INTRODUCTION AND PATHOPHYSIOLOGY

Flexor tenosynovitis is a hallmark of rheumatoid arthritis (RA) and other inflammatory arthropathies, though it often presents more insidiously than its dorsal extensor counterpart. The volar location of the flexor tendons, constrained by the thick palmar fascia and the rigid retinacular pulley system, masks the classic visual signs of synovial proliferation. Consequently, the bulk of the hypertrophic tenosynovium expands within closed anatomical spaces, leading to profound biomechanical and neurological consequences.

The pathophysiology is driven by the formation of rheumatoid pannus—a highly vascular, hyperplastic synovial tissue that secretes proteolytic enzymes, matrix metalloproteinases (MMPs), and inflammatory cytokines. This pannus not only mechanically interferes with tendon excursion but also directly invades the tendon substance (infiltrative tenosynovitis), leading to structural weakening. Furthermore, the increased volume within the carpal tunnel compresses the median nerve, while in the digits, it causes triggering, restricted active flexion, and eventual tendon rupture.

Clinical Pearl: Always maintain a high index of suspicion for flexor tenosynovitis in the rheumatoid patient presenting with carpal tunnel syndrome. Median nerve decompression without concomitant flexor tenosynovectomy in these patients will fail to address the underlying pathology and may lead to delayed tendon rupture.

CLINICAL PRESENTATION AND EVALUATION

Wrist and Palmar Manifestations

Tenosynovitis occurs most frequently on the volar surface of the wrist and the volar aspects of the digits. Patients typically present with a progressive, painful fusiform swelling extending from the mid-palm to the distal interphalangeal (DIP) joint.
* Median Nerve Compression: The most common early manifestation of wrist flexor tenosynovitis is secondary carpal tunnel syndrome.
* Decreased Excursion: A gradual, painful decrease in active finger flexion is noted, often with a discrepancy between active and passive range of motion (ROM), indicating tendon tethering or partial rupture.
* Palpation: The synovium feels thickened and boggy. Nodules may be palpable along the tendon sheath during excursion, and crepitus or grating is frequently present.

Digital Triggering

In the digits, flexor tenosynovitis frequently leads to triggering within the zone II flexor sheath. Unlike idiopathic trigger finger, which is typically caused by a discrete A1 pulley stenosis, rheumatoid triggering is multifactorial:
1. Tenosynovial Hypertrophy: Diffuse thickening of the synovium catching within the pulley system.
2. Intratendinous Nodules: Rheumatoid nodules forming within the tendon substance.
3. Camper's Chiasm Impingement: Catching of the flexor digitorum profundus (FDP) as it passes through the decussation of the flexor digitorum superficialis (FDS).
4. Partial Ruptures: A ruptured slip of the FDS (often the ulnar slip) rolling up and catching within the sheath.

THE MANNERFELT LESION AND TENDON RUPTURE

Flexor tendon rupture in rheumatoid patients is less common than extensor tendon rupture but presents a significantly more complex surgical challenge. Ruptures occur via two primary mechanisms: infiltrative (biological degradation) and attritional (mechanical abrasion).

The Mannerfelt Lesion

The most notorious attritional rupture in the rheumatoid hand is the Mannerfelt lesion. Progressive radiocarpal destruction and scaphoid rotary subluxation lead to the erosion of the volar wrist capsule and radiocarpal ligaments. This exposes the underlying rough, irregular radial osteophytes directly to the flexor tendons traversing the carpal tunnel.
* The Flexor Pollicis Longus (FPL) is typically the first tendon to rupture due to its radial and deep position against the scaphoid and radius.
* If left untreated, the attritional process progresses ulnarly, sequentially rupturing the FDP to the index finger, followed by the FDP to the long finger.

Surgical Warning: A patient with RA who suddenly loses active interphalangeal (IP) joint flexion of the thumb must be presumed to have a Mannerfelt lesion until proven otherwise. Prompt surgical exploration is mandatory to prevent sequential rupture of the adjacent digital flexors.

Digital Flexor Ruptures

Within the digits, ruptures are typically infiltrative. The FDP or FDS may weaken and rupture silently, or present acutely following a minor loading event. The exact location of the rupture (sublimis vs. profundus) can be indeterminate on physical examination due to profound secondary joint stiffness and diffuse swelling.

SURGICAL MANAGEMENT: FLEXOR TENOSYNOVECTOMY

The primary goal of flexor tenosynovectomy is to prevent tendon rupture, decompress the median nerve, and relieve pain. While tenosynovectomy is highly effective for pain relief and preventing further degeneration, patients must be counseled that a concomitant improvement in joint motion may not be achieved due to pre-existing joint contractures and tendon adhesions.

Indications

• Persistent flexor tenosynovitis unresponsive to 3–6 months of optimal medical management (including Disease-Modifying Antirheumatic Drugs [DMARDs] and biologics).
• Clinical signs of impending tendon rupture (e.g., severe crepitus, sudden loss of active motion).
• Secondary carpal tunnel syndrome with progressive neurologic deficit.
• Severe, locking trigger digits that fail conservative therapy.

Operative Technique: Wrist and Carpal Tunnel

1. Positioning and Anesthesia: The patient is positioned supine with the arm on a hand table. A proximal pneumatic tourniquet is applied. Regional anesthesia (brachial plexus block) or general anesthesia is utilized.
2. Incision: An extended carpal tunnel incision is made, crossing the wrist crease in a zigzag fashion to prevent scar contracture, extending proximally into the distal forearm over the flexor carpi radialis (FCR).
3. Decompression: The transverse carpal ligament is divided completely. The median nerve is identified, neurolysed if necessary, and gently retracted with a vessel loop.
4. Tenosynovectomy: The hypertrophic tenosynovium is meticulously dissected from the FDS, FDP, and FPL tendons. This requires individualizing each tendon and excising the visceral and parietal synovium using tenotomy scissors or a rongeur.
5. Floor Inspection (Crucial Step): The floor of the carpal tunnel must be inspected. If a volar capsular defect and radial osteophytes are present (Mannerfelt pathology), the osteophytes must be aggressively rongeured or burred smooth.
6. Capsular Repair: The volar capsule should be repaired. If the defect is too large, a local flap of the pronator quadratus or a slip of the flexor retinaculum can be interposed to cover the raw bone and protect the tendons.

Operative Technique: Digital Flexor Tenosynovectomy

1. Incision: A Bruner zigzag incision or a mid-lateral incision is made over the affected digit, extending from the distal palmar crease to the DIP joint.
2. Exposure: The neurovascular bundles are identified and protected. The flexor tendon sheath is exposed.
3. Pulley Preservation: The A2 and A4 pulleys must be strictly preserved to prevent bowstringing. The A1, A3, and A5 pulleys, along with the intervening cruciform pulleys, can be excised to access the synovium.
4. Synovial Excision: The tenosynovium is excised from around and between the FDS and FDP tendons. Traction on the tendons allows delivery of the unexposed portions into the surgical windows.
5. Management of the FDS: If the FDS is heavily infiltrated or if a slip is partially ruptured and causing triggering at Camper's chiasm, excision of the ulnar slip of the FDS is highly recommended. This decompresses the sheath, reduces the volume of tendon gliding through the A2 pulley, and significantly lowers recurrence and reoperation rates.

MANAGEMENT OF FLEXOR TENDON RUPTURES

Treating flexor tendon ruptures in the rheumatoid hand is notoriously difficult. The biological environment is hostile, the tendon ends are often severely degenerated, and the retinacular pulley system is frequently compromised.

Pitfall: Primary end-to-end repair of a rheumatoid flexor tendon rupture is almost universally doomed to fail due to the poor quality of the tendon substance. Furthermore, free tendon grafting in the rheumatoid digit has an unacceptably high failure rate due to dense adhesion formation and poor vascular beds.

Reconstructive Strategies for FPL Rupture

When the FPL ruptures at the wrist (Mannerfelt lesion), several options exist depending on the patient's functional demands and the condition of the IP joint:
* Tendon Transfer: The most reliable functional reconstruction is transferring the FDS of the ring finger (FDS IV) to the distal stump of the FPL. This provides excellent strength and restores active thumb flexion.
* Segmental Grafting: Occasionally, if the FPL muscle belly remains contractile and the distal stump is healthy, a short segmental tendon graft (e.g., palmaris longus) can be interposed at the wrist level. This is the only location in the rheumatoid hand where flexor tendon grafting is generally considered acceptable.
* IP Joint Arthrodesis: If the thumb IP joint is already destroyed, unstable, or fixed in hyperextension (which severely hampers pinch kinematics), arthrodesis of the IP joint in 10-15 degrees of flexion is the procedure of choice. This provides a stable post for pinch and eliminates the need for tendon reconstruction.

Reconstructive Strategies for Digital Flexor Ruptures

• Isolated FDP Rupture: If the FDS is intact and PIP joint motion is functional, the FDP stump is excised to prevent triggering, and the DIP joint is stabilized via arthrodesis or tenodesis.
• Combined FDP and FDS Rupture: If both tendons are ruptured, the digit is rendered flail. Because grafting is contraindicated, the most reliable salvage procedure is stabilization of both the PIP and DIP joints via arthrodesis in a functional cascade (increasing flexion from the index to the small finger).

PERSISTENT PROXIMAL INTERPHALANGEAL (PIP) JOINT SYNOVITIS

While flexor tenosynovitis affects the volar structures, the PIP joint itself is frequently the site of persistent intra-articular synovitis. The hyperplastic synovium stretches the collateral ligaments and the extensor central slip, leading to boutonnière deformities and joint destruction.

The Role of Synovectomy

Historically, PIP joint synovectomy was a highly common procedure. However, since the advent and widespread use of modern disease-modifying antirheumatic drugs (DMARDs) and biologic therapies (e.g., TNF-alpha inhibitors), the incidence of refractory PIP synovitis has declined significantly.

Nevertheless, surgical synovectomy remains a highly useful operation for persistent, isolated PIP joint synovitis that fails to respond to systemic therapy and local corticosteroid injections. It can be performed simultaneously on all four fingers of one hand, often in conjunction with extensor or flexor tenosynovectomies.

Surgical Approach to the PIP Joint

1. Incision: A dorsal longitudinal or gently curved incision is made over the PIP joint.
2. Extensor Mechanism: The extensor mechanism is exposed. The joint can be accessed via two primary intervals:
   • Dorsolateral Approach: Incising between the central slip and the lateral bands bilaterally.
   • Chamay Approach: A distally based V-shaped incision through the central slip (requires meticulous repair and alters postoperative rehabilitation).
3. Synovectomy: The collateral recesses are thoroughly cleared of synovium using a small rongeur or curette. Care must be taken to preserve the collateral ligaments and the volar plate.
4. Closure: The extensor mechanism is meticulously repaired to prevent a secondary boutonnière deformity.

POSTOPERATIVE PROTOCOL AND REHABILITATION

The success of flexor tenosynovectomy relies heavily on rigorous postoperative rehabilitation. The primary enemy of the rheumatoid hand post-surgery is stiffness secondary to adhesion formation.

• Immediate Postoperative Phase (Days 1-3): The hand is immobilized in a bulky compressive dressing with a volar plaster splint. The wrist is positioned in neutral, with the metacarpophalangeal (MCP) joints in 70 degrees of flexion and the IP joints in full extension. Elevation is critical to minimize edema.
• Early Active Motion (Days 3-14): The bulky dressing is removed, and a thermoplastic resting splint is fabricated. Supervised hand therapy is initiated immediately. Active and active-assisted range of motion exercises for the digits are performed hourly to promote tendon gliding and prevent adhesions.
• Late Phase (Weeks 2-6): Sutures are removed at 10-14 days. Strengthening is delayed until 4-6 weeks postoperatively to allow capsular repairs (if performed at the wrist) to heal. Night splinting may be continued to prevent flexion contractures.

In cases where tendon transfers or arthrodeses were performed, the rehabilitation protocol must be strictly modified to protect the repairs (e.g., 4 weeks of immobilization for arthrodesis, or a modified Kleinert/Duran protocol for tendon transfers).

CONCLUSION

Flexor tenosynovitis in the rheumatoid hand is a destructive process that threatens both the mechanical integrity of the tendons and the neurological function of the hand. Early recognition of volar swelling, triggering, and median nerve compression is essential. When medical management fails, meticulous flexor tenosynovectomy, decompression of the carpal tunnel, and prophylactic management of bony prominences (Mannerfelt lesions) are highly effective in preserving hand function. In the event of tendon rupture, the surgeon must abandon primary repair and grafting in favor of reliable salvage procedures such as tendon transfers and strategic arthrodeses to restore a stable, functional hand.