PO · EP 09 · ORTHOTICS
Before You Listen
Episode Setup
- Topic in one line: the three mechanical classes of upper limb orthoses (static, dynamic, static-progressive) and the joint-naming convention (WHO, EWHO, SEWHO); the wrist-hand orthosis short list (resting hand, functional position, cock-up, thumb spica); the wrist-driven flexor hinge orthosis (WDFHO) that converts active wrist extension into mechanical pinch in C6 tetraplegia; the master peripheral nerve injury–deformity–splint table (radial = wrist drop, cock-up; ulnar = claw hand, anti-claw; median = ape hand, opponens); and the ulnar paradox explaining why low (distal) ulnar lesions cause worse clawing than high (proximal) lesions.
- Prerequisites: functional anatomy of the brachial plexus and the three major peripheral nerves of the upper limb (radial, median, ulnar) with the muscles each innervates and the cutaneous distributions; the concept of tenodesis as passive finger flexion driven by wrist extension via the long flexor tendons; the segmental motor levels of the cervical spinal cord (C5 deltoid/biceps, C6 wrist extensors, C7 triceps, C8 finger flexors, T1 intrinsics); the viscoelastic properties of connective tissue (creep and stress relaxation) that underpin the static-progressive splinting principle.
- Runtime: approximately 30 minutes for Part 1.
- Scope boundary: Part 1 builds the splint vocabulary, the tenodesis machinery, and the master nerve table. Part 2 takes that vocabulary into the elbow, shoulder, and humeral shaft, then runs the SCI orthosis-by-level matrix and the rheumatoid arthritis and burn splinting protocols, and closes with the dynamic-versus-static-progressive evidence in elbow contracture management.
Vignette. A 19-year-old man sustains a complete C6 spinal cord injury (American Spinal Injury Association Impairment Scale [AIS] grade A) in a diving accident. Six weeks into inpatient rehabilitation, manual muscle testing shows full strength of the deltoid, biceps, brachialis, and rotator cuff bilaterally; both wrist extensors (extensor carpi radialis longus [ECRL] and extensor carpi radialis brevis [ECRB]) test 4/5; triceps and all finger flexors and intrinsic hand muscles test 0/5. He has been working with the occupational therapist on transfer mechanics and beginning to use a manual wheelchair with rim modifications. The therapist reports that he has been performing aggressive passive finger flexor stretching during evening wash-out routines and that his finger flexors now feel “loose” on passive ranging. He is highly motivated and has a supportive family. He asks what orthosis would maximize his independence in feeding, grooming, and writing.
Which upper extremity orthosis is the device of choice at this neurological level, what muscles must be intact for the orthosis to function, what specific rehabilitation behavior described in the vignette could undermine the orthosis even if it is appropriately fitted, and what is the approximate pinch force this orthosis generates and what category of activities does that force support?
(Answer at the end of this chapter)
Section 1: Mechanical Classification of Upper Limb Orthoses and the Wrist-Hand Orthosis Family
Bottom line: upper extremity orthoses are classified by mechanical function as static (no movable parts, immobilize), dynamic (springs/rubber bands/outriggers, apply constant mobilizing force), or static-progressive (turnbuckle/ratchet, hold at end-range with non-elastic incremental adjustment); the wrist-hand orthosis family includes the resting hand splint in the intrinsic-plus or anti-deformity position, the functional position splint with the thumb in opposition, the cock-up splint for radial nerve palsy and carpal tunnel, and the thumb spica for de Quervain, scaphoid fracture, and gamekeeper’s thumb.
Upper extremity orthoses serve four overlapping functions: immobilization, mobilization, restriction, and functional substitution. The choice of strategy depends on the underlying pathology, the phase of tissue healing, and the patient’s functional goals. Before naming a specific device, the prescriber commits to one of three mechanical categories, because the category determines the indication.
Static orthoses have no movable components. They rigidly hold a joint or chain of joints in a fixed position. Their roles are to protect healing structures, prevent unwanted motion, maintain joint alignment, and prevent contracture. The principle is complete rest of the target tissue. Indications include acute inflammation, post-surgical immobilization, fracture management, and nighttime positioning during nerve recovery. Dynamic orthoses contain movable elements (rubber bands, springs, outrigger systems) that apply a controlled mobilizing force, allowing or assisting joint motion in a therapeutic direction. Indications include tendon repair protocols, nerve palsy substitution, and contracture management following the low-load prolonged stretch (LLPS) principle. Static-progressive orthoses are hybrids: like static splints they have no elastic components, but they incorporate an adjustable mechanism (turnbuckle, serial cast, ratchet) that the clinician or patient incrementally advances to progressively stretch a contracted joint. Tissue is held at its current end-range without elastic recoil and undergoes creep (gradual deformation under sustained load) and stress relaxation (decreasing resistance at a maintained length).
The dynamic versus static-progressive distinction is heavily tested. Dynamic equals constant mobilizing force via elastic elements. Static-progressive equals end-range hold via a non-elastic, incrementally adjustable mechanism. Both target range of motion. Dynamic recoils as the joint approaches end-range; static-progressive does not recoil at all, so the tissue creeps at the new length.
Upper extremity orthoses are named by the joints they cross: WHO (wrist-hand), EWHO (elbow-wrist-hand), and SEWHO (shoulder-elbow-wrist-hand).
The resting hand splint is the workhorse static WHO. It positions the wrist and hand in the intrinsic-plus or anti-deformity position: wrist in 20-30 degrees of extension, MCP joints in 70-90 degrees of flexion, IP joints in 15-20 degrees of slight flexion, and the thumb midway between radial abduction and palmar opposition. This position places the MCP collateral ligaments on stretch (they are taut in flexion), preventing the MCP extension contracture that develops in the edematous or immobilized hand; the slight IP flexion prevents IP flexion contracture without overstretching the volar plate. Indications include rheumatoid arthritis flares, burn injuries, post-surgical immobilization, acute inflammation, and overnight positioning during nerve recovery. The resting hand splint and burn hand splint share the same anti-deformity position because the edematous burned hand collapses into MCP extension, IP flexion, thumb adduction, and wrist flexion, every one of which the anti-deformity posture reverses.
The functional position splint differs from the resting hand splint in exactly one detail: the thumb is positioned in opposition rather than midway between abduction and opposition. The result is the hand in optimal grasp posture, with the thumb pad facing the fingertips. It is chosen when motor recovery is anticipated (post-stroke, post-nerve injury) so the patient can resume functional grasp the moment recovery occurs. It is also the orthosis of choice for combined high median-ulnar nerve palsy, where every intrinsic is lost and the hand needs to be parked in the most useful possible static posture.
The cock-up splint, also called the wrist extension splint, is a static WHO that maintains the wrist in 20-30 degrees of extension while leaving the fingers and thumb completely free. Volar (palmar) cock-up designs lie on the palmar surface (excellent wrist support, partially blocks palmar sensation and grip). Dorsal cock-up designs lie dorsally and free the palm, which is preferred when palmar clearance for grip and sensation matters. The most-tested indication is radial nerve palsy (wrist drop): the splint substitutes for paralyzed wrist extensors and restores the tenodesis effect for grip. Other indications include carpal tunnel syndrome (night splint), wrist extensor tendinitis, de Quervain tenosynovitis (with a thumb component), and general wrist pain.
The thumb spica splint immobilizes the thumb carpometacarpal (CMC) and MCP joints, with the IP joint typically free to preserve tip pinch. Short thumb spica immobilizes the thumb only with the wrist free (first CMC osteoarthritis). Long thumb spica includes wrist immobilization (scaphoid fracture, because the scaphoid sits at the base of the thumb ray). Indications include de Quervain tenosynovitis (APL and EPB tendinitis at the first dorsal compartment), gamekeeper’s or skier’s thumb (UCL injury at thumb MCP), scaphoid fracture (long), first CMC OA, Bennett fracture, and thumb MCP or CMC sprains. The IP joint is left free to preserve tip pinch.
Source: Mikael Granberg, “Full hand orthose backside” — CC BY-SA 4.0. https://commons.wikimedia.org/wiki/File:Full_hand_orthose_backside.jpg
High Yield — Mechanical classification and the wrist-hand orthosis family
- Static orthoses = no movable parts; immobilize and protect (post-surgical, RA flare, nerve recovery overnight).
- Dynamic orthoses = springs, rubber bands, outriggers; apply CONSTANT mobilizing force; for nerve palsy substitution, tendon repair protocols, and contracture stretch (LLPS).
- Static-progressive orthoses = turnbuckle or ratchet; NON-elastic incremental adjustment to end-range; exploits creep and stress relaxation.
- Naming: WHO (wrist-hand), EWHO (elbow-wrist-hand), SEWHO (shoulder-elbow-wrist-hand).
- Resting hand splint = intrinsic-plus / anti-deformity position: wrist 20-30 deg extension, MCP 70-90 deg flexion, IP slight flexion, thumb midway abduction/opposition; same as burn hand splint.
- Functional position splint = same as resting hand BUT thumb in opposition; choice for combined high median-ulnar palsy.
- Cock-up splint = wrist 20-30 deg extension, fingers free; for radial nerve palsy (restores tenodesis), carpal tunnel night splint, wrist tendinitis.
- Thumb spica = CMC + MCP immobilized, IP free; SHORT (thumb only) for first CMC OA; LONG (includes wrist) for scaphoid fracture; also de Quervain and gamekeeper’s thumb.
Mnemonic — “Resting hand = burn hand; thumb position separates resting from functional”
Both the resting hand splint and the burn hand splint sit in the intrinsic-plus / anti-deformity position, because the burned, edematous hand collapses into the position of deformity (MCP extension, IP flexion, thumb adduction, wrist flexion) and the splint counteracts each tendency. The single feature that converts a resting hand splint into a functional position splint is moving the thumb from “midway between abduction and opposition” into opposition, ready for pinch. When a board stem describes a patient with anticipated motor recovery (post-stroke, post-nerve injury), the answer shifts from resting to functional, because functional position has the thumb pre-positioned for grasp.
Think of a piece of cold taffy. If you grab it and give it a quick violent yank, it snaps in half. But if you hold that same piece of cold taffy and just apply a steady, unyielding, gentle pulling pressure to it, initially it resists, it feels solid. But over time, as you maintain that exact same physical load, the internal structure of the taffy begins to yield. It slowly elongates. That is creep.
— PO-09-a podcast, ~8:22