Key Biomechanical Insights For Treating Dance Injuries
Technique. Have the patient perform maximal active plantarflexion of the ankle. As you are at eye level with the patient’s ankle, use a straightedge to look for an angular deviation between the distal sagittal third of the leg and the proximal midline of the foot just distal to the talar dome. This should include the dorsal talar/navicular/cuneiform surface but not the metatarsals.
Norms. In female dancers, the norm is 8 degrees or 5 degrees plantarflexed to the tibial line (ballet, modern, respectively). In male dancers, the norm is 3 degrees or 0 degrees plantarflexed versus the tibial line (ballet/modern).
Evaluating Ankle Dorsiflexion With The Knee Flexed
Dorsiflexion of the ankle with the knee flexed (DKF). We actually have DKF when we descend stairs, squat and run up bleacher steps if our calves fatigue. When a dancer has DKF, it is called a demi-plié. The demi-plié is the position from which a dancer (and basketball player) accelerates each leap and absorbs landing shock. Dancers with too little demi-plié may incur symptomatic anterior ankle impingements that are often accompanied by osteophytosis at the anterior ankle margin. Dancers with too much DKF can also suffer anterior impingement injuries as high DKF correlates with a weak or hypotonic soleus, the muscular delimiter of the demi-plié. Low DKF can also cause anterior impingement injury in the non-dancer so it is important to be able to measure it precisely.
DKF technique. The patient lies in a supine position. The examiner holds the sole at 90 degrees to the exam surface while assisting the patient in flexing the knee until reaching ankle end-range of motion. At this moment, the foot will be forced to plantarflex beyond the previously maintained position perpendicular with the exam surface.
Maintaining the patient’s ankle end-range of motion, the examiner assists the patient in slightly extending the hip until the sole again is perpendicular with the exam surface. This is the measurement position. The examiner drops an imaginary plumb line, parallel to the exam surface, from the face of the patella down to the foot. Then he or she notes where the plumb line falls in relation to the foot (first MPJ, talonavicular joint, 2 inches distal to the tip of hallux, etc.).
DKF norms. In male dancers, the norm for DKF is from the first MPJ to 1/2 inch distal to the hallux tip. In female dancers, the norm for DKF is from the first MPJ to 1 inch distal to the hallux tip.
Key Pointers For Assessing The DKE Position
Dorsiflexion of the ankle with the knee extended (DKE). This is a measurement of gastroc tension or “calf flexibility.” When calves are too tight, the patient may have resulting tensile injuries such as forced subtalar and midtarsal pronation, and Achilles tendinitis. Patients with calves that are too loose are susceptible to injuries from inadequate eccentric (decelerative) or concentric (accelerative) gastroc function. In addition, excessive DKE over-recruits the flexor hallucis longus (FHL) as an accessory ankle plantarflexor. The FHL is also responsible for medial stabilization of the ankle en pointe, and toggling between pointe and demi-pointe. FHL tendinitis is called the “dancer’s tendinitis” due to this FHL multitasking in dancers.
Too much DKE also correlates with heel and leg impact problems like heel bruises and tibial or fibular stress fractures. A hyperflexible calf is like a bungee cord that is too long. The DKE technique uses no goniometer and allows clinicians to measure with more of a linear value rather than radial value. I define DKE as the minimal slope of the shoe necessary to enable subtalar neutral. Due to the overpowering mechanical advantage of the gastroc, if a patient has a negative 3/4-inch DKE, the foot will pronate in any shoe with a heel height less than 3/4 inch. Conversely, the gastroc will not reach full length/tension in shoes higher than a 3/4-inch slope. This sets the stage for eccentric injuries.