The Study Of Trapeziometacarpal Joint Anatomy And Stress View Radiograph In The Evaluation Of Trapeziometacarpal Joint Laxity

Objective To study the course, adjacence, appearance and structure characteristic of the trapeziometaearpal joint of the thumb, and their function in stabilizing the TM joint. Radiographic evaluation of this joint is difficult owing to the obliquity of the articulation. We obtain a bilateral stress radiograph of the thumbs to measure CMC joint laxity. We hypothesized that this technique would be reliable.we get the original data including radial subluxation of the first metacarpal base, besides we compare the differences between men and women.Method10adult forearm without deformity and trauma were obtained.Dissect and observe the courser,adjacence,appearance and structure characteristic of the trapeziometaearpal joint.Obtain the lengths and changes of those ligaments stabilizing the trapeziometaearpal joint during thumb motion and observe the changes of joint stability when one of them was cut. A stress radiograph was obtained of66patients without injuring the trapeziometaearpal joint, the elbows flexed to90°bilaterally with the subject seated, the forearms held about10cm apart and pronated approximately45°inneutral deviation, and actively press thumb together with the metacarpophalangeal (MCP) and interphalangeal joints touching. The MCP joint is held in slight flexion at15°to20°and the interphalangeal joint is positioned at0°extension.A PA radiograph was obtained of30patients in hospital with the thumb in resting position as control group.Two measurements were performed:radial subluxation of the first metacarpal base, first metacarpal articular width.Two hand surgeon performed measurements using digital calibration.T-test were performed to assess the reliability.Resules①here are5main ligaments around the trapeziometaearpal joint,include the beak ligamentn dorsoradial ligament、intermetacarpal ligaments posterior oblique ligament and ulnar collageral ligament.The dorsal ligament complex contains dorsoradial ligament and posterior oblique ligament.The resting TM joint is lax and unstable,but it becomes stable when the thumb is in opposition station. In the final phase of opposition, the volar beak of the thumb metacarpal locks into the trapezium recess pivot area as part of a cantilevered force couple. The other part of this cantilevered force couple is the tension in the dorsal ligament complex,which provides the compression to convert a lax, unstable, incongruous joint into a rigidly stable, congruous TM joint. Screw home torque rotation is the key to TM joint stability. The intrinsic abductor pollicis brevis muscle abducts the thumb at the TM joint. The opponens pollicis then rotates the thumb so that the flexor brevis,adductor pollicis and flexor pollicis longus can further compress the TM joint. A previously lax, subluxable, incongruous TM joint thus gains articular congruence and rigid stability for power pinch and grasp during the final phase of opposition, the screw home torque rotation. The trapezium recess is the pivot area; the volar beak ligament is not the pivot point. The dorsal ligament complex becomes obliqueand shortens under tension as the TM joint space is compressed during screw home torque rotation in the last phase of opposition.If the dorsal ligament complex is cut, the TM joint gross instability and the joint dislocates,even if the volar beak ligament is intact, the TM joint will still dislocate.@A total of66volunteers (41men and25women) were imaged. The average of the RS measurement is4.27mm (range1-8mm)and the AW measurement is13.52mm (range10-17.3mm). The average RS/AW subluxation ratio is0.32. Women showed significantly greater radial subluxation compared to men (P=0.026). Inter-rater reliability for radial subluxation and articular width showed high agreement using the t-test (P=0.23)Conclusion The keys to TM anatomy, function, and stability are the beak of the thumb metacarpal, the recess in the trapezium (adjacent to the volar beak ligament) into which the volar beak inserts, and the dorsal ligament complex (including dorsal oblique ligament and radiadorsal ligament). These anatomical keys permit screw home torque rotation in the final phase of opposition, which creates stability for power pinch and grasp. The stress view radiograph evaluates laxity and joint abnormalities of the trapeziometacarpal articulation,and showed high agreement.