We are delighted that our article sparked discussion of the importance of
reestablishing the joint line in knee replacements after tumor resection. Dr.
Springfield presents a clear tutorial on how to accomplish this: match the
femoral resection and replacement lengths, and then match the tibial resection
and replacement lengths. This tautology is everyone's goal. For various
reasons, we were not always able to achieve it.Nevertheless, discussion of the average technical adequacy of the procedure
misses the point. Citing the high joint line in our patients as the cause
("their mean LT/HI... ratio of 1.3 is clearly abnormal and indicates
that, on the average, the joint lines are abnormally high"), Dr.
Springfield overlooks the paradox that the LT/HI ratio was low in patients
with impingement (0.9). This vitiates his argument. Curiously, the high ratios
that he understandably criticizes (1.4) were found in patients without any
impingement. When the reader looks at the data, it is clear that the ratios
are not so important and another cause for patellar impingement should be
sought. Even when the joint line is reproduced accurately (in our case, with a
minimum 15 to 17-mm tibial cut, 3-mm metal-backed tray, and either a 12 or
14-mm polyethylene tibial bearing), the problem still occurs. Why?