So increasing the Tibia length (bilateral) only is likely to promote arthritis in the hip and knee, however increasing the Femur length (bilateral) only has no known long term issues?
NO! The study was made on 1152 CADAVERIC femurae and tibia, from common people, NOT subject to CLL, without any "increasing" in bone lenght whatsoever.
It's interesting and apparently the first study to evaluate ORIGINAL proportion T/L in regards to arthritis.
But it does not compare in any way the amounts of lengthening in the two bones with afterwards arthritis. It is not a study on the correlation of any elongation whatsoever (either tibia or femur). It's not correct to directly extrapolate the study to CLL.
Why? For several reasons, one of which is that short people usually have shorter tibias also in relative terms. So the study could have concluded also, or INSTEAD, that taller people have more arthritis in certain parts of the body (as other studies also show), due to any reason related to that and not only higher proportion of tibia/femur (eg: taller = heavier weight; bigger tibias AND femurs,...). Big bodies exert more pressure on certain articulations, like knees (and are more prone to some heart diseases, BTW, for example).
Furthermore, one has to take into account diferences in proportions among individuals, populations and diferent initial height, very relevant for the evaluation of proportions, safety, and deciding which bone and by how much amount to lenghten.
Dr. Assayag has a big scientific and academic "authority" but I am also used to read and interpretate scientific articles. He prefers clearly to do femurs elongation and it's simpler indeed.
But tibias may be saffer in several important circumstances, for example, clots, if formed there, are less prone to make all the way up to the lungs, heart or brain and cause lethal thrombosis.
To sum up, a lot of things must be taken into consideration when planning CLL. In general terms, tibias are better for proportions.
This study adds relevant information but it isn't in any way a demonstration that "femurs are better ".