Comparative analysis of isolated male epispadias: concealed versus nonconcealed cases in a Chinese tertiary hospital

Abstract

Isolated male epispadias typically presents with preputial defects and dorsal urethral dehiscence. A less common subtype, known as concealed epispadias, is distinguished by an intact prepuce. Despite its clinical relevance, there is limited literature on this variant. In this study, we retrospectively analyzed the clinical data of 86 pediatric patients with isolated male epispadias treated in Beijing Children’s Hospital (Beijing, China) from May 2004 to July 2023, including 19 cases of concealed epispadias and 67 of nonconcealed epispadias. We compared clinical characteristics, preoperative diagnostics, surgical techniques, postoperative outcomes, and sexual function during follow-up between the concealed and nonconcealed groups. No significant differences were observed between the two groups regarding surgical methods, postoperative complications, or rates of urinary incontinence. However, notable distinctions were found in the age at initial diagnosis, timing of surgery, frequency of incontinence, location of the urethral meatus, and postoperative urinary incontinence scores (all P < 0.05). Given the absence of penopubic epispadias in concealed cases, we categorized glans and penile epispadias within nonconcealed epispadias as distal epispadias (n = 40) and subsequently compared them with concealed epispadias cases. The postoperative urinary incontinence scores did not differ significantly between the concealed and distal epispadias groups. These findings suggest that concealed epispadias represents a relatively milder form of the condition, characterized by the absence of penopubic involvement, lower rates of urinary incontinence, and favorable surgical outcomes. However, the intact prepuce in concealed cases underscores the need for careful identification and early diagnosis.

INTRODUCTION

Isolated male epispadias (IME) is the mildest phenotype within the exstrophy–epispadias complex, with an estimated incidence of approximately 1 in 101 000 male births.1 IME can be classified into three main subtypes: glanular epispadias (GE), penile epispadias (PE), and penopubic epispadias (PPE). Characteristic features of IME typically include dorsal curvature, a ventrally hooded prepuce, and dorsal skin defects.2 However, a unique subtype known as concealed epispadias has recently gained attention. This variant is distinguished by the presence of an intact prepuce, which can complicate the diagnosis.3,4,5,6 The intact foreskin not only poses diagnostic challenges but may also affect surgical decision-making and outcomes.7 Currently, few studies have included large enough cohorts to thoroughly examine how an intact prepuce influences the diagnosis of epispadias, the severity of associated urinary incontinence, and surgical results. Given the scarcity of data, the present study aims to address this gap by sharing our institution’s experience with concealed epispadias. We performed a comparative analysis between concealed and nonconcealed IME cases, focusing on continence status and surgical outcomes.

PATIENTS AND METHODS

Patients

This retrospective study included pediatric patients treated at Beijing Children’s Hospital, Capital Medical University (Beijing, China), who were diagnosed with IME and underwent urethroplasty between May 2004 and July 2023. The inclusion criteria were isolated male epispadias without concurrent bladder exstrophy and primary urethroplasty performed at our institution. Patients with bladder exstrophy or those who did not undergo surgery were excluded from the analysis. The study was approved by Ethics Committee of Beijing Children’s Hospital, Capital Medical University (Approval No. [²⁰²⁴]-E-050-R) and the requirement for individual consent for this retrospective analysis was waived.

Data collection

Demographic data were analyzed, including the type of epispadias, timing of diagnosis and surgery, continence status, treatment approach, and length of hospital stay. Postoperative complications and continence status were assessed during follow-up, which included phone consultations regarding complications, penile appearance, urinary continence, sexual function, and fertility. Urinary continence was defined as the absence of urine leakage or the need for diapers for at least 3 months during periods of rest or physical activity. Incontinence improvement was defined as either complete resolution or a reduction in the frequency or volume of urine leakage compared to preoperative levels. In cases of persistent urinary incontinence, the International Consultation on Incontinence Questionnaire (ICIQ) was utilized for evaluation.8 Urodynamic data were collected from patients who underwent urodynamic studies (UDS) as part of our comprehensive research protocol. Patients were stratified into two groups, concealed IME and nonconcealed IME, based on prepuce status. In the nonconcealed IME group, cases without PPE were further classified according to the location of the urethral meatus: those with openings at the glans or penile shaft were grouped as distal IME. We employed the Pediatric Penile Perception Score (PPPS) to assess postoperative penile appearance.9 A custom scoring system was developed with parental input, categorizing appearance satisfaction into three grades. Grade I was characterized by satisfactory penile length, normal urinary stream, and minimal social impact. Grade II was characterized by reduced penile length, visible scarring, and normal urinary flow. Grade III was characterized by reduced penile length, abnormal urination pattern, and postvoid dribbling. Eighty-six patients underwent surgical intervention performed by two surgeons from the Beijing Children’s Hospital, Capital Medical University, each possessing 30 years of extensive surgical experience. The primary surgical techniques utilized for urethral defect repair included the Thiersch–Dulay technique and the modified Cantwell–Ransley procedure.10,11,12

Thiersch–Duplay procedure

The patient was placed in the supine position, with a traction suture applied to the glans for stabilization. Two parallel longitudinal incisions, approximately 1.2 cm apart, were made extending from the dorsal urethral meatus to the glans tip. These incisions were deepened to reach the superficial tunica albuginea of the corpora cavernosa, preserving a central urethral plate flap. The glans wings were then mobilized laterally. A circumferential incision was made around the prepuce, and the penile skin was dissected down to the base. Dorsal fibrous tissue was released to alleviate any dorsal tethering, and if residual ventral curvature was observed, ventral plication of the tunica albuginea was performed. The urethral plate was then tubularized to the tip of the glans, followed by medial suturing of the glans wings to create a natural glans contour and reposition the urethral meatus. Subcutaneous tissue was used to cover the newly formed urethra. An 8F Foley catheter was inserted for bladder drainage. The ventral prepuce was divided and rotated dorsally to restore the typical penile appearance before applying a dressing.

Modified Cantwell–Ransley procedure

In this procedure, parallel longitudinal incisions were made from both sides of the external urethral meatus, following the same initial steps as in the Thiersch–Duplay technique. The urethral plate was carefully dissected from the corpora cavernosa, allowing for the lateral separation of the corpora (Figure 1a). The urethral plate was tubularized and transferred to a ventral position. To correct any residual curvature, the two corpora cavernosa were rotated dorsally and sutured into place (Figure 1b). The glans wings were then sutured medially, and the urethral meatus was repositioned accordingly. An 8F Foley catheter was inserted for bladder drainage, and the ventral foreskin was divided and rotated dorsally to restore a more typical penile appearance (Figure 1c and 1d).

Figure 1.

Key intraoperative situation diagram of the modified Cantwell–Ransley procedure. (a) The urethral plate and the bilateral corpus cavernosum were meticulously separated. (b) The urethra was placed on the ventral side of the penis, and the penile intracavernous rotation suture was used to correct the curvature. (c) Anteroposterior views of the penile appearance at the conclusion of the surgical procedure. (d) Lateral views of the penile appearance at the conclusion of the surgical procedure.

Statistical analyses

Data analysis was conducted using SPSS software version 25.0 (IBM, Armonk, NY, USA). The Shapiro–Wilk test was employed to assess the normality of variable distributions. Continuous variables with a normal distribution were expressed as mean ± standard deviation (s.d.), and group comparisons were performed using the independent samples t-test. Continuous variables that did not follow a normal distribution were represented as median and interquartile range [IQR]. Differences between groups were analyzed using the χ² test or Fisher’s exact test for categorical variables. Nonparametric variables were compared using the Mann–Whitney U test or the Kruskal–Wallis test, as appropriate. A two-sided P < 0.05 was considered statistically significant.

RESULTS

Comparison of the concealed IME group and the nonconcealed IME group

A total of 86 cases of IME were analyzed, comprising 19 (22.1%) cases of concealed IME and 67 (78.9%) cases of nonconcealed IME. Follow-up data were available for 63 patients (16 concealed and 47 nonconcealed), with follow-up durations ranging from 6 months to 216 (mean ± s.d.: 77.6 ± 54.0) months. The ages at follow-up for the concealed and nonconcealed IME groups were comparable, averaging 117.2 ± 47.5 months and 116.6 ± 58.9 months, respectively. In the concealed IME cohort, 2 patients were diagnosed at birth, while the remaining 17 were identified with epispadias at an average age of 54.1 months, primarily due to the presence of a concealed penis. Table 1 summarizes the preoperative, postoperative, and continence characteristics of the 86 patients. A significant difference was found in the preoperative incidence of urinary incontinence between the concealed and nonconcealed IME groups (42.1% vs 67.2%, P = 0.047). In the concealed IME group, the urethral opening was more frequently located at the glans (n = 14, 73.7%), with fewer instances in the penile region (n = 5, 26.3%), a distribution that was significantly different from the nonconcealed IME group (P < 0.01). Although no significant differences in surgical techniques were observed between the groups, the concealed IME group had a longer mean operative time compared to the nonconcealed IME group (P = 0.016).

Table 1.

Comparison between concealed and nonconcealed isolated male epispadias

Characteristic	Concealed IME	Nonconcealed IME	P
Age at the first detection (month), mean±s.d.	48.3±29.3	0a	<0.01
Age at surgery (month), median (IQR)	57 (38–88)	26 (21–37)	<0.01
Incidence of overflow incontinence, n/total (%)	8/19 (42.1)	45/67 (67.2)	0.047
Diagnosis, n/total (%)			<0.01
GE	14/19 (73.7)	19/67 (28.4)
PE	5/19 (26.3)	21/67 (31.3)
PPE	0/19 (0)	27/67 (40.3)
Surgical procedure, n/total (%)			0.685
Mitchell–Bagli repair	0/19 (0)	1/67 (1.5)
Thiersch–Duplay technique	10/19 (52.6)	41/67 (61.2)
Modified Cantwell–Ransley procedure	9/19 (47.4)	25/67 (37.3)
Operation duration (min), mean±s.d. or median (IQR)	139.4±53.6	105.0 (80.0–125.0)	0.016b
Hospital length of stay (day), mean±s.d. or median (IQR)	10.0 (7.0–13.0)	13.5±5.4	0.007b
Postoperative complications, n/total (%)	0	15/67 (22.4)	0.054
Incidence of overflow incontinence, n/total (%)c	5/16 (31.3)	28/47 (59.6)	0.050
ICIQ score, mean±s.d.	8.8±4.1	14.0±5.0	0.027
Postoperative appearance of the penis, n/total (%)			0.929
Grade I	3/16 (18.8)	8/47 (17.0)
Grade II	8/16 (50.0)	21/47 (44.7)
Grade III	5/16 (31.2)	18/47 (38.3)

^aAll nonconcealed epispadias were detected at birth. ^bMann–Whitney U test. ^cBased on follow-up data. IQR: interquartile range; IME: isolated male epispadias; GE: glanular epispadias; PE: penile epispadias; PPE: penopubic epispadias; ICIQ: International Consultation on Incontinence Questionnaire; s.d.: standard deviation

Postoperative complications were more common in the nonconcealed IME group, but the difference did not reach statistical significance. Complications were observed in 15 (22.4%) cases, including 13 instances of urethral fistula, one case of penile dehiscence with a urethral fistula, and one case of cutaneous sinus. Both the groups demonstrated improvements in urinary continence following surgery, as shown in Figure 2. The ICIQ score, used to assess the severity of urinary incontinence, was significantly lower in the concealed IME group compared to the nonconcealed IME group (8.8 vs 14.0, P = 0.027).

Figure 2.

Follow-up of urinary incontinence before and after surgery. IME: isolated male epispadias; GE: glanular epispadias; PE: penile epispadias; PPE: penopubic epispadias.

There were no statistically significant differences between the two groups concerning postoperative penile appearance grades. In terms of sexual function, 12 patients (age as mean ± s.d.: 121.1 ± 41.2 months) from the concealed IME group and 21 patients (age as mean ± s.d.: 149.0 ± 57.6 months) from the nonconcealed IME group demonstrated normal erectile function. Additionally, 4 patients from the nonconcealed IME group (mean follow-up: 198 months) displayed normal ejaculatory function. No patient reported sexual activity or childbearing at the time of the last follow-up in February 2024, and some were lost to follow-up or had unclear data regarding sexual function.

Comparison of the concealed IME group and the distal IME group

Patients with GE and PE in the nonconcealed IME group were classified as the distal IME group for statistical analysis (Table 2). Preoperative urinary incontinence was observed in 20 out of 40 patients (50.0%) in the distal IME group, which did not differ significantly from the concealed IME group (P = 0.570). However, there were notable differences between the two groups in terms of median age at the time of surgery (57.0 months for the concealed IME group vs 29.5 months for the distal IME group, P < 0.05). No statistically significant differences were found between the groups concerning surgical approaches, diagnostic type, operative duration, hospital length of stay, postoperative complications, incidence of overflow incontinence, or postoperative ICIQ scores (all P > 0.05). A longer operative time was noted for the distal IME cases compared to the nonconcealed IME group. This difference may be attributed to the predominance of the Thiersch–Duplay technique, which was utilized in 21 out of 27 PPE cases. The Thiersch–Duplay technique was associated with shorter operative time compared to the Modified Cantwell–Ransley procedure, highlighting the impact of surgical method selection on operative duration. Follow-up data on sexual function indicated that 12 patients in the distal IME group (age as mean ± s.d.: 129.6±44.9 months) were capable of achieving normal erections, with one case demonstrating normal ejaculatory function.

Table 2.

Comparison of concealed isolated male epispadias and distal isolated male epispadias groups

Characteristic	Concealed IME	Distal IME	P
Age at the first detection (month), mean±s.d.	48.4±29.3	0a	<0.01
Age at surgery (month), median (IQR)	57.0 (38.0–88.0)	29.5 (22.0–53.0)	0.001
Incidence of overflow incontinence, n/total (%)	8/19 (42.1)	20/40 (50.0)	0.570
Diagnosis, n/total (%)			0.058
GE	14/19 (73.7)	19/40 (47.5)
PE	5/19 (26.3)	21/40 (52.5)
Surgical procedure, n/total (%)			0.992
Thiersch–Duplay technique	10/19 (52.6)	21/40 (52.5)
Modified Cantwell–Ransley procedure	9/19 (47.4)	19/40 (47.5)
Operation duration (min), mean±s.d. or median (IQR)	139.4±53.6	105.0 (82.0–131.0)	0.059b
Hospital length of stay (day), mean±s.d. or median (IQR)	10.0 (7.0–13.0)	11.8±4.9	0.108b
Postoperative complications, n/total (%)	0/19 (0)	5/40 (12.5)	0.165
Incidence of overflow incontinence, n/total (%)c	5/16 (31.3)	14/29 (48.2)	0.268
ICIQ score, mean±s.d.	8.8±4.1	13.2±4.8	0.088
Postoperative appearance of the penis, n/total (%)			1.00
Grade I	3/16 (18.8)	5/29 (17.2)
Grade II	8/16 (50.0)	14/29 (48.3)
Grade III	5/16 (31.2)	10/29 (34.5)

^aAll nonconcealed IME cases were detected at birth. ^bMann–Whitney U test. ^cBased on follow-up data. IQR: interquartile range; IME: isolated male epispadias; GE: glanular epispadias; PE: penile epispadias; ICIQ: International Consultation on Incontinence Questionnaire; s.d.: standard deviation

Preoperative urodynamic data and clinical features of 5 cases

Preoperative UDS were performed on five patients, with the results presented in Table 3. Three patients with concealed IME exhibited relatively normal UDS parameters and were free of urinary incontinence. However, the patient No. 4 demonstrated unstable detrusor muscle activity during the bladder filling phase, accompanied by a weakened detrusor reflex and increased pelvic floor tension during voiding. The two patients in the nonconcealed IME group had preoperative urinary incontinence, which persisted postoperatively as evidenced by elevated ICIQ scores.

Table 3.

Continence and preoperative urodynamic examination in 5 patients

Characteristic	Patient No. 1	Patient No. 2	Patient No. 3	Patient No. 4	Patient No. 5
Clinical presentation	Concealed	Concealed	Concealed	Nonconcealed	Nonconcealed
Diagnosis	GE	GE	GE	PE	PE
Age (month)	160	74	88	28	23
Mean peak flow (ml s−1)	-	22	8	7	-
Bladder compliance	Normal	Normal	Normal	Normal	Normal
Maximum bladder capacity (ml)	360	230	185	90	80
Stability of bladder detrusor muscle	Stable	Stable	Stable	Instable	Stable
Urethral closure pressure (cmH2O)	48	-	24	-	-
Pelvic floor muscle	Relaxation	-	Relaxation	Tension	Relaxation
Mean postvoid residual (ml)	0	-	0	0	0
Preoperative continence	Continent	Continent	Continent	Incontinent	Incontinent
Postoperative continence	Continent	Continent	Continent	No improvement	No improvement
Postoperative ICIQ score	-	-	-	14	11

GE: glanular epispadias; PE: penile epispadias; ICIQ: International Consultation on Incontinence Questionnaire; -: not available

DISCUSSION

Concealed IME with an intact prepuce is an exceptionally rare presentation of epispadias, with only a few cases documented in the literature over the past decade. A total of 26 cases have been reported in five studies.5,6,13,14,15 Shahat et al.6 reported that concealed IME accounts for 21.6% of all IME cases, indicating an increased recognition of this variant in recent years. However, there remains considerable debate regarding the embryological origins of concealed epispadias with an intact prepuce. By the 8^th week of embryogenesis, the genital tubercle migrates posteriorly, forming the penile shaft. This positions the urethral groove, which connects to the distal urogenital sinus, dorsally on the penis. Failure of the urethral groove to fuse in the midline can result in epispadias. Foreskin development begins around the 12^th week, with the urogenital sinus extending into the penis and opening into the urethral groove. The urogenital folds on either side of the groove then fuse from proximal to distal; the medial folds close to form the urethra, while the lateral folds unite to form the penile skin and foreskin.3,16,17,18 McCahill et al.3 hypothesized that concealed IME may arise from excessive growth of the preputial plate, causing distal fusion of these folds and coverage of both the glans and urethral defect. However, this hypothesis does not fully account for cases of concealed IME involving the proximal urethra.

Diagnosis in nonconcealed IME cases is usually straightforward due to distinctive penile features, such as an exposed urethral plate (Figure 3a). Conversely, concealed IME poses significant diagnostic challenges. A tight prepuce can prevent glans eversion, leading to frequent misdiagnoses as a simple concealed penis and complicating the identification of underlying urethral defects before surgery (Figure 3b–3d). In our study, only 2 (10.5%) out of 19 cases were correctly diagnosed at birth. The majority, 11 (57.9%) cases, were identified during physical examinations prompted by a concealed penis, while 6 (31.6%) cases were discovered during circumcision or corrective surgery for penile concealment, leading to referral for epispadias repair. To improve preoperative diagnostic accuracy for concealed IME, clinicians should remain alert to the possibility of associated epispadias in cases of concealed penis. Identifying key clinical signs and symptoms is crucial. Patients presenting with preoperative urinary incontinence or dorsal penile bulging during urination should be evaluated for possible epispadias. Additional indicators include penile curvature, a broad and flattened glans, or a widened gap between the corpora cavernosa. In ambiguous cases, imaging studies such as ultrasound or pelvic X-rays can be beneficial. Dorsal urethral defects seen on ultrasound or pubic symphysis separation noted on X-ray can support a diagnosis of epispadias. In instances where concealed IME is unexpectedly diagnosed intraoperatively, the surgical plan should be adjusted accordingly. Surgeons may either proceed with genital reconstruction or halt the operation and refer the patient to a specialized center for further management.

Figure 3.

Comparison of the appearance of concealed and nonconcealed IME. This is the appearance of one concealed and one nonconcealed IME. (a) The urethra was dehisced to the middle of the penile body, and the overlying prepuce was not seen. (b) The appearance of a concealed penis with an intact prepuce. (c) A pronounced longitudinal tear on the dorsal aspect of the glans. (d) A green arrow pointing to a prominent urethral defect on the dorsal glans was visible as the prepuce was shed.

For patients unexpectedly found to have epispadias during surgery, due to a missed preoperative diagnosis and subsequent exposure of the urethral defect during circumcision, management should be guided by the clinical context. If single-stage urethral reconstruction is feasible, the surgery should proceed. However, if conditions are suboptimal, it is advisable to defer urethral repair. The treatment for concealed epispadias with an intact prepuce primarily involves two aspects: preputial reconstruction and urethral repair.14 Common surgical techniques for urethral repair include the modified Cantwell–Ransley and Mitchell–Bagli procedures.6,19,20 For GE and PE, a simpler approach involving anterior repositioning of the urethral meatus may suffice. If penile curvature cannot be corrected through detachment of the corpora cavernosa from the pubic bone’s fascial tissue, the Cantwell–Ransley technique is recommended. This procedure involves transverse incisions in the tunica albuginea of both corpora cavernosa, followed by longitudinal suturing, enabling dorsal extension and penile straightening. Due to potential confusion between concealed epispadias and micropenis, preoperative testosterone therapy has been employed in some cases of concealed epispadias with an intact prepuce, though its efficacy remains limited.12 In our study, there was no significant difference in the choice of surgical approach between concealed and nonconcealed IME cases. However, while 15 postoperative complications occurred in the nonconcealed IME group, no complications were observed in the concealed IME cohort. Additionally, hospital stays were shorter in the concealed IME group, likely due to the lower surgical complexity associated with GE and PE, which resulted in reduced trauma and quicker recovery.

Similar to other cases of concealed penis, postoperative penile length is a key determinant of patient satisfaction in concealed IME.3,13 Thomas et al.20 reported that 89% of patients were dissatisfied with penile appearance and required revision surgery during follow-up. In our study, satisfaction with penile appearance was similar between the concealed and nonconcealed IME groups. Up to 82.5% (52/63) of patients and their parents expressed dissatisfaction with penile appearance, which correlated strongly with visible penile length. Other factors contributing to dissatisfaction included hypertrophic scars and redundant foreskin. Techniques such as releasing the suspensory ligament of the pubis and anchoring the membranous layer of the penile root and pubic symphysis at 3-, 6-, and 9-o’clock positions can enhance penile length and exposure, improving satisfaction. Additionally, in cases of severe obesity, partial resection of the fat pad above the pubic symphysis can facilitate penile exposure by reducing tension on the penile skin, thus restoring the penile-pubic angle.21,22,23

A previous study has suggested that urinary incontinence in distal IME is due to both proximal urethral dilation and histological abnormalities at the bladder neck.24 In our analysis, the concealed IME group exhibited lower rates of urinary incontinence pre- and postoperatively compared to the nonconcealed group, and their postoperative ICIQ scores were also lower. However, no statistically significant difference was found in urinary incontinence rates between the concealed and distal IME groups before or after surgery. Notably, PPE, as the most severe form of IME, was associated with more significant sphincteric damage and higher rates of urinary incontinence.25 In contrast, PPE was rarely seen in the concealed IME cohort. Postsurgical lengthening of the urethra and pubertal prostate development can enhance urinary control by increasing outlet resistance. For patients with persistent urinary incontinence postoperatively, bladder neck reconstruction may be considered. Imaging modalities such as ultrasound and X-rays can provide preliminary assessments of bladder neck integrity and pubic symphysis status. Findings may guide decisions regarding further invasive tests, such as UDS and voiding cystourethrography. In our study, 80.0% (4/5) of postoperative UDS showed reduced bladder capacity, aligning with observations from Kaefer et al.26 To our surprise, all patients in our study had normal bladder compliance, whereas Kaefer et al.26 reported predominantly high bladder compliance.

This study has several limitations. Due to its retrospective design, some data were missing, including preoperative ICIQ scores and complete urodynamic information. Follow-up constraints meant that assessments of postoperative penile appearance relied on a mix of objective observations and subjective feedback from parents, lacking a more detailed and comprehensive analysis. Some parents were not fully aware of their child’s sexual function during follow-up, and some children were hesitant to discuss sensitive topics like erections or ejaculation, which may have introduced bias. Additionally, the follow-up period was too short for a thorough evaluation of reproductive outcomes. Given the rarity of IME and the limited existing research, our center remains committed to improving diagnostic and treatment expertise. We aim to deepen understanding of this condition and lay the groundwork for future studies. In future research, we need to conduct longer follow-up and more detailed investigations.

CONCLUSION

Concealed IME is a rare variant of IME, characterized by the inability of the penile body to evert, which complicates preoperative diagnosis and increases the risk of misdiagnosis. In patients presenting with a concealed penis or phimosis, a meticulous physical examination and a detailed inquiry into the history of urinary incontinence can offer preliminary indications of potential underlying urethral anomalies. Compared to nonconcealed IME, concealed IME demonstrates a lower incidence of preoperative urinary incontinence and fewer postoperative complications.

AUTHOR CONTRIBUTIONS

JYL and BY provided substantial contributions to collect the dataset, conceive the study idea, participate in data analysis, conduct statistical analyses, and draft the manuscript. MCY and ZHL were involved in the data collection. HCS supervised the study and drafted the manuscript. WPZ was the initiator of the project and research, provided the surgical data, and participated in the study design and coordination. All authors read and approved the final manuscript.

COMPETING INTERESTS

All authors declare no competing interests.