Monday, May 10, 2010

Orchids and Subscapularis Tears

Photo by van swearingen

The Star of Bethlehem orchid is one of the best arguments for the existence of evolution and natural selection.

This orchid (the Madagascan star orchid Angraecum sesquipedale) has a foot long nectar tube that hangs from its back. Darwin predicted what the pollinator of this orchid would look like, over forty years before its actual discovery:

"In several flowers sent to me by Mr. Bateman I found nectaries eleven and a half inches long, with only the lower inch and a half filled with nectar....It is, however, surprising that any insect should be able to reach the nectar....In Madagascar there must be moths with proboscides capable of extension to a length of between ten and eleven inches! This belief of mine has been ridiculed by some entomologists."

In 1903, a giant Madagascan hawk moth with such a long tongue was discovered, and was given the name Xanthopan morganii praedicta, Latin for "predicted moth".

Photo by kqedquest

Darwin was able to predict the existence of an unexpected moth in Madagascar, a striking example of the predictive and explanatory power of the theory of evolution.

In a different sphere of science, the powerful technology of MRI can predict the existence of an unexpected clinical condition. Twelve year-old boy who is a baseball pitcher, with pain after an injury:

Axial T2 fatsat image reveals a complete avulsion of the subscapularis muscle and tendon (yellow arrows). The avulsed bone and cartilage fragment (red arrows) are also seen.

A sagittal T2 fatsat image depicts visualizes the subscapularis tendon footprint, which is now replaced by fluid:

Injuries to the rotator cuff of children are often not suspected by the clinician, due to their rarity. There are only a few reports in the literature, and most of these describe injuries to the subscapularis, often avulsion fractures. The few reports that do exist about subscapularis tendon injuries often describe this injury in throwing athletes, although other sports can be involved, including wrestling and hockey.

Conventional radiographs and CT may reveal a flake of bone related to the avulsion injury. Even when radiographs are initially normal, repeat radiographs several weeks after injury may reveal soft tissue calcification in some cases (Tarkin et al, AJSM 2005, 33:596-601). MRI is very useful in this patient population, as it will assess the shoulder area for multiple causes of pain, including growth plate injuries, rotator cuff tears, and glenohumeral instability.

Thus, when evaluating an adolescent athlete with shoulder pain, one must keep in mind the possibility of an injury to the rotator cuff, particularly when symptoms suggest rotator cuff dysfunction.

1) Tarkin et al., "Rotator Cuff Tears in Adolescent Athletes", AJSM 2005, 33:596-601.
2) Kleposki et al., "Rotator Cuff Injuries in Skeletally Immature Patients", Orthop Nursing 2009, 28:134-138.
3) Sugalski et al., " Avulsion Fracture of the Lesser Tuberosity in an Adolescent Baseball Pitcher", AJSM 2004, 32:793-796.
4) White and Riley, "Isolated avulsion of the subscapularis insertion in a child. A case report". JBJS Am 1985, 67:635-636.

Vic David MD