This paper investigates the mechanical behavior and design of a patent pending device called a load range weight bearing indicator (LWBI), which provides upper and lower range indication to patients with lower extremity injuries as part of a partial weight bearing rehabilitation. The LWBI consists of two opposing stacks (a.k.a. double stack) of snap domes—bistable mechanical elements that snap through only when a threshold weight is applied—sandwiched between a load transfer plate and base plate. The mechanical behavior of a LWBI has been characterized by testing single and double stacks of snap domes in a rigid aluminum fixture using a universal testing machine. Single stacks of two to eight snap domes each exhibited very predictable and repeatable buckling behavior (i.e., stack buckling load is simply the sum of individual snap dome buckling loads) when deflected at speeds typical for patients walking with a regular gait. The double stack configuration only works when supporting legs of the opposing snap dome stacks are offset by half the angle between adjacent legs. The lower load stack buckles first, while the higher load stack buckles at its threshold load because of the very low force required to keep the lower load stack collapsed. While the presence of a spacer has little effect on the double stack buckling behavior under controlled rate deflection in a precision test fixture, it was required for proper functioning of a LWBI prototype probably because of looser dimensional tolerances. The type of substrate that snap dome stacks are in contact with has little effect on the buckling loads as long as the material is not too soft. Finally, the speed of deflection within the expected range of ambulating patients has an insignificant effect on the LWBI’s buckling behavior. A LWBI prototype was designed based on the observed characteristics of the snap dome double stack with a spacer plate between the upper and lower load stacks. The prototype was installed in a recess in the insole of a biomechanical shoe beneath the patient’s heel. The shoe with LWBI was tested by various subjects pushing on a force plate and the upper and lower buckling loads were clearly indicated to the subject by audible and tactile click and measured as ground reaction force versus time. Future work will focus on further testing of the device and refinement of the design for various medical appliances.

1.
Augat
,
P.
,
Merk
,
J.
,
Ignatius
,
A.
,
Margevicius
,
K.
,
Bauer
,
G.
,
Rosenbaum
,
D.
, and
Claes
,
L.
, 1996, “
Early, Full Weightbearing With Flexible Fixation Delays Fracture Healing
,”
Clin. Orthop. Relat. Res.
0009-921X,
328
, pp.
194
202
.
2.
Buckwalter
,
J. A.
, 1996, “
Effects of Early Motion on Healing of Musculoskeletal Tissues
,”
J. Hand Surg. [Am.]
,
12
, pp.
13
24
. 0363-5023
3.
Chow
,
S. P.
,
Cheng
,
C. L.
,
Hui
,
P. W.
,
Pun
,
W. K.
, and
Ng
,
C.
, 1992, “
Partial Weight Bearing After Operations of Hip Fractures in Elderly Patients
,”
J. R. Coll. Surg. Edinb
0036-8835,
37
, pp.
261
262
.
4.
Perren
,
T.
, and
Matter
,
P.
, 1996, “
Feedback Controlled Weightbearing Following Osteo-Synthesis of the Lower Extremity
,”
Swiss Surg.
1023-9332,
2
, pp.
252
258
.
5.
Pilliar
,
R. M.
,
Cameron
,
H. U.
,
Welsh
,
R. P.
, and
Binnington
,
A. G.
, 1981, “
Radiographic and Morphologic Studies of Load-Bearing Porous-Surfaced Structured Implant
,”
Clin. Orthop. Relat. Res.
0009-921X,
156
, pp.
249
257
.
6.
Wood
,
G. W.
, 2003, “
General Principles of Fracture Treatment
,”
Campbell’s Operative Orthoaedics
,
10th ed.
,
S. T.
Canale
, ed.,
Mosby
,
St. Louis, MO
, Vol.
3
, p.
2714
.
7.
Eisele
,
R.
,
Weickert
,
E.
,
Eren
,
A.
, and
Kinzl
,
L.
, 2001, “
The Effect of Partial and Full Weight-Bearing on Venous Return in the Lower Limb
,”
J. Bone Joint Surg. Br.
0301-620X,
83-B
(
7
), pp.
1037
1040
.
8.
Banks
,
A. S.
, and
McGlamry
,
E. D.
, 1989, “
Charcot Foot
,”
J. Am. Podiatr. Med. Assoc.
8750-7315,
79
(
5
), pp.
213
234
.
9.
Armstrong
,
D. G.
,
Todd
,
W. F.
,
Lavery
,
L. A.
,
Harkless
,
L. B.
, and
Bushman
,
T. R.
, 1997, “
The Natural History of Acute Charcot’s Arthropathy in a Diabetic Foot Specialty Clinic
,”
J. Am. Podiatr. Med. Assoc.
8750-7315,
87
(
6
), pp.
272
278
.
10.
Tveit
,
M.
, and
Kärrholm
,
J.
, 2001, “
Low Effectiveness of Prescribed Partial Weight Bearing: Continuous Recording of Vertical Loads Using a New Pressure-Sensitive Insole
,”
Scand. J. Rehabil. Med.
0036-5505,
33
, pp.
42
46
.
11.
Baxter
,
M. L.
,
Allington
,
R. O.
, and
Koepke
,
G. H.
, 1969, “
Weight-distribution Variables in the Use of Crutches and Canes
,”
Phys. Ther.
0031-9023,
49
(
4
), pp.
360
365
.
12.
Warren
,
C. G.
, and
Lehmann
,
J. F.
, 1975, “
Training Procedures and Biofeedback Methods to Achieve Controlled Partial Weight Bearing: An Assessment
,”
Arch. Phys. Med. Rehabil.
0003-9993,
56
, pp.
449
455
.
13.
Winstein
,
C. J.
,
Christensen
,
S.
, and
Fitch
,
N.
, 1993, “
Effects of Summary Knowledge of Results on the Acquisition and Retention of Partial Weight Bearing During Gait
,”
Physical Therapy Practice
,
2
(
4
), pp.
40
51
.
14.
Winstein
,
C. J.
,
Pohl
,
P. S.
,
Cardinale
,
C.
,
Green
,
A.
,
Scholtz
,
L.
, and
Waters
,
C. S.
, 1996, “
Learning a Partial-Weight-Bearing Skill: Effectiveness of Two Forms of Feedback
,”
Phys. Ther.
0031-9023,
76
(
9
), pp.
985
993
.
15.
Gray
,
F. B.
,
Gray
,
C.
, and
McClanahan
,
J. W.
, 1998, “
Assessing the Accuracy of Partial Weight-Bearing Instruction
,”
Am. J. Orthop.
1078-4519,
27
(
8
), pp.
558
560
.
16.
Dabke
,
H. V.
,
Gupta
,
S. K.
,
Holt
,
C. A.
,
O’Callaghan
,
P.
, and
Dent
,
C. M.
, 2004, “
How Accurate is Partial Weightbearing?
Clin. Orthop. Relat. Res.
0009-921X,
421
, pp.
282
286
.
17.
Vasarhelyi
,
A.
,
Baumert
,
T.
,
Fritsch
,
C.
,
Hopfenmüller
,
W.
,
Gradl
,
G.
, and
Mittlmeier
,
T.
, 2006, “
Partial Weight Bearing After Surgery for Fractures of the Lower Extremity—Is It Achievable?
Gait and Posture
0966-6362,
23
, pp.
99
105
.
18.
Chiverton
,
N.
, and
Akowuah
,
E. F.
, 2003, “
Partial Weightbearing in the Elderly Patient Following Proxmity Femoral Fractures—A Feasibility Study
,”
J. Bone Joint Surg. Br.
0301-620X,
85-B
, (SUPP I), p.
37
.
19.
Schwartz
,
M. S.
, 1995,
Biofeedback: A Practitioner's Guide
,
Guilford Press
,
New York
.
20.
Miyazaki
,
S.
, and
Iwakura
,
H.
, 1978, “
Limb-Load Alarm Device for Partial-Weight-Bearing Walking Exercise
,”
Med. Biol. Eng. Comput.
0140-0118,
16
(
5
), pp.
500
506
.
21.
Wolf
,
S. L.
, and
Binder-Macleod
,
S. A.
, 1982, “
Use of the Krusen Limb Load Monitor to Quantify Temporal and Loading Measurements of Gait
,”
Phys. Ther.
0031-9023,
62
(
7
), pp.
976
982
.
22.
Wannstedt
,
G.
, and
Herman
,
R.
, 1978, “
Use of Augmented Sensory Feedback to Achieve Symmetrical Standing
,”
Phys. Ther.
0031-9023,
58
(
5
), pp.
553
559
.
23.
Batavia
,
M.
,
Gianutsos
,
J. G.
,
Vaccaro
,
A.
, and
Gold
,
J. T.
, 2001, “
A Do-It-Yourself Membrane-Activated Auditory Feedback Device for Weight Bearing and Gait Training: A Case Report
,”
Arch. Phys. Med. Rehabil.
0003-9993,
82
, pp.
541
545
.
24.
Gradisar
,
I. A.
, 1972, “
Partial Weight Bearing Warning Device
,” U.S. Patent No. 3,702,999.
25.
Pfeiffer
,
E. A.
, 1974, “
Device for Sensing and Warning of Excessive Ambulation Force
,” U.S. Patent No. 379,1375.
26.
Sipe
,
J. J.
, 1974, “
Load Signaling Device for a Patient’s Foot
,” U.S. Patent No. 3,974,491.
27.
Goforth
,
W. P.
, 1987, “
Multi-Event Notification System for Monitoring Critical Pressure Points on Persons With Diminished Sensation of the Foot
,” U.S. Patent No. 4,647,918.
28.
Confer
,
R. G.
, 1988, “
Force Sensing Insole for Electro-Goniometer
,” U.S. Patent No. 4,745,930.
29.
Ratzlaff
,
M. H.
,
Grant
,
B. D.
, and
Frame
,
J. M.
, 1989, “
Systems for Measurement and Analysis of Forces Exerted During Human Locomotion
,” U.S. Patent No. 4,814,661.
30.
Sugarman
,
E. D.
,
D'Antonio
,
N. F.
, and
D'Antonio
,
N. J.
, 1989, “
Warning System for Excessive Orthopedic Pressures
,” U.S. Patent No. 4,858,620.
31.
Gray
,
F. B.
, 1993, “
Force Monitoring Shoe
,” U.S. Patent No. 5,269,081.
32.
Thomas
,
B. R.
,
Steinman
,
H.
, and
Alley
,
S. D.
, 1993, “
Orthopedic Weight Monitor
,” U.S. Patent No. 5,253,654.
33.
Fullen
,
G.
, and
Fullen
,
J. G.
, 1994, “
System for Continuously Measuring Forces Applied to the Foot
,” U.S. Patent No. 5,323,650.
34.
Gray
,
F. B.
, and
Parris
,
J. L.
, 1994, “
Device for Measuring Force Applied to a Wearer's Foot
,” U.S. Patent No. 5,357,696.
35.
Schmidt
,
R. N.
,
Chizeck
,
H. J.
, and
Diefes
,
R. S.
, 1995, “
Foot Force Sensor
,” U.S. Patent No. 5,408,873.
36.
Schmidt
,
R. N.
, and
Diefes
,
R. S.
, 1997, “
Foot Weight Alarm
,” U.S. Patent No. 5,619,186.
37.
Bechmann
,
P.
, 2000, “
Load Signaling Device for a Patient's Foot
,” U.S. Patent No. 6,031,463.
38.
Gray
,
F. B.
,
Parris
,
J. L.
,
Gray
,
D. H.
, and
Riffert
,
R. G.
, 2000, “
Force Monitoring Shoe
,” U.S. Patent No. 6,122,846.
42.
Walczyk
,
D. F.
, and
Kerdok
,
A. E.
, 2002, “
Mechanical Weight Bearing Indicator for the Foot
,” U.S. Patent No. 6,405,606.
43.
Walczyk
,
D. F.
, and
Bartlet
,
J. P.
, 2007, “
An Inexpensive Weight Bearing Indicator Used for Rehabilitation of Patients With Lower Extremity Injuries
,”
ASME. J. Med. Devices
,
1
(
1
), pp.
38
46
.
44.
45.
Walczyk
,
D. F.
, and
Bornhoft
,
S.
, 2009, “
Device for Mechanical Weight Bearing Indication With Load Range Capability
,” U.S. Patent 7,493,810, Issued on Feb. 24.
46.
Ordway
,
N. R.
,
Mann
,
K. A.
,
Walczyk
,
D.
,
Young
,
M.
, and
Simpson
,
R. B.
, 2009, “
Effectiveness of Partial Weight Bearing in Lower Extremity Injury Patients Using a Weight Bearing Indicator
,”
Proceedings of the Orthopaedic Research Society 55th Annual Meeting
, Las Vegas, NV, Feb. 22–25.
You do not currently have access to this content.