Many individuals referred for orthotic evaluation have limited passive range of motion (PROM) at the talocrural joint. These restrictions commonly accompany neurologic pathologies such as stroke, 1–6 cerebral palsy, 7–12 traumatic brain injury, 13–14 and multiple sclerosis, 15 as well as various neuromuscular pathologies. 16–17 Soft-tissue limitations are also common after immobilization following bone and/or soft-tissue injury 18 or with orthopedic diagnoses such as plantar fascitis. 18–19 These restrictions can be due to soft-tissue tightness, hypomobility of the joint itself, or some combination of the two factors. For effective orthotic construction, it is essential that proper assessment be made regarding the cause of limited ankle PROM. The purpose of this review is twofold. First, the functional biomechanics of the foot and ankle complex will be reexamined. Next, the clinical implications of soft-tissue limitations at the talocrural joint will be discussed, emphasizing the role of orthotic devices in the management of heelcord tightness and compensatory dorsiflexion at the midtarsal joint.
ANATOMY AND MOTION OF THE ANKLE FOOT COMPLEX
The foot is typically divided into three sections: (1) the hindfoot (or rearfoot), composed of the talus and calcaneus; (2) the midfoot, consisting of the cuboid, navicular, and cuneiforms; and (3) the forefoot, containing the metatarsals and phalanges. The hindfoot of the ankle consists of two joints. The talocrural joint is the articulation of the tibia and fibula with the talus, and the subtalar joint (STJ) is the articulation between the talus and calcaneus.
Motion at the talocrural joint is primarily dorsiflexion and plantarflexion. However, motion is actually triplanar as the joint axis is not purely in the sagittal plane, but extends posteriorly (20–30 degrees) and inferiorly (10 degrees) on the lateral side as illustrated in Figure 1 a. 20 Thus talocrural dorsiflexion is accompanied by slight lateral movement of the foot, while slight medial movement of the foot occurs with plantarflexion. 20Table 1 summarizes the normal sagittal plane PROM available at this joint.
The rotational axis of the talocrural joint is controversial. Arguments have been presented that it simulates a simple fixed hinge joint. 21–24 Others, however, have identified that the joint axis changes considerably during range of motion. 25–27 An accurate talocrural axis location is necessary for alignment of articulated external fixators to the ankle joint. In establishing this location, researchers found that the best-fit axis orientation was 8.8 degrees inversion and 8.4 degrees external rotation. 28 The axis displayed changes in frontal plane orientation in the direction of eversion during plantarflexion when moving from 10 degrees of dorsiflexion to 25 degrees of plantarflexion. However, horizontal plane directional changes towards external or internal rotation for the same range of motion were inconsistent. 28 These findings correspond with the single hinge axis orientations reported by Inman 29 (8 degrees inversion, 6 degrees external rotation) and Bogert et al. 21 (7.0 degrees inversion, 6.8 external rotation).
STJ movement, summarized in Table 1, 30–37 occurs around a single triplanar axis in the direction of pronation and supination (Figure 1 b). There are discrepancies in the nomenclature used to describe the STJ triplanar movement. These inconsistencies can cause confusion if the reader is not careful to understand the author’s definition of terms. For example, while Hollinshead, Root, and Norkin and Levangie define the triplanar STJ motion as pronation and supination, while Kapanji and Norkin and White call these motions inversion and eversion. 20,30,35,38,39 For clarity in this paper, the triplanar motion of supination will be defined as movement of the distal component of the foot into inversion, plantarflexion, and adduction. Pronation will be defined as movement of the distal component of the foot into eversion, dorsiflexion, and abduction. In addition, it should be noted that when viewing the joint from a sagittal plane, the angle of inclination of the calcaneus decreases as the STJ moves from supination to pronation. 30
The transverse tarsal joint of the midfoot is also known as the midtarsal joint, and it consists of the articulations formed by the talonavicular and calcaneocuboid joints. In weight bearing, the navicular and cuboid are relatively more fixed than the talus and calcaneus, so movement at this joint is primarily that of the calcaneus and talus moving on the immobile navicular cuboid complex. 40 These two joints are theorized to have individual axes of motion: the longitudinal axis at the talonavicular joint and the oblique axis at the calcaneocuboid joint (Figure 1c and 1 d). 35,36,41 Movement at the longitudinal axis is primarily into eversion/inversion with 8 degrees of movement available, 36 while movement at the oblique axis is primarily into dorsiflexion/plantarflexion, as well as some abduction/adduction with a total of 22 degrees of movement available. 20,30,36,41–44 In combination, motion around these two axes produces supination and pronation (Refer to Table 1 for exact ranges). Midtarsal joint motion is unusual in that it is dependent on the position of the STJ. 20,41–44 As long as the STJ is pronated, the two midfoot axes diverge and become relatively parallel, leaving the midtarsal joint mobile and free to move. If the STJ is supinated, the oblique and longitudinal axis converge, and the midfoot is locked and immobile. 20,40,43 Thus the subtalar and midtarsal joints are interdependent, and dorsiflexion, for example, can be obtained at the oblique axis of the midtarsal joint only in conjunction with pronation of the STJ. 2,20,36,40–45 The midtarsal joint is very mobile when the STJ is pronated, and relatively immobile when it is supinated. 30,40,41,46 Phillips and Phillips’44 work demonstrated exponentially increasing mobility at the midtarsal joint as the STJ moved from neutral into pronation, with only minimal mobility when the STJ was in a supinated position. Likewise, Tiberio et al. 47 measured dorsiflexion, a large component of oblique axis midtarsal joint motion as well as talocrural joint motion, in the combined ankle foot complex with the STJ pronated or in a neutral position. They consistently found approximately 10 degrees more DF range when measuring in STJ pronation as compared to neutral.
Motion at the tarsometatarsal joint occurs so that the metatarsals obtain a stable position on the ground. Transmetatarsal joint motion is greater when there is inadequate mobility at the more proximal joints of the foot. Each ray is capable of moving in a slightly different triplanar motion, although as a whole there is a great deal of interdependence in the mobility at these five tarsometatarsal joints. 20 The metatarsophalangeal joints and interphalangeal joints move primarily in flexion and extension with some abduction/adduction. 20 A good review of the distal joint movement possible at each joint is provided by Norkin and Levangie. 20
MEASUREMENT OF RANGE OF MOTION AT THE TALOCRURAL, SUBTALAR, AND MIDTARSAL JOINTS
In clinical measurement, it is often difficult to isolate the complex motion of the foot and ankle complex to a single joint. This has been noted by several authors. 13,24,47,48 For example, measurements of dorsiflexion often include the motion occurring at both the talocrural and the midtarsal joint. 13,20,47,48,49 Likewise, supination often includes joint movement occurring simultaneously at the subtalar and midtarsal joints. 44,46 The STJ, however, can pronate (abduction, eversion, and dorsiflexion) while the midtarsal joint supinates (adduction, inversion, and plantarflexion) if necessary in order to place the forefoot flat on the floor. 44,46 Range of motion also varies depending on whether measurement is occurring in the weight bearing or nonweight bearing position. 49 In addition, there are several different measurement techniques in common usage. 13,35,39,47–53 These factors account for some of the variation in range of motion noted in the different sources referenced in Table 1.
There are several commonly accepted methods of measuring ankle dorsiflexion using either a goniometer or a torque controlled measurement device. 13,39,47,48 The proximal line of the goniometer is usually lined up with the head of the fibula, with the fulcrum either over the lateral malleolus or dropped distal to it at the base of the foot. The placement of the distal arm can vary, either running parallel to the plantar surface of the foot, the fifth metatarsal, or the calcaneus. 39,48 Measurement values obtained are significantly different under each of these three conditions. 48 The torque controlled measurement device used by Mosley and colleagues controls the passive application of force during measurement. 13 However, the landmarks utilized are different from those discussed above. The angle is measured from the head of the fibula to the lateral malleolus and directly on to the head of the fifth metatarsal, thus resulting in different numerical ranges for normal dorsiflexion. Reliability of goniometric measurement at the foot and ankle is also an issue. While intrarater reliability is usually high (ICC = 0.90), 49 interrater reliability has a range of 0.50–0.72 49
Ankle dorsiflexion range of motion is commonly measured with the knee flexed and extended to fully assess all components of the triceps surae complex. These methods can assist in ruling out joint versus soft-tissue hypomobility. It is not uncommon for an individual to have adequate dorsiflexion when the knee is flexed, but not with it extended, suggesting that the two joint gastrocnemius muscle running from above the knee to the calcaneus is the more limited in range than the one joint soleus muscle running from below the knee to the calcaneus.
Several methods are used to locate the STJ pronation, supination, and neutral positions. In the open kinetic chain method, 35,49 the head of the talus of the nonweight bearing foot is palpated while the forefoot is passively pronated and supinated until a midposition is reached where the talar head is equally palpable medially and laterally. The calcaneus is then bisected and its position is measured in relation to a bisection of the lower leg. Intrarater reliability for this measurement is r = 0.06–0.32, 50,51 and interrater reliability is r = 0.00–0.77. 50,51,52 Closed chain subtalar neutral position is measured similarly but in full weightbearing. 51 Intrarater reliability for this measurement was 0.14 to 0.18 51 and interrater reliability 0.15. 51 A more reliable measure is simple calcaneal inversion/eversion in weight bearing, with the calcaneus bisected and its position measured in relation to a bisection of the lower leg. Using this method, interrater reliability is 0.91 in the bilateral stance and 0.75 in the unilateral stance. 52 Several other measurement techniques are being used, 39,51–53 but reliability is a problem where it has even been assessed. Norkin and White 39 present two methods of measuring midtarsal joint supination and pronation when the STJ is stabilized, however reliability of these methods has not been established. Because of the lack of and/or poor reliability found in the available studies, measurements of supination and pronation of the STJ and midtarsal joints should be viewed with appropriate caution.
THE ROLE OF DORSIFLEXION DURING WALKING
Adequate ankle range of motion is important for many functional activities. Ankle DF mobility is necessary in normal daily activities such as standing up from sitting, reaching activities in standing, and dynamic standing balance, 13,54–56 yet its role has been most frequently studied in gait. 7,9 Normal gait requires a minimum of 5 degrees of ankle dorsiflexion with knee extension 30,37,42,45 in order for the tibia to move normally forward over the foot during stance phase.
With loss of talocrural joint range during walking, both distal and proximal compensatory strategies can be used to varying degrees and in different situations. Proximal compensations involve changes in movement patterns proximal to the foot and ankle, including changes in step length. With unilateral loss of range of motion, the individual sometimes walks with a “step to” gait, advancing the unimpaired foot only up to the impaired foot during swing phase. Unilateral loss can also be compensated for by an early heel rise during stance phase, usually accompanied by increased flexion at the hip and/or trunk, or knee hyperextension, in order to shift the body weight forward over the foot. During swing phase, the foot is usually lifted higher off the ground with increased hip and knee flexion to allow foot clearance 37 because dorsiflexion is not available. With bilateral losses, very short steps with early heel rise in stance phase and exaggerated hip and knee flexion in swing phase become necessary, again due to the abbreviated forward weight shift possible during each step.
These proximal compensations for decreased dorsiflexion result in a slower and more energy demanding gait. 37 Small step length limits speed, and more energy is required because the center of gravity cannot be shifted as smoothly and efficiently over the foot during stance phase. This, however, is not the case with purely distal compensatory strategies, where step length and smooth forward weight transfer are preserved. In these cases, the DF available distally at the midtarsal joint, in conjunction with pronation, is used to supplement limited talocrural DF. As long as STJ pronation is possible, the midtarsal joint will provide additional functional dorsiflexion range during the progression of stance phase. Body weight will force the ankle foot complex into maximal STJ and midtarsal joint pronation, maximizing midtarsal joint dorsiflexion to supplement talocrural joint dorsiflexion.
There is a limited amount of elasticity available in the muscle, tendon, ligament, and fascial structures of the foot and ankle complex. Muscle has the greatest elasticity in response to stretch. Muscle tissue lengthens smoothly with the application of force, and when the force is terminated, it returns to its original length. This action is similar to the stretching and then releasing of a rubber band. The ligament, tendon, and fascia structures are relatively less elastic than muscle. These tissues will stretch elastically to a varying but smaller degree than muscle. Muscle can then be pictured as a thin, very stretchable rubber band, while tendon, ligament, and fascia are thicker, denser, and less stretchable rubber bands. Once the elastic range has been utilized, further stretching can occur in the plastic range. Plastic changes refer to the deformation that occurs when force is applied in this range. Again, the tissue lengthens, but, in this case, when the force is released, the tissue does not return to its original length and remains relatively elongated. 18 Once tissue is stretched past the plastic range, rupture occurs. Elastic and plastic changes are illustrated diagrammatically in Figure 2.
With forward weight shift, available range in the foot and ankle joints is first gained from the most elastic elements of the system, primarily muscle. Next, the ligaments supporting the oblique axis of the midtarsal joint that normally limit midfoot dorsiflexion, the plantar calcaneonavicular ligament (or spring ligament), the long (or superficial layer of the plantar calcaneocuboid ligament) and short (or deep layer of the plantar calcaneocuboid ligament) plantar ligaments, and the bifurcate ligament 20,30,43,57 are preferentially stretched before the Achilles tendon because these midfoot ligaments offer less resistance than the extremely thick connective tissue of the Achilles tendon. 18 Particularly in adults, body weight frequently stretches these ligaments into their plastic range, resulting in permanent plastic deformation of the ligaments and ligamentous laxity in a hypermobile midfoot.
To illustrate the actions of the tendons and ligaments of the foot and ankle, consider bending the system shown in Figure 3 containing one thick and a set of two thin rubber bands in series. As force is gradually applied to bend the system, the thin bands will be stretched first before the thick band. Likewise in the foot, as the body attempts to move forward over the foot in stance, the continued force of the body weight pushes the foot into dorsiflexion. Over time with the repeated stretching forced by the forward progression of body weight over the foot, the thinner ligaments of the midfoot are preferentially stretched into their plastic ranges. Thus persistent talocrural DF tightness over a prolonged period of time frequently results in an excessively pronating foot at the STJ along with dorsiflexion and abduction at the oblique axis of the midtarsal joint. This abnormal foot position is commonly seen in the chronic stroke patient 54 or the older child with cerebral palsy. 7 It should also be noted that the hypermobile midfoot that develops as a result of this compensatory midtarsal DF may lead to additional problems over time. Excessive pronation causes cumulative stress though the skeletal system and can lead to pain at the foot and ankle as well as proximally at the knee joint and in the low back area. 18,30,58
THE ROLE OF ORTHOIC DEVICES IN THE MANAGEMENT OF SOFT-TISSUE TIGHTNESS AT THE TALOCRURAL JOINT
Orthotic devices have several roles in the management of the individual with limited soft-tissue mobility at the ankle. First, a passive stretching splint may be used to increase range of motion. Second, an ankle foot orthosis (AFO) may be worn to make the individual’s walking safer and more functional. Heelcord tightness, however, is very common in these individuals, and the AFO, if correctly designed, can not only help maintain range, but can also provide dynamic stretching to the triceps surae musculotendinous complex during walking. Finally, an orthotic device may be constructed to lessen secondary pain due to chronic severe pronation. This pronation problem is often the result of soft-tissue tightness and can be lessened by treating the underlying tightness with a combination of exercise and an appropriate orthotic intervention.
Splinting has long been an accepted method to increase PROM 59–62 by providing a prolonged stretching force to the musculotendinous unit. Ankle stretching splints can provide this prolonged stretch for a period of multiple hours, and they have the benefit of being removable, both for improved mobility, and so that individuals with the potential for skin breakdown can be easily assessed. 59 Animal studies have elaborated the role of prolonged stretch on local passive viscoelastic elements of muscle and tendon. When muscle is placed on stretch for a prolonged period of time, an increased number of sarcomeres develop in series as compared to normal muscle, 63 and the accumulation of excess connective tissue normally found in immobilized muscle tissue is prevented. 64 The tendon is also responsive to stretch. Normally, collagen fibers in immobilized tendons become disorganized over time. However, when a tendon is placed on prolonged stretch, this disorganization is reversed. 65 It remains unclear whether prolonged stretch affects primarily the muscle, the tendon, or both. It is also unknown exactly how long a prolonged stretch must be applied in order to stimulate changes, such as the formation of new sarcomeres, in the musculotendinous unit. 13,49
Dorsiflexion stretching splints, however, do not always differentiate between dorsiflexion at the talocrural versus the midtarsal joint because the primary stretching force is often applied at the distal end of the foot. Without control of the STJ, the foot will pronate. As discussed earlier, in the connected chain of joints that make up the foot and ankle complex, dorsiflexion occurs first at relatively more stretchable ligaments supporting the midfoot rather than the dense Achilles tendon of the talocrural joint (Figure 3). 2,20,42,43,45,47 This difficulty in targeting the stretching force precisely to the talocrural joint, however, is easily managed with a proper understanding of the anatomy and biomechanics of the foot and ankle complex. A subtalar neutral position is maintained while molding the splint, and the orthotic device is built with adequate support insuring that the foot remains in STJ neutral during use. Stretching forces are then directed specifically to the talocrural joint rather than at the midfoot, which is maintained in a locked and immobile position.
In summary, orthotic devices are often built for individuals either to improve mobility or because of pain due to excessive pronation. An underlying component of both problems is heelcord tightness. What is not always recognized is that correctly designed bracing can produce a dynamic stretching force. The dynamic weight bearing stretch obtained during normal functional activity such as standing up and walking is one of the most effective ways to increase range of motion 54 in that the person completes the stretch multiple times daily during functional activities. In order to target the stretching force specifically to the talocrural joint during gait, the foot must be supported to prevent pronation during midstance as the tibia moves forward over the foot. If not, the stretch again occurs at the midfoot before the talocrural joint, and over time this results in an even more pronated foot with a hypermobile midtarsal joint. There are three areas to consider to optimize the dynamic stretching: (1) contouring of the foot piece; (2) distal and proximal pronatory forces; and (3) ankle mobility.
THE ROLE OF THE CONTOURED FOOT PIECE IN PREVENTING EXCESSIVE PRONATION
Orthotic designs that contour the foot piece under the arches can help prevent excessive STJ pronation and resultant compensatory midfoot dorsiflexion by supporting the foot in STJ neutral. In this way the oblique axis of the midtarsal joint can be prevented from moving into dorsiflexion. During casting, the foot can be easily maintained in STJ, neutral and well contoured arches can be molded into the plaster bandage. However, use of a customized contoured footplate, as shown in Figure 4, casted as the base of the negative mold allows more precise alignment, which can be especially helpful for individuals, such as children and hypertonic individuals, whose feet are difficult to maintain in good alignment throughout the casting process.
Although typically only the thin, volume critical supramalleolar level orthoses (SMAFOs), sometimes known as dynamic ankle foot orthoses, have been constructed with a contoured footplate, 66 this design feature can be built into the base of any orthosis or serial cast. 13 Earlier hypotheses about “inhibitive footplates” theorized that contouring under the sole of the foot stimulates certain reflexes thereby inhibiting spasticity. 67–70 Current theory, however, related to biomechanical alignment, offers a more acceptable rationale for the inhibitory effect sometimes found in bracing. 54,66 It is hypothesized that the effectiveness of this footplate contouring is related to maintaining the foot in good biomechanical alignment and thereby preventing excessive compensatory DF of the midfoot in conjunction with pronation. 66 It has also been suggested that contouring increases the contact of the whole foot with the ground, increasing the base of support and thus decreasing abnormal balance reactions and “grabbing” with the toes. 54 The good biomechanical alignment provided by the footplate contouring, stabilizing the calcaneus in a neutral position, is also probably a factor in the inhibitory effect of the footplate, providing a better foundation for normal movement patterns. 54,66 Nonetheless, it is probable that the principle effect of the contouring is to direct the dorsiflexion force (or moment) provided by the body weight moving forward over the foot during stance from the midtarsal joint backward to the talocrural joint where it should normally be occurring. This is supported by the changes in foot loading patterns found by Mueller and colleagues 71 in a hemiplegic adult wearing a volume critical SMAFO.
The foot piece contouring should include support under the medial longitudinal arch, the lateral peroneal soft-tissue arch, and the anterior transverse arch 30 (Figure 5 a–c). The angle of inclination of the calcaneus is maintained by a supporting stirrup under the medial longitudinal arch and lateral peroneal soft-tissue arch 30 (Figure 5 d). By preventing the decline in the angle of inclination (Figure 5 d), the calcaneus cannot move into the necessary pronated position allowing compensatory midfoot dorsiflexion, thus any stretching forces into dorsiflexion produced in normal gait are targeted to the talocrural joint.
Incorporation of this type of contoured footplate into a dynamic stretching splint has been shown to be an effective means of increasing talocrural range in an adult with cerebral palsy. 72 Other single subject studies have examined the effectiveness of incorporating contoured footplates into bracing. Zachazewski et al. 73 treated a young man presenting with post traumatic brain injury with a right tone-inhibiting AFO and found improvements in gait. Harris and Riffle 74 noted improved standing balance in a child with spastic quadriplegia with the use of inhibitive ankle foot orthoses. Embrey et al. 75 found more normal stance knee flexion in the gait of a child with spastic diplegia when using a supramalleolar level AFO with contouring to maintain foot alignment. Mueller et al. 71 evaluated the effects of a volume critical SMAFO during gait in a hemiplegic adult following stroke and found more normal foot loading patterns when wearing the AFO than without. A final study noted improvement in gait in a hemiparetic individual wearing a supramalleolar level AFO with a contoured footplate as compared to a prefabricated thermoplastic AFO and no brace. 76 The limitations of these single case studies is that the authors did not compare the orthosis with a contoured foot piece to one without the contouring.
Several group studies have compared individuals who have worn an AFO with a contoured footplate to those who either wore a standard orthosis or did not wear any orthotic device. The results of these studies, however, present a less compelling case about the importance of a contoured foot piece. The first study 77 compared the stride characteristics in three hemiplegic adults wearing no brace, a volume critical SMAFO, and a prefabricated thermoplastic posterior leaf spring AFO. The individuals using a SMAFO showed increased gait velocity, stride length cadence, and single leg support as compared to those wearing a posterior leaf spring AFO or no brace however, no statistical analysis was completed in this study.
Two other group comparison studies using statistical comparisons have been completed. In the first, the gait of 10 children with spastic cerebral palsy (hemiplegia and diplegia) was examined without bracing, with a volume critical SMAFO, and with a solid ankle below knee height thermoplastic AFO. 78 While both orthoses improved stride length, decreased cadence, and reduced excessive plantarflexion as compared to the no brace condition, there was no statistical difference between the two types of orthoses. A second study examined the gait of eight children with spastic diplegic cerebral palsy comparing four conditions: (1) no brace; (2) an articulating AFO with a plantarflexion stop without a contoured foot piece; (3) an articulating AFO with a plantarflexion stop and with a contoured foot piece (tone-reducing AFO or TRAFO); and (4) a SMAFO with a contoured foot piece. 79 It is unclear whether the SMAFO used in this study was fabricated from regular thickness polypropylene or the very thin, flexible polypropylene that is unique in the volume critical SMAFO. It is described as being fabricated from the same thickness of material as the other braces used in this project. Stride length was significantly improved from the no shoes to TRAFO condition, and the most heel strike dorsiflexion was found with the TRAFO and followed by the AFO, then the SMAFO. The most plantarflexion occurred at push-off in the SMAFO and followed by the no brace, the AFO, and then the TRAFO condition. Kinetic values also varied at the ankle. However, the authors believe that the statistically significant changes at the ankle can be accounted for by the presence or absence of the plantarflexion stop. This is the only study that directly compared two braces that were identical except for the addition of a contoured footplate. The results of all of the research studies are summarized in Table 2.
It should be noted that several technical difficulties exist in motion analysis technology when used to evaluate supramalleolar level bracing. Both of the above comparison studies utilized Motion Analysis Corporation’s reflective markers that must be placed over specific bony landmarks including the lateral malleolus. Supramalleolar level bracing extends over both malleoli in order to provide structural integrity and support. Therefore markers must be placed over the brace material with this and the higher levels of bracing. Ideally, in articulated brace designs, the external ankle hinge should track smoothly over the malleolus during ankle motion. Likewise, in solid ankle designs there should be minimal ankle motion. Thus under these two conditions, reflective markers placed externally over the brace will accurately record ankle motion. However, with a SMAFO design, the ankle component of this orthosis does not track uniformly with the malleolus, which leads to inaccurate measurement of ankle movements. As of yet, there is no adequate solution to this technological problem as SMAFO level orthoses lose their structural integrity if they are cut back over the malleoli to allow more accurate marker placement. Because of this, analysis of SMAFO kinematic ankle motion data is not meaningful.
CONTROL OF DISTAL PRONATORY FORCES: TRANSVERSE FOOT FOREFOOT ALIGNMENT
A second aspect of the contoured footplate that assists in preventing compensatory midfoot dorsiflexion is the careful attention to transverse alignment of the forefoot to the rearfoot. With excessive pronation in weight bearing, the forefoot tends to abduct relative to the hindfoot. 30 The opposite occurs with supination. During casting, since the metatarsal heads must be parallel to and come in contact with the supporting surface of the floor, it is not possible to obtain neutral midfoot and hindfoot alignment in a normal foot if the forefoot is allowed to deviate substantially in the transverse plane. 66 When casting the complex and moving foot of children or individuals with severe spasticity, such as athetoid cerebral palsy or head injury, it is often difficult to maintain good transverse alignment, preventing transverse forefoot deviation, while at the same time maintaining good frontal and sagittal alignment. Use of the contoured footboard assists this process greatly by preventing the forefoot from abducting excessively in the brace and eliminating this additional distal pronatory force that pushes the foot further into midfoot and STJ pronation.
CONTROL OF PROXIMAL PRONATORY FORCES
Finally, consideration must be made of the passive proximal rotational forces contributing to STJ pronation. In weight bearing, tibial/fibular as well as femoral internal rotation forces are normally translated down into the ankle and foot, forcing the STJ into pronation at midstance. 37,58 Clinically, these passive proximal forces become an increasingly significant component as the individual becomes heavier, so consideration of the proximal rotational forces becomes more critical in adults as compared to children. Control of excessive passive proximal pronatory forces may be critical if stretching is to be directed to the talocrural joint. Again, STJ pronation must be prevented in order to lock the midfoot and prevent compensatory midtarsal dorsiflexion. Supramalleolar and lower level orthoses provide no control of rotational movement of the tibia and fibula. A conventional below knee height orthosis must be utilized to assist in maintaining normal alignment of the tibia and fibula in the transverse plane. It should also be noted that the flexible, volume-critical design of the SMAFO was created in order to allow some degree of transmission of these proximal rotatory forces through the foot and ankle. 66 Therefore, even though these SMAFOs are constructed with footplate contouring and attention to distal malalignment control, both of which decrease pronatory forces, they may not be an adequate solution if the proximal pronatory forces are large, as frequently occurs with adults.
ANKLE MOBILITY: SUPRAMALLEOLAR HEIGHT, ARTICULATED, AND SEMI-RIGID ANKLE DESIGNS
In order to transmit a dynamic weight bearing stretching force to the talocrural joint, the orthotic design must allow freedom of motion into dorsiflexion at this joint. Two primary methods are available to do this. First, the device can extend only as high as the malleoli, offering no direct control of the movement through the ankle. Foot orthoses and SMAFOs fall into this category. The second method is to apply a conventional height thermoplastic AFO with an articulating orthotic ankle joint. It could be argued that the semi-rigid solid ankle AFO design and its flexible derivative, the posterior leaf spring AFO, offer some limited ankle dorsiflexion mobility, but recent studies of their mechanical characteristics show off-axis talocrural malalignment 80 and poorly controlled collapse into variable dorsiflexion patterns under a weight bearing load. 80–83 Through appropriate design, articulated AFOs normally permit controlled and graduated dorsiflexion range, 84 and they more closely mimic talocrural axis rotation as compared to solid or posterior leaf spring orthoses. The clinical importance of accurate articulated co-axial joint alignment is to avoid a mechanical mismatch of internal talocrural joint motion and external orthotic motion. This reduces friction with its resultant skin breakdown 80 while also avoiding abnormal compressive forces to the articular surfaces and excessive tension to ligaments that constrain the joint. Articulated orthotic systems also form the foundation for proximal motion controls, providing the availability of limited orthotic joint stops for individual settings and selective patient mobility requirements. 85–87
The decision to use a mobile ankle joint if there is limited ankle dorsiflexion range of motion depends on many factors, including the medical diagnosis and prognosis, the duration of the tightness, and the age and activity level of the individual. Significant heelcord range can be gained in older adults even with long-standing histories of heelcord tightness. 71 Also, even with gastrocnemius muscle limitations in gait, some range may be available in the soleus muscle and this can be dynamically stretched through weight bearing, especially as the individual moves from sitting to standing.
Heelcord tightness is a prevalent problem in many diagnostic groups. Orthotic devices can be designed to increase soft-tissue range of motion at the talocrural joint. This requires special attention in order to prevent STJ pronation and compensatory dorsiflexion at the midtarsal joint. Orthotic interventions involve both passive and dynamic weight bearing stretching through splinting and orthoses. The devices must be designed to maintain the STJ in neutral and prevent pronation in order to lock the midfoot into its immobile position, thereby preventing compensatory midfoot dorsiflexion. In addition, both distal and proximal forces that push the STJ into pronation must be assessed to determine if these forces are a factor in the given individual’s case. If so, these must also be addressed in the orthosis design. For example, proximal forces pushing the foot into pronation may demand a conventional height articulated AFO rather than a SMAFO. If these factors are effectively accounted for, an orthotic device can be built, and it will assist in increasing or maintaining heelcord length.
We want to thank Lynne Wagner, PT, PhD and Bette Bonder, PhD, OTR/L, FAOTA for their review of the manuscript. Illustrations were drawn by Jeff Fetherston, LOP, LPed.
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