TF Knee Disarticulation Lecture

History of KD Amputations

• advocated in preanesthetic era

  • efficiency of procedure

  • limited associated bleeding

  • technique does not violate the medullary canal

• fell out of favor in early 1900s

  • poor distal soft tissue coverage

  • limited prosthetic options

  • poor functional outcomes

• resurgence in the last 25 years

  • prosthetic advances (4 bar polycentric knee unit)

    • biggest advance in past 25 years

  • modifications in surgical techniques (use of gastrocnemius as terminal padding)

Patient Inclusion Criteria

• traumatic injuries or those with oncologic conditions

  • transtibial salvage amputation is not feasible

• diabetes of vascular dysfunction

  • low functional demands and is limited ambulatory potential

  • direct load transfer - enhanced feedback and proprioception

    • this is due to WB on the femoral condyles

Pros/Cons of this length of amputation

Retention of the full femoral length represents both the principle advantage and disadvantage of KD amputation.

PROS

• stable/potentially end bearing terminal residual limb

• long lever arm

• intact native insertion for the adductor magnus

• avoids commonly found contractures

CONS

• distal residual limb can be bulky

  • due to natural anatomy of the femur

• some degree of knee level discrepancy

Surgical Techniques

In the image there is not patella.

There is a procedure that you shave the sides of the distal femoral shaft in order to reduce the bulbous shape at the end of the femur.

Posterior Myocutaneous Flap

Results in

• faster healing time

• better WB with the gastrocnemius flap

It is standard practice to leave the patella in tact.

What is the discrepancy here?

• the Knee Centers are not level and do not tend to be level in this kind of amputation.

Prosthetic Management

• estimated 2% or less of the overall amputee population in the United States

• less bony and muscular disruptions

  • more balanced muscular control at the hip

  • limb that is capable of load bearing at distal end

• length of limb precludes ability to match knee centers (functional and aesthetic considerations)

Clinical Considerations - Outcomes

• improving prosthetic control (long lever arm)

• comfortable distal loading through articular surface of condyles

• bulbous shape of distal femur (anatomic suspension)

Socket Design

• prosthetic socket brim located well below the level of the IT

  • less pressure on the groin

  • sitting comfort

  • freedom of hip ROM

• tissue management is still important

• account for bony anatomy (patella)

Suspension - Anatomical

• self-suspending prosthesis: takes advantage of narrowed bony dimensions just proximal to the femoral condyles

  • foam inner socket (double wall socket)

  • window/door in frame (flexible inner socket)

Anatomic Suspension

• requires very intimate fit - can lead to localized atrophy

  • continued narrowing of ML dimension

  • allows some degree of pistoning

• progressively lose favor in recent years - particularly among adults

Suspension - Suction

Suction - liner based suction suspension techniques

• improves the prosthetic connection and cyclical impact trauma (due to less pistoning)

• gel liners in combination with an air expulsion valve or low profile lanyard

• gel liners can be custom made depending on anatomy

Polycentric Knees

• adds minimal length to the thigh

• allows the shin of prosthesis to fold beneath the distal socket (swing phase and sitting)

• although they provide more stability, this is not usually of need of patients with KD amputations

Component Selection

• Polycentric vs Single Axis Knees

  • this is a clinical decision that must be made by the prosthetist and patient -

    • asses knee center discrepancy, activity level of the patient, all other “physical and history” items you would evaluate for a patient with AKA

Alignment Considerations

• similar to alignment of transfemoral prostheses but with a few considerations

  • load is generally applied through distal femoral condyles when standing or ambulating

  • coronal plane in SLS - forces are concentrated on medial aspect of patient’s upper thigh and distal lateral femoral condyle

Alignment considerations

• proximal medial brim should have gentle flares or flexible material to gently and evenly distribute pressure

Bilateral KD Causes

• most are the result of medical complications from diabetes and PVD

  • as disease progresses, patients may have undergone several previous surgeries (partial foot, BKA, AKA)

  • use of unilateral prosthesis can be a good predictor of success as a bilateral amputee

• trauma is another large contributor to this patient population (war-related injuries, MVA, etc.)

• infections such as strep infections and diseases such as meningococcal septicemia or necrotizing fasciitis (may have UE amputations as well )