The human ankle is a complex load bearing joint that consists of just three bones. These three bones include the tibia, fibula and talus. These three unique bones work in conjunction to provide the range of motion necessary to complete our daily activities such as walking, jumping or running. Injuries of the ankle joint can be complex and debilitating. This article discusses injuries of the talar dome. The talar dome is the rounded portion on the top of the talus that articulates with the bones of the leg (tibia and fibula). Injuries to the talar dome are called talar dome lesions, transchondral fractures, osteochondral fractures, bone contusions or osteochondral defects (OCD's).

Injuries of the talar dome have been discussed in the medical literature since the mid nineteenth century. In 1959, Berndt and Hardy were the first to recognize the unique nature of these injuries.  They called these injuries transchondral fractures. What Berndt and Hardy described was a classification of fractures found immediately beneath the surface of the cartilage of the talar dome. Berndt and Hardy described four stages of transchondral fractures.

Berndt and Hardy Classification of Talar Dome Fractures

Stage I - Focal compression of the subchondral bone (bone beneath the cartilage)

Stage II - Focal compression of the subchondral bone with partial detachment of a fragment of cartilage

Stage III - Focal compression of the subchondral bone with a fully detached fragment of cartilage, still situated in place at the site of injury

Stage IV - Focal compression of the subchondral bone with a fully detached fragment of cartilage, detached from the site of injury and floating in the joint space
 

The term transchondral refers to an injury applied to the bone across the cartilage. 'Across the cartilage' is actually a very accurate description of how transchondral fractures occur. As an analogy, think of the injury sustained by an apple when it falls from a tree. The skin appears normal, yet the supporting structure of the flesh of the apple is damaged. This example is very similar to what happens in a transchondral talar dome fracture. As the force of an injury is applied to the cartilage, the subchondral bone collapses in a localized fracture. As a result, the surface of the ankle joint becomes irregular. Motion on this irregular surface creates pain and inflammation within the joint. In severe cases, such as stages III and IV, the injured fragment of bone and cartilage becomes detached creating even greater irregularities in the surface of the joint.

In a talar dome fracture, the injury to the subchondral bone crushes the normal blood supply to the site of the injury. The term aseptic necrosis is used to describe this type of an injury to bone. Aseptic (no infection) necrosis (death) is the single greatest influence that inhibits healing of talar dome fractures. Its' interesting to note that the cartilage of the ankle derives most of it's nourishment from the fluid in the ankle joint, called synovial fluid, and not from the same blood supply that supplies the damaged bone. This explains why the cartilage at the site of a talar dome fracture can remain viable as the bone beneath it fails to heal.

The vast majority of transchondral fractures of the talus occur following ankle sprains. Approximately 2-6% of acute ankle sprains have transchondral fractures of the talar dome. Additionally, ankle fractures of the tibia (inside ankle bone) and the fibula (outside ankle bone) may result in transchondral talar dome fractures. The tibia and fibula, in addition to the talar dome, may also sustain transchondral fractures.

Diagnosis of Transchondral Fractures of the Talar Dome

The diagnosis of a transchondral fracture of the dome of the talus is often missed during early examination of an ankle sprain or ankle fracture. Transchondral dome fractures are usually identified when patients fail to respond to conservative care for sprains and fractures. Follow-up examination at 6-8 weeks post injury should include an x-ray. Plain x-ray can often identify a transchondral fracture. If clinical suspicion exists but no sign of fracture is seen on x-ray, and MRI or CT scan can be used to further identify these lesions. MRI will often find bone edema or swelling of the bone following injury suggestive of a stage 1 OCD. Bone scans and arthrography are not typically used to diagnose OCD's due to their poor specificity for these lesions.

Treatment of Transchondral Talar Dome Fractures

Initial treatment of talar dome fractures is often delayed due to the fact that the symptoms of a talar dome fracture are very similar to the symptoms of an ankle sprain. The decision to treat conservatively or surgically is based upon the radiographic appearance, size, location within the joint and stage. Stages I through IV may at some time require surgical correction based upon the response to conservative care. The following table summarizes the treatment of talar dome fractures.

Treatment of Talar Dome Fractures by Stage

Stage I - Weight bearing/non-weight bearing casting, rest, physical therapy.

Stage I defects may respond to rest. Rest may include decreased activity, use of an ankle brace or use of a walking cast.  The size and location of the talar dome fracture plays a big role in the time that it takes to return to normal, pain free activity. Also, stage I lesions do not result in significant collapse of the talar dome or focal avascular necrosis. Therefore, the prognosis for stage I OCD's is very good. Once a Stage I lesion has fully healed, a residual flat spot, or defect may remain on the surface of the talus. If this defect results in chronic pain with activity, it may require surgical repair.  Healing of stage I OCD's may take up to 12 months.

Stage II - Arthroscopic debridement of the injury with subchondral drilling.

Stage II lesions rarely respond to rest and typically will require at least an arthroscopic procedure to repair the residual defect found in the surface of the talus. Arthroscopic procedures are performed through small 1/4 incisions to gain access to the ankle joint. Arthroscopy is used to debride, or grind away the damaged or collapsed bone and cartilage. In addition to arthroscopic debridement, subchondral drilling is used to stimulate blood flow to the injury site. Subchondral drilling is a surgical technique used to break through the thick subchondral bone (beneath the cartilage). This can be accomplished with a drill or wire and completed through the same small incisions used for arthroscopic surgery. Medial dome lesions can be difficult to access through an anterior approach. Medial dome lesions can be accessed by drilling through the medial malleolus using a Micro Vector Drill Guide available from Smith Nephew Orthopedics.

Arthroscopic debridement of the ankle (with or without drilling) is performed in a hospital or surgery center. Anesthesia is usually a general although a spinal block can be used. The procedure takes about 45 minutes to perform. Most patients are able to bear weight the same day. Sutures will be in place for two weeks during which time, the patient will be allowed to return to many of their normal activities. The majority of healing following this procedure takes place within the first two months after surgery although remodeling of the cartilage may take up to a year to complete.

Stage III - Arthroscopic debridement of the injury, subchondral drilling and synovectomy of the joint.

Stage III lesions may respond to arthroscopic techniques and transchondral drilling. In many cases, the body of the talus may require bone grafting to insure proper healing. This type of grafting incorporates both donor bone and donor cartilage in a technique called an OAT's procedure (osteo-articular transfer procedure). Osteochondral grafts are performed for two reasons; (a) restore the supporting surface of the joint and (b) replace damaged bone and cartilage that has failed to heal after a reasonable period of conservative care. Donor graft for an OAT's procedure can come from three different sources. (1) Autogenous osteochondral (bone and cartilage) can be harvested from non-weight bearing surfaces of the knee and transplanted into the sited of the talar fracture. (2) A number of companies manufacture synthetic graft material that can also be used including Nexa Orthopedics. (3)Fresh frozen osteo-chondral allografts may be used for OAT's procedures with success rates reported as high at 75% at 5 years post surgery and 63% at 14 years post surgery. (1,2,3,4,5) An allograft is a graft taken from a human donor other than the recipient. Fresh means that the graft was harvested within 24 hours of the donor's death and the time from graft harvest to implantation is 7 days or less. Recent studies have shown that fresh allografts can be refrigerated prior to implantation for up to 44 days with chondrocyte viability of 67%. This time between harvest and implantation is important in that it allows the graft supplier adequate time to prepare, test and sterilize the graft.

The method of treatment for stage III lesions varies, therefore it is difficult to determine normal healing times for repair of stage III lesions. In most cases, we can assume that the treatment for stage III lesion will be similar to stage II but the operative time and healing time will take a bit longer than that of a stage II lesion. Many cases will require a period on non-weight bearing in a hard cast below the knee.

Stage IV - Arthroscopic debridement with subchondral drilling and possible revision of the injured talus with a bone graft.

Stage IV lesions may respond to arthroscopic techniques but typically require open revision with curettage or OAT's grafting. Most lateral dome fractures can be reached with arthroscopic techniques since they tend to occur in the anterior lateral aspect of the ankle. Medial dome lesions, on the other hand, tend to occur in the posterior aspect of the ankle and are difficult to access with arthroscopy. To access the medial aspect of the ankle, the tibia often has to be broken and retracted to visualize the medial dome lesion.

The location of the transchondral fracture is important when determining the type of graft to be used in a stage III-IV lesion. Autogenous grafts taken from the knee can only be used in areas that are flat. Flat grafts are appropriate for the central dome. But most transchondral fractures of the talus occur on the shoulders of the talus. Since the shoulders are round, a rounded graft is needed to contour to the shape of the talus.

The following images show a trans-tibial approach for a stage 4 medial talar dome lesion with a free osteochondral graft taken from the great toe joint. Medial talar dome lesions are typically found in the central to posterior aspect of the talar dome and are therefore often inaccessible to arthroscopic procedures and techniques. Therefore, an osteotomy must be placed through the tibial to access the ankle. Image 1 shows access to the ankle through the tibia and site preparation of the talar dome. Due to hardening of the talar dome, a new fresh bone bed is stimulated by drilling the bone and placing synthetic bone dowels in the dome of the talus. Image 2 shows the graft donor site (under the text) and osteochondral graft ready for placement. Image three shows the graft in position and held in place by two small 1.5mm screws. Post-operative management for this case includes 6 weeks in a hard cast followed by 4 weeks in a walking cast.

Long term follow-up of talar dome lesions shows that despite the type of treatment, many patients with talar dome transchondral fractures will continue to have ankle pain and swelling over the course of their lives. The prognosis for transchondral fractures depends in part upon the severity of the injury, the age and general health status at the time of injury and whether the patient is a smoker. Grafting used in stage III and IV lesion is rarely successful in patient who are smokers. Both autogenous and allogenic grafts depend upon the ingrowth of new blood vessels. This process is called angiogenesis. Angiogenesis is significantly inhibited in smokers.

Transchondral - across the cartilage.

Chondral - refers to cartilage.

Transchondral talar dome fractures occur at the anterior lateral shoulder of the talus and less commonly at the posterior medial shoulder of the talus. The shoulder(s) of the talus is the transitional curve between the flat upper dome and the sides of the talus.

Transchondral talar dome fractures occur secondary to trauma such as an ankle fracture or sprain. 

Most talar dome fractures are the result of trauma. The type of trauma may vary and can be as simple as an ankle sprain. Talar dome fractures are also seen in complex trauma such as a fall from a roof or ladder or perhaps an automobile accident. In most cases, the initial injury will show no immediate signs of a talar dome fracture and will subsequently be treated as a simple ankle sprain.

Follow-up examination, several weeks after the original injury may allow an opportunity to see a new set of symptoms, different than what was originally thought to be a simple sprain. Symptoms of a sprain tend to be localized to the ligament that was injured. In the ankle, the majority of sprains are on the outside of the ankle (fibula).

Talar dome fractures exhibit more diffuse symptoms. Pain is not localized to the outside segment of the ankle, but is diffuse through-out the entire ankle. Pain may or may not be present with weight bearing. Talar dome fractures will increase in pain with activity. Swelling may be present and is typically diffuse and found across the entire front of the ankle joint.

X-rays of the joint show a small area of darkened bone adjacent to the surface of the talus. This area correlates to the area of injury. Occasionally, a corresponding injury of the tibia may also be visualized on x-ray.

The differential diagnosis of this condition should include;

Arthritis

High ankle sprain

Septic joint

Soft tissue adhesion

• Ankle Sprain

• Posterior Tibial Tendon Dysfunction

• Peroneal Tendonitis

• Arch Pain

• Ankle Pain

This article was written by Jeffrey A. Oster, DPM and last updated 4/28/10.

Schoenfeld AJ, Leeson MC, Grossman JP. Fresh-rozen Osteochondral Allograft Reconstruction of a Giant Cell Tumor of the Talus. J Foot ankle Surg. 46:144-148, 2007