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Technical Note: The Development and Use of a Floating T-Strap on a Double Upright Metal AFO to Correct Coronal–Plane Pathologies and Reduce Skin Shear

Sherk, Kyle A. CPO

JPO Journal of Prosthetics and Orthotics: January 2008 - Volume 20 - Issue 1 - p 24-26
doi: 10.1097/JPO.0b013e31815efdf9
Article
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Ankle-foot orthoses (AFOs) have been used to correct both sagittal and coronal plane ankle motion deviations and improve the mechanics of the ankle during gait. The addition of a T-strap to the AFO was the primary correction to coronal plane deviations of the ankle until thermoplastics became common place in the orthotics and prosthetics industry. There are only a few articles on alternatives to the textbook styles of T-straps available for practitioners to reference when the textbook styles are insufficient to correct the patient's ankle deviation. This article presents a patient who had many indications for a T-strap and complicating factors for its use. A new alternative to the textbook T-strap styles is presented as the solution for this patient along with a general fabrication technique. The patient was able to forego a standard break-in period for skin adaptation and begin wearing the AFO with the floating T-strap full time without complications to their skin.

A new alternative to the textbook T-strap styles is presented as the solution for this patient, along with a general fabrication technique. The floating T-strap offers another option for correcting coronal-plane ankle deformities, especially when used with motion at the AFO ankle joint. This design modification should allow for more force to be applied to the ankle superior to the malleolus, thereby eliminating the need for a practitioner to try multiple designs in order to correct the anatomical deviation.

KYLE SHERK, CPO, is affiliated with Hanger Prosthetics and Orthotics, Oklahoma City, Oklahoma.

Disclosure: The authors declare no conflict of interest.

Correspondence to: Kyle Sherk, CPO, Bachelor of Science: Biomedical and Mechanical Engineering, Hanger Prosthetics and Orthotics, 4301 North Classen Blvd, Oklahoma City, OK 73118; e-mail: kylesherk@hotmail.com

The metal ankle-foot orthosis (AFO) has been used to correct ankle pathologies for years. Coronal plane ankle pathologies require a T-strap for correction in addition to the metal AFO.1 Severe pathologies may require the use of a double T-strap to distribute the force required for correction over a larger area to reduce skin pressure.2 One major issue, however, with a T-strap on a metal AFO is the possibility of the skin rubbing against any portion of the T-strap once sufficient tension is placed on the T-strap to correct the pathology.3 Neuropathic patients are especially at risk for skin breakdown due to their compromised sensitivity, which is an indication for the metal orthosis. Older patients with fragile skin can also be at risk from the increased shear on their skin. Motion at the ankle joint only increases the chances of a shear-related skin reaction along the T-strap's edges.

Historically, the metal AFO has been the orthosis of choice for correcting any ankle pathology. The use of thermoforming plastics in orthotic practice has reduced the use the metal AFO to returning patients who wish to continue to use the same style of orthosis, those with severe neuropathy, patients that are intolerant of the increased heat retention from the plastic against the skin or that present with fluctuating edema.1 Patients that choose to remain in the same style of orthosis will, most likely, have all ready had adaptive skin changes to the increased pressure and shear4,5 along the proximal edge of the strap from previous T-strap use. Though this may reduce the chances of a new T-strap causing an adverse skin reaction, it does not eliminate the possibility due to the new, stiff leather or minor changes in placement of the T-strap. Previously untreated neuropathic patients are duly at risk of an adverse skin reaction from the leather putting pressure directly over the thin malleolus-area skin that has not undergone adaptation4,6 and their compromised topical sensation. Patients intolerant to the increased heat of a plastic AFO would be the least at risk of the predominant patient divisions for skin breakdown from a T-strap, though their presentation may also include neuropathy, edema, or fragile skin. Fluctuating edema can increase the amount of skin exposed to the T-strap: not in a pressure-reducing fashion but in a manner that can increase the number of areas susceptible to shear. Fluctuating edema can also alter the area of skin that is exposed to the pressure exerted by the T-strap from one day to another or throughout a given day, prolonging the adaptation period for the exposed skin areas.

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CASE STUDY

Several of the above issues with fitting a T-strap came together in one patient: a 58-year-old woman who had been wearing a double-upright metal AFO to correct left drop foot secondary to degenerative neuropathy. The patient gave verbal consent for this case study to be written and submitted, provided no identifying information was conveyed. The patient lacked nearly all topical sensation below her knee on the left side and had lost all muscle function save plantar-flexion, which was normal (5/5). The patient also presented with mild ankle valgus, which had caused her medial malleolus to contact the medial upright of her current AFO. A new metal AFO with dorsiflexion-assist ankle joints was fabricated with a medial T-strap to correct the ankle valgus. The AFO was delivered with break-in period instructions, and the patient was informed to continue to watch her skin closely for redness or blistering. A week later, a 7 mm diameter blister had developed on the medial aspect of the patient's Achilles' tendon at the proximal edge of the T-strap and the patient returned for adjustments to the AFO. Off-loading padding was added to the T-strap. This mildly reduced the friction on the patient's skin but the blister continued to grow over the next week. At the next follow-up appointment, the blister was about 9 mm in diameter. As the patient did not want to discontinue the use of the AFO while the blister healed, several strategies were discussed to relieve the rubbing of the T-strap on the Achilles' tendon area including the use of moleskin, multiple sock layers, and reducing the tension on the T-strap until the skin could thicken to accommodate the shear stress upon it. The patient was followed up 1 month later with the blister healed to a 2 mm diameter scab, but the patient was not wearing the T-strap sufficiently tight to correct her ankle valgus. The double T-strap was considered but dismissed, as it increased the distance from the anatomic ankle joint to one of the straps which could lead to more motion between the skin and proximal strap along with adding more areas for the skin to experience shear against the T-strap during the breaking period. A different T-strap design was fabricated that lowered the posterior strap to the level of the proximal shoe counter while maintaining the body of the strap at the level of the malleolus. This design did remove the possibility of the posterior rubbing but also reduced the efficiency of the T-strap to correct the patient's ankle valgus. Lacking any other designs to attempt for the patient, a “floating ” T-strap was fabricated (Figure 1). The following design criteria were used in fabricating the T-strap: it moves with the patient's shank above the malleolus, is tied to the shoe to limit proximal migration, is padded to prevent breakdown over bony prominences (tibia or fibula) and is easy to don and doff. The patient was able to comfortably don the orthosis and sufficiently tighten the T-strap to correct her ankle valgus without developing any skin breakdown along any of the floating T-strap's edges. At a 1-year follow-up, the patient was still satisfied with the floating T-strap's correction and ease of use, except when it occasionally fell into the shoe during donning. The patient stated that she had not worn the new AFO (with the floating T-strap) for several months after it was delivered to allow her skin to fully heal. She was able to begin wearing the new AFO full time without a break-in period and without any adverse skin reactions to her recollection. The patient had not developed any palpable skin thickening along the edges of the floating T-strap at the date of the follow-up.

Figure 1.

Figure 1.

Observations from this case study show that the floating T-strap is as efficient at correcting coronal plane deformities as the conventional T-strap. Reduced skin shear is assumed based on the lack of skin adaptations surrounding the floating T-strap. This observation is hard to quantify without a gait lab to ascertain and compare the exact amounts of motion between conventional, double and floating T-straps during ambulation with a metal AFO. It is thought that the movement allowed by the floating T-strap would decrease the break-in period needed for new T-strap users when compared with a conventional T-strap, though further testing is needed. Furthermore, the amount of corrective force applied should be comparable to that of the double T-strap and greater than the conventional T-strap based on the change in placement from the malleolus1 to the distal shank. The manner of fabrication of the floating T-strap also allows for it to be more easily added to an existing AFO when compared with adding a conventional T-strap. The height of the floating T-strap can easily be checked and adjusted when the patient has the finished AFO donned then attached before final delivery.

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FABRICATION

The floating T-strap in this case study was fabricated from 4-oz leather for backing, ¼-inch Aliplast foam (approximate durameter: 15–20) for padding, 2-oz stretch leather for covering, and two ribbons of 4 inches of ¾-inch cotton strapping for attachment. The 4-oz leather was trimmed around most of the stamp-plate used to cutout a conventional T-strap and then the distal edge was cut to cup anteriorly, superiorly, and posteriorly around the malleolus (Figure 2). The ¾-inch cotton strapping was sewn to the 4-oz leather on either side of the malleolus cutout. Aliplast was glued to the 4-oz leather on the area thought to contact the bone and surrounding tissues, then skived along the all but the proximal edge. The 2-oz leather was stretched along the long axis of the T-strap and glued in place, and then sewn in place with a lip rolled onto to the outside of the T-strap along the proximal and distal edges to round the edges that the bone is exposed to (Figure 3). The floating T-strap can be sewn to the shoe before or after the AFO stirrup is attached as the cotton strapping falls on either side of the stirrup (Figure 4). Folding the cotton strapping back under itself at the shoe attachment point will prevent wear-related unraveling; this was not done for Figure 4 and unraveling became evident immediately. Elastic strapping was not was used, as its lifetime is difficult to estimate and the available supply was not very supple. Dacron® was also considered for the attachment straps but changed to cotton in the final fabrication as the cotton offered less resistance to motion for the floating T-strap. Dacron could easily be used to reinforce the buckle holes when a buckle closure is used to prevent leather stretch over time.

Figure 2.

Figure 2.

Figure 3.

Figure 3.

Figure 4.

Figure 4.

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CONCLUSIONS

The floating T-strap offers another option for correcting coronal-plane ankle deformities, especially when used with motion at the AFO ankle joint. This design modification should allow for more force to be applied to the ankle superior to the malleolus, therefore eliminating the need for a practitioner to try multiple designs to correct the anatomical deviation. The inclusion of padding should provide a more uniform pressure distribution over bony prominences earlier in the life of the floating T-strap compared with a leather-only T-strap without the added overall stiffness.

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REFERENCES

1. New York University School of Medicine and Post-Graduate Medical School. Ankle, knee and hip orthoses. In: Lower-Limb Orthotics. New York: Prosthetic-Orthotic Publications; 1986:131–166.
2. Samberg HH. The two-buckle T-strap: a modification of the conventional T-strap. Arch Phys Med Rehabil 1969;50:290–291.
3. Shoe T-strap for ankle and foot control. BMJ 1969;4:47.
4. Goldstein B, Sanders J. Skin response to repetitive mechanical stress: a new experimental model in pig. Arch Phys Med Rehabil 1998;79:265–272.
5. Sanders JE, Goldstein BS, Leotta DF. Skin response to mechanical stress: adaptation rather than breakdown—a review of the literature. J Rehabil Res Dev 1995;32:214–226.
6. Nola GT, Vistnes LM. Differential response of skin and muscle in the experimental production of pressure sores. Plastic and reconstructive surgery 1980;66:728–733.
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ADDITIONAL REFERENCES

7. Bhalaik V, Chhabra S, Walsh HP. Bilateral coexistent calcaneonavicular and talocalcaneal tarsal coalition: a case report. J Foot Ankle Surg 2002;41:129–134.
8. Hurvitz EA, Ellenberg MR, Lupo R, et al. Orthotic technique for dystonia musculorum deformans. Arch Phys Med Rehabil 1988;69:892–894.
9. Williams A. A study of factors contributing to skin breakdown. Nurs Res 1972;21:238–243.
Keywords:

T-strap; AFO; orthosis; fabrication

© 2008 American Academy of Orthotists & Prosthetists