Shock Absorbing Crutches

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En1000: Projects in Engineering Design

"The Smart Crutch" - a novel shock absorbing crutch

Project Summary:

The Smart Crutch seeks to redefine one of the oldest rehabilitative medical devices. By eliminating traditional rubber tips with a novel shock absorbing base, the patient's gait will be softer, smoother, and more consistent with the normal walking step. Furthermore, the crutches are collapsible to increase storage efficiency during travel.

The Smart Crutch primarily seeks to reduce the shock of traditional crutches. By reducing shock, the novel base will increase stability and boost the psychological and physical well-being of a disabled individual. The shock absorbing properties will be quantified by having an individual ambulate over a vertical force platform and analyze the vertical force and resulting frequency vibrations. The increased stability and smoother gait pattern will be determined by analyzing patient opinion and examining the data from the force platform. A crutch that can reduce shock and create a smoother gait for the patient, will ultimately translate into a quicker step and faster recovery.

In short, this capstone research project will analyze the shock from crutches by means of a vertical force platform, and develop a new prototype crutch that dampens the shock during ambulation.

Intro:

The Smart Crutch seeks to reduce the shock of traditional rubber tipped crutches, increase stability during ambulation, and increase the psychological and physical well-being of a disabled individual. A smoother and softer gait will ultimately translate into a quicker step and a faster recovery.

Individuals who will benefit from this solution are patients with a lower extremity injury, broken leg, or amputation. Lower extremity amputees who temporarily cannot use their prosthesis due to a skin disorder will greatly benefit from the Smart Crutch. Amputees with skin disorders cannot use their prosthesis for minimum 1-2 weeks, forcing them to resort to crutches. As a result, all amputees have at least one pair of crutches at home for emergencies.

The user-needs that I am addressing with the Smart Crutch are:

Reducing the shock of traditional rubber tipped crutches by using a novel shock absorbing base
Facilitating a softer and smoother gait
Encouraging a quicker step
Enabling a faster recovery
Increasing portability and storage efficiency

Background:

Here is my background research into existing solutions with pictures:

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Previous Shock Absorbing Crutch Prototypes in EN 1000

Designing a new prototype shock absorbing crutch has been investigated in previous EN 1000 courses. Below are two shock absorbing crutch final prototypes that were built by former students in EN 1000. Both of these shock absorbing crutch prototypes were analyzed by physical therapists, and determined to be too unstable for patient use. There is a significant challenge in engineering a crutch that exhibits both shock absorbing properties and maintains total patient stability during ambulation.

1. "Pogo-Stick" Crutch

The pogo-stick crutch prototype integrates a spring dampener into a traditional rubber tipped crutch.

2. Fiberglass Shaft Crutch

The fiberglass shaft crutch is shown on the left.

The pogo-stick crutch is shown on the right.

Web links:

Inspiration for the "Smart Crutch" concept:

Unique Crutch Design

http://images.businessweek.com/ss/06/03/crutches/source/5.htm

Futuristic "S_UPPORT" Crutch

http://www.tuvie.com/s_upport-efficient-plastic-crutch

Ossur Prosthetic Feet

http://www.ossur.com/prosthetics/feet

Ossur Cheetah Flex Foot

http://www.ossur.com/?pageid=3547

GP Canes: Home Mobility Products

http://www.shop.gpcanes-n-more.com/main.sc;jsessionid=335F090DCEC6C2CD5D6BC842D76F4D02.qscstrfrnt04

Pros and Cons of the "Smart Crutch" and the "Traditional Rubber Tipped Crutch":

Plus and Minus for the User:
	Good	Bad
Traditional Rubber Tipped Crutch	1. Cheap 2. Good stationary balance	1. Increased shock from ambulation presents a significant challenge for individuals with arthritis and carpal tunnel syndrome. 2. Doesn't emulate the normal walking step.
Smart Crutch	1. Reduces the shock of traditional crutches using a novel shock absorbing base 2. Facilitates a softer and smoother gait 3. Encourages a quicker step 4. Enables a faster recovery 5. Increases portability and storage efficiency	1. Higher cost

Intellectual Property:

Many engineers and inventors have created prototypes that merge lower extremity prosthetic technology with traditional crutches. These six patents display how prosthetic technology can be used to engineer a novel shock absorbing base for traditional crutches:

Link to all six patents:

http://v3.espacenet.com/searchResults?locale=en_EP&AB=crutch+prosth*&ST=quick&compact=false&DB=EPODOC

Patent 1: Mobility Assistance Apparatus and Method CA 2519683 (A1)

http://v3.espacenet.com/publicationDetails/biblio?adjacent=true&KC=A1&date=20070315&NR=2519683A1&DB=EPODOC&locale=en_EP&CC=CA&FT=D

Patent 2: mobility assistance apparatus and method US 2005016572 (A1)

http://v3.espacenet.com/publicationDetails/biblio?adjacent=true&KC=A1&date=20050127&NR=2005016572A1&DB=EPODOC&locale=en_EP&CC=US&FT=D

Patent 3: Crutch Device US 6494919 (B1)

http://v3.espacenet.com/publicationDetails/biblio?adjacent=true&KC=B1&date=20021217&NR=6494919B1&DB=EPODOC&locale=en_EP&CC=US&FT=D

Patent 4: CRUTCH DEVICE WO 0124758 (A1)

http://v3.espacenet.com/publicationDetails/biblio?adjacent=true&KC=A1&date=20010412&NR=0124758A1&DB=EPODOC&locale=en_EP&CC=WO&FT=D

Patent 5: Central Crutch FR 2611492 (A1)

http://v3.espacenet.com/publicationDetails/biblio?adjacent=true&KC=A1&date=19880909&NR=2611492A1&DB=EPODOC&locale=en_EP&CC=FR&FT=D

Patent 6: Ambulation Assistance Device US 3986502 (A)

http://v3.espacenet.com/publicationDetails/biblio?adjacent=true&KC=A&date=19761019&NR=3986502A&DB=EPODOC&locale=en_EP&CC=US&FT=D

My Proposed Solution:

I will be using a lightweight wooden prosthetic foot encased in a plastic cover as the primary replacement to the traditional rubber tipped crutch. The shock absorbing characteristics of the Smart Crutch will derive from a "Mini Sleeve Style Air-Powered Spring," which will be mounted above the prosthetic foot. The air spring will be fastened to the crutch with a custom made attachment fabricated on a lathe.

Requirements:

Requirements:The Smart Crutch must pass the "force plate test" to ensure the device absorbs more shock than traditional rubber tipped crutches. Furthermore, the Smart Crutch must be evaluated by an individual other than myself, indicating the device increases patient stability and facilitates a smoother and softer gait.
Constraints: A force plate will be used to determine the shock of conventional rubber tipped crutches. These values will be compared with the vertical force data resulting from the Smart Crutch.
Evaluation criteria: (1) Force Plate Test and (2) External Evaluation

First Prototype:

Brainstorms:

First Prototype: (here are my pictures, videos, schematics, drawings, brainstorm notes, and parts list)

Parts List

1. Conventional Aluminum Push-Button Crutches, purchased from GP Canes-n-More for $44.10

2. Thin-Sleeve Style Air-Powered Spring, Mini Sleeve Style, 2.1'' Stroke, 3.6'' Extended Height, purchased from McMaster-Carr for $42.48 (x2)

3. Valve for Mini and Sleeve Style Air Springs, purchased from McMaster-Carr for $10.24 (x2)

4. Easy-to-Machine Aluminum (alloy 2011), 1'' Diameter, 1' Length, purchased from McMaster-Carr for $18.35

Total material cost for a pair of shock absorbing crutches: $167.89

Aluminum rod stock used to machine the following connecting part in order to fasten the crutch to the air spring.

First Test and evaluation:

The Smart Crutch (left) and the Conventional Rubber Tipped Crutch (right)

Assembly of the Smart Crutch.

Results:

After constructing the first prototype "Smart Crutch" or shock absorbing crutch, I conducted a basic test to ensure the device was safe and stable. The "Mini Sleeve Style Air-Powered Spring" which provides the crutch with shock absorbing properties was inflated to a pressure of 40 PSI with a bicycle pump. The maximum pressure is 100 PSI with a maximum load of 600 lbs.

The first test conducted was the gait test. The gait test was to determine if the Smart Crutch and air spring would conform to the standard human walking gait, and result in smooth ambulation. This test consisted of a few paces down a hallway in the basement of the engineering building. As shown in the first half of the video, the Smart Crutch and air spring demonstrated effortless ankle flexion and extension. Smooth ankle flexion and extension is essential to maintain a normal walking gait.

The second test was the stability test. If the shock absorbing crutch cannot hold the body weight of a human being in a stable upright position, then the purpose of a crutch is defeated. As evidenced in the second half of the video, the point between the air spring and the prosthetic foot demonstrated severe lateral buckling. In a real clinical situation, this lateral buckling between the air spring and the prosthetic foot would have caused the patient to fall over, resulting in a severe injury.

Therefore, prototype 1 passed the gait test, demonstrating angular moments, a fluid gait, and precise ankle flexion and extension. However, prototype 1 failed the stability test, by demonstrating lateral buckling between the air spring and the prosthetic foot.

The below video shows both the gait test and the stability test. The gait test is the first half of the video, and the stability test is the second half of the video. Notice the severe lateral buckling at the end of the video, causing prototype 1 to fail.

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Video showing the gait test and the stability test.

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Video demonstrating the portability of prototype 1.

Second Prototype

The first prototype failed the stability test due to lateral buckling between the air spring and the prosthetic foot. Prototype 2 will address the problem of prototype 1, by eliminating the buckling problem. I have decided to temporarily eliminate the prosthetic foot for prototype 2, and use just the air spring for the shock absorbing crutch. However, the base of the air spring is a flat tractionless plastic, and anyone using a crutch with this type of base would slip and fall instantly. Therefore, in order to create traction and maximum friction on the base of the air spring, I decided to attach a sanding disk on the bottom. However, the sanding disk had a shaft with a larger thread, making it incompatible with the 5/16''-18 thread of the air spring. In order to mount the sanding disk to the base of the air spring, I took a file and filed down the larger thread to a smooth shaft. I then took a 5/16''-18 DIE, and threaded the smooth shaft with the proper thread. The assembly of prototype 2 was complete after the sanding disk was screwed into the base of the air spring.

Smart Crutch Prototype 2

Prototype 2 displaying the sanding disk attached to the bottom of the air spring.

Assembly of prototype 2. The sanding disk is shown with the 5/16''-18 thread from the die.

Results:

The "Mini Sleeve Style Air-Powered Spring" which provides the crutch with shock absorbing properties was inflated again to a pressure of 40 PSI with a bicycle pump.

Again, my first test conducted was the gait test. The gait test was to determine if the Smart Crutch and air spring would conform with the standard human walking gait, and result in smooth ambulation. This test consisted of a few paces down a hallway in the basement of the engineering building. As shown in the video, the Smart Crutch and air spring demonstrated effortless ankle flexion and extension.

Again, the second test was the stability test. If the shock absorbing crutch cannot hold the body weight of a human being in a stable upright position, then the purpose of a crutch is defeated. As shown in the video, there was no lateral buckling.

Therefore, prototype 2 passed the gait test, demonstrating angular moments, a fluid gait, and minimal ankle flexion and extension. By eliminating the prosthetic foot, the amount of ankle flexion/extension was reduced. The base of Prototype 2 appeared to flex like a plunger, not the typical flexion and extension displayed by the ankle joint. Regardless, Prototype 2 passed the stability test, by eliminating the lateral buckling from prototype 1.

However, a new problem surfaced. Minutes after pacing back and forth with the new air spring only "Smart Crutch," I noticed the air spring was not holding air. The air leak was causing the air spring to slowly deflate, causing a rapid drop in air pressure.

The below video shows both the gait test and the stability test. The video also shows how the air spring has slightly deflated due to an air leak. I decided to investigate the air leak by submerging the air spring in a bucket of water in order to determine the source. The air leak was found to be at the junction where the air nozzle screws into the air spring. Eventhough the air nozzle was very tightly secured by a wrench, there was still an air leak. I decided to use teflon tape or an adhesive to seal the air leak.

The air leak would explain why there was lateral buckling with prototype 1. If there wasn't an air leak, prototype one could have been successful in the stability test.

Since prototype 1 and prototype 2 failed due to lateral buckling and an air leak respectively, I will repair the air leak before proceeding to prototype 3. Prototype 3, will be the final prototype, combining the better of the first two prototypes. Prototype 3 will undergo the force plate test, which will determine if the Smart Crutch is in fact a shock absorbing crutch that is superior to conventional rubber tipped crutches.

Once the air leak is fixed, I will retest both prototype 1 and prototype 2.

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Video showing the gait test and the stability test for prototype 2.

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Video demonstrating the portability of prototype 2.

Final Results (Prototype 3):

After analyzing the successes and failures of the first two prototypes, I have decided a shock absorbing crutch with a prosthetic foot is the optimal solution for realistic ankle flexion/extension, maximum stability, and maximum shock absorption. A major problem that was discovered with the first two prototypes was an air leak at the junction between the air nozzle and the air spring. After successfully wrapping the threads of the air nozzle with teflon tape, and screwing the nozzle back into the air spring, the air leak was finally eliminated. This was verified by submerging the air spring filled with 40 PSI in a bucket of water, and noticing no air leak.

After the air leak was resolved, I retested both prototypes 1 and 2, and found that the prosthetic foot no longer experienced lateral buckling.

Prototype 3, or the final concept, will consist of two identical crutches based on the prosthetic foot concept in prototype 1.

The final prototype will undergo the following five tests:

1. Simple Gait Test: to determine if the Smart Crutch and air spring would conform with the standard human walking gait, and result in smooth movements. This test consisted of a few paces down a hallway in the basement of the engineering building. This test will ensure the lateral buckling problem is resolved.

2. Stability Test: to determine if the shock absorbing crutch can hold the body weight of a human being in a stable upright position.

3. Force Plate Test with Conventional Rubber Tipped Crutches: to determine the vertical forces associated with standard crutch ambulation.

4. Force Plate Test with Smart Crutch: to determine the vertical forces associated with shock absorbing crutch ambulation. The compression forces should be reduced in the shock absorbing prototype.

5. Force Plate Test with individual other than myself (J.D.).

Final Prototype used for testing.

PASPort Force Platform PS-2141, Dell Laptop, and DataStudio software were used to quantify shock absorbing properties

of the traditional rubber-tipped crutch and the shock absorbing crutch.

Trial A: Subject: M.H.

The red and magenta lines (run 8 and run 9 respectively) represent subject M.H. walking twice over the force plate with traditional rubber tipped crutches.

The green and blue lines (run 10 and run 11 respectively) represent subject M.H. walking twice over the force plate with the shock absorbing "Smart Crutch."

This data was recorded using a one dimensional force plate that measured vertical force (N) over a designated period of 10 seconds.

This data shows that for subject M.H., the traditional rubber tipped crutch exhibited approximately 450 N of vertical force during ambulation.

In contrast, the shock absorbing "Smart Crutch" exhibited approximately 325 N of vertical force, indicating a 125 N decrease in vertical force.

Therefore, trial A displays the shock absorbing crutch can reduce impact during ambulation by 125 N.

Trial B: Subject: J.D.

The black line (run 7) represents subject J.D. walking once over the force plate with traditional rubber-tipped crutches.

The orange line (run 12) represents subject J.D. walking once over the force plate with shock absorbing crutches.

This data shows that for subject J.D., the traditional rubber-tipped crutch exhibited approximately 500 N of vertical force during ambulation.

In contrast, the shock absorbing crutch exhibited approximately 400 N of vertical force during ambulation.

Therefore, trial B displays the shock absorbing crutch can reduce impact during ambulation by 100 N.

Amplitude and Frequency Spectrum.

This graph demonstrates the amount of vibration in both the traditional rubber tipped crutch and the shock absorbing crutch.

The traditional rubber-tipped crutch, shown in blue, displayed higher frequency vibration than the shock absorbing crutch, shown below in red.

As a result, the prosthetic foot and air spring in the shock absorbing crutch were able to reduce the amount of vibration and reduce the amount of shock during ambulation.

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Subject M.H. ambulating with shock absorbing crutches.

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Subject J.D. ambulating over the force plate with traditional rubber-tipped crutches.

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Subject J.D. ambulating over the force plate with shock absorbing crutches.

Concluding Remarks:

In summary, the shock absorbing crutch utilized several major engineering concepts from the past four years. This capstone project used major engineering concepts from the following courses: organ replacement, biomaterials, instrumentation design, dynamics/vibrations, and statics. The ultimate result was a novel shock absorbing crutch that did in fact reduce the amount of vertical force during ambulation. By averaging the results from trial A and trial B, the shock absorbing crutch was able to reduce the vertical impact force by 112.5 N, in comparison to the traditional rubber tipped crutch. This shows that the prosthetic foot and air spring significantly contribute to reducing vertical force during ambulation. In addition, the prosthetic foot and air spring enabled the shock absorbing crutch to exhibit lower frequency vibration in comparison to the traditional rubber tipped crutch.

Eventhough the shock absorbing crutch served its purpose this prototype is not ready for commercialization. The major drawback of the shock absorbing crutch is cost. A traditional rubber-tipped crutch is very cheap, costing between $30-40 per pair. In contrast, a pair of shock absorbing crutches cost $167.89 to construct. Unless there is a significant medical reason that a patient needs a crutch that can reduce vertical force during ambulation, nearly all individuals with short term lower extremity injuries will choose the cheap rubber-tipped crutches. However, individuals such as lower extremity amputees, who are accustomed to the high cost of prosthetic devices, might be very interested in purchasing a shock absorbing crutch to increase their quality of life. The $167.89 cost for a pair of shock absorbing "Smart Crutches" are very cheap compared to current prosthetic devices on the market.

In conclusion, further patient research will be required to determine what additional improvements need to be made for the shock absorbing crutch. For now, the shock absorbing crutch achieved its objective of reducing vertical impact force during ambulation, and exhibiting lower frequency vibration in comparison to traditional rubber tipped crutches.