Detecting The Cause Of Chronic Ankle Pain

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Here is a MRI of an ankle that reveals increased intrasubstance signal and thickening within the peroneus brevis tendon.
Babak Baravarian, DPM

The MRI reveals a chronic tear with thickening of the anterior-talofibular ligament. There is marrow edema of the distal fibula without sign of fracture. The MRI confirms the radiographic findings of the bone fragment in the lateral gutter and the absence of osteochondral lesions. Tendon examination reveals normal tendon anatomy except for thickening and increased intra-substance signal within the peroneus brevis tendon. This increase in signal is present 3 cm proximal to the fibular malleolus and extends distally 1 cm past the anterior tip of the fibular malleolus.
Diagnostic Answers
1. You can rule out an osteochondral lesion due to a negative radiograph and MRI. Furthermore, with osteochondral lesion pain, the patient will have deep joint pain with a feeling of locking of the joint from time to time. Although this is still a possibility, it is highly unlikely. If you’re still suspicious, order a CT scan.
2. Sinus tarsi syndrome secondary to a tear of the interosseous ligament or inflammation is possible but not very likely. You must take care to avoid confusing sinus tarsi pain with peroneal tendonitis or tear as the two locations are in close proximity and difficult to diagnose. The MRI did not show any inflammation of the sinus tarsi or ligament tear in that region.If you are not convinced, try a diagnostic block of the sinus tarsi and make sure that the block is deep so as not to involve the peroneal tendon region.
3. It is obvious a great deal of the symptoms in this patient are secondary to a chronic anterior ankle instability. You can see the tear on the MRI and the patient notes instability with toe motions. Furthermore, there is a large bone fragment in the lateral fibular gutter, which is usually secondary to an avulsion fracture of the tip of the fibular at the attachment points of one or more lateral ankle ligaments.
4. The ultimate question in this case is why does the patient have involvement of the peroneal tendons and why has it only flared up in the past two months? Furthermore, is this a problem that requires treatment or is it a secondary symptomatic problem? Usually, peroneal pain is secondary to an acute tear or an overuse injury of the tendon.
In this case, it is due to an overuse injury, secondary to the ankle instability. In cases of chronic ankle instability, it is not uncommon to have pain in the region of the peroneal tendons as they attempt to stabilize the lateral ankle region. It is rare to have a combination of peroneal tendon tear and ankle instability secondary to a ligament tear both on an acute basis. In most cases, there is a chronic instability which leads to peroneal tendonitis and possible partial intrasubstance tears. However, in most cases, the increased intrasubstance signal we see on the MRI is secondary to a tendonitis and not a tear of the tendon.
Diagnosis And Treatment
The best way to differentiate peroneal tendonitis from a partial tear is to immobilize the ankle for a short period of time. If the tendonitis resolves and the pain in the posterior ankle decreases, you’re likely dealing with a secondary problem. If the pain persists in the posterior peroneal region, there is a likely a partial tear.
I place the patient in a BK walker for two weeks, following with one week of a lace-up ankle brace. If the pain resolves with the ankle brace, the intrasubstance signal is a tendonitis. If you are still on the fence, you should check the peroneal tendons for tears at the same time you repair the anterior ankle ligament and remove the loose bone in the lateral gutter.
Where you make the incision will depend on whether you are performing any peroneal work. If you intend to check the peroneal tendons, make a lateral incision on the surface of the fibula. Undermine the skin to reach the anterior ankle and the peroneal tendons. If you are not performing peroneal work, make an anterior ankle incision on the anterior aspect of the fibula, curving the incision posteriorly on the distal aspect of the fibula.
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