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A RELIABLE AND ACCURATE METHOD OF MEASURING ORTHOSIS-WEARING TIME. Robert M. Havey, B.S., Thomas M. Gavin, C.O., Avinash G. Patwardhan, Ph.D., Steven B. Pawelczak, Kamal N. Ibrahim, M.D., Hines, IL.
BACKGROUND: Orthosis-wearing compliance is considered to be an important factor in the outcome of orthotic treatment for idiopathic scoliosis, spinal fractures, low back pain and postoperative implant protection. To date, their are no known studies correlating wearing time with outcome of treatment, despite the fact that wearing time may be considered as "dosage" of orthotic treatment. Traditionally, orthoses for scoliosis were prescribed for 23 hour per day wearing. In recent years, new innovations in orthoses design yielded some orthoses indicated for part-time wearing. Both these wearing regimes were arrived at empirically and the truth is that dosage related effects of orthotic treatment is still unknown. Currently, the issue of "part-time" versus "full-time" orthosis wearing for idiopathic scoliosis has not been resolved. Despite one study by Katz and another study by Rowe showing much poorer results for people prescribed a part-time type of orthosis (such as the Charleston Bending Brace, Fig 1.) as opposed to those prescribed full-time type of orthoses (such as a Boston Brace, Milwaukee brace etc.), many people still feel that, in their experience, that part time brace wearing is "effective enough" to yield a good outcome. Also, for the adult with spinal injuries, the effect of orthosis wearing on outcome of treatment is also not known.
1. THE BOSTON BRACE 2. THE CHARLESTON
SYSTEM BENDING BRACE
(For Full-time Wearing) (For Part-time Wearing)
Figure 3. Katz et. al shows that patients who wore the Boston Brace (BB) had a significantly better outcome than those who wore the Charleston Bending Brace (CBB).
(From: Katz DE, Richards S, Browne RH and Herring JA. A Comparison between the Boston brace and the Charleston bending brace in adolescent idiopathic scoliosis. Spine 1997;22:1302-12).
Figure 4. Rowe et al shows better results for patients who reported wearing their brace full-time. (From: Rowe DE, Bernstein SM, Riddick MF, Adler F, Emans JB. A meta-analysis of the efficacy of nonoperative treatment for idiopathic scoliosis. J Bone Joint Surg [Am] 1997;79-A:664-74).
STATEMENT OF PROBLEM
To date, there has been no reported accurate and reliable method to objectively measure patient orthosis- wearing time. Until a method is available, dosage related effects of orthotic treatment will not be well understood by clinicians.
OBJECTIVE
To develop and test an accurate and reliable device to measure spinal orthosis wearing time.
METHODS
Design of the Compliance Monitor
Three main components:
1. Sensors to determine if the orthosis is being worn,
2. Data logger to acquire and save the sensor data,
3. Personal computer interface for programming the data logger and to retrieve recorded data.
Sensors
Force Sensitive Resistors (FSR's) (Vista Medical Ltd., Winnipeg, Manitoba, Canada) were used as pressure-threshold switches to determine the "on-off" wearing state of the spinal orthosis (Fig 5). The FRS's were connected to the data logger by stainless steel wires.
Figure 5. Four Force Sensitive Resistors are used as pressure switches for compliance monitor.
Data Logger
The data logger is a battery-operated computer consisting of a low power microcontroller, a real-time clock, nonvolatile memory, and sensor interface. The data logger was programmed to sample the "on-off" state of the FSR's at preset intervals. The date, time, and the on-off status of the sensors were saved when the current sensor readings were different than the last saved values. (Figure 6)
Figure 6. Data Logger for the Compliance Monitor.
Figure 7. The compliance monitor is miniature and may be well concealed in orthoses.
Figure 8. 4 FSR's are connected to the data logger and powered with a 3-volt lithium battery.
Programming and Data Retrieval
A personal computer with custom "Windows© software and a serial port was used to program the data logger and to download wearing-time data at the conclusion of testing. The software was capable of:
1. Viewing the real-time "on/off" states of the FSR's,
2. Reading and setting the real-time clock,
3. Reading from and writing to the memory,
4. programming the sampling interval.
Figure 9. The Compliance Monitor Being Sealed Into A Pad On A Cash© Orthosis.
Figure 10. The Compliance Monitor May Be Fabricated Into Custom Made Orthoses.
Testing
Nine normal volunteer subjects wore custom molded, bi-valved TLSO's for up to 40 hours while maintaining manual diaries of donning and removal events (Figure 11). This test was to assess the ability of the compliance monitor to accurately measure orthosis wearing time when exposed to activities of daily living. Manual wearing-event diary was kept for post-test comparison to wearing time recorded by the data logger. Digital wristwatches were used for the purpose of maintaining manual diaries.
Figure 11. Volunteer subject wearing custom molded TLSO instrumented with a compliance monitor.
RESULTS
Nine volunteer subjects wore their TLSO's for an average of 7 days (range: 3-14 days), yielding an average total wearing time of 29 hours, 37 minutes (range: 6 hours, 40 minutes-45 hours, 40 minutes). The average daily wearing time was 4 hours, 14 minutes (range: 9 minutes-8 hours, 30 minutes), with an average orthosis wearing-time interval of 3 hours, 39 minutes (range: 9 minutes-11hours, 54 minutes). The values of the total orthosis wearing time, average daily wearing time, and average wearing-time interval calculated from the data logger records for each subject agreed well with the values calculated from the data recorded in the subjects manual diary (mean difference: 0.9%, SD: 2.2%). 73 orthosis wearing-time intervals (time period between orthosis donning and removal) were recorded over the duration of this test. The linear regression performed on the orthosis wearing-time intervals obtained from the normal volunteer subject tests yielded an R2 value of 0.998 with a slope of 0.998 (p<0.0001) (Figure 12).
Figure 12. Regression analysis reveals an excellent correlation between manually kept subject diaries and recorded wearing-time. Monitor is quite accurate and reliable.
This study was carried out at the Musculoskeletal Biomechanics Laboratory at the Veterans Administration Hospital Hines and was fully supported by a grant from the Rehabilitation Research and Development Service of the Veterans Administration.
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