Purpose

The thumb carpometacarpal (CMC) joint, comprised of the trapezium (TM) and 1st metacarpal (MC), is a primary location of osteoarthritis (OA), which affects 20% of women and 6% of men over age 45 (1). Thumb CMC OA is commonly diagnosed and graded using radiographs (2), but radiography suffers from poor grading reliability (3). Magnetic resonance imaging (MRI) utilizes non-ionizing radiation and permits evaluation of not only osseous anatomy, but also soft tissue structures around the thumb CMC joint (4). Quantitative MRI (qMRI) of articular cartilage also provides a numerical basis for evaluation of OA and has shown high measurement repeatability (5). qMRI techniques, such as delayed gadolinium enhanced MRI of cartilage (dGEMRIC), have been applied to the thumb CMC joint (6), but requires the use of exogenous contrast agents. It is advantageous to explore additional qMRI techniques which mitigate these technical challenges. Therefore, the purpose of this study was to evaluate the feasibility of performing non-contrast T1ρ and T2 mapping of the articular cartilage in the thumb CMC joint.

Methods

The study was IRB approved with informed written consent. Subjects: 9 volunteers, 3M / 6F, 37.8±11.6 y.o. (mean ± SD), with asymptomatic thumb CMC joints. Image Acquisition: Scanning was performed on a clinical 3T scanner (GE Healthcare) with an 8 channel phased array hand/wrist coil (Invivo, Gainesville, FL). Morphologic multi-planar fast-spin-echo (FSE) images were acquired: echo time (TE): 24 ms, repetition time (TR): 4000 ms, receiver bandwidth (RBW): ±50 kHz, acquisition matrix (AM): 512x352, number of excitations (NEX): 2, field-of-view (FOV): 9 cm, slice thickness (SL): 2-3 mm. Quantitative T1ρ and T2 mapping was performed to evaluate the articular cartilage (7): TR: 7.8 ms, 4 TSLs: 0-60ms, with ΔTSL=20ms, and spin lock frequency=500 Hz, or 7 TEs: 0-45 ms with ΔTE=6.4ms. Both quantitative series utilized: FOV:10 cm, SL: 2 mm, AM: 256 x 160, RBW: ±41.7 kHz. Image Evaluation: The CMC volar oblique and dorsal deltoid ligaments were assessed for abnormal signal intensity or the presence of a tear (8) and the TM and MC articular surfaces were evaluated using a modified Outerbridge score: intact cartilage, partial thickness loss, or full thickness loss. T1ρ and T2 values of the articular cartilages were calculated (Matlab, Natick, MA) using a mono-exponential decay fitting method (9). The articular surfaces were segmented into Dorsal (D), Volar (V), Radial (R), and Ulnar (U) regions as well as separate quadrants (DR, DU, VR, VU) on the TM and MC bones. Statistical Analysis: A Signed Rank test was performed to detect differences of cartilage T1ρ and T2 values for the TM and MC between regions (R/U and D/V). A one way repeated measures analysis of variance was performed to detect differences of T1ρ and T2 values across all quadrants on each bone. Significance was set at p<0.05.

Results

All TM and MC articular surfaces had intact cartilage (Figure 1). A majority of dorsal deltoid ligaments were normal (7/9), with the remainder evaluated as “scarred”, while all volar oblique ligaments (9/9) were evaluated as normal. Representative T1ρ and T2 maps are shown in Figure 2. T1ρ and T2 values did not differ between the D/V or R/U regions, or among the quadrants evaluated in the TM or MC (p>0.05 for all comparisons, Figure 3). Regional and quadrant values of T1ρ and T2 tended to be prolonged on the TM as compared to the MC, but was not significant (p>0.05).

Discussion

Functional tasks of the thumb CMC joint, such as grasp and fine pinch, may be limited by pain attributable to OA. MRI provides a means to non-invasively and quantitatively evaluate the articular cartilage and surrounding soft tissue joint structures. This study of asymptomatic individuals detected no cartilage degeneration and found no differences of regional or quadrant specific T1ρ or T2 values on either the TM or MC. The uniformity of T1ρ and T2 values may be attributed to the lack of degeneration present. Since cartilage thinning during OA is known to occur primarily within the volar regions of each bone (10,11), we may anticipate concomitant differences of T1ρ and T2. Future evaluations will benefit from increased subject enrollment to permit comparisons between genders and among OA grades.

Conclusion

This study showed that quantitative T1ρ and T2 mapping is feasible at the human thumb CMC joint, and provides a normative dataset with which to compare values generated in thumb CMC joints of symptomatic individuals. TM articular cartilage tended to have slightly prolonged T1ρ and T2 values as compared to MC articular cartilage in this asymptomatic cohort.

Acknowledgements

The authors would like to acknowledge Roseanne Zeldin RT-(R)(M) Jung Joo RT-(R)(MR) for their assistance with this project.

References

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