For comparative purposes, the common base 
plane that had been milled on the corners 
of the aluminum block was considered to 
at a 10.00mm elevation in the stereo model. 
It was decided to plot lmm real world contour 
intervals above and below this common plane. 
Thus, the contours that were plotted were at 
| 7mm elevation intervals in the stereo model. 
| The 10.00mm base plane in the model trans- 
lated to an elevation of 2.286mm in the real 
world. Low points in each concave pocket 
were measured stereometrically, the loca- 
tions marked and the elevations indicated. 
High points on the top surfaces and saddle 
of the component were also recorded. 
The polyethylene tibial component was first 
measured photogrammetrically, before the 
initial cycle in the MIT testing machine. 
It was then subjected to several wear 
cyclings in the machine under different 
loading conditions. Measurements were 
made on the component after each test, 
both manually and photogrammetrically, and 
the amount of wear was noted. The final 
and most severe cycling consisted of 61 hours 
in the machine with an intentional misalign- 
ment, simulating certain clinical problems. 
The comparative results of the photogram- 
metric measurement after this most severe 
cycling are shown in Figure 8, on the manu- 
Script from the K-480 stereoplotter. The 
data has been transformed to real world 
values. The solid contours on the manu- 
Script represent the prosthesis before 
cycling. The broken contours show the 
wear after the final cycling.  Grooves were 
  
Figure 7 — The Kelsh K-480 plotter. 
  
+4.157 
      
  
+ 1100 
  
  
   
  
     
B RÀ 
ZZ 1 SET = 
ZU zz. * 
  
  
BASE PLANE AT 2.286 mm 
(MILLED CORNERS OF ALUMINUM BLOCK) 
  
  
Figure 8 — The manuscript from the Kelsh 
K-480, with the wear after the 61 hour 
cycling indicated by the dashed lines. 
39