osteometry; the measurement of the bones 133 



iii. angles 



1 Retroversion angle 



2 Inclination angle 



3 Biaxial angles 



These angles are involved in the description of the noticeable bend 

 which the upper end of the tibia makes with the remainder of the shaft, 

 best seen when the bone is in profile. They are best measured with a 

 protractor upon a projection on a sheet of paper, drawn from a bone 

 placed horizontally above it, with the lateral (outer) aspect uppermost. 

 Certain essential points and lines are first located on the bone and then 

 projected upon the paper. 



The termini of the mechanical axis are first determined as follows, 

 and marked on the bone with a pencil. The proximal point is the center 

 of the deepest portion of the articular surface of the inner condyle, (B) 

 and the distal one is in the middle of the very slight ridge that runs 

 sagitally across the distal articular surface {A). The line drawn through 

 these is the mechanical axis. The next is the determination of the plane 

 of inclination of the articular surface of the medial condyle, which is 

 effected by placing a steel needle tangent to the surface and in a dorso- 

 ventral direction, and fixing it in the desired position with wax. ( JK) 



When these preliminaries are done the bone is placed in a horizontal 

 position above a large sheet of paper lying on the table, with the lateral 

 (outer) surface facing directly upwards, and the essential points projected 

 upon the paper, precisely beneath its position on the bone. The hold- 

 ing of the bone may be effected by means of a clamp upon an iron retort 

 stand, and the projections drawn by diagraph or parallelograph. Indeed, 

 a fairly accurate projection may be made by placing the bone almost in 

 contact with the paper, and then tracing around it with a pencil from which 

 the wood upon one side has been whittled away. The pencil must be 

 held perpendicularly. This need not be a complete contour tracing, 

 but must include the accurate locating of the two points in the two artic- 

 ular surfaces above mentioned, two points along the course of the steel 

 needle, as far apart as convenient, and bits of the contour of the sides of 

 the shaft in the vicinity of the nutrient foramen. 



When these points are located, connecting lines are drawn through 

 and between these as follows: — (see Fig. 38) 



(a) The mechanical axis; from the distal articular point, A, to 

 the proximal one, B. 



(b) The line EF, directly across the shaft, about 2 cm below 

 (distal to) the tuberosity nurti. This line, limited at both 

 sides by the shaft contours, is bisected at C, which is the 

 point sought. 



(c) The diaphysial axis; drawn from the point A, in common with 

 the former axis, through the point C, coming out proximately 

 wherever it may. (here, in the figure, at D) 



