Spondylolysis

Spondylolysis refers to the bone defect in the pars interarticularis. It is caused by repeated trauma or physical stress to the biomechani-cally vulnerable lamina between the superior and inferior articular facets. Spondylolysis divides a vertebra into the superior and inferior segment. The former segment includes the vertebral body, pedicles, transverse processes, and superior articular facet and the latter the inferior articular facet, laminae, and spinous process. Spondylolysis is an important disease that causes lasting low-back pain, especially in gymnasts (Jackson et al. 1976; Collier et al. 1985). The incidence ranges from 3% to 10%. A hereditary trait has been reported (Jackson et al. 1976).

Radiographic features vary according to disease stage: (a) osteopenic band in the early stage, (b) obvious bone defect across the lamina in the established stage, and (c) reactive sclerosis or callus formation and bony reunion in the late and cured stage (Fig. 9.62A). Spondylolysis, the bilateral form in particular, is frequently complicated by the anterior slippage or spondylolisthesis of the superior segment of the divided vertebra. CT is ideal for accurate anatomical investigation of spondylolysis and its associated lesions such as disk herniation, intervertebral foraminal narrowing, and neural canal indentation. MRI is another excellent modality for diagnosing bone defect, disk her-niation, nerve compression, and soft-tissue changes.

Planar scintigraphy is not so helpful in defining bone defects because many fail to accumulate tracer visibly (Lusins et al. 1994). Furthermore, there is no predictable pattern of correlation between the radiographic and scin-tigraphic findings (Gelfand et al. 1981). Indeed, we performed pinhole scintigraphy in seven patients with proven spondylolysis, but none yielded a positive result (Fig. 9.62B).

Intervertebral Foraminal Narrowing

Fig. 9.62A, B Spondylolysis and spondylolisthesis. A Lateral radiograph of L4 and L5 vertebrae in a 45-year-old man with back pain shows a large bone defect involving the pars interarticularis of the L4 vertebra (open arrows) and mild anterior sliding. A small osteophyte is seen (arrow) (aj apophyseal joint). B Lateral pinhole scin-tigraph portrays no abnormal tracer uptake in the spondylolysis defect. However, the anterior sliding of the L4 vertebra is clearly delineated by virtue of increased tracer uptake in the osteophyte and lower endplate, the sign of the secondary osteochondrosis (arrow)

Fig. 9.62A, B Spondylolysis and spondylolisthesis. A Lateral radiograph of L4 and L5 vertebrae in a 45-year-old man with back pain shows a large bone defect involving the pars interarticularis of the L4 vertebra (open arrows) and mild anterior sliding. A small osteophyte is seen (arrow) (aj apophyseal joint). B Lateral pinhole scin-tigraph portrays no abnormal tracer uptake in the spondylolysis defect. However, the anterior sliding of the L4 vertebra is clearly delineated by virtue of increased tracer uptake in the osteophyte and lower endplate, the sign of the secondary osteochondrosis (arrow)

Bilateral Spondylolytic Defects

Fig. 9.63A, B High-resolution SPECT of acute spondylolysis. A Lateral radiograph of L5-S1 in a 41-year-old female with sudden back pain shows a band-like bone defect across the pars interarticularis (arrow). B High-resolution SPECT demonstrates small ovoid "hot" areas in the pars interarticularis bilaterally (arrow)

Fig. 9.63A, B High-resolution SPECT of acute spondylolysis. A Lateral radiograph of L5-S1 in a 41-year-old female with sudden back pain shows a band-like bone defect across the pars interarticularis (arrow). B High-resolution SPECT demonstrates small ovoid "hot" areas in the pars interarticularis bilaterally (arrow)

Pars Defect

Fig. 9.64A, B Spondylolisthesis. A Anteroposterior radiograph of the lumbosacral spine in a 47-year-old man with disabling back pain demonstrates an ovoid "double bone density" overlapping the base of the sacrum (open arrows). B Anterior pinhole scintigraph shows the characteristic "ovoid vertebra" sign, indicating anterior and downward sliding of the L5 vertebra (arrows)

Fig. 9.64A, B Spondylolisthesis. A Anteroposterior radiograph of the lumbosacral spine in a 47-year-old man with disabling back pain demonstrates an ovoid "double bone density" overlapping the base of the sacrum (open arrows). B Anterior pinhole scintigraph shows the characteristic "ovoid vertebra" sign, indicating anterior and downward sliding of the L5 vertebra (arrows)

Spondylosis appears to be one of uncommon situations in which pinhole scintigraphy makes little contribution to the diagnosis. The likelier reasons are that the collimator-to-object distance is too great to image a small defect in the pars interarticularis and that old defects do not concentrate tracer visibly (Collier et al. 1985; Lusins et al. 1994). High-resolution SPECT can be recommended for acute spondylolysis as it can eliminate overlap, enhancing image contrast (Fig. 9.63). However, it is not useful for ancient or healed lesions (Collier et al. 1985; Lusins et al. 1994).

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