Abstract
Varus-producing distal femoral osteotomy (DFO) is an established procedure to correct
genu valgum in patients with osteoarthritis and gait abnormalities. DFO has also been
proposed for the treatment of patellar instability in patients with valgus alignment.
However, it is not known how DFO affects parameters associated with patellar instability.
This study evaluated radiographic changes after DFO with variable degrees of correction
on six cadaveric knees, with the hypothesis that improving mechanical alignment would
improve radiographic parameters related to patellar instability. Controlled laboratory
is the study design. Six lower-limb cadaveric specimens were obtained after approval
by the Institutional Review Board. A lateral opening wedge DFO was performed on each
specimen with correction blocks of 6, 10, and 14 mm. The mechanical axis, tibiofemoral
angle (mTFA), distal femoral angle (mDFA), Caton Deschamps index (CDI), insall salvati
index (ISI), tibial tubercle to trochlear groove distance (TT-TG), and patellofemoral
congruence angle (PFCA) were measured on computed tomography (CT) scans at baseline
and after each correction block. At baseline, a mean varus alignment of the limbs
was observed (mTFA: 2.7 ± 2.8 degrees, mDFA: 87.6 ± 1.0 degrees). The baseline patellar
height was normal (CDI: 0.9 ± 0.2, ISI: 1.0 ± 0.1). Statistically significant decreases
in mechanical axis and TT-TG distance and increases in mDFA and mFTA were found with
increasing block size. The TT-TG distance was decreased by −1.6 mm (95% confidence
interval [CI]: −2.27 to −0.86), −3.8 mm (95% CI: −4.8 to −2.8), and −4.0 mm (95% CI:
−5.4 to −2.7) with a 6, 10, and 14 mm block, respectively. No differences were observed
in patellar height when measured with CDI or ISI after any block size. In a cadaveric
model, DFO significantly affects the mechanical axis and TT-TG distance. Specifically,
this study found a mean decrease in TT-TG of −3.8 mm when performing a 10 mm opening
wedge osteotomy. No changes in patellar height were observed.
Keywords
patellar instability - distal femoral osteotomy - genu valgum - radiologic measurements