The incidence of congenital upper limb and hand abnormalities is approximately 0.25% (1, 2). Among these, polydactyly and syndactyly are clinically common (3), while congenital metacarpal agenesis is rare, typically presenting as cleft hand deformity. Research on congenital fifth metacarpal agenesis remains extremely limited; a literature review identifies only four relevant reports (Table 1) (4–7). Notably, complex hand malformations involving fifth metacarpal agenesis combined with polydactyly and syndactyly (without associated syndromes) have not been documented in the literature.

For congenital metacarpal absence, no classification systems or treatment guidelines exist, though thumb polydactyly classifications have been proposed (8). The Oberg-Manske-Tonkin (OMT) classification roughly categorizes congenital hand malformations (9, 10). Surgery for hand deformities is typicallyperformed at 6–18 months to restore partial function and improve aesthetics (11). Surgical approaches include skin incision techniques (12–15), bone reconstruction (15, 16), and muscle insertion repair (17), all aimed at enhancing finger function. Thus, hand surgeons must design personalized plans to minimize complications and optimize mobility/appearance.

This case report describes congenital absence of the fifth metacarpal with polydactyly and syndactyly, presenting surgical management, early follow-up outcomes, and a literature review. The study aims to: (1) assess the rationale and feasibility of surgical intervention; (2) evaluate early efficacy by comparing pre- and postoperative status; (3) explore the combination of fifth metacarpal absence with other malformations and derive treatment strategies from existing literature.

The optimal surgical timing for congenital hand malformations is generally 6–18 months (18, 19), with the primary goals of restoring partial hand function and achieving satisfactory aesthetics (20). Delayed surgery may exacerbate deformities during growth, impairing hand function and quality of life; aesthetic deficits can also impose social and psychological burdens (21). Thus, preoperative confirmation of diagnosis, associated abnormalities, and syndromic associations is critical. Inaccurate diagnosis or inadequate differential diagnosis may worsen outcomes (22).

For congenital fifth metacarpal agenesis with associated malformations, management strategies vary based on finger function. Buckwalter et al. (6) reported 7 cases of congenital fifth metacarpal agenesis, 4 of which were associated with other malformations. Among these 7 patients, 2 with thumb agenesis underwent index finger pollicization, 1 underwent web space deepening, 1 underwent little finger amputation, and the remaining 3 opted for conservative management. Eren F et al. (7) reported a case of bilateral congenital fifth metacarpal agenesis without associated malformations. The patient presented with normal hand function but sought medical attention due to cosmetic dissatisfaction, ultimately opting for conservative management. Peker F et al. (5) reported a case of congenital absence of the metacarpal, where the ring and little fingers shared the fourth metacarpal to form a common metacarpophalangeal joint. The left ring and little fingers showed reduced web space at the proximal interphalangeal joints, with hypoplasia and shortening compared to the contralateral side. Despite limited motion without significant dysfunction, the patient sought surgery for cosmetic concerns, undergoing proximal phalangeal wedge osteotomy of the little finger with mini-plate fixation of the osteotomy site. Barnett SA et al. (4) reported a case of congenital fifth metacarpal agenesis in the right hand, with the ring and little fingers sharing the fourth metacarpal to form a common metacarpophalangeal joint. The inter-digital web space between the ring and little fingers was shallow, and the little finger exhibited flexion deformity with hypoplasia; other fingers had normal function. The patient ultimately underwent little finger amputation.

In our reported case, unlike those in the previous literature review, congenital absence of the fifth metacarpal is accompanied by polydactyly and syndactyly, without other limb malformations or associated syndromes. Previous surgical interventions described in the literature have limited reference value for surgical management. We were inspired by the study by Bergmeister K et al. (23) in which the entire fifth metacarpal was resected due to metacarpal bone tumor. Subsequently, autologous iliac bone graft was harvested and fused with the fourth metacarpal, followed by fixation of the proximal end of the proximal phalanx of the little finger to the grafted iliac bone at a 30° flexion angle. Postoperative follow-up showed that the patient had good hand function, except for fusion at the metacarpophalangeal joint of the little finger. Thus, we divided the articular surface of the third metacarpal into two separate surfaces using bone wax, forming joints with the middle and ring fingers respectively. Preliminary follow-up results showed satisfactory outcomes, though long-term functional efficacy requires further observation. For joint ligament management, contracted-side ligaments were released while the contralateral ligaments were sutured; partial tendon preservation was performed to enhance functional mobility of the remaining fingers. Regarding the transposition of the ring finger to the third metacarpal and the little finger to the fourth metacarpal for metacarpophalangeal joint formation: preoperatively, the ring finger had minimal voluntary movement, whereas the little finger retained voluntary function. Our strategy prioritized preserving fingers with voluntary function to maximize residual hand function, a decision validated by initial follow-up. Additionally, the distal phalanx of the supernumerary digit was preserved to avoid nail bed injury and optimize the cosmetic appearance of the ring finger.

In previously reported cases, conservative management or web space deepening was preferred for patients with good function but cosmetic dissatisfaction. For those with hypoplastic little fingers and limited mobility, little finger amputation was an option.Given the greater rarity and complexity of our reported case compared to previous ones, more considerations were required to achieve both cosmetic improvement and functional recovery.

Given the paucity of reference cases, surgical planning was guided by principles for polydactyly and syndactyly in children. Intraoperatively, after resecting the original fourth finger, the third metacarpal head was split into two articular surfaces; the phalanges and metacarpals were then realigned and stabilized with Kirschner wires. Although a satisfactory cosmetic outcome was achieved postoperatively, no significant improvement was observed in the mobility of the 3rd to 5th fingers. Potential contributing factors include: 1. Incomplete matching of the metacarpophalangeal joints after realignment, resulting in restricted joint mobility; joint stiffness secondary to Kirschner wire fixation; 2. Incomplete tendon-bone healing following tendon preservation and insertion reconstruction; hypoplasia of digital tendons with insufficient flexion/extension strength; tendon adhesions; 3. Joint capsule contracture with restricted mobility; 4. Inadequate postoperative rehabilitation exercises. In contrast to the approach described by Bergmeister K et al. (23), we avoided direct metacarpophalangeal joint fusion in functional position, as our patient was a 7-month-old infant with growth potential.

We report a rare case of congenital fifth metacarpal agenesis combined with polydactyly and syndactyly. Preoperatively, the left hand presented with obvious deformity and restricted function. Following preoperative deliberation, the aforementioned surgical procedures were performed. Initial follow-up showed satisfactory outcomes, though long-term results require further follow-up and observation.