Congenital thumb polydactyly is one of the most common clinical hand deformities in children. Due to its various types and significant impact on hand function, the postoperative outcome is often variable. The timing of surgery for congenital thumb polydactyly has not yet reached a unified conclusion and is one of the main reasons affecting postoperative outcome. Data and methods I. Clinical data 102 cases of 119-finger congenital polydactyly of the thumb were admitted from August 2008 to December 2011, 67 cases (65.7%) were male and 35 cases (34.3%) were female; the minimum age was 2 months, the maximum age was 13 years old, and the average age was 1.62±2.36 years old; 3 cases of 3-finger floaters (the minimum age was 2 months, the maximum age was 7 months), 23 cases on the left hand, 62 cases on the right hand, and 3 cases of 3-finger floating fingers (the minimum age was 2 months, the maximum age was 7 months). There were 23 cases of left hand, 62 cases of right hand and 17 cases of both hands; 5 cases were associated with syndactyly. All children underwent preoperative clinical examination and imaging, and were classified according to Wassel’s typology, and individualized surgical plans were formulated. Wassel typing According to the X-ray film of the affected limb, Wassel typing was carried out on 116 fingers: Type I distal phalangeal bifurcation 4 fingers (3.8%), Type II distal phalangeal duplication 18 fingers (17.0%), Type III proximal phalangeal bifurcation 16 fingers (15.1%), Type IV proximal phalangeal duplication 39 fingers (36.8%), Type V metacarpal bifurcation 8 fingers (7.5%), Type VI metacarpal duplication 9 fingers (7.1%), Type VI metacarpal duplication 8 fingers (7.1%), and Type V metacarpal duplication 9 fingers (7.5%). Metacarpal bone duplication type 9 fingers (8.5%), type VII three-jointed phalanges type 12 fingers (11.3%). Surgical timing According to the thumb ossification center appeared time to choose the timing of surgery: Wassel Ⅰ, Ⅱ type, surgery is chosen in 1 year and 6 months after the ossification center of the distal phalanx; Ⅲ, Ⅳ type, surgery is chosen in 1 year after the center of the proximal phalanx ossification; and Ⅴ, Ⅵ type, surgery is chosen in 2 years old after the center of the metacarpal ossification in 6 months; Wassel Ⅶ type surgery can be chosen in 2 years old in 6 months; floating finger in Surgery is performed within 6 months of age. Surgical method The surgical plan is designed according to the type of polydactyly and the degree of joint mobility before surgery. Surgical incision is usually made in the shape of a shuttle or Z-shaped incision. For Wassel type I, the nail, nail bed and phalanx of the polydactyly are completely excised, and an appropriately sized skin flap is trimmed to rebuild the shape of the thumb; for type II, the attachment point of extensor digitorum tendon and the interphalangeal joint capsule of the radial side should be dissected, and attention should be paid to preserving the lateral collateral ligament attached to the base of the last phalanx, and the expanded cartilage on the distal radial side of the proximal phalanx should be trimmed to rebuild the joint capsule; for types III and IV, the extra cartilage should be removed during surgery, and the joint capsule should be rebuilt. Type III and IV surgery will be excess distal and proximal phalanges to be resected, repair the cartilage at the distal end of the metacarpal bone, such as the metacarpophalangeal joint ulnar deviation (or radial deviation) is serious, give the reset to the interphalangeal joints and metacarpophalangeal joints fixed by 0.8 mm fine Kirschner’s needle, rebuild the lateral collateral ligaments and flexion/extension tendons, repair the metacarpophalangeal joint capsule and fixation to the proximal phalangeal radial side of the retained finger; Type V and Type VI surgical procedures and proximal type of polydactylosis similar to that of the multiple digits, will polydactylous digits resected Type V and VI were similar to the proximal polydactyly, and after resection of the polydactyly, the lateral collateral ligament and flexor-extensor tendon were reconstructed and their tension was adjusted appropriately, and then the piriformis muscle stop was reconstructed in order to restore the function of the thumb to the palm. Results In this group, 81 cases were followed up for 3 to 27 months after surgery, with an average follow-up of 11.6 months. According to the modified Tada score, which is an assessment of the mobility, stability, force line of the preserved finger joints and the family’s subjective evaluation, the results showed that there were 62 excellent cases, 17 good cases, 12 moderate cases, and 3 poor cases; 2 cases showed secondary ulnar deviation deformity at 2 years postoperatively, and their appearance was improved after reoperation, and 1 case showed improvement in the shape of the metacarpophalangeal joints at 3 years postoperatively. The metacarpophalangeal joint of one finger had residual epiphysis on the radial side 3 years after surgery, which was resected and reconstructed at the stop of the abductor digitorum brevis muscle. The rest of the children were satisfied with the position of the preserved finger, good appearance and development, and the function of the palm and finger was basically restored to meet the needs of normal sports and daily life. Discussion Congenital polydactyly of the thumb has a high incidence and various types of deformity, especially affecting the hand function significantly. The aim of surgical treatment is to consider both the patient’s postoperative appearance and functional needs. It is important to note that polydactyly is not simply an excess of tissue, but rather an anatomical abnormality, disordered arrangement, and dysplasia. Therefore, the surgery is not a simple excision of the polydactyly, but a reconstruction of the appearance and anatomical structure. The timing of surgery is particularly important because the anatomical variability of the polydactyly is large and the intraoperative situation is often more complex than imagined. If the age of surgery is too young, the abnormal tissue structure and function are difficult to recognize, and the postoperative period is likely to lead to residual deformity; on the contrary, if the age of surgery is too old, the polydactyly can directly affect the normal thumb development and function, and even cause thumb dysfunction, which affects the life treatment of the child. Tada et al [8] believe that the optimal age should be chosen from 6 months to 1 year, and Tang Heping et al suggest that the timing of surgery should be around 2 years of age. We believe that it is more objective to choose the timing of surgery according to the time of the appearance of the ossification center of the thumb, which can minimize the chance of intraoperative damage to preserve the ossification center of the thumb. Generally, the ossification center of the distal phalanx of the thumb appears at the age of 1 year and 6 months, the ossification center of the proximal phalanx appears at the age of 1 year; and the ossification center of the first metacarpal bone appears at the age of 2 years and 6 months. Therefore, for Wassel type I and II, the timing of surgery should be chosen at the age of 1 year and 6 months, and for Wassel type Ⅲ and Ⅳ, the timing of surgery should be chosen at the age of 1 year; and for Wassel type Ⅴ, type Ⅵ, and type Ⅶ, surgery is preferred at the age of 2 years and 6 months. Wassel type V, VI, VII, at 2 years and 6 months of age. It should be pointed out that although Wassel type VII is a complete duplication of the phalanges with one of the fingers being a three-jointed phalanx, it is not suitable to be operated around 1 year of age considering its complex structure and abnormal development, especially when the three-jointed phalanx is used as a preserved finger, so we usually put it into surgery after 2 years and 6 months of age. The metacarpals and phalanges of the hand have only one epiphysis with longitudinal growth potential, and the epiphyses of the first metacarpal and all the phalanges grow proximally, while the epiphyses of the remaining metacarpals grow distally. Therefore, Wassel type Ⅰ, Ⅱ type of polydactyly should be as far away as possible from the proximal end of the distal phalanx when performing polydactyly, Wassel type Ⅲ, Ⅳ should be as far away as possible from the proximal end of the proximal phalanx, and Wassel type Ⅴ, type Ⅵ should avoid damaging the proximal metacarpal epiphysis of the first metacarpal bone as much as possible, especially when type Ⅰ, Ⅲ, Ⅴ type of bone amputation should pay attention to preventing damage to the epiphysis. Early appearance of congenital polydactyly after surgery is relatively satisfactory, but with the growth of age, some children may have secondary deformity. Yu Xiling et al. counted 197 cases of surgery for polydactyly and 12 cases showed secondary deformities. Common secondary deformities include retained ulnar or radial deviation, metacarpophalangeal cartilage residue, and scar contracture deformity. The causes of these deformities were mainly related to poor timing of surgery, improper treatment of residual tendons after resection of multiple fingers, insufficient or excessive revision of the distal end of the proximal phalanx, and short fixation time with Kirschner’s pin. In this group, two cases were caused by poor repair of the joint capsule and lateral collateral ligament, resulting in ulnar deviation deformity, and one case was caused by insufficient repair of the cartilage of the distal metacarpal bone, resulting in the residual epiphysis on the radial side of the metacarpophalangeal joint, which was basically restored in shape and function after reoperation for correction. In conclusion, the surgical treatment of congenital polydactyly of the thumb should not only pursue the aesthetic appearance, but also rebuild the function of the thumb. The timing of surgery should be based on the time of the appearance of the ossification center of the thumb. For complex polydactyly with severe deformity and large structural variations, preoperative evaluation should be done, individualized treatment plan should be formulated, fine operation should be carried out, and regular follow-up should be carried out for a long period of time after the surgery.