Anatomical Variations in Bilateral Hand Oligodactyly: A Case Analysis of Cleft Hand

Abstract

Background: Hand oligodactyly is a rare congenital malformation characterized by fewer than five digits. Although several clinical and radiological studies have been reported, detailed anatomical investigations remain scarce. This study aimed to describe the morphological characteristics of bilateral hand oligodactyly through dissection. Case Presentation: A bilateral hand oligodactyly with thumb and 3 fingers on each hand was found in a 77-year-old Korean female donor. The study was approved by the Institutional Review Board of Sungkyunkwan University (IRB No. SKKU 2023-02-012). Results: Diverse variations were observed in most structures of the hand, including the palmar aponeurosis, tendons of the flexor digitorum superficialis, the flexor digitorum profundus, and the flexor pollicis longus, lumbricals, interossei, and metacarpals. Connections between flexor and extensor tendons were also found, and each variation differed between the two hands. Conclusions: These structural differences highlight the developmental complexity of hand oligodactyly and offer valuable insights for facilitating appropriate surgical strategies. This study has also provided new insights into congenital anomalies that underscore their relevance in developmental biology.

1. Introduction

Hand oligodactyly is a congenital anomaly in which some digits are absent, which is a common feature of the congenital malformations of the upper limb. The latter can be classified into four primary categories: radial dysplasia (also referred to as radial longitudinal deficiency), ulnar dysplasia (ulnar longitudinal deficiency), cleft hand (also known as split hand, ectrodactyly, lobster claw, or central oligodactyly), and symbrachydactyly [1,2,3].

Previous studies have documented various cases of hand oligodactyly and highlighted the improvements in hand function that are possible following surgical interventions [1,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. For example, Baek and Kim (2016) [5] demonstrated that surgical techniques such as syndactyly division, corrective osteotomy, flexor plasty, and joint arthrolysis can enhance both the functionality and appearance of the hand by addressing the specific anatomical and functional needs of specific patients. Similarly, Sykes (1991) [13] described that both typical and atypical cleft-hand deformities vary in severity and so require individualized surgical planning. That author also mentioned that surgical treatments should be performed early, and that these procedures often involve complex reconstructions of both bone and soft tissue in severe cases.

Most of the previous studies have primarily focused on external contours, radiographic findings, and ultrasound appearance, with detailed anatomical investigations of internal structures in hand oligodactyly being rare. For instance, a British professional tennis player with congenital oligodactyly has achieved remarkable competitive success, bringing broader awareness to this anomaly. However, a thorough anatomical study of oligodactyly has yet to be reported.

This study aimed to elucidate the detailed anatomical variations in cases of bilateral hand oligodactyly. The analysis has provided insights into the structural characteristics and variations associated with this rare malformation. The results of this study are also expected to deepen the understanding of the developmental biology underlying congenital hand anomalies and provide a foundation for developing more effective surgical strategies for these deformities.

2. Case Presentation

A case of bilateral hand oligodactyly with thumb and 3 fingers on each hand was found in a Korean 77-year-old female donor. The anatomical structures were examined bilaterally in the hands and forearms of the individual. After documenting the characteristics of muscles, tendons, nerves, and arteries, they were all removed to leave only the bones. This process enabled a detailed analysis of the hand joints, the number and types of individual bones, as well as their shapes. This study received approval from the Institutional Review Board of the Sungkyunkwan University (IRB No. SKKU 2023-02-012; approval date: 8 February 2023).

3. Results

The donor exhibited bilateral hand oligodactyly, with each hand having a thumb and 3 fingers and both hands showing cleft-hand deformities, which were more severe on the right. Both forearms appeared normal.

3.1. Left Hand

3.1.1. Forearm and Wrist

The distal antebrachial fascia (ABF) was thickened, and the median nerve (MN) was widened toward the carpal tunnel (Figure 1A). Forearm muscles appeared normal, but the flexor digitorum superficialis (FDS) tendon for the fourth digit was thin (Figure 1B). The FDS tendons to the third and fourth digits were superficial, while that to the second was deeper. The pronator quadratus extended more proximally than usual.

3.1.2. Palm

Several tendinous slips of the FDS attached to the extensor expansion (EE) and the metacarpophalangeal (MCP) joint of the second digit. In the web between the second and third digits, the second tendon of the FDP extended dorsally and attached to the extensor digitorum communis (ED) tendon that was attached to the second digit (Figure 2A,B). An unusual connection was observed between the FDP and the flexor pollicis longus (FPL) tendons (Figure 2C). Three lumbricals and three palmar interossei were identified.

3.1.3. Dorsum

The MCP joint of the second digit was formed by two metacarpals (second metacarpal [MC2] and third metacarpal [MC3]), with dual ED tendons inserting on this digit (Figure 3A). Five metacarpals were confirmed, with a protruding third metacarpal [MC3] attached with the fourth metacarpal (MC4). Among four dorsal interossei, the third was small and thin (Figure 3B).

3.2. Right Hand

3.2.1. Forearm and Wrist

Forearm muscles were typical. The ABF was thickened distally, but the MN appeared normal.

3.2.2. Palm

A thin FDS tendon was attached to the deep side of the flexor retinaculum (FR), and the palmar aponeurosis extended into deep structures (Figure 4A). FDS tendons inserted into the second and third digits, with one dividing into two slips at the third digit (Figure 4B). The FPL tendon inserted into the second digit, while no extrinsic tendon attached to the first digit. FDP tendons attached to the third and fourth digits (Figure 4C). Multiple tendinous slips from the FDP extended toward the ED, thick fascia that covered the surface of MC3, and deep transverse metacarpal ligament of digit (Figure 5). A delicate tendon from the FR inserted into the MCP joint of the first digit (Figure 6).

Three lumbricals were observed. One formed a lambda shape, extending to the dorsum and EE of the third digit. Another arose proximally and attached to fascia over MC2 (Figure 7). Deep transverse metacarpal ligaments were prominent.

3.2.3. Dorsum

The EI tendon divided, attaching to the first and second digits. Three ED tendons were present, with one coursing obliquely to the fourth digit. A cleft extended deeply between the second and third digits (Figure 8).

3.3. Bones of the Left and Right Hands

The left hand contained five metacarpals with a horizontal Y-shaped configuration of MC3 and hypertrophy of the second proximal phalanx. The right hand had four metacarpals with a V-shaped fusion between MC3–MC4 and a small accessory bone between MC2–MC3 and the carpus. Capitohamate fusion was present on the right; pisiform was absent on the left (Figure 9).

4. Discussion

This study investigated the rare case of bilateral hand oligodactyly, revealing asymmetrical malformations in bones, muscles, and tendons. Structural anomalies differed significantly between hands. These findings, summarized in

Table 1. Structural variations in bilateral hand oligodactyly.

	Left	Right
Palmar Aponeurosis	Normal	Attached to the Deep Structures Between MC2 and MC3
Wrist	ABF thicker at the distal forearm
Median nerve	Wider at the carpal tunnel and distal forearm	Normal
Radial artery	A distinct branch of the radial artery coursed on the thenar muscles	Normal
Forearm muscles	Normal	Normal
FDS tendon	4	3
FDP tendon	4 (attached to the ED tendon)	3 (attached to the ED tendon)
FPL	Normal	connected to the second digit (like an FDP tendon)
Intertendinous connection between FPL and FDP	Present	Normally absent
PQ	Extended proximally	Normal
PI	3	3
Lumbrical	3	3 (abnormal shapes and attachments)
Deep transverse metacarpal ligament	Distinct and thick between the second and third digits and between the third and fourth digits
ED	4	3
Extensor indicis proprius	Normal	First and second digits
Metacarpal	5	4
DI muscles	4 (first DI had a hypertrophied portion that attached to the radial side of the second digit)	3 (smaller)
Tendon attached to the first digit	Normal	From MCP junction to distal phalanx
Carpal bone	7 (pisiform absent)	7 (capitohamate fusion)
Other	Complicated structures between MC2 and MC3

ABF, antebrachial fascia; FDS, flexor digitorum superficialis; FDP, flexor digitorum profundus; MCP, metacarpophalangeal; FPL, flexor pollicis longus; ED, extensor digitorum communis; DI, dorsal interosseous; MC2, second metacarpal; MC3, third metacarpal; PQ, pronator quadratus; PI, palmar interosseous. Each number indicates the number of each structure.

and Figure 10, provide insights into the variability and developmental complexity of this congenital condition.

In the left hand, MC2 and MC3 articulated with the proximal phalanx of the second digits. The right hand also displayed significant abnormalities, with the absence of one metacarpal resulting in only four metacarpals. This deficiency appeared to have contributed to the cleft-hand deformity being more pronounced in the right hand. An additional small bone was observed in the right hand between the bases of MC2 and MC3 and the carpal bones, which might have arisen from incomplete development of the metacarpals.

Grasping and pinching are fundamental functions of the hand [17], which might have been compromised in the present case. Initiating grasp movements requires finger extension through contraction of the intrinsic hand muscles with flexion of the MCP joint [18,19]. In the present case, the abnormal attachment of the lumbricals might have hindered the proper initiation of the grasp movement. The abnormal connection between the FDP and the extensor might also have disrupted force transmission so as to reduce the grip strength. Furthermore, the absence of one or more fingers in hand oligodactyly leads to a decrease in flexion strength [20]. The pinch movement occurs when the first digit opposes and contacts the second and third digits to grasp an object [21]. The donor in the present study had a second digit that showed radial deviation and a smaller first web space, suggesting that pinch movements would have been performed using the third and fourth digits. Thickening of the second digit might also have hindered pinch movements, potentially affecting actions such as holding a pen [22].

Baek and Kim (2016) [5] classified oligodactyly with a first digit into two types based on the morphology of the thumb and the pattern of missing digits: Type I, featuring a normal first digit, and Type II, characterized by first-digit hypoplasia. In the present donor, the left hand corresponded to Type I, with a normal first digit and an absent central digit, whereas the right hand corresponded to Type II, showing first-digit hypoplasia and a more-severe central ray deficiency. The metacarpals were hypertrophied in cases with a missing central digit in a previous report [5], and the metacarpals in the present donor showed abnormal configurations: horizontal Y and V shapes between the MC2 and MC3 and between the MC3 and MC4 in the left and right hands, respectively. A hypertrophied proximal phalanx of the second digit of the left hand, which articulated with two metacarpals, was observed in the current study.

Conrad and Ezaki (2002) [1] demonstrated a spectrum of oligodactyly in cleft hands, ranging from central clefts with digit incorporation to severe digit loss. In the present donor, the left and right hands exhibited central clefts extending to the metacarpal bases, with four digits remaining, aligning with the type of cleft hand with four digits of the previous report [1]. Swanson et al. (1984) [14] found that capitohamate fusion predominated in the cases of total or partial defects of the ulna with humeroradial synostosis, though trapezium–scaphoid fusion was observed in some instances. Havenhill et al. (2005) [8] similarly reported the capitohamate fusion in a case of ulnar longitudinal deficiency. While the current case involved central ray deficiency rather than ulnar longitudinal deficiency, capitohamate fusion was observed in the right hand.

Tada (1984) [15] reported operative findings for the cases of central ray deficiency of the hand, distinguishing between deficiency and syndactylous types. In the deficiency type, the long flexor and extensor tendons were inserted directly at the bony-defect stump, without connections to adjacent tendons. In contrast, the syndactylous type displayed partial insertion of the flexor and extensor tendons at the bony stump of the third digit, with additional tendinous connections to the adjacent fourth digit. In both the left and right hands of the present case, the FDP tendon crossed dorsally to connect to the ED tendon, which represents an unusual anatomical variation. Additionally, in the left hand, a tendinous slip of the FDS tendon to the second digit was observed attaching to the MCP joint of the same digit. In the right hand, the EI tendon divided into two slips that attached to the first and second digits. The FPL tendon typically inserts into the first digit, but in the right hand this was instead redirected to the second digit, likely resulting in impairments of first-digit flexion, grip strength, and fine motor control.

Limb development and digit development are orchestrated by key signaling centers that coordinate growth along three axes: proximodistal (shoulder to fingertip), anteroposterior (first to fifth digit), and dorsoventral (dorsum of the hand to palm). The apical ectodermal ridge (AER) secretes fibroblast growth factors (FGFs) that promote limb elongation along the proximodistal axis, while the ZPA (zone of polarizing activity) releases Sonic Hedgehog (Shh) that guides anteroposterior patterning [23,24]. The dorsoventral polarity is established by Wnt7a and EN1 signals in the ectoderm [25]. These pathways interact via feedback loops, such as Shh inducing FGF4 in the AER, ensuring coordinated limb development [26]. Disruptions to these mechanisms can lead to defects such as polydactyly (extra digits) or syndactyly (fused digits) [27]. In addition, Wnt signaling, HOX genes, and BMP (bone morphogenetic protein) signaling are associated with congenital limb malformations [28]. Specifically, hand oligodactyly is considered to result from defects in SHH-FGF signaling—which plays crucial roles in cell proliferation and differentiation—that lead to incomplete hand development [29,30].

In conclusion, hand oligodactyly is not merely the incomplete development of bone, but also includes malformation of all related structures including muscles and tendons, as demonstrated in this case of cleft hand. The results of this study have provided valuable anatomical insights into this malformation and useful reference information for understanding its structural complexity, and are expected to help design appropriate surgical treatments.