Orthoses
Conservative treatment eases PTTD impact
BY ROGER MARZANO, CPO, CPed
To understand how conservative treatment of posterior tibial tendon dysfunction affects gait, the function of the posterior tibial tendon in normal gait must first be clarified. Action of the posterior tibial tendon begins at its origin at the tibialis posterior muscle, which is found deep in the posterior compartment of the leg, at the beginning of the posterior surfaces of the proximal tibia and fibula, as well as the interosseous membrane of the leg. The PT tendonis formed in the distal third of the leg and travels posterior to the medial malleolus and on to its broad insertion at the nav-icular tuberosity, the plantar capsule of the medial navic-ular-cuneiform joint, and the plantar medial cuneiform. The origin and insertion create the desired normal actions across three joints of the foot/ankle complex.
Those actions primarily consist of plantar flexion of the talocruraljoint, inversion of the sub talar joint, and locking of the transverse tarsal joint, which in turn provides the rigid lever necessary for normal propulsion. With this action in mind, the importance of normal tendon function and length cannot be overemphasized.
Figure 1. The rigid UCBL orthosis is commonly prescribed for triplanar control of the foot.
Pathophysiology of the tendon includes elongation caused by the repetitive strains of supination and inflam-
mation associated with tenosynovitis, which contributes further to degeneration or rupture of the tendon. Johnson and Strom1 and Myerson2 classified posterior tibial tendon dysfunction into four stages involving classification of tendon degeneration and bony alignment. Some form of conservative treatment is most often prescribed for the latter three stages. Of these, end-stage deformities are the least responsive to intervention with orthoses.
Much has been written about the pathophysiology of the tibialis posterior tendon, including discussion of the presence of an accessory navicular contributing to the pathology; most authors agree that PTTD can cause severe deformities in the foot. Gastrocnemius and/or soleus con-tractures can contribute further to breakdown of the talon-avicular joint and must be considered when treating PTTD conservatively. Dysfunction of the tibialis posterior tendon can severely affect the performance of the foot/ankle complex, and can be further complicated by valgus alignment of the knee, which may be a contributing factor and is often seen by those treating PTTD.
To further understand the effects of PTTD on gait, we need to review possible treatment alternatives. Conservative intervention often begins with footwear. Extended medial counters, flared heels and soles, and broad midfoot construction are all desirable characteristics that can help when shoes fit and are worn appropriately. In the later stages of PTTD, custom-made shoes may be the only available footwear alternative due to the significant deformities often seen with this disorder.
Footwear treatments
Footwear modifications are often helpful in managing the myriad of clinical presentations associated with PTTD. Reinforcing the medial counter of the shoe with crepe or other materials can help the shoe support the foot and prevent breakdown of the medial column of the foot. Medial sole flaring and wedging can help attain the desirable effect of reducing tension on the posterior tibial tendon when used either in conjunction with or independent of the medial counter reinforcement. In more fixed deformities, splitting and widening, or relasting, when used with a custom foot orthosis, is an excellent method of widening the base of the shoe to provide strong medial column support. This shoe modification also allows for the forefoot abduction so often seen with this deformity, and serves to reduce lateral toe pressures.
Rigid rocker soles can assist in providing a rigid lever for better toe-off capabilities and can smooth out the gait of those with later stages of PTTD. It is important to note that the rocker sole should be sanded in the line of progression, which is unique to each patient based on the severity of the foot deformity.
Orthotic options
Foot orthoses are frequently prescribed as a primary treatment alternative for those with PTTD. A basic rule that can be followed when offering recommendations to or fitting patients with PTTD is that the more flexible the foot structure, the more rigid the orthoses can be. Conversely, the more rigid the foot structure, the more shock absorbent the orthoses should be. Another important point when providing foot orthoses for this pathology is to evaluate and recognize any equinus contractures that are present. If the foot cannot dorsiflex 10° with the knee extended and the calcaneus at neutral or slightly inverted, a heel lift may need to be incorporated in the orthosis. This will serve to reduce the forces acting about the subtalar joint, further minimizing midfoot collapse.
Those patients in the early stages of this disorder, while the foot still has some flexibility, appear to find rigid orthoses more amenable to their condition. The UCBL orthosis has, since its development, been commonly prescribed for triplanar control of the foot (Figure 1). The high medial and lateral walls of the orthosis work to limit pronation and forefoot abduction while the heel cup controls the eversion tendencies associated with PTTD. Softer multidensity designs can be effective and comfortable when treating more significant deformities. Hindfoot and forefoot posting are critical components in any foot ortho-sis and can make or break the attempt at conservative treatment.
Since hypermobility of the first ray and forefoot varus in some goes hand in hand with this pathology, full-length orthoses can and should incorporate the forefoot posting necessary to assist the dysfunctional foot with propulsive needs at heel-off and toe-off.
Ankle foot orthoses provide an additional conservative treatment alternative when conventional shoe and foot orthosis therapy fails. Traditionally, a double-upright AFO attached to a custom or medical-grade shoe, with or without a medial t-strap, has been a mainstay of AFO use for the PTTD foot. Thermoplastic designs can and should be considered for this patient population, particularly the short articulated AFO with an incorporated soft interface.
The short articulated AFO (Figure 2) is an excellent treatment alternative for those with PTTD, as the short anterior shell helps reduce the internal rotation of the tibia that accompanies pronation. The incorporated soft interface can provide medial forefoot varus posting to help align the foot and at the same time protect the medial bony prominences seen with this foot disorder.3
When presented with significant end-stage nonopera-tive deformities, a solid ankle or a patellar tendon bearing (PTB) design AFO may be the only option left. The solid ankle AFO or PTB can assist in controlling end-stage patients by reducing the advancement of the tibia over the planted weight-bearing foot, further diminishing pronato-ry stresses and providing maximum hindfoot control. The PTB-design AFO is a necessary option for those deformities or secondary ankle-joint arthrosis often seen in later stages. Any AFO that limits ankle-joint motion should be used in conjunction with a rocker sole to provide for lost motion and to minimize gait irregularities.
Altered gait
With these basic conservative treatment objectives outlined, we can begin to understand the impact of these treatment alternatives on gait as well as the influence this disorder has on gait when no treatment options are attempted. In normal human locomotion, it is necessary for the ankle to dorsiflex 10° over the planted foot with the knee in extension. This dorsiflexion takes place from the foot-flat to heel-off stages of gait. It is at this time that the posterior tibial tendon is most active to reduce longitudinal arch depression and begin locking the midtarsal joint for efficient propulsion, including ankle plantar flexion at heel-lift and toe-off.
In the dysfunctional foot, the longitudinal arch depresses excessively, the forefoot abducts further, and the midtarsal joint never achieves a locked position. Because of this action, the talar head continues on a plantar-grade course, the forefoot abducts even further, and the dorsiflexion needed for tibial advancement takes place at the midfoot rather than the ankle, never allowing the foot to become a rigid lever for propulsion. Continued ambulation with this faulty alignment will progressively shorten the gastrocnemius-soleus complex, further feeding the progression of this disorder. The resulting antalgic gait presents in several ways.
There is a shorter stance phase on the affected extremity due to pain avoidance, as well as marked decrease in stride length to minimize the painful pronato-ry forces exerted on the foot. The shorter stride length is also a product of the marked increase in forefoot abduction, which, at the same time, shortens the distal lever that the foot normally creates for efficient propulsion, further minimizing stance-phase timing. It is important to note knee alignment in this patient population, in that many of those treated for PTTD also have a predisposing valgus alignment of the knee. The valgus alignment of the knee widens the base of support, which further increases the valgus hindfoot stresses normally present in gait. All of these points combined make for painful, energy-inefficient gait.
Orthoses and footwear can have a tremendous impact on these gait deviations, as well as decreasing significant pain and progression of the deformity. Medial posting, whether on the orthosis or the shoe, can reduce the endpoint of the deformity and provide a more stable, better aligned medial column for propulsive phases of gait. Reducing the forefoot abduction, either with a UCBL or by adjusting the lateral trimlines of an AFO, combined with medial or sometimes even lateral forefoot posting, will help align the forefoot. Medial hindfoot posting and a mild heel elevation may help reduce the hindfoot valgus position and the negative effects of a shortened gas-trocnemius and soleus, while at the same time reducing the subfibular impingement often associated with PTTD. The heel counter of the shoe, the heel cup of the UCBL, and the tibial component of an AFO all work to reduce hindfoot valgus or excessive eversion and can be effective in maintaining better alignment of the subtalar complex, improving the efficiency of the foot/ankle complex as a whole.
Any changes that can help minimize the flexible deformities, as well as stabilize the more rigid structures, will result in a more energy-efficient gait with longer strides,and greater distances traveled with less discomfort. The benefits of shoe modifications that help to normalize gait, particularly rocker soles with extended shanks for those with more significant involvement, cannot be underestimated. They serve to advance the tibia over the foot by simulating dorsi-flexion and plantar flexion, while the extended shank can simulate the rigid column necessary for normal propulsion and at the same time reduce pain and increase endurance.
It would be difficult to determine what percentages pain and inefficient biomechanics contribute to disruption of normal gait, but we do know that PTTD affects a large part of our patient population. By addressing faulty mechanics, improving alignments, and decreasing endpoints of the deformities using various conservative modalities, we can have a tremendous impact on the efficiency of normal human locomotion, and more importantly, reduce the associated pain often seen with posterior tibial tendon dysfunction.
Conservative measures are usually effective to some degree, and more emphasis on prevention through footwear and orthoses can have a significant impact on overall foot health. Many of the patients we treat for plantar fasciitis, Morton's neuroma, and tarsometatarsal arthrosis may also be suffering with the deformities frequently seen with PTTD. Whatever the reason, PTTD can affect gait significantly, but we can respond with focused treatment and implement sound alternatives as outlined here to direct patients toward a more normal gait. %
Roger Marzano, CPO, CPed, is past president of the Pedorth-ic Footwear Association and is employed by Yanke Bionics in Akron, OH, as a staff clinician.
References
1. Johnson KA, Strom DE. Tibialis posterior tendon dys
function. Clin Orthop Rel Res 1989;239:196-206.
2. Myerson MS. Adult acquired flatfoot deformity. J Bone
Joint Surg 1996;78A:780-792.
3. Marzano R. The shorter cure for tibialis posterior tendon
dysfunction. Biomechanics 1995; 2(10):43-45
