Pertinent Anatomy and Classifications
Fine motor function of the hand is based on independent digital motion. Supple web spaces facilitate digital abduction, flexion, and extension for activities of daily living. Normal interdigital abduction ranges from 70–80 degrees at the first web space (between the thumb and index finger) to 30–40 degrees at the remaining (second, third, and fourth) web spaces. The second, third, and fourth web spaces or commissures gently slope at an approximate 45 degrees angle from proximal-dorsal to distal-palmar starting at the metacarpophalangeal (MCP) joint and ending just proximal to the midpoint of proximal phalanx. The second and third commissures are typically U-shaped and the fourth web space is typically V-shaped. The natatory ligaments help to form the web contour at the junction between the glabrous and nonglabrous skin.
During embryogenesis, the hand and upper extremity develop from the upper limb bud that emerges from the lateral body wall at 26 days of gestation. Upper limb development generally proceeds in a proximal-to-distal fashion with the hand plate appearing by day 37. During typical development, the hand plate forms individual rays between days 41 through 54 of gestation. Complete separation of the digits occurs through apoptosis, or programmed cell death, of the interdigital tissue, which occurs in a distal-to-proximal fashion. Syndactyly, or “webbed fingers,” is a congenital anomaly that results from a failure of interdigital apoptosis, leading to residual skin, soft tissue, and sometimes bone connecting adjacent digits ( Fig. 7.1A–C ).
Syndactyly is the second or third most common congenital hand anomaly, and it occurs in approximately 1.3–1.9 per 10,000 live births. It more commonly occurs in males (3:2) and has a racial predilection toward whites more than African Americans. Morphologically, syndactyly occurs bilaterally more often than unilaterally (7:3). Syndactyly has a predilection for specific web spaces with the third web space (between the long and ring fingers) being most common. The “5-15-50-30” rule can be used to remember the frequency of web space involvement from first to fourth. Although most cases are sporadic, up to 50% of syndactyly cases can be hereditary, with the most common pattern being autosomal dominant with variable penetrance. Most commonly, syndactyly presents as an isolated malformation, but it can also be found in association with other skeletal anomalies or syndromes such as symbrachydactyly, cleft hand, ulnar longitudinal deficiency, synpolydactyly, acrocephalosyndactyly (Apert, Crouzon, and Pfeiffer syndromes), acrocephalopolysyndactyly (Carpenter and Noack syndromes), oculodentodigital dysplasia, and orofaciodigital dysplasia. Although amniotic band syndrome represents a separate entity, as the etiology is due to intrauterine scarring rather than a true malformation, syndactyly can also occur in this syndrome and presents as acrosyndactyly ( Fig. 7.2A–C ). In these cases, there is a soft tissue only connection at the distal tips of the involved digits with a separation or fenestration proximally.
In 2010, the International Federation of Societies for Surgery of the Hand classification was modified into the Oberg, Manske, and Tonkin (OMT) classification to incorporate an improved understanding of the genetic and molecular basis of congenital hand and upper limb anomalies. The OMT classification placed syndactyly into Group I, or “malformation”, and into the subtype “failure of hand plate formation/differentiation.” However, syndactyly is more commonly described by the clinical morphology of the involved digits. The extent of digital involvement can be described as “complete” syndactyly if the connection extends the entire length of the digits (from commissure to fingertip) or “incomplete” syndactyly if the distal portion of the digits are separate ( Fig. 7.1A–C ). Syndactyly can be further characterized by the type of tissue involved in the connection between digits. In “simple” syndactyly, the involved digits are connected by skin and soft tissue. Simple syndactyly can also present with a common nail plate shared by the two adjoined digits—termed synonychia. In simple syndactyly, the joints, ligaments, and tendons are typically normal. “Complex” syndactyly involves an osseous connection between adjacent phalanges, in addition to the soft tissue connections. “Complicated” syndactyly refers to the interposition of accessory phalangeal or abnormal bones between digits, and can also involve anomalous nerves, tendons, and/or muscles. Other classification systems have been described for syndromic syndactyly including the Upton classification specifically for Apert syndrome with Type 1 (spade hand), Type 2 (mitten hand), and Type 3 (rosebud hand), in addition to further subdivision based on angular and rotational deformities.
Syndactyly: Preoperative Evaluation
In most cases, syndactyly is detected at birth, and early consultation with a hand surgeon is sought. The diagnosis of syndactyly is obviously not subtle, but, occasionally, mild simple incomplete syndactyly is not recognized by parents or brought to the attention of a hand surgeon. Simple inspection will reveal the extent of the syndactyly (simple vs. complete) and the presence or absence of a synonychia. Careful observation will often allow the treating provider to distinguish between simple, complex, and complicated syndactyly. The degree of active and passive MCP joint and interphalangeal (IP) joint motion should be measured with a goniometer and recorded. Poorly formed flexion or extension creases generally indicates restricted or absent joint motion and suggests complex or complicated syndactyly. Standard plain radiographs of the affected hand should be obtained at 6–12 months old to further characterize the type of syndactyly. In most cases, a single posteroanterior radiograph is sufficient to delineate the osseous elements and determine whether there is fusion of adjacent phalanges.
In the case of syndactyly associated with a syndrome, examination of the remainder of the extremity, chest wall, feet, and head will reveal additional abnormalities. Poland syndrome is one of the most common syndromes that has syndactyly and typically presents with unilateral symbrachydactly and pectoralis major deficiency. Genetic evaluation and counseling should be sought for all cases of syndactyly presenting as part of a syndrome. In select cases, a preoperative electrocardiogram (EKG) may be warranted to screen for prolonged QT interval that occurs in Timothy syndrome and can cause ventricular tachyarrhythmia leading to cardiac arrest. This extremely rare syndrome is also associated with a flattened nasal bridge, low-set ears, a small upper jaw, a thin upper lip, small misplaced teeth, developmental delay, and autism—in addition to ulnar-sided syndactyly. Due to the rarity of this syndrome, routine screening with an EKG is not necessary.
Surgical reconstruction is recommended for most cases with the occasional exception of a mild, simple incomplete syndactyly that does not impact function. In addition, there are rare cases of complex or complicated syndactyly in which surgical reconstruction is not recommended. These contraindications include digits with substantial instability or absent anatomic structures that would inhibit digit function if surgically separated. Caution should also be exercised when a “super digit” is encountered. This term is used to describe a single oversized digit supported by two metacarpals (Type I) or a single metacarpal that supports two or more digits distally (Type II). In these cases, although surgical separation may be technically feasible and could improve cosmesis, hand function could be compromised due to the unpredictability of postoperative alignment, motion, and function.
The timing of surgical reconstruction remains controversial, but is primarily based on the pattern of web space involvement and the type of syndactyly. Syndactyly involving border digits (small ring or thumb–index) and some forms of complex syndactyly may benefit from earlier release at 6–12 months old. When border digits are involved, earlier surgery is recommended to avoid a flexion contracture and angular deformity, which occur due to disparate length and growth of the syndactylized digits ( Figs. 7.1C and 7.3 ). In general, syndactyly reconstruction before 12 months old has been associated with a higher incidence of scar contracture and web creep. For this reason, in the absence of a progressive flexion contracture or angular deformity, surgery can be timed between 18 months and 3 years old without compromising ultimate fine motor function. In younger children with bilateral deformity, both hands may be treated concurrently. This decreases overall anesthetic exposure and is optimally performed with two surgical teams performing simultaneous procedures on both hands. Staged reconstruction for bilateral syndactyly may be preferred by the surgeon or family. When adjacent web spaces are involved, most surgeons recommend staged reconstruction to minimize the risk of digital ischemia or loss.
Syndactyly of the thumb–index web space is the least common, but associated with the greatest surgical complexity. This is due to the large length discrepancy between the thumb and index finger as well as the complex motion of the thumb. Patients often present with web space narrowing and a thumb flexion contracture preoperatively that requires surgical reconstruction initially to separate the digits, but also to both deepen and adequately widen the space to allow normal position and function of the thumb ( Fig. 7.4A–D ).
A preoperative therapy evaluation and treatment are not often indicated in children with syndactyly. A therapist may be consulted if contractures or angular deformities are present, and preoperative intervention including orthotics or caregiver education on stretching would support surgical goals and anticipated outcome. A general screen of functional hand use, grasp patterns, and developmental skills could be beneficial in challenging cases to determine if any adaptations or intervention would be beneficial to support age appropriate activity ( Figs. 7.1C and 7.3 ).
Surgical Steps
Syndactyly reconstruction is one of the most common procedures performed in congenital hand surgery. Reconstructive surgery is performed under general anesthesia with the patient supine on a standard operating table with the upper limb positioned on a hand table. A tourniquet is used for skin incision and flap elevation to optimize visualization and limit the risk of inadvertent injury to the neurovascular bundles. The specific surgical technique for release varies based on the particular web space under reconstruction and the morphology of the involved digits. Although the specific surgical approach and flap design may vary depending on the specific case and surgeon preference, there are several universal surgical principles (see Box 7.1 ).
- 1.
Release border digits early to prevent progressive flexion contracture and angular deformity of the adjacent digit.
- 2.
Staged surgical reconstruction is recommended when multiple adjacent web spaces are involved. Vascular compromise can occur if surgery is performed on both sides of a single digit, and both the ulnar and radial digital arteries are compromised.
- 3.
Ligation of a digital artery may be required to achieve optimal web space depth in cases where the common digital artery bifurcates distally.
- 4.
A robust, local vascularized flap should be used to create the commissure and minimize the risk of scar formation and web creep.
- 5.
Interdigitating lateral zigzag flaps should be used to avoid longitudinal scar contracture.
- 6.
Full-thickness skin grafting should be used to cover bare areas. Avoid split-thickness skin grafting or healing by secondary intention, as this results in excessive scarring and contracture.
In patients with complete syndactyly, a variety of different surgical incisions have been proposed, but all use a dorsal skin flap measuring two-thirds the length of the proximal phalanx to reconstitute the web commissure with interdigitating zigzag flaps for coverage of the lateral border of each of the involved digits ( Fig. 7.5A and B ). After marking the skin incision, the tourniquet is inflated and the dorsal skin flaps are raised, while preserving longitudinal veins when possible. The volar skin flaps are raised next, taking care to identify and protect the digital neurovascular bundles. The bifurcation of the common digital artery must be identified. In cases where the bifurcation is atypically distal, the surgeon must decide between an incomplete release or ligation of one of the two proper digital arteries. In general, ligation of a single digital artery is acceptable, but the safety of this maneuver should be confirmed with temporary application of a microvascular clamp on the target vessel and tourniquet deflation to assure that this is no concern for vascular insufficiency. All fibrous connections between the digits are then sharply divided. In complex syndactyly, osseous connections are divided with a scalpel or small osteotome. After a complete release is achieved, the skin flaps are rotated into position, allowed to interdigitate, and secured with absorbable suture. The tourniquet should be deflated to confirm perfusion of both digits and each flap. There is typically a bare spot on the dorsal ulnar aspect of the radial digit and the dorsal radial aspect of the ulnar digit that are covered with full-thickness skin graft from the hypothenar region, volar wrist, upper arm, or groin. The skin grafts should be fenestrated to allow egress of hematoma that could otherwise compromise graft adherence. In cases of incomplete syndactyly, the general approach described earlier may be substituted with simple skin rearrangement utilizing simple z-plasty, four-flap z-plasty, double-opposing z-plasty, or other similar techniques.
Application of the immediate postoperative dressing is one of the most important steps. Nonadherent petroleum-impregnated gauze, such as Xeroform (Kendall/Covidien, Mansfield, MA), should be applied to suture lines and over the full-thickness skin graft. The web space should then be packed with cotton balls soaked in mineral oil. Postoperative immobilization depends on the age and maturity of the patient, but most children are placed into a long arm mitten cast with the elbow at 90 degrees of flexion and a supracondylar mold to avoid inadvertent cast removal by the child. The cast and dressings are typically removed 2–4 weeks after surgery and therapy is initiated.
Syndactyly: Postoperative Evaluation
Consultation to therapy for evaluation following syndactyly reconstruction is dependent on the complexity of the surgery and the preference of the surgeon and center. A patient may be referred immediately following cast removal for orthotic fabrication, otherwise a consult may not be made unless the patient presents with later development of complications requiring therapeutic intervention, such as hypertrophic scarring. A thorough evaluation may not be mandatory in most syndactyly reconstruction cases; however, this section highlights measures and outcome assessments most appropriate to assess motion, digital deformity, web creep, and scar integrity. A general assessment of edema, grip/pinch strength, and sensation may be indicated and are not reviewed in further detail. The use of objective outcome measures, when possible, is important for therapists to incorporate into practice to support the role of therapy and use of evidence-based practice.
Range of Motion
The therapist should consider functional impact on prehension patterns specific to the released web space as well as the child’s developmental level. Documentation should include functional motion detailing joint position, digit function, as well as types of grasp and pinch patterns utilized with comparison to the contralateral side. It includes details of active digit adduction and abduction of bilateral hands to note any active deficits. Additional observations should include details of the child’s ability to perform sufficient composite digit flexion to reach the distal palmar crease, spontaneous hand use, and any observed pain behaviors with motion. In cases of syndactyly of the thumb–index web space, a thorough assessment of thumb motion and function is indicated as the thumb is cited to be responsible for at least 40% of hand functionality. Objective assessment of digit motion can be achieved through measuring the total active motion (TAM) of each digit rather than that of individual joint. TAM is the combined degrees of active flexion of the IP joints minus the degrees of extension deficits at these joints. The normal TAM of a digit is approximately 175 degrees.
Digital Deformity
Digital rotation toward supination or protonation can be measured with a goniometer comparing the plane of the distal phalanx to the plane of the proximal phalanx. Digital angulation can be assessed with goniometer placement along the dorsal longitudinal aspects of the joints and corresponding phalanges to determine the degree of deviation.
Web Creep
Web creep is a common postoperative complication and is defined as the distal migration of the commissure following a syndactyly reconstruction. Web creep can be assessed using a five point scoring system developed by Withey and colleagues . This scale grades web creep based on the location of the web relative to the MCP and proximal interphalangeal joints (see Table 7.1 ).
| 0 | Soft web, abduction mirrors the adjacent web or Equivalent web on the Other Hand |
| 1 | No web advancement, but thickening of the web with reduced span |
| 2 | Creep of web to 1/3 of the distance between base of the web and PIP crease |
| 3 | Creep of the web to 2/3 of the distance between base of the web and PIP crease |
| 4 | Creep of the web to the PIP crease |
Scar Integrity
Detailed documentation of scar integrity allows for ongoing assessment to monitor maturation. The modified Vancouver scar scale is an outcome measure originally developed for assessment of scars following a burn, but has been cited in the literature as a tool to assess scar integrity following syndactyly reconstruction. This scale allows users to quantify the pigmentation, vascularity, pliability, and height of a scar in comparison to a patient’s normal skin (see Table 7.2 ). The terminology used in this scale provides therapists with more consistent and objective language to describe subjective parameters of scar appearance and mobility. Consistent documentation through serial photographs of scar maturation is beneficial for ongoing assessment and monitoring of potential changes in joint positioning and scar presentation.
| Pigmentation | 0—normalminimal variation from normal skin pigmentation |
| 1—hypopigmentation | |
| 2—hyperpigmentation | |
| |
| Vascularity | 0—normal |
| 1—pink | |
| 2—pink to red | |
| 3—red | |
| 4—red to purple | |
| 5—purple | |
| Pliability | 0—normal |
| 1—supple—flexible with minimal resistance | |
| 2—yielding—scars give way to pressure with a moderate resistance, do not move as a solid mass of scar | |
| 3—firm—moves as a solid, inflexible unit | |
| 4—banding—“ropes” of scar tissue that blanches with stretch, does not limit range of motion | |
| 5—contracture—limits range of motion | |
| Height | 0—flat scars, flush with normal skin |
| 1—<2 mm | |
| 2—2–5 mm | |
| 3—>5 mm |
Syndactyly: Postoperative Immobilization
Factors surrounding the surgical complexity and specific anatomic structures involved in the reconstruction determine the length of postoperative immobilization. If the reconstruction involves skin grafting only, a bulky postoperative dressing is applied, as noted earlier, with an overlying long arm mitten cast to prevent shearing and graft failure. The cast is typically removed after 2–4 weeks depending on the individual case. Reconstruction involving pinning may require increased immobilization to allow sufficient healing. Following a thumb–index web space reconstruction, 4–6 weeks of immobilization is sometimes recommended before pin removal due to the high complexity of the reconstruction with the goal of maintaining a broad web space. Further immobilization through orthotic intervention is not always indicated and is rather dependent on surgeon and center preferences, as well as the surgical complexity.
Syndactyly: Postoperative Orthotics
The primary goal of orthotic intervention following an initial therapy referral is often for protection of the postoperative hand. The secondary roles of a postoperative orthotic focus on scar management and positioning to prevent complications of digital deformity and web creep. A child’s age and tolerance to orthotic wear plays an important role in decision making. Fabrication of hand- or forearm-based orthotic is dependent on the complexity of the reconstruction and the therapeutic goals. If the child does not require an orthotic for protection of the reconstructed digits, an elastomer web spacer custom mold is sufficient to improve scar appearance and prevent web creep (see Table 7.3 ).
| Goals of Orthotic | Orthotic Design | Wear Schedule | |
|---|---|---|---|
| Simple syndactyly |
| No protection/positional needs: | Overnight 6–12 months, until scar maturation achieved |
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| Protection/positional needs: | All times, except supervised exercise and bathing | |
| Hand or forearm based | Gradual wean during day with sufficient graft/scar healing | |
| Overnight 6–12 months, until scar maturation | ||
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| Complex syndactyly |
| Hand or forearm based | All times, except supervised exercise and bathing |
|
| Gradual wean during day with sufficient graft/scar healing | |
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| Overnight 6–12 months, until scar maturation | ||
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| Thumb–index syndactyly |
| Hand-based c-bar | All times, except supervised exercise and bathing |
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| Gradual wean during day with sufficient graft/scar healing | |
| Continue daytime wear if limited active thumb motion to prevent contracture | ||
| Forearm-based thumb spica with c-bar | Overnight 6–12 months, until scar maturation | |
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