Standard evaluation and diagnosis of pincer-type femoroacetabular impingment (FAI) relies on anteroposterior (AP) radiographs, clinical evaluation, and/or magnetic resonance imaging (MRI). However, the current evaluation techniques do not offer a method for accurately defining the amount of acetabular rim overcoverage in pincer-type FAI. Several studies have remarked on the particular problems with radiographic evaluation, including beam divergence, difficulty with defining the acetabular rim, and pelvic tilt. Some studies have proposed methods to mitigate these issues; however, radiographic analysis still relies on projected and distorted images, making it difficult to acquire an accurate quantitative estimate of the amount of crossover. We propose a technique that utilises computed tomography (CT) data to accurately quantify the amount of acetabular crossover while accounting for known diagnostic problems, specifically pelvic tilt.

This work describes a novel method that utilises CT data of a patient's afflicted hip joint region to assess the amount of acetabular overcoverage due to pincer deformity. The amount of overcoverage was assessed using a spline curve defined through the segmentation of the acetabular rim from CT data. To mitigate pelvic tilt, the user selected points to define both the pubic symphysis and the promontory in a lateral digitally reconstructed radiograph. The algorithm corrected the pelvic tilt by adjusting to a defined neutral position (in our case, a 60°), and the user adjusted for slight rotation differences ensuring there was a vertical line connecting the symphysis and the sacrococcygeal joint.

After successfully repositioning the pelvis, the algorithm computed the amount of acetabular overcoverage. The algorithm identified the superolateral point of the acetabulum and the most inferior points of the anterior and posterior rim. A line, the mid-acetabular axis, was constructed between the superolateral point and the midpoint of the most inferior points on the anterior and posterior rims; the mid-acetabular axis was extended anterior and posterior to create a plane. Crossover occurred when the anterior rim of the acetabulum intersected this plane. If an intersection occurred, the algorithm measured the length of the mid-acetabular axis, and the length and width of the section representing overcoverage. These points were then projected onto anteroposterior DRRs and again measured to generate a basis of comparison.

We tested our method on four cadaveric specimens to analyze the relationship between radiographic assessment and our technique. We simulated varying degrees of impingement in the cadavers by increasing the amount of pelvic tilt and defining that as the neutral position for a given trial. Moreover, we assessed interobserver variability in repositioning the pelvis as to the effect this would have on the final measurement of crossover length and width.

The software achieved consistent, quantitative measurements of the amount of acetabular overcoverage due to pincer deformity. When compared with conventional radiographic measurements for crossover, there was a significant different between the two modalities. Specifically, both the ratios of crossover length to acetabular length and crossover width to crossover length were less using the CT-based approach (p < 0.001). Moreover, there were no significant differences between observers using our approach.

The proposed technique can form the basis for a new way to diagnosis and measure acetabular overcoverage resulting in pincer impingement. This computational method can help clinicians to accurately correct for tilt and rotation, and subsequently provide consistent, quantitative measurement of acetabular overcoverage.

Prospective match cohort study of disc degeneration progression over ten years with and without baseline discography

To compare progression of common degenerative findings between lumbar discs injected ten years earlier with those same disc levels in matched subjects not exposed to discography

Seventy-five subjects without serious low back pain illness underwent a protocol MRI and a L3/4, L4/5 and L5 S1 discography in 1997. A match group was enrolled at the same time and underwent the same protocol MRI examination. Subjects were followed for ten years. At 7 to 10 years after baseline assessment, eligible discography in controlled subjects underwent another protocol MRI. MRI graders, blind to group designation, scored both groups for qualitative findings.

Well matched cohorts, including 50 discography subjects and 52 control subjects met eligibility criteria for follow up evaluation. In all graded or measured parameters, discs that had been exposed to puncture and injection had greater progression of degenerative findings compared to control (non-injected) discs: progression of disc degeneration, 54 discs (35%) in the discography group compared to 21 (14%) in the control group (p=0.03); 55 new disc herniations in the discography group compared to 22 in the control group (p=0.0003). New disc herniations were disproportionately found on the side of the annular puncture (p=0.0006). The quantitative measures of disc height and disc signal also showed significantly greater loss of disc height (p=0.05) and signal intensity (p=0.001) in the discography disc compared to the control disc.

This study demonstrates that the dimensions of the LSP change with age. Increases in LSP height occur with age. More impressive increases in LSP width occur with advancing age. This study suggests that loss of lumbar lordosis is correlated with changing LSP morphology. The increased width of the LSP with age influences access to the spinal canal, particularly if midline-preserving approaches are attempted in the ageing population. There is increased bone volume for bone grafting procedures with increasing age. The reduced distance between LSPs with age may influence design of implants that stabilize this region of the spine, and occur not only as a result of disk space narrowing, but also as a consequence of increased LSP dimensions.