Subtalar Osteoarthritis: Diagnosis and Treatment Options
Subtalar osteoarthritis (STOA) is often secondary to chronic ankle sprains or trauma, which seriously affects the quality of life of patients. As many as 78% of chronic ankle instability patients develop posttraumatic ankle osteoarthritis. The subtalar joint refers to the joint between the talus and the calcaneus. It is a complex joint involved in human locomotion and plays an important role in shock absorption and propulsion. This joint is designed to provide either a flexible shock absorption construct to the foot or a rigid propulsive one.
Every time the subtalar joint is everted, or in valgus, the foot will become a flexible structure because the transverse tarsal joints are unlocked. When the subtalar joint inverts, the transverse tarsal joints lock themselves, and this provides a rigid lever arm, which is beneficial for locomotion . The subtalar joint is divided by the sinus tarsi, into the talocalcaneonavicular joint anteriorly and talocalcaneal joint posteriorly. This fact explains why just the posterior subtalar facet is visible from the more classic surgical approaches, which do not violate the sinus tarsi.
A detailed history and physical examination must be performed when a patient presents with subtalar pain. Difficulty when walking on uneven grounds is a classic symptom, which is taught but not always present. Pain is typically found in the posterolateral aspect of the hindfoot, close and around the sinus tarsi area, or it can radiate from the posterolateral to the posteromedial aspect, including the posterior aspect of the hindfoot. Rarely, pain will be found at the anterior aspect of the hindfoot, where the ankle joint is assumed to be the source of pain. Motion at the subtalar joint is not easy to examine, because subtalar joint range of motion can be mistaken for ankle joint motion, but contralateral examination can help. Hindfoot alignment is a prerequisite, with the patient standing, from the front and from the posterior aspect. Normal mechanics must be checked; for example, when asking the patient to stand on the tip of the toes, the hindfoot must invert, and when the foot lands on the ground, a smooth eversion and pronation must occur.
The onset of clinical symptoms of pain and dysfunction may occur years or decades after the original injury. Patients present with ankle and hindfoot joint pain that is worse with activity or weight bearing, and instability, stiffness, or swelling that is initially relieved by rest. The onset of symptoms is usually insidious with slow progression over time.
Imaging evaluation must be tailored to specific clinical scenarios and includes weight bearing radiography that utilizes standard and specialty views, computed tomography which can be performed with a standard or a weight bearing technique, magnetic resonance imaging, and ultrasound evaluation. Imaging generally begins with radiographic imaging of the ankle. Most providers obtain complete leg standing radiographs, which include the foot. Some may order classic axial or Salzman views.
Computed tomographic (CT) scan is also useful because it evaluates the extent of the deformity, besides ruling out a coalition. Single-photon emission CT has been in use in the last few years because it allows identifying the source of pain when internal fixation is present, especially in posttraumatic cases whereby the origin of pain is not well defined by conventional imaging methods. Magnetic Resonance Imaging (MRI) can also be used if needed since plain films do not permit full characterisation of non-ossified structures, such as articular cartilage, marrow tissue and synovial fluid any early change of degeneration can be missed. In addition, the bones and joints have complicated shapes making diagnosis of joint space narrowing or degeneration difficult to diagnose on plain standing radiographs without special views.
Nonoperative treatment should aim to reduce pain, limiting somehow hindfoot motion. Classic conservative treatments include weight modifications, analgesic medications, subtalar joint injections, shock absorption elements such as shoes or insoles, and special insoles made to limit hindfoot motion. Medially posted insoles can reduce eversion movements with respect to the hindfoot, and therefore, may help in controlling subtalar pain. Rocker bottom shoes have become popular over the past decade.
Intraarticular injection of glucocorticoids with or without anesthetic is a popular treatment option for ankle OA as well as for other forms of arthritis throughout the body. This treatment option is often employed when subtalar osteoarthritis is refractory to the more conservative modalities. Generally, the wide variability in reported efficacy may be attributed with post-traumatic ankle arthritis to the equally variable success rate of needle positioning—30– 80%—when solely using manual palpation for guidance . Employing ultrasound to guide injections has increased the upper limit of the needle positioning success rate—32– 97%—and decreased the rate of complications related to manual error .
US guided subtalar joint injections can be challenging due to the contours of the foot and ankle. There are three different approaches described and frequently used: posteromedial, posterolateral and anterolateral. Posterolateral approach is the most commonly used. The posterolateral approach provides the opportunity to perform the injection using a long-axis approach (in plane) relative to the transducer, thus enabling visualization of the entire needle shaft and tip throughout the procedure .
Viscosupplementation (VS) has gained traction in the treatment of post-traumatic ankle arthritis, including the talocrural and subtalar joints. A study by Murphy et al. demonstrated efficacy regarding injections of hyaluronic acid (HA) VS as an adjunctive treatment for symptomatic ankle arthritis using pre- and posttreatment Foot and Ankle Outcome Scores . Further, a recent systematic review of VS in ankle OA determined this treatment modality to have good efficacy in improving patient functionality scores; though, not significantly better than other nonoperative modalities .
One recent study compared corticosteroid injections versus hyaluronic acid mixed with corticosteroid injections in twenty-five patients with subtalar osteoarthritis. It was shown that the group receiving both hyaluronic acid and corticosteroid had better pain and function at four, twelve and twenty four weeks compared to the corticosteroid injections alone.
Injection of local anesthetic, while giving very short-term pain relief, may assist in determining the patient’s source of pain in the presence of multiple confounding factors. In addition to confirming the placement of the needle during fluoroscopically guided joint injection, intraarticular administration of contrast may demonstrate the presence of communication between the ankle joint and the subtalar joint. Such communication results in medications being delivered to both joints and needs to be considered when interpreting symptom relief and when planning further surgical procedures, such as ankle fusion or subtalar fusion .
There is paucity in evidence in regards to platelet rich plasma (PRP) for subtalar osteoarthritis, although there is data suggesting benefits of platelet rich plasma for ankle osteoarthritis. Mei-Dan et al. studied the efficacy of intra-articular hyaluronic acid vs PRP injections over a 28- week follow-up period in 30 patients with osteochondral lesions of the talus . They found that patients in the PRP group reported less pain and better functionality. Angthong et al. observed an improvement in pain, with a mean follow-up of 16 months following the PRP injection; however, MRI studies did not show any radiological improvements . Repetto et al. reported that PRP injections once a week for a month were effective in delaying the indication for surgery in patients with ankle OA .
When conservative treatment fails, a surgical intervention is justified. Subtalar arthrodesis is an accepted surgical treatment of subtalar pathologic conditions whereby conservative treatments have failed to provide a successful outcome. Common indications for subtalar fusion are post traumatic or degenerative arthrosis, arthritis, talocalcaneal coalitions, and complex deformities.
Arthroscopic subtalar arthrodesis has proven to offer at least similar results, and may achieve higher rates of fusion and lower complication rates than open techniques. It has been shown to be a safe and reliable procedure, provided surgical technique is carefully followed. It provides a high union rate without needing supplementation by bone graft, with an acceptable rate of complications. Overall, AOFAS scores improved significantly and patient satisfaction was acceptable for more than five years .
In summary, subtalar osteoarthritis is often secondary to chronic ankle sprains or trauma, which seriously affects the quality of life of patients. It will likely be encountered in a sports medicine practice and providers need to be comfortable with diagnosis and treatment options. Use of the ultrasound or fluoroscopy makes injections into the subtalar joint feasible and accurate. Emerging evidence exists for viscosupplementation and more studies are needed with platelet rich plasma or stem cell therapy. When conservative measures do not produce satisfactory results, surgical intervention is indicated.
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