Bilateral fast magnetic resonance imaging of the operated carpal tunnel

The effect of landmarks and bone motion on posture-related changes in carpal tunnel volume

BACKGROUND

Deviated wrist postures have been linked to carpal tunnel syndrome development, yet the effect of posture on carpal tunnel volume remains unclear. The purposes of this study were (i) to evaluate the effect of boundary definitions on tunnel volume estimates in neutral and non-neutral (30 degrees flexion, 30 degrees extension) wrist postures and (ii) to develop a biomechanical wrist simulation to predict posture-related changes in tunnel volume.

METHODS

Two carpal tunnel volume measures were calculated using (i) ulnar bony landmarks and (ii) radial and ulnar bony landmarks identified directly from magnetic resonance imaging (MRI) scans. A third volume measure combined computerized tunnel reconstructions with modelled bone surfaces to calculate an anatomically landmarked volume. Six individual simulations were then generated to predict volume in the flexed and extended postures based on individual carpal bone motions.

FINDINGS

Boundary definitions influenced the absolute volume in each posture and the relative changes between postures. Relative to fully reconstructed volumes, radial and ulnar landmarked volumes were 15-25% larger across postures (681 (SD 467) mm(3); P=0.01), while the ulnar-only landmarked volumes were 10-20% smaller (562 (343) mm(3); P<0.01). Simulation predicted volumes were not significantly different from the reconstructed anatomically landmarked volumes, with less inter-individual variability between postures compared to MRI-based volumes.

INTERPRETATION

Comparison of volume measures indicated the importance of capturing posture-related changes in the orientation of the proximal and distal tunnel boundaries, and revealed potential sources of error associated with volume reconstruction. Simulations can enable changes in tunnel dimensions to be related to bone movements throughout a range of motion.

Quantitative MRI of the wrist and nerve conduction studies in patients with idiopathic carpal tunnel syndrome

OBJECTIVE

To correlate morphological findings of idiopathic carpal tunnel syndrome (CTS) with the function of the median nerve.

METHODS

In this study, 105 wrists of 105 women patients with idiopathic CTS, and 36 wrists of 36 female volunteers were subjected to nerve conduction studies and MRI. Cross sectional area, signal intensity ratio, and the flattening ratio of the median nerve, carpal tunnel area, flexor tendon area, synovial area, and intersynovial space, and the palmar bowing of the transverse carpal ligament (TCL) were quantified by MRI and correlated with the severity of the disease determined by nerve conduction studies.

RESULTS

Cross sectional areas of the median nerve, flexor tendons, and carpal tunnel, and the palmar bowing of the TCL of the CTS groups were greater than in the control group, but differences were not detected among the CTS groups for the area of the flexor tendons and the carpal tunnel. Enlargement, flattening, and high signal intensity of the median nerve at the distal radioulnar joint level were more significant in the advanced than in the earlier stages of the disease. Increase in palmar bowing of the TCL was less prominent in the most advanced group. Linear correlation between the area of the carpal tunnel and palmar bowing of the TCL was noted.

CONCLUSION

Severity of the disease could be judged by evaluating not only longitudinal changes of signal intensity and configuration of the median nerve, but also palmar bowing of the TCL. Increased palmar bowing of the TCL was found to be associated with an increase in the area of the carpal tunnel.

Results of carpal tunnel release

We evaluated, by means of a prospective study, the results of carpal tunnel release both clinically and electrophysiologically in 188 patients with a carpal tunnel syndrome. A questionnaire was completed by patient and surgeon pre- and post-operatively (6 and 12 months after operation), when physical examination, electromyography and nerve conduction tests were also performed. Full pre- and post-operative results were available for 136 patients and 82% of the patients were satisfied with the results of the operation. Symptoms caused by median nerve compression showed the greatest improvement and no fixed patterns with regard to unsatisfactory results were found. If pain persisted in the wrist, many patients considered the operation to have been unsuccessful. Electrophysiological improvement occurred in all patients and at 12 months follow-up, median nerve conduction was normal in 21% of cases. Thus distal sensory latency remained abnormal in 79% of the patients, emphasizing the need for caution when recurrence of carpal tunnel syndrome is diagnosed in such cases.

Magnetic resonance imaging of the wrist

MR imaging of the wrist has the unique capability of simultaneously demonstrating bone and soft tissue structures. Its exquisite sensitivity for detecting bone marrow edema makes it and ideal screening tool for diagnosing radiographically occult osseous injuries and areas of AVN. This, together with its ability to provide a comprehensive, non-invasive assessment of the ligaments, tendons, nerves, and components of the TFC make MRI a very powerful tool for evaluating patients with wrist pain of uncertain etiology. Its exact role in the work-up of these patients has not been entirely established, but with further advances in technology and the radiologist's understanding of wrist anatomy and pathology, MRI is assuming a more central role in this clinical setting.