When Patients Present With Posterior Ankle Impingement

Posterior ankle impingement can be a result of a number of entities including soft tissue impingement, a prominent bony process or unfused ossicles. Patients typically relate pain with forced or repeated plantarfleixon at the ankle, which can cause acute and chronic impingement/synovitis or bony contusions as well as restricted motion in the ankle or subtalar joint. This condition is frequent among ballet dancers, football players, soccer players and cross-country runners.

Variations in anatomy including an os trigonum, prominent posterolateral talar process (Stieda process) or prominent superior aspect of the calcaneus can predispose patients to the development of posterior ankle impingement. In addition to the variance in anatomy, the shape of the talus can contribute to the contribution of posterior ankle impingement. This repetitive plantarflexion allows the posterior lip of the tibia to displace over the back of the talus and causes impingement on these anatomic variations.

Patients typically present with posterolateral ankle pain that plantarflexion of the ankle joint or motion of the flexor hallucis longus tendon exacerbates. Symptoms can present after an injury, which can lead to a fracture of a Stieda process or disruption of the synchondrosis of the os trigonum. More frequently, however, symptoms develop insidiously through repeated plantarflexion and chronic impingement of the soft tissues and bone.

Key Diagnostic Insights
The physical examination typically involves eliciting pain with direct pressure over the affected area either in the posterolateral or posteromedial ankle joint. Extreme plantarflexion can exacerbate the pain. Range of motion of the hallux can cause pain in the affected region due to the proximity of the flexor hallucis longus tendon with the os trigonum or direct contribution through inflammation and involvement of the tendon itself.

One can thoroughly evaluate the posterior ankle structures with a good clinical evaluation and radiographs as well as advanced imaging including computed tomography (CT) scans or magnetic resonance imaging (MRI). A radiograph will typically show smooth edges with dense cortical bone or fracture of the tubercle. An MRI will often show the extent of the bone marrow edema and can help distinguish any involvement of the flexor hallucis longus tendon as there will often be fluid within the tendon sheath.

A Guide To The Surgical Approach
After the failure of conservative care, surgical resection of the posterior process can provide patients with relief of their impingement symptoms. One can remove the posterior process and debride the soft tissue either arthroscopically or with an open approach depending on the size and location of the lesion/impingement.

A direct open approach can be either lateral or medial depending on the location of pathology. When utilizing a medial approach, one would make a vertical incision between the Achilles tendon and medial malleolus. Deepen the incision but take care to avoid the neurovascular bundle. Bear in mind that this is a more cavernous approach and the risk of neuritis is high.  

Proceed to incise the deep posterior compartment directly over the flexor hallucis longus muscle belly along the lateral border of the tendon. Retract the tendon medially and the posterior process will be directly visible. Utilizing an osteotome, one can reshape the posterior aspect of the talus. The surgeon can also debride the flexor hallucis longus tendon as needed and release the tendon in the fibro-osseous tunnel if there is any stenosis. One typically leaves the deep compartment open and performs subsequent closure of the operative site.

An alternate open approach, which is more common, is through a posterolateral incision. This incision can provide great direct visualization of the impingement and is typically safer based on our experience. Place the incision just posterior to the peroneal tendons. Carry dissection to the posterior ankle and subtalar joint with care to avoid the sural nerve. Once you are at the level of the joint, the posterior process is directly visible and you can remove the posterior process with an osteotome. When removing the posterior process, take extreme care to avoid plunging medially into the neurovascular bundle. Surgeons can inspect the peroneal tendons at the same time they are examining concomitant pathology.

If the impingement is amenable to arthroscopic removal/debridement, make standard posterior portals medially and laterally to the Achilles tendon. Triangulation of your arthroscope and shaver is important as you advance further into the posterior capsule of the ankle and subtalar joint. The flexor hallucis longus tendon is the landmark as the neurovascular bundle is immediately medial. One may remove the posterior process in one piece or remove it in several pieces based on its size and ease of removal. Adequate debridement of the soft tissues and running the ankle/subtalar joint through range of motion is important to make sure there is no further impingement.

If there is stenosis of the flexor hallucis longus tendon, one may also release this from the posterolateral tubercle and follow the fibrous tunnel to the subtalar joint. An alternative arthroscopic approach can be via a subtalar joint/sinus tarsi approach and using a switch sticking maneuver to get to the posterolateral joint for debridement of posterior impingement.

Case Study: Addressing Posterolateral Ankle Pain And Restricted Subtalar Joint Motion
A 15-year-old female presents with gradual onset of posterolateral ankle pain and restricted subtalar joint motion. The patient previously had conservative treatment with orthotic management for a known calcaneonavicular coalition. She first noticed the current pain after starting work at a ranch and wearing cowboy boots.

The patient failed conservative care including cortisone injection into the affected area. Imaging studies showed a calcaneonavicular bar with a large posterior process causing impingement with plantarflexion and attempted range of motion of the subtalar joint. The MRI showed an increase in signal intensity in the posterior process as well as synovitis of the flexor hallucis longus tendon.

Treatment included a posterior ankle arthrotomy with removal of the posterior talar process, synovectomy and resection of the calcaneonavicular bar. Postoperatively the patient wore a compression splint for 10 days and then transitioned to a removable cast boot to allow for early range of motion of the midfoot, subtalar and ankle joints. She did a course of home physical therapy but did not present to formal physical therapy. At the three-month follow-up visit, she was back to ranching and using the elliptical trainer without symptoms.   

In Conclusion
Posterior ankle impingement most commonly occurs in an active patient population with repeated plantarflexion as a mechanism for causing pain. One can manage symptoms conservatively with activity modifications or surgically with removal/debridement of the cause of impingement. Recovery after surgery can begin almost immediately following suture removal. Patient history and imaging are important in the diagnosis of posterior ankle impingement with favorable results following treatment of this condition.

Dr. Yurgelon is a Fellow with the Silicon Valley Foot and Ankle Reconstructive Fellowship at the Palo Alto Medical Foundation in Mountain View, Calif.

Dr. Jennings is affiliated with the Department of Orthopedics and Podiatry at the Palo Alto Medical Foundation in Mountain View, Calif. She is a Fellow of the American College of Foot and Ankle Surgeons.

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