Understanding Bilateral Pars Defect: A Common Condition Among Elite Adolescent Athletes

Bilateral pars defect, also known as spondylolysis, is a condition characterized by a fracture or weakening of the pars interarticularis, which is the weakest part of the posterior vertebral arch. This condition is more common among certain groups of individuals, including divers, rowers, gymnasts, weight lifters, wrestlers, and throwing track and field athletes.

Studies have shown that male-to-female ratios range from 2:1 to 3:1, indicating a higher prevalence among males. In addition, elite adolescent athletes are more likely to experience spondylolysis, with an incidence rate of 8-15%. The general population's incidence rate is significantly lower, ranging from 3-6%.

Children and adolescents are particularly prone to fatigue pars fractures due to their developing spines. As individuals age, the strength of the neural arch increases until around the age of 50. However, sport-specific maneuvers that involve repetitive twisting, rotation, and extension can still result in stress injuries.

Isthmic spondylolysis is a type of fatigue fracture that occurs in the pars interarticularis isthmus, which is the weakest part of the posterior vertebral arch. This condition is often caused by repetitive stress and hyperextension or rotatory forces.

Research has also found that first-degree relatives of individuals affected by spondylolysis are more likely to develop the condition themselves, with an incidence rate of 19% compared to the general population. While the acquired theory is the most widely accepted explanation for spondylolysis, there is evidence suggesting a genetic component may contribute to its development.

Interestingly, congenital anomalies such as spina bifida occulta are often associated with pars defects. Spondylolisthesis, a condition characterized by the forward displacement of the upper vertebra relative to the caudal vertebra, is also related to spondylolysis and occurs in approximately 25% of cases.

Repetitive bone stress is considered the earliest sign of disease, and it can lead to bone remodeling and potentially result in spondylolysis. The spectrum of pathologies in the pars interarticularis ranges from bone stress and pars fracture (spondylolysis) to isthmic spondylolisthesis, representing an anterior vertebral slippage.

In some cases, these lesions can develop asymptotically and only become symptomatic later in life when the injury becomes chronic. As a result, it is essential for athletes and individuals with a history of repetitive sports injuries to be aware of the risk factors associated with bilateral pars defect and seek medical attention if they experience any symptoms.