the US population. A slip or fracture of the intravertebral joint is usually acquired between the ages of 6 and 16 years, but remains unnoticed until adulthood. Roughly 90 percent of these isthmic slips are low-grade (less than 50 percent slip) and 10 percent are high-grade (greater than 50 percent slip). It is divided into three subtypes: A: pars fatigue fracture B: pars elongation due to multiple healed stress effects C: pars acute fracture Severity Classification by degree of the slippage, as measured as percentage of the width of the vertebral body: Grade I spondylolisthesis accounts for approximately 75% of all cases. Grade I: 0–25% Grade II: 25–50% Grade III: 50–75% Grade IV: 75–100% Grade V: greater than 100% Signs and symptoms Symptoms of lumbar anterolisthesis include: A general stiffening of the back and a tightening of the hamstrings, with a resulting change in both posture and gait. A leaning-forward or semi-kyphotic posture may be seen, due to compensatory changes. A "waddle" may be seen in more advanced causes, due to compensatory pelvic rotation due to decreased lumbar spine rotation. A result of the change in gait is often a noticeable atrophy in the gluteal muscles due to lack of use. Generalized lower-back pain may also be seen, with intermittent shooting pain from the buttocks to the posterior thigh, and/or lower leg via the sciatic nerve. Other symptoms may include tingling and numbness. Coughing and sneezing can intensify the pain. An individual may also note a "slipping sensation" when moving into an upright position. Sitting and trying to stand up may be painful and difficult. Physical Exam The major components of the physical exam for spondylolisthesis consists of observation, palpation, and maneuvers. The most common finding is pain with lumbar extension. The following physical involves specific assessment for spondylolisthesis. However, a general examination, most importantly neurological examination, must be done to rule out alternative causes for signs and symptoms. Neurological examination is often normal in patients with spondylolisthesis, but lumbosacral radiculopathy is commonly seen in patients with degenerate spondylolisthesis. Observation The patient should be observed walking and standing. Most patients present with a normal gait. An abnormal gait is often the sign of a high grade case. A patient with high grade spondylolisthesis may present with a posterior pelvic tilt causing a loss in the normal contour of the buttocks. An antalgic gait, rounded back and decreased hip extension, can