	−1,016	−0,16	−0,275	−0,506
SCFE vs non-SCFE control group	p-value	0,31	0,873	0,783	0,613
contralateral hips vs non-SCFE control group	Z	−1,51	−0,022	−0,702	−0,788
contralateral hips vs non-SCFE control group	p-value	0,131	0,982	0,483	0,431

Table. 3. Measurements at the level of the proximal 1/4 of the line joining the acetabular roof to the inferior pelvic teardrop

Study group		AVA	PASA	PWA
SCFE	Mean	1,93	101,17	76,63
	N	27	27	27
	Standard deviation	7,60	11,08	7,65
unaffected contralateral hips	Mean	2,10	101,86	71,52
	N	21	21	21
	Standard deviation	7,93	12,49	6,94
non-SCFE control group	Mean	7,06	100,95	70,52
	N	108	108	108
	Standard deviation	6,60	11,88	11,47

Table. 4. Mann–Whitney U test of differences between the three study groups for measurements at the level of the proximal 1/4 of the line joining the acetabular roof to the inferior pelvic teardrop

		AVA	PASA	PWA
SCFE vs contralateral hips	Z	−0,042	−0,156	−2,236
SCFE vs contralateral hips	p-value	0,967	0,876	0,025
SCFE vs non-SCFE control group	Z	−2,855	−0,074	−2,356
SCFE vs non-SCFE control group	p-value	0,004	0,941	0,018
contralateral hips vs non-SCFE control group	Z	−2,621	−0,278	−0,342
contralateral hips vs non-SCFE control group	p-value	0,009	0,781	0,733

There is still a lack of agreement on the pathogenesis of SCFE.

A review of the literature reveals that reports on the relationship between acetabular morphology and the risk of SCFE tend to be inconsistent [4, 5, 15, 16].

Analysis of 3D models of the hip joint acetabulum in the SCFE group in our study indicated a flattening of the posterosuperior quadrant of the acetabulum in 66.66% of the hips affected by SCFE (18 out of 27 hips). Such flattening in contralateral hips without SCFE was observed only in 9.5% (two out of 21 hips), and in only 6.5% (7 out of 108 hips) in the non-SCFE control group. It is worth mentioning that we observed the flattening of the posterosuperior quadrant of the acetabulum in both acute and chronic SCFE cases. Consistent with Valera M et al. [11], closed-type acetabulum (type I), defined as the invisible posterior acetabular joint surface, was observed only in SCFE hips (11.11% 3 out of 27 hips) in our study. In the contralateral hips without SCFE signs and in the non-SCFE control group, we observed only type II of the posterior wall with visible posterior acetabular joint surface. Many authors report no difference between the acetabular version of SCFE hips and healthy controls; [4, 8, 17, 18] however, many indicate that in SCFE hips, a tendency for acetabular retroversion is observed [5, 16, 19, 20].

Like other authors [9, 20], we observed a lower acetabular version in SCFE and unaffected hips relative to the control group, at the femoral head center. However, these differences were not statistically significant (p > 0.05). We also observed no significant differences in acetabular roofing percentage between SCFE, the unaffected hips, and the control group (p = 0.596 and p = 0.31, respectively). The acetabular version angle was lower, with a tendency toward retroverted orientation at the proximal hip level. At this level in our group, we observed statistical significance relative to the control group for both SCFE (p = 0.004) and unaffected hips (p = 0.009). The lack of statistical significance in the differences regarding the acetabular version at the center of the femoral head is in line with Monazzam et al [5]. It remains unclear whether acetabular retroversion is primarily related to the mechanical etiology of SCFE or whether it is a secondary adaptive reaction of the acetabulum.

Similar to the work of Hesper T et al. [20], in our group, the mean posterior acetabular sector angle in the SCFE hips was lower than in unaffected hips, but slightly higher than in the control group. We observed such a tendency for measurements at the hip joint's middle and upper quarter, but these differences were not statistically significant (p > 0.05).

For the posterior wall analysis, we assessed the posterior wall angle. At the level of the hip center, the values were similar in all groups, with no statistically significant differences. When assessing the PWA values at the upper hip level, where we observed flattening on the 3D acetabular models, we noticed they were higher for all groups, but specifically for SCFE. The mean values of the PWA angle for the SCFE group were significantly higher than in the contralateral hip (p = 0.025) and the control group (p = 0.018). In the superior aspect of the hip, we found that the acetabular orientation was more retroverted in the SCFE group. However, at the same time, we observed an increase in the PASA value in the SCFE hips; therefore, we cannot confirm that a more retroverted acetabular orientation is associated with less posterior acetabular support.

In analysis of axial CT scans, PWA better defines the morphology of the posterior wall than the sector angle. As the PWA angle increases, the mechanical shearing forces at the femoral physis may increase—this requires further research. It is also essential to analyze the spatial relationship between the acetabular posterior wall morphology and the epiphyseal tubercle, a major epiphyseal stabilizer that can provide a rotational pivot point for slippage.

To our knowledge, this study is the first to present comprehensive, detailed data on the posterior wall morphology and the correlation of AVA°, PASA°, PWA°, and acetabular roofing with 3D acetabular models in patients with SCFE.
Limitations of this study are the retrospective design and selection of a control group from CT scans performed due to abdominal or urinary disorders, excluding any problems with hip joints based on medical history.

Hips with SCFE tend to be flattened at the posterosuperior quadrant of the acetabulum and have higher PWA values, especially at the upper hip level, which may be a predisposing morphologic factor or a consequence of the increased shearing stress across the physis.
Based on the morphology of the posterior acetabular wall, we found three type I (closed) and 24 type II (open) hips in the SCFE group. In the contralateral hips and non-SCFE control group, we observed only type II of the posterior wall.
PWA better defines the morphology of the posterior wall than the PASA.

Funding: This paper was not funded. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.

Conflicts of Interest:

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Author's contributions:

Ł.W. designed the study and drafted the manuscript. Ł.W. R.T. P.F. and M.D. collected data. Ł.W. conducted the data analysis. Ł.W prepared the final version of the manuscript. Ł.W. R.T. P.F. and M.D. critically reviewed and edited the manuscript. All authors have read and agreed to the published version of the manuscript.

Informed Consent Statement:

Ethical approval was obtained by the Ethics Committee of the Silesian Medical University in Katowice, Poland (BNW/NWN/0052/KB/250/23) for the study. All procedures in the study were in accordance with the ethical standards of the institutional and /or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Data Availability Statement: The data generated and analyzed in the current study are available from the corresponding author on reasonable request.

Consent to Participate / Consent to Publish - Informed consent was waived due to retrospective nature of the study by Ethics Committee of the Silesian Medical University in Katowice, Poland.

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No competing interests reported.

Acetabular posterior wall morphology in slipped capital femoral epiphysis: A three-dimensional and true axial computed tomography matched-cohort study

Status:

Version 1

Abstract

Aims

Methods

Results

Conclusions

Figures

1. Introduction

2. Materials and Methods

3. Results

4. Discussion

5. Strengths and limitations

6. Key messages

Declarations

References

Additional Declarations

Status:

Version 1