Link to Figures Show Figures
	Article Text Figures References
	Send Link Send HTML Article

New Concepts in Orthotic Management of the Adult Hyperpronated Foot: Preliminary Findings

Gerald D. Bowman, CO, MBAPO

ABSTRACT

The untreated pronated foot runs the risk of developing into a painful hyperpronated foot. Conventional foot orthoses often are prescribed to correct the misalignments but usually fail due to intolerable interface pressures.

The rationale behind a new type of orthosis is given, and its success is measured by means of subjective pain relief. Preliminary data are presented on six patients exhibiting symptoms of pain who were fitted with the orthosis and asked to compare results with those of previous treatments. Pain relief reported from use of the orthosis ranged from 60 percent to 100 percent, with a mean of 82.5 percent.

Introduction

The adult hyperpronated foot (HPF) (see Figure 1) presents a complex and challenging orthotic problem. It often is asymptomatic with patients complaining primarily of secondary internal rotatory-related problems, such as knee and back pain or the visible deformity of completely flattened arches.

Hyperpronation is caused by various factors and can affect patients gradually or rapidly, as seen with a posterior tibial tendon rupture (1-4). The fundamental basis for the development of a HPF is a pronation imbalance (5).

The actual development usually follows a specific chain of events. Whereas the foot has mechanisms to physically block excessive supination to make it a rigid lever in late stance, pronation is designed to be flexible so the foot can absorb shock and adapt to uneven terrain. It is therefore controlled by soft tissue structures. When subjected to continuous repetitive stress resulting from pronation imbalance, these structures will begin to exhibit signs of strain. If allowed to continue, eventually the individual joints of the feet will be stressed. If not treated at this stage, the joints will begin to separate and eventually sublux. Once this process is complete, the foot can be classified as hyperpronated. In addition to the pronation-related pain, the foot may now be subjected to bony changes and resulting arthritic pain (5).

The pronated foot exhibits the following structural components:

• reduction in height of arches;
• calcaneal eversion and plantarflexion;
• talus moves anterior, inferior and medial and internally rotates;
• midtarsal joint axes align; and
• forefoot abducts, dorsiflexes and spreads.

Conversely, the HPF consists of all of the above components but to an exaggerated degree. The HPF presents with the arches of the feet completely flattened and the joints displaced to the point where they can be considered subluxed.

Several factors have been cited as essential for neutral positioning: a strong tibialis posterior, a firm plantar aponeurosis, an adequate deltoid ligament, an adequate, properly placed spring ligament and a neutrally placed nonconstricted tendoachilles (6). In addition to these factors, there arguably also are neutral forefoot and rearfoot alignment. Treatment of the pronated foot often is achieved through maintaining integrity of the supporting tissues, ensuring full ranges of movement (particularly at the tibiotalor joint), and the use of plantar foot orthoses to maintain neutral alignment.

However, the goal of treatment with the HPF is quite different. Simple plantar foot orthoses that correct any functional misalignment fail due to insufficient integrity in the joints and soft tissue structures to maintain the alignment. Hence the foot will continue to hyperpronate. The primary function of plantar foot orthoses is partial relief of midfoot/arch pain, which is likely to be only short-term. The goal of orthotic treatment should be to sufficiently realign the foot to place the joints back within their normal range. In so doing, the orthosis will improve the foot's function, reduce the pain resulting from rotatory forces joint and soft tissue strain, and prevent further deterioration to the joints (see Figure 2) .

Treatment is further complicated by the presence of a plantarflexion contracture, which restricts natural ankle dorsiflexion during stance phase of the gait cycle. As specified by Perry (7), any limitation that restricts dorsiflexion to less than 5 degrees by the 30-percent point of the gait cycle represents an abnormal restraint that will evoke compensatory changes. A stable foot will compensate through early heel lift, knee hyperextension or forward trunk lean (7). The pronated foot also compensates for the loss of ankle dorsiflexion range through increased pronation, which allows dorsiflexion at the foot to occur through two mechanisms. First, subtalor joint pronation being triplaner has a component of dorsiflexion and, second, subtalor pronation places the axes of the midtarsal joint in alignment (8), making the foot flexible and allowing midtarsal pronation (of which the primary movement is dorsiflexion). In the HPF, this motion of midtarsal joint pronation/dorsiflexion is excessive and appears to become the major compensatory mechanism to allow smooth forward progression.

If this compensatory movement is blocked, as with a rigid University of California--Berkeley Laboratory (UCBL)-type orthosis, two things are likely to occur. First, the foot still will try to pronate to compensate for the plantarflexion contracture, thereby increasing the pressures applied by the orthosis to the medial and lateral borders. Second, the leg will be forced to adopt a second compensatory mechanism of early heel lift, knee hyperextension or forward trunk leaning, resulting in a shortened stride length and reduced velocity (7), thereby impairing function. Therefore, as with the normal foot, a certain amount of pronation becomes essential for good function.

To achieve these goals of treatment requires the application of three-point force systems that accurately relate to the axes of the major joints of the foot. For many years, the UCBL foot orthosis has been the standard orthotic intervention for the HPF (9). However, this orthosis relies on stabilization of the foot through pressure into the medial longitudinal arch using the windlass casting technique, which, although an excellent orthosis for many situations, fails to apply the necessary three-point force systems to adequately control hyperpronation. As a result, acceptance of the UCBL may be difficult due to excessive, intolerable interface pressures (particularly in the areas of the navicular and the fifth metatarsal).

This orthosis often is modified with "sustentaculum tali" or "heel grasp" corrections to the cast (10) and/or made with more rigid materials, which greatly improves the application of forces. Although usually successful in the pediatric population, this orthosis often fails in the adult HPF where the forces generated are considerably greater due to intolerable pressures created as the foot attempts to pronate at midstance and is rigidly blocked. In addition, the orthosis may be even bulkier and more difficult to accommodate in the patient's shoes. For these reasons, the orthosis often is discarded in favor of soft arch supports that, as previously mentioned, provide only partial and temporary relief of the symptoms.

Subjects and Method

Due to the previously mentioned difficulties with fitting the hyperpronated population with UCBL orthoses, a new design was created to meet the following objectives: 1) realign the foot sufficiently to reduce the strain on the medial and plantar structures, 2) be pressure tolerable and 3) be able to fit the patient's present shoes.

The design of the new orthoses incorporated three main features. First, the position and extent of the modifications were such as to accurately apply three-point force systems to provide all of the controls necessary (see Figure 3) . Second, the orthosis was designed to have an inherent degree of flexibility in all three planes. This flexibility permits easier acceptance of the pressures (11) as the orthosis flexes or "gives" each time excessive pronation imbalance forces are generated during the gait cycle. Great care needs to be taken with the application of this principle since too much flexibility in the orthosis could detract from the rigidity required to maintain the three-point force systems that control the pronation. Third, asymmetrical trimlines were used, allowing the orthosis to be cut away in areas where no force was needed, thus reducing the size of the orthosis to accommodate patients' footwear.

To differentiate the orthosis from other designs, the name pronation control foot orthosis (PCFO) was adopted.

Two features are vital to the production of the PCFO, namely the cast modifications and the trimlines. For the impressions, standard plaster wrap casting techniques were used, taken in a semi-weightbearing position with the patient seated on a chair and the foot in contact with the ground. Hand pressure was applied to the foot if necessary to maintain the foot in a neutral alignment.

Cast Modifications

Modifications for the PCFO are similar to those described by Colson and Bergland (10), including removal of plaster in the posterior aspect of the longitudinal arch and the medial aspect of the heel inferior to the sustentaculum tali. In addition, further plaster is removed directly beneath the anterior aspect of the talus, the navicular and the cuboid to further stabilize the midtarsal joint in the sagittal plane (see Figure 4) . Plaster additions are made to the metatarsals to ensure no restriction of plantarflexion of the rays and to the base of the heel to stabilize the orthosis.

Trimlines

As specified, trimlines are designed primarily to allow graded flexibility in the orthosis but also to reduce the bulk compared to the standard UCBL orthosis. These two principles work together with the use of cutouts. The orthosis was based on the trimlines of the UCBL but with removal of material posteriorly, medially and laterally in the areas where no pressure is needed, to ensure flexibility in all three planes (see Figure 5 and Figure 6 ).

The PCFO is manufactured from polypropylene with a finished thickness of approximately 4 mm (see Figure 7) .

To determine the effectiveness of the PCFO, after a minimum of three months with their orthoses, patients were asked to complete a questionnaire (see Figure 8) . Patients were requested to complete a series of questions indicating location and severity of pain, previous treatments with noted pain relief and pain relief generated with the PCFO. It was concluded maintenance of pain relief over the three-month period of time would be a reasonable indicator that the ultimate goal of realignment was accomplished.

Over a period of 10 months, nine patients, two female and seven male, were fitted with the orthosis. All patients were fitted bilaterally.

To be included within the results, patients had to meet the following criteria: hyperpronation of one or both feet, pain in lower back or lower extremities, dorsiflexion range of tibiotalor joint to a minimum of 90 degrees, use the PCFOs for a minimum of three months, and cooperation with the weaning-in procedure.

Results

Of these nine patients, three were excluded from the results. One patient could not be recontacted, and two patients had no pain (ages 17 and 29).

Of the remaining six patients, ages ranged from 14 to 64 years with a mean of 48.3 years. (Three patients were 59 or older.) All patients could be considered overweight (12). The average weight of the males was 204 lbs, and the average of the two females was 165 lbs.

Responses from the questionnaires showed pain distributions to be varied (see Table A) with only midfoot/arch pain being common among all patients. The effectiveness of previous treatments both initially and then three months following commencement of treatment also was stated, and all patients expressed dissatisfaction with their previous treatments (see Table B) .

Finally, patients were asked to compare the results achieved with their PCFOs. Results for pain relief percentage remained the same three months following initial treatment with the PCFO as they did at initial treatment. The range was 60 percent to 100 percent, with a mean of 82.5 percent (see Table C) .

Discussion

Through the application of accurate force systems coupled with flexible control, the PCFO was shown to effectively reduce pain. All patients continued to wear their orthoses, which indicates the orthoses were tolerable and easy to accommodate in footwear.

Some patients stated their functional abilities were improved with the orthoses. Comments made included "I was able to walk farther," and "I walked better," further indicating that, along with the maintenance of pain relief, the ultimate goal of realignment of the joints was being achieved.

On examination of patients' standing posture in the orthoses, the author contends complete correction of the foot to a neutral alignment was not achieved. However, sufficient correction was achieved to place the foot within its "normal" pronation range, thereby considerably reducing the strain on the joints and the soft tissues.

Conclusion

The conclusions drawn from these results may be limited by the fact that the questionnaire used is not a known validated instrument. In addition, it was unfortunate that direct comparisons with UCBL orthoses were not possible since none of the patients included in these preliminary results had previously worn these orthoses. However, these results do appear to indicate the PCFO may be an improved orthotic solution to the problem of the hyperpronated foot over many other treatment methods.

Further results are needed to confirm the benefits of the PCFO and compare their effectiveness with that of the UCBL orthosis. Practitioners interested in trying the PCFO should be aware the orthosis has the disadvantage of being more difficult and time-consuming to produce due to the accuracy required in the modifications and trimlines.

References:

1. Funk DA, Cass JR, Johnson KA. Acquired adult flat foot secondary to posterior tibial tendon pathology. JBJS 1986;66A: 95-108.
2. Jahss MH. Spontaneous rupture of the tibialis posterior tendon: clinical findings, tenographic studies and a new technique of repair. Foot & Ankle 1982;3:158-66.
3. Johnson K. Tibialis posterior tendon rupture. Clin Orthop 1982;177:140-7.
4. Mann RA, Thompson FM. Rupture of the posterior tibial tendon causing flat foot. JBJS 1986; 67A: 556-61.
5. Caillet R. Foot and ankle pain: painful disorders of the adult foot. 2nd ed. Philadelphia: F.A. Davis Co., 1983;105-29.
6. Gould N, Moreland M, Alvarez R, Trevino S, Fenwick J. Development of the child's foot. Foot & Ankle 1989;9:5:241-5.
7. Perry J. Gait analysis. Normal and pathological function. Thorofare, N.J.: Slack Inc. 1992;51-87,185-223.
8. Mann RA. Biomechanics of the foot . In: American Academy Orthopaedic Surgeons (ed) atlas of orthotics: biomechanical principles & application, 1975.
9. Henderson WH, Campbell JW. UCBL shoe insert--casting and fabrication. Bull Pros Res 1969;Spring:215-35.
10. Colson JM, Bergland G. An effective orthotic design for controlling the unstable subtalar joint. Orth & Pros 1979;55:1:39-49.
11. Hylton N. Postural and functional impact of dynamic AFOs and FOs in a pediatric population. JPO;2:1:40-53.
12. Report of the Dietary Guidelines Advisory Committee on the dietary guidelines for Americans, 1995.