Patella infera may occur after reconstruction of the I anterior cruciate li
gament (ACL), high tibial osteotomy and total knee replacement (TKR), Restr
iction of movement of the knee and pain may result. Our aim was to compare
the incidence and to assess the effects of patella infera after TKR and uni
compartmental knee replacement (UKR),
We reviewed radiographs of the knees of 84 patients who had had either TKR
or UKR as part of a randomised, controlled trial. The length of the patella
r tendon was measured on serial radiographs taken before, at eight months a
nd at five years after operation,
There was no significant change in the length of the patellar tendon after
UKR, but a significant reduction was observed after TKR, Five years after t
he operation, the shortening of the tendon had increased to a mean of 3.5 m
m, Of the knees with TKR reviewed at five years, 34% developed patella infe
ra, defined as 10% or more of shortening, compared with 5% of those with UK
R, Shortening was greatest in those knees which had required a lateral rele
ase; in this subgroup the mean shortening was 7.2 mm, Shortening correlated
with restriction of movement and pain in the knee.
Our study has shown that patella infera develops in most patients after TKR
with lateral release, and in approximately 25% of patients after TKR witho
ut this additional procedure, Patella infera rarely occurs after UKR, It is
associated with restriction of movement and pain in the knee, It may be an
effect of the more extensive exposure required to perform TKR and may, in
part, explain the better clinical results of UKR.