A Practical Approach, Second Edition=Ronald D. Ho.pdf

POSTNATAL DEVELOPMENTAL MILESTONES 977ossification centers of the proximal epiphysis join to form a single compound proximal epiphysisbetween the ages of 5 and 7 years (2). Histological studies demonstrate that a compound proximalepiphysis forms as early as 2 or 3 years of age (19, 2).The proximal epiphysis of the humerus is responsible for up to 80% of the growth in lengthof the diaphyseal shaft (21). When diaphyseal growth is complete, fusion of the proximal epiphysisoccurs. Fusion of the proximal epiphysis has been reported to occur at ages ranging from 12 to 19years in females and 15.75 to 20 years in males (2).Ossification in the distal epiphysis of the humerus occurs via 4 separate secondary centers thatdevelop in the capitulum, medial epicondyle, lateral epicondyle, and trochlea. By the age of 2years, the secondary ossification center of the capitulum is evident; however, this center may alsoappear as early as 6 months after birth (2). The secondary ossification center of the medialepicondyle is usually visible by age 4 but develops slowly thereafter (2). Development of thesecondary ossification center in the trochlea begins with the appearance of multiple foci at the ageof 8 years. Soon after appearance, the trochlear epiphysis becomes joined to the capitulum.Ossification in the lateral epicondyle is evident by the age of 10 years.The secondary centers of the capitulum, trochlea, and lateral epicondyle join with each otherbetween the ages of 10 and 12 years. Fusion of these structures with the diaphyseal shaft beginsposteriorly and leaves an open line above the capitulum, lateral trochlea, and proximal lateralepicondyle which becomes fused at approximately the age of 15 years.The ossification center in the medial epicondyle does not fuse with the capitulum, trochlea, andlateral epicondyle prior to uniting with the diaphyseal shaft. In females and males, fusion has beenseen to occur at ages ranging from 11 to 16 and 14 to 19 years, respectively (22, 2).3.1.2 FemurIn the femur, primary ossification centers of the diaphysis appear during the prenatal period.The epiphysis that is found at the distal end of the femur is the largest and fastest growingepiphysis in the body (2). This secondary ossification center is the first long bone epiphysis thatappears during skeletal development and one of the last to fuse (2). This distal epiphysis thatdevelops from a single center of ossification usually appears during prenatal weeks 36-40; however,some variation in the time of appearance exists. For example, in premature infants, this center isnot always present and some studies have found that the distal femoral epiphysis is sometimesvisible as early as prenatal week 31. Even so, the distal epiphysis is always visible by the postnatalage of 3 months (15, 20, 23, 22).At birth, the distal femoral epiphysis of females is about 2 weeks more advanced than that ofmales. By the time of puberty, girls are about 2 years more developmentally advanced than boys (2).During postnatal months 6-12, the distal epiphyseal plate begins to develop and the epiphysistakes on an ovoid shape (2). During postnatal years 1 to 3, the width of the epiphysis increasesrapidly as ossification spreads throughout the epiphyseal region. When females and males reachages 7 and 9, respectively, the epiphysis is as wide as the metaphysis (2).The distal epiphysis is responsible for approximately 70% of the longitudinal growth of thefemur (24, 25, 2). When growth of the femur is complete, fusion of the distal femoral epiphysisoccurs. Fusion of the distal femoral epiphysis occurs in females and males between the ages of 14to 18 and 16 to 19 years, respectively (2).At the proximal end of the femur, 3 to 4 separate secondary centers of ossification develop.Unlike those in the proximal epiphysis of the humerus, these centers develop and fuse independentlywith either the neck or shaft of the femur. At birth, the proximal epiphyseal growth plate is dividedinto 3 sections, medial, subcapital, and lateral subtrochanteric portions. By the age of 2 years, theneck has grown and divided the epiphyseal region into the head and the greater trochanter. Thelesser trochanter lies below and medial to the epiphyseal region. The head, greater trochanter andlesser trochanter each develop a separate secondary ossification center. The center in the head of© 2006 by Taylor & Francis Group, LLC