Tendon Transfers for Ulnar Nerve Palsy: Zancolli Lasso Procedure, Stiles-Bunnell Transfer, and Claw Correction
In short
Severe ulnar clawing cripples functional grasp; the Zancolli lasso procedure redirects flexor digitorum superficialis slips into A1 pulleys to permanently eliminate clawing.
In this guide (4 sections)
The Surgical Biomechanics of Ulnar Claw Deformity Correction
Complete, irreversible low ulnar nerve palsy (distal to the forearm flexor branches) paralyzes the third and fourth lumbricals and all seven interossei muscles. This produces the severe 'ulnar claw hand': the fourth and fifth metacarpophalangeal (MCP) joints hyperextend under the unopposed pull of the Extensor Digitorum Communis (EDC), while the interphalangeal (PIP and DIP) joints collapse into fixed flexion under the uncoordinated pull of the deep flexors (FDP).
The biomechanical goal of tendon transfer for ulnar clawing is simple yet profound: restore active MCP flexion. Once the MCP joints are prevented from hyperextending, the extrinsic extensor tendons can direct their tensile force distally into the lateral bands, naturally straightening the PIP and DIP joints. The Zancolli Lasso procedure achieves this by looping slips of the Flexor Digitorum Superficialis (FDS) around the A1/A2 pulleys and suturing them back onto themselves, creating a permanent active volar flexion tether.
Surgical Reconstructive Procedures for Ulnar Claw Correction
| Surgical Procedure / Technique | Donor Tendon & Rerouting Architecture | Insertion / Anchor Point | Biomechanical Advantages & Limitations | |
|---|---|---|---|---|
| Zancolli Lasso Procedure (Gold Standard) | FDS of ring finger split into two slips (or individual FDS per digit) | Looped around A1 or A2 pulley and sutured back to itself ('lasso') | Simple, reliable; preserves distal IP flexion; eliminates MCP hyperextension | |
| Stiles-Bunnell Transfer | FDS of middle or ring finger split into four slips | Routed through lumbrical canals into radial lateral bands of digits 4 and 5 | Directly powers IP extension; risks PIP hyperextension (swan-neck deformity) | |
| Brand Intrinsic Transfer (ECRB/ECRL) | ECRB or ECRL lengthened with free tendon graft (plantaris/palmaris) | Routed volarly across intermetacarpal spaces into lateral bands | Utilizes strong wrist extensor; requires free tendon graft harvesting | |
| Palmaris Longus Dynamic Transfer (Camitz) | Palmaris longus lengthened with strip of palmar fascia | Looped into A1 pulleys of ring and small fingers | Expendable donor; weaker flexion power than FDS lasso |
Standardized Clinical Rehabilitation Protocols and Lasso Retraining
- Dorsal Blocking Splint Protection (Weeks 0 to 4): Fabricate a custom thermoplastic dorsal blocking splint holding the wrist in 20 degrees of flexion and the fourth and fifth MCP joints in 45 degrees of flexion with the IP joints completely free; continuous wear protects the delicate 'lasso' tendon loops from excessive tensile strain.
- Early Protected Place-and-Hold MCP Flexion Drills (Week 4): Initiate gentle active-assisted MCP flexion exercises: passively flex the MCP joints into 60 degrees of flexion and instruct the patient to gently hold the position using light active muscle contraction; avoid composite fist formation against resistance.
- Functional Hand Opening and Object Release Coordination (Weeks 6 to 12): Advance to functional grasping and releasing drills: teach the patient to open their hand flat to grasp soda cans, balls, and mugs; the Zancolli lasso eliminates finger clawing, allowing smooth, coordinated hand opening without catching on objects.
Frequently Asked Questions
How does a 'lasso' surgery straighten my curled claw fingers?
Your surgeon takes a small strip of a bending tendon in your palm and loops it through the entrance of your finger tunnel like a tiny lasso, stitching it back onto itself. This lasso acts like a permanent anchor that pulls your main knuckle forward, which automatically allows your fingertip to straighten out completely.
Will having this surgery make my fingers too weak to bend into a fist?
No. You have two separate tendons that bend each finger (a deep one and a superficial one). The surgeon uses only one of them for the lasso, leaving your deep tendon completely intact so you can still make a strong, powerful fist.
How long will I need to wear a splint after a claw-correction tendon transfer?
You will wear a protective plastic splint continuously for about 4 weeks while the stitched tendon loops heal together securely. After 4 weeks, you begin gentle exercises with your hand therapist, gradually weaning off the splint by Week 6 to 8.
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