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Hyperpronation in dancers: incidence and relation to calcaneal angle.

Pronation of the foot is one of the planar movements made at the subtalar joint. It occurs during mid-stance of the normal gait cycle when the forefoot makes initial contact with the ground. This motion allows the foot to adapt to weight distribution, thus enabling shock absorption. (1,2) Excessive pronation, or hyperpronation, is thought to be a common foot problem, affecting about 20% of people worldwide (3); however, the specific prevalence among dancers is unknown.

The etiology of hyperpronation (often called "rolling in" when referring to dancers) is multifactorial. It can be the result of a compensatory mechanism seen in structural deformities (4) such as tibial varum and varus forefoot or rearfoot. (1,5) In dancers, it is thought to be a compensatory technique used to increase turnout--or a sequela of other compensatory techniques used to increase turnout (6)--when there is insufficient hip external rotation to achieve the classical ballet aesthetic. (1)

The compensatory turnout techniques have been well described elsewhere, (7) but will be briefly discussed here (Table 1). A dancer commonly "sways" the lower back (into hyperlordosis) and then slightly flexes at the knees or subtly relaxes the knee extensors. This causes an anterior pelvic tilt and hip flexion, both of which relax the ilio-femoral (or Y-) ligament of the hip and allow for increased hip external rotation. This anatomical relationship explains why turnout is more easily achieved in ballet's second position or when the dancer is bending forward at the hips, as in a cambre. In a second strategy, while in demi-plie, the dancer commonly rotates the feet outward, grips the floor with the toes, and then extends the knees, causing the feet to appear more turned out (Fig. 1B). The knee joint allows for external rotation in flexion but not in extension, due to the screw-home mechanism of the femoral condyles. Therefore, the dancer often needs to grip the floor with the toes to maintain the rotation with straight legs. Finally, the dancer's feet commonly "roll in" (i.e., hyperpronate) in an attempt to compensate for the torque on the knee from forced distal turnout (Fig. 1B).

Research suggests that total turnout is the combination of approximately 60[degrees] to 70[degrees] of external rotation at the hip and 10[degrees] to 35[degrees] from the remaining lower extremity. (7) Dancers who use compensatory strategies can achieve an average of 25.4[degrees] extra "functional" turnout, but more extreme compensation has been associated with significantly elevated self-reported injury rates. (6) At the ankle joint alone, excessive pronation stretches the supporting ligaments and tendons of the plantar and medial aspects of the foot and ankle, jeopardizing maintenance of the medial arch of the foot. (2) Excessive demands are then placed on the extrinsic muscles of the foot in an effort to stabilize the arch. This may predispose the tendons and their associated synovial sheaths and attachments to medial tibial stress syndrome, flexor hallucis longus tendonitis, or plantar fasciitis. (1,3,6) In dancers, hyperpronation may also lead to difficulty when resupinating the foot to go on pointe. (8)

[FIGURE 1 OMITTED]

Hyperpronation has been implicated in the development of injuries further up the kinetic chain as well, (2,8,9) including patellofemoral pain syndrome (PFPS) and retropatellar chondropathy (RPCP) from increased tibial torsion. (10) This tibial "rotatory malalignment" is thought to affect patellar tracking, which can result in injury over time. (4,11-13) Hyperpronation has been associated with an increased risk for non-contact anterior cruciate ligament (ACL) injuries, (14-16) (medial) sesamoiditis, (8,17) Achilles tendonitis, (1,8,17-19) leg length discrepancy, (13) stress fractures, (1) hallux valgus, and bunions. (2) Lastly, it has been associated with low back pain, in that internally rotating lower extremity forces predispose to flexion or abduction of the hips, anterior pelvic tilt, and increased lumbar lordosis. (5,20,21)

The incidence and prevalence of hyperpronation in dancers is unknown; however, for a multitude of reasons, it is thought that dancers may be predisposed to developing hyperpronation or symptoms caused by it. For one, dancers' feet are largely unsupported during dance activity. Many dance styles are performed barefoot, in slippers, or in "split-sole" shoes that lack arch support. (22) As mentioned previously, dancers are also frequently required to dance with extensive hip external rotation ("turnout"), regardless of their anatomical make-up. (1,17,23) Joint hypermobility may also play a role, as data suggest that hypermobile dancers may be valued during the training years but naturally selected out of the professional ranks due to injury. (24)

Healthcare providers have achieved little consensus with regard to methods for assessing the severity of hyperpronation in the general patient population, much less among dancers or other athletes. Measurement of the calcaneal angle, representing calcaneal eversion in relation to the tibia, has been previously described as a relatively easy method of estimating the degree of hyperpronation (9,25-28) in comparison with tests such as the navicular drop test (7) or measuring dorsal arch height with the Sit-to-Stand test. (29) However, the association between calcaneal angle and clinical severity of hyperpronation (as assessed by the healthcare provider) has not been determined. A calcaneal angle less than 2[degrees] is thought to be consistent with no hyperpronation, (10) but grading systems of clinical severity do not exist for angles beyond that. In the dance population, even less is known about the relationship between physical exam techniques, measurements of hyperpronation, and functional outcomes in dancers who hyperpronate.

Therefore, this study was designed to investigate the incidence of symptoms related to foot hyperpronation in dancer-patients and to evaluate the correlation between the calcaneal angle and the clinical severity of hyperpronation.

Materials and Methods

This study took place at the Medical Center for Dancers and Musicians (MCDM) in The Hague, The Netherlands, between July 2008 and January 2009. It was part of a larger study that examined the use and effectiveness of orthotics in dancers diagnosed with complaints related to hyperpronation. All study protocols and questionnaires were approved by the Medisch Ethische Toets Commissie ZuidWest Holland (METC ZWH).The study participants were volunteers, who signed consent forms prior to participation. All questionnaires used were available in both Dutch and English.

Chart Review

At the time of chart review, the readily available (last six years) archive of the MCDM patient data filing system contained a total of 2,427 different dancers' charts. These were all non-selectively and alphabetically explored to identify patients who had presented with complaints related to hyperpronation of the feet and been prescribed orthotics. All of the dancers had been seen and diagnosed by the same physician over this time frame. The dancers selected for study had to meet the following inclusion criteria: an injury or chief symptom thought to be related to foot hyperpronation, and receipt of a prescription from the senior author for custom-made orthotics. Also, the specialty dance medicine clinic's referral policy requires that patients must be dancing a baseline minimum of 3 hours per week when uninjured in order to be seen. After screening for inclusion criteria eligibility, patients' charts were de-identified, and data were collected regarding the chief complaint, history of present symptoms, and results of the physical exam, including the degree of hyperpronation of one or both feet.

Calcaneal Angle and Clinical Severity

To investigate the relationship between the calcaneal angle and the severity of hyperpronation, dancer-patients who were seen at the clinic during the study period and prescribed orthotics for symptoms related to hyperpronation were asked for consent to have the first investigator take measurements of the calcaneal angle at the time of their visit. These dancers had to meet the inclusion criteria listed above for the dancers in the chart review. Those who were found on physical exam to have hyperpronation that was not thought to be related to the complaints were excluded. All dance styles, ages, and both genders were included. All patients seen during the study period were examined and diagnosed by the same physician (the senior investigator), who is a performing arts medicine orthopaedic surgeon and director of the MCDM. Therefore, the exam technique and level of dance medicine expertise were constants across all patients in the study. The measurement of the calcaneal angle and examination by the senior physician occurred independently of one another.

[FIGURE 2 OMITTED]

Estimating the Clinical Severity of Hyperpronation

The degree of hyperpronation was graded based on a scale that the senior author has used clinically for the last 20+ years. In this portion of the physical exam, the physician was seated in front of the standing barefoot patient. The physician observed "rolling in" of the feet and the valgus position of the ankle with the dancer in a relaxed stance after maximal inversion and eversion of the ankles. Then, the hallux was extended (dorsiflexed) at the MTP joint while the other digits remained on the floor. This maneuver, known as the Hubscher maneuver or Jack test, (30) causes eversion of the foot back to neutral positioning. The visual estimation of the amount of "rolling in" with the dancer at rest, plus the amount of correction needed to obtain neutral position during the Hubscher maneuver, were used to grade the severity of hyperpronation, from + to +++ (mild to severe). Each foot was examined separately. Thus, a patient with chart score of +/++ had a right foot with a mild degree of hyperpronation and a left foot with moderate hyperpronation. Although each foot was examined separately, for the purposes of this study the participant was classified as being an overall mild, moderate, or severe hyperpronator based on the more severe foot.

Measuring the Calcaneal Angle

The calcaneal angle represents calcaneal eversion in relation to the tibia. (10) It is calculated as the angle between a line bisecting the calcaneus, and a line bisecting the lower leg. In this study, to make the measurement more precise, the two lines bisecting the lower leg and the calcaneus were drawn on the patient by the investigator with a blue pen. The calcaneal angle was then measured using a goniometer (Fig. 2). The patient was positioned in a relaxed stance on a 20 cm high footstep with both feet and lower legs exposed. The investigator was positioned behind the patient such that the lower one-third of the lower leg was at eye-level. The upper half of the goniometer was aligned with the lower third of the calf, the lower half with the calcaneus, and the angle formed by the calcaneal eversion was read and recorded. The same goniometer was used for all measurements.

Statistical Analysis

Statistical analysis was performed using SPSS (version 17.0) statistical software (Chicago, Illinois, USA). To investigate the differences in calcaneal angles between the different hyperpronation groups separately (for example, between mild and severe hyperpronators), the Student's t-test was used. To compare the three hyperpronation groups for the difference in calcaneal angle, a one-way ANOVA was used. To investigate the relation between the calcaneal angle and the degree of hyperpronation, the [chi square] test and the Pearson correlation were used. In the analyses, each foot was treated as an individual subject. The level of significance was set at p < 0.05.

Results

Chart Review

Study Participants

In the chart review, 737 of 2427 patients met the inclusion criteria (30%). A total of 24 patients (2 males, 22 females; mean age: 25.0 [+ or -] 15 years; range: 10 to 68 years) agreed to participate in measuring their calcaneal angle at the time of their visit. Demographic data are displayed in Table 2.

Incidence and Severity of Hyperpronation

Based on chart review, symptomatic hyperpronation occurred in 30% (N = 737) of dancers seeking treatment at the MCDM over the last 6 years. Of these 737 charts, the degree of hyperpronation was recorded in 371 charts (50.3%). According to the classification system described in the Methods section, 50.7% (N = 188) of patients were classified as mild (+), 37.2% (N = 138) as moderate (++), and 12.1% (N = 45) as severe (+++) hyperpronators. In 77 dancers (21.0%), the right and left feet displayed asymmetric hyperpronation. There was no significant difference in the degree of hyperpronation between all right and left feet ([X.sup.2] = 0.78, p = 0.85).

Diagnoses Related to Hyperpronation

Per chart review, the most common diagnosis related to hyperpronation was retropatellar chondropathy (RPCP), found in 75 (10%) of the dancer-patients. This was followed by FHL-tendonitis in 56 dancers (6.7%) and lumbago in 47 dancers (6.4%): see Table 3. Among the "Other" diagnoses not mentioned in the Table were: piriformis syndrome, sesamoidalgia, and anterior impingement of the ankle. Approximately one-third of all conditions involved the knee.

Calcaneal Angle and Clinical Severity

The calcaneal angle was measured in 24 patients (48 feet). Among mildly (+) hyperpronated feet the mean calcaneal angle was 4.9[degrees] ([+ or -] 1.9[degrees], range 2[degrees] to 8[degrees]), in moderately (++) hyperpronated feet 7.5[degrees] ([+ or -] 3.5[degrees], range 2[degrees] to 16[degrees]), and in severely (+++) hyperpronated feet the mean calcaneal angle was 10.2[degrees] ([+ or -] 3.0[degrees], range 7[degrees] to 16[degrees]). The calcaneal angles among all mild, moderate, and severe hyperpronators differed significantly (H = 13.45, p = 0.0012). The angles differed significantly between + and ++ hyperpronation (95% CI [-6.06, -0.87], p = 0.01), and between + and +++ hyperpronation groups (95% CI [-7.67, -2.95], p = 0.0002). There were no significant differences between ++ and +++ hyperpronation groups (95% CI [-4.95, 1.25], p = 0.23), (Fig. 3). There was a linear relationship between the calcaneal angle and degree of hyperpronation (95% CI [1.25, 4.14], p = 0.0006; Pearson's [r.sup.2] = 0.97).

[FIGURE 3 OMITTED]

Discussion

Hyperpronation of the foot is a common physical exam finding and thought to be related to, if not causative of, certain somatic injuries. This is the first study to examine the incidence of hyperpronation in dancer-patients seen at a high-volume referral center for performing artists. It is also the first study to examine the correlation between the calcaneal angle and the clinical severity of hyperpronation. Results suggest that hyperpronation is a prevalent and important finding in dancers.

Based on the six-year chart review of 2,427 dancers seen at our performing arts medicine clinic, the investigators estimate the incidence of hyperpronation in dancers seeking treatment to be 30% (most were mildly hyperpronated). This incidence in dancers is higher than previously reported estimates of the general population (20%). (3) It is difficult to make reliable comparisons between studies, given that there are no guidelines for diagnosing or classifying hyperpronation. However, we believe that the role of hyperpronation in compensatory turnout techniques, as well as the higher prevalence of hypermobility among dancers compared to the general population, may contribute to the higher incidence of symptomatic hyperpronation found in this study. We also recognize that the true prevalence of hyperpronation in dancers may be even higher, given that only dancers who had chief complaints thought related to hyperpronation (and thus prescribed orthotics) were included in the study. Incidentally found hyperpronation in dancers who had an unrelated complaint was not counted. Also, we only examined injured dancers presenting to clinic, rather than perform a screening exam of community non-patient dancers. Nevertheless, one of the strengths of this study's estimation was the large sample size of dancers available by chart review, which would otherwise be difficult to obtain in the community.

There is currently no standardized way of measuring hyperpronation that also gauges clinical severity. Other classification methods such as applying the criteria of a navicular drop of >15 mm, (31) the presence of a medial talonavicular bulge, (32) a calcaneal eversion angle of >9.2[degrees] and a medial longitudinal arch of < 134.6[degrees], (33) likely select for the most severe cases of hyperpronation. Other methods for measuring hyperpronation are often time-consuming and not practical for a healthcare provider to apply in daily practice. In this study, the calcaneal angle correlated strongly with the clinician's judgement of hyperpronation severity (+, ++, +++). The technique for measuring calcaneal angle and for performing the Hubscher maneuver is a relatively simple and efficient method that can be done in minutes. We recognize that clinical judgement is an important part of the global assessment of a patient's hyperpronation. The grading system used in this study, for example, is based on the experience of the attending physician. This judgement in part develops with time and experience; however, given the linear relationship between the calcaneal angle and the grading scale by Hubscher maneuver, healthcare providers may find goniometry to be useful when developing their clinical acumen.

There were several limitations to this study. Most limiting was the small number of dancers available when investigating the relationship between the calcaneal angle and the degree of hyperpronation (N = 24). Another limitation is that the method of categorizing the study patients by severity of hyperpronation (+ to +++) was subjective. As mentioned, there is currently no standard among healthcare providers for physically examining or grading hyperpronation on a clinical scale, especially in the dancer-patient. The benefit of using the + through +++ system in this particular paper was that it has been used in clinical practice with thousands of dancer-patients by a physician who is extensively trained in the field of performing arts medicine. Furthermore, this methodology excluded inter-operator effect by using only one examiner.

Conclusion

The incidence of hyperpronation causing symptoms or musculoskeletal injury is common among dancers presenting to healthcare providers. Assessment of hyperpronation should be included in the physical exam of all dancers with foot, knee, hip, and back complaints. The calcaneal angle can be a useful adjunct to the Hubscher maneuver for grading hyperpronation. More research is needed to find the best physical examination tool that correlates with clinical severity of hyperpronation. Healthcare providers can play a unique role in educating dancers about hyperpronation as a risk factor for injury and encouraging avoidance of potentially injurious compensatory turnout techniques.

Caption: Figure 1 Classical dancer performing a demi-plie: A. Correct alignment; B. Due to insufficient external rotation at the hip, this dancer incorrectly grips the floor with her toes and hyperpronates at the subtalar joint bilaterally.

Caption: Figure 2 Measuring the calcaneal angle using a goniometer.

Caption: Figure 3 Calcaneal angle across degrees of hyperpronation. Three different degrees are shown: + (mild hyperpronation), ++ (moderate hyperpronation), and +++ (severe hyperpronation). There were statistically significant differences found between the mild and moderate degrees, and between the mild and severe degrees of hyperpronation (p < 0.05).

References

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Relana ME Nowacki, M.D., is at the Maastricht University Medical Center, Maastricht, The Netherlands. Mary E. Air, M.D., is in the Department of Physical Medicine and Rehabilitation, University of Washington, Seattle, Washington. A. B. M. Rietveld, M.D., B.A.(mus.), is at the Medical Centre for Dancers and Musicians, The Hague, The Netherlands.

Correspondence: Relana ME Nowacki, M.D., 6224 CE Maastricht, The Netherlands; r.nowacki@alumni.maastrichtuniversity.nl.
Table 1 Compensation for Lack of Sufficient Hip Turnout

Dancers use three compensatory mechanisms (often simultaneously) to
force distal external rotation

1. The dancer sways the lower back while slightly flexing at the
knees, causing anterior pelvic tilt and increased hip flexion.

2. The dancer forms a small demi plie and externally rotates at the
knees. She then extends the legs fully, but must grip the toes on
the floor to maintain the position (Fig. 1B).

3. The dancer hyperpronates at the foot to compensate for increased
torque from forced external rotation at the ankles and knees (Fig.
1B).

Table 2 Demographic Data of Study Participants in the Chart Review

Variable                          Study Group Chart Review (N = 737)

Age at consult MCDM, M (SD)                   25.3 (12.0)
Female, n (%)                                 614 (83.3)
Male, n (%)                                   123 (16.7)
Degree of hyperpronation, n (%)
  Mild (+)                                    186 (25.2)
  Moderate (++)                               138 (18.7)
  Severe (+++)                                 43 (5.8)
Level of dancer, n (%)
  Professional                                199 (27.0)
  Teacher                                      13 (1.8)
  Student                                     316 (42.9)
  Amateur                                     203 (27.5)

Variable                          Study Group Calcaneal Angle (N = 24)

Age at consult MCDM, M (SD)                   24.8 (15.0)
Female, n (%)                                  22 (91.7)
Male, n (%)                                     2 (8.3)
Degree of hyperpronation, n (%)
  Mild (+)                                       6 (25)
  Moderate (++)                                15 (62.5)
  Severe (+++)                                  3 (12.5)
Level of dancer, n (%)
  Professional                                  1 (4.2)
  Teacher                                       2 (8.3)
  Student                                      10 (41.7)
  Amateur                                      11 (45.8)

Table 3 The Most Common Diagnoses among Dancers Presenting with
Hyperpronation-Related Complaints

Diagnosis                                N (%)

Retropatellar chondropathy             75 (10.2)
Lumbago                                 70 (9.5)
FHL-tendonitis                          56 (7.6)
Apexitis patellae (Jumpers' knee)       31 (4.2)
Rotatory malalignment                   30 (4.1)
Hallux valgus                           27 (3.7)
Metatarsalgia                           26 (3.5)
Nonspecific knee complaints             26 (3.5)
Shin splints                            25 (3.4)
Patellofemoral syndrome                 21 (2.9)
Posterior impingement ankle             21 (2.9)
Meniscopathy                            19 (2.6)
Sinus tarsi syndrome                    15 (2.0)
Nonspecific foot or ankle complaints    14 (1.9)
Other                                  281 (38.1)
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Author:Nowacki, Relana M.E.; Air, Mary E.; Rietveld, A.B.M.
Publication:Journal of Dance Medicine & Science
Date:Jul 1, 2012
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