Abstract
Background
Wu et al. introduced a modified radiographic system that allows classification of all forms of CTD with excellent interobserver and intraobserver reliability. No study to date has evaluated the radiographic characteristics of Wu et al. type C3 CTD with osseous attachment at the level of the metacarpal.
Objective
This study aimed to evaluate the radiographic features of type C3 CTD according to the system of Wu et al., to describe the different anatomical subtypes of the duplication, and to propose a categorization approach to distinguish diverse surgical strategies based on the radiographic anatomy of this specific subtype of duplication.
Methods
We performed a retrospective analysis of 215 patients (221 thumbs) diagnosed with Wu et al. type C3 CTD at our Institution between 2015 and 2021. We evaluated all CTDs by examining the alignment of the interphalangeal (IP) and metacarpophalangeal (MP) joints and by assessing the presence of abnormal hypertrophic epiphysis of the primary thumb on posteroanterior (PA) radiographs. The proposed classification system has four types: Type I with good alignment of both MP and IP joints, Type II with ulnar deviation of the MP joint, Type III with radial deviation in the MP joint and Type IV with abnormal hypertrophic epiphysis of the distal phalanx of the main thumb with ulnar deviation of the IP joint with or without ulnar deviation of the MP joint.
Results
There were 140 male and 75 female patients with CTD (221 thumbs). There were 65 left, 144 right and 6 bilateral forms. The right-to-left, male-to-female and unilateral-to-bilateral ratios were 2.2:1, 1.9:1 and 35.8:1 respectively. The mean age at surgery was 22.3 ± 11.8 months (range, 8–80). The proposed classification system allowed the classification of all CTDs (n = 221). Specifically, 53 fingers were classified as Type I (24%), 136 as Type II (61.5%), 21 as Type III (9.5%), and 11 as Type IV (5%).
Conclusion
The proposed system is based on radiographic pathoanatomy and complements that of Wu et al. by identifying four distinct subtypes of deformity. It has the potential to improve inter-professional communication and guide surgery in patients with Wu et al. type C3 CTD. However, our results are preliminary and further research is needed to validate them.
Level of evidence
III.
Keywords: Congenital thumb duplication, Wu et al. classification, Radiographic anatomy, Interphalangeal and metacarpophalangeal joint alignment, Surgical options
Introduction
Congenital thumb duplication (CTD) is one of the most common hand anomalies observed in children [1–3] and is characterized by osseous anomalies such as bifurcation or hypertrophy of the phalanges or metacarpals, with or without malalignment, and misplacement of the tendons or thenar muscle [4–8]. To achieve good appearance and function of the thumb, surgical treatment should go beyond simple excision of the supernumerary thumb and include appropriate osseous and soft tissue reconstruction or Bilhaut-Cloquet surgery [9–12].
Wassel-Flatt type V CTD, which is characterized by an osseous attachment at the level of the metacarpus, is a rare anomaly, accounting for 6.6–10% of all CTDs [1, 3, 12]. In addition, limited studies with small sample sizes have focused solely on Wassel-Flatt type V CTD, particularly with regard to radiographic characteristics, anatomic subtypes and related surgical strategies [13, 14]. Although the surgical technique for Wassel-Flatt type V and type VII is similar, no study to date has evaluated the radiographic characteristics of CTD with osseous attachment at the level of the metacarpal.
Bessho et al. operated on 17 cases of Wassel-Flatt type V CTD using a pulp pinch without opponensplasty and osteotomy; their study showed that this technique often resulted in satisfactory outcome [13]. In addition, their study reported that 2 out of 17 cases had radial deviation of the first metacarpophalangeal joint of the main thumb, although no radiographs were taken. In another study, Mete et al. reported a rare case of Wassel-Flatt type V CTD in a 42-year-old man who presented with a swan-neck deformity and underwent plain radiography and computed tomography (CT) to guide surgery [14]. However, CTDs in which an extra thumb appears as a triphalangeal digit rather than a primary digit were not included in these studies.
To overcome some of these limitations, Wu et al. introduced a modified radiographic system that allows classification of all forms of CTD with excellent interobserver and intraobserver reliability [15]. Specifically, type C3 CTD in the Wu et al. classification includes all types of Wassel-Flatt type V CTD that have duplications connected by a bony attachment, regardless of the presence of a typical bifid metacarpal [15]. In addition, the Wu et al. classification also includes certain Wassel-Flatt type VII CTDs in which the extra thumb, but not the main thumb, is triphalangeal and connected to the main digit by bony fusion at the metacarpal level [1, 15].
The aim of this study was to evaluate the radiographic features of type C3 CTD according to the system of Wu et al. [15], to describe the different anatomical subtypes of the duplication, and to propose a categorization approach to distinguish different surgical strategies based on the radiographic anatomy of this specific subtype of duplication.
Materials and methods
After obtaining institutional review board (316B01) approval and informed consent from the parents or guardians of the study participants, we retrospectively reviewed the medical records of 215 patients (n = 221 fingers) diagnosed with type C3 CTD according to the system of Wu et al. at our Institution between August 2015 and April 2021.
The inclusion criteria for this study were:1) a confirmed diagnosis of type C3 CTD according to the system of Wu et al. [15]; 2) complete clinical and radiological data, and 3) surgery performed exclusively at our center.
Patients with incomplete clinical and radiographic data, CTD other than type C3 according to the system proposed by Wu et al. and those treated elsewhere were excluded.
Wu et al. C3 CTD subtypes
The identification of the different Wu et al. C3 CTD subtypes is essentially based on the alignment of the interphalangeal (IP) and metacarpophalangeal (MP) joints and an abnormal hypertrophic epiphysis of the main thumb, but not of the supernumerary thumb:
Type I (no deviation) identifies cases in which there is no axial deviation at the level of the IP and MP joints of the main thumb (no radial or ulnar deviation);
Type II (ulnar deviation of the MP joint) identifies cases in which there is ulnar deviation of the main thumb at the level of the MP joint, while the IP joint is well aligned;
Type III (radial deviation of the MP joint) identifies cases in which there is radial deviation of the main thumb at the level of the MP joint, while the IP joint is well aligned;
Type IV (hypertrophic epiphysis) is characterized by hypertrophic epiphysis of the distal phalanx with or without distal bony deformity of the proximal phalanx, and the IP joint of the main thumb deviates toward the ulna with or without ulnar deviation of the MP joint (Fig. 1).
Fig. 1.
Four subtypes of Wu et al. type C3 CTD11: Type I (no deviation), Type II (ulnar deviation of the MP joint), Type III (radial deviation of the MP joint), and Type IV (hypertrophic epiphysis)
Surgical options
Understanding the clinical and radiographic anatomy of the duplication can help guide the selection of the optimal surgical procedure.
Type I (no deviation): Excision of the supernumerary thumb, flattening of the bifurcated metacarpal, and reconstruction of the thenar muscle of the main thumb (Fig. 2) [6, 11, 15].
Fig. 2.
Surgical reconstruction of type I duplications. Excision of the supernumerary thumb, flattening of the bifurcated metacarpal, and reconstruction of the thenar muscle
Type II (ulnar deviation of the MP joint): Excision of the supernumerary thumb, reconstruction of the thenar muscle of the MP joint of the main thumb, and osteotomy of the metacarpal with reconstruction of the periosteal ligament/sleeve (Fig. 3).
Fig. 3.
Surgical reconstruction of type II duplications. Excision of the supernumerary thumb, corrective osteotomy of the metacarpal, and reconstruction of the thenar muscle and ligament/periosteal sleeve
Type III (radial deviation of the MP joint): Excision of the supernumerary thumb, osteotomy of the metacarpal, release of the contracture, ulnar collateral ligament tightening of the MP joint, and reconstruction of the thenar muscle of the MP joint of the main thumb (Fig. 4).
Fig. 4.
Surgical reconstruction of type III duplications. Resection of the supernumerary thumb, contracture release (CR), ulnar collateral ligament (UCL) tightening of the MP joint, reconstruction of the thenar muscle (TM)
Type IV (hypertrophic epiphysis): Excision of the supernumerary thumb, epiphyseal osteotomy of the distal phalanx, collateral ligament reconstruction, and thenar muscle reconstruction of the MP joint of the main thumb (Fig. 5A); metacarpal osteotomy and periosteal ligament/sleeve reconstruction may also be performed (Fig. 5B).
Fig. 5.
Surgical reconstruction of type IV duplications. Two procedures are possible: A) resection of the supernumerary thumb, reconstruction of the thenar muscle and collateral ligament/periosteal sleeve, and corrective osteotomy of the hypertrophic epiphysis of the distal phalanx; B) resection of the supernumerary thumb, reconstruction of the thenar muscle, corrective osteotomy of the hypertrophic epiphysis of the distal phalanx and metacarpal, and reconstruction of the thenar muscle and ligament/periosteal sleeve
Statistical analysis
All statistical analyses were performed using the SPSS 22.0 statistical package (SPSS, Chicago, IL, USA). Categorical parameters are expressed as frequencies and percentages. Quantitative data are expressed as mean ± standard deviation and range. The chi-squared test was used to compare sex, side, level of bifurcation, and size of thumb duplication in these groups. The tests were two-tailed and a p-value of < 0.05 was considered significant.
Results
From a data set of 2108 patients (n = 2300 CTDs) [1, 2], a total of 140 male and 75 female patients with type C3 CTD according to Wu et al. [15] (221 thumbs; 65/30.2% left and 144/67.0% right) met the inclusion criteria; there were 6 bilateral forms (2.8%). The right-to-left, male-to-female and unilateral-to-bilateral ratios were 2.2:1, 1.9:1 and 35.8:1 respectively. The mean age at surgery was 22.3 ± 11.8 months (range, 8–80).
Of the 221 thumbs, 167 (75.6%) and 54 (24.4%) were classified as type V and VII, respectively, according to the Wassel-Flatt system [3], whereas all 221 thumbs were classified as type C3 according to Wu et al. [15], with 53 fingers classified as type I (24%), 136 as type II (61.5%), 21 as type III (9.5%), and 11 as type IV (5%).
Table 1 describes patient demographics, including gender, laterality, size of comparable duplications, and type of surgical procedures according to Wu et al. type C3 CTD subtypes. The rate of metacarpal bifurcation at the proximal level of type I (79.2%), III (90.5%) and IV (54.5%) was significantly higher than that in type II (27.2%) (p < 0.001). In addition, bifurcation level, but not sex, side, and size of comparable duplications, were associated with Wu et al. system (p < 0.001) (Table 1).
Table 1.
Wu et al. [11] system according to demographic characteristics of patients
| Characteristics n, % | Sex | Laterality | Hypoplastic duplications of comparable size | Bifurcation level | Surgical procedures | Total | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Male | Female | Right | Left | Bilateral | Yes | No | Distal | Proximal | ||||
| Wu et al. type C3 CTD subtypes | I | 38 (71.7) | 15 (28.3) |
31 (58.5) |
18 (34.0) |
4 (7.5) |
1 (1.9) |
52 (98.1) |
11 (20.8) |
42 (79.2) |
ER: 53 |
53 (24.0) |
| II |
83 (61.0) |
53 (39.0) |
94 (69.7) |
35 (25.1) |
7 (5.2) |
2 (1.5) |
133 (98.5) |
99 (72.8) |
37 (27.2) |
ER: 118 CO: 18 |
136 (61.5) |
|
| III |
16 (76.2) |
5 (23.8) |
14 (66.6) |
6 (28.6) |
1 (4.8) |
1 (4.8) |
20 (95.2) |
2 (9.5) |
19 (90.5) |
ER: 20 CO: 1 |
21 (9.5) |
|
| IV |
7 (63.6) |
4 (36.4) |
5 (45.5) |
6 (54.5) |
0 (0) |
0 (0) |
11 (100) |
5 (45.5) |
6 (54.5) |
ER: 10 CO: 1 |
11 (5.0) |
|
| Total |
144 (65.2) |
77 (34.8) |
144 (65.2) |
65 (29.4) |
12 (5.4) |
4 (2.7) |
215 (97.3) |
117 (52.9) |
104 (47.1) |
- | 221 | |
| chi-squared | 2.322 | 3.075 | 2.145 | 59.691 | - | - | ||||||
| p value | 0.515 | 0.383 | 0.504 | 0.000 | - | - | ||||||
ER: Simple excision and soft tissue reconstruction; CO: Corrective osteotomy
Table 2 describes the alignment characteristics of the IP and MP joints of the first thumb in patients with Wu et al. type C3 CTD subtypes. There were 9 cases (81.8%) and 2 cases (18.2%) of both IP and MP joint deviation and only IP joint deviation in type IV, respectively. All cases had only MP joint deviation in type II and III and no deviation in type I. The difference between each subtype was significant (p < 0.001) (Table 2).
Table 2.
Alignment of the interphalangeal (IP) and metacarpophalangeal (MP) joints of the main thumb according to the system of Wu et al. [11]
| IP and MP alignment | Deviation level | Total | ||||
|---|---|---|---|---|---|---|
| No | IP | MP | Both | |||
| Wu et al. type C3 CTD subtypes | I |
53 (100) |
- | - | - |
53 (24.0) |
| II | - | - |
136 (100) |
- |
136 (61.5) |
|
| III | - | - |
21 (100) |
- |
21 (9.5) |
|
| IV | - |
2 (18.2) |
- |
9 (81.8) |
11 (5.0) |
|
| Total |
53 (24.0) |
2 (0.9) |
157 (71.0) |
9 (4.1) |
221 | |
| chi-squared | 300.430 | - | ||||
| p value | 0.000 | - | ||||
Discussion
Our study showed that Wu et al. type C3 CTDs can be classified into four subtypes (I, II, III, and IV) based on the alignment deviation of the IP and MP joints of the first thumb and the presence of hypertrophic epiphysis, and includes Wassel-Flatt type V and some type VII CTDs. The proposed classification systems include similar types of duplications and can potentially improve communication between specialists and guide their selection of surgical strategies [3, 15].
Our research found that Wu et al. type C3 CTD is highly prevalent in right-sided male patients, which is consistent with most previous reports. In particular, Wu et al. (n = 167) [1], Lin et al. (n = 32) [2], Yao et al. (n = 243) [12], and Li et al. (n = 243) [16] reported a male-to-female ratio of 1.6–2.6 to 1, whereas our series (n = 221) reported 1.9 to 1. These previous studies also reported right-to-left and unilateral-to-bilateral ratios of 1.7-2 to 1 and 2.7–4.2 to 1, respectively, whereas our series reported 2.2 to 1 and 35.8 to 1, respectively. These discrepancies may be related to differences in sample size, environmental factors, ethnicity, diet, economic status, and level of medical care [1, 2, 12, 16–18].
Of the 221 fingers in our series, 167 (75.6%) were Wassel-Flatt type V and 54 (24.4%) were type VII [3]. However, the surgical techniques for type VII CTD, in which an extra thumb appears as a triphalangeal digit but not as a primary digit, are similar to those for type V. In this study, based on the radiographic features of the alignment of the IP and MP joints of the first thumb and their pathoanatomy, we introduced a classification system that merges Wassel-Flatt type V and type VII CTD [1, 3, 4, 15]. To date, no study has evaluated the radiographic characteristics of CTDs with bony attachment at the level of the metacarpus in order to propose a system to facilitate the selection of the surgical strategy. All type C3 CTDs by Wu et al. could be classified according to this system, with type II being the most common (ulnar deviation of the MP joint; 61.5%), followed by type I (good alignment of both the IP and MP joints; 24%), type III (radial deviation of the MP joint; 11%), and type IV (hypertrophic epiphysis; 5%). This finding is important because the alignment of the IP and MP joints of the main thumb, as well as its size, may influence the choice of surgical treatment [19, 20]. In our series, there were only 6 (2.7%) hypoplastic duplications of comparable size, so excision of the extra thumb, soft tissue and bone reconstruction can be performed as a primary option instead of the Bilhaut-Cloquet procedure [5, 6, 11, 12]. In particular, the Bilhaut-Cloquet technique has some limitations, including physeal growth arrest, joint stiffness, technical difficulty in joining all segments of a duplicated thumb, and nail plate deformity [19–22]. In this study, we found that type III, type II, and type I CTDs with hypoplastic duplications of comparable size accounted for only 4.8%, 1.5%, and 1.9% of cases, respectively.
In our opinion, surgical treatment should vary according to the four subtypes of type C3 CTD according to Wu et al. [15]. Previous research has described age at surgery as an important prognostic factor because it reduces the risk of anesthesia, lack of functional pinching, and lack of perceived aesthetic appearance. In our cohort of patients, we observed that children with worse functional and aesthetic outcomes were younger than those with good results, both functionally and aesthetically.
For patients with type I deformity, treatment should include excision of the extra thumb, flattening of the bifurcated metacarpal and reconstruction of the thenar muscle of the main thumb (Fig. 2) [3, 13].
In cases of type II deformity, surgery should include excision of the accessory thumb, reconstruction of the thenar muscle, and corrective osteotomy of the metacarpal (Fig. 3), although no study has evaluated the amount of metacarpal deviation that requires osteotomy in this specific subtype of CTD. However, there are some studies of Wassel type IV CTD that recommend metacarpal osteotomy based on the amount of MP joint deviation. For example, Luangjarmekorn et al. reported that corrective metacarpal osteotomy should be performed when MP joint deviation exceeds 30° [23], whereas Gao et al. suggested corrective osteotomy when MP joint deviation exceeds 15° [22], while Hong et al. recommended a cut-off of 10.8° [24]. However, their studies may not accurately reflect the true anatomical deviation due to the inaccurate deviation angle measured on a non-standardized anteroposterior or posteroanterior thumb radiograph before surgery. In particular, the pathoanatomical characteristics of the accessory digits, which are connected to the main digits by a joint that is significantly different from the bone, may influence the selection of surgical strategies. For our patients, we suggest that metacarpal osteotomy should be performed if a preoperative standard AP radiograph of the thumb shows deviation of the metacarpal.
Type III deformity is characterized by complex pathoanatomy, including 1st -2nd metacarpal contracture and metacarpal deformity resulting in MP joint dislocation with radial deviation but no IP joint deviation, ulnar capsular laxity of the MP joint, abnormal position of the thenar muscle, and absence of hypoplastic duplications of comparable size in most cases (86.4%). In these patients, surgical management includes release of the contracture, ulnar capsular tightening of the MP joint, reconstruction of the thenar muscle with or without reconstruction of the ligament/periosteal sleeve, and metacarpal osteotomy (Fig. 4).
Surgical strategies for patients with type IV deformity must take into account the complex pathoanatomic features of the deformity, including hypertrophic epiphysis of the distal phalanx and ulnar deviation of the metacarpal, as well as abnormal position of the thenar muscle and proximal phalangeal deformities (Fig. 5A). Surgery should include excision of the accessory thumb, corrective osteotomy of the hypertrophic epiphysis of the distal phalanx, reconstruction of the ligament/periosteal sleeve, and repositioning of the thenar muscle, with indications for corrective osteotomy of the metacarpus similar to those of type II (Fig. 5B). In addition, one case in our study also had a bony deformity of the proximal phalanx with the need for a proximal phalangeal osteotomy.
It is important to note that this study has a number of limitations. First, it is a descriptive and retrospective study. However, it includes a substantial cohort of patients with Wu et al. type C3 CTD, which allows the identification of 4 different subtypes according to their pathoanatomic features. Second, although the radiographic features of type C3 CTD may provide practical clinical information, they have not been tested to guide surgical management or to determine their reliability, and therefore, the impact on surgical management remains potential. Third, only a limited number of patients have undergone excision and reconstruction of the supernumerary thumb using our proposed procedure. Therefore, to verify their reliability and practicality, further clinical studies with large sample sizes and long-term follow-up of patients treated with different procedures should be conducted.
Conclusions
A comprehensive and easy-to-use classification system is needed in clinical practice. Our proposed system, based on radiographic pathoanatomy, identifies four distinct subtypes of C3 CTDs and may improve interprofessional communication and theoretically guide surgical indications. However, our results are preliminary and further research is needed to validate them.
Author contributions
All the authors have been actively involved in the planning and enactment ofthe study, and have also assisted with the preparation of the submitted article. JianPing Wu, MM, (Contribution: designed this study, performed measurements and prepared the manuscript). Kai Hong, PhD, (Contribution: statistical analysis and performed measurements). Hai Zhao, MM, (Contribution: statistical analysis and performed measurements). Jun Chu, MM, (Contribution: collected and extracted the data). ChenChen Xu, MM, (Contribution: collected and extracted the data). YuanXin Zhu, PhD, (Contribution: collected and extracted the data). XingQi Zhao, PhD, (Contribution: performed measurements). MingWei Zhu, PhD, (Contribution: performed measurements). JingChun Li, MM, (Contribution: statistical analysis). YiQiang Li, PhD, (Contribution: statistical analysis). YuanZhong Liu, BM, (Contribution: statistical analysis). Federico Canavese, PhD, (Contribution: made the critical revisions). HongWen Xu, PhD, (Contribution: made the critical revisions). All authors read, provided feedback, and approved the final manuscript.
Funding
This work was supported by funding from Guangzhou Municipal Health and Family Planning Commision (20231A011039) and Basic and Applied Basic Research Foundation of Guangdong Province (2023A1515220214).
Data availability
No datasets were generated or analysed during the current study.
Declarations
Ethical approval
Approval from our institutional review board was obtained for this retrospective study. All procedures performed in studies involving human participants 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.
Competing interests
The authors declare no competing interests.
Clinical trial number
Not applicable.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
JianPing Wu, Kai Hong and Hai Zhao contributed equally to this work.
Contributor Information
JianPing Wu, Email: gfewjp@163.com.
HongWen Xu, Email: gzfezxgk@163.com.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
No datasets were generated or analysed during the current study.