The JBJS Quiz of the Month is a collection of 10 relevant questions from each orthopaedic subspecialty. The questions are drawn from JBJS Clinical Classroom, which houses over 4,500 questions and 3,100 learning resources. Take the Quiz to see how you score against your peers!

NOTE: This quiz does not earn users CME credits. The questions must be answered within Clinical Classroom to earn CME credits.

A defect in the apical ectodermal ridge (AER) will lead to which of the following types of congenital limb difference?
    • Transverse deficiency
    • The AER regulates proximal-to-distal limb development. Therefore, a defect in the AER results in a transverse deficiency.


    • Syndactyly
    • Syndactyly occurs as a result of failure of apoptosis in the developing web space.


    • Constriction band syndrome
    • Constriction band syndrome results from an amniotic band wrapping around an appendage in utero. This is a deformation rather than a malformation.


    • Mirror Hand
    • Mirror hand occurs as a result of a duplicated zone of polarizing activity (ZPA) such that both sides of the hand are ulnarized.