Re: rejection of cloned cartilage

Dear Rafe,

First, let me apologize for not answering your question sooner. The 
academic summer included meetings and a little vacation time for me. 

The basic answer to your question is not a question of rejection, but 
rather of anatomy. You are partially correct in inferring load bearing 
demands as a limiting factor. The load there is very high, and to my 
knowledge, "cloned" cartilage is as yet not as tough and durable as the 
natural version. But primarily, it has to do with the location. There's 
nothing mysterious in the local environment, but rather, there is simply no 
room for a surgeon to work there without causing more damage to the joint 
than would be repaired by the implant. I checked some websites that offer 
anatomical illustrations, but couldn't find a really good one that 
illustrates the specifics, so you may want to consult an anatomy text to 
explore this further.

Basically, the medial collateral ligament, the one that connects the femur 
to the tibia on the "inside" of the knee, and the cartilage meniscus that 
cushions the top of the tibia just inside that ligament (the "medial 
chondyle", the inner of the two "knobs" at the top of the tibia) and bears 
the load transferred from the femur, are "welded" to the medial surface of 
the tibal chondyle. There's no way to access the medial side of the upper 
surface of the tibia to add cartilage without stripping these away and 
causing all sorts of potential additional problems. On the outer side, 
there is a space between the lateral collateral ligament and the tibia, 
giving a surgeon more room to work. Also, the lateral chondyle (i.e., the 
outer "knob") of the tibia is less completely covered by cartilage 
meniscus, again giving more access surgically without disturbing as much of 
the normal knee structures. 

I hope this answers your question, and again, my apologies for making you 
wait.


Paul Odgren, Ph.D.
Dept. of Cell Biology
University of Massachusetts Medical School
Worcester