Three-dimensional knee joint contact forces during walking in unilateral transtibial amputees
Introduction
Individuals with unilateral transtibial amputations have altered gait mechanics and muscle coordination patterns relative to non-amputees (e.g., Fey et al., 2010, Silverman and Neptune, 2012), 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 (Burke et al., 1978, Lemaire and Fisher, 1994, Melzer et al., 2001, Norvell et al., 2005, Struyf et al., 2009). However, the biomechanical mechanisms that contribute to the increased prevalence remain unclear.
The etiology of OA is not completely understood, but is partially attributed to increased and/or atypical joint loading (Maly, 2009, Morgenroth et al., 2012). Thus, the increased prevalence of OA in the intact knee of amputees may be a result of greater joint loading relative to the residual leg and non-amputees. Studies of amputee walking have shown elevated intact leg ground reaction forces (GRFs) and joint kinetics relative to the residual leg (Nolan et al., 2003, Royer and Koenig, 2005, Sanderson and Martin, 1997, Silverman et al., 2008) and non-amputee subjects (Nolan and Lees, 2000). Amputees also often have greater stance times on the intact leg relative to the residual leg (e.g., Isakov et al., 2000, Nolan et al., 2003), which may result in greater force impulses in the intact leg knee joint. Identifying differences in knee joint loading in amputees relative to non-amputees is important for understanding the potential biomechanical mechanisms that contribute to the high prevalence of OA in this population.
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 (Fey and Neptune, 2012). However, inverse dynamics-based intersegmental forces often underestimate joint contact forces, as they do not account for the compressive forces from muscles (Zajac et al., 2002). In addition, altered muscle coordination patterns (Fey et al., 2010, Powers et al., 1998, Winter and Sienko, 1988) and increased co-contraction of the residual leg vasti and hamstring muscles (e.g., Culham et al., 1986, Isakov et al., 2001, Pinzur et al., 1991) in transtibial amputee walking likely influence the knee joint contact forces.
A significant challenge to investigating joint contact forces is the extreme difficulty, if not impossibility, of measuring them in vivo. In contrast, musculoskeletal modeling and simulation provide an ideal framework to estimate joint contact forces and quantify the contributions of individual muscles during dynamic movements (e.g., Sasaki and Neptune, 2010, Shelburne et al., 2006, Zajac et al., 2003). The gastrocnemius and soleus muscles have been shown to be large contributors to the knee joint contact force in non-amputee walking (Lin et al., 2010, Sasaki and Neptune, 2010, Shelburne et al., 2006), which may lead to asymmetric knee loading in unilateral transtibial amputees because they no longer have the functional use of these muscles in the residual leg.
The objective of this study was to investigate differences in knee joint contact forces in both the residual and intact legs relative to non-amputees during steady-state walking using three-dimensional musculoskeletal models and forward dynamics simulations. We expected that the peak knee contact forces and stance phase force impulses would be greater in the intact knee relative to the residual leg and non-amputees. In addition, individual muscle contributions to the knee contact forces were quantified to identify the potential biomechanical mechanisms that may contribute to the increased prevalence of OA in the intact knee.
Section snippets
Experimental data collection
Previously-collected kinematic, GRF and electromyographic (EMG) data were used to generate the forward dynamics simulations (Fey et al., 2010, Silverman et al., 2008). Briefly, the data were collected from 14 individuals with transtibial amputation and 10 non-amputees walking overground at 1.2±0.06 m/s (Table 1). Subjects provided informed consent to participate in the experimental protocol approved by an Institutional Review Board. Kinematic data were collected at 120 Hz and GRF and EMG data
Walking simulation results
The experimental kinematics and GRFs were reproduced by the walking simulations in that the three stance simulations largely remained within two standard deviations (2SD) of the experimental walking trials. The residual leg stance simulation had an average difference of 7.11° (2SD=10.54°) across all degrees of freedom and 5.65% body weight (BW, 2SD=5.35%BW) from the average amputee experimental data. The intact leg stance simulation had an average difference of 5.27° (2SD=10.41°) and 5.07%BW
Discussion
The intact and non-amputee peak forces and impulses were larger than in the residual leg in the axial and M/L directions (Table 3, Table 4). The peak anterior force in the intact leg was also larger than the residual leg. These results agreed with our expectations and are supported by previous experimental studies that have shown the greater GRFs on the intact and non-amputee legs relative to the residual leg (Nolan et al., 2003, Sanderson and Martin, 1997, Silverman et al., 2008). The average
Conclusion
The simulations showed the axial and M/L peak knee contact forces and stance phase knee impulses were smaller in the residual leg relative to the intact and non-amputee legs. In the axial direction, the peak knee contact force was higher in the intact leg relative to the non-amputee leg while the knee contact impulse was greater in the non-amputee leg. These results suggest that the peak knee contact force may be more important than the knee contact impulse in explaining the high prevalence of
Conflict of interest statement
There was no conflict of interest in the preparation or publication of this work.
Acknowledgments
This work was supported by the National Science Foundation Grant no. 0346514.
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