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How A New Generation Implant Can Treat Symptomatic Pes Plano Valgus

An increasing number of pediatric, adolescent and adult patients are presenting to surgeons with symptomatic pes plano valgus as a primary diagnosis or secondary to posterior tibial tendon dysfunction. The diagnosis and treatment of this disorder can be both challenging and rewarding for the foot and ankle surgeon and the patient.
Chambers first reported the extraarticular subtalar arthroereisis in 1946 and the use of a bone graft to elevate the sinus tarsi and decrease pronation.1 LeLelievre reported a similar procedure in 1970.2 The procedure and technique became popular in the United States when Subotnick described inserting a custom carved silicone conical wedge in the sinus tarsi space.3 In 1976, Smith described placing a stemmed polyethylene block (STA-PEG procedure) into the floor of the sinus tarsi.4 Lundeen modified the implant’s dorsal aspect for a smoother transition of the talus over the implant.5
These procedures and implants were primarily used to treat children and young adolescents. Brancheau, et. al., reported the use of a titanium screw in 1996.6 Lepow reported on the titanium Conical Subtalar Implant (CSI) and the Domed Subtalar Implant (DSI) in 2003.7
Flexible pes plano valgus is considered a weightbearing collapse of the medial longitudinal arch, which appears normal when weightbearing. During midstance, one can observe a maximally pronated subtalar joint with an averted calcaneus, often with abduction of the forefoot on the rearfoot.8 Commonly, there would be an associated ankle equinus deformity.

The history of present illness usually includes symptoms of clumsiness, limping or antalgic gait, fatigue and associated sedentary behavior, night pain or cramps. Pedal ligamentous laxity with a hypermobile/unstable subtalar joint is present with possible ankle equinus and related foot and ankle deformities.9 In older patients with chronic posterior tibialis tendon dysfunction, pain and progressive foot deformity are present.10
Radiologic examination consists of weightbearing AP and LAT views in the angle and base of gait. Often, a calcaneal axial view may help rule out tarsal coalitions. On the AP view, measure the talocalcaneal (Kite’s angle) and talar first metatarsal angles. Additionally, one may observe a talonavicular subluxation. On lateral views, measure the calcaneal inclination, talar declination and talar first metatarsal (Meary’s angle). Additionally, an anterior break in the cyma line is consistent with pes plano valgus. Utilize ankle and/or medial oblique views for further determination of the presence of tarsal coalition and tendon/ligamentous damage secondary to posterior tibialis tendon dysfunction.
One would develop treatment algorithms based on the patient’s age and severity of deformity. Numerous procedures have been described including the subtalar extra arthroereisis with or without ancillary bone and soft tissue procedures.
The objectives of subtalar arthoereisis include symptomatic relief, improving biomechanical function and improving foot function and appearance. The subtalar joint implant allows preservation of the subtalar anatomy while limiting excess pronatory motion. One would accomplish this by limiting the anterior and plantar migration of the talus, often with a tendo-Achilles lengthening or gastrocnemius resection, to negate the influence of ankle equinus on the foot. Anticipated outcomes include decreased frontal plane heel valgus, improved medial arch height on weightbearing and decreased pronatory subtalar joint and midtarsal joint motion.

Pertinent Pearls For Using The CSI
The CSI’s implant geometry accommodates the sinus tarsi anatomy, aids in insertion and allows for adjustments in blocking motion. The implant is available in six sizes and the length varies with the diameter for anatomic fit. Progressively softened threads reverse the edge effect that may lead to pain (sinus tarsitis) yet those threads are also designed to resist migration. Features also include apertures to allow for soft tissue ingrowth. The instrument system is fully cannulated to guide accurate insertion.

In regard to the procedure, one would place a 2- to 4-cm incision on the lateral aspect of the subtalar joint within the relaxed skin tension lines. Continue blunt dissection to the lateral subtalar capsule. Make a small incision there to allow for access of a dissection scissor, which dilates the sinus tarsi space. Then proceed to insert the cannulated probe and advance it in a twisting motion toward the medial foot near the talonavicular joint, gently tenting (not exiting) the skin. Then place a guide pin through the probe and remove the probe assisted by a thumb press. Place a trial sizer into the sinus tarsi gently over the guide pin to approximately one-third to one-half the distance across the subtalar space.
Assess range of motion and perform intraoperative fluoroscopy to confirm the location. Note the laser-scored ruler on the insertion instrument as the skin drapes over the proximal aspect of the instrument. Upon loading the foot with the proper sized implant, one should observe decreased talonavicular joint subluxation, decreased talar declination and limited calcaneal eversion.
If an associated equinus deformity is present, perform a tendo-Achilles lengthening or gastrocnemius resection prior to the arthroereisis.
Post-op care includes a weightbearing cast for two to four weeks followed by offloading in a below the-knee boot for two to four additional weeks, depending on additional procedures. Follow this with progressive weightbearing. Patients should limit impact sports for two to three months, depending on additional procedures.

What The Data Reveals
Ten non-associated podiatric surgeons from various regions of the United States submitted demographic data and measurement results of five preoperative and postoperative angles on 120 patients undergoing the CSI implant with or without additional procedures.11

Independent statisticians performed an analysis using a paired t test and a two-way analysis of variance (ANOVA). The paired t test on angles taken preoperatively compared to those taken postoperatively (degree of change) were highly statistically significant with a p value of < 0.0001. An ANOVA test, used to evaluate the effects of variables of age and operative limb, indicated no difference for all angles. The variable of additional procedures yielded a minor difference in the calcaneal inclination angle only but it was not statistically significant.
A similar 2003-04 survey tracked 39 patients from five non-associated surgeons. Similar results were reported from the first year of tests.12
Clinical evaluation of the CSI arthroereisis implant demonstrates highly statistically significant improvement in all five of the standard angles evaluated. The objectives of symptomatic reduction, improvement in biomechanical function, and improvement of foot position appearance were all met and consistent with the statistics that were evaluated. These cross-sectional surveys will continue annually for five years. During the sixth year, we will attempt to recall those patients from years one and two for reevaluation and comparative measurements.

By Gary M. Lepow, DPM, MS, FACFAS, and Scott MacTavish, DPM
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