Mirror hand and its management: a case report

Abstract

Background

Mirror hand is a rare congenital anomaly. Most of these cases are sporadic and associated with defective sonic hedgehog during embryogenesis. In this report, we present the case of a child with this rare congenital anomaly and its management.

Case presentation

A 2.5-year-old Asian female child presented with left-sided Al Qattan type 1A ulnar dimelia with restriction of wrist and elbow range of motion. Radiological examination revealed duplication of ulna with polydactyly. Management of mirror hand is a great surgical challenge, so preoperative planning and staged management is essential for the functional outcome of this condition. We successfully achieved fine and gross motor skills of the hand with acceptable cosmetic results at 2 years of follow-up.

Conclusion

It is crucial to remember that early intervention, ideally between 18 and 24 months of age, is key for optimal functional outcomes. Meticulous preoperative planning and surgical technique are essential. Long-term follow-up and parental counseling about the need for supervised physical therapy are important for managing secondary deformities. Additionally, digital subtraction angiography should be performed to rule out any associated neurovascular malformations.

Introduction

Mirror hand is a rare congenital anomaly of the upper extremities. The typical mirror hand is characterized by a defective preaxial border of the hand and forearm with duplication of the ulna and components of the ulnar ray distally, with all digits in one single plane. This gives an impression of two hands placed opposite to each other with longitudinal fusion of radial rays and radius along the preaxial border. The ulna on the preaxial side is usually hypoplastic with radial deviation of the hand, with a comparatively shorter limb than on the contralateral side [1]. There is an absent thumb with duplication of the carpal bone on the ulnar side. The most consistent finding in the forearm is an absent radius with two ulnae opposing one another, thereby restricting elbow motion (along with poorly developed brachialis and biceps) and forearm rotation (restricted supination). Absent radius is associated with absent wrist extensors, resulting in defective wrist extension [2].

Other associated anomalies of mirror hand include ipsilateral congenital dislocation of the shoulder [3], hypoplastic capitulum [3], duplication of the humeral head [4], syndactyly (bony or soft tissue), and internal organ malformations (congenital hypertrophic pyloric stenosis, multicystic kidney) [5].

There is still debate to delineate the best possible method of surgical treatment of these complex anomalies. There are very few case reports in the literature, probably fewer than 100, with considerable anatomical variations.

Case presentation

We present a case of Al Qattan [6] type 1A ulnar dimelia in a 2.5-year-old female Asian child. The condition involved the left side, featuring an absent thumb, two ulnae, and eight fingers with soft tissue syndactyly of the two most radial digits. There are no associated syndromic features. She was the second child of non-consanguineous parents with insignificant antenatal history. There was no history of any congenital anomaly in her siblings. Systemic examination was normal.

The child had flexion deformity of 10° at the wrist, with a further 20–40° of active range of motion. She has active flexion of 40–50° at the elbow, with limited forearm rotation (Fig. 1). The ipsilateral shoulder range of motion was grossly 90° normal. On examination of the hand, there was a crude finger grasp but no selective fine finger motion.

Fig. 1

Clinical picture of the hand preoperatively

Investigations

On radiological evaluation (Fig. 2) of the upper limb, there was duplication of the ulna articulating with the humerus, and well-formed metacarpal bones except for the middle metacarpal, which was hypoplastic. All the fingers were triphalyngeal, except the fifth most radial finger, which is redundant with two phalanges. There was soft-tissue syndactyly of radial-most digits. Digital subtraction angiography was performed, and aberrant vascular malformations were ruled out.

Fig. 2

Radiograph showing articulation of duplicated ulna with the humerus

Treatment

A two-stage reconstruction of the hand was planned for the child. In stage 1, we planned pollicization of the third radial-most digit for oppositional grasp, along with amputation of two radial-most syndactyly fingers (Figs. 3, 4). After giving the Ezaki incision [7], flaps were raised on the ulnar and radial side of the first web space. The neurovascular bundle of the finger intended for pollicization was identified and followed proximally along with the radial vessel of the ulnar finger up to 1 cm proximal to the bifurcation. Radial-most syndactyly fingers were amputated after ligation of the radial vessel away from bifurcation and subperiosteal dissection of respective metacarpal bone. A dorsal flap was raised in the adipovenous plane, conserving dorsal veins. The fillet flaps with intact vascularity were used to reconstruct the first web space. The dorsal interosseous muscle along with the periosteal strip was hitched to the radial lateral band and palmar interosseous to the ulnar lateral band. The distal epiphysis of the second metacarpal was excised to restrict the growth, and proximally, the metaphyseal flare was cut with a bone cutter. The proximal metacarpal was sutured with distal physis using 2.0 Ethibond to achieve the final position of extension, pronation of 110°, and abduction of 45°. The procedure provided the child with a functional thumb and five fingers (with a nonfunctional redundant finger, i.e., fifth radial-most digit).

Fig. 3

Intraoperative pictures

Fig. 4

Intraoperative pictures

An above-elbow slab was given for 3 months. A polyvinyl chloride opposition splint was given after 3 months, and range-of-motion exercises were advised. Stage 2 was planned after 1 year of primary surgery, in which the nonfunctional fifth most radial digit was amputated with reconstruction of the transverse metacarpal ligament. With this staged approach, we were able to provide the child with an esthetic upper limb with a functional thumb and four digits (Figs. 5, 6).

Fig. 5

Clinical picture of outcome, showing esthetic and functional thumb and four fingers (immediate postoperatively and 2 years postoperatively)

Fig. 6

Clinical picture of outcome, showing esthetic and functional thumb and four fingers (immediately postoperatively and 2 years postoperatively)

Discussion

Mirror hand anomalies are a spectrum of developmental disorders that include duplication of hand and wrist elements to elbow and shoulder involvement. Current literature includes several case reports of ulnar dimelia, all of which are probably incomplete duplications of the hand. The International Federation of Societies of Surgery of the Hand (IFSSH) has classified this anomaly as duplication, although complete substitution of preaxial components is very rare [8].

Most cases of mirror hand are sporadic with very rare genetic syndrome association [9, 10].

Sounders and Gasseling described the possible embryogenesis of the mirror hand as an ectopic location of the zone of polarizing activity cells or defective sonic hedgehog gene, which is involved in anterior–posterior axis differentiation [2, 11]. Other mechanisms described are defects in the positional differentiation of part of the ray which is governed by the HOX gene or translocation breakpoint of the location 14q13 [12, 13].

The literature recommends hand reconstruction before the child’s second birthday, during which time the child develops fine motor skills, which makes the occupational therapy easier after surgery owing to cortical plasticity. It is recommended that pollicization be delayed until the child reaches 18 months of age, to allow sufficient growth of the hand. Surgery would be bit more challenging at a later age (> 3 years) because of ongoing stiffness [3].

In our case, the child presented late after their second birthday and the treatment (Fig. 7) yielded satisfactory results. However, it is crucial to remember that early intervention, ideally at between 18 and 24 months of age, is key for optimal functional outcomes. In our patient, after careful observation by the operating surgeon and occupational therapist, we found that the child was consistently using the third radial-most finger as a thumb (scissoring grasp), which was mobile with robust intrinsic and extrinsic muscle tendon groups, which proves that the child was a good candidate for pollicization. So, we decided that pollicization would help this child to obtain fine motor skills even at 2.5 years of age.

Fig. 7

Timeline of the case report and surgeries performed

The parents were instructed to perform passive range-of-motion exercises of fingers and asked to observe the child while playing to identify the best-suited finger for pollicization. Early pollicization tends to yield better outcomes. Thumb reconstruction in mirror hand is a technically demanding procedure that requires proper preoperative planning owing to the wide variation in anatomy and complexity. Nevertheless, successful outcomes have been reported in neglected cases of mirror hand managed with pollicization and excision of extra digits in adolescent patients [3, 14]. In our patient, the operating surgeon had enough experience in pollicization surgeries. We followed a stepwise technical approach to position the thumb in the desired position and achieved satisfactory mobilization of muscle tendon units during surgery. After surgery, we kept the child under close follow-up by the occupational therapist, who played a crucial role in teaching the child how to use the new thumb to its maximum potential. So, our experience suggests that long periods of physical therapy and training may be essential to maximize cortical reorganization and functional outcome if index is surgery delayed.

Al-Qattan et al. [6] reported a case of mirror hand with polydactyly with one ulna and one hypoplastic radius and described a classification of variations of the mirror hand. Guilty et al. [15] discussed the management and surgical challenges of a true ulnar dimelia case, while Rayan et al. [7] described the anatomical variations in ulnar dimelia cases. Other reported cases include a forearm with both a radius and ulna and eight digits in the hand, and a mirror hand with multiple fingers but distinguishable radius and ulna [2, 4]. Barton et al. described a hand with multiple fingers, two ulnae (one rudimentary), and one radius [16]. Complete duplication of the hand, although rare, has also been documented [17].

Surgical challenges in treating mirror hand arise from neurovascular anatomical variations, such as duplication of the ulnar artery, shortening of the radial nerve, absence of the radial artery, and abnormal arterial arches [18]. Preoperative three-dimensional (3D) printing has been suggested to better understand the complex anatomy before surgery [19]. The goals of surgical management in mirror hand include pollicization of the best-suited digit (better functional digit on the preaxial border) along with selective amputation of supernumerary digits. The extra redundant skin and intrinsic musculature of amputated digits are used for reconstruction of the first web space and thenar eminence to create a functional thumb. The extensor tendons of ablated digits can be used to augment the wrist extensors if there is a preoperative flexion deformity of the wrist.

Conclusion

It is crucial to remember that early intervention, ideally at between 18 and 24 months of age, is key for optimal functional outcomes. Apart from age, the other crucial factors that define the outcome are meticulous preoperative planning, surgical technique, surgeon experience, and postoperative occupational therapy. Long-term follow-up and parental counseling about the need for supervised physical therapy are important for managing secondary deformities. Additionally, digital subtraction angiography should be performed to rule out any associated neurovascular malformations.