Sagittal plane blocks

Sagittal plane blocks

A number of factors block motion in the sagittal plane at one of 3 pivot sites or rockers that are assumed to cause abnormal function.

Plantar calcaneus

Plantar aspect of calcaneus is rounded to allow the foot to “roll over” it at heel contact. Abnormalities will occur if there is some sort of, for example, traumatic alteration to the shape of the calcaneus. This tends to impede forward momentum during initial foot contact.

Ankle Joint

Restriction of motion at the ankle joint impedes forward progression (see equinus, above)

Metatarsophalangeal joint

65 degrees of dorsiflexion is the assumed minimum considered to be needed at the first MPJ:
• A structural hallux limitus (SHL) is considered present when the non-weightbearing range of motion of the first MPJ is less than this 65 degrees
• A functional hallux limitus (FHL) is considered present when the non-weightbearing range of motion of the first MPJ is greater than this 65 degrees, but during gait, the range of motion is not available. This can be a momentary/temporary block

If SHL or FHL is present the foot’s autosupport mechanisms will not get established nor will there be a transfer from the oblique to the transverse metatarsal head axis. This permanent (SHL) or temporary (FHL) block occur when the power input from above is at its greatest for forward progression, so this power has to be stored or dissipated. This dissipation will be reflected as secondary motions at other sites.

The possible assumed compensations for SHL and FHL are generally considered to be (Dananberg, 1987):
1) Altered heel lift:
• the next most proximal joint to the first MPJ that allows motion in the sagittal plane is the midtarsal joint  midtarsal joint pronates or “collapses” late in stance
• heel lift is delayed because of this
• visualised as late midstance pronation
• referred to as SARP – Secondary Active Retrograde Pronation

2) Vertical toe off:
• this is a continuation of the delayed heel lift – heel lift is maximally delayed
• the foot is just lifted of the ground
• the gait is slow, apropulsive and laborious
• the heel does not leave the ground by the time of contralateral heel contact  this is a very inefficient way to move forward

3) Increased lateral weightbearing:
• the ‘weight flow’ that is initially directed to the lateral column fails to shift medially as weight is not transferred from the oblique to the transverse metatarsal head axis
• occurs when the foot’s autosupport do not get established
• detectable by in-shoe pressure measuring systems
• also tends to cause excessive lateral forefoot shoe wear, despite excessive foot pronation
• this explains the paradox of a flexible forefoot valgus with lateral forefoot shoe wear and lateral plantar forefoot callus

4) Abducted and adducted toe off:
• if FHL or SHL are present, the body will follow the path of least resistance to get around it
• if the hip is in an externally rotated position  get around a FHL or SHL by directing weight flow medial to it  an abducted toe off
• the same will happen if the hip is internally rotated

5) Flexion compensation of the body:
• flexion compensation occurs at the middle of single limb support
• the knee failure to fully extend (more flexed)
• the hip is in a more flexed position
• the lumbar spine will be straighter (lumbar flexion)

Orthoses management of sagittal plane block at first metatarsophalangeal joint:
Aimed at enhancing motion in the sagittal plane  facilitates the foot’s autosupport. Does this by facilitating first ray plantarflexion by one or some of the following techniques:
1) additional plaster in the medial arch of the positive model used to fabricate foot orthoses  orthoses will drop away from first ray  allows plantarflexion
2) cut out the orthoses shell under the first ray to allow more plantarflexion
3) the use of posting/padding under the lateral metatarsal heads – sometimes could also use padding plantar to the proximal phalanx of the hallux
4) a rearfoot post that inverts the calcaneus will also allow the first ray to plantarflex
5) Kinetic Wedge™ is a forefoot extension on the foot orthoses that is softer under the first metatarsal head  promote first ray plantarflexion and hallux dorsiflexion

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