A recent study (Andriacchi et al., 2004) examined the relationship between loading and motion at the knee during walking and the response in healthy cartilage relative to cartilage with osteoarthritis. Healthy cartilage thickness increased on the medial condyle in subjects with a higher adduction moment based on a significant (P < 0.05) positive correlation between the ratio of medial to lateral condyle thickness and adduction moment (see Figure 77.7). In contrast, for osteoarthritic cartilage, the medial to lateral condyle thickness ratio decreased with an increase in the adduction moment.
In patients with knee osteoarthritis, it has been shown that individual variations in the mechanics of walking can influence the rate of progression of knee osteoarthritis (Miyazaki et al., 2002) and the outcome of treatment for medial compartment osteoarthritis at the knee (Prodromos et al., 1985; Wang et al., 1990). For example, varus alignment of the knee has been related to the presence and progression of medial compartment knee osteoarthritis. This type of alignment theoretically would place higher load on the medial side of the knee. A surgical procedure, the high tibial osteotomy (HTO), involves realigning the tibial plateau to reduce the load on the medial compartment of the knee. Patients who adopt a gait pattern with a low adduction moment following surgery and patients with less severe disease have a better outcome with an HTO and a slower rate of disease progression (Prodromos et al., 1985; Wang et al., 1990).
Patients with knee osteoarthritis typically walk with greater knee adduction moments than age-matched control subjects (Miindermann et al., 2004), which is also a strong predictor for the presence (Baliunas et al., 2002; Gok et al., 2002; Schnitzer et al., 1993), severity (Miindermann et al., 2004; Sharma et al., 1998), and rate of progression (Miyazaki et al., 2002) of medial compartment knee osteoarthritis. In addition, patients with knee osteoarthritis seem to experience a smaller range of knee flexion during the stance phase of walking (Childs et al., 2004; Kaufman et al., 2001; Messier et al.,
b Knee Adduction Moment [%Bw*Ht]
Figure 77.7 Femoral cartilage thickness increases with load for healthy cartilage and decreases with load for cartilage with osteoarthritis (OA). a. The load bearing regions of interest (ROI) are indicated by the rectangular areas shown on the color thickness map of the femoral cartilage. b. The medial-to-lateral ratio of the average ROI thickness was correlated to the adduction moment normalized as percentage body weight times height (%Bw*Ht) for an osteoarthritic group and a healthy group.
1992) that is associated with a smaller net quadriceps moment (Kaufman et al., 2001).
As previously noted, the adduction moment at the knee has been related to the progression and treatment outcome for medial compartment osteoarthritis at the knee. In a recent study (Mundermann et al., 2004) of 44 patients (88 knees) with osteoarthritis of the medial compartment of the knee, it was shown that the adduction moment at the knee during walking was significantly lower in patients with less severe disease. Severity of the disease was assessed by a clinical rating system reported by Kellgren and Lawrence (K-L) (Kellgren and Lawrence, 1963). Patients were diagnosed to have knee osteoarthritis in one or both knee joints based on clinical, radiographic data, and K-L grades ranged from 1 to 4 (most severe) for both knees. A statistically significant increase in knee adduction moment was found for knees with K-L grade 3 or 4 compared to asymptomatic matched control knees (P = 0.039) and for knees with K-L grade 3 or 4 compared to knees with K-L grade equal to or smaller than 2. In addition, the mechanical axis varus alignment was significantly greater in patients with more severe osteoarthritis.
These results suggest that differences in the adduction moment are less likely the initial cause for osteoarthritis, but rather the effect of morphological changes in the pathological joint such as medial compartment joint space narrowing. This increase in adduction moment at later stages of osteoarthritis may lead to an accelerated rate of disease progression. Some patients may be able to alter their walking mechanics to reduce their maximum knee adduction moment at very early stages of the disease and reduce the rate of progression. This explanation is supported by the fact that patients with less severe knee osteoarthritis appear to have different gait mechanics than asymptomatic control subjects and are able to reduce the adduction moment by walking slower during everyday activities.
The primary changes in gait that occur with increasing age are slower walking speeds, reduced step length, and increased double support time (Kerrigan et al., 1998; Riley et al., 2001; Winter et al., 1990). It has been suggested (DeVita and Hortobagyi, 2000) that age causes a redistribution of joint torques and powers, with the elderly using their hip extensors more and their knee extensors and ankle plantar flexors less than young adults when walking at the same speed. This shift in power generation could be caused by the physiological changes in muscle (Frontera et al., 2000; Jubrias et al., 1997; Kent-Braun and Alexander, 1999; Lindle et al., 1997; Stackhouse et al., 2001; Stevens et al., 2003), where the knee extensor muscles in the elderly are simply not capable of producing similar forces than in young adults.
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