Ankle arthrosis commonly occurs after a major traumatic ankle injury. A pilon fracture may cause arthrosis of the tibiotalar (ankle) joint; a depressed calcaneal can cause subtalar arthritis. Arthrosis is also seen after less severe injuries, especially if those injuries cause malalignment. Unlike the knee and hip, the ankle joint is relatively uncommon site for the development of primary (idiopathic) osteoarthritis. Arthrosis of the ankle is also treated with methods that would not be used in the knee or hip, as loss of motion to limit pain is fairly much better tolerated in the ankle. Thus, bracing and (in more extreme cases) surgical fusion is a commonly used methods of treatment.
The ankle joint (talocrural or tibiotalar joint) is formed between the distal tibia and fibula and proximal talus. The superior talar dome has three articulating surfaces – medial, central, and lateral – that articulate with the medial malleolus, tibial plafond, and lateral malleolus, respectively. These articulations provide bony stability to the ankle joint when it is in a neutral or dorsiflexed position. In plantarflexion, the ankle joint has considerably less bony contact, and relies more in that position on the surrounding ligaments to provide the majority of stability.
The hindfoot consists of the calcaneus and talus. The inferior aspect of thel talus articulates with the calcaneus inferiorly, forming the subtalar joint. The subtalar joint facilitates inversion and eversion of the foot.
The talus is mostly covered by articular cartilage, leaving little bone for vascular penetration. This lack of vascularity predisposes the talus to slow healing and avascular necrosis.
Pathophysiology of osteoarthritis
The ankle joint surfaces are highly conforming, that is the surfaces have broad areas of contact. This allows the forces of weight-bearing to be spread out over a maximally large area and in turn minimizes focal joint pressure (Figure 2).
Injuries that damage the articular surfaces can decrease contact area, leading to high pressure in certain spots and predisposing the joint to further damage and arthrosis.
The process of osteoarthritis begins with the breakdown of the joint surface and irritation of the synovium. Thereafter, there is impairment of chondrocyte function and sclerosis of the bone. In the final phase, there is overt disorganization and degeneration. Specifically, when the smooth articular cartilage is damaged, it becomes rough. Friction against the rough surface creates cartilage particles. The synovium absorbs these particles and may undergo a chronic low-grade inflammatory response, producing enzymes that cause further damage. In severe osteoarthritis (Figures 3 and 4), erosion of the articular surface can expose subchondral bone, allowing synovial fluid to enter the cancellous bone causing cysts. The subchondral bone may also thicken due to focal loading
Osteoarthritis of the ankle and hindfoot is generally post-traumati. Primary arthritis of the ankle, in contrast to the knee and hip, is rare.
Figure 2: Normal ankle joint. Credit: http://www.footeducation.com/wp-content/uploads/2010/08/Ankle-Arthritis-Figure-1.png
Figure 3: x-ray of severe ankle arthritis. Note joint space narrowing at the talocrural joint. Credit: http://www.footeducation.com/wp-content/uploads/2010/08/Ankle-Arthritis-Figure-2.jpg
Figure 4: x-ray of subtalar arthritis. Note joint space narrowing at subtalar joint. Credit: http://www.footeducation.com/foot-and-ankle-conditions/subtalar-arthritis/figure-1-subtalar-arthritis/
Osteochondral lesions of the talus can be thought of as a form of localized arthrosis: there is focal cartilage (and possibly bone) damage involving a relatively small portion of the ankle joint (Figure 5), although often the remainder of the ankle joint is normal. Osteochondral lesions of the talus are caused by compressive and rotational forces that shear the cartilage and crush the underlying subchondral bone. Osteochondral lesions of the talus can involve cartilage only, cartilage and bone, subchondral bone with intact cartilage, or be cystic; they can also be classified according to whether they are stable/unstable and whether they are displaced or undisplaced.
Virtually all lateral lesions are due to trauma compared to only 60% of medial lesions. Lesions not caused by trauma may be caused by chronic overload to the foot, repeated microtrauma, avascular necrosis, and congenital factors.
Osteochondral lesions of the talus have poor healing due to the general avascularity of articular cartilage but also the tenuous vascular supply of the talus itself.
Figure 5: x-ray of medial osteochondral lesion of the talus. Credit: http://www.footeducation.com/wp-content/uploads/2010/08/OCD-Figure-3.jpg
Patient presentation will vary depending on the type and location of arthrosis. In general, patients with hindfoot arthritis will present with pain, stiffness, and swelling. Symptoms are often exacerbated by activity. It is important to determine the exact nature, location, duration, and progression of symptoms to narrow down the type of arthrosis and structures affected.
Localizing the area of maximal discomfort can narrow the differential. In the case of ankle osteoarthritis, pain is often on the anterior aspect of the ankle joint. In subtalar arthritis, the pain is often localized to the lateral hindfoot. Patients with talar lesions often complain of localized ankle pain on either the medial or lateral sides of the ankle.
Identifying aggravating and alleviating factors can also help to identify the location of the arthritis. Pain with plantarflexion can indicate a posterior lesion, while dorsiflexion may aggravate an anterior lesion. In fact, some patients may wear high-top boots or shoes after they discover that these shoes alleviate symptoms by preventing excess dorsiflexion. Subtalar arthritis is commonly aggravated by walking on uneven ground because inversion/eversion occurs primarily at the subtalar joint.
Crepitus, catching, locking, grinding or the sensation of a loose body should increase your suspicion for an OLT with an unstable fragment. However, some patients with OLTs are asymptomatic and identified as an incidental finding on an MRI for another problem.
Patients with ankle or hindfoot arthrosis frequently describe a history of trauma to the joint. It is important to determine the type of injury – fracture or sprain – and the structures involved. A history of ankle inversion injury that doesn’t improve with conservative treatment should heighten the examiner's suspicion for a persistent cartilage injury.
In patients in whom a history of trauma is not recalled, asking about personal history or family history of inflammatory arthritis (ex. rheumatoid arthritis) is important, though inflammatory arthritis normally presents elsewhere before affecting the ankle.
When evaluating a patient, check the alignment of the lower extremity –including the alignment of the knees and the hindfoot.
Determine the motion of the ankle and hindfoot joints by assessing ankle dorsiflextion and plantarflexion -and hindfoot inversion and eversion.
Assess for ankle stability using an anterior drawer test.
Other physical exam findings may include a joint effusion, tenderness to palpation over medial and/or lateral joint lines, decreased strength or calf atrophy from relative disuse.
Subtalar arthritis will tend to have hindfoot swelling, tenderness within the tarsal sinus, pain with inversion/eversion, and limited ROM at the subtalar joint. As always, perform a detailed neurovascular exam to look for weakness, loss of sensation, and decreased or absence of sdstal pulses.
Radiographic imaging is used to confirm a clinical diagnosis of arthrosis and often establishes the definitive diagmosis of arthritsi. Weight-bearing anterior-posterior, lateral, and mortise/oblique views of the ankle and foot are required. Two additional views can also be used to evaluate the subtalar joint:
- Broden’s view: Foot internally rotated 45 degrees. X-ray angled 10-40 degrees cephalad. Used to evaluate the posterior subtalar facet.
- Canale view: Foot pronated 15 degrees. X-ray aimed 75 degrees from horizontal on AP view. Used to evaluate the tarsal sinus.
Plain x-rays may demonstrate one or more of the four cardinal signs of arthritis:
1. narrowing of the joint space,
2. bone spurs (osteophytes),
3. subchondral cysts, and
4. bone whitening (subchondral sclerosis).
Radiographic imaging will not catch a purely cartilage injury or underlying bone edema. In these cases, if arthrosis is suspected but not visualized on x-ray, other imaging modalities (CT and MRI) are necessary to visualize the lesion. These modalities may also help determine if there is another source of pain (e.g., posterior tibial tendonitis, peroneal tendonitis, etc.).
MRI is a powerful tool because it can assess concomitant soft tissue pathology and chondral lesions with great accuracy (Figures 7 and 8). However, an MRI should only be ordered when there is a specific clinical question that needs to be answered (ex. “Does this patient have a OLT that is not seen on plain x-rays?”) and the answer to that question will change your management (Given this patient’s symptoms if he/she has a large OLT on MRI I will recommend surgery).
An MRI is rarely used in the diagnosis or treatment of ankle osteoarthritis, but it is more useful when focal talar lesions are suspected. MRI is the most sensitive tool for diagnosing these lesions because of its ability to detect bone bruising, cartilage damage, or fluid surrounding the lesions
Figure 7: MRI of medial OLT. Credit: http://www.orthopaedicsone.com/display/Main/Osteochondral+lesions+of+the+ankle
Figure 8: MRI of lateral OLT. Credit: http://www.footeducation.com/wp-content/uploads/2010/08/OCD-Figure-2.jpg
Laboratory tests are generally not useful in diagnosing primary arthrosis but can be used to exclude other conditions such as rheumatoid arthritis and gout.
A diagnostic injection of local anesthetic into the ankle or subtalar joint can also confirm a diagnosis of ankle or subtalar arthritis. For example, if the pain is relieved for a few hours with an injection into the subtalar joint it suggests that the pain is likely originating from that joint.
Osteoarthritis of the ankle and hindfoot is less common than in other limb joints, partly because primary osteoarthritis of the foot and ankle is rare compared to the knee and hip. In a study by Saltzman et al (PMID: 16089071), of 639 patients with ankle arthritis, 70% were post-traumatic, 12% were rheumatoid in nature, and only 7% were idiopathic primary osteoarthritis. Loss of function and disability (limited walking ability, chronic pain, lower limb instability) are long-term consequences of ankle and hindfoot arthrosis.
Many conditions can present like ankle and hindfoot arthrosis.
Before deciding on a diagnosis of arthrosis, it is necessary to rule out the possibility of inflammatory arthritic conditions like rheumatoid arthritis, gout, and infectious arthritis. Obtaining a personal and family history of arthritis will help to narrow the differential. Lab tests like CBC, ESR, CRP, and immunohistochemistry can also help to identify inflammatory arthritic conditions.
Trauma is often the cause of arthrosis. The precipitating injuries include those such as a pilon fracture which damage the surfaces directly; ankle fractures that heal with asymmetric joint loading, or even recurrent ankle sprains that cause repetitive shear injuries to the ankle joint.
Avascular necrosis (also known as osteonecrosis) may present with symptoms typical of arthrosis before overt joint destruction is seen.
Monoarthritis of the ankle or hindfoot is usually post-traumatic. The absence of such a history can be thought of as a red-flag to prompt investigation of a systemic condition that may be responsible.
Non-operative treatment is indicated in mild to moderate arthrosis. It normally involves oral non-steroidal anti-inflammatory drugs and/or analgesics, physical therapy, and ankle stabilization. General exercise and activity modification can also help to prevent pain and progression of symptoms. In severe cases, intra-articular corticosteroid injection may be necessary to provide short-term pain relief.
Physical therapy is an important aspect of non-operative care early in the course of treatment, to maintain range of motion, strength, and proprioception and thereby decrease the likelihood of leg atrophy over time. Exercise may help maintain an ideal body weight because a high BMI can lead to excessive force on the affected joints.
Ankle support is an important aspect of non-operative care that can minimize painful joint motion and relieve pressure points. There are many ankle support options ranging from simple over-the-counter shoewear modification to braces to custom-molded ankle-foot orthoses (AFOs).
Operative treatment is indicated in patients with severe osteoarthritis when conservative treatment has failed. Several different surgical options exist for the treatment of osteoarthritis.
Arthroscopy: Arthroscopic procedures include synovectomy, debridement, loose body removal, excision of bone spurs, and chondroplasty. Effectiveness has not been assessed in randomized controlled trial, however.
Tibial osteotomy: Some cases of ankle arthritis stem from a tibial deformity that leads to poor load distribution across the ankle joint. Tibial osteotomy can correct alignment, and improve load distribution across the ankle joint. It is indicated in young patients with a varus or valgus deformity and mild to moderate arthritis caused by a tibial deformity.
Ankle arthrodesis (Figure 9): Ankle arthrodesis (tibiotalar fusion) is one of the most predictable means of reliving severe pain from ankle arthritis. The fusion can be performed open or arthroscopically – fusion rates are similar between the two, about 80 to 90%. The major disadvantage of arthrodesis is that it sacrifices the plantarflexion and dorsiflexion movements of the ankle joint. The lack of ankle motion from fusion may be mildly impairing and may also accelerate arthrosis in the subtalar joint.
Figure: Ankle arthrodesis (ankle fusion). In order to maximize the motion in surrounding joints following fusion, the ankle should be positioned in neutral dorsiflexion and slight hindfoot valgus (heel angled to the outside). Credit: http://www.orthopaedicsone.com/display/Main/Ankle+arthritis
Total ankle arthroplasty (TAA): In this procedure, the surgeon replaces the damaged tibial plafond and talus with an artificial joint (Figure 10). It is ideal for a lightweight, sedentary, older patient with end-stage osteoarthritis who has minimal deformity, good range of motion, a good soft tissue envelope, and is unwilling to undergo fusion in the affected joint. Ankle replacements normally rely on proximal fixation in the tibia and subsequent proximal fixation in the tibia and fibula.
Figure 10: Total ankle arthroplasty requiring syndesmotic fusion. Credit: http://www.orthopaedicsone.com/display/Main/Ankle+arthritis
Subtalar arthrodesis: Fusion of the subtalar joint (Figure 11) is the best treatment for subtalar arthritis that has failed non-operative treatment. This procedure involves removing the joint cartilage and subchondral bone and attaching the two sides of the subtalar joint with screws and bone grafts. Again, the tradeoff inherent in any fusion procedure (loss of pain at the price of loss of motion) applies here as well.(The procedure can be extended to include the talo-navicular and calcaneo-cubiod joints; this is called a "triple arthrodesis".)
Figure 11: x-ray of subtalar arthrodesis (subtalar fusion). Credit: http://www.footeducation.com/foot-and-ankle-conditions/subtalar-arthritis/figure-2-subtalar-fusion/
Debridement and microfracture: This is the most common approach for treating standard size talar lesions. The unstable cartilage is arthroscopically trimmed back and then the bony base is cracked with a pick or drill ("microfractured") to stimulate bleeding and subsequent formation of a fibrin clot. The fibrin clot that fills the defect undergoes transformation into fibrocartilage (type I cartilage). It is successful in about 80% of cases in which the less is less than <15mm. (If the articular surface is intact, yet there is a lesion right below it, drilling the talus from distal to proximal, up to, but not through, the articular surface (so called "retrograde drilling") may be used.
Transplantation of osteochondral tissue: Several transplantation techniques exist to replace lost articular cartilage including osteochondral autograft or allograft transplantation (OATS) and autologous chondrocyte implantation (ACI). These procedures are usually reserved for lesions that have failed debridement and micro fracture, or those too large to attempt it.
During the OATS procedures (Figure 13), cylinders of cartilage and underlying bone are harvested from the femoral condyle or trochlea and placed within the lesion (not unlike hair plugs). . The ACI procedure comprises harvesting autologous chondrocytes, expanding them in a laboratory culture and then re-implanting this larger mass of cells into the lesion, covered by a periosteal patch or collagen matrix.
Figure 13: OATS plug placed in medial talus. Credit: http://www.orthopaedicsone.com/display/Main/Osteochondral+lesions+of+the+ankle MAYBE A MORE SCHEMATIC ILLUSTRATION WOULD BE HELFUL, but I could not find one on google images....JB)
Since ankle and hindfoot arthrosis are normally caused by trauma, risk factors are the same as those for ankle and hindfoot injuries including ankle sprains and fractures. Sports like soccer, football, and basketball have an increased risk of these injuries and therefore have an increased risk of arthrosis.
Some congenital deformities of the foot (e.g. clubfoot) place the patient at increased risk for ankle and hindfoot arthrosis.
Aviator astragalus is an old term referring to compression fractures of the talus, a pattern of injury seen in World War I aviators who crashes their planes. This term is now only a historical curiosity, because modern military aviators who crash typically do not survive the event.
Talar dome lesion
Examine the ankle and hindfoot for tenderness, deformity, and instability
Differentiate ankle and hindfoot arthrosis from other types of arthritis based on history, physical exam, imaging, and other diagnostic testing
Localize arthrosis to the talocrural or subtalar joint