Speed Effects on Knee Joint Loading in People with Unilateral Transtibial Amputation Ryan D. Wedge PT, PhD1*#, Alexander Clark1* Brian R. Umberger PhD**, Frank C. Sup***, John D. Willson1* *Dept of Physical Therapy, East Carolina University; **School of Kinesiology, University of Michigan; ***Department of Mechanical and Industrial Engineering, University of Massachusetts # Corresponding Author (wedger19@ecu.edu); Data was collected at the University of Massachusetts Amherst (Amherst, MA)
Introduction
People with unilateral lower limb amputation have a greater prevalence of knee osteoarthritis (OA) in the intact limb compared to people without amputation [1].
Greater OA prevalence may be due to greater load magnitude or stance time duration on the intact limb compared with the prosthetic limb [2], leading to greater cumulative loading, which has been linked to OA [3].
Slower walking speeds reduce peak knee loads [4], therefore that may be one reason why people with amputation generally walk slower than able-bodied people [5] even though it increases stance time.
It is unclear how these combined consequences of walking speed affect per-step loads, and loads over a given distance. The purpose of this preliminary study was to understand tibiofemoral joint loading between the prosthetic and intact limbs across gait speeds.
We hypothesized that people with unilateral amputation would have greater peak forces and impulses on the intact limb compared with the prosthetic limb.
Methods
Four people with unilateral transtibial amputation from non-vascular causes (2 female; mass: 65.6 ± 9.1 kg; height 177.2 ± 9.2 cm; years 38.5 ± 9.9 years; preferred walking speed: 1.24 ± 0.04 m·s-1)
Participants walked overground at preferred and ± 20% preferred speed
Motion capture marker data collected at 240 Hz and ground reaction force data collected at 2400 Hz
Preferred speed was determined by timing 6 m in the middle of a 10 m walk for 3 trials [6].
Tibiofemoral contact forces were estimated with an established model [7]. Joint kinematics and kinetics were calculated using an inverse dynamics approach. Muscle force estimates for the quadriceps, hamstrings and gastrocnemius were derived from the resulting net joint moments across stance phase using published muscle moment arms as a function of joint angle and muscle cross sectional areas. Muscle forces and joint reaction forces were combined to yield total tibiofemoral joint axial force, which was distributed to the medial and lateral proximal tibia in a manner to achieve the calculated frontal plane knee joint moment.
The gastrocnemius was removed when estimating joint contact force on the prosthetic limb because the gastrocnemius does not perform the same biomechanical role after a transtibial amputation.
Two way (limb x speed) ANOVA (α=0.05) to test for differences in medial and lateral tibiofemoral joint contact peak force and force impulse.
Results
The intact limb had significantly greater peak force (p<0.001) and significantly greater impulse (p<0.001) than the prosthetic limb during stance across speeds, except for the lateral impulse speed effect (p<0.508) (A-D).
Medial tibiofemoral peak forces had a significant (p<0.002) interaction between limb and speed, indicating that intact and prosthetic limb medial compartment peak forces increased with greater speeds, but only for the intact limb (C).
Discussion
Greater tibiofemoral peak force and force impulse have been associated with medial knee OA in able bodied [3] and people with unilateral amputation [8].
Based on our preliminary results, people with unilateral amputation generally experience both greater peak force and force impulse on the intact limb than the prosthetic limb regardless of walking speed, and medial compartment peak forces increase directly with walking speed for the intact limb.
Interventions to reduce inter-limb loading asymmetry during walking may reduce this OA risk factor. However, the effects of such interventions on other aspects of walking such as gait stability and metabolic cost of transport require further study.
Significance
In this preliminary study, people with unilateral amputations utilizing prostheses have greater knee loads on the intact limb that may promote OA onset or progression. Minimizing inter-limb loading asymmetry through gait re-training may prevent secondary disability.
Acknowledgements
Funded through NSF-NRI (IIS-1526986). Data collected with assistance from Andrew LaPre and Mark Price.
References
1. Norvell et al. (2005) APMR; 2. Sanderson & Martin (1997) G&P; 3. Maly et al. (2013) G&P; 4. Waters & Mulroy (1999) G&P; 5. Lenton et al. (2018) PloS One; 6. Johnson et al. (2020) G&P; 7. Barrios & Willson (2017) JAB; 8. Miller et al. (2017) PeerJ