Anatomy of vertebral body showing location of pars interarticularis. Reprinted from D’Hemecourt 
The defect can either be asymptomatic or associated with significant low back pain. The hyperlordosis practiced by dancers with either weak abdominal muscles, tight thoracolumbar fascia, or incorrect technique increases the stress on the L5-S1 joint . There are likely several other contributing risk factors, although ultimately symptomatic spondylosis is a condition of overuse of the spine. While there are certain hereditary risk factors, an increased prevalence is seen in individuals who participate in sports, especially those that place increased stress on the lower spine as a result of repeated extension and rotation, such as gymnastics, figure skating, and dance . The majority of defects occur at the L5 level (85–95%), with the next most commonly affected level being L4 (5–15%) .
Physical Examination and Diagnosis
The most common complaint in patients suffering from symptomatic spondylolysis is low back pain. This is typically unilateral, although it can be bilateral and may radiate to the buttock, around to the lateral aspect of the hip, or into the proximal lower limb. The onset of pain may be acute or gradual and is typically worsened after prolonged exertion. Activities that involve lumbar hyperextension, particularly while standing on one foot as in arabesque, are often known to exacerbate pain.
Tenderness to palpation is not always present. If significant spondylolisthesis is present, a step-off may be palpated. The most significant finding on examination is pain reproduced by the one-legged extension maneuver. During this test the patient stands on one leg and is directed by the examiner to lean backward in an attempt to recreate the pain (Fig. 6.3).
Radiographic and advanced imaging modalities assist in the diagnosis. Plain radiographs are helpful in ruling out underlying specific diagnoses and can also help to describe degenerative spine changes. Spondylolisthesis is often visible on plain X-ray . However, only about 20% of pars defects can be seen on oblique view . Advanced imaging modalities such as MRI and CT are more sensitive in picking up the pars defect and can also detect other musculoskeletal causes of back pain. MRI is preferable over CT in the younger population, given its lack of radiation exposure. On MRI, the injury is visualized as bony edema, and in more advanced cases a distinct fracture line can often be seen (Fig. 6.4). In cases of spondylolisthesis, MRI will also determine the condition of the intervertebral disk at the affected level and evaluates for canal or foraminal stenosis that can result in neural compression  (Fig. 6.5).
Edema of the pars interarticularis on T2-weighted MRI indicating stress reaction of the bone
Anterior slippage of L5 on S1 vertebrae in spondylolisthesis
Treatment always begins with conservative measures, including modification of activity, rest, and physical therapy. Exercises should concentrate on relieving spasm and tightness in the hip flexors, quadriceps, and hamstrings, as well as avoiding any extension stresses on the spine. Core strengthening of the abdominal, trunk, and multifidus muscles is also essential. The use of nonsteroidal anti-inflammatory drugs (NSAIDs) should be discouraged due to their propensity to slow down bony healing .
Bracing treatment is required in the initial period, until the patient becomes pain-free. The effect of bracing unloads the posterior elements of the spine and reduces the amount of shear stress across the pars . Patients with spondylolisthesis should be followed clinically and with radiographs every 6–12 months to monitor for progression of the slip.
Management of spondylolysis is often done clinically, with the resolution of pain and ability to return to prior activities indicative of successful healing. Repeated imaging, either with MRI or CT, may be indicated in patients who do not have the expected course of symptomatic improvement. Healing may not always produce a solid bony union, but the patient will often become pain-free as a result of fibrous healing. Minimum treatment time in the brace of six weeks is often needed, after which the patient can be progressed slowly back to dance activity if pain-free. This is often started initially in the brace and advanced as guided by symptoms.
Persistent pain after a six-month period of nonoperative management should be considered for surgical intervention . Approximately 9–15% of cases of spondylolysis will undergo surgery . Other indications for surgical treatment include the development of neurological deficits and segmental spine instability.
Scheuermann’s Kyphosis (Juvenile Kyphosis)
Scheuermann’s kyphosis is a rigid kyphotic deformity of the thoracic or thoracolumbar spine occurring in adolescents . It is an abnormality of the vertebral epiphyseal growth plates. Typically, it involves anterior wedging of three consecutive vertebral bodies of at least 5° each. The etiology of this condition is multifactorial and includes genetic factors, repetitive microtrauma, necrosis ring apophysis, and tight hamstrings. The incidence is reported as 1–8%, affecting males and females equally . A severe roundback deformity may also be seen in the adolescents. This is less of a fixed deformity than a secondary reaction to muscular imbalances and poor posture . The characteristic findings on imaging noted below will not be seen in this condition.
Physical Examination and Diagnosis
The most common complaint is poor posture or cosmetic deformity. Hamstring tightness and flattening of the thoracolumbar spine are often seen. In 80% of patients, the disease is asymptomatic . When pain is present it is often exacerbated by forward flexion and located in the thoracic area over the kyphotic deformity. The onset of pain is usually gradual exacerbated by activity, and improves with rest. In true Scheuermann’s kyphosis the curvature is not correctable by hyperextension or lying supine.
On plain radiographic imaging, a thoracic kyphosis of greater than 35° is diagnostic, with the apex commonly seen between T7 and T9 . Other features that may be noted are as follows: irregular upper and lower endplates with Schmorl’s nodes, disk-height loss, and associated apophyseal ring fractures (Figs. 6.6 and 6.7).
Scheuermann’s kyphosis in a 15-year-old boy. a Sagittal 2D CT reconstruction image demonstrates midthoracic kyphosis with anterior wedging of at least three consecutive vertebrae with presence of Schmorl nodes. b Sagittal 3D CT reconstruction image demonstrates midthoracic kyphosis with anterior wedging of at least 3 consecutive vertebrae and the presence of Schmorl nodes. Republished with permission of Rodriguez and Poussaint 
Scheuermann’s kyphosis in a 14-year-old boy. Sagittal T2-weighted image demonstrates thoracic kyphosis with mild anterior wedging of the T10–T12 vertebral bodies, slight disk space irregularity, and Schmorl nodes. Minimal annular bulges slightly indent the ventral aspect of the thecal sac. Republished with permission of Rodriguez and Poussaint 
Treatment should entail postural exercises as well as trunk extensor strengthening and pectoralis stretching. Hamstring tightness should be addressed, as one biomechanical theory presumes that tight hamstrings prevent anterior pelvic tilt on forward bending, transmitting the bending stresses to the thoracic spine .
When the kyphotic curve reaches 60°, thoraco-lumbo-sacral orthosis (TLSO) bracing is instituted . The kyphotic curve does not then tend to progress further, and bracing with a gradual return to activities can help to alleviate the pain during exercise.
Sacroiliac (SI) Dysfunction
The function of the SI joint(s) is to transfer forces from the legs and pelvis to the trunk. This requires rotational motion of the posterior hemipelvis . As the pelvis develops from childhood through puberty, this joint transitions from flat and hypermobile to being rougher, more undulated, and less mobile.
Due to the requirement for turnout in the dancer, there is an increased amount of stress translated across the pelvis. SI dysfunction is often multifactorial, resulting from a combination of asymmetry in strength and flexibility between sides. For example, a tight psoas muscle will result in relative downward and anterior deviation of the pelvis on the affected side. This stresses the SI joint and can also load and tighten the contralateral iliotibial (IT) band.
Physical Examination and Diagnosis
SI joint pain is typically located over the area of the joint itself and may radiate into the buttocks, groin, or posterior thigh. Pain is usually exacerbated by jumping, hyperextension, and abduction positions, especially if accompanied by forced turnout.
Physical examination may reveal tenderness to palpation at the site of the SI joints. Weakness or tightness in the psoas and/or tightness in the ITB with a positive Ober’s test (often on the contralateral side) may also be present. Specific SI joint loading maneuvers may reproduce the pain. These include thigh thrust, sacral distraction, sacral compression, and iliac torque testing. The flexion-abduction-external rotation, or FABER test, can also be used to assess hip joint or SI pathology. This is performed with the dancer lying supine with the leg being tested placed in a “figure 4” position. The examiner then applies force to the bent knee and a positive test occurs when the dancer’s pain is reproduced or range of motion is restricted.
Imaging with plain films of the pelvis is helpful to evaluate the bony morphology of the hip and pelvis complex, but the SI joints almost always appear normal. MRI can also be used, which may show inflammation at the SI joints and help to evaluate for other potential causes of pain, such as stress injuries of the pelvis or lumbar disk pathology.
Treatment involves a biomechanical evaluation to identify causative and aggravating factors. Attention should be focused on ensuring symmetrical mobility of the hip flexors and ITB. Activation of the transverse abdominal stabilizing muscles (transverse abdominus, lower portions of the internal oblique) has been shown to have a stabilizing effect on the SI joint .
For acute pain, a period of rest, NSAIDs, and physical therapy to address these factors is helpful. Manual therapy can also help to mobilize the joint. In recalcitrant cases, cortisone injection into the SI joints can also be considered.
Spinous Process Apophysitis
Skeletally immature dancers differ from mature dancers because of their open growth plates (physes). The physes are at risk of injury either during an acute traumatic event or as a result of repeated stress, in which case the pain may present more insidiously. An apophysitis occurs when a tuberosity is stressed in traction . Due to the different rates of maturation of the male and female skeletons, male athletes tend to present with physical injuries one to two years later than female athletes. In addition, dancers may show delayed skeletal maturity and therefore may present at a later age than athletes in other sports.
Physical Examination and Diagnosis
Spinous process apophysitis may mimic the symptoms of spondylolysis. Presentation often involves diffuse low back pain reproduced with hyperextension maneuvers, but it is not localized to one side or the other. Tenderness to palpation on the spinous process may be present. Resisted extension from a flexed position may cause pain, as this results in traction stress on the dorsal spinous process . Radiographs are usually unremarkable. Bone or SPECT scans may be required to differentiate spinous process apophysitis from spondylolysis .
Treatment involves avoiding hyperextension, and bracing can often be helpful. A time period of four to six weeks of rest and immobilization is usually sufficient to allow full return to activities.
Discogenic Back Pain
The intervertebral disks primarily act as shock absorbers in the spine. They are composed of a central soft, gelatinous ring called the nucleus pulposus and an outer ring of annulus fibrosus (Fig. 6.8). This outer ring is heavily infused with pain fibers.