Biomechanical Foot Orthotics: A Retrospective Study

Transcription

1 l/88/ $02.00/0 THE JOURNAL OF ORTHOPAED~C AND SPORTS PHYSICAL THERAPY Copyright C by The Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Association Biomechanical Foot Orthotics: A Retrospective Study ROBERT DONATELLI, MA, PT,* CINDY HURLBERT, PTt DAVID CONAWAY, DO* RICK ST. PIERRE, MD9 Foot orthotics are becoming recognized as an important consideration in the correction of lower extremity alignment and mechanical dysfunctions. There are many different foot orthotics on the market today claiming to relieve pain and enhance foot function. Unfortunately, minimal research has been conducted investigating the effectiveness of foot orthotics in adult patient populations. The purpose of this study was to determine the degree of pain relief experienced by patients, the ability of patients to return to their previous levels of activity associated with the duration of use of the orthotics, and patient compliance. This study also discusses the specific deformity for which the orthotic was prescribed and the degree of posting necessary to compensate for the deformity. Fifty-three subjects, 20 males and 33 females, responded to a questionnaire survey. The type of foot deformity and the orthotic prescription are also presented for each subject. The responses to the questions were correlated with an individual patient chart review. In addition, chi-square analysis was used to determine the level of significance between the specific deformity and the age and weight of the patients. The level of significance was determined between the patient's ability to adjust to the orthotics and their continued use of the orthotics. Finally, the significance of the orthotic treatment was compared to four other treatment interventions. Ninety-six percent of the patients reported relief from pain with the use of the prescribed foot orthotic. Ninety-four percent of the patients were still wearing the orthotic, and 52% reported that they would not leave home without them in their shoes at the time the survey was conducted. Seventy percent of the patients reported that they were able to return to their previous level of activity with the use of the foot orthotics. The term foot orthotic has many different meanings to various types of practitioners. The literature describes many different types of foot orthotics such as flexible, semirigid, rigid, functional, biomechanical, san splint, sorbothotics, silicone insoles, power soles, University of California Burkley Lab (UCBL), Helfet foot orthotics, Whitman, Roberts, Schaffer plate, Robert-Whitman, Thomas heel, and accommodative 0rthotics.l- 3, The clinician can become confused and frustrated in deciding what kind of foot orthotics to use for different foot deformities. Instructor at Emory University in the Advanced Masters Degree Program. Orthopaedics. Atlanta, GA t Master's student Orthopaedic Physical Therapy, Georgia State University. Atlanta. GA $Associate Professor, West Virginia College Osteopathic Medicine. Clinical Instructor of Orthopaedics at Hospital Corp. America, Lilburn. GA Clinical Assistant Professor Orthopaedic Surgery, Emory University, Atlanta. GA The purpose of this study was to analyze the effectiveness and the prescription of foot orthotics made of semirigid plastic material, by using a posttreatment survey. The semirigid material used in this study was made of a plastic and fiberglass base. FOOT MECHANICS The role of the biomechanical orthotic is to control excessive and potentially harmful subtalar and midtarsal joint movement during the stance phase of gait.4 At heel strike the subtalar joint should function from it's neutral or inverted positi~n.~." Rootz5 defines neutral as one-third of the total range of motion of the subtalar joint from the full everted position (Fig. 1) As the calcaneus begins to bear weight it must move into eversion, as the subtalar joint pronates (Fig. 2). The pronation of the subtalar joint normally assists in shock absorption, adjusts to changes in terrain,

2 206 DONATELLI ET AL JOSPT Vol. 10, No. 6 and transmits the transverse plane movements of the lower extremity into the The talus, the proximal bone of the subtalar joint, has been described as the extension of the tibia into the foot. The talus is designed to act as the torque convertor of the lower limb.13,25 Transverse rotations of the lower extremity are converted at the subtalar joint into talar movements of plantar flexion in the sagittal plane and adduction in the transverse plane.25 Foot orthotics attempt to alter abnormal foot function during the stance phase of gait. Pronation should normally occur immediately after heel strike. Maximum pronation occurs at the end of the footflat phase, or after approximately 25% of the stance phase has occurred. During the remaining 75% of the stance phase, the foot is preparing for push-off by becoming a rigid lever.13, At midstance the subtalar joint func- tions from a neutral position, allowing the metatarsal heads full contact with the weightbearing surface and the calcaneus to function near a perpendicular position to the supporting surface. In this study the foot orthotics were designed to allow the subtalar joint to function as close as possible from a neutral position. The subtalar joint pronates rapidly at heel?trike to attenuate the weight-bearing forces. When the subtalar joint pronates the calcaneus everts and the talus plantarflexes, thus reducing the height of the ankle joint and leg.25 Knee flexion at heel strike is another shock absorbing mechanism.25 The combination of subtalar joint pronation and knee flexion Fig. 1. Inversion and eversion of the calcaneus in the open kinetic chain. S, Inversion of the calcaneus (subtalar joint), two-thirds of the total range of motion; N, neutral position of the calcaneus (subtalar joint); P, eversion of the calcaneus (subtalar joint), one-third of the total range of motion. Fig. 2. A, Pronation of the subtalar joint, anterior view. 1, Articulation of the cuboidcalcaneus; 2, articulation of the talusnavicular (1 and 2 are more parallel); 3, sustentaculum tali; 4, calcaneus; 5, talus; 6, tibia; 7, fibula. B, Pronation of the subtalar joint, posterior view. 4, Calcaneus; 5, talus; 6, tibia; 7, fibula. affords the lower extremity maximum force attenuation. Supination of the subtalar joint occurs from midstance to toe-off. Supination facilitates the formation of a rigid lever in the push-off phase of gait.25 Root et alz5 describe a locking up of the subtalar and midtarsal joints in supination. The axes of the talonavicular and calcanealcuboid articulations are in a more perpendicular relationship to each othep5 (Fig. 3). Thus, pulley systems are established to enhance extrinsic muscle function. For example, the cuboid pulley allows the peroneus longus to function as a stabilizer of the first ray.25. The peroneus pulls the proximal aspect of the first ray posteriorly against the lesser tarsus area facilitating plantar flexion in push-off.25 ABNORMAL MECHANICS When the subtalar joint is in a fully pronated position the axes of the talonavicular and calcanealcuboid joints are more parallel'6~23~25 (Fig. 2A). The parallel alignment permits greater mobility of the midtarsal and subtalar joint^.'^ If pronation occurs beyond the initial 25% of the stance phase a rigid lever for push-off is never fully a~hieved.'~ The cuboid is closer to the ground, producing a less efficient pulley system for the peroneus Iongus. Thus, stabilization of the first metatarsaltarsal joint does not occur, resulting in a hypermobility of the first ray. Plantarflexion of the first ray is ineffective during the push-off phase. Hy-

3 JOSPT December 1988 BIOMECHANICAL FOOT ORTHOTICS 207 Fig. 3. Subtalar joint supination, the articulation of the cuboidcalcaneus and talus-navicular are more perpendicular. A, Anterior view: 1, articulation of cuboid-calcaneus; 2, articulation of talus-navicular; 3, sustentaculum tali; 4, calcaneus; 5, talus; 6, tibia; 7, fibula. 6, Posterior view: 4, calcaneus; 5, talus; 6, tibia; 7, fibula. Fig. 4. A, Forefoot varus, uncompensated. 7, First ray; 2, talusnavicular articulation; 3, cuboid-calcaneal articulation; 4, calcaneus; 5, talus; 6, tibia; 7, fibula. B, Compensated forefoot varus. 1, First ray; 2, talus-navicular articulation; 3, cuboidcalcaneal articulation; 4, calcaneus; 5, talus; 6, tibia; 7, fibula. permobility of the first ray secondary to excessive pronation is considered by MaCrea14 and Di- Giovanni and Smith8 as the major factor in development of a forefoot varus deformity. According to Root et al.25 two common osseous deformities of the midtarsal joint are the forefoot varus and forefoot valgus. Root et al. described forefoot varus as inversion of the forefoot on the rearfoot with the subtalar joint in neutral and the midtarsal joint pronated (Fig. 4A).25 The forefoot varus deformity alone is not destructive to the foot. However, the method of compensation is detrimental to the normal foot mechanics. The subtalar joint pronates to com- pensate for the forefoot varus deformity (Fig. 48).5,14,25 In addition to the compensatory pronation, the subtalar joint must continue to pronate for shock attenuation and torque conversion. The combination of normal and compensatory pronation is excessive and may be destructive to the foot and ankle. To summarize, at heel strike pronation of the subtalar joint occurs causing the calcaneus to move into eversion. In the presence of forefoot varus the subtalar joint pronates beyond 25% of the stance phase into midstance and toe-off. The subtalar joint may never resupinate during the stance phase, preventing the formation of a rigid lever at push-off. Thus, the unstable foot at pushoff can result in microtrauma and pathologies such as hallux valgus, neuromas, tailors bunions, capsulitis, and/or synovitis of the first metatarsaltarsal joint.25 Root et al. describe forefoot varus as a primary deformity that is compensated for by the subtalar joint.25 MaCrae14 states that excessive pronation is the cause of hypermobility of the first ray. The hypermobility of the first ray produces a dorsiflexed first ray or forefoot supination. Forefoot valgus is defined by Root et al. as eversion of the forefoot on the rearfoot with the subtalar joint held in neutral.25 BIOMECHANICAL ORTHOTICS The functional or biomechanical orthotic attempts to control the velocity and the degree of excessive movement of the subtalar joint during the stance phase of gait.28 Smith et al2' reported that semirigid orthotics reduced the amount and the rate of calcaneal eversion during running. Controlling eversion of the calcaneus allows normal pronation to occur from heel strike to footflat. One method of controlling pronation with an orthotic is with a rearfoot medial edge.'^.^^ The rearfoot correction is built into the orthotic and is designed to position the subtalar joint at heel strike as close as possible to neutral (Fig. 5). The biomechanical foot orthotic is also designed to support forefoot deformities. The orthotic correction for the forefoot is an attempt to bring the ground closer to the medial column. This forefoot correction is referred to as a forefoot varus post (Fig. The forefoot post and the rearfoot post may be intrinsic or extrinsic. For example, a varus position is built into the orthotic when an intrinsic varus post is prescribed. An

4 DONATELLI ET AL JOSPT Vol. 10, No. 6 Forefoot Deformity Forefoot varus left Forefoot varus right Forefoot valgus left Forefoot valgus right Rearfoot eversion left* Rearfoot eversion right Rearfoot varus left Rearfoot varus right TABLE 1 Forefoot and rearfoot deformities Mean Degrees Range No. of Patients Eversion was measured in the standing position. talar joint as close as possible to its neutral position. METHODS Fig. 5. Extrinsic rearfoot post in a permanent semirigid orthotic, medial post or wedge. Fig. 6. Forefoot post medial wedge or medial post. 1, First ray; 2, rearfoot neutral; 3, medial wedge of post in forefoot. extrinsic post is added onto the orthotic with an acrylic plastic material. The permanent orthotic prescription was based on the measurements noted in Table 1. Ninetyfive percent of the patients received a forefoot varus post averaging 5.2O, and 9l0/0 of the patients received a rearfoot varus post averaging 4.5O. As previously noted, the forefoot post was designed to support the varus deformity. The rearfoot post was prescribed to position the sub- Patients were referred to physical therapy for gait analysis and orthotic prescription. The diagnosis varied as one would expect. The most common diagnoses included pes planus and chondromalacia. Pes cavus was diagnosed once. The patient ages ranged from years for females and years for males. Thirty-three females and 20 males were evaluated. The average weight for females was 136 Ibs and 177 Ibs for males. A biomechanical evaluation was performed on every patient to determine the degree of forefoot deformity, the range of motion of the subtalar joint, the mathematical neutral position of the subtalar joint, and the compensatory calcaneal inversion or eversion in the standing position. A complete examination was performed on the lower extremity. Rotational deformities and frontal plane deformities, such as genu varum were identified. Patients with the above deformities were eliminated from the study. The hip flexors, iliotibial band, hip adductors, hip external and internal rotators, hamstrings, gastrocnemius, and soleus muscle groups were evaluated for flexibility. The flexibility testing was performed in prone and sidelying. Standard tests such as Thomas test for hip flexor tightness, and Ober's test for iliotibial band tightness, were used to determine muscle extensibility. Patients demonstrating muscle tightness causing restrictions in joint range of motion were instructed in stretching exercises. The degree of forefoot deformity was evaluated by placing the patient in the prone position with the feet resting over the edge of the table. A goniometer was used to measure the forefoot/ rearfoot relationship with the subtalar joint held in the neutral position. One arm of the goniometer

5 JOSPT December 1988 BIOMECHANICAL FOOT ORTHOTICS 209 was placed over the metatarsal heads, and the other was moved to a position in space perpendicular to the calcaneal neutral position. The methods used to measure the forefoot deformity and the range of motion of the subtalar joint are de scribed by Root and Burns et a1.5v24 The functional aspects of the foot and ankle during the stance phase of gait were observed with the subjects running and walking on a treadmill. The gait analysis was totally subjective and based on observation by the physical therapist. The patients were observed with and without the orthotics in the running shoes. Patients were then asked to determine comfort with the orthotics "- during running on the treadmill. Changes were made in the orthotics to ensure comfort. All the patients were initially fitted with temporary, soft orthotics. AlliMed Inc. (Alimed Inc., 297 High St., Dedham, MA ) supplied the materials for fabrication of the temporary orthotics. Aliplast inner soles were used for the temporary orthotics. Nickleplast and rubber wedges were used to fabricate the appropriate posts in the forefoot and rearfoot. The posts were glued to the inner soles and secured with tape. The B *I prescription for posting the temporary orthotic has based on the biomkhanical evaluation. Forefoot and rearfoot posts were added to control the abnormal movements. Temporary orthotics were worn on an average of 6-8 weeks. The patient was seen in the office during the trial period of wearing the temporary orthotics to make adjustments in accordance with their pain relief. In addition, 12 patients were treated with ultrasound and electric stimulation to enhance their pain relief. The ultrasound was used over areas of pain and chronic inflammation. The electric stimulation was used over trigger points palpated within the gastrocnemius and soleus muscle bellies. Patients were instructed in stretching exercises to loosen tight muscle groups, such as the gastrocnemius and so leu^.^ A neutral case was made to fabricate permanent semirigid orthotics. All casts were sent to an orthotic laboratory for fabrication of the permanent foot orthotics. The permanent orthotics were made with a fiberglass and plastic material (Fig. 7, A and B). The method of nonweightbearing neutral casting was identical to the procedure described by Burns et al6 The prescription for the permanent orthotics was based on re-evaluations and the success of the temporary orthotics prescription. Re-evaluations were performed on sub-..., I ) 8 <. Fig. 7. A, Semi-rigid sport orthotic with an intrinsic forefoot post and extrinsic rearfoot post (varus posts); B, semirigid sport orthotic with extrinsic forefoot and rearfoot posts (varus posts). sequent visits in which the patient reported the degree of pain relief from the use of the foot orthotics. A questionnaire was used to collect the information. The questions determined the success of the orthotics by assessing pain relief, satisfaction with the orthotics, an adjustment period with the orthotics, continued use of the orthotics over a 2- year period, and the ability of the patient to return to their previous level of activity. The patient responses were divided into three groups according to length of time in the permanent orthotics: 3 months (17 patients), 3-6 months (9 patients), and 6 months-2 years (27 patients). The information obtained from the questionnaire was reviewed and categorized according to the success of the orthotics as noted above. In addition, chi-square analysis was also used to test the categorical survey data. The criteria for significance selected for the study was p I RESULTS The most common forefoot deformity observed in this study was forefoot varus. Ninety-five per-

6 21 0 DONATELLI ET AL JOSPT Vol. 10, No. 6 cent of the patients evaluated in the study demonstrated a forefoot varus. The average forefoot varus deformity measured was 8.4O (Table 1). The average rearfoot compensatory eversion of the calcaneus was measured at 7.8' in the standing position (Table 1). Forefoot varus was, in the authors' opinion, the major cause of abnormal pronation during the stance phase of gait. Conversely, forefoot valgus was observed on one patient in this study. Eighty-one questionnaires were sent out and 53 were returned (65%). Twenty-eight (53%) of the patients were treated with orthotics alone. Twenty-two (47%) of the patients received other treatment in addition to orthotics. The additional treatments included, exercises and/or ultrasound and high voltage electrical stimulation. Ten patients received stretching exercises to reduce tightness in the gastrocnemius and soleus muscle. Seven patients received ultrasound, electrical stimulation, and orthotics and 5 received orthotics, exercises, and ultrasound/electricai stimulation (Table 2). The data was analyzed to establish if a relationship existed between the four treatment interventions and the patients' residual pain (N = 46 x2 = 5.628, df = 9, 0.01 < p < 0.95). No relationship was found to exist between the orthotic therapy and the use of electric stimulation, ultrasound, or exercises. Thus, one might conclude that within this patient population, the foot orthotics were responsible for the results and that the additional treatments applied were of little added benefit. It is also important to note the primary treatment was the use of foot orthotics. The results indicated the most frequent complaint of pain was located at the foot (39%) and the knee (31 76). The second most common areas of discomfort included ankle pain and posterior medial shin splints. Fifty percent of the patients complained of pain in one joint and 50% complained of multiple joint pain. Bilateral complaints tended to occur at the knee (40%) and the foot (39%). The mean age was 35 years old for females and 31 for males. In the population described, orthotics intervention was effective in relieving pain for 96% of the patients. Ninety percent of the patients treated with orthotics alone reported relief from their pain (Table 2). The patient's age and degree of forefoot varus in this study represent variables which are independent of each other (N = 59 x2 = 3.915, df = 15, c p < 0.995). No statistically significant relationship exists in this patient population between age and degree of forefoot varus. The patient's weight was also found to vary independent of the degrees of forefoot varus (N = 51 x2 = , df = 15, < p < 0.95). The patients' weight or age could not be considered a predictor of the degree of forefoot varus. Ninety-one percent of the patients reported they were very satisfied or satisfied with the orthotics (55% very satisfied and 36% satisfied). Nine percent of the patients were not satisfied with the orthotics. The dissatisfaction was a result of the orthotics becoming frayed, flattened, torn, and/or excessively worn with use. A relationship was identified between the patients' satisfaction with their orthotics and the status of their pain which was rated as unchanged, reduced, or eliminated (N = 53 x2 = , df = 6, p < 0.005). The relationship between satisfaction with the orthotics and pain relief was found to be significant. Eighty-one percent of the patients reported a 3-day adjustment period for wearing the permanent orthotics. The patient's ability to adjust to their orthotic quickly was related to their continued use of the orthotics (N = 53 x2 = 8.539, df = 2, 0.01 c p c 0.025). Ninety-four percent reported they were still wearing their orthotics at the time of the survey. Fifty-two percent would not leave home without the orthotics in their shoes, and 42% used them only during the activity that originally produced the pain. TABLE 2 Success Rate of Orthotics-Relief of Pain Com~leted Questionnaire No. of Patients Percent Total response to orthotics questionnaire Pain relief from orthotics alone Pain relief from orthotics and exercises Pain relief from orthotics and modalities Pain relief from orthotics, exercise and modalities No pain relief orthotics alone

7 JOSPT December 1988 BIOMECHANICAL FOOT ORTHOTICS 21 1 TABLE 3 Abnormal Pronation Deformity and Orthotics Posting Average forefoot varus post Average rearfoot varus post Average forefoot varus deformity Average rearfoot everted position in standing 5.2' 4.5' 8.4' 7.8' Note: 61% of the forefoot varus deformity was corrected by posting and 57% of the rearfoot deformity was compensated by posting. Seventy percent of the patients were able to return to their previous level of activity; jogging, walking, aerobics, tennis, basketball, and golf. In this population of recreational athletes, an elimination or reduction of pain did not correlate significantly with their return to previous levels of sports activities (N = 53 x2 = 3.586, df = 2, 0.10 < p < 0.95). These patients reported a return to their previous level of sports regardless of the presence or absence of pain. The most common complaint expressed was the inability to fit the orthotics in all types of footwear, especially dress shoes (29%). There were two patients who reported no relief from the initial pain and one patient who stopped wearing the orthotics completely. DISCUSSION The results of the study indicate that functional or biomechanical foot orthotics can be useful in treating a variety of foot, ankle, and lower extremity syndromes. This study investigated the use of foot orthotics for the treatment of the recreational athlete in a range of sporting activities. Prior to orthotic intervention, all the patients suffered pain during their specific sport, limiting their level of activity. This study identified a forefoot varus deformity as the most common foot deformity in this study. Rearfoot eversion was the primary compensation observed for the forefoot varus noted during the stance phase of gait. The orthotics used in this study were designed with a rearfoot varus post (medial wedge) to control the excessive calcaneal eversion movement of the subtalar joint. In addition, a forefoot varus (medial) post was added to the orthotics to prevent the need for compensatory subtalar motion in the push-off phase of gait. This investigation indicated that a complete correction of the forefoot and rearfoot deformities observed with abnormal pronation was not necessary. As noted in Table 3, the posting (medial wedges) supported approximately 60% of the deformity. The forefoot post was, on an average, 4% greater than the rearfoot post. No relationship was found between the amount of forefoot varus and the patient's age or weight. An important clinical relationship was found to exist between a quick adjustment period and the continued use of the foot orthotics. The authors have observed that often patients are fitted for permanent semirigid foot orthotics before a trial period is used to help determine the individual prescription. It is the authors' belief that the use of temporary orthotics allows the clinician the opportunity to make the permanent prescription more specific to the patients' deformities. A more specific prescription means less adjustment time and continued use of the foot orthotics. Furthermore, we determined that those patients who were more satisfied with their orthotics, reported the most pain relief. Thus, better fitting foot orthotics mean a quicker adjustment period, greater patient satisfaction, more perceptible relief, and better patient compliance with the use of the orthotics. More extensive analysis of the efficacy of this form of intervention with specific injuries to the lower extremity will help to refine the process of orthotic prescription. The information presented here is an attempt to make the practitioner aware of the role biomechanical orthotics can play in treatment of overuse injuries to the lower extremity. Furthermore, the study indicates the importance of a biomechanical evaluation, a trial period in temporary orthotics, and gait analysis to determine the proper orthotic prescription. Too often orthotics are fabricated without a detailed evaluation of the lower extremity. If such a study was repeated, it would be of benefit to include a control population not receiving foot orthotics. This would allow for additional statistical comparisons to be continued. SUMMARY A retrospective survey of recreational athletes receiving biomechanical, semirigid foot orthotics for various lower extremity problems was conducted. Patients responded by questionnaire. Orthotic intervention was effective in relieving pain for 96% of the patients responding to the survey. Based on the results of this study, the success of foot orthotic therapy can be measurably increased by refining the criteria used for prescribing orthotics and improving the techniques used to biomechanically evaluate the foot. Special thanks to Micheal Wooden, PT, for his assistance with this study.

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