- Email: [email protected]
Influence of prosthesis alignment on the standing balance of below-knee amputees
Influence of prosthesis alignment on the standing balance of below-knee amputees E Isakov
MD, MSC’,
J Mizrahi
DSC*,l,
Z Susak
MD’, I
Ona
cp3,
N Hakim
BSC’
‘Biomechanics Laboratory, Loewenstein Rehabilitation Hospital, Ra’anana; *Department of Biomedical Engineering and the Julius Silver Institute of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa; and 3’Gapim’ Ltd, Loewenstein Hospital Branch, Ra’anana, Israel
Summary The effect of alignment of the prosthesis on the standing balance of below knee amputees was investigated in this work. Alignment variations consisted of varus and valgus tilt and plantar- and dorsiflexions. The foot-ground reaction forces measured in the anteroposterior, mediolateral, and vertical directions as well as global parameters describing the total sway activity, asymmetry, and weight-bearing imbalance were used to compare the various alignment positions studied. The results indicate the presence of a common standing pattern in below-knee amputees, where activity of the foot-ground reaction forces in the anteroposterior direction is significantly higher in the contralateral limb compared with the amputated limb. It was also found that the varus and valgus alignments were the least stable of all alignments.
Relevance This study has shown that below-knee amputees were able to adapt themselves to alignment changes and to keep their balance almost unaffected, even when standing took place under malaligned conditions. It demonstrates the uses and limits of postural sway parameters in the procedure of optimizing the alignment of below knee prostheses. Key words:
ch.
Below-knee-amputee,
Biomech.
prosthesis alignment,
1994; 9: 258-262,
postural sway, foot-ground
July
Introduction Alignment of a prosthesis is established by the relative geometrical position and orientation of the various prosthetic components such as the socket, shaft, joints, and foot. Optimal alignment is a crucial factor for the successful rehabilitation of the amputee. No less important are the quality of the fit of the socket, quality of suspension, mass properties of the prosthesis, and cosmesis1-4. A comfortable prosthesis permits ambulation at minimal metabolic cost, without affecting or damaging Failure to provide a satisfactory alignthe stump’-‘. ment may result in problems for the amputee such as difficulties in walking, stump pain, or tissue breakReceived: 18 January 1993 Accepted: 14 June 1993 Correspondence and reprint requests to: Dr Eli Isakov, Biomechanics Laboratory. Loewenstein Rehabilitation Hospital, Ra’anana, PO Box 3. Israel 43100 0 1994 Butterworth-Heinemann 0268-0033/94/040258-05
Ltd
reaction force
down’. Unfortunately, modern methods of alignment still rely extensively on the skill and judgement of the prosthetist, with no clear guidelines for correct alignment . During dynamic alignment of a below-knee amputee (BKA), the prosthetist inspects the patient while standing and walking and records patient’s comments. Factors such as experience, understanding of the cause of posture deviations, information on zones of overload at the stump-socket interface, and feedback received from the patient assist the prosthetist in making alterations to the geometrical configuration of the prosthesis until an acceptable alignment is achieved. Several investigators have attempted to establish the optimal range of alignment which is acceptable to the BKA patient. Zahedi et a1.9 measured this range via subjective impression of several prosthetists and direct feedback from the patient. Hannah et al. lo investigated the effect of changing prosthetic alignment on gait, via indices of symmetry between limbs. Andres and Stimmel” examined the effect of alignment on gait kinematics by comparing the anatomical side with the
lsakov
prosthetic side. They showed that maximum symmetry of kinematic parameters does not always correspond with a subjectively determined optimal alignment. Therefore, gait symmetry should not be the only goal of the clinician when aligning a prosthesis. Standing still is an unstable position that requires a constant regulation involving muscle contraction in the lower limbs 12. The foot-ground reactive forces are the direct resultant of the lower limbs musculature activity. The standing BKA will adapt himself to the prosthesis alignment through accommodation by the contralateral limb. Therefore, use of unilateral measurement techniques’“.lJ has the disadvantage of not considering interaction of the contralateral limb. Hence monitoring of both limbs simultaneously is essential to determine the combined effect of alignment on standing balance. The present study was addressed to investigate the following: (1) the foot-ground forces pattern obtained in standing of BKA while the prosthesis is optimally aligned; (2) whether changes in prosthesis alignment influence the bilateral foot-ground forces pattern and the standing sway activity.
et al.: Prosthesis alignment in below-knee amputees
259
tested was considered optimal and was therefore taken as the reference position. The optimal alignment was changed by tilting the pylon in the anterior, posterior, medial, and lateral directions. For this purpose the USMC adjustable modular system (P202004000) attached to the socket bottom was used. The maximal tilt in each direction, obtained by manoeuvering the coupler, was nine degrees.
Evaluation parameters The force traces obtained included a transient, slow oscillation (approximately 0.1 Hz), above which more rapid oscillations (1 Hz and higher) were superimposed. A procedure was established to rectify these rapid oscillations and to compute their average amplitudes. The transient oscillations served as a baseline. From these amplitude averages (obtained for the AP, ML, and vertical directions) the following parameters were determined: 1. Total sway activity (TSA) represented of the added force amplitude averages ML directions (Figure 1)
the resultant in the AP and
Method
TSA
Subjects We assessed three volunteers, one female and two males, with traumatic below-knee amputation. The sides of amputation for the three subjects respectively were right, left, and right; ages 45, 30, and 52 years; masses 75, 78, and 90 kg; heights 1.62, 1.80, and 1.80 m; and times from amputation 15, 19, and 25 years. All were excellent walkers who used their prostheses on a regular basis and were conducting an active normal family life.
AP( I) +
AP(r) Equipment Foot-ground forces were evaluated by means of a force-measuring system consisting of two Kistler Z-4305 platforms. These force plates were collaterally installed for adjacent positioning of both feet during standing. The foot-ground reaction forces in the vertical, anteroposterior, and mediolateral directions were simultaneously monitored for both feet during the test. The force signals from the Kistler amplifiers (type 9803), with gains set at 5 N/V for the AP and ML directions and at 100 N/V for the vertical direction, were transferred to an on-line IBM PC through a multichannel AD converter at a sampling rate of 50 Hz. The test was conducted while the subject was wearing his or her regular prosthesis. All subjects used a modular patellar-tendon-bearing (PTB) prostheses with belt suspension and a solid ankle cushioned heel (SACH) foot. Since the subjects were excellent walkers and were satisfied with their prostheses, the existing prosthesis alignment in each of the three amputees
ASYM
AP( d-NV
1) PI ML(r)
- ML( 1)
Figure 1. Pictorial demonstration of the definition of total sway activity (TSA) and asymmetry (ASYM).
260
Clin. Biomech.
1994; 9: No 4 Table 1. AP force in amputated and sound legs, expressed as a percentage of body weight. The difference between the two legs was significant at the 0.1% level (PC 0.001) AP force (% B Wt x 700) Alignment changes Optimal Valgus Varus Plantarflexion Dorsiflexion
Amputated
leg
Mean
SD
2.92 3.58” 3.80” 3.22 3.12
0.43 0.58 0.77 0.73 0.82
*The difference with respect to significant at the 5% level (P
2. Asymmetry
(ASYM) represented the resultant of the subtracted force amplitude averages in the AP and the ML directions (Figure 1) 3. Weight-bearing imbalance (WBI) was defined in the vertical direction to express the difference between the average forces supported by each of the legs: leg - Force in the sound leg Body weight
= WBI
The more refined definitions for TSA and ASYM are based on amplitude averages of the rectified signal15, as opposed to previous definitions16, which were based on the peak-to-peak amplitudes of the signal.
Experimental
Mean
SD
11.14
2.44 3.23 1.61 2.17 3.18
11.62
11.36 10.62 11.93 alignment
was
There were five different testing conditions: optimal alignment, anterior tilt, posterior tilt, lateral tilt, and medial tilt. As walking could result in adaptation to the new alignment, the subject was requested to remain seated between tests. The procedures of prosthesis optimization and alignment changes were conducted by an experienced technician. In every position tested the following parameters were monitored for evaluation: AP and ML forces for each leg as well as TSA, ASYM. and WBI. The significance level of the differences obtained was determined by using Student’s T test.
Figure 2. Subject during standing test.
Force in amputated
optimal
Sound leg
procedure
All tests were conducted while the subject was standing with eyes closed. A preliminary Romberg test was conducted in all subjects to establish integrity of equilibrium’7~‘8. On the testing day subjects were ascertained to be free of stump pain or any other problem. The subject was asked to stand comfortably with one leg on each platform (Figure 2). The angle between both feet was 20 degrees and the distance between the heels was set at 30 cm. Each test was performed three times and the average was taken. Each test lasted 2.5 s.
Results
The results for AP and ML forces in the amputated and contralateral legs are detailed in Table 1 and Table 2. The AP force differences between the amputated and contralateral limb were found to be highly significant in all alignment positions. The measured ML force did not differ significantly. We also compared for each leg the AP and ML forces in each alignment position to the AP and ML forces in the optimal position. In the amputated limb the AP and ML forces in varus tilting and the AP in the valgus
Table 2. ML force in amputated and sound legs, expressed as a percentage of body weight. The difference between the two legs was insignificant at the 5% level (P
Amputated
limb
Sound limb
Mean
SD
Mean
SD
3.13 4.01 4.52” 3.53 4.40
1.16 1.54
4.06 3.95 3.62 3.63 3.77
0.78 1.16 0.60 1.oo 0.90
1.05 1.37
1.82
*The difference with respect to significant at the 5% level (PcO.05).
optimal
alignment
was
lsakov et al.: Prosthesis alignment Table 3. TSA, ASYM, and WBI expressed Alignments
Optimal Valgus Varus Plantarflexion Dorsiflexion
as a percentage
TSA (% Bwt x 100)
in below-knee
of body weight for all alignment
amputees
positions
ASYM (% BWt x 100)
WBI /% BWt)
Mean
SD
Mean
SD
Mean
SD
15.77 17.20 lj.20 15.57 17.15
2.80 4.08 2.27 3.48 4.56
8.27 8.03* 7.63 7.36 8.83
2.11 3.02 1.50 1.73 2.48
5.71 3.88 6.07 6.90 8.52
3.13 3.61 4.61 5.42 7.97
*The difference with respect to optimal
alignment
261
was found significant at the 0.1% level (P
tilting were significantly higher than in the optimal position. In the contralateral limb no significant differences were found between the optimal and other alignments. The measured TSA, ASYM, and WBI in all alignment positions are detailed in Table 3. The standing TSA obtained with optimally aligned prosthesis was compared with the TSA in the different measured alignments. Changing the prosthesis alignment did not influence significantly the TSA of the standing BKA. Asymmetry (ASYM) and weight bearing imbalance (WBI) were also verified. Neither ASYM nor WBI differed significantly between the optimal and the other tested alignment configurations, except for ASYM in the valgus tilting, which was significantly higher in this position.
Discussion
Human standing, as much as walking, is a non-uniform and asymmetrical event. A large variability in foot-ground forces and in sway activity among the healthy have been reported during such tasks19*20. Therefore it may be assumed that each person adapts himself or herself differently to the standing position where a restful upright results also in minimal energy cost. that asymmetrical standing, as We assume asymmetrical gait, might be acceptable and comfortable to the patient. Isakov et al.*l investigated quality of gait in aged amputees for vascular reasons and young traumatic above-knee amputees and found that although gait was asymmetrical, it required lower energy cost and was therefore less fatiguing. Moreover, Winter and Sienko22 suggested that an ambulating amputee cannot perform optimally when gait is symmetrical, and therefore proposed that a new nonsymmetrical criterion should be sought. Symmetry in this case refers more to the respective motor patterns than to the gait kinematics. One of the main goals in prosthetic rehabilitation is to reach an optimal alignment of the prosthesis. However, it should be borne in mind that the resulting alignment of the entire limb-prosthesis assembly is not less important. In fact, in some cases it is necessary to construct a ‘mal-aligned’ prosthesis in order to achieve a satisfactory overall alignment of the entire
limb and to face stump-specific problems such as, knee flexion contracture and severe genu varum. Use of unilateral force-measuring techniques such as strain gauge instrumentation of prosthetic pylons13, pylon dynamometers14, and solitary force plate23, all have the disadvantage of not considering interaction of the contralateral limb. In this study we have used a method that measures separately and simultaneously the foot-ground forces in both lower limbs 15,16,21.Forces in the AP and ML directions were measured while standing with wellaligned BK prostheses and with four different alignment variations. From the force records, parameters of balance were calculated and analysed. In standing with an optimally aligned prosthesis, activity of the contralateral limb in the AP direction was significantly higher when compared with the amputated limb. However, there were no significant differences between the two limbs when comparing forces in the ML direction. Such a standing pattern was found to be common to all four alignment positions. A possible explanation is that an inert prosthesis is incapable of compensating for the missing function of the joints of an anatomical foot and ankle. This imposes on the musculature of the contralatereal limb an additional balancing activity in the AP direction. This increased level of activity of the contralateral limb prevails in the optimal alignment as well as in the modified alignments in the AP direction. However, the amputated limb activity increased significantly in the AP and ML directions when the prosthesis was tilted into varus, and in the AP direction only when tilted into valgus. The measured total sway activity relates directly to the level of foot-ground forces in both legs. The amount of TSA obtained with a well-aligned prosthesis did not differ significantly from the obtained results while standing with the tilted prosthesis. We can therefore assume that the standing, well-trained, BKA is able to adapt himself to drastic alignment changes and to preserve his well-balanced position. Conclusions
We have demonstrated the presence of a common standing pattern in BKA where activity of foot-ground forces in the AP direction is significantly higher in the contralateral limb as compared to the amputated limb.
262
Clin. Biomech.
1994;
9: No 4
We
also found that the varus alignment was less Finally BKAs are able to adapt comfortable. themselves to alignment changes and to keep their balance almost uneffected, even when standing is under objective uncomfortable conditions.
Acknowledgement
9 Zahedi MS, Spence WD, Solomonidis
SE, Paul JP. Alignment of lower limb prostheses. J Rehabil Res Dev 1986; 23(2): 2-19 10 Hannah RE, Morrison JB, Chapman AE. Prostheses alignment: Effect on gait of persons with below-knee amputations. Arch Phys Med Rehabill984; 65: 159-62 11 Andres RO, Stimmel SK. Prosthetic alignment effects on gait symmetry: a case study. Clin Biomech 1990; 5: 88-96 12 Johansson R, Magnusson M. Human postural dynamics. Biomed Eng 1991; 18(6): 413-37
This study was supported by the Fund for Promotion Research at the Technion.
of
References Porter D, Roberts VC. A review of gait assessment in the lower limb amputee. Part 2: Kinetic and metabolic analysis. Clin Rehabill989; 3: 157-68 Nissen SJ, Newman WP. Factors influencing reintegration to normal living after amputation. Arch Phys Med Rehabif 1992; 73: 548-9
Burgess EM. Amputations.
Surg Clin North Am 1983;
63(3): 749-70
Skinner HB. Effeney DJ. Gait analysis in amputees. Am J Phys Med 1985; 64(2): 82-9
Fisher SV, Gullickson G. Energy cost of ambulation in health and disability: literature review. Arch Phys Med Rehabill978;
59: 124-33
Sulzle H, Pagliarulo M, Rodgers M, Jordan C. Energetics of amputee gait. Orthop Clin North Am 1978; g(2): 358-62 Baker PA, Hewison SR. Gait recovery pattern of unilateral lower limb amputees during rehabilitation. Prosthet Orthot Int 1990; 14: 80-4
Levy SW. Skin problems of lower extremity amputees.
13 Jones D, Paul J. Analysis of variability in pylon transducer signals. Prosthet Orthot 1973; 2: 35-50 14 Wilson AB Jr, Pritham C, Cook T. Force-line visualisation system. Prosthet Orthot 1979; 3: 85-7 15 Isakov E, Mizrahi J. Ring H et al. Standing sway and weight-bearing distribution in people with below-knee amputation. Arch Phys Med Rehabill992; 73: 174-8 16 Mizrahi J. Susak Z. Bi-lateral reactive force pattern in postural sway activity of normal subjects. Biol Cybern 1989; 60: 297-305
17 Jansen EC, Larsen RE, Olsen MB. Quantitative Romberg’s test. Acta Neurol Stand 1982; 66: 93-9 18 Thyssen HH, Brynskov J, Jansen EC. Munster-Swendsen J. Normal ranges and reproducibility for the quantitative Romberg’s test. Acta Neurol Stand 1982; 66: 100-4 19 Ekdahl C, Jarnlo GB. Andersson SI. Standing balance in healthy subjects. Stand J Rehabil Med 1989; 21: 187-95 20 Horak FB. Clinical measurement of postural control in adults. Phys Ther 1987; 67(12): 1881-5 21 Isakov E, Susak Z, Becker E. Energy expenditure and cardiac response in above-knee amputees while using prostheses with open and locked knee mechanisms. Stand J Rehabil Med Suppll985; 12: 108- 11
22 Winter DA, Sienko SE. Biomechanics of below-knee amputee gait. J Biomech 1988; 21(5): 361-7 23 Vittas D, Larsen TK, Jansen EC. Body sway in below-knee amputees. Prosthet Orthot Int 1986; 10:
Prosthet Orthot Int 1980: 4: 37-44
Jh ns 0
139-41
Department
of
Hopkins ::;;;eciic
M1’.1)1(:AI.
INSI‘I’I‘UI‘IONS
c
Advancesin OrthopaedicBiomechanicsand their ClinicalApplications HYATT REGENCY BALTIMORE H BALTIMORE, MARYLAND, USA W THURSDAY - SUNDAY, OCTOBER 27 - 30,1994
This three and a half-day symposium will review Ihe recent advances in musculoskelelal joint biomechanics and their applications in various subspecialties in orthopaedic surgery. Lectures will be given by internationally recognized experts and Johns Hopkins’ Orthopaedic Surgery faculty.
Major topics include among others: MUSCULOSKELETAL SYSTEM: IMAGING/SIMULATION/ANIMATION
?? HAND AND UPPER EXTREMITY BIOMECHANICS
TOTAL JOINT REPLACEMENT
?? TISSUE REPAIR AND REGENERATION
OSTEOTOMY OF PELVIS, HIP AND KNEE MOTION ANALYSIS AND COMPUTERAIDED REHABILITATION ORTHOPAEDIC ONCOLOGY AND LIMB SALVAGE SURGERY
?? SPORTS MEDICINE AND RELATED RESEARCH w
CARTILAGE AND SOFT TISSUE MECHANICS
Symposium Directors EDMUND Y. S. CHAO, PH.D. Professor and Vice Chairman for Research RICHARD N. STAUFFER, Professor and Chairman Orthopaedic Surgery
M.D.
AMA Category 1 Crrdits For Further Information OfIicc of Continuing Education Johns IIopkins Medical Institutions Turner Building ‘720Kutland Avenue Baltimore, Maryland, USA 212052195 (410) 9552959
??
Fax (410) !)5.5-0807
MD, MSC’,
J Mizrahi
DSC*,l,
Z Susak
MD’, I
Ona
cp3,
N Hakim
BSC’
‘Biomechanics Laboratory, Loewenstein Rehabilitation Hospital, Ra’anana; *Department of Biomedical Engineering and the Julius Silver Institute of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa; and 3’Gapim’ Ltd, Loewenstein Hospital Branch, Ra’anana, Israel
Summary The effect of alignment of the prosthesis on the standing balance of below knee amputees was investigated in this work. Alignment variations consisted of varus and valgus tilt and plantar- and dorsiflexions. The foot-ground reaction forces measured in the anteroposterior, mediolateral, and vertical directions as well as global parameters describing the total sway activity, asymmetry, and weight-bearing imbalance were used to compare the various alignment positions studied. The results indicate the presence of a common standing pattern in below-knee amputees, where activity of the foot-ground reaction forces in the anteroposterior direction is significantly higher in the contralateral limb compared with the amputated limb. It was also found that the varus and valgus alignments were the least stable of all alignments.
Relevance This study has shown that below-knee amputees were able to adapt themselves to alignment changes and to keep their balance almost unaffected, even when standing took place under malaligned conditions. It demonstrates the uses and limits of postural sway parameters in the procedure of optimizing the alignment of below knee prostheses. Key words:
ch.
Below-knee-amputee,
Biomech.
prosthesis alignment,
1994; 9: 258-262,
postural sway, foot-ground
July
Introduction Alignment of a prosthesis is established by the relative geometrical position and orientation of the various prosthetic components such as the socket, shaft, joints, and foot. Optimal alignment is a crucial factor for the successful rehabilitation of the amputee. No less important are the quality of the fit of the socket, quality of suspension, mass properties of the prosthesis, and cosmesis1-4. A comfortable prosthesis permits ambulation at minimal metabolic cost, without affecting or damaging Failure to provide a satisfactory alignthe stump’-‘. ment may result in problems for the amputee such as difficulties in walking, stump pain, or tissue breakReceived: 18 January 1993 Accepted: 14 June 1993 Correspondence and reprint requests to: Dr Eli Isakov, Biomechanics Laboratory. Loewenstein Rehabilitation Hospital, Ra’anana, PO Box 3. Israel 43100 0 1994 Butterworth-Heinemann 0268-0033/94/040258-05
Ltd
reaction force
down’. Unfortunately, modern methods of alignment still rely extensively on the skill and judgement of the prosthetist, with no clear guidelines for correct alignment . During dynamic alignment of a below-knee amputee (BKA), the prosthetist inspects the patient while standing and walking and records patient’s comments. Factors such as experience, understanding of the cause of posture deviations, information on zones of overload at the stump-socket interface, and feedback received from the patient assist the prosthetist in making alterations to the geometrical configuration of the prosthesis until an acceptable alignment is achieved. Several investigators have attempted to establish the optimal range of alignment which is acceptable to the BKA patient. Zahedi et a1.9 measured this range via subjective impression of several prosthetists and direct feedback from the patient. Hannah et al. lo investigated the effect of changing prosthetic alignment on gait, via indices of symmetry between limbs. Andres and Stimmel” examined the effect of alignment on gait kinematics by comparing the anatomical side with the
lsakov
prosthetic side. They showed that maximum symmetry of kinematic parameters does not always correspond with a subjectively determined optimal alignment. Therefore, gait symmetry should not be the only goal of the clinician when aligning a prosthesis. Standing still is an unstable position that requires a constant regulation involving muscle contraction in the lower limbs 12. The foot-ground reactive forces are the direct resultant of the lower limbs musculature activity. The standing BKA will adapt himself to the prosthesis alignment through accommodation by the contralateral limb. Therefore, use of unilateral measurement techniques’“.lJ has the disadvantage of not considering interaction of the contralateral limb. Hence monitoring of both limbs simultaneously is essential to determine the combined effect of alignment on standing balance. The present study was addressed to investigate the following: (1) the foot-ground forces pattern obtained in standing of BKA while the prosthesis is optimally aligned; (2) whether changes in prosthesis alignment influence the bilateral foot-ground forces pattern and the standing sway activity.
et al.: Prosthesis alignment in below-knee amputees
259
tested was considered optimal and was therefore taken as the reference position. The optimal alignment was changed by tilting the pylon in the anterior, posterior, medial, and lateral directions. For this purpose the USMC adjustable modular system (P202004000) attached to the socket bottom was used. The maximal tilt in each direction, obtained by manoeuvering the coupler, was nine degrees.
Evaluation parameters The force traces obtained included a transient, slow oscillation (approximately 0.1 Hz), above which more rapid oscillations (1 Hz and higher) were superimposed. A procedure was established to rectify these rapid oscillations and to compute their average amplitudes. The transient oscillations served as a baseline. From these amplitude averages (obtained for the AP, ML, and vertical directions) the following parameters were determined: 1. Total sway activity (TSA) represented of the added force amplitude averages ML directions (Figure 1)
the resultant in the AP and
Method
TSA
Subjects We assessed three volunteers, one female and two males, with traumatic below-knee amputation. The sides of amputation for the three subjects respectively were right, left, and right; ages 45, 30, and 52 years; masses 75, 78, and 90 kg; heights 1.62, 1.80, and 1.80 m; and times from amputation 15, 19, and 25 years. All were excellent walkers who used their prostheses on a regular basis and were conducting an active normal family life.
AP( I) +
AP(r) Equipment Foot-ground forces were evaluated by means of a force-measuring system consisting of two Kistler Z-4305 platforms. These force plates were collaterally installed for adjacent positioning of both feet during standing. The foot-ground reaction forces in the vertical, anteroposterior, and mediolateral directions were simultaneously monitored for both feet during the test. The force signals from the Kistler amplifiers (type 9803), with gains set at 5 N/V for the AP and ML directions and at 100 N/V for the vertical direction, were transferred to an on-line IBM PC through a multichannel AD converter at a sampling rate of 50 Hz. The test was conducted while the subject was wearing his or her regular prosthesis. All subjects used a modular patellar-tendon-bearing (PTB) prostheses with belt suspension and a solid ankle cushioned heel (SACH) foot. Since the subjects were excellent walkers and were satisfied with their prostheses, the existing prosthesis alignment in each of the three amputees
ASYM
AP( d-NV
1) PI ML(r)
- ML( 1)
Figure 1. Pictorial demonstration of the definition of total sway activity (TSA) and asymmetry (ASYM).
260
Clin. Biomech.
1994; 9: No 4 Table 1. AP force in amputated and sound legs, expressed as a percentage of body weight. The difference between the two legs was significant at the 0.1% level (PC 0.001) AP force (% B Wt x 700) Alignment changes Optimal Valgus Varus Plantarflexion Dorsiflexion
Amputated
leg
Mean
SD
2.92 3.58” 3.80” 3.22 3.12
0.43 0.58 0.77 0.73 0.82
*The difference with respect to significant at the 5% level (P
2. Asymmetry
(ASYM) represented the resultant of the subtracted force amplitude averages in the AP and the ML directions (Figure 1) 3. Weight-bearing imbalance (WBI) was defined in the vertical direction to express the difference between the average forces supported by each of the legs: leg - Force in the sound leg Body weight
= WBI
The more refined definitions for TSA and ASYM are based on amplitude averages of the rectified signal15, as opposed to previous definitions16, which were based on the peak-to-peak amplitudes of the signal.
Experimental
Mean
SD
11.14
2.44 3.23 1.61 2.17 3.18
11.62
11.36 10.62 11.93 alignment
was
There were five different testing conditions: optimal alignment, anterior tilt, posterior tilt, lateral tilt, and medial tilt. As walking could result in adaptation to the new alignment, the subject was requested to remain seated between tests. The procedures of prosthesis optimization and alignment changes were conducted by an experienced technician. In every position tested the following parameters were monitored for evaluation: AP and ML forces for each leg as well as TSA, ASYM. and WBI. The significance level of the differences obtained was determined by using Student’s T test.
Figure 2. Subject during standing test.
Force in amputated
optimal
Sound leg
procedure
All tests were conducted while the subject was standing with eyes closed. A preliminary Romberg test was conducted in all subjects to establish integrity of equilibrium’7~‘8. On the testing day subjects were ascertained to be free of stump pain or any other problem. The subject was asked to stand comfortably with one leg on each platform (Figure 2). The angle between both feet was 20 degrees and the distance between the heels was set at 30 cm. Each test was performed three times and the average was taken. Each test lasted 2.5 s.
Results
The results for AP and ML forces in the amputated and contralateral legs are detailed in Table 1 and Table 2. The AP force differences between the amputated and contralateral limb were found to be highly significant in all alignment positions. The measured ML force did not differ significantly. We also compared for each leg the AP and ML forces in each alignment position to the AP and ML forces in the optimal position. In the amputated limb the AP and ML forces in varus tilting and the AP in the valgus
Table 2. ML force in amputated and sound legs, expressed as a percentage of body weight. The difference between the two legs was insignificant at the 5% level (P
Amputated
limb
Sound limb
Mean
SD
Mean
SD
3.13 4.01 4.52” 3.53 4.40
1.16 1.54
4.06 3.95 3.62 3.63 3.77
0.78 1.16 0.60 1.oo 0.90
1.05 1.37
1.82
*The difference with respect to significant at the 5% level (PcO.05).
optimal
alignment
was
lsakov et al.: Prosthesis alignment Table 3. TSA, ASYM, and WBI expressed Alignments
Optimal Valgus Varus Plantarflexion Dorsiflexion
as a percentage
TSA (% Bwt x 100)
in below-knee
of body weight for all alignment
amputees
positions
ASYM (% BWt x 100)
WBI /% BWt)
Mean
SD
Mean
SD
Mean
SD
15.77 17.20 lj.20 15.57 17.15
2.80 4.08 2.27 3.48 4.56
8.27 8.03* 7.63 7.36 8.83
2.11 3.02 1.50 1.73 2.48
5.71 3.88 6.07 6.90 8.52
3.13 3.61 4.61 5.42 7.97
*The difference with respect to optimal
alignment
261
was found significant at the 0.1% level (P
tilting were significantly higher than in the optimal position. In the contralateral limb no significant differences were found between the optimal and other alignments. The measured TSA, ASYM, and WBI in all alignment positions are detailed in Table 3. The standing TSA obtained with optimally aligned prosthesis was compared with the TSA in the different measured alignments. Changing the prosthesis alignment did not influence significantly the TSA of the standing BKA. Asymmetry (ASYM) and weight bearing imbalance (WBI) were also verified. Neither ASYM nor WBI differed significantly between the optimal and the other tested alignment configurations, except for ASYM in the valgus tilting, which was significantly higher in this position.
Discussion
Human standing, as much as walking, is a non-uniform and asymmetrical event. A large variability in foot-ground forces and in sway activity among the healthy have been reported during such tasks19*20. Therefore it may be assumed that each person adapts himself or herself differently to the standing position where a restful upright results also in minimal energy cost. that asymmetrical standing, as We assume asymmetrical gait, might be acceptable and comfortable to the patient. Isakov et al.*l investigated quality of gait in aged amputees for vascular reasons and young traumatic above-knee amputees and found that although gait was asymmetrical, it required lower energy cost and was therefore less fatiguing. Moreover, Winter and Sienko22 suggested that an ambulating amputee cannot perform optimally when gait is symmetrical, and therefore proposed that a new nonsymmetrical criterion should be sought. Symmetry in this case refers more to the respective motor patterns than to the gait kinematics. One of the main goals in prosthetic rehabilitation is to reach an optimal alignment of the prosthesis. However, it should be borne in mind that the resulting alignment of the entire limb-prosthesis assembly is not less important. In fact, in some cases it is necessary to construct a ‘mal-aligned’ prosthesis in order to achieve a satisfactory overall alignment of the entire
limb and to face stump-specific problems such as, knee flexion contracture and severe genu varum. Use of unilateral force-measuring techniques such as strain gauge instrumentation of prosthetic pylons13, pylon dynamometers14, and solitary force plate23, all have the disadvantage of not considering interaction of the contralateral limb. In this study we have used a method that measures separately and simultaneously the foot-ground forces in both lower limbs 15,16,21.Forces in the AP and ML directions were measured while standing with wellaligned BK prostheses and with four different alignment variations. From the force records, parameters of balance were calculated and analysed. In standing with an optimally aligned prosthesis, activity of the contralateral limb in the AP direction was significantly higher when compared with the amputated limb. However, there were no significant differences between the two limbs when comparing forces in the ML direction. Such a standing pattern was found to be common to all four alignment positions. A possible explanation is that an inert prosthesis is incapable of compensating for the missing function of the joints of an anatomical foot and ankle. This imposes on the musculature of the contralatereal limb an additional balancing activity in the AP direction. This increased level of activity of the contralateral limb prevails in the optimal alignment as well as in the modified alignments in the AP direction. However, the amputated limb activity increased significantly in the AP and ML directions when the prosthesis was tilted into varus, and in the AP direction only when tilted into valgus. The measured total sway activity relates directly to the level of foot-ground forces in both legs. The amount of TSA obtained with a well-aligned prosthesis did not differ significantly from the obtained results while standing with the tilted prosthesis. We can therefore assume that the standing, well-trained, BKA is able to adapt himself to drastic alignment changes and to preserve his well-balanced position. Conclusions
We have demonstrated the presence of a common standing pattern in BKA where activity of foot-ground forces in the AP direction is significantly higher in the contralateral limb as compared to the amputated limb.
262
Clin. Biomech.
1994;
9: No 4
We
also found that the varus alignment was less Finally BKAs are able to adapt comfortable. themselves to alignment changes and to keep their balance almost uneffected, even when standing is under objective uncomfortable conditions.
Acknowledgement
9 Zahedi MS, Spence WD, Solomonidis
SE, Paul JP. Alignment of lower limb prostheses. J Rehabil Res Dev 1986; 23(2): 2-19 10 Hannah RE, Morrison JB, Chapman AE. Prostheses alignment: Effect on gait of persons with below-knee amputations. Arch Phys Med Rehabill984; 65: 159-62 11 Andres RO, Stimmel SK. Prosthetic alignment effects on gait symmetry: a case study. Clin Biomech 1990; 5: 88-96 12 Johansson R, Magnusson M. Human postural dynamics. Biomed Eng 1991; 18(6): 413-37
This study was supported by the Fund for Promotion Research at the Technion.
of
References Porter D, Roberts VC. A review of gait assessment in the lower limb amputee. Part 2: Kinetic and metabolic analysis. Clin Rehabill989; 3: 157-68 Nissen SJ, Newman WP. Factors influencing reintegration to normal living after amputation. Arch Phys Med Rehabif 1992; 73: 548-9
Burgess EM. Amputations.
Surg Clin North Am 1983;
63(3): 749-70
Skinner HB. Effeney DJ. Gait analysis in amputees. Am J Phys Med 1985; 64(2): 82-9
Fisher SV, Gullickson G. Energy cost of ambulation in health and disability: literature review. Arch Phys Med Rehabill978;
59: 124-33
Sulzle H, Pagliarulo M, Rodgers M, Jordan C. Energetics of amputee gait. Orthop Clin North Am 1978; g(2): 358-62 Baker PA, Hewison SR. Gait recovery pattern of unilateral lower limb amputees during rehabilitation. Prosthet Orthot Int 1990; 14: 80-4
Levy SW. Skin problems of lower extremity amputees.
13 Jones D, Paul J. Analysis of variability in pylon transducer signals. Prosthet Orthot 1973; 2: 35-50 14 Wilson AB Jr, Pritham C, Cook T. Force-line visualisation system. Prosthet Orthot 1979; 3: 85-7 15 Isakov E, Mizrahi J. Ring H et al. Standing sway and weight-bearing distribution in people with below-knee amputation. Arch Phys Med Rehabill992; 73: 174-8 16 Mizrahi J. Susak Z. Bi-lateral reactive force pattern in postural sway activity of normal subjects. Biol Cybern 1989; 60: 297-305
17 Jansen EC, Larsen RE, Olsen MB. Quantitative Romberg’s test. Acta Neurol Stand 1982; 66: 93-9 18 Thyssen HH, Brynskov J, Jansen EC. Munster-Swendsen J. Normal ranges and reproducibility for the quantitative Romberg’s test. Acta Neurol Stand 1982; 66: 100-4 19 Ekdahl C, Jarnlo GB. Andersson SI. Standing balance in healthy subjects. Stand J Rehabil Med 1989; 21: 187-95 20 Horak FB. Clinical measurement of postural control in adults. Phys Ther 1987; 67(12): 1881-5 21 Isakov E, Susak Z, Becker E. Energy expenditure and cardiac response in above-knee amputees while using prostheses with open and locked knee mechanisms. Stand J Rehabil Med Suppll985; 12: 108- 11
22 Winter DA, Sienko SE. Biomechanics of below-knee amputee gait. J Biomech 1988; 21(5): 361-7 23 Vittas D, Larsen TK, Jansen EC. Body sway in below-knee amputees. Prosthet Orthot Int 1986; 10:
Prosthet Orthot Int 1980: 4: 37-44
Jh ns 0
139-41
Department
of
Hopkins ::;;;eciic
M1’.1)1(:AI.
INSI‘I’I‘UI‘IONS
c
Advancesin OrthopaedicBiomechanicsand their ClinicalApplications HYATT REGENCY BALTIMORE H BALTIMORE, MARYLAND, USA W THURSDAY - SUNDAY, OCTOBER 27 - 30,1994
This three and a half-day symposium will review Ihe recent advances in musculoskelelal joint biomechanics and their applications in various subspecialties in orthopaedic surgery. Lectures will be given by internationally recognized experts and Johns Hopkins’ Orthopaedic Surgery faculty.
Major topics include among others: MUSCULOSKELETAL SYSTEM: IMAGING/SIMULATION/ANIMATION
?? HAND AND UPPER EXTREMITY BIOMECHANICS
TOTAL JOINT REPLACEMENT
?? TISSUE REPAIR AND REGENERATION
OSTEOTOMY OF PELVIS, HIP AND KNEE MOTION ANALYSIS AND COMPUTERAIDED REHABILITATION ORTHOPAEDIC ONCOLOGY AND LIMB SALVAGE SURGERY
?? SPORTS MEDICINE AND RELATED RESEARCH w
CARTILAGE AND SOFT TISSUE MECHANICS
Symposium Directors EDMUND Y. S. CHAO, PH.D. Professor and Vice Chairman for Research RICHARD N. STAUFFER, Professor and Chairman Orthopaedic Surgery
M.D.
AMA Category 1 Crrdits For Further Information OfIicc of Continuing Education Johns IIopkins Medical Institutions Turner Building ‘720Kutland Avenue Baltimore, Maryland, USA 212052195 (410) 9552959
??
Fax (410) !)5.5-0807