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Metacarpophalangeal joint arthroscopy
The metacarpophalangeal (MCP) joint is ideally suited for arthroscopic evaluation. The MCP joint represents a single compartment, the bony and tendinous landmarks are easy to identify, and the neurovascular structures are remote from the portals; hence there is a short learning curve. It is mostly used for synovectomy and loose body removal but it has some applications following trauma as well.
Anatomy and methodology
Ropars et al. investigated the course of the superficial radial nerve (SRN) and the potential risk for injury during trapeziometacarpal (TM) or thumb MCP joint arthroscopy. They dissected the SRN in 30 forearms and measured the distances of the 3 major branches of the nerve (SR1, SR2, and SR3) from the radial metacarpophalangeal (MCP-r) and ulnar metacarpophalangeal (MCP-u) portals. The MCP-r portal was always situated dorsally and very closely to SR3, at a mean distance of 1 mm (range, 0–5 mm). The MCP-u portal was also situated dorsally to SR2-D1 at a mean distance of 3.7 mm (range, 1.5–6.5 mm).
Rozmaryn and Wei studied 24 MCP joints in 6 cadaveric hands using a 2.5-mm small-joint arthroscope and 5 pounds of overhead traction using a radial portal and an ulnar portal. The number of arthroscopic observations they describe include:
- (1)
a consistent tripartite configuration of the main radial and ulnar collateral ligaments with characteristic changes in relative fiber orientation as the digit goes from extension to flexion;
- (2)
nonvisualization of the accessory collateral ligament from inside the joint;
- (3)
transitional amorphous capsular fibers connecting the collateral ligaments to the volar plate and dorsal capsule (DC);
- (4)
four synovial recesses (radial, ulnar, volar, and dorsal-proximal);
- (5)
a metacarpal head and proximal phalanx;
- (6)
a consistent circumferential meniscal equivalent around the margin of the proximal phalanx articular surface;
- (7)
the sesamoid-metacarpal articulation in the thumb MCP joint.
Hidalgo-Diaz et al. compared horizontal and vertical traction for MCP joint arthroscopy in the fingers other than the thumb in 8 patients. Arthroscopy was performed using dorsomedial and dorsoradial portals. The average duration of patient set-up was 17.75 minutes in the horizontal traction group and 32 minutes in the vertical traction group. The average tourniquet time was 56.75 minutes in the horizontal traction group and 71 minutes in the vertical traction group.
Physical examination and imaging
The examination of the finger MCP joints is straightforward. Inspection should include observation for swelling, synovitis, volar joint subluxation, and ulnar drift. The collateral ligaments are tested by applying radial and ulnar stress with the MCP joints in full flexion. The sagittal band fibers should be inspected to rule out any ulnar subluxation of the extensor mechanism or incomplete MCP extension. Standard AP, lateral, and oblique radiographs should be performed to evaluate the joint surfaces and look for periarticular erosions. MRI can be useful in detecting any significant joint synovitis.
Indications
Inflammatory arthritis
MCP joint arthroscopy is useful in evaluating the status of the articular cartilage and synovial proliferation, especially in rheumatoid arthritis (RA) ( Fig. 22.1 ). A synovial biopsy and synovectomy can be performed without the need for arthrotomy 
( ).
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