Inside Insights On Orthotic Modifications

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Addressing Range Of Motion Issues At The First MPJ: How The Kinetic Wedge Can Help

   Justin Wernick, DPM, says one of the most common podiatric dilemmas is identifying when to expedite the range of motion at the first metatarsophalangeal joint (MPJ) or when to block range of motion. In the clinical assessment, he says it is important to determine the off-weightbearing range of motion of the hallux. The demand in gait for dorsiflexion of the hallux is 55 to 85 degrees. Dr. Wernick says this is determined by the amount of knee flexion, usually 35 degrees and plantarflexion, which is approximately 25 degrees.

   Knowing the length of an individual’s step is very important in this assessment. The longer the step length, the more demand there is for dorsiflexion at the metatarsophalangeal joint, according to Dr. Wernick. He notes that if an individual walks with a rapid cadence or is involved with sports, there will be a greater demand for dorsiflexion. If the range of motion is at least 20 degrees or greater, Dr. Wernick will attempt to expedite motion by:

   • supinating the subtalar joint;
   • maintaining the medial architecture of the foot; and
   • using a Kinetic Wedge™ forefoot modification.

   Dr. Wernick notes the wedge is designed to promote the plantarflexion-eversion motion of the first ray via the wedge’s shape (wider medially) and its density (softer under the head).

   The wedge’s proximal angle is designed to act as does the first ray axis, says Dr. Wernick, and the distal angle compliments the axis of the hallux. By controlling the rearfoot, he can restore the contour of the arch and increase the plantarflexion angle of the first ray. Combining these efforts with the Kinetic Wedge will increase motion at the first MPJ, notes Dr. Wernick.

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   With almost every orthotic device, Dr. Burns will use rearfoot posting to try to stabilize the device at heel contact and to put the device in a position that allows some rock in the direction of eversion. He says this allows the normal pronation that must occur early in stance in response to the internal leg rotation. The effect of rearfoot posting is limited to this initial loading phase of gait and he notes it quickly loses any effect as the forefoot loads.

   Another common modification for Dr. Wernick is a medial arch platform. He commonly hears the complaint that the medial flange of the device irritates the arch of the foot, which is due to many factors but is usually a result of a tight calf. To help reduce the problem, he advises placing a medial arch platform on the positive cast. As Dr. Wernick says, this modification will turn the medial edge of the orthotic away from the foot, making the orthotic more comfortable to wear. In addition, he notes the medial arch platform has no effect on the height or contour of the arch so the device maintains full control of the foot.

   A reduced or omitted rearfoot undercut is another part of Dr. D’Amico’s armamentarium. As he says, most labs normally undercut the rearfoot by approximately 10 degrees to allow better shoe fit. However, he cautions that this also causes premature lateral post wear, resulting in lateral tipping of the device.

   Since many people today wear footwear with counters as wide as athletic type footwear, Dr. D’Amico says there is no need for a standard undercut. However, he notes those who wear a standard type dress or work shoe may still need an undercut. For sports footwear, Dr. D’Amico does not include the rearfoot undercut. He says this enables better rearfoot stability and alignment.

   Dr. Burns commonly uses a ¼-inch heel lift to compensate for equinus. He will also use the modification to take advantage of the “whole foot supination” that occurs with ankle joint plantarflexion. He reminds DPMs that ankle joint motion is triplanar and a significant amount of inversion and adduction often occurs with plantarflexion around the ankle joint axis.

Other Pertinent Modifications

   To help prevent the lateral stability that is sometimes associated with orthoses, Dr. Blake will use either a Denton modification or isolated lateral column reinforcement.

   Dr. D’Amico commonly uses a Morton’s extension to the interphalangeal joint of the hallux. He will add this extension to a forefoot varus post that has been extended to the sulcus or extend the distal arm of a Kinetic Wedge in the same manner. Dr. D’Amico says this modification extends the functional length of the first ray in Morton’s syndrome and plantarflexes a functionally hyperextended hallux segment, which improves weightbearing.

   Topcovers can be among Dr. Burns’ modifications. “I do not like topcovers used as ‘decoration’ but I like to use materials that add some usefulness to an orthotic device,” he says.

   To that end, he will use materials like closed cell neoprene (such as Spenco) to absorb shear forces to prevent blisters in athletes or skin shear in the insensate foot. His other common topcover materials include Plastazote (Zotefoams) or TufFoam to add some “dynamic molding,” particularly under the forefoot.

   A calcaneal inclination angle modification can be helpful for flexible adult onset flatfoot, opines Dr. Wernick. When the midtarsal joint collapses, he notes a lowering of the inclination angle of the calcaneus accompanies the collapse. To resist this lowering, he uses this modification to control sagittal plane motion at the midtarsal joint by supporting and resisting the distal portion of the calcaneus from dropping. He accomplishes this by removing 1/4 to 1/2 inch of material from the area under the distal calcaneus and the cuboid on the positive plaster cast, and then forming the shell to this contour.

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