Take a look at the cross-section of a femur in Figure 11. A bone is made up largely of porous tissue. As a child grows taller, mainly under the influence of GH or "Growth Hormone" (another hormone from the pituitary gland), calcium makes the bones harder and stronger. One major source of calcium is dairy products, which is why a child should drink milk to strengthen the bones.

As the child grows older and enters puberty, testosterone (in the case of boys) or oestrogen (in the case of girls) works together with growth hormone to increase bone strength by depositing more calcium within the bone, a process known as calcification. A bone grows mainly lengthwise and towards the end of puberty or in early adult life, its rate of growth begins to decrease. The bone stops growing altogether when there is sufficient calcification and when the epiphyseal plates (items 1) "fuse" or harden, thus creating physical barriers to further growth at the ends of the bone.

Hypogonadal teenagers, such as those with Kallmann's syndrome, have little or no testosterone or oestrogen present in their bodies and therefore normal calcification cannot occur during puberty. Consequently, the epiphyseal plates do not appear until long after the normal age of puberty, fusing only partially (item 2) and occasionally failing to fuse at all (item 3). The result is that the bones, especially those in the arms and legs, have continued to grow beyond the normal age of puberty. As you will see in the answer to Question 13, these bones also tend to be weaker than normal healthy bones, because of the inadequate calcification.

Long arms and legs are relatively common characteristics of many forms of hypogonadism. When they appear together, this used to be and sometimes still is referred to rather misleadingly as eunuchoidism. A eunuch is a male who has had his testes removed by castration and subsequently becomes hypogonadal, unable to maintain normal testosterone levels. A eunuchoid has physical characteristics resembling those of a eunuch, but these have become apparent not as a result of castration, but due to a hormonal deficiency such as that found in Kallmann's syndrome. The term "eunuchoidism" is a little inaccurate because long arms and legs are not only observed in hypogonadal men (which the word "eunuchoid" implies) but also in hypogonadal women.

One medical definition of eunuchoidism is when a person's span (the distance from fingertip to fingertip) exceeds his or her height. Normally, one would expect the span to be as much as 4 or 5 inches greater than the height. Normally, the span and height are roughly equal (Figure 12). Many of those with hypogonadism also tend to be of above average height.

Eunuchoidism is more common amongst those hypogonadal people who remain untreated beyond the normal age of puberty. Treatment would have allowed the bones to grow and strengthen almost normally. However, once it has been established that you have eunuchoidism, it is unlikely that your height will ever match your span, because even if you continue growing, your span will also increase; i.e. you will always have some degree of eunuchoidism.