Congenital thumb dysplasia
【Overview】.
Thumb hypoplasia is a large group of congenital thumb deformities. In thumb hypoplasia, from short thumb deformity to complete absence of the thumb, all belong to the category of thumb hypoplasia. It can be a malformation that exists alone or may be one of the symptoms of the syndrome.
[Etiology and pathogenesis
The etiology of thumb hypoplasia is unknown. It may be due to defective formation of embryonic limb buds during embryonic development, and its pathogenesis is similar to that of radial bulbar hand, or it may be caused by impaired differentiation of limb buds during development. In the past, a considerable number of infants with congenital hand and upper limb deformities were delivered after pregnant women took reactive stop. Genetic factors also play an important role.
Diagnostic points
Typing and staging
Thumb hypoplasia is characterized by a thin, small, short thumb, incomplete function, or complete absence of the thumb. Foreign scholars classify thumb dysplasia into five categories: ① short thumb deformity; ② inward thumb dysplasia; ③ abductor thumb dysplasia; ④ floating thumb deformity; ⑤ missing thumb. This classification is difficult to define for complex thumb deformities and is less commonly used clinically. To overcome these deficiencies, Wang Wei classified thumb dysplasia into the following five categories to facilitate the selection of treatment options.
Category 1 Congenital absence of the thumb. The thumb is completely absent in a four-fingered deformed hand. The thumb, 1st metacarpal, carpometacarpal joint and greater trochanteric muscle are absent.
Type 2 Polydactylic thumb loss. The thumb is absent, the affected hand has five or six fingers, the radial marginal finger is a typical three-jointed phalangeal finger with elongated fingers, the 1st metacarpal is a finger-type metacarpal, the center of ossification is located at the distal end of the metacarpal, and the greater interphalangeal muscle is absent.
Type 3 Floating thumb. The thumb is shaped like a fleshy pendant, with only the cutaneous tip dangling from the radial edge of the hand. The thumb has tiny phalanges, the first metacarpal joint is absent, and the first metacarpal bone and carpometacarpal joint are severely hypoplastic or absent. In addition to the skin and subcutaneous tissue, the floating thumb has blood vessels and nerves attached to the hand, and there is no attachment of bone or joint.
Category 4 Non-functional short thumb deformity. The thumb is short, small, and thin, and its degree of shortening varies. The 1st metacarpal is very small, and the metacarpophalangeal and carpometacarpal joints are severely dysplastic, with no stable joint structures. The thumb attachment site may be located in a different plane on the radial side of the hand, there is no functional tiger’s mouth, or the tiger’s mouth is narrow, the greater interosseous muscle is hypoplastic, and the thumb extensor and flexor tendons are hypoplastic, which is a category between the floating thumb and the dysfunctional thumb deformity.
Category 5: Inadequate short thumb deformity. Characterized by a short thumb, the end of the thumb cannot reach near the interphalangeal joint of the index finger and the thumb is thin. This type of thumb may have a short metacarpal or may be a deformity that exists in isolation. Different degrees of short thumb deformity have different morphological and functional defects, which can be summarized as follows: (1) short, thin or flat broad thumb; (2) narrow or deformed tiger’s mouth; (3) dysplasia of the greater interphalangeal muscle; (4) instability of the metacarpophalangeal joint and laxity of the ulnar collateral ligament; (5) dysplasia or absence of the extensor tendon; (6) absence or dysplasia of the finger flexor tendon, etc.
In the classification of thumb dysplasia, the classification of Manske (1995) has some reference value (Table 1).
In the above classification, categories 1, 2 and 3 are all short thumb deformities, and in the description of category 2 and 3 deformities, the functional defects of short thumb deformities are described in more detail and have practical value (Figure 1).
Table 1 Classification of thumb hypoplasia
Figure 1 Classification of congenital thumb hypoplasia
A. congenital thumb deficiency; B. polydactylic thumb deficiency; C. floating thumb;
D. Non-functional short thumb deformity; E. Non-functional short thumb deformity
【Treatment Overview
The treatment of thumb hypoplasia includes two aspects: one is the reconstruction of the thumb, and the other is the functional reconstruction of the dysfunctional thumb. Reconstruction of the thumb: Applicable to thumb dysplasia of the 1st, 2nd and 3rd categories of Wang Wei’s classification. The functional reconstruction of thumb insufficiency is applicable to the functional reconstruction of thumb deformity of the 4th and 5th category of thumb deformity and the 2nd and 3rd category of thumb deformity of Manske’s classification, i.e. short thumb deformity.
The methods of bunion reconstruction are finger bunion, toe graft bunion or other surgical methods. In clinical practice, finger bunion is the preferred surgical option, and toe graft is also an optional surgical option. By 1997, several cases of toe transplantation for congenital bunion reconstruction had been performed worldwide, and the follow-up results were satisfactory, proving that they functioned well and that the transplanted toes could grow with age.
1.Finger bunionization Can be used for deformities such as bunion deficiency, multi-finger bunion deficiency and floating bunion, and also for radial bulbar hand bunion defect reconstruction. In this type of deformity, the common pathological and anatomical features are.
(1) Absence of the 1st metacarpal bone, or severe hypoplasia with the absence of a saddle-shaped 1st carpometacarpal joint capable of movement in 3 axial directions.
(2) Absence or severe dysplasia of the thumb phalanges and lack of a broad 1st phalanx.
(3) Absence or severe hypoplasia of the greater interphalangeal muscle group, absence or severe hypoplasia of the thumb extension, thumb flexion and thumb extension longus;
(4) It is often associated with dysplasia of the blood vessels and nerves of the entire hand and forearm. These deformities may be associated with abnormal vascular development of the limbs and other organs, and should be examined and diagnosed before surgery to exclude contraindications to surgery.
Timing of surgery: Buck-Gramcko has performed this type of surgery on infants as young as 11 weeks. As long as the child is in good general condition, surgery can usually be performed at 1 to 3 years of age. At this time, the tendons, vessels and nerves are very small and require microscopic repair in order to effectively recreate the function of the thumb and its power tendons.
In the case of finger bunion, the design of the flap should be done first according to the deformity, then the 1st metacarpal and carpometacarpal joints, the bunion finger to metacarpal position and the power reconstruction of the bunion finger should be carried out, and the postoperative protection with braces and functional training should be used.
2, Toe graft thumb reconstruction Toe graft thumb reconstruction or other methods of thumb reconstruction can be used for congenital bunion dysplasia, but the preferred option is still finger thumbing surgery.
3. Treatment of Class 4 and 5 bunion dysplasia Treatment for short bunion deformity and other associated deformities and functional defects. Since the degree of morphology and functional defects of short thumb deformities varies greatly, there is a great deal of flexibility in the design of treatment methods, and it is advisable to involve an experienced physician when designing the surgical plan for the first time.
The correction of short thumb deformity and functional defects include: ① short thumb; ② narrow tiger mouth; ③ dysplasia of the inner hand muscle; ④ dysplasia of the outer hand muscle; ⑤ instability of the metacarpophalangeal joint, often manifested as laxity of the ulnar collateral ligament. For these elements, lengthening of the thumb phalanx and metacarpal bone lengthening, correction of tiger mouth deformity, transfer of tendons to reconstruct the dynamic function of the dysplastic external hand muscles, and reconstruction of the opposite metacarpal muscle is appropriate for dysplastic internal hand muscles, mainly the large interphalangeal muscle. The lateral collateral ligaments are fixed with anterior transposition, or tendon membrane grafting and lateral collateral ligament reconstruction to tighten the lax lateral collateral ligaments on the ulnar side of the metacarpophalangeal joint.