Erik J. Wolf

Three-dimensional joint reaction forces and moments at the low back during over-ground walking in persons with unilateral lower-extremity amputation

BACKGROUND Abnormal mechanics of locomotion following lower-extremity amputation are associated with increases in trunk motion, which in turn may alter loads at the low back due to changes in inertial and gravitational demands on the spine and surrounding trunk musculature. METHODS Over-ground gait data were retrospectively compiled from two groups walking at similar self-selected speeds (~1.35m/s): 40 males with unilateral lower-extremity amputation (20 transtibial, 20 transfemoral) and 20 able-bodied male controls. Three-dimensional joint reaction forces and moments at the low back (L5/S1 spinal level) were calculated using top-down and bottom-up approaches. Peak values and the timings of these were determined and compared between and within (bilaterally) groups, and secondarily between approaches. FINDINGS Peak laterally-directed joint reaction forces and lateral bend moments increased with increasing level of amputation, and were respectively 83% and 41% larger in prosthetic vs. intact stance among persons with transfemoral amputation. Peak anteriorly-directed reaction forces and extension moments were 31% and 55% larger, respectively, among persons with transtibial amputation compared to controls. Peak vertical reaction forces and axial twist moments were similar between and within groups. Peak joint reaction forces and moments were larger (3-14%), and the respective timing of these sooner (11-62ms), from the bottom-up vs. top-down approach. INTERPRETATION Increased and asymmetric peak reaction forces and moments at the low back among persons with unilateral lower-extremity amputation, particularly in the frontal plane, suggest potential mechanistic pathways through which repeated exposure to altered trunk motion and spinal loading may contribute to low-back injury risk among persons with lower-extremity amputation.

Comparison of the Power Knee and C-Leg during step-up and sit-to-stand tasks

For U.S. military service members with transfemoral amputations there are different prosthetic knee systems available that function differently. For example the C-Leg(®) (C-Leg, Otto Bock Healthcare, GmbH, Duderstadt, Germany) is a passive microprocessor knee, and the Power Knee™ (PK, Ossur, Reykjavík, Iceland) provides active positive power generation at the knee joint. This study examined both step-up and sit-to-stand tasks performed by service members using C-Leg and PK systems to determine if the addition of positive power generation to a prosthetic knee can improve symmetry and reduce impact to the remaining joints. For both tasks, average peak sagittal knee powers and vertical ground reaction forces (GRFs) were greater for the intact limb versus the amputated limb across PK and C-Leg groups. For the sit-to-stand task, peak knee power of the amputated limb was greater for PK users versus C-Leg users. Vertical GRFs of the intact limb were greater for the C-Leg versus the PK. The performance of the PK relative to the C-Leg during a STS task illustrated few differences between components and no effect on the intact limb.

Transfemoral amputations: the effect of residual limb length and orientation on gait analysis outcome measures.

BACKGROUND The level of function achieved following a transfemoral amputation is believed to be affected by surgical attachment of the remaining musculature, resulting orientation of the femur, residual limb length, and eventual prosthetic fit. METHODS Twenty-six subjects underwent gait analysis testing in the current preferred prosthesis more than twenty-four months postamputation. The femoral length and orientation angles of each subject were measured from standing postoperative radiographic scanograms. The subjects were separated into groups for analysis on the basis of the femoral shaft angles and the residual limb length ratios. Gait analysis was performed to collect kinematic and temporospatial parameters. RESULTS A good correlation was observed between residual femoral length and trunk with regard to forward lean (r = -0.683) and lateral flexion (r = -0.628). A good correlation was also observed between residual femoral length and pelvic motion with regard to pelvic tilt (r = -0.691) and obliquity (r = -0.398). A moderate correlation was observed with speed (r = 0.550), indicating that subjects with shorter residual limbs experienced a greater excursion in the torso and pelvis, while walking at a slower self-selected pace. A significant correlation (r = 0.721, p < 0.001) was observed between the femoral shaft abduction angle and the residual femoral length; the shorter the residual limb, the more abducted it was. CONCLUSIONS The length of the residual femur substantially influences temporospatial and kinematic gait outcomes following transfemoral amputation, and appears to be more important than femoral orientation with regard to these parameters.

Persons with unilateral transfemoral amputation experience larger spinal loads during level-ground walking compared to able-bodied individuals

BACKGROUND Persons with lower limb amputation walk with increased and asymmetric trunk motion; a characteristic that is likely to impose distinct demands on trunk muscles to maintain equilibrium and stability of the spine. However, trunk muscle responses to such changes in net mechanical demands, and the resultant effects on spinal loads, have yet to be determined in this population. METHODS Building on a prior study, trunk and pelvic kinematics collected during level-ground walking from 40 males (20 with unilateral transfemoral amputation and 20 matched controls) were used as inputs to a kinematics-driven, nonlinear finite element model of the lower back to estimate forces in 10 global (attached to thorax) and 46 local (attached to lumbar vertebrae) trunk muscles, as well as compression, lateral, and antero-posterior shear forces at all spinal levels. FINDINGS Trunk muscle force and spinal load maxima corresponded with heel strike and toe off events, and among persons with amputation, were respectively 10-40% and 17-95% larger during intact vs. prosthetic stance, as well as 6-80% and 26-60% larger during intact stance relative to controls. INTERPRETATION During gait, larger spinal loads with transfemoral amputation appear to be the result of a complex pattern of trunk muscle recruitment, particularly involving co-activation of antagonistic muscles during intact limb stance; a period when these individuals are confident and likely to use the trunk to assist with forward progression. Given the repetitive nature of walking, repeated exposure to such elevated loading likely increases the risk for low back pain in this population.

Amputee locomotion: Lower extremity loading using running-specific prostheses

Carbon fiber running-specific prostheses (RSPs) have allowed individuals with lower extremity amputation (ILEA) to actively participate in sporting activities including competitive sports. In spite of this positive trait, the RSPs have not been thoroughly evaluated regarding potential injury risks due to abnormal loading during running. Vertical impact peak (VIP) and average loading rate (VALR) of the vertical ground reaction force (vGRF) have been associated with running injuries in able-bodied runners but not for ILEA. The purpose of this study was to investigate vGRF loading in ILEA runners using RSPs across a range of running speeds. Eight ILEA with unilateral transtibial amputations and eight control subjects performed overground running at three speeds (2.5, 3.0, and 3.5m/s). From vGRF, we determined VIP and VALR, which was defined as the change in force divided by the time of the interval between 20 and 80% of the VIP. We observed that VIP and VALR increased in both ILEA and control limbs with an increase in running speed. Further, the VIP and VALR in ILEA intact limbs were significantly greater than ILEA prosthetic limbs and control subject limbs for this range of running speeds. These results suggest that (1) loading variables increase with running speed not only in able-bodied runners, but also in ILEA using RSPs, and (2) the intact limb in ILEA may be exposed to a greater risk of running related injury than the prosthetic limb or able-bodied limbs.

Reliability of 3D gait data across multiple laboratories

The aim of this study was to analyze the repeatability of gait analysis studies performed across multiple trials, sessions, and laboratories. Ten healthy participants (6 male/4 female, mean age of 30, mean BMI of 24kg/m(2)) were assessed in 3 sessions conducted at each of the three Centers of Excellence for Amputee Care within the Department of Defense. For each test session, kinematic and kinetic parameters were collected during five walking trials for each limb. One independent examiner at each site placed markers on the subjects. Biomechanical data were collected at two walking speeds: self-selected and Froude speed. Variability of the gait data was attributed to inter-trial, inter-session, and inter-lab errors for each subject. These error sources were averaged across all ten subjects to obtain a pooled error estimate. The kinematic errors were fairly consistent at the two walking speeds tested. Median inter-lab kinematic errors were <5.0° (median 2.3°) for all joint angle measurements. However, the kinetic error differed significantly between walking speeds. The median inter-lab kinetic error for the self-selected speed was 0.112Nm/kg (ICR 0.091-0.184) with a maximum of 0.226Nm/kg. The errors were greatly reduced when the subjects walked at their Froude speed. The median inter-lab error was 0.048Nm/kg (ICR 0.025-0.078, maximum 0.086). These data demonstrate that it is possible to get reliable data across multiple gait laboratories, particularly when gait speed is standardized across testing sessions. A key similarity between sites was the use of identical anatomical segment definitions for the respective gait models.

Mediolateral Joint Powers at the Low Back Among Persons With Unilateral Transfemoral Amputation

OBJECTIVE To analyze mediolateral joint powers at the low back during gait among persons with and without unilateral transfemoral amputation to better understand the functional contributions of tissues in and around the low back to altered lateral trunk movements in this population. DESIGN Retrospective analysis of biomechanical gait data. SETTING Gait laboratory. PARTICIPANTS Twenty persons with unilateral transfemoral amputation and 20 uninjured controls (N=40). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Net joint powers, and total generation (+) and absorption (-) energies, at the low back (L5/S1 spinal level) were analyzed in the frontal plane using inverse dynamics analyses on over-ground gait data collected at self-selected walking speeds (∼1.3m/s). RESULTS Compared with uninjured controls, 4 distinctly larger positive phases of mediolateral joint power at L5/S1 were evident in persons with transfemoral amputation, occurring before and after each heel strike. Total generation energies throughout the gait cycle were also larger (P<.001) among persons with transfemoral amputation (4.8±1.4J) than among uninjured controls (1.3±0.7J). CONCLUSIONS Larger positive phases of joint power at L5/S1 in the frontal plane support previous suggestions that persons with transfemoral amputation use a more active mediolateral trunk movement strategy, although such an active trunk movement strategy with transfemoral amputation may contribute to higher metabolic energy expenditures and low back pain risk.

Performance of conventional and X2® prosthetic knees during slope descent

BACKGROUND Individuals with transfemoral amputation often have difficulty descending sloped surfaces due to increased lower extremity range of motion and torque requirements. The X2®, a new microprocessor-controlled prosthetic knee, claims to improve gait over sloped terrain. The aim of this study was to evaluate how experienced prosthesis users descended a sloped surface using the X2®, compared to a conventional knee, either mechanical (MECH) or microprocessor (MP). METHODS Descent technique and biomechanics were assessed in 21 service members with unilateral transfemoral amputation as they descended an instrumented 10° slope at a self-selected walking velocity. FINDINGS Use of the X2® in the MECH group resulted in greater hill assessment scores (8.5 to 11.0, P=0.026), due primarily to decreased reliance on handrail use. The use of the X2® in the MP group increased prosthetic knee flexion to a median of 6.4° at initial contact (P=0.002) and 73.7° in swing (P=0.005), contributing to longer prosthetic limb steps (P=0.024) and increased self-selected velocity (P=0.041). Additionally, the use of the X2® in the MP group increased prosthetic limb impact peaks (11.6N/kg, P=0.004), improving impact peak symmetry to -1.3% (P=0.004). INTERPRETATION Decreased reliance on handrail use as MECH users descended in the X2® indicate improved function and perhaps greater confidence in the device. Additional biomechanical improvements for existing MP users suggest potential longer-term benefits with regard to intact limb health and overuse injuries.

Mechanical testing for three-dimensional motion analysis reliability

The purpose of this study was to use simple mechanical tests to evaluate the reliability of three-dimensional motion analysis systems and biomechanical models. Three different tests were conducted at four motion analysis laboratories where clinical care and research studies are routinely performed. The laboratories had different motion capture systems, different types and number of cameras, different types and numbers of force plates and different biomechanical models. These mechanical tests evaluated the accuracy of the motion capture system, the integration of the force plate and the motion capture system, and the strength of the biomechanical model used to calculate rotational kinematics. Results of motion capture system accuracy tests showed that, for all labs, the error between the measured and calculated distances between markers was less than 2mm and 1° for marker separations which ranged from 24mm to 500mm. Results from the force plate integration tests demonstrated errors in center of pressure calculation of less than 4mm across all labs, despite varied force plate and motion system configurations. Finally, errors across labs for single joint rotations and for combined rotations at the hip and knee were less than 2° at the hip and less than 10° at the knee. These results demonstrate that system accuracy and reliability can be obtained allowing the collection of comparable data across different motion analysis laboratories with varying configurations and equipment. This testing is particularly important when multi-center studies are planned in order to assure data consistency across labs.

Use of a Powered Versus a Passive Prosthetic System for a Person with Bilateral Amputations during Level-Ground Walking

ABSTRACT Persons who have had bilateral lower-limb amputations, especially transfemoral amputation, must use biomechanical compensations to ambulate. Compensations during gait produce abnormal loads on the body and may reduce efficiency. Recent prosthetic advances have attempted to mimic the lost musculature by adding power to knee and ankle systems. A patient with bilateral amputations (right transtibial, left transfemoral) was evaluated 10 months after injury. The patient initially presented wearing a passive prosthetic system and was then fit with a powered prosthetic system and allowed to acclimate for 1 month. Kinematic and kinetic data were collected while the patient walked overground wearing both systems. The patient showed greater symmetry of step length, decreased vertical ground reaction force, and increased limb transition work using the powered system. Biomechanical variables showed some improvements when using a powered prosthetic system, which may indicate increased mechanical efficiency and decreased lower-limb loading.