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A NEW JOINT-FORMATION 
By ales HRDLICKA 

The specimen herein described shows in a very remarkable 
and beautiful way the great vis medicatrix naturcE, It consists of 
bones of the left arm and forearm, found by Mr Harlan I. Smith 
during his exploration of a prehistoric burial-place on the Fox 
farm at Mayslick, Kentucky. This exploration was conducted 
under the direction of the department of anthropology of the 
American Museum of Natural History. To the officers of the 
museum I am greatly indebted for the privilege of studying this 
interesting specimen, and for permission to publish the following 
description and the accompanying photographic illustration. 

As will be seen from the plate (xxvil) the interest of the 
specimen lies mainly in the fact of a new joint-formation between 
the head of a dislocated radius and a bony process proceeding 
from the distal end of the humerus. 

The genetic history of the new joint, from what we can ob- 
serve in the bones, is as follows : Originally there were here the 
three normal, and in all probability already adult, bones of the 
arm and the forearm. Subsequently the ulna became fractured a 
little above the middle. This was probably an incomplete frac- 
ture, and at the same time there took place a complete forward 
dislocation of the head of the radius, but without either this bone 
or the humerus being injured. Neither the fracture nor the dis- 
location was reduced. The broken ulna became united by a 
small callus. More callus bone was thrown out around the spine 
of the proximal segment, which was inclined to and possibly at 
times touched the interosseous border of the radius, and event- 
ually this part of the proximal segment became united to the 
radius by an osseous band nearly 3 cm. wide. 

The head of the radius remained fully dislocated, and has un- 

550 



AMERICAN ANTHROPOLOGIST 



N. S., VOL. 1, PL. XXVll 




A NEW JOINT-FORMATION 

a. The bones separated. 3. The bones in position 



hrdlicka] a new JOINT-FORMATION 551 

dergone apparently no change whatever, unless it is a very slight 
lengthening. This supports the probability that the bones at 
the time of the fracture and dislocation were those of a fully de- 
veloped adult. There is no indication that the humerus was in 
any way injured ; nevertheless, at some time after the injury, 
there started from the anterior border, and partly also from the 
external surface of the humerus, immediately above the coronoid 
fossa, a bony process, which grew forward, downward, and slightly 
outward until it exactly met the free and, as already stated, 
unchanged head of the radius, forming with this head not an 
ankylosis, but a new, free joint. The mean length of this process 
is 3.1 cm. ; its circumference at its middle is 3.5 cm. ; the diam- 
eters of the joint are antero-posteriorly 2.2 cm., and laterally 2.4 
cm. The process ends in an articular socket which is 7 mm. 
deep in the center, but as parts of the border are broken on one 
side, it might have been i mm. deeper. The surface of the 
socket presents in the middle an irregular row of large vascular 
perforations, but outside of these it is for the greater part 
smooth, and there can be no doubt that it was covered with 
synovium. The distal two-thirds of the process are entirely free 
from the humerus. 

We have here, in brief, then, the following conditions : The 
normal and apparently uninjured humerus sends out through all 
the parts superposed a regular new formation — a veritable pro- 
cess — to meet, support, and form a joint with the head of the dis- 
located radius almost an inch and a half distant. Such formations 
are no doubt extremely rare in man. I have no personal knowl- 
edge of anything closely similar, and I am unable to find such a 
case described. Regenerations of bone to which the condition 
in the specimen is related, are much more frequent in the 
lower animals than in man. 

As to the exciting cause of the new process of bone, it most 
probably was a moderate injury of either the ligaments or the 
periosteum of the distal end of the humerus.