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Hip-disarticulation PROSTHETICS2

prostheticsA Hip-Disarticulation consist of the removal of the entire leg at the hip joint and results in the loss of 3 major limb joints: The ankle, the knee and the hip jointDouglas G. Smith, MD comments in an article in the magazine In-Motion:

Trying to overcome the loss of three weight-bearing joints, rather than one or two, is extremely complicated. Living with a transfemoral amputation is about 10 times as tough as living with a transtibial amputation, and living with a hip- or pelvic-level amputation is perhaps 100 times harder. Walking, standing, and even sitting balance something that most of us take for granted are greatly affected by amputations at the hip or pelvis

prostheticsHip-Disarticulations (HD) accounts for only 0.5% of lower extremity amputations in the United States and is mostly performed for: (listed by number of occurrence)

Malignant musculoskeletal tumors (most often in younger patients) Limb ischemia (perivascular disease and complications to diabetes) Trauma (such severe traumas often result in the death of the patient)Severe lower limbs infections (chronic skin or bone infection) As a result. . . . . . .

prostheticsMost prosthetist have little experience with this type of amputationOnly 20% of hip amputees use a prosthetic leg full-time (i.e. 8 to 12 hr./day) From these 20%, only a small minority use a prosthetic leg without a cane or crutchThis small minority of full time users without walking aids consists primarily of the young patients with malignant tumors.There is a persistent belief within the medical community that most middle aged hip-disarticulation amputees will ambulate with crutches or a wheelchair only!!!* Consent is is a bit of a misnomer as I had to choose between 1) hip-disarticulation or 2) slowly dying from infection or 3) slowly dying from the I.V. Vancomycin (antibiotic of last resort) eating my body away.I REMEMBER CLEARLY THE SURGEON EXPLAINING TO ME, AS I WAS SIGNING THE CONSENT* PAPERS PRIOR TO THE SURGICAL PROCEDURE, THAT I WAS GOING TO SPEND THE REST OF MY LIFE ON CRUTCHES

prosthetics

I am not an athlete (165lbs/511), and certainly not young (52+), yet..I am a full-time user AND I walk without a cane and I live a full life and do just about everything I want.Granted, there are some limitations. Yes, I cant play tennis anymore. Big deal! Yes, I cant ride motorcycles anymore. That, I do miss indeed but its not the end of the world.Is the prosthesis comfortable? Hell no! But it beats using crutches all day.Biggest problem with using crutches is that we loose the use of our hands. People are always surprised when I say this. What I mean is that we cannot carry things easily when using crutches.

prostheticsThe key to success is to become deeply involved in the process.It is easy to believe that This is as best as it can be!. These highly trained professional prosthetists have done their best but I still cant walk with the damn leg. It hurts, I keep on falling (This I did. 3 broken wrists, 1 rib). Therefore, I must be the problem. I am not just good enough. I am too old. I am not trying hard enough. I am too weak, etcTrue! This highly trained professionals try hard butThey lack experience in this domain.They dont have the time to do it right and,These types of prosthetic legs are finicky to set up. It takes days of incremental adjustments to get it just right. (i.e. Efficient to use (not tiring) and stable)For example, on my current leg, there are 44 set-screws and other adjustments, all interacting with each other, altering the geometry and other parameters of the leg.

Prosthetics - socketThe first socket was a disaster. Eventually, my prosthetist relented and accepted to build a second one at no cost. Including many modifications I had suggested during numerous discussions.This socket is much better but by no mean GOOD.From what I have read in several technical articles, it could be much better.The problem consist of:1) Finding a prosthetist, that actually knows what he is talking about. Not so easy, as they all claim to be experts.2) COST. For most non amputees, it is always a surprise. A socket cost around $12,000! (Yes, you are reading right!) and, the icing on the cake is MOST insurances do not pay at all, or pay only a minor fraction of the cost. Prosthetics are included in insurance contracts under durable medical equipment*. YES, it is covered but maximum payment is limited to. $2,000/year. Nobody check these things unless they lose a limb.*BTW: I wish they were durable. I have yet to find a knee that last more than 2 years!!

Prosthetics - socketSide ViewBack ViewCarbon Fiber SocketDeep recesses over the iliac crest provides positive support, limiting pumping and increasing toe clearance (my idea)Otto Bock 7E7 hip joint (titanium)Triple ski-boots type ratchets and straps providing a TIGHT fit of the socket around the pelvis for improved feel and controlNon stretchable heavy duty straps preventing change in socket geometry with timeNote: I did the strapping system and ratchet buckles. The dimensions of the straps are critical in maintaining the proper shape of the socket. Earlier system used fabric straps that used to stretch over time.

Prosthetic components

The cost of prosthetic components is just astronomical

A typical knee will cost between $10,000 and $30,000

A computerized knee between $30,000 and $40,000

A foot between $2,000 and $5,000

A typical pyramid adapter $400 (Al) or $800 (Ti)

Prosthetic components2014 CHEVROLET MALIBUIncredibly complex machine with thousands of parts. The results of a century of research in advanced materials and complex alloys with cutting edge electronics and unparalleled durability with minimum service. 4-cylinder 2-liter 259HP turbocharged engine, 6 speed automatic transmission, curb weight 3,547lbs$30,000TEH-LIN KneeGRAPHLITE frameENDOLITE hydraulicsA few bits or carbon fiberA handful of ball bearingsA simple hydraulic cylinderCurb weigh 5lbsMAKE SENSE DOESNT IT? Which one would you choose for $30,000?

Hd prosthesisThe first challenge with a hip disarticulation (HD) prosthetic leg is: WHERE TO LOCATE THE HIP JOINT?The Canadian-Type HD prosthesis was developed in 1954. The hip joint is located on the front of the socket. It is connected to the knee joint with an angled tube in such a way that the axis of the knee is posterior to the single equivalent force.Single Equivalent Force(~Projection of CG)

Hd prosthesis

Single Equivalent Force(Projection of CG)

Knee Axis

Hd prosthesis

Knee Joint

Knee AxisSEF

The knee axis is posterior to the SEF line. The resulting moments will force the knee to bend in the direction indicated by the arrows.However, the knee is already fully extended and cannot extend further.THE KNEE IS STABLE123

Hd prosthesisThe SEF line is posterior to the knee axis. The resulting moments will force the knee to bend in the direction indicated by the arrows.1The knee will buckle under load.2THE KNEE IS UNSTABLE3

Knee Joint

Knee AxisSEF

ALIGNMENT is the process of setting up the geometry of the leg

THE BIOMECAHNICS OF an HD prosthesis** From Charles W. Radcliffe

Note that at heel strike the knee is almost unstable. AK amputees use their extensor muscles to increase stability. HD amputees CANT!!

SEF posterior to knee axis. The knee bends.

Bump stop in hip joint helps bending the knee

Prosthetic componentsHip Joint (Ti)Male/female pyramidAdapter to refine hip/kneeGeometry (Ti)Angled pyramid adapter (15) (Ti)Knee rotator (Critical for driving)Sliding adapter (Ti)GRAPHLITE/ENDOLITESingle Axis KneeHeight adjustable adapter (Ti)Sliding adapter (Ti)OSSUR Flex Foot (Carbon Fiber)

Hip Joint (Ti)Male/female pyramidAdapter to refine hip/kneeGeometry (Ti)Angled pyramid adapter (15) (Ti)Knee rotator (Critical for driving)Sliding adapter (Ti)GRAPHLITE/ENDOLITESingle Axis KneeHeight adjustable adapter (Ti)Sliding adapter (Ti)OSSUR Flex Foot (Carbon Fiber)Single axis knees are not recommended for HD prosthesis. True but, A WELL ALIGNED single axis knee works very well in an HD prosthesis

Pylon (al)Angled pyramid adapter (10) (Ti)Knee rotator (Critical for driving)Offset adapter (Ti)THE-LIN 5-BAR KNEECARBON Pylon with Ti adapterCarbon Shock AbsorberOSSUR Reflex VSP FootHD Prosthesis using the TEH-LIN TGK-5PSO Polycentric 5-Bar Pneumatic knee with adjustable centroid

LlHD toe clearanceRLKNEE JOINTFOOTGROUND FLOORTT = R-LToe Clearance T

HD toe clearanceKNEE JOINTFOOTGROUND FLOORTT = R-LToe Clearance T

Toe clearance is always an issue for all above knee (AK) amputees and a very big issue for HD amputees.If the toes hit the floor during the swing phase, the knee may not lock at heel strike and buckle under load, resulting in a fall.AK amputees have good control of their prosthetic knee and the interface socket/stump provides enhanced proprioception. HD amputees do not!To minimize such event, it is customary to shorten the prosthetic leg. However, this results in a non symmetrical gait and pronounced limp.What should we do then?

HD toe clearanceOne way to minimize the toe clearance is to increase L.

The graph shows that by increasing L by 200mm, we gain 8mm of toe clearance. That may not sound a lot but I can clearly feel a change of 1 or 2mm in length.

However, for practical and cosmetic reasons, we want the prosthetic knee to be at the same level as the good knee and for the same reasons we want the prosthetic foot to be the same size as the good foot.l=170mm

L=500-700mmSO, WHAT DO WE DO?

HD toe clearanceTHE POLYCENTRIC KNEE

All polycentric knees commercially available are 4-bar designs. The 5-bar knees are 4-bar knees with adjustable geometry.

In the 4-bar linkage A-B, C-D, the rotation center of the segment B-D relative to A-C is located at the intersection the lines passing through A-B and B-D. This virtual center of rotation is called the centroid (or centrode by the O&P community)

l=170mm

L > 500mmCentroidCentroid Trajectory

The centroid is not fixed but is a function of the angle of the knee. Note that the centroid moves in the vertical direction AND in the posterior/anterior direction. This has important consequences in term of alignment and stability.

The polycentric knee allows to increase the distance L without moving the knee. It is possible to gain up to 10mm in toe clearance with some polycentric knees.

HD toe clearanceTKNEE JOINTFOOTGROUND FLOORT = R-LToe Clearance T

We need to build a foot/shin/knee assembly in such a way that the toes will rise in the final phase of the swing.Between = 0 and = 1 , < 90For > 1 = 90 = 90 under loadOr, we move the foot!

1

=90