Anatomic Evaluation of the Sacroiliac Joint: A Radiographic Study with Implications for Procedures.

BACKGROUND: Sacroiliac joint (SI) pain is increasingly being recognized as a source of low back pain. Injections and percutaneous type procedures are performed to treat symptomatic joints. However, there are limited studies available assessing the anatomy of the SI joint in vivo among patients with pain. OBJECTIVES: The purpose of this study was to provide more precise information on the dimensions and orientation of the SI joint using a new technique for the radiographic evaluation of this joint. STUDY DESIGN: Observational study. SETTING: Emergency department METHODS: Three dimensional computed tomographic (CT) reconstructions of the pelvis were formatted from 100 SI joints in 50 patients who had clinically indicated abdominal/pelvic scans. These images were manipulated to evaluate the SI joint in multiple planes and measure its dimensions, area, and relationship to anatomic landmarks such as the anterior superior iliac spine (ASIS) and posterior superior iliac spine (PSIS). RESULTS: Of the 50 patients, 23 were men and 27 women. Their mean age was 47.6 years (± 18.1). The SI joint consists of a superior limb which measures 39.7 mm (± 4.8) in length, and an inferior limb which measures 54.3 mm (± 5.1), oriented at an angle of 100.1° (± 8.1) to one another. The mean area of the joint was 1276.8 mm2 (± 189.8). The horizontal distance from the ASIS to the front of the superior SI joint is 75.4 mm (± 8.4). The horizontal distance from the PSIS to the back of the superior SI joint is 43.9 mm (± 5.6). The joint stretches 7.5 mm (± 5.9) cephalad and 38.1 mm (± 6.4) caudal to the PSIS, and 35.4 mm (± 8.8) cephalad and 10.2 mm (± 11.4) caudal to the ASIS. LIMITATIONS: CT scans were performed with patients lying supine, while most SI joint procedures are performed with a patient prone. However it is doubtful that the bony anatomic landmarks would change appreciable in this largely immobile joint. These patients were seen in the emergency department for a variety of conditions related to abdominal and pelvic pain, and not exclusively for SI joint pain. CONCLUSIONS: Treatment of the SI joint by surgeons and interventionalists is hampered by the limited number of anatomic studies in the literature. Our study presents the SI joint as a 2-limbed structure, sitting from slightly above the level of the PSIS rostrally to slightly below the level of the ASIS caudally. Palpation of these landmarks may assist in directing physicians to the joint. To begin an interventional pain procedure, with a patient lying prone, this data supports tilting the x-ray image intensifier 10 degrees caudal past the vertical anteroposterior (AP) view for optimal approach of the SI joint's inferior limb. The needle entry should be about 44.1 mm (1.75 inches) caudal to the PSIS. The image intensifier should have a 12 degree left lateral oblique view for injection of the right SI joint, and a 12 degree right lateral oblique view for the left SI joint.

Magnetic resonance imaging-based topographical differences between control and recurrent patellofemoral instability patients.

BACKGROUND: Plain films and computed tomography (CT)-based imaging were the first to establish measurements that evaluated patellar instability. Limited research has shown the efficacy of magnetic resonance imaging (MRI) in evaluating these established measurements. PURPOSE: To identify morphological differences between normal knees and those with patellofemoral instability on MRI to determine what measurements are significant and how MRI-based means differ from historical means based on radiograph and CT imaging. STUDY DESIGN: Case control study; Level of evidence, 3. METHODS: Eighty-one controls and 40 patients with recurrent patellar instability between 2006 and 2010 were reviewed. The control patients had a history and an examination negative for patellofemoral symptoms. Patients with patellar instability had a history of at least 2 frank patellofemoral joint dislocations (PFJDs). The MRI images were obtained on the nonweightbearing knee in full extension. Measurements of patellar tilt, trochlear morphologic characteristics, and tibial tuberosity-trochlear groove (TTTG) distance were evaluated on axial slices, and patellar height was measured on sagittal images. Trochlear shape was assessed at the proximal and distal trochlea. RESULTS: All measurements of patellar tilt (mean ± SD) were found to be significantly different between the 2 groups. For patellar height, the Insall-Salvati ratio (control, 1.08 ± 0.02; PFJD, 1.26 ± 0.03) and Caton-Deschamps ratio (control, 1.13 ± 0.02; PFJD, 1.29 ± 0.03) proved to be significantly different. Trochlear morphologic characteristics had numerous measurements prove to be significantly different proximally and distally. These included classic measurements such as sulcus angle (control, 148.48° ± 0.94°; PFJD, 165.57° ± 2.65°) and lateral trochlear inclination (control, 21.27° ± 0.66°; PFJD, 13.31° ± 1.36°) proximally and less established measurements such as the ratio of external (lateral) trochlea to internal (medial) trochlea (control, 1.51 ± 0.05; PFJD, 2.11 ± 0.17), a measurement of facet asymmetry. CONCLUSION: The MRI-based patellar tilt measures proved to be an excellent group of measurements for delineating between controls and those with instability. Patella alta ratios, such as Insall-Salvati and Caton-Deschamps, demonstrated a statistically significant difference between normal and recurrent dislocators. Trochlear measurements proved significantly different at the proximal and distal trochlea. Our findings demonstrate that MRI is appropriate to help discern recognized pathologic abnormalities that characterize patellofemoral instability.

Incidence and prevention of intervertebral cage overhang with minimally invasive lateral approach fusions.

STUDY DESIGN: Radiographic review. OBJECTIVE: To evaluate the incidence and degree of cage overhang in minimally invasive spinal (MIS) fusions, when using either the direct lateral interbody fusion (DLIF) or extreme lateral interbody fusion (XLIF) techniques. SUMMARY OF BACKGROUND DATA: Among the difficulties surgeons face during a MIS lateral interbody fusion is to assess the proper placement of the cage without the use of direct visualization. Determining the proper length of the cage using AP view fluoroscopy can be misleading. As the axial profile of the vertebral body is oval, inserting the cage anterior or posterior to the maximal width point requires adjustment of the cage's length. METHODS: The incidence and degree of cage overhang were measured using magnetic resonance imaging (MRI) and computed tomography (CT) studies from patients that underwent a MIS lateral interbody fusion. To determine the adjustment needed when the cage is inserted at various sagittal sites, the coronal spans of normal vertebral endplates were measured. RESULTS: Forty-five percent of the cages were placed in the central portion, 34% were located in the anterior 1/3, and 7% were located in the posterior 1/3 of the disc space. Of the anterior positioned cages, 45% were found to be overhanging outside of the boundaries of the intervertebral disc space. The average measured lateral protrusion was 7.8 +/- 3.6 mm, and anterior protrusion was 9.8 +/- 3.3 mm. The vertebral body width measured 41.7 +/- 6 mm at the anterior 1/3, 50 +/- 4 mm at the mid, and 49 +/- 1 mm at the posterior 1/3. Compared with the midvertebral width, the vertebral body width at the anterior 1/3 was decreased by 16.5% +/- 0.9% (P < 0.05). CONCLUSION: The risk of placing an excessively long cage, when the insertion site is located in the anterior 1/3 of the disc, is relatively high, when performing MIS lateral approach interbody fusions. When using an anterior entry point for the insertion of the cage, choosing a 15% shorter cage length compared with that measured on the AP should prevent anterolateral protrusion of the cage.