ABSTRACT
NOTE: Dislocations are described according to the position of the distal bone relative to normal joint alignment.
GRADING OF COLLATERAL LIGAMENT SPRAIN Grade I: Gross stability with microscopic tear Grade II: A grossly intact ligament with some abnormal laxity when joint is stressed Grade III: Complete tear of collateral ligament with gross instability
ANATOMY n Features of metacarpophalangeal (MP) joint ligament box complex that resist ligament
injury and dislocation • Protected position at base of finger • Intrinsic ligamentous structure • Surrounding support structures, which include flexor and extensor tendon systems, sagittal
bands, and tendons of the intrinsic muscles
n Volar plate • Forms floor of joint • Supported laterally by deep transverse metacarpal (intervolar plate) ligament that links each
ligament box complex to the adjacent joint3 (Fig. 66-1) n Cam effect
• A cam is a construct that translates rotary motion into linear motion. • The rotary flexion of the MP joint places linear stretch on the collateral ligaments. • The metacarpal head has a nonspherical shape and is wider on the volar side. Therefore the
collateral ligaments become stretched taut in flexion relative to extension. • There is broader, more stable articulation between the metacarpal head and proximal
phalanx with more than 70 degrees of flexion. This produces increased lateral stability when the MP joint is in flexion and allows some abduction-adduction when the joint is in extension.
