Bwwchanics,
1975. Vol. 8. pp. 369-373.
Pergamon
Press.
Printed
m Great
Britain
MEASUREMENTS OF REPETITIVE OF THE KNEE”?
ACTIVITIES
P. C. MCLEODJ D. B. KE-ITIXEAMP,(~ V. SRINIVASAN$ and 0. L. HENDER~ON~/ University of Arkansas, Graduate Institute of Technology, Little Rock. Arkansas. U.S.A.
Abstract-Reconstructive procedures for the arthritic knee. particularly internal prostheses. must include data on the type and frequency of knee activities if wear and loosening are to be evaluated. A description of the instrumentation and method for measuring type and frequency of knee motion in the home environment is presented. The instrumentation consists of an electrogoniometer and a miniature tape recorder to measure sagittal-plane knee motion and a data-reduction system (playback unit) that produces a d.c. voltage representative of knee motion as a function of time. The frequency and type of knee movements for specific activities-such as walking, ascending and descending stairs and sitting-and non-specific activities have been determined for normal subjects, providing a data base for subsequent comparison with arthritic subjects. Instrumentation and a method of recording a history of knee movement have been developed. and initial data indicate a high frequency of repetitive acts in the home environment.
INTRODUCTION One of the important items given in reports of various orthopaedic operative procedures is follow-upthe duration of time between an operation and evaluation of that operation. For the evaluation of a prosthetic joint implant, the duration of follow-up implies usage. It is well known, however, that follow-up and usage are not synonymous; and hence, patients with low activity levels are preferentially selected for study in order to minimize wear and loosening of prosthetic knee implants. If the complications of prosthetic wear and loosening are to be adequately evaluated, the data must include the duration of follow-up, the forces associated with various activities, the frequency of activity, and the type of activity (Frankel, 1973). Instrumentation here described is designed for use in the home environment to determine the type and the frequency of activities such as walking, sitting, rising and ascending and descending stairs. Information on frequency and type of activity has been obtained for a time interval of 50 hours from nine normal subjects with an average age of 28yr. INSTRUMENTATION The goal of the project is to provide an instrument that can be worn by post-operative patients with * Received 12 November 1974. t This work was supported in part by a grant from the Orthopaedic Research and Education Foundation, and presented at the Orthopaedic Research Society Meeting, Dallas, Texas, 17 January 1974. $ Department of Electronics and Instrumentation, University of Arkansas Graduate Institute of Technology. 5 Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, Indiana, U.S.A. )I Division of Orthopaedic Surgery, University of Arkansas Medical Center.
prosthetic knee implants to record the angular movements of the knee in the sagittal plane while causing a minimum of discomfort and bother. The sagittalplane motion was chosen because the angular movement of the knees in flexion-extension is descriptive of the type of activity (Laubenthal et al., 1972). The instrumentation consists of the electrogoniometer and recorder worn by the patient (Fig. l), the tape playback electronic circuits, and the galvanometric recorder. The electrogoniometer, which is worn on the knee containing the implant, consists of a thighcalf attachment and a potentiometer, the wiper arm of which is made to move with the angular motion of the knee in the sagittal plane. The connection between the wiper arm of the potentiometer and the calf cuff is designed with a sufficient degree of freedom so that motion of the knee in the transverse and coronal planes does not interfere with the measurement. The potentiometer mount is designed so that its angular relation to the thigh cuff can be varied to permit alignment of the potentiometer mount with the femur. The linkage to the thigh cuff is also adjustable in length, permitting it to be fastened comfortably on the upper leg and then adjusted so that the center of the potentiometer is opposite the center of rotation of the knee. The shaft of the potentiometer is attached through the coupling to the calf cuff. The electronics for recording flexion-extension data have been built into a small, battery-operated Sony TC-40 cassette recorder (Fig. 2) that is worn either on a chest strap or a belt strap. It is well known that miniature cassette tape recorders demonstrate a sizeable variation in tape speed due to eccentricities within their rolling parts, i.e. bearing chatter, periodic frictional drags, and aperiodic frictional drags. These fluctuations cause a frequency modulation of the information being recorded. During playback, this frequency modulation appears as noise in the output.
369
370
P. C. MCLEODet al.
Reference oscilldor
Flexion
Fig. 3. Block diagram of the electronic circuit added to the Sony TC-40 Recorder. In order to produce a signal-to-noise ratio which would later lend itself to automatic electronic data reduction, it was necessary to remove as much of the noise generated by instantaneous tape speed variations as possible. A high signal-to-noise ratio was obtained by using two oscillators, a recording network, and two frequency-to-voltage converters in the playback unit. The recording electronic circuits (Fig. 3) consist of a voltage-controlled oscillator and a reference oscillator. The frequency of the voltage-controlled oscillator, one to 2 kHz is determined by the motion of the tibia relative to the femur. The reference oscillator operates at a constant frequency of 5 kHz. The power for these two oscillators is derived from the battery pack in the Sony recorder. The signals from these two oscillators are electrically added and are recorded on chromium dioxide magnetic tape. In the playback electronic circuits (Fig. 4), the frequencies from the two oscillators are separated by the use of RCA phase-locked loops. Phase-locked
-
Reference phase locked loop; (5 kbix)
loops are devices which track a frequency over a given range and produce a d.c. voltage output which is directly proportional to the frequency. In other words, the phase-locked loops are performing as frequency-to-voltage converters. The voltage from the phase-locked loop that follows the movement of the knee and the voltage from the phase-locked loop that views the constant frequency of 5 kHz are applied to the inputs of a difference amplifier which removes all noise components common to both channels. The output of the difference amplifier thus contains the information associated with angular variations of the knee with the low-frequency noise essentially eliminated. It is also necessary to filter out higher-frequency noise, such as that generated by 60-cycle line problems and 120-cycle radiation from fluorescent lighting, since this noise is not introduced equally in both channels. Thus, the difference amplifier is followed by an active filter network-a low pass filter with a flat frequency response from d.c. to 15 Hz. The filter highfrequency cutoff of 15 Hz does not eliminate any of the information relative to the angular movement of the knee. The output signal from the filter is amplified to give the desired voltage vs frequency relationship and is recorded by a Century Model GBO460 light beam galvanometric recorder. The described instrumentation package produces waveforms that are descriptive of each knee motion in the sag&al plane that occurs at the time of the recordings. The output voltage vs the input voltage, as measured at the wiper arm of the potentiometer worn on the knee, is linear to within f 1% over a range that would constitute an angular variation considerably greater than that experienced by a normal knee. In addition, with the playback electronic circuits adjusted to produce a change in the output voltage of four volts per 140” motion of the potentiometer, the system possesses a 40 dB signal-to-noise ratio.
-
Input from _ tape recorder
I _
+&
Active phose locked loop
-
Eoseline set
Fig. 4. Block Diagram of the electronic circuit employed to reproduce flexion as a function of time from the magnetic tape.
Fig. 1. Electrogoniometer and portable recorder. Fig. 2. Circuit board containing the electronic circuit added to the Sony TC-40 Recorder recording of flexion
(Facing p. 370)
to permit
Fig. 5.(a) Front view of the electrogoniometer and recorder as worn by the sub.ject. (b) Side vieu of the electrogoniometer and recorder as worn by the subject.
371
Repetitive activities of the knee
I
1
wtmg
and
rlrlng
Fig. 8. Flexion waveforms for sitting and rising for the normal knee. Fig. 6. Flexion waveforms for walking for the normal knee. METHOD
The electrogoniometer (Kettelkamp et al., 1970) was attached to each subject in the laboratory as shown in Figs. 5(a,b); and a reference recording was obtained while the subject walked, climbed and descended stairs, and sat on and rose from a chair. The position of the goniometer was marked on the subject’s thigh and calf with a marker pen. The subject was then taught to remove and reapply the goniometer until she could do it satisfactorily, and she was instructed in the use of the tape recorder. The subject wore the goniometer for intervals of one hour, noting the time and date of the recording and the type of activity recorded (housework, kitchen work, tending children, etc.). Type and frequency of activity were obtained by playing the tape through an oscillo-
I
/--
I *et
__I
scope and manually counting the types of activities based on the known pattern of motion for those activities (Laubenthal et al., 1972). The activities recorded were walking (Fig. 6), ascending and descending stairs (Figs. 7a, b), sitting and rising (Fig. 8), and undifferentiated knee motion (Fig. 9). Running can be determined with this technique but was not recorded by any of the subjects. RESULTS
Fifty hours of recording were obtained from eight women, aged 2341, and one man aged 29. The women were a11wives of medicA students or of orthopaedic residents. The total repetitions for different activities for 50 hours recording time were 14,425 steps walking, 5212 undifferentiated motions, 242 climbing stairs, 197 descending stairs, 223 sitting, and 214 rising. The averages per hr were 289 steps walking, 104 undifferentiated motions, 5 ascending stairs, 4 descending stairs, 4 sitting and 4 rising. The average number of repetitive acts by type of occupational activity is presented in Table 1. The average number of repetitive acts by hour of the day is given in Table 2. The average number of alt knee motions was 410 per hour, or 683 motions per minute.
I
DISCUSSION
Instrumentation has been presented for the determination of frequency and type of repetitive knee activity. Since continuous monitoring of a given subject r
-=.
Fig. 7(b). Flexion waveforms for descending stairs for the normal knee.
Fig.
9. Flexion
-
waveforms for undifferentiated motions for the normal knee.
knee
P. C. MCLEODet al.
372
Table 1. Average number of repetitive acts by types of occupational activity Occupation
HOWS
HOUSWWk
15.67
Kitchen Work
16.00
Laundry
4.00
Child
6.83
245
90
1
1
5
5
7.50
404
162
17
11
3
3
Care
Yard llork
Undiff. Ilotionlhr
Stairs Uplhr
Stairs Dovmlhr
301
96
3
3
6
244
91
2
2
7
7
276
103
5
5
5
4
Stepsfhr
is not possible, data gained by using this method must be considered as representative rather than as absolute. Even with this limitation, the determination of the frequency and of the type of activity probably will be of greater value in the evaluation of wear and Ioosening of knee implant prostheses than is the activity implied by the term “follow-up” in current reports. Determination of knee activity using this method depends upon recognizing patterns of motion which are specific for given activities. We have had extensive experience using the three-plane electrogoniometer on abnormal knees, including 33 total knee arthroplasties. Though the patterns of sagittalplane motion differ from normal, the patterns are usually activity specific. The only situations in which sagittal-plane motion cannot be used to determine activity are for walking if the patient walks stiff-legged or has no knee motion and for stairs if the patient uses the knee in the extended position both up and down stairs. This method for determining repetitive activities requires an intelligent and cooperative patient. Data reduction is time consuming and currently presents a severe limitation to the acquisition of the large number of measurements needed for correlation with subsequent prosthetic wear and loosening. The authors are now working on automatic data-reduction instrumentation. Seedhom et al. (1973) used a pedometer to obtain information on the number of walking steps, but the pedometer is a simple instrument that cannot differentiate between various activities. This inability is a
Sltting/hr
Risjnglhr
6
serious limitation if the activities can eventually be used in calculating cumulative or repetitive loads and in the estimation of shear forces which are probably greatest with activities involving the loaded, flexed knee (i.e. sitting and rising, and ascending and descending stairs, as noted by Jones, 1973, and Smidt, 1973). The information from housewives with normal knees provides a basis for comparison with housewives after knee-replacement prosthesis, although the overall activity from our subjects probably exceeds the activity of normal women of an older age group. The number of steps (gait cycles) taken by our subjects compares closely to the number taken by elderly persons on vacation (determined by Seedhom et al., 1973), 42433000 walking cycles (steps) per day. Of speculative interest was the combined total of all knee motion, which averaged 410 per hr, or 6.83 per min. This frequency would be compatible with the theory that knee motion is necessary for articular cartilage nutrition and also with the sensation of discomfort and stiffness associated with prolonged sitting or immobility. SUMMARY The authors have developed instrumentation for determining the frequency and type of knee motion occurring in the home environment. Knee motion was recorded from a single-plane electrogoniometer with three planes of freedom on a modified portable tape recorder. Activity was determined by the pattern of
Table 2. Average number of repetitive acts by hour of the day Time
7-8 D-9 9-10 10-11 11-12 12-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 3-9
Hours of Recording Time
a.m. a.m. a.m. a.m. a.m. p.m. p.m. p.m. p.m. p.m. p.m. p.m. p.m. D.L.
Steps/hr
280
278 271 271 305 348 187 281 266 233 413 242 400 293
Urdiff. E!otion/hr
Still-S tJp/hr
Sittfnglhr
Rlsloglhr
95 lii 114 4 6
z3 132 76 104 :: 140
1’0
1;: 126
: 1
Repetitive activities of the knee knee motion. Data from nine normal people working about the house and yard provided average hourly activities of 289 walking steps, 5 ascending stairs, 4 descending stairs, 4 sitting, 4 rising and 104 undifferentiated knee motions. Thus, the frequency of knee motion is very high in normal people performing common daily activities. REFERENCES
Frankel, V. H. (1973) Panel on functional analysis. Internal structural prostheses. A Report of a Workshop on Fundamental Studies for Internal Structural Prostheses. pp. 75- 77. National Academy of Sciences.
373
Jones, G. B. (1973) Total knee replacement-the Walddius hinge. Clin. Orthop. 94, X-57. Kettelkamp, D. B., Johnson, R. J., Smidt, G. L., Chao. E. Y. S. and Walker, M. (1970) An electrogoniometric study of knee motion in normal gait. .r. Bone Jnt Surg. 52-A, 775-790. Laubenthal, K. N., Smidt, G. L. and Kettelkamp. D. B. (1972) A quantitative analysis of knee motion for activities of daily living. Phrs. Ther. 52, 3442. Seedhom, B. -B., Longton. E. B., Dawson, D. and Wright, V. (1973) Biomechanics background in the design of a total replacement knee prosthesis. Acta Orthop. Be/. 39, 164-180.
Smidt, G. L. (1973) Biomechanical analysis of knee flexion and extension. J. Biomechanics 6, 19-92.
1975. Vol. 8. pp. 369-373.
Pergamon
Press.
Printed
m Great
Britain
MEASUREMENTS OF REPETITIVE OF THE KNEE”?
ACTIVITIES
P. C. MCLEODJ D. B. KE-ITIXEAMP,(~ V. SRINIVASAN$ and 0. L. HENDER~ON~/ University of Arkansas, Graduate Institute of Technology, Little Rock. Arkansas. U.S.A.
Abstract-Reconstructive procedures for the arthritic knee. particularly internal prostheses. must include data on the type and frequency of knee activities if wear and loosening are to be evaluated. A description of the instrumentation and method for measuring type and frequency of knee motion in the home environment is presented. The instrumentation consists of an electrogoniometer and a miniature tape recorder to measure sagittal-plane knee motion and a data-reduction system (playback unit) that produces a d.c. voltage representative of knee motion as a function of time. The frequency and type of knee movements for specific activities-such as walking, ascending and descending stairs and sitting-and non-specific activities have been determined for normal subjects, providing a data base for subsequent comparison with arthritic subjects. Instrumentation and a method of recording a history of knee movement have been developed. and initial data indicate a high frequency of repetitive acts in the home environment.
INTRODUCTION One of the important items given in reports of various orthopaedic operative procedures is follow-upthe duration of time between an operation and evaluation of that operation. For the evaluation of a prosthetic joint implant, the duration of follow-up implies usage. It is well known, however, that follow-up and usage are not synonymous; and hence, patients with low activity levels are preferentially selected for study in order to minimize wear and loosening of prosthetic knee implants. If the complications of prosthetic wear and loosening are to be adequately evaluated, the data must include the duration of follow-up, the forces associated with various activities, the frequency of activity, and the type of activity (Frankel, 1973). Instrumentation here described is designed for use in the home environment to determine the type and the frequency of activities such as walking, sitting, rising and ascending and descending stairs. Information on frequency and type of activity has been obtained for a time interval of 50 hours from nine normal subjects with an average age of 28yr. INSTRUMENTATION The goal of the project is to provide an instrument that can be worn by post-operative patients with * Received 12 November 1974. t This work was supported in part by a grant from the Orthopaedic Research and Education Foundation, and presented at the Orthopaedic Research Society Meeting, Dallas, Texas, 17 January 1974. $ Department of Electronics and Instrumentation, University of Arkansas Graduate Institute of Technology. 5 Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, Indiana, U.S.A. )I Division of Orthopaedic Surgery, University of Arkansas Medical Center.
prosthetic knee implants to record the angular movements of the knee in the sagittal plane while causing a minimum of discomfort and bother. The sagittalplane motion was chosen because the angular movement of the knees in flexion-extension is descriptive of the type of activity (Laubenthal et al., 1972). The instrumentation consists of the electrogoniometer and recorder worn by the patient (Fig. l), the tape playback electronic circuits, and the galvanometric recorder. The electrogoniometer, which is worn on the knee containing the implant, consists of a thighcalf attachment and a potentiometer, the wiper arm of which is made to move with the angular motion of the knee in the sagittal plane. The connection between the wiper arm of the potentiometer and the calf cuff is designed with a sufficient degree of freedom so that motion of the knee in the transverse and coronal planes does not interfere with the measurement. The potentiometer mount is designed so that its angular relation to the thigh cuff can be varied to permit alignment of the potentiometer mount with the femur. The linkage to the thigh cuff is also adjustable in length, permitting it to be fastened comfortably on the upper leg and then adjusted so that the center of the potentiometer is opposite the center of rotation of the knee. The shaft of the potentiometer is attached through the coupling to the calf cuff. The electronics for recording flexion-extension data have been built into a small, battery-operated Sony TC-40 cassette recorder (Fig. 2) that is worn either on a chest strap or a belt strap. It is well known that miniature cassette tape recorders demonstrate a sizeable variation in tape speed due to eccentricities within their rolling parts, i.e. bearing chatter, periodic frictional drags, and aperiodic frictional drags. These fluctuations cause a frequency modulation of the information being recorded. During playback, this frequency modulation appears as noise in the output.
369
370
P. C. MCLEODet al.
Reference oscilldor
Flexion
Fig. 3. Block diagram of the electronic circuit added to the Sony TC-40 Recorder. In order to produce a signal-to-noise ratio which would later lend itself to automatic electronic data reduction, it was necessary to remove as much of the noise generated by instantaneous tape speed variations as possible. A high signal-to-noise ratio was obtained by using two oscillators, a recording network, and two frequency-to-voltage converters in the playback unit. The recording electronic circuits (Fig. 3) consist of a voltage-controlled oscillator and a reference oscillator. The frequency of the voltage-controlled oscillator, one to 2 kHz is determined by the motion of the tibia relative to the femur. The reference oscillator operates at a constant frequency of 5 kHz. The power for these two oscillators is derived from the battery pack in the Sony recorder. The signals from these two oscillators are electrically added and are recorded on chromium dioxide magnetic tape. In the playback electronic circuits (Fig. 4), the frequencies from the two oscillators are separated by the use of RCA phase-locked loops. Phase-locked
-
Reference phase locked loop; (5 kbix)
loops are devices which track a frequency over a given range and produce a d.c. voltage output which is directly proportional to the frequency. In other words, the phase-locked loops are performing as frequency-to-voltage converters. The voltage from the phase-locked loop that follows the movement of the knee and the voltage from the phase-locked loop that views the constant frequency of 5 kHz are applied to the inputs of a difference amplifier which removes all noise components common to both channels. The output of the difference amplifier thus contains the information associated with angular variations of the knee with the low-frequency noise essentially eliminated. It is also necessary to filter out higher-frequency noise, such as that generated by 60-cycle line problems and 120-cycle radiation from fluorescent lighting, since this noise is not introduced equally in both channels. Thus, the difference amplifier is followed by an active filter network-a low pass filter with a flat frequency response from d.c. to 15 Hz. The filter highfrequency cutoff of 15 Hz does not eliminate any of the information relative to the angular movement of the knee. The output signal from the filter is amplified to give the desired voltage vs frequency relationship and is recorded by a Century Model GBO460 light beam galvanometric recorder. The described instrumentation package produces waveforms that are descriptive of each knee motion in the sag&al plane that occurs at the time of the recordings. The output voltage vs the input voltage, as measured at the wiper arm of the potentiometer worn on the knee, is linear to within f 1% over a range that would constitute an angular variation considerably greater than that experienced by a normal knee. In addition, with the playback electronic circuits adjusted to produce a change in the output voltage of four volts per 140” motion of the potentiometer, the system possesses a 40 dB signal-to-noise ratio.
-
Input from _ tape recorder
I _
+&
Active phose locked loop
-
Eoseline set
Fig. 4. Block Diagram of the electronic circuit employed to reproduce flexion as a function of time from the magnetic tape.
Fig. 1. Electrogoniometer and portable recorder. Fig. 2. Circuit board containing the electronic circuit added to the Sony TC-40 Recorder recording of flexion
(Facing p. 370)
to permit
Fig. 5.(a) Front view of the electrogoniometer and recorder as worn by the sub.ject. (b) Side vieu of the electrogoniometer and recorder as worn by the subject.
371
Repetitive activities of the knee
I
1
wtmg
and
rlrlng
Fig. 8. Flexion waveforms for sitting and rising for the normal knee. Fig. 6. Flexion waveforms for walking for the normal knee. METHOD
The electrogoniometer (Kettelkamp et al., 1970) was attached to each subject in the laboratory as shown in Figs. 5(a,b); and a reference recording was obtained while the subject walked, climbed and descended stairs, and sat on and rose from a chair. The position of the goniometer was marked on the subject’s thigh and calf with a marker pen. The subject was then taught to remove and reapply the goniometer until she could do it satisfactorily, and she was instructed in the use of the tape recorder. The subject wore the goniometer for intervals of one hour, noting the time and date of the recording and the type of activity recorded (housework, kitchen work, tending children, etc.). Type and frequency of activity were obtained by playing the tape through an oscillo-
I
/--
I *et
__I
scope and manually counting the types of activities based on the known pattern of motion for those activities (Laubenthal et al., 1972). The activities recorded were walking (Fig. 6), ascending and descending stairs (Figs. 7a, b), sitting and rising (Fig. 8), and undifferentiated knee motion (Fig. 9). Running can be determined with this technique but was not recorded by any of the subjects. RESULTS
Fifty hours of recording were obtained from eight women, aged 2341, and one man aged 29. The women were a11wives of medicA students or of orthopaedic residents. The total repetitions for different activities for 50 hours recording time were 14,425 steps walking, 5212 undifferentiated motions, 242 climbing stairs, 197 descending stairs, 223 sitting, and 214 rising. The averages per hr were 289 steps walking, 104 undifferentiated motions, 5 ascending stairs, 4 descending stairs, 4 sitting and 4 rising. The average number of repetitive acts by type of occupational activity is presented in Table 1. The average number of repetitive acts by hour of the day is given in Table 2. The average number of alt knee motions was 410 per hour, or 683 motions per minute.
I
DISCUSSION
Instrumentation has been presented for the determination of frequency and type of repetitive knee activity. Since continuous monitoring of a given subject r
-=.
Fig. 7(b). Flexion waveforms for descending stairs for the normal knee.
Fig.
9. Flexion
-
waveforms for undifferentiated motions for the normal knee.
knee
P. C. MCLEODet al.
372
Table 1. Average number of repetitive acts by types of occupational activity Occupation
HOWS
HOUSWWk
15.67
Kitchen Work
16.00
Laundry
4.00
Child
6.83
245
90
1
1
5
5
7.50
404
162
17
11
3
3
Care
Yard llork
Undiff. Ilotionlhr
Stairs Uplhr
Stairs Dovmlhr
301
96
3
3
6
244
91
2
2
7
7
276
103
5
5
5
4
Stepsfhr
is not possible, data gained by using this method must be considered as representative rather than as absolute. Even with this limitation, the determination of the frequency and of the type of activity probably will be of greater value in the evaluation of wear and Ioosening of knee implant prostheses than is the activity implied by the term “follow-up” in current reports. Determination of knee activity using this method depends upon recognizing patterns of motion which are specific for given activities. We have had extensive experience using the three-plane electrogoniometer on abnormal knees, including 33 total knee arthroplasties. Though the patterns of sagittalplane motion differ from normal, the patterns are usually activity specific. The only situations in which sagittal-plane motion cannot be used to determine activity are for walking if the patient walks stiff-legged or has no knee motion and for stairs if the patient uses the knee in the extended position both up and down stairs. This method for determining repetitive activities requires an intelligent and cooperative patient. Data reduction is time consuming and currently presents a severe limitation to the acquisition of the large number of measurements needed for correlation with subsequent prosthetic wear and loosening. The authors are now working on automatic data-reduction instrumentation. Seedhom et al. (1973) used a pedometer to obtain information on the number of walking steps, but the pedometer is a simple instrument that cannot differentiate between various activities. This inability is a
Sltting/hr
Risjnglhr
6
serious limitation if the activities can eventually be used in calculating cumulative or repetitive loads and in the estimation of shear forces which are probably greatest with activities involving the loaded, flexed knee (i.e. sitting and rising, and ascending and descending stairs, as noted by Jones, 1973, and Smidt, 1973). The information from housewives with normal knees provides a basis for comparison with housewives after knee-replacement prosthesis, although the overall activity from our subjects probably exceeds the activity of normal women of an older age group. The number of steps (gait cycles) taken by our subjects compares closely to the number taken by elderly persons on vacation (determined by Seedhom et al., 1973), 42433000 walking cycles (steps) per day. Of speculative interest was the combined total of all knee motion, which averaged 410 per hr, or 6.83 per min. This frequency would be compatible with the theory that knee motion is necessary for articular cartilage nutrition and also with the sensation of discomfort and stiffness associated with prolonged sitting or immobility. SUMMARY The authors have developed instrumentation for determining the frequency and type of knee motion occurring in the home environment. Knee motion was recorded from a single-plane electrogoniometer with three planes of freedom on a modified portable tape recorder. Activity was determined by the pattern of
Table 2. Average number of repetitive acts by hour of the day Time
7-8 D-9 9-10 10-11 11-12 12-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 3-9
Hours of Recording Time
a.m. a.m. a.m. a.m. a.m. p.m. p.m. p.m. p.m. p.m. p.m. p.m. p.m. D.L.
Steps/hr
280
278 271 271 305 348 187 281 266 233 413 242 400 293
Urdiff. E!otion/hr
Still-S tJp/hr
Sittfnglhr
Rlsloglhr
95 lii 114 4 6
z3 132 76 104 :: 140
1’0
1;: 126
: 1
Repetitive activities of the knee knee motion. Data from nine normal people working about the house and yard provided average hourly activities of 289 walking steps, 5 ascending stairs, 4 descending stairs, 4 sitting, 4 rising and 104 undifferentiated knee motions. Thus, the frequency of knee motion is very high in normal people performing common daily activities. REFERENCES
Frankel, V. H. (1973) Panel on functional analysis. Internal structural prostheses. A Report of a Workshop on Fundamental Studies for Internal Structural Prostheses. pp. 75- 77. National Academy of Sciences.
373
Jones, G. B. (1973) Total knee replacement-the Walddius hinge. Clin. Orthop. 94, X-57. Kettelkamp, D. B., Johnson, R. J., Smidt, G. L., Chao. E. Y. S. and Walker, M. (1970) An electrogoniometric study of knee motion in normal gait. .r. Bone Jnt Surg. 52-A, 775-790. Laubenthal, K. N., Smidt, G. L. and Kettelkamp. D. B. (1972) A quantitative analysis of knee motion for activities of daily living. Phrs. Ther. 52, 3442. Seedhom, B. -B., Longton. E. B., Dawson, D. and Wright, V. (1973) Biomechanics background in the design of a total replacement knee prosthesis. Acta Orthop. Be/. 39, 164-180.
Smidt, G. L. (1973) Biomechanical analysis of knee flexion and extension. J. Biomechanics 6, 19-92.
