John was 19 years old and had been in training for carpentry for two years. He was fit and worked out at the gym three days a week doing circuit training and lifting forty kg of weight at a time. Since his growth spurt at approximately age 15, he had had low back pain and this had worsened over the last two years with the bending and awkward lifting needed in his job. He found on occasions he needed to lie down in his lunch break to reduce the discomfort and he had been taking regular ibruprofen and paracetamol for some time to cope. When he had time away from the gym and work his back pain improved but did not go completely.
John had no medications, no medical problems and no partner. He came to his GP as he had decided his condition needed investigation. On examination the GP elucidated that the pain was maximal over L5/S1 region centrally and bilaterally. John’s back movements were full and normal although he complained flexion, extension and lateral rotation hurt at extremes of movement. The GP initially ordered a plain x-ray because of the unusual duration of John’s pain and the impact on his future career. The x-ray showed John had a pars interarticularis defect at L5 and a fused L5/S1.
Pars interarticularis defects are congenitally potential weaknesses in the pars interarticularis. They may be related to spina bifida occulta.1 When the patient is symptomatic due to stress fracture of the pars, there is often a lordotic pose and the hamstring muscles are tight. There is typically paraspinal muscle tenderness. Pars interarticularis defects may have a genetic association and there is an increased incidence in first degree relatives of those affected.2
These defects are aggravated by extension activities, as these increase the load on the pars. Such sudden loads (especially with repeated lumbar flexion and extension), and injuries may cause a stress fracture from ongoing mechanical stress to the pars, and is most common in childhood. It is also not unusual for the fracture to be missed by parents, as it is due to chronic stress and so the final acute injury may be relatively painless. The fractured region is called “spondylolysis” and is a unilateral or bilateral stress fracture of the narrow bridge between the upper and lower pars interarticularis. It is most common between ages six to ten years, and the next most common age group for such acute fractures to occur is in the teenage years, during the growth spurt. At this age, the L5 vertebra can slip forward on S1, producing what is known as “an isthmic spondylolisthesis”. This can cause an asymmetrical pressure on the L5 and S1 discs, with sciatica if nerve outlets are irritated. Early osteoarthritis is an end result. The most common level of a spondylolytic lesion is at the L5 level, estimated at 85-95%, followed by the L4 level, estimated at 5-15%.2 The risk factors for teenage spondylysis are competitive sports, later teenage years and training more than two hours a day.2
The management of these defects when they are symptomatic includes physiotherapy, a lumbar brace, analgesia and modification of activities. Generally, the prognosis is best if spondylolysis is identified and managed early. Surgery is usually avoided unless absolutely necessary.
1. Licina, P. Surgery for Low Back Pain. How to treat, Australian Doctor. 12 May 2006
2. Malanga, G. Pars Interarticularis Injury. Medscape. 20 October 2015