ULNAR DEFICIENCES

Ulnar longitudinal deficiencies are rare, congenital malformations that affect the ulnar aspect of the limb that can involve the ulna, ulnar digits, and ulnar aspect of proximal joints. Combined with radial deficiencies, the pair accounts for the two most common types of congenital longitudinal deficiencies of the arm, but ulnar deficiencies occur far less frequently and are not typically described by the term “club hand” like those on the radial side.  Ulnar deficiencies are 4-10x less common than radial sided deficiencies.  Ulnar deficiencies can result in a spectrum of malformations, from minor digital involvement to complete absence of the ulna, carpal bones, and digits with hypoplasia of the joints, muscles, tendons, ligaments, nerves, and blood vessels. The radius may also be affected.  Although usually sporadic and rarely associated with visceral abnormalities ulnar deficiencies are rarely associated with visceral anomalies, musculoskeletal conditions like scoliosis and phocomelia are frequently comorbid with ulnar deficiencies. Conservative interventions are recommended for most patients and may be adequate for milder deficiencies in which function is not severely compromised, while surgery is necessary for more aggressive cases.^1-3,11,12

Pathophysiology

• Although some cases of inheritance have been reported, the majority of ulnar deficiencies occur sporadically and no related chromosome abnormality has been identified¹
• Development of the human forelimb is evident during the 4th week after conception (day 26) as a lateral bulge or limb bud, and its development occurs along the proximal-distal, antero-posterior (or radio-ulnar), and dorso-ventral axes^1,4
• Ulnar deficiencies typically occur due to an error in radio-ulnar development, which is mitigated by the zone of polarizing activity.
• The zone of polarizing activity (ZPA), located on the posterior margin of the limb bud, controls the radioulnar patterning through the mediation of the concentration of sonic hedgehog (SHH) gene.
  • SHH signals from the ZPA regulate the activity of the apical ectodermal ridge, which gives positive feedback to the ZPA by fibroblast growth factor signals.
  • Normally, higher concentrations of SHH ar4e present on the ulnar side to signal for small finger development, while lower concentrations are present on the radial side, in a gradient type fashion, to signal for thumb development.
  • Insults that disrupt ZPA formation or SHH function  can affect formation of the ulna and/or ulnar digits, and are therefore thought to be responsible for creating ulnar deficiencies.^1,4
  • Abnormal upregulation of SHH on the ulnar side can lead to ulnar polydactyly.  While abnormal downregulation can lead to ulnar deficiency.  Conversely, abnormal upregulation of SHH on the radial side (where SHH concentrations are meant to be low) leads to radial deficiency.
  • Because the ZPA is located on the posterior/ulnar side of the limb bud, ulnar deficiencies happen with earlier insults, while radial deficiencies happen with later insults. This is also why ulnar deficiencies often have concomitant radial deficiencies.
  • Antiproliferative agents like busulfan may induce an ulnar deficiency depending on the developmental stage of exposure.^1,11,12

Related Anatomy

• Ulnar deficiencies are highly variable in their clinical presentation, and abnormalities may be present in all of the bones of the limb, but almost all patients have absent ulnar-sided digits⁵
• While radial deficiency is usually complete and associated with aplasia or hypoplasia to the radial side of the hand, ulnar deficiency is typically partial and may be accompanied by severe abnormalities of both the ulnar and radial sides of the hand⁵
• Most ulnar deficiencies are unilateral, with the left limb being affected more commonly than the right; its classic presentation is ulnar shortening with radial bowing and abnormal digits, with the elbow abnormal or fused in most cases.
  • Although the ulna may be partially or completely absent, a cartilaginous anlage is often present
  • The hand and carpus are almost always affected, with as many as 70% of patients having thumb abnormalities
  • Up to 90% of hands have missing digits and 30% have syndactyly³
  • Several classification systems have been devised to describe ulnar deficiencies, with the Bayne classification system being used most commonly:
    • Type 0
      • Normal radius and ulna with normal elbow function
      • Deficiencies of the carpus and/or hand only, such as absence/hypoplasia of digits and carpal bone absence or coalition
    • Type I
      • Hypoplasia of the ulna, with mild ulnar wrist deviation
      • Minor radial bowing
      • Absence/hypoplasia of the ulnar digits is common
      • Proximal and distal ulnar epiphyses present
    • Type II
      • Partial aplasia of the ulna, usually the distal end, with mild ulnar wrist deviation
      • Distal ulnar anlage
      • Significant radial bowing, with anlage acting as a tether
      • Presence/absence of progressive radial head dislocation
    • Type III
      • Complete absence of the ulna, with less ulnar wrist deviation and no anlage
      • Severe carpal and digital deficiencies
      • Straight radius
      • Unstable elbow
    • Type IV
      • Complete absence of the ulna, with ulnar wrist deviation and a fibrocartilaginous anlage attached to the ulnar carpus
      • Radiohumeral synostosis at the elbow
      • Severe radial bowing
      • Humeral internal rotation and forearm pronation
    • Type V
      • Complete absence of the ulna, with less ulnar wrist deviation
      • Straight radius
      • Radiohumeral synostosis at the elbow
      • Severe carpal and digital deficiencies
      • Humeral bifurcation or large medial condyle^2,3,6,7
  • There is also a subtype for each deficiency class based on the first web space:
    • Type A: normal first web space
    • Type B: mild first web and thumb deficiencies
    • Type C: moderate to severe first web and thumb deficiencies
    • Type D: absent first web and/or thumb³

Incidence and Related Conditions

• The incidence of ulnar deficiencies is 1–7.4 per 100,000 live births⁸
• Ulnar deficiencies are approximately 4–10 times less common than radial deficiencies⁹
• Ectrodactyly
• Metacarpal synostoses
• Phocomelia
• Syndactyly
• Delta phalanx
• Capitate-hamate coalition
• Scoliosis
• Absent patella
• Club foot
• Fibula and mandibular deficiency
• Proximal femoral focal deficiency
• Goltz syndrome

Differential Diagnosis

• Radial deficiency
• Arthrogryposis multiplex congenita
• Proximal radioulnar synostosis
• Multiple pterygium syndrome