[Computerized tomography of the meniscus with a stress device]

PURPOSE

We investigated the usefulness of a mechanical stress device to increase widening of the articular rima in CT studies of the meniscus on forced varus and valgus.

MATERIAL AND METHODS

September 1997 to October 1998, we examined 284 patients with symptoms and clinical signs of meniscal injury. CT was performed during forced varus and valgus, depending on the site of the suspected damage, in 70 of 284 patients. We used an FOV of 18 cm, with a potential difference of 140 kVp and power of 170 mA. The reconstruction matrix was 512 x 512 and acquisition time was 3 s. A set of 8-10 partially overlapping scans were acquired craniocaudally, with slice thickness of 1.5 mm and gap of 1 mm. The mechanical strainer was locked in the correct position and a second set of 4-5 images acquired at the meniscus. Then the patients were submitted to arthroscopy to check the radiological findings.

RESULTS

CT performed in forced varus and valgus had 96.8% specificity, 97.3% sensitivity and 97.1% diagnostic accuracy. Sensitivity was 100%, specificity 96% and diagnostic accuracy 98% in the medial meniscus, while we had 88.9%, 100% and 94.7% respectively in the external meniscus.

CONCLUSIONS

CT with a mechanical stress device was extremely useful in defining the meniscal loose edge. It also showed the exact shape and complexity of meniscal injury, even in the cases with narrow articular rima or those where conventional CT had performed poorly.

[High-resolution ultrasonography in the study of carpal tunnel syndrome]

We investigated the reliability of some US signs in the diagnosis of the carpal tunnel syndrome. We carried out a single-blind study with 13-MHz high resolution probes and electromyography on 132 patients with clinical evidence of the carpal tunnel syndrome; a control group of 20 asymptomatic patients was also submitted to US. Eighty-six of 107 patients with US signs of the carpal tunnel syndrome were then submitted to surgical decompression (resection of the transverse carpal ligament), while the extant 21 patients underwent conservative treatment and clinical follow-up. To diagnose the carpal tunnel syndrome, we considered the following US patterns: median nerve changes (swelling before its entrance into the carpal tunnel and flattening in the tunnel itself), palmar bowing of the flexor retinaculum, thickening of the transverse carpal ligament and increased depth of the carpal tunnel, as measured from the apex of the transverse carpal ligament convexity to the underlying carpal bone. Median nerve changes were unreliable signs and were missing in many cases: only 45 of 107 patients exhibited median nerve swelling before and/or its flattening in the carpal tunnel (42%). Such indirect signs as the thickening of the transverse carpal ligament in chronic cases were demonstrated in 94 of 107 patients with the carpal tunnel syndrome (88%) and canal deepening in all unilateral carpal tunnel syndromes was shown in 92 of 107 patients (87%); both these signs proved to be much more reliable. The palmar bowing of the flexor retinaculum was also difficult to demonstrate in surgical patients or in those with connective tissue fibrosis within the tunnel: this sign was demonstrated in 80 of 107 patients with the carpal tunnel syndrome confirmed with electromyography (75%). Tanzer and Rietze reported median nerve changes observed at surgery in 43% and 66% of their patients, respectively. Recent MR findings in asymptomatic wrists have demonstrated that the normal median nerve has an elliptical shape inside the carpal tunnel. To conclude, high resolution US exhibited 96% sensitivity, 95% specificity and 93% diagnostic accuracy and proved to play a major role in the diagnosis of the carpal tunnel syndrome.