Anterior impingement syndrome in dancers

Successful treatment of injuries in classical ballet starts with an understanding of the basic positions and common movements which can lead to overuse injury. The five basic positions involve maximum turnout of the hips to achieve the foot position. Inadequate hip turnout results in excessive knee or ankle external rotation and rolling in of the ankle to achieve the desired foot position (Fig. 1). Rolling in excessively stretches the medial ankle and compresses the anterior lateral ankle which can contribute to anterior impingement. Plié (Fig. 2) is the common dance movement contributing to anterior impingement and the “rolled in” position of the foot exaggerates the lateral compressive forces worsening the problem.

Anterior impingement in athletes is either secondary to hypertrophied soft tissue interposed in the anterior ankle joint or proliferation of osteophytes (Fig. 3) that limit the open space between the anterior lip of the tibia and the dorsal talar neck. Different theories have been proposed to account for the pathologic changes. Because impingement often occurs in athletes subject to forced plantar flexion (soccer players kicking or dancers en pointe (Fig. 4)) one proposed mechanism is that traction on the anterior capsule results in spurs that then impinge. Different studies have rebuked this theory. Tol et al. in a study of soccer players found that the spurs typically occur in the location of ball impact without excessive plantar flexion being achieved suggesting that the impact and not traction of the capsule results in the spurring [2]. Tol in a cadaveric study demonstrated that the location of the osteophytes does not correspond with the attachment points of the capsule. He also located hypertrophied soft tissue in the anterior joint overlying the capsule that was compressed between the tibia and the talus with ankle dorsiflexion [3]. His conclusion was that traction could not be responsible for the spurs and that hypertrophied soft tissue in the anterior ankle was likely responsible for impingement symptoms.

Current thinking is therefore that osteophyte formation is secondary to repetitive ankle sprains or repetitive microtrauma as one would find with a ball impact or contact between the anterior tibia and talar neck with repetitive loaded dorsiflexion in ballet. Once the osteophytes form, the space available for ankle dorsiflexion diminishes likely resulting in soft tissue impingement, inflammation, hypertrophy, and pain [4]. The presence of osteophytes does not always correlate with impingement suggesting that soft tissue changes must also be necessary. This is supported by the finding that anterior osteophytes are very common in dancers occurring in 59% without symptoms of impingement. This study also demonstrated that talar osteophytes were particularly prominent in dancers [5]. It is also well accepted that soft tissue impingement can occur without the presence of osteophytes. Ankle arthroscopy has demonstrated anterior impingement from the anterior inferior tibiofibular ligament [6] and from hypertrophied synovium in the absence of significant osteophytosis [7].

Athletes with anterior impingement often have a history of multiple ankle sprains and present complaining of pain and some swelling in the anterior ankle aggravated by loaded dorsiflexion of the ankle. Experienced dancers may not have a history of ankle sprain but complain of increasing pain through training and performance especially with plié positions and landing from jumps. Dancers are often very sensitive to body position and note a loss of dorsiflexion in the affected ankle usually noted as a loss of ability to plié on the affected side (Fig. 5). The key physical finding is tenderness to palpation along the anterior joint line. Osteophytes at the anterior lateral or anterior medial joint line can often be palpated with the foot in some plantar flexion. Weightbearing full dorsiflexion of the ankle with the foot flat will often show some limitation on the affected side and reproduce symptoms.

Nihall et al. in a review of 11 dancers with anterior ankle impingement treated arthroscopically provides a profile of the typical dancer presenting with impingement [7]. The patients included 7 women and 4 men all professional or pre-professional dancers performing primarily ballet. The women had been dancing for a mean of 18 years and the men 10 years. They danced between 12 and 30 h/week. All reported prior ankle trauma, primary sprains and two fractures. All had tenderness inferiorly or anterior-laterally and all had pain with plié.

Milloy et al. in 2003 describe a sign they found useful to diagnose synovial soft tissue impingement in the anterior lateral ankle in patients complaining of persistent pain following inversion injury [8]. They first manually dorsiflex the symptomatic ankle and note pain that reproduced symptoms. They repeat the maneuver (for left ankle) with right palm on calcaneus and thumb applying pressure to the lateral gutter. Increased pain with this maneuver is theoretically secondary to the displacement of hypertrophic synovium in to the joint and denotes a positive test. Seventy-three patients underwent ankle arthroscopy. Forty-one had a positive test and 37 of those had synovial hypertrophy in the latter gutter (sensitivity of 94.8%). Of 32 patients with negative sign, 2 had synovial hypertrophy (specificity of 88%).

Imaging of suspected anterior impingement starts with plain weightbearing radiographs of the ankle. As discussed above, the diagnosis is primarily clinical but imaging is necessary to rule out other causes of anterior ankle pain and confirm the presence and location of osteophytes that need to be removed to achieve the best surgical results. Plain radiographs including AP and mortise views are less helpful for the diagnosis of impingement, but will demonstrate other causes of ankle pain including fracture, mortise disruption, OCD, and arthritis. The identification of arthritis is important to plan treatment because the surgical results with arthroscopy are significantly worse if arthritis is present [9]. A lateral view will often demonstrate the tibial and talar osteophytes associated with anterior impingement. Adding an oblique view with the beam 45° craniocaudal and the foot plantar flexed with the leg 30° externally rotated will increase the detection of medially located tibial and talar osteophytes [10[k1]]. CT scanning can also be used to identify osteophytes contributing to impingement and in areas with easy access to CT, this is often the preferred method of identifying bony changes in the ankle, especially if plain films are non-diagnostic in the setting of clinical impingement.

It is well accepted that anterior impingement can occur without the formation of osteophytes secondary to entrapment of hypertrophied synovium or torn anterior lateral ligaments [11[k2]]. MRI has been studied to evaluate its accuracy to identify purely soft tissue impingement. T1 and proton density axial views demonstrating thickened synovium in the anterior lateral joint space or hypertrophy of the anterior talo-fibular ligament are the findings most consistently associated with impingement at arthroscopy [12[k3]]. The identification of chondral injury to the anterior aspect of the joint is also helpful as this finding decreases the likelihood that arthroscopic debridement of anterior osteophytes and hypertrophied tissue will result in significant improvement.