Reduction in Thigh Muscle Strength Occurs Concurrently but Does Not Seem to Precede Incident Knee Pain in Women: Data From the Osteoarthritis Initiative Cohort

Abstract

Objective: The aim of the study was to investigate whether muscle strength declines before or concurrent with incident knee pain in subjects with and without radiographic knee osteoarthritis.

Design: Osteoarthritis initiative participants with incident knee pain (occurrence of infrequent/frequent knee pain during the past 12 mos at two consecutive follow-up time points (either years Y3 + Y4 or Y4 + Y5) were compared with controls (no incident knee pain) with 2-yr changes in knee extensor strength during BL➔Y2 (before) and Y2➔Y4 (concurrent).

Results: Two hundred two knees (49% women, 40% radiographic knee osteoarthritis) displayed incident pain, and 439 did not (46% women, 23% radiographic knee osteoarthritis). Women with radiographic knee osteoarthritis displayed a significantly greater (P = 0.04) reduction in knee extensor strength concurrent with incident pain compared with controls (mean = -17.6 N vs. +4.5 N), but men did not. A similar trend was observed in women without radiographic knee osteoarthritis, but this was not statistically significant (P = 0.08). There was no significant relationship with change in extensor strength before incident pain (P ≥ 0.43).

Conclusions: These results suggest that in women, incident knee pain is accompanied by a concurrent reduction in knee extensor strength, whereas loss in strength does not precede incident knee pain. The findings encourage interventional studies that attempt to attenuate a decline in extensor strength once knee symptoms occur.

Trial registration: ClinicalTrials.gov NCT00080171.

Conflict of interest statement

Dr. Ruhdorfer and Dr. Culvenor have no disclosure of interest.

Figures

Figure 1.. Participant selection

for cases with knee pain incidence at year 3 or 4 and control knees with no pain throughout the observation period. For the selection process pain frequency (SX), Numeral Rating Scale (NSR), Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC) knee pain score, and isometric thigh muscle strength were used. KLG=Kellgren-Lawrence grade.

Figure 2.. Study design:

Cases had no knee pain from baseline to year 2 but reported incident knee pain, i.e. frequent or infrequent knee pain, at year 3 or year 4 that needed to persist the subsequent follow-up time point. Controls had no knee pain throughout basline to year 4.

Figure 3. AB:

2-year % changes (with 95% confidence intervals) in knee extensor strength in women and men without and with established radiographic knee osteoarthritis (OA) in the time prior (baseline [BL] to year 2 [Y2]) and concurrent (Y2 to Y4) to the incidence of knee pain. The asterisks indicate p≤0.05 for BL vs Y2 or Y2 vs Y4.