MCP Joint Anatomy

The metacarpophalangeal joint is a condyloid (ellipsoid) joint permitting flexion, extension, abduction, adduction, and limited rotation. Key anatomical structures include the collateral ligaments (taut in flexion, lax in extension - critical for rehabilitation), accessory collateral ligaments, volar plate, and the dorsal extensor hood mechanism. In rheumatoid arthritis, synovitis leads to progressive destruction with stretching of the radial sagittal band, ulnar subluxation of the extensor tendons, and the characteristic ulnar drift deformity. The intrinsic muscles (interossei and lumbricals) contribute to deformity through their altered line of pull.

PIP Joint Anatomy

The proximal interphalangeal joint is a bicondylar hinge joint with primary motion in the sagittal plane (flexion-extension). Stability is provided by proper and accessory collateral ligaments, the volar plate, and the central slip of the extensor mechanism. The PIP joint withstands forces up to 3 times body weight during pinch grip. In osteoarthritis, marginal osteophytes (Bouchard nodes) form dorsally and laterally. In rheumatoid arthritis, progressive synovitis leads to boutonniere deformity (central slip attenuation, PIP flexion, DIP hyperextension) or swan neck deformity (PIP hyperextension, DIP flexion).

CMC Joint Anatomy

The thumb carpometacarpal joint is a saddle (sellar) joint between the trapezium and first metacarpal base, permitting opposition, flexion, extension, abduction, and adduction. The joint is stabilized by the anterior oblique (beak) ligament (most important for stability), dorsoradial ligament, posterior oblique ligament, and intermetacarpal ligament. Primary osteoarthritis preferentially affects this joint in postmenopausal women due to ligamentous laxity and repetitive loading. Pantrapezial arthritis extends to the scaphotrapezial and trapeziotrapezoid joints.

Indications for Small Joint Arthroplasty

MCP Arthroplasty:

• Rheumatoid arthritis with painful joint destruction and ulnar drift (primary indication)
• Post-traumatic arthritis with preserved bone stock
• Osteoarthritis (less common, generally good bone stock)
• Failed previous arthroplasty requiring revision

PIP Arthroplasty:

• Osteoarthritis with stiffness greater than 30 degrees flexion contracture (motion desired)
• Rheumatoid arthritis (more guarded outcomes than MCP)
• Post-traumatic arthritis
• Select cases of psoriatic arthritis with adequate bone stock

Thumb CMC Arthroplasty:

• Eaton Stage II-IV thumb CMC osteoarthritis refractory to conservative management
• Post-traumatic arthritis of first CMC
• Failed previous CMC surgery
• Pantrapezial arthritis (may require STT arthrodesis in addition)

Contraindications

Absolute Contraindications:

• Active infection (local or systemic)
• Absent or severely deficient extensor mechanism
• Severe bone loss precluding implant fixation
• Fixed deformity not correctable at surgery (consider arthrodesis)
• Non-functional hand (no reconstructive benefit)

Relative Contraindications:

• Young, high-demand manual laborers (consider arthrodesis)
• Index finger PIP (arthrodesis preferred for pinch stability)
• Severe soft tissue contractures
• Inadequately controlled inflammatory arthritis
• Non-compliant patient unable to follow postoperative protocol

Implant-Related Complications

Silicone Implant Fracture:

• Incidence: 50-70% at 10-year follow-up
• Often asymptomatic due to maintained capsular integrity
• Clinical significance: Only treat if symptomatic (pain, instability, crepitus)
• Management: Observation if asymptomatic; revision arthroplasty or arthrodesis if symptomatic

Silicone Synovitis:

• Incidence: 5-10% of silicone arthroplasties
• Pathophysiology: Foreign body reaction to silicone particles
• Clinical features: Swelling, pain, osteolysis on radiographs, may mimic infection
• Management: Synovectomy with implant exchange or conversion to arthrodesis; titanium grommets may reduce wear particle generation

Implant Subsidence/Loosening:

• More common with anatomic designs (SRA, pyrocarbon) than silicone
• Risk factors: Poor bone quality, malalignment, high activity level
• Presents with progressive pain and loss of motion
• Management: Revision with bone grafting or conversion to arthrodesis

Deformity Recurrence

Recurrent Ulnar Drift (MCP):

• Results from inadequate soft tissue balancing at index surgery
• Progressive stretching of radial sagittal band repair
• Continued rheumatoid disease activity
• Prevention: Meticulous soft tissue technique, disease control
• Management: Revision soft tissue procedure or revision arthroplasty

Boutonniere or Swan Neck Recurrence (PIP):

• Central slip attenuation leads to boutonniere recurrence
• Lateral band subluxation causes swan neck
• May require extensor reconstruction or conversion to arthrodesis

Other Complications

Infection:

• Early: Wound infection, treat with antibiotics and wound care
• Deep/chronic: Implant removal, debridement, delayed reconstruction
• Rheumatoid patients at higher risk due to immunosuppression

Stiffness:

• Common, especially at PIP level
• Prevention: Early protected motion, compliant patient
• Treatment: Aggressive therapy; manipulation under anesthesia rarely helpful

Instability:

• Results from ligament insufficiency or bone loss
• May require revision with constrained implant or arthrodesis

MCP Arthroplasty Outcomes

Swanson Silicone (RA):

• Pain relief: 85-90% report significant improvement
• Arc of motion: Average 30-40 degrees (improvement from pre-op)
• Ulnar drift correction: 80-90% initially, some recurrence over time
• Patient satisfaction: 80-85% at long-term follow-up
• Implant survival: 81% at 17 years (revision as endpoint)
• Implant fracture: 50-70% radiographically but often clinically silent

Predictors of Good Outcome:

• Rheumatoid arthritis (better than OA or post-traumatic)
• Adequate bone stock
• Good soft tissue quality
• Compliant with therapy protocol
• Well-controlled systemic disease

PIP Arthroplasty Outcomes

Silicone (RA and OA):

• Motion gain: Modest (average arc 40-50 degrees)
• Pain relief: 75-80%
• Stiffness more common than at MCP level

Surface Replacement/Pyrocarbon (OA):

• Motion: Average arc 50-60 degrees
• Survival: 85-90% at 5 years, limited longer-term data
• Higher complication rate than silicone (dislocation, loosening)
• Best in OA with intact ligaments

Thumb CMC Arthroplasty Outcomes

LRTI/Trapeziectomy:

• Pain relief: 90-95% report significant improvement
• Pinch strength: Returns to 80-90% of contralateral by 1 year
• Grip strength: Similar recovery
• Patient satisfaction: Greater than 90%
• Subsidence: Universal but not clinically significant
• Return to function: 3-6 months (longer than digit arthroplasty)

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3. Trail IA, Martin JA, Nuttall D, Stanley JK. Seventeen-year survivorship analysis of silastic metacarpophalangeal joint replacement. J Bone Joint Surg Br. 2004;86(7):1002-1006.

4. Vermeulen GM, Slijper H, Feitz R, et al. Surgical management of primary thumb carpometacarpal osteoarthritis: A systematic review. J Hand Surg Am. 2011;36(1):157-169.

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9. Chung KC, Burns PB, Kim HM, et al. Long-term followup for rheumatoid arthritis patients in a multicenter outcomes study of silicone metacarpophalangeal joint arthroplasty. Arthritis Care Res. 2012;64(9):1292-1300.

10. Waljee JF, Chung KC. Objective functional outcomes and patient satisfaction after silicone metacarpophalangeal arthroplasty for rheumatoid arthritis. J Hand Surg Am. 2012;37(1):47-54.

In Australia, small joint arthroplasty of the hand is predominantly performed by fellowship-trained hand surgeons and plastic surgeons with hand subspecialty interest. Rheumatoid arthritis, historically the primary indication for MCP arthroplasty, has decreased in prevalence and severity due to aggressive early disease-modifying therapy, leading to fewer patients requiring surgery for severe rheumatoid hand deformity. Primary osteoarthritis of the thumb CMC joint remains the most common indication for small joint arthroplasty procedures in Australian practice.

The Swanson silicone implant and similar designs (NeuFlex) are TGA-approved and widely available. Pyrocarbon implants are available but at significantly higher cost, typically reserved for specific indications in younger patients with osteoarthritis or post-traumatic arthritis where motion preservation is critical. The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) does not currently track small joint arthroplasty outcomes, limiting registry-based outcome data. Hand surgery societies including the Australian Hand Surgery Society (AHSS) provide guidance on training and best practice.

Rehabilitation following small joint arthroplasty in Australia is provided by certified hand therapists, typically accessed through public hospital outpatient services or private hand therapy practices. Early involvement of hand therapy is critical for optimal outcomes, particularly for the dynamic splinting protocols required following MCP arthroplasty. Access to specialized hand therapy services may be limited in rural and remote areas, which should be considered when counselling patients about postoperative requirements.