Groningen, The Netherlands
Thumb and Finger Abnormalities
Extra Thumb or Finger(s)
Complaint: there is an extra thumb or there are too many fingers.
Assessment: there is an extra thumb or there are more than four fingers.
radial polydactyly (preaxial polydactyly, extra thumb)
ulnar polydactyly (postaxial polydactyly, extra little finger)
central polydactyly (extra finger)
ulnar dimelia (mirror hand)
Explanatory note: polydactyly. There is an extra thumb, little finger or other finger.
An extra thumb occurs in eight out of every 10,000 births. What is often called a double thumb is in fact a split thumb and is generally unilateral. The most accepted classification is that of Wassel (Fig. 8.1). This classification is based on the level of the split, starting at the distal phalanx. Splitting of the thumb tends to be sporadic. Only with a triphalangeal thumb may there be an autosomal dominant anomaly that may be hereditary. Other abnormalities that can be present are congenital anomalies of the spinal column, tibial hypoplasia or aplasia, cleft palate or anal atresia. A split thumb is also present in several syndromes (Table 8.1).
Wassel classification (1969) for a split thumb. The classification is based on the level of the split, starting in the distal phalanx. Type I: splitting of part of the distal phalanx (2 %). Type II: splitting up to the interphalangeal joint (15 %). Type III: splitting up to the proximal phalanx (6 %). Type IV: complete splitting-up of the thumb (43 %). Type V: splitting up to the metacarpal bone (10 %). Type VI: splitting up to the carpometacarpal joint (4 %). Type VII: complete double thumb, in which one of the split thumbs has three phalanges (triphalangeal thumb) (20 %) (Redrawn from: Wassel HD. The results of surgery for polydactyly of the thumb. Clin Orthop Relat Res. 1969;64:175–93)
Syndromes with a split or extra thumb
Acrocephalopolysyndactyly (Carpenter type)
An extra little finger is the most common type of polydactyly (Fig. 8.2). According to the classification of Stelling and Turek there are three types: type A presents with a rudimentary little finger without phalanges. In type B there is a complete duplication of the little finger. In type C not only the little finger but also the fifth metacarpal is duplicated (Fig. 8.3). Type C is very rare.
Extra little finger of the left hand
According to the classification of Stelling (1963) and Turek (1967), there are three types of extra little fingers. In type A there is a rudimentary little finger without phalanges, in type B there is a completely duplicated little finger, and in type C not only the little finger but also a duplicated fifth metacarpal bone (Redrawn from: Stelling F. The upper extremity. In: Fergusion AB, editor. Orthopedic surgery in infancy and childhood. Williams & Wilkins; 1963. p. 304–8; Turek SL. JB Lippincott, Philadelphia. 1967;123)
An extra little finger is often associated with other hand anomalies such as syndactyly, triphalangeal thumb, absence of a thumb, nail anomalies and a coalition of carpal bones. These types of hand anomalies are also seen combined with radioulnar synostosis or anomalies of the lower extremity such as polydactyly of the toes, curvature of the femur, hypoplasia or aplasia of the tibia or fibula, and other irregularities of the postural and locomotor apparatus such as hemivertebrae or dwarfism. Additional anomalies may also be seen such as a hydrocephalus, harelip, dental abnormalities, ocular abnormalities, deafness and mental retardation. There may also be other anomalies such as hypogonadism, horseshoe kidney, bladder obstruction, a micro penis, anal atresia and Hirschsprung disease (large intestine). The extra little finger can also be part of a syndrome (see Table 8.2).
Syndromes with an extra little finger
Biemond II syndrome
Ellis-van Creveld syndrome
Orofaciodigital syndrome type I
Orofaciodigital syndrome type II
In a central polydactyly there is an extra index, middle or ring finger (3.5 % of all polydactylies). Tendons, nerves and blood vessels of the extra finger tend to be abnormal. The same applies to growth plates of the extra finger, often leading to ulnar or radial deviation.
Ulnar dimelia is also known as mirror hand because the ulnar part of the forearm and hand are present as a mirror image. A mirror hand is a very rare and a mostly unilateral anomaly. The entire literature describes fewer than 100 cases. There is a double ulna and ulnar side of the hand, while the radius and the radial part of the hand are absent. The thumb is always absent. Both parts of a mirror hand are usually not entirely symmetrical, and seven fingers are more common than eight (Fig. 8.4). The function of the hand is very limited. The elbow and the wrist are usually widened, and the forearm and upper arm tend to be shorter. There may be irregularities in the shoulder blade, clavicle, humerus and shoulder joint. The capitulum is absent and the trochlea is duplicated in the elbow. The elbow is generally stiff. The biceps and brachialis muscles do not insert into the forearm but into the distal part of the humerus. The musculature and vascular systems of the forearm and hand are also abnormal. Another irregularity that often occurs on its own is fibular dimelia, with a duplication of the fibula and outer toes and absence of the tibia and the tibial part of the foot and the big toe and second toes.
Ulnar dimelia or mirror hand. This is a duplication of the ulna and the ulnar side of the hand, with an absent radius (starting at the elbow) and radial part of the hand. The thumb is always absent. Both parts of a mirror hand tend not to be entirely symmetrical, and seven fingers are more common than eight (Redrawn from: Green DP. Operative hand surgery. 2nd ed. Churchill Livingstone. New York, Edingburgh, London, Melbourne; 1988)
Supplementary assessment: if a mirror hand is suspected, X-rays of the hand, elbow, forearm and wrist (Fig. 8.4).
Primary care treatment: none. Occasionally the general practitioner would sometimes tie a tight string around the base of a rudimentary little finger causing necrosis. This is no longer carried out because of the risk of neuroma formation, but also because it is often difficult for parents to accept this situation. One should be aware of other possible additional congenital anomalies.
When to refer: referral to a hand surgeon between the first and second years of life.
Secondary care treatment: surgery is recommended between 9 and 15 months of age.
One part of the split thumb tends to be clearly larger than the other part. In such cases, the smallest part is excised (Fig. 8.5). In types I, II and III (Fig. 8.1) the central part is resected and the remaining parts are coapted (Bilhaut-Cloquet procedure). Sometimes it makes sense to limit resection of the central part to the soft parts and nails (Fig. 8.6).
Treatment of extra (left) thumb. Most of the time one part of the split thumb is clearly larger than the other. In such cases, the smallest part is removed. In this particular case, with a completely split thumb, a part of the radial side of the metacarpal head has to be resected, and to prevent instability reconstruction of the radial ligament has to be carried out (Redrawn from: Marks TW, Bayne LG. Polydactyly of the thumb: abnormal anatomy and treatment. J Hand Surg Am. 1978;3:107–16)
(a) The central part can be resected (Bilhaut-Cloquet procedure) if the splitting is equally large in types I, II and III. (b) Sometimes it makes sense to limit resection of the central part to the soft tissue and nails (Redrawn from: Marks TW, Bayne LG. Polydactyly of the thumb: abnormal anatomy and treatment. J Hand Surg Am. 1978;3:107–16)
Type A: resection of the rudiment. Type B: ablation of the extra little finger. Type C: resection of the extra little finger and metacarpal.
Resection of the extra finger. This is technically very difficult and it is a tall order to obtain an acceptable appearance and function in the hand in such cases.
This is extremely difficult, if not impossible to treat, and the procedure can only be performed by a highly experienced hand surgeon specialized in congenital hand abnormalities.
Gigant Growth of Thumb and/or Finger(s)
Complaint: immediately after birth it is noticeable that the thumb and/or one or several fingers are much larger than normal.
Assessment: overgrowth of the thumb and/or fingers (Fig. 8.7). There is normal sensation. The interphalangeal and metacarpophalangeal joints have normal mobility in children.
Macrodactyly of the left hand
non progressive type
Explanatory note: macrodactyly. This is a rare, non-hereditary anomaly that accounts for 0.9 % of all congenital hand abnormalities. In 10 % of cases there is a syndactyly. The cause is unknown. The joints of the affected thumb or finger may become stiff during adulthood. There are two types of macrodactyly: non-progressive and progressive.
Non progressive type
During growth the thumb and/or finger(s) remain proportional to the normal digits.
The macrodactyly becomes disproportionately larger than the rest of the hand during childhood.
Supplementary assessment: hand X-rays.
Primary care treatment: none.
When to refer: the parents usually want advice with referral to a specialist (pediatric plastic surgeon or hand surgeon).
Secondary care treatment: macrodactyly. Removal of the excess soft parts on one side of the affected thumb or finger(s), and 3 months later on the other side. Simultaneously, all the growth plates of the affected thumb or finger(s) are curetted. The operation is carried out when the thumb and/or finger(s) have reached adult length. It may be helpful to compare the situation with the thumb or finger(s) of the parent of the same sex. There are also shortening methods with segmental resection of the nerves that are then microscopically sutured end-to-end if the above technique is insufficient. The most common complication is recurrent macrodactyly of the thumb or finger(s) and necrosis of the skin. In some cases the entire affected finger and metacarpal bone have to be resected.
Complaint: crooked or bent finger.
Assessment: crooked or bent finger.
Explanatory note: camptodactyly. This is a congenital flexion contracture of the proximal interphalangeal joint (Fig. 8.8). It affects 1–2 % of the population, usually the little finger. The anomaly is bilateral in two-thirds of cases. When it is unilateral it tends to affect the right hand. There are three types of camptodactyly. Type I: is seen in infancy. Type II: is seen in adolescence. Type III: occurs as part of an underlying syndrome such as the Russel-Silver syndrome.1
Camptodactyly. This is a congenital flexion contracture of the proximal interphalangeal joint, usually of the little finger (arrow)
This is a rare, progressive palmar and radial curvature of the distal phalanx usually involving the little finger (Fig. 8.9). The cause is unknown. It typically affects preadolescent females, usually bilaterally. This anomaly doesn’t usually cause many problems, and treatment is generally not required.
(a) Kirner deformity. This is a progressive, palmar and radial curvature of the distal phalanx of the little finger. (b) It is only in rare cases that multiple osteotomies are necessary to correct it (Redrawn from: Carstam N, Eiken O. Kirschner’s deformity of the little finger. J Bone Joint Surg. 1970;52A:1663–5)
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