Positional MR imaging of normal and injured knees.

OBJECTIVES: This study uses a practical positional MRI protocol to evaluate tibiofemoral translation and rotation in normal and injured knees. METHODS: Following ethics approval, positional knee MRI of both knees was performed at 35° flexion, extension, and hyperextension in 34 normal subjects (mean age 31.1 ± 10 years) and 51 knee injury patients (mean age 36.4 ± 11.5 years, ACL tear n = 23, non-ACL injury n = 28). At each position, tibiofemoral translation and rotation were measured. RESULTS: Normal knees showed 8.1 ± 3.3° external tibial rotation (i.e., compatible with physiological screw home mechanism) in hyperextension. The unaffected knee of ACL tear patients showed increased tibial anterior translation laterally (p = 0.005) and decreased external rotation (p = 0.002) in hyperextension compared to normal knees. ACL-tear knees had increased tibial anterior translation laterally (p < 0.001) and decreased external rotation (p < 0.001) compared to normal knees. Applying normal thresholds, fifteen (65%) of 23 ACL knees had excessive tibial anterior translation laterally while 17 (74%) had limited external rotation. None (0%) of 28 non-ACL-injured knees had excessive tibial anterior translation laterally while 13 (46%) had limited external rotation. Multidirectional malalignment was much more common in ACL-tear knees. CONCLUSIONS: Positional MRI shows (a) physiological tibiofemoral movement in normal knees, (b) aberrant tibiofemoral alignment in the unaffected knee of ACL tear patients, and (c) a high frequency of abnormal tibiofemoral malalignment in injured knees which was more frequent, more pronounced, more multidirectional, and of a different pattern in ACL-tear knees than non-ACL-injured knees. KEY POINTS: • Positional MRI shows physiological tibiofemoral translation and rotation in normal knees. • Positional MRI shows a different pattern of tibiofemoral alignment in the unaffected knee of ACL tear patients compared to normal control knees. • Positional MRI shows a high prevalence of abnormal tibiofemoral alignment in injured knees, which is more frequent and pronounced in ACL-tear knees than in ACL-intact injured knees.

Accuracy of ultrasound in the characterization of superficial soft tissue tumors: a prospective study.

OBJECTIVE: To prospectively evaluate the accuracy of ultrasound in defining the specific nature of superficial soft tissue masses as well as determining malignancy. MATERIALS AND METHOD: Eight hundred twenty-three superficial soft tissue masses were prospectively evaluated with ultrasound by one of five experienced musculoskeletal radiologists. The radiologist at the time of examination provided one to three specific differential diagnoses and the perceived level of confidence with regard to each diagnosis. Clinical and ultrasound diagnoses were compared with the histological diagnosis to determine accuracy. Tumor malignancy was determined by histology or clinical/imaging follow-up. RESULTS: Histological correlation was present for 219 (26.6%) of the 823 masses. Compared with histology, the accuracy of clinical and ultrasound examination for determining specific tumor type was 25.6% and 81.2% respectively considering all differential diagnoses provided. Radiologists were "fully confident" with the ultrasound diagnosis in 585 (71.1%) of 823 masses overall. In this setting, when compared with histology, the diagnostic accuracy of ultrasound was 95.5%. When the radiologist was "not fully confident," accuracy was 41.3% for the first differential diagnosis and 60.9% for all differential diagnoses. Diagnostic accuracy improved with increasing radiologist experience. Sensitivity, specificity, positive predictive value, and negative predictive value of ultrasound for identifying malignant tumor were 93.3%, 97.9%, 45.2%, and 99.9% respectively. CONCLUSIONS: One can be "fully confident" at characterizing over two-thirds of superficial soft tissue masses based on ultrasound appearances and, in this setting, diagnostic accuracy is very high. Ultrasound examination is also highly accurate at discriminating benign from malignant superficial soft tissue masses.

Developmental cervical spinal canal size: population reference range.

Background: The developmental size of the cervical spinal canal varies considerably. Neural compression and injury are more likely with a developmentally small spinal canal. This study was designed to develop a population reference range for developmental cervical spinal canal size for the Hong Kong population. Methods: Prospective study of 522 ambulatory patients (256 males, 266 females, mean age 55±18 years; range, 20-89 years) who underwent computed tomography (CT) neck examinations. Using a manually operated segmentation program, spinal canal, and vertebral body cross-sectional area (CSA), anteroposterior (AP) sagittal diameter, and width were measured at each level from C3-C7. Patient height and weight were measured. Results: Considerable variation in spinal canal size existed with, for example, a 164-168% variation exists for males and females between the largest and smallest spinal canal CSA at C5. All spinal canal measurements increased slightly with height (r=0.25-0.36, P<0.001), while vertebral body AP sagittal diameter increased with age (r=0.48-0.51, P<0.001). All spinal canal measurements were larger (<0.0001) in males. Although spinal canal CSA was larger in males (at C5, males 276.0±41.5 mm2; females 252.6±38.4 mm2), relative to vertebral body CSA, spinal canal CSA was larger in females. Arbitrary population thresholds indicating the smallest 25% spinal canal CSA and AP sagittal diameter as well as other parameters were defined. Conclusions: There is a large variation in developmental cervical spinal canal size within the Hong Kong population. A reference range of developmental spinal canal size was developed which will enable an objective assessment of an individual's cervical spinal canal size relative to the wider population.