Anatomy and Development of the Upper Extremity:
- The upper extremity consists of mesenchyme covered by ectoderm. The limb grows by proliferation of mesenchyme.
- 4 weeks / 26 Days: Limb bud formation begins
- 37 days: Hand Plate formation
- 6 weeks: Finger buds
- 6-8 weeks / 44-54 days: Finger separation
- 8-12 weeks: Ossification
Genetics of upper extremity development:
- Hox gene family: implicated in regulating limb growth and differentiation
- Limb develops along three axes: proximo-distal, anteroposterior (or radial/ulnar), and dorsoventral
- Promximo-distal Development:
- AER (apical dermal ridge): This is a thickened ridge of ectoderm that responds to fibroblast growth factors (FGF) to controls limb outgrowth.
- Failure of AER leads to a truncated limb
- BMP (bone morphogenetic protein) plays a role in cell death during hand formation
- Failure of BMP results in syndactyly
- Anteroposterior or Radial/Ulnar Differentiation:
- ZPA (zone of polarizing activity): ecodermal region present in the posterior aspect of the developing upper limb and is responsible to radio/ulnar differentiation of the upper extremity driven by sonic hedgehog protein (SHH)
- Failure of the ZPA results in mirror hand deformity (mirror hand deformity has a central finger with identical flanking fingers).
- Dorsoventral development
- Dorsal ectoderm drives the development of the dorsal/volar characteristics of the limb under the control of WNT7a (wingless-type)
- WNT7a causes EN-1 expression on the ventral side of the limb leading to ventralization EN-1 results in ventral differentiation
- WNT7a leads to LMX1B expression on the dorsal side of the limb leading to dorsal differentiation.
Types of Failure in Embryonic development:
- Failure of differentiation includes syndactyly, symbrachydactyly (associated with Poland syndrome- absent pectoralis muscle, breast development), camptodactyly, clinodactyly
- Failure of formation includes cleft hand and longitudinal deficiencies.
- Duplication includes mirror hand deformity, polydactyly.
- Overgrowth includes macrodactyly.
- Undergrowth includes brachydactyly.
Common Congenital Hand Anomalies:
Syndactyly: variable fusion between two adjacent fingers:
- Complete involves the entire commissure, including the nail bed
- Incomplete involving the partial digit
- Simple involves fusion only through the skin
- Complex is fusion involving bone
- Complicated involves multiple structures including bones, joints, tendons, muscles and neurovascular structures.
- Timing of Treatment:
- In general it is recommended to wait until 1 year when complications are reduced
- For involvement of border digits (small finger or thumb) you may consider earlier separation to prevent tethering and shortening of the neighboring digits
- Goal is to complete reconstruction by 24 months
- Treatment of syndactyly
- Simple syndactyly:
- Webspace: Reconstructed by dorsal rectangular flaps for the webspace with the limit of dissection at the bifurcation of the digital arteries
- Digit separation: dorsal and volar digital flaps are created to reconstruct the joint spaces. Areas that can not be covered need FTSG
- Multiple Digits: The separation is staged with the first and fourth web spaces first, followed by the second and third spaces in two separate operations
- Associated syndromes include Apert’s syndrome which is associated with coronal craniosynostosis, midfacial abnormalities and complex syndactyly of the hands and feel
- Postaxial polydactyly: extra digit on the ulnar sided hand
- Most common type of polydactyly and it effects African Americans disproportionately with an incidence of 1:143 live births
- Type A: fully formed duplicate digit
- Treated with surgery to remove the extra digit and maintain stability of the small finger
- Type B: nubbin or poorly developed ulnar duplication
- Treatment: suture ligation if a small skin bridge exists vs. surgical excision
- Preaxial polydactyly describes thumb duplication.
- Wassel classification: I-V- to correctly classify count the number of affected bones.
- Wassel I: incomplete distal phalanx duplication (one bone).
- Wassel II: complete distal phalanx duplication (two bones).
- Treatment options:
- 1: Excision of the radial portion of the bone and stabilization with collateral ligament reconstruction via a ligamentous and periosteal flap
- 2. Bilhaut-Cloquet: excision of central bone and soft tissue and combination of the duplicated bones
- Wassel III: incomplete proximal phalanx duplication (3 bones).
- Wassel IV: complete proximal and distal duplication (4 bones)- This is the most common thumb duplication.
- Treatment is to excise the radial portion of the bone and stabilize with collateral ligament reconstruction. It is most important to maintain the ulnar collateral ligament for thumb stability at the MCP joint. Also need reposition of eccentric flexor and extensor tendons, as well as identifying and reattach the abductor pollicis brevis.
- Wassel V: incomplete duplicated metacarpal
- Wassel VI: duplicated metacarpals
- Wassel VII: triphalangeal thumb (7 bones total- 3 on normal side and 4 on other (triphalangeal duplication).
Radial longitudinal deficiency: hypoplasia and dysplasia of radius and or thumb.
- Type I: short distal radius
- Type II: hypoplastic radius
- Type III: partial absence of the radius
- Type IV: total absence of the radius
- Thrombocytopenia absent radius syndrome (TAR): TAR or thrombocytopenia absent radius syndrome is an autosomal recessive disorder characterized by absent radius with relatively normal thumb, thrombocytopenia.
- Holt Oram Syndrome: autosomal dominant disorder with radial longitudinal deficiency accompanied by either atrial or a ventricular septal defect.
- VACTERL: (vertebral deformities, anal atresia, cardiac abnormalities, trachoesophageal fistula, renal agenesis, and limb deformities). Best predictor of inpatient mortality is cardiac disease.
- Fanconi Anemia: autosomal recessive pancytopenia, invariably fatal, treated with bone marrow transplantation.
- Patients with radial longitudinal deficiency should undergo chromosomal breakage test for earlier detection. Additional screening with spinal X-rays, cardiac echocardiography, renal ultrasonography, CBC.
- Do not manifest with aplastic anemia on routine blood testing until after 3 years.
Thumb Hypoplasia: All patients with radial longitudinal deficiency have thumb hypoplasia but not all patients with thumb hypoplasia have radial longitudinal deficiency
- Blauth classification:
- I: minimal hypoplasia with full complement of neurovascular and musculoskeletal elements that are small in size. No surgical treatment necessary
- II: all bones present, but hypoplastic. Instability of ulnar collateral ligament of the MCP joint and thenar hypoplasia.
- IIIA: CMC joint intact however there is poor active motion at MCP and IP joints.
- IIIB: deficient CMC joint with absence of trapezium, aplastic proximal first metacarpal head, absence of MP/IP joint motion.
- IV: pounce flottant or floating thumb. No muscular or skeletal attachments between thumb and hand. Absent CMC
- V: absent thumb.
- Blauth Type II, IIIA: Treatment is MCP joint stabilization with opponensplasty and deepening of first web space.
- Blauth Type IIIB or higher: Treatment is thumb amputation and index pollicization.
- Timing: Performed between 3 months- 3 years. It is important to perform before child learns pinch.
- Surgery Procedure: Procedure requires shortening the index finger metacarpal and repositioning of metacarpal head to become the CMC
- Index MP joint becomes new thumb CMC joint
- Index PIP becomes thumbs MP joint
- Index DIP becomes thumbs IP joint
- Index proximal phalanx becomes the metacarpal
- EDC becomes APL
- EIP can become EPL
- Dorsal interosseous becomes Abductor pollicis brevis
- Palmar interosseous becomes ADDuctor pollicis
** Remember PAD/DAB to remember the intrinsic (palmar ADDucts, dorsal Abducts)
- For pollicization, do not need thumb CMC joint present. Other reconstruction options include great toe to thumb transfer (need metacarpal present)
Amniotic Band Syndrome or constriction band syndrome:
Cause: Due to low amniotic fluid which leads to constriction rings. Responsible for 12% of all congenital limb deformities, has no known genetic transmission.
Associated factors: include prematurity, low birth weight, and young multigravida mothers, oligohydramnios.
- Vary from skin dimpling to digital amputation
- Acrosyndactyly is pathognomonic for amniotic band syndrome (joined fingers except distally)
- Can result in compartment syndrome (edema, bullae, followed by compartment syndrome and volkmann’s contracture)
- Bullae is the sign to look for and is the sentinel lesion
- Treatment: excision of the constriction band. Initially you may limit your excision to 50% followed by the other 50% 3-6 months later. This results in rapid resolution in edema.
- Treatment of compartment syndrome is constriction band excision (tested)
- Definition: painless and progressive nontraumatic contracture of the PIP joint. Affects 1% population (will typically show Xray of contracted PIPJ).
- Treatment: Typically treated with nonoperative treatment including static splinting. Surgery should be last option!
- Definition: excessive radial or ulnar deviation of a digit which can be caused by a delta phalanx or bracketed epiphysis
- Definition: progressive palmar and radial curvature of the distal phalanx of the little finger that presents in preadolescence
Congenital Trigger Finger:
- Presentation: Presents as flexion at IP joint of thumb, sporadic locking
- Etiology: presents more commonly in the ulnar digits with associated malformations of superficial and deep flexors
- Treatment: Observation at 1 year, treatment after three years. If you go to surgery you typically need A1 pulley release with tenoplasty of the chiasm and partial opening of the A2 pulley generally necessary
- In trigger thumb there is often development of a pathopneumonic “notta’s node” or enlargement of the flexor tendon proximal to the A1 pulley
- Definition: congenital overgrowth disorder and represents 1% of upper extremity congenital anomalies. Digital enlargement involves all tissue types and maintains patterns of growth and anatomic relationships within the affected portion of the hand
- Treatment: if affected fingers are sensate, then debulking procedures and epiphysiodesis (premature closure of growth plates) are performed at IP and MP joints.
- Associated syndromes: Can be associated with neurfibromatosis (von Recklinghausen’s disease)
Brachydactyly: shortened fingers
- Treatment is aimed at keeping pinch
- Attempt to reconstruct small and ring fingers to facilitate grip and opposition
- Perform treatment at 8-12 months of age
- If there is no functional deficit then reconstruction is not necessary
- Shoulder dystocia found to be the risk factor most associated with birth brachial plexus injuries (cesarean delivery protective)
- Salter Harris: fractures that involve the physis (extra octave if not involving the physis)
- I: transphyseal
- II: transphyseal but exit through metaphysis
- III: transphyseal but exit the epiphysis and joint
- IV: both epiphysis and physis, exiting through metaphysis
- V: crush injuries to physis
- Infants that undergo upper extremity reconstruction procedures should be placed in a long arm cast