Management of the Partial Foot Amputee

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Management of the Partial Foot Amputee

• Gait Workshop at
• Biomechanics Laboratory,
• U of Sydney
• July 2005

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• 3.2.2 SURGICAL GOALS
• 'To remove the pathologic condition which
  interferes with function, causes disability or
  threatens life so that rehabilitation can be
  instituted' (Mueller and Sinacore, 1994).

Figure 1 - Lines of standard forefoot/midfoot
amputations (From Vitali, et al., 1978, pp. 128).
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• Biomechanical Complications
• www.gentili.net.amputations
• An equinus deformity often results from forefoot
  amputations, especially the Lisfranc
  (metatarsocuneiform joint) and the Chopart
  (talonavicular and calcaneocubiod joints)
  amputation (Chang, et al., 1995).
• In a TMA the tendons of extensor hallucis longus,
  extensor digitorum longus and peroneus tertius
  muscles are sectioned. These muscles act to
  dorsiflex the foot at the ankle, if they are
  sectioned, an imbalance between the anterior and
  posterior muscle groups exists. This leads to the
  Achilles tendon working unopposed, thus creating
  an equinus deformity (Barry, et al., 1993). To
  overcome this, an Achilles tendon lengthening
  procedure is performed.
• This loss of dorsiflexion range of motion can
  lead to excessive loading at the distal edge of
  the residuum during gait and lead to skin
  breakdown (Chang, et al., 1994).

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3.2.5 SURGICAL TECHNIQUE The following surgical
technique is summarised from Gregory, Peters and
Harkless, 1992. Figure 5 illustrates a
transmetatarsal amputation procedure.
Figure 5 - Transmetatarsal amputation procedure
(From Sanders, 1986, pp. 102).
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Partial Foot Gait

• Dr Michael Dillon
• Clinical observation suggests
• Residuum rotates within shoe/prosthesis
• Prostheses do not have a socket
• Prostheses do not have a stiff toe lever
• Triceps surae atrophy
• Reduced plantarflexion
• Amputees cant stand on their toes

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Literature suggests

• Prostheses restore the lost foot length or
  lever-arm (Condie 1970, Rubin 1984, Pullen 1987,
  Stills 1987, Weber 1991, Mueller and Sinacore
  1994, Saunders 1997, Sobel 2000)
• Function is improved by maintaining residual foot
  length and ankle motion (Wagner 1985, Mueller et
  al1986, Barry etal 1993, Helm 1994, Pinzur at al
  1997, Sobel 2000)
• MYTHS??

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Method

• Amputee subjects (n8),
• 5 unilat (TMT, Lisfranc, Chopart)
• 3 bilat (MTP, Lisfranc, Chopart)
• Aetiology trauma or gangrene
• Normal subjects (n8), age, ht, wt, sex matched
• Apparatus Peak Motus 3D motion analysis system,
  AMTI force platform

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Partial Foot Gait

• For all conditions the motion is biased towards
  DF. The forefoot should contribute 10 degrees of
  plantarflexion relative to rearfoot. There is
  none in barefoot PFA in preparation for toe-off
  and closer to normal with boot and CTO.
• Knee is held at gt10 degrees F throughout the gait
  cycle. Knee F is delayed, amplitude diminished
  in barefoot.
• Over stance phase the hip moved from a flexed
  position to extended position, and returns to
  flexion during swing phase. Amplitude is
  diminished in barefoot.

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Moment

• Is the rotational version of force. It is the
  turning effect around the centre of rotation. It
  is generated by muscles or an external force
  acting on the segment. Magnitude of a moment
  depends on size of the force and the distance
  from the centre of rotation. (Newton.metres)

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Partial Foot Gait

• Ankle moment in barefoot is toward plantarflexion
  throughout stance. VGRF vector remained
  posterior to the ankle joint centre.
• Traditional and CTO bring ankle jt moment in
  sagittal plane closer to normal, but only at 30
  stance.
• Knee has F moment to 20 stance, E moment to 50
  stance, F moment again to 80, then E to toe off.
  Boot is more normal, CTO is further towards
  normal.
• Hip has extensor moment in first half of stance
  and flexor in the second half. Moments increase
  from barefoot to Traditional to CTO. F moment in
  barefoot is delayed to after toe-off, but before
  toe-off for traditional and CTO.

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Power

• Is the rate at which work is done. The moment
  multiplied by the angular velocity of the joint.
  The area under the power curve is the work done
  for that period.

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Joint Power

• Is an indication of how hard the muscles around
  that joint are working.
• Is the rate at which energy is expended or
  absorbed
• Area under the graph
• Negative power means muscles are absorbing
  energy.
• Positive power means energy is generated by the
  muscles around the joint.

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Partial Foot Gait

• In barefoot, ankle jt power is () generating
  from 20 90 of stance. The traditional has
  periods of absorption and generation. CTO has
  large absorbing periods early in stance and
  generation prior to toe-off.
• Knee jt powers are near normal.
• Hip jt power have increasing amounts in
  traditional and CTO.

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Results

• Once the MT heads had been amputated, the GRF did
  not continue to progress distally along the
  length of the residuum but remained well behind
  the distal end throughout most of stance phase
• In the TMT and Lisfranc Amputees fitted with toe
  fillers, foot orthoses or slipper sockets, the
  distal end of the residuum was located at 58-65
  of shoe length.
• The largest VGRF occurred at 45 of the gait
  cycle and did not progress past the distal end of
  the residuum until after contralateral heel
  contact in double limb support.

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• Significant reduction in peak power generation
  across the ankle were observed on the affected
  limbs of all amputees except the bilat MTP amp.
• Bilat MTP amp small reductions in power
  generation, COP excursion, but not joint angular
  velocity or ankle ROM.
• TMT amp power generation 0.72W/kg
• Lisfranc amp power generation 0.91W/kg
• Chopart amp 0.78W/kg (unilat), 0.32W/kg (bilat)
  due to elimination of joint range rather than
  COP.
• Normal 2.56 to 5.06W/kg
• Reduced due to diminished ankle moment coupled
  with reduced joint angular velocity.

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Results

• Reductions in work across the affected ankles
  were compensated for by increased power
  generation at the hip joint (ipsilateral or
  contralateral). The kinetic patterns observed
  were variable.

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Results

• In the Chopart amputees fitted with clamshell
  devices demonstrated the COP was able to progress
  well beyond the distal end of the residual limb
  shoe length commensurate with the 2nd peak VGRF.

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Discussion

• The COP remained proximal to the distal end of
  the residuum until contralateral heel contact
• It is difficult to determine why these amputees
  adopted this gait pattern
• Spare the distal residuum from extreme forces
• Reduce the requirement of the triceps surae
• Toe fillers, foot orthoses, AFOs and slipper
  sockets seemed unable to restore the effective
  foot length
• The clamshell PTB prosthesis incorporated a
  substantial socket
• Toe levers were made from carbon fibre plates or
  prosthetic feet

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Discussion

• One of the primary functions of the ankle is to
  generate power necessary to walk.
• Once the metatarsal heads were affected, power
  generation was negligible irrespective of
  residual foot length
• Lisfranc and TMT amputees, performed as much work
  across the ankle as did the Chopart amputees who
  had no ankle motion.
• The primary reason for partial foot amputation is
  to capitalize on the ankles contribution to
  walking.
• There is little benefit to be gained by striving
  to maintain residual foot length and ankle motion.

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Discussion

• Once amputation has compromised the metatarsal
  heads, maintaining foot length should no longer
  be the primary surgical objective.
• Aim for residuum that has good distal skin
  coverage and primary intention healing.
• Given that the ankle did not contribute greatly
  to the work required to walk and the likelihood
  of complications with fitting most amputees,
  abandon below ankle designs and go for a
  clamshell design where risks are minimized.

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Conclusion

• Gait analysis on normals provided foundation
  for our understanding of PFA
• Gait analysis was used to provide more accurate
  description of gait and prosthetic fitting.
• Insights from gait analysis challenged
  misconceptions and forced reflection on clinical
  practice
• Improved understanding of what didnt work has
  led clinicians to pursue advancements in design.