Managing patients after an ankle arthrodesis requires a good understanding of the mechanical objectives considered when making recommendations for postoperative conservative management. Residual alignment and distal pathomechanics are often the predominant factors precipitating pedorthic and/or orthotic need after ankle arthrodeses. Recognizing forefoot to hindfoot alignment, as well as tibial and knee angular considerations is necessary to fully succeed in helping those with residual discomfort or pathology. It is also necessary to foresee and discuss the need to accommodate and correct any length discrepancies and mechanical issues relative to the loss of ankle dorsiflexion and plantar flexion before the patient's surgical procedure. This paper will serve to explain the need and describe the methods in managing those after ankle fusions with pedorthic and orthotic modalities.
There are several objectives that should be considered based upon the clinical presentation with the primary often being the correction of the leg length discrepancy seen with some ankle fusions. Often the fusion will just be enough to accentuate an already existing shortened extremity, combined with the slightly altered gait, culminating in low back and or hip pain symptoms. Another objective is to provide for the loss of range of motion the fusion creates and to minimize the increased distal stresses. Examples of pathology occasionally seen or exacerbated after ankle fusions include, but are not limited to, hallux rigidus symptoms, sesamoiditis, transfer metatarsalgia, tibialis posterior tendonitis, plantar fasciitis, tibial, fibular, or metatarsal stress fractures, and an increase in symptoms relative to mildly degenerative distal articulations. Other objectives include assistance in simulation of plantar and dorsiflexion, accommodation of any residual deformity (equinus or varus), and provision of shock absorption.
Footwear needs after an ankle fusion may be unchanged, but often require some consideration as to the design and heel height. Ankles fused in slight equinus or those with a cavus foot structure may benefit from a higher heel construction versus flatter soled walking or athletic shoes. Generally, softer soled footwear works better to help with impact absorption and helps to simulate dorsiflexion and plantar flexion as a rocker-soled shoe would. Lace up, Velcro, t-straps, or a higher vamp construction also assists with minimizing heel slippage and allows for inside shoe heel lifts to be used to correct for leg length discrepancies of one half inch or less. Some consideration may have to be given for malleolar irritation from the counter of the shoe. This can usually be solved with a small inside shoe heel lift or footwear with soft rolled collars may be particularly helpful. The recent increase in the development and sales of softer soled, health conscious footwear has enabled those with ankle fusions significant latitude in footwear selection and subsequent comfort derived from them. Shoes with removable sock liners are valuable for those wearing prescription or over the counter foot orthoses. Most importantly, the patient should understand the shape and size of the shoe should match the shape and size of their foot. Many of the styles and designs worn preoperatively may not be viable selections due to their poor fit or construction characteristics. Remember, nothing feels better than a well-fit shoe.
Footwear modifications may enhance the outcome of an ankle fusion by working to smooth out gait anomalies and providing for lost motion. The most common modification necessary for those with an ankle fusion is a rocker sole. The rocker sole modification serves to facilitate the advancement of the tibial shank over the planted foot in light of a significant loss of dorsiflexion and plantar flexion (Fig. 1). The rocker sole may be supplemented with an extended steel shank in the presence of distal motion related pathology, particularly that of degenerative arthrosis.
Another footwear modification often used when caring for the fused ankle is a SACH (Solid Ankle Cushion Heel) modification (Fig. 2). This modification serves to simulate plantar flexion, cushions heel impact, and reduces the flexion moment about the knee generated at heel strike. Research has shown that a solid ankle (fixed ankle) foot orthosis induces a knee flexion moment at heel strike, and a knee hyperextension moment at heel off and toe off phases of gait. These principles easily apply to those with an ankle fusion. 1 It is very important to evaluate the quadriceps strength of those under consideration for an ankle fusion caused by the subsequent knee stressors created. This could dramatically impact the successful outcome, particularly those affected with poliomyelitis, Charcot Marie tooth disease, or any other neurologic process that may cause knee instability or weakness. Variations in rocker sole designs, as well as managing any leg length discrepancies, can certainly impact proximal joint stability.
The third most frequently dispensed shoe modification after an ankle fusion is a heel and sole elevation (Fig. 3). With the development of lightweight shoe modification materials, heel and sole elevations can be performed to a wide variety of newer, more fashionable, yet stable footwear. If the foot was fused in slight plantar flexion, the elevation can accommodate the alignment and facilitate a smoother rollover without a significant lateral displacement of the center of gravity that significant leg length discrepancies will undoubtedly create. Discrepancies less than one half inch may be corrected with an inside shoe elevation, any inequality greater than one half inch, should be measured for an external heel and sole elevation.
The final most frequently performed shoe modification after an ankle fusion is outflaring of the sole. The outflare serves to provide medial and lateral stability and provides stability to the distal articulations. In the case of a residual varus alignment, a lateral outflare can minimize symptoms associated with this positioning and can be incorporated into any of the other modifications previously discussed.
FOOT ORTHOSES CONSIDERATIONS
Foot orthoses may be indicated after an ankle fusion to help protect and align any residual forefoot to hindfoot alignment considerations. A patient with forefoot valgus or varus, or hypermobility of the first ray, may increase the stresses to the subtalar and midtarsal articulations and can precipitate postoperative distal pathology. A softer, multi-density designed foot orthosis, with aforementioned posting, can enhance fusion outcomes for several reasons (Fig. 4).
Primarily, a softer orthosis works to supplement lost shock-absorbing characteristics, while replacing any (if any) lost height of the affected extremity. A significant heel cushion can help to absorb heel impact while at the same time as correcting any minor length discrepancy. The orthosis secondarily works to correct any forefoot to hindfoot alignment considerations to reduce proximal stresses.
The foot orthosis may work to accommodate any residual plantar flexion, and allow the patient to use flatter soled footwear versus some form of heeled footwear as needed. Also, any foot orthosis will work to support the longitudinal and transverse arches, which evenly distributes plantar pressures and minimizes local overloads. In addition to footwear modifications, a well-constructed foot orthosis may enhance the clinical outcome after an ankle fusion while reducing any postoperative discomfort.
ANKLE FOOT ORTHOSES CONSIDERATIONS
Often, an ankle fusion is being performed to eliminate the need for bracing, as in the case of degenerative, arthritic ankle, or in the hemiparetic or neurologic patient. Unfortunately, some postoperative complications may present the need for ongoing use of an ankle foot orthosis. The two most common pathologies that may require using some type of ankle foot orthosis are tibial and or fibular stess reactions and/or fractures, and tibialis posterior tendonitis or dysfunction. In the case of a stress reaction proximal to the fusion site, a solid ankle foot orthosis with an anterior shell, plus or minus patellar tendon bearing characteristics may be indicated (Fig. 5). This device is normally used to calm down the stress symptoms and is eventually discontinued in most instances, with the exception of the rheumatoid or diabetic populations, where it may be required indefinitely.
The second design for an ankle foot orthosis is the short articulated ankle foot orthosis (Fig. 6). This orthosis was developed specifically for hindfoot and midfoot pathologies, particularly tibialis posterior tendon dysfunction and subtalar osteoarthrosis, which makes this device extremely useful in those with distal symptoms after an ankle fusion. 2 The incorporation of a soft, foot orthosis within the ankle foot orthosis can correct any forefoot to hindfoot alignment deviations while absorbing shock within the orthosis. Usually, the use of any ankle foot orthosis after an ankle fusion is temporary in nature but may be a necessary in managing any subsequent postoperative symptoms or complications.
Successful management of those who have undergone an ankle fusion is dependent upon a comprehensive understanding of the objectives of postoperative footwear considerations, modifications, and orthoses used to enhance the clinical outcome of this procedure. It is important for the surgeon to educate the patient that the procedure may still require some degree of postoperative pedorthic or orthotic intervention to assist in the short or long term follow-up outcome.
There are no studies to support how these techniques raise or better the clinical outcome, but in the case of any residual alignment consideration or complication, pedorthic and orthotic intervention should be an adjunct treatment alternative. Although much of this theory is anecdotal at best, this author has seen the benefits of good postoperative pedorthic care often enough to believe that every ankle fusion patient should be introduced to a pedorthist or orthotist at some point after the procedure, if to do nothing more than to provide sound footwear advice.