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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   Dr. Burns often uses a plantar fascial accommodation. He prefers having an orthotic device fit exactly to the plantar surface of the foot when holding the foot in the position in which he is trying to encourage it to function. He says one accomplishes this fit with minimal alteration of the shape of the arch of the positive model (minimal arch fill). However, Dr. Burns notes that when the device fits so closely, some patients get irritation from the central band of the plantar fascia.

Q: What are the most appropriate indications for using a highly inverted orthotic such as the Blake inverted orthotic? Conversely, what problems have you encountered when prescribing such a device?

   A: Dr. Blake prescribes highly inverted orthotics for a severe pronated position with a resting calcaneal stance position (RCSP) of over 5 degrees everted. He also uses these orthoses for patients with severe pronation that is difficult to control with standard devices. He will likewise use the device for patients with severe alignment issues due to the high tibial varum needing foot inversion.

   When it comes to working with highly inverted devices, Dr. Blake says they may lead to too much supination. Other possible issues are irritation of the arch as the first metatarsal attempts to plantarflex. In addition, the device may lift the foot too high in the shoe, causing heel slippage or shoe irritation (especially in pes cavus).

   Dr. D’Amico prescribes the Blake inverted cast modification for peroneal spastic flatfoot secondary to subtalar arthritis or tarsal coalition, and also for posterior tibial tendon dysfunction/adult- acquired flatfoot. He will also consider the orthosis when treating a difficult to control hypermobile flatfoot with ligamentous laxity, especially in an obese patient.

   The problems Dr. D’Amico has encountered with the device include medial arch discomfort and lateral slippage. In many patients, he says one can avoid slippage with a lateral flange. However, when peroneal spasm is present, the force of pull may be too great to tolerate this modification. In addition, arch discomfort may be due to the foot trying to defeat the severe angular correction built into the device. Dr. D’Amico says this is especially true with adaptive shortening and/or spasm of peroneal tendons. He says supinatory exercises to stretch the peroneals can help prior to dispensing this type of orthotic. Incorporating a medial arch cushion into the device is often helpful, according to Dr. D’Amico.

   In contrast, Dr. Burns is “not a fan” of highly inverted orthoses. “The shape of the orthotic has to be altered too extensively in the arch and I like the shell to fit very closely to the arch of the foot in the position around which I am trying to control,” he explains.

Q: The successful use of a medial Kirby skive has been well documented. When would you choose to prescribe a lateral Kirby skive?

   A: Dr. Blake uses the lateral Kirby skive for supination problems. He notes that one can gauge the device’s success by temporarily placing felt on the present orthotic inside the lateral heel cup. If lateral instability improves, he notes one can send the positive casts back to the lab for a lateral skive. The lateral Kirby skive produces the best change in an already flat heel cup with vertical walls, according to Dr. Blake.

   Dr. Burns seldom uses a lateral Kirby skive. He says the device’s only indication is for lateral instability at heel strike and when the plantar projection of the subtalar joint axis falls under the lateral plantar calcaneal tubercle. If the axis projection is near the lateral aspect of the heel, he finds it more useful to incorporate a lateral flare on the heel of the shoe or consider some leg to foot control with an ankle foot orthosis.

   Similarly, Dr. D’Amico does not use a lateral Kirby skive modification. However, he does acknowledge the device’s potential value in reducing lateral rearfoot forces in a rigid cavus or uncompensated rearfoot varus foot with accompanying lateral instability.

Dr. Blake is a Past President of the American Academy of Podiatric Sports Medicine. He practices in San Francisco.

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