Hip
Osteoarthritis as the cause for Knee Osteoarthritis in the Multicenter
Osteoarthritis Study

Background/Purpose:

While
the hip and knee are linked biomechanically, there have been no studies of the
risk of knee OA in persons with hip OA.  Unilateral hip OA has been shown to
increase dynamic load and bone mineral density in the contralateral knee, thus theoretically
putting the contralateral knee at risk for OA development.  However, weak hip
abductor muscles which can be seen in hip OA can lead to an increased knee
adduction moment on the ipsilateral leg, possibly increasing risk for knee OA ipsilaterally. 
We examined the risk of knee OA in those with hip OA in the Multicenter
Osteoarthritis Study (MOST).  We secondarily tested whether hip OA increased
the risk of ipsilateral or contralateral knee OA.

Methods:

MOST
is a NIH funded longitudinal cohort study of risk factors for knee OA.  For radiographic
hip OA assessment, we used long limb films which included hip imaging obtained
at baseline.  For knee OA assessment, PA and lateral weight bearing films were
obtained at each examination up to 84 months and read for tibio-femoral and
patella-femoral OA.  The exposure groups were subjects with or without radiographic
hip OA at baseline, and we excluded persons with any radiographic knee OA at
baseline.  The outcome was incident radiographic knee OA at any of the
follow-up exams (30, 60, or 84 months). 

For
the 1st analysis, we assessed the risk of radiographic knee OA in subjects with
or without radiographic hip OA.  The risks of incident radiographic knee OA were
compared among the exposure groups after excluding any subjects with hip
replacements during follow-up.  The analysis was adjusted for knee OA risk
factors including age, sex, BMI, knee injury/surgery, leg length inequality.  

For
the 2nd analysis, we assessed the risk of contralateral and ipsilateral knee OA
in subjects with unilateral radiographic hip OA in a matched within-person
analysis.  We examined the risk of incident radiographic knee OA (ipsilateral
vs contralateral to the affected hip).

Results:

For
the 1st analysis, of the 989 subjects eligible, the risk of incident radiographic
knee OA in subjects with any radiographic hip OA was greater than risk of
incident radiographic knee OA in subjects without radiographic hip OA (see
table).  For the 2nd analysis, there was a trend for incident radiographic knee
OA for the contralateral side, but this did not meet statistical significance
(see table).

Conclusion:

Subjects
with radiographic hip OA had an increased risk of incident radiographic knee
OA.  While our findings were limited by small numbers, we did not find a
special association of hip OA with either contralateral or ipsilateral knee OA,
suggesting that in persons with hip OA, both knees are at increased risk of OA.