Fig. 2.1
Leg length measurement. Photograph courtesy of James Koepfler
Joint Hypermobility Syndrome
Joint hypermobility is a condition in which most of the synovial joints move beyond the “normal” limits. It is recognized as a feature of heritable disorders of the connective tissue (changes in the collagen fiber structure regulated by the fibrous protein genes) and is generally identified by use of the Beighton scale [26]. Among dancers hypermobility refers to weak joint stability. It is the result of long and loose ligaments and certain structural deviations such as shallow joint surfaces, making dancers with hypermobility more vulnerable to musculoskeletal injury and to prolonged periods of post-injury recovery [27–30].
Hypermobility characteristics are considered by dancers to be of great aesthetic benefit, with general agreement that they confer advantages in career advancement [31, 32]. From a medical point of view, hypermobility is a genetic phenomenon [33, 34], yet some authorities claim that it is related to years of incorrect technical execution of dance exercises, which is capable of exacerbating the condition [35].
Among young dancers (aged 8–16 years) joint hypermobility was found to be very common and showed an increased prevalence with increasing age [20]. This is likely due in part to some self-selection of body type, with dancers who could not match what is perceived to be the “perfect” dance movements performed by their hypermobile counterparts dropping out [2, 36, 37]. Teachers frequently promote this process by favoring those dancers who exemplify the aesthetically “correct body shape” to become professionals [2, 36, 37].
Hypermobility should be addressed in young dancers, as pubertal hypermobile female dancers are at high risk for suffering from chronic musculoskeletal pain and arthralgia [2, 36, 37]. It has been frequently observed that young female dancers with hypermobility and resulting pain have lower motivation, higher prevalence of dropout from their ballet career, and greater risk for injuries compared to their peers [32, 35, 36, 38].
Knee Laxity
Screening examination should include:
Laxity around the knee joint: medial/lateral laxity of the knee (Fig. 2.2);
Fig. 2.2
Knee lateral (a) and medial (b) laxity assessments. Photographs courtesy of James Koepfler
Lachman test and drawer test;
Medial/lateral mobility of patella in extended knee; and
Medial/lateral mobility of patella in 30° of knee flexion.
In one study adolescent dancers (12–14 years old) with patellofemoral pain syndrome were found to have greater prevalence of patellar laxity in the extended knee and in 30° flexion of the knee compared to non-injured dancers [39]. It was suggested that excessive lateral tracking of the patella increased the forces and stresses between the patellar articular surface and the femur throughout knee ROM [39]. Although another study showed that patellar mobility was not associated with the development of patellofemoral pain syndrome [39], knee instability should be screened as it might predispose the dancer to overuse injuries [40].
Passive Joint ROM
Dancers should be screened for the most important joints’ ROM (Fig. 2.3):
Fig. 2.3
From left to right: Upper row, combined passive ankle and foot plantar flexion (pointe); passive plantar flexion of the ankle joint. Second row, passive dorsiflexion of the ankle joint; passive external rotation of the hip joint; passive internal rotation of the hip joint. Third row, passive abduction of the hip joint; active extension of the hip joint; passive flexion of the hip joint. Bottom row, passive flexion of the knee joint; lower back and hamstring flexibility. Reprinted with permission from Steinberg et al. [43]
Hip (flexion, extension, abduction, external rotation, internal rotation);
Knee (flexion, extension);
Ankle (dorsiflexion, plantar flexion);
Foot (en pointe); and
Combined joints’ ROM (lower back and hamstring).
The ROM measurement procedure was described previously by a number of experts in dance medicine who determined the norms and movements essential in dance-related screening [41, 42] (Table 2.1).
Table 2.1
Passive joint ROM: physician observations and classifications into 3 groups: hypo ROM (> −1 S.D. of mean), average ROM (±1 S.D. of mean), and hyper ROM (> +1 S.D. of mean), based on ROM distribution for each joint obtained from 1314 dancers aged 8–16 years [43]
Joint | Passive movement | Physician observations | Classifications |
|---|---|---|---|
Foot and ankle | Dorsiflexion | The angle between the long axis of the medial border of the tibia and the long axis of the medial aspect of the foot | Limited ROM ≤ 5° Average ROM 6–15° Hyper ROM ≥ 16° |
Plantar flexion | The angle between the long axis of the medial border of the tibia and the manually palpated navicular | Limited ROM ≤ 45° Average ROM 46–64° Hyper ROM ≥ 65° | |
En pointe | The angle between the long axis of the medial border of the tibia and the manually palpated distal head of the first metatarsal | Limited ROM ≤ 75° Average ROM 76–90° Hyper ROM ≥ 91° | |
Knee | Extension | In the extended knee, the angle between the long axis of the thigh and the long axis of the tibia | Average ROM 0° Hyper ROM ≥ 5° |
Flexion | In the flexed knee, the angle between the long axis of the thigh and the long axis of the tibia | Limited ROM ≤ 140° Average ROM 141–150° Hyper ROM ≥ 151° | |
Hip | Active extension | In the active extended hip, the angle between the midaxillary line (the axis on the greater trochanter) and the long axis of the thigh between the greater trochanter and the lateral epicondyle of the femur | Limited ROM ≤ 20° Average ROM 21–39° Hyper ROM ≥ 40° |
Flexion | In flexed hip, the angle between the midaxillary line (the axis on the greater trochanter) and the long axis of the thigh between the greater trochanter and the lateral epicondyle of the femur | Limited ROM ≤ 135° Average ROM 136–150° Hyper ROM ≥ 151° | |
Abduction | Hip abducted in frontal plane in neutral rotation (of the hip) with the foot perpendicular to the floor. Range was measured between a line from the umbilicus and the symphysis pubis and the long axis of the abducted thigh (between the umbilicus and the patella) | Limited ROM ≤ 45° Average ROM 46–59° Hyper ROM ≥ 60° | |
External rotation | In the flexed knee and externally rotated hip, the angle between the vertical axis and the anterior border of the tibia | Limited ROM ≤ 50° Average ROM 51–60° Hyper ROM ≥ 61° | |
Internal rotation | In the flexed knee and internally rotated hip, the angle between the vertical axis and the anterior border of the tibia | Limited ROM ≤ 45° Average ROM 46–65° Hyper ROM ≥ 66° | |
Lower back and hamstrings | Flexion | In extended knees and planter-flexed ankles, the dancer leaned forward with the forehead toward her knees | Limited ROM ≤ 1 cm distance between forehead and knees. Hyper ROM ≥ forehead touching the knees |
The term joint ROM is defined by the “musculotendinous unit length” and the “musculotendinous unit flexibility,” and thus refers to the ROM available in a single joint [44, 45]. Several factors affect joint ROM in a particular joint, including the shape of the articulating surface, the shape of the articular capsule, ligamentous structures, the structure of the bony surfaces, muscle fat content, and muscle tension. All of these are genetically determined [46, 47]. There are clinical guidelines and norms for evaluating each specific joint (such as the hip, knee, and ankle joints) and each specific passive movement (such as flexion, extension, and rotation), which are normally measured with a goniometer [48, 49]. Increased joint ROM can create the illusion of perfect movements or positions, and has therefore been identified as a prerequisite for successful dancers [2, 50].
The classic question “Which came first, the chicken or the egg?” is relevant with regard to ROM. There are two schools of thought; for decades there was an argument in the literature as to whether joint ROM is solely dictated by genetics or if long periods and intensity of dance training may increase joint ROM. We should also question whether deviant joint ROM (insufficient or excessive) increases the risk of injury. With regard to the first question, in most studies dancers manifested greater joint ROM compared to non-dancers [43, 51]. A study of 1314 young female dancers found that ROM did not improve or diminish with age, but rather was preserved [43]. The ability of dancers to retain joint flexibility with age is probably due to regular training, as ROM in non-dancers tends to decrease with age [43]. Conversely, Hamilton et al. [2] explain that the desired dancer en pointe ROM (90°–100°) results from constant stretching and skeletal modeling while the bones are growing. It was suggested that improvement in hip external rotation ROM was attributable to structural changes in the femur (anteversion/retroversion of the femoral neck) as a result of the growth process controlled by hormonal changes during the spurt period, along with capsular stretching [2, 52].
Concerning the relationship between a deviated joint ROM and the risk of injury, insufficient or excessive joint ROM have been suggested as important intrinsic characteristics that may alter the biomechanics of dance movements and therefore be associated with dance injuries [2, 9, 50, 53, 54]. For example, insufficient ankle plantar flexion was found to be more common among injured dancers [53]; hyper (increased) joint ROM in the lower extremity was found to be associated with increased rate of ankle/foot paratendonitis [4]; and dancers who practice en pointe in “turnout” position with insufficient joint stability predispose themselves to injury [55].
Dancers with increased (hyper) joint ROM may exhibit excessive motion, inappropriate direction of forces, and failure of the muscles acting around the joints to keep the correct kinematic movement pattern, which can result in injuries to the affected tissues [56, 57]. Conversely, dancers who lack the required joint ROM for ideal positions tend to develop compensatory strategies [56, 58], which, in turn, may lead to an injury [28, 57]. Nevertheless, a study by Steinberg et al. [9] reported opposing results: dancers with decreased hip and ankle/foot joint ROM were found to be less prone to develop patellofemoral pain syndrome [54], and Wiesler et al. [59] reported no predictive relationship between ankle ROM measurements and injury in 148 elite adolescent pre-professional dancers.
The correct conclusion probably lies in the sample size and the cohort studied. Most compensatory movements probably contribute to pathologies. However, the large group studied [52] who underwent screening demonstrated that lack of “ideal” ROM does not necessarily cause injuries if ROM is not forced by compensations.
Unlike hypermobile (unstable) joints, which demand greater effort from the muscles around the joint to stabilize and control movement in order to prevent injuries, the mirror image of limited ROM needs “only” to avoid forcing a non-existing range, and hence prevent negative compensation and injuries.
Anatomical Alignment
Screening young dancers for joint malalignment and structural deviations may reduce the risk for related injuries (Table 2.2):
Table 2.2
Anatomical anomalies
Joint | Anomalies | Physician observations (in an anatomical position) | Definition of a positive testa |
|---|---|---|---|
Foot and ankle | Longitudinal arch planus (LAP)/Longitudinal arch cavus (LAC) | Viewing the medial aspect of the foot, an increased height of the medial longitudinal arch indicates LAC, and reduced height of the medial longitudinal arch, with its margins touching the ground, indicates LAP. | Planus: Forefoot inversion, pes planus Cavus: Forefoot eversion |
Calcaneal valgus/varum | Viewed from behind, for varum the calcaneus is inverted when the subtalar joint is in a neutral position; for valgus the calcaneus is everted when the subtalar joint is in a neutral position | Varum: >5° inversion from calcaneal midline Valgus: <5° eversion from calcaneal midline | |
Hallux valgus | Viewing the dorsal aspect of the foot, hallux valgus is present when the first metatarsal is lateromedially oriented and the proximal phalanx mediolaterally oriented. A callus is also present at the medial aspect of the head of the first metatarsal. | >15° at MTP | |
Knee | Valgus/varum | Viewing the anterior aspect of the lower extremities, with the knees fully extended: valgus is considered if the tibia has a valgus angulation in comparison to the femur (the dancer’s knees touch and the ankles do not); varum is considered present if the tibia has a varum angulation in comparison to the femur (the dancer’s ankles touch and her knees do not). The knees are in correct alignment when the hips are neutral in rotation and the patellae are facing directly forward. | Knee valgus: Q angle >22° in females, >18° in males with knees extended. Knee varum: Space between the right and left knee with feet together in stance |
Genu-recurvatum | Viewing the lateral aspect of the lower extremities with the knees fully extended, genu-recurvatum is considered present if the femur is fully extended and the legs have a posterior angulation | >10° Hyperextension | |
Back | Scoliosis | (A) Magee’s “skyline” view: any deviation from the normal posture: the head is straight on the shoulders; the posture of the jaw is normal; the tip of the nose is in line with the sternum; the trapezius neck line is equal on both sides; the shoulders are level; the clavicles are level; there is no protrusion, depression, or lateralization of the sternum, ribs, or costocartilage; the waist angles are equal, and the arms are equidistant from the waist; the carrying angle at each angle is equal, the palms of both hands face the body in the relaxed standing position; the high points of the iliac crest are the same on both sides; the ASIS are level; the pubic bone is level; the knees are straight; the heads of fibula are level; the ankles are level; the arches of the feet are equal on both sides; the feet angle out equally; there is no bowing of bones. (B) The Adams forward-bend test: when the dancer flexes her spine forward from a standing position scoliosis is considered when any hump on one side and a hollow on the other is detected. A positive test means that a rib hump deformity is noted in the thoracic region, or that an angle of trunk rotation is evident in the thoracolumbar or lumbar region. | Adams forward-bend test: thoracic: no posterior rib hump at 30° Lumbar: no increased muscle bulk at 90° of forward flexion |
Knee valgum/varum
Forefoot adduction
Hind-foot varum/valgum
Longitudinal arch cavus/planus (splay foot)
Hallux valgus
Lordosis
Scoliosis
Limited data are available regarding an association between static postural alignment and injuries. One study found a correlation between scoliosis and injuries among dancers aged 8–16 years [9]. Most other studies measured the dynamic alignment of dancers during active dance movements, suggesting that poor dynamic lower extremity alignment increased the risk of injury among young dancers [53, 61].
Hallux Valgus
Hallux valgus is a common deformity in the female population as a whole, and among athletes and dancers in particular [19, 62]. Prevalence of hallux valgus among young dancers (age 8–16 years) is very high (40%), and increases from pre-pubertal age (8–10 years: 32.7%) to pubertal age (11–13 years: 45.6%) [19]. Hallux valgus in dancers may result from various factors, such as the genetic component; the increased lever arm of the long hallux acting on the MP joint through an extreme ROM; increased stress on the MP joint during demi-pointe work; forced turnout (leading to rolling in) in demi-plié that also leads to excessive internal rotation of the tibia; and excessive movements such as en pointe work [62–64]. It has been suggested that hyper-pronation (“rolling in”) can result in abnormal pressure distribution throughout the foot, which can place the dancer at risk for developing hallux valgus [65]. To summarize, genetic predisposition together with faulty technique might be the inappropriate combination that explains the high rate of hallux valgus in dancers. The greater the deformity the higher the chance that it will adversely influence the dancing by causing pain, bursitis, and limited ROM—all of which negatively impact the performance of the dancer. As surgical correction of hallux valgus deformities in dancers may decrease the power or ROM at the first MP joint muscles and ligaments [66], the most common recommendation for dancers is to adhere to conservative measures and avoid corrective surgery, preserving the range of dorsiflexion at the joint, which is a necessity for dancers [62].
Hallux valgus was found to be associated with other spinal and lower extremity joint mal-alignments such as scoliosis and knee varum [19], but no correlation between h/week of ballet practice and hallux valgus or h/week of en pointe dancing and hallux valgus have been reported among dancers [19, 63]. Given the prevalence and severity of hallux valgus with increasing age, it is suggested that hallux valgus is mostly related to hereditary anatomical factors and to incorrect technical execution [63].
Scoliosis
There is a high incidence of scoliosis in athletic girls and dancers compared to their age-matched controls [67, 68]. In a screening examination performed by an orthopedic surgeon utilizing the Magee’s “skyline” view (Fig. 2.4a) and the Adams forward-bend test (Fig. 2.4b), the prevalence of scoliosis was found to be 24–30% among recreational dancers, 30% among adolescent ballet dancers, and 24% in young professional dancers [15, 18, 69]. Scoliosis had already been noted in 22.6% of dancers at the age of 9, a prevalence that increased slightly to 26.3% at 16 years old [18].
Fig. 2.4
Magee’s “skyline” view (a) and the Adams forward-bend test (b). Photographs courtesy of James Koepfler
The relationship between factors such as growth processes, intensive exercise, and scoliosis is not clear. A number of researchers have claimed that dance is a highly repetitive activity that imposes high stress on the immature spine, and that ballet training may delay menarche and predispose dancers to develop scoliosis and stress fractures [15, 68, 70]. Furthermore, it is suggested that the stresses exerted on the scoliotic spine over many years may be associated with an increased incidence of specific injuries to the scoliotic dancers [70], with a high incidence of injuries such as low back pain [9, 15, 18, 53]. Other researchers have claimed that intensive dance training may improve scoliosis [71], as dance classes involve symmetric and balanced exercises. Hence, no differences were found between scoliotic and non-scoliotic dancers in training impact parameters (mean age at which students started dance classes, mean h/week of dance practice, and mean number of years of practice) [18].
Identifying other anatomical anomalies during screening of a scoliotic dancer is important, as mal-alignments such as knee varum, genu-recurvatum, long-plantar planus, splay foot, and hallux valgus were found more frequently among scoliotic dancers than non-scoliotic dancers [18].
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