High prevalence of osteoarthritis in the intact leg knee joint of transtibial amputees may be related to peak knee contact forces rather than knee contact impulses, according to recently published study results.
“Individuals with unilateral transtibial amputations have altered gait mechanics and muscle coordination patterns relative to non-amputees, which may lead to the onset of joint disorders with prolonged use. For example, transtibial amputees have an increased prevalence and early onset of osteoarthritis (OA) and pain in the intact leg knee joint relative to the residual leg and non-amputees. However, the biomechanical mechanisms that contribute to the increased prevalence remain unclear,” the researchers wrote. “Recent work has investigated knee joint intersegmental forces across a range of walking speeds and found no significant differences between the intact and residual legs or between the intact and non-amputee legs. However, inverse dynamics-based intersegmental forces often underestimate joint contact forces, as they do not account for the compressive forces from muscles. In addition, altered muscle coordination patterns and increased co-contraction of the residual leg vasti and hamstring muscles in transtibial amputee walking likely influence the knee joint contact forces.”
Researchers used previously collected kinematic, ground reaction force and electromyographic data from 14 patients with a transtibial amputation and 10 non-amputees to generate forward dynamics simulations of the stance phase when the joint contact forces were highest in the amputee residual leg, amputee intact leg and non-amputee left leg.
In the axial and mediolateral directions, researchers found greater peak tibiofemoral contact forces and impulses in the intact and non-amputee legs vs. the residual leg. While the intact leg had a greater peak axial contact force vs. the non-amputee leg, researchers found a greater stance phase joint contact impulse in the non-amputee leg. In the non-amputee and intact legs, the largest contributors to joint contact forces were the vasti and hamstrings in early stance and the gastrocnemius in late stance, with the soleus and gluteus medius largely contributing through dynamic coupling even though they do not span the knee joint, according to study results. The prosthesis contributed largely to joint forces in the residual leg whereas the soleus contributed in the intact and non-amputee legs.
“We expected peak forces and impulses to be greater in the unaffected side of people with amputations relative to non-amputees because they have a greater prevalence of developing OA on that side, but we found that while the intact leg peak axial force was greater, the stance phase axial force impulse was not,” Anne K. Silverman, assistant professor in the Department of Mechanical Engineering at Colorado School of Mines, told O&P Business News. “These results indicated to us that the peak force may be more important in understanding the development of [OA].”
Prevention of OA
While the researchers investigated joint loading, previous studies have shown that bodyweight, prior trauma, joint laxity, joint malalignment and altered loading distribution also influence the risk of OA. In their research, Silverman and colleagues found one of the contributing factors to a greater peak force in the intact leg was due to the hamstrings. According to Silverman, training amputees to alter muscle coordination could help reduce the peak force in the hamstring, which may reduce the risk of OA.
Silverman said it will be important to use a complex model of the knee joint in future studies of amputee walking to help further pinpoint what mechanisms can lead to the increased prevalence of OA, while patient-specific simulations may reveal how “individual prosthetic devices, movement strategies and remaining residual leg musculature contribute to knee contact loading and eventual OA development.”
“In the future we plan to investigate the loading distribution in the knee joint. In this study, we quantified the net force, but there could certainly be differences in how this net load is distributed in the joint. This distribution is likely important in understanding the development of a disorder like OA,” Silverman said. “[OA] generally presents itself in the medial compartment of the knee more often than the lateral compartment of the knee, for example. Thus, understanding the loading distribution across compartments could give us much more information regarding the increased prevalence of OA in people with lower-limb amputations.” — by Casey Tingle
Disclosure: Silverman has no relevant financial disclosures.