Hand splinting are provided to people who need protection and support for painful, swollen or weak joints and their surrounding structures. Their designs make sure you position your wrist and hands correctly. There are two types of hand or wrist splint: splints used for resting joints of the wrist and hand.

1. BIOMECHANICAL PRINCIPLE OF HAND
SPLINTING
Poly Ghosh, MPO
NILD,
KOLKATA

2. BASIC FORCE SYSTEM
 Two force system operates splint functions depending on
external configurations of splints
1. Linear oriented three point pressure system- acts on
articular splint, influence joint motion by immobilization,
mobilization, restriction or torque transmission forces.
2. Multiple opposing two point pressure system – acts on
non articular circumferential splint, i.e coaptation splint.
Provides support to healing structure including repaired
digital pulleys, stable fractures and soft tissue damaged
from overuse or repetitive stress.

3. CONT..
 Splints with three point pressure systems have a middle reciprocal force.
The magnitude (fm) of which is the sum of the opposing proximal (F1) and
distal (F0) forces.
 With circumferential configuration ,coaptation splints do not have a middle
reciprocal system.

4. INCREASE THE AREA OF FORCE APPLICATION
 Splinting materials are, to varying degrees, rigid, their improper application
to the extremity may cause damage to the cutaneous surface and underlying
soft tissue as a result of excessive pressure.
 Minimal subcutaneous tissue to disperse pressure, such as over bony
prominences, or in areas where the inherent structure of the splint
predisposes to increased pressure of mechanical counterforces
 Pressure =total force/area of force application
 indicates that a force of 25 gm applied over an area of 1 cm by 1 cm would
result in a pressure of 0.25 gm per square millimeter. If, however, the same
25 gm of force were distributed over an area of 5 cm by 5 cm, the pressure
per square millimeter would be decreased to 0.01 gm, or 1—25 the pressure
per square millimeter. In other words, increasing the area of force
application decreases the pressure

5.  Clinically, this has the following implications:
(1) wider, longer splints are more comfortable than short,
narrow splints
(2) rolled edges on the proximal and distal aspect of a palmar splint and the
distal aspect of a dorsal splint cause less pressure than do straight edges
(3) continuous uniform pressure over a bony prominence is preferable to
unequal pressure on the prominence
(4) a contiguous fit

6.  A dorsal phalangeal bar of thermoplastic disseminates
pressure over the dorsum of the phalanx.
 With minimized pressure forces and improved
mechanical factors, patient comfort is enhanced
by splints with greater contact area.

7.  Rolled edges allow for dissemination of pressure over
a greater area,

8.  A congruous fit over bony prominences will
reduce the possibility of soft tissue damage by
evenly dispersing pressure forces over a larger area.

9.  Designed to facilitate adjustments as edema
diminishes, this two piece metacarpal fracture
splint has excellent contiguous fit.
 splint components are narrow and
the resultant force is great .

10.  Elastomer lining
 Padded materials
 Rounded corners and smooth splint edges
Not only increase splint cosmesis, they diminish
The effects of force on the splint material and
Help decrease excessive pressure on underlying skin.

11. INCREASE MECHANICAL ADVANTAGE
 Mechanically, splints are simple machines, levers,
That work in equilibrium. Incorporating forces,
axis of Rotation, moment arms, and resistances
 Function of splints may fail because of
Inattention to the lever systems at play
Between the splint and the extremity or
Between individual splint parts.
 The splint is considered a first-class lever.

12.  When the wrist is in neutral position, the forearm
trough works as a force arm (FA), and
the palmar metacarpal bar functions as the resistance
arm (RA).

13.  The forearm trough (FA) decreases in length ,
the palmar support and resistance remained
unchanged, the force at the proximal end of the
splint would be twice as great resulting in patient
discomfort and considerably magnifying the chances
for pressure problems of the underlying soft tissue.

14.  Similar concepts is applicable to any rigid support
regardless of shape.
 If the weight of the hand, its direction of force,
and the length of the palmar support are constant,
lengthening the forearm trough decreases the
resulting force at the end of the splint.
 With the wrist bar placed in extension, the splint
continues to act as a first-class lever, but the direction
of the resistance line of action is altered. FLA,

15. CONT…
 MA=Force arm (di)/ Resistance arm(d0)
 Given a constant resistance, resistance line
of action, and resistance arm, the amount of force
at the opposite end of the first-class lever may
be decreased by increasing the length of the
force arm.
 the force arm was 8 inches, the mechanical
advantage was 3.2, but the mechanical advantage
was decreased to 1.6 when the forearm trough
was shortened to 4 inches.
 Splints with greater mechanical advantage
produce less proximal force, resulting in
diminished pressure and increased comfort.

16. CONT…
 Strap placement is critical to achieving optimum
mechanical function of splints.
 Straps are not placed strategically at maximum
lengths of splint lever arms
 Straps must be attached as far distally and
proximally on a splint as possible.
 The amount of force generated on the proximal
attachment may be computed for progressively
increased attachment lengths when the resistance,
resistance line of action, and resistance arm remain
Unchanged.
 A longer force arm will result in a longer
attachment bar and increased mechanical advantage.

17. USE OPTIMUM ROTATIONAL FORCE
 Optimum splint effectiveness can be achieved
without producing patient frustration or
increased tissue damage through joint compression
or separation.
 Any force applied to a bony segment to mobilize
a joint may be resolved into a pair of concurrent
rectangular components acting in definite directions.

18. CONT….
 Mobilization traction should be applied at a 90°
angle to Harness.
 At 90° the translational force is zero, resulting in
no element of joint compression or distraction.
 Eliminating translational forces, a 90° angle of
pull allows the full magnitude of mobilization
assist to be on the wrist joint.

19. CONT….
 A 90° angle of the mobilization assist to
the mobilized segment must be maintained
as passive joint motion changes.
 In splint designs that incorporate secondary
joints, two or more rotational forces affect
digital joint motion.
 A 90° angle of approach of a dorsal
phalangeal bar to the proximal phalanx
prevents proximal or distal migration of
the bar.

20. CONT….
 The magnitude of the parallel forces of a
three-point pressure splint remain constant
with the proximal interphalangeal joint in
various degrees of flexion.
 The rotational and translational components
of the proximal and distal forces change until
at 60° the compression force (translational) on
the joint is nearly two-thirds that of the
rotational force.
 The greater the flexion deformity the less
effective the splint becomes in its ability to
correct the deficit.
 Mobilizing force be perpendicular to the joint axis of rotation to ensure that
equal tension is placed on both of the joint’s collateral ligaments

21. CONSIDER THE TORQUE EFFECT
 Torque equals the product of the force times the
length of the arm on which it acts (T = Fi ¥ di).
 Amount of torque depends on the distance between
the joint axis and the point of attachment of the
mobilization assist.
 Torque increases as the distance between the
two increases if the applied force is held constant.
 Too much distal advancement may result in
an inferior angle of the traction device or in
attenuation of ligamentous structures.

22. CONSIDER THE RELATIVE DEGREE OF PASSIVE MOBILITY
OF SUCCESSIVE JOINTS
 All joints within a longitudinal ray exhibit stiffness,
they may be splinted in unison.
 If an inequality of passive motion exists,
the splint must be adapted to stabilize the
normal, secondary joints within the segment.
 The rotational force is dissipated in unwanted motion at
the secondary mobile joints,
 Results in potential damage to these normal
Joints.
 Ineffective traction on the stiffened primary
joints.

23. CONTROL REACTION EFFECT AT SECONDARY JOINTS
 When mobilization traction is applied to
primary joints, reaction displacement may
occur at secondary joints if the amount of
stiffness is markedly different between
primary and secondary joints.
 Reaction displacement is problematic at
secondary finger MP joints.
 Imbricated palmar plates, are not held in full flexion.

24. CONSIDER THE EFFECTS OF RECIPROCAL PARALLEL FORCES
 A first-class lever system is basic to splinting
of the hand,
 The splint acting as the proximal and distal
counterforces to the forces of the hand and forearm
and a strap at the axis of the splinted segment providing
the reciprocal middle force.
 In a first-class lever system in equilibrium,
the combined downward weights must be
opposed by an equal upward force at the
axis: A + B = C.

25. CONT…
 The middle force in splinting is frequently placed
over a joint.
 Minimizes the amount of pressure exerted
on the underlying soft tissue.
 When the mechanical advantage (MA) is
increased, the magnitude of the middle
opposing force is decreased.

26. CONT….

27. CONT…

28. USE APPROPRIATE OUTRIGGER SYSTEM
 Placements and positioning of outrigger
Allow 90 degree angle of force application
Of mobilization assits.
 Outrigger force systems differ depending
on the height of the outrigger,
 Outrigger design must be coordinated
with individual patient requirements.

29. INCORPORATE ARTICULATED COMPONENTS APPROPRIATELY
 Articulated splints protect healing soft tissue
structures and improve function.
 Aligned with anatomical joint axes
 “Piston”on the extremity as active movement
occurs - causing shear forces and friction.

30. INCREASE MATERIAL STRENGTH BY PROVIDING CONTOUR
 the design of a splint and the materials to be used for,
one must take care to match the design to the
material properties.
 When a large force is placed on a flat, thin
piece of material, the counterforce produced by
the material is insufficient
 material is contoured into a half-cylinder shape,
the material has, in mechanical terms, become
stiffer and produces a greater counterforce,

31. ELIMINATE FRICTION
 Kinetic friction occurs when surfaces in contact with each other move
relative to one another.
 Difference in density exists between the surfaces, the harder surface may
begin to erode the softer.
 Kinetic friction may occur between the splint and the extremity or between
contiguous cutaneous surfaces.
 Result in skin irritation, blistering, and eventual breakdown.
 Friction caused by a splint usually indicates poor fit, improper joint
alignment, or inefficient fastening devices.
 Good contiguous fit, proper joint alignment, strategic placement of straps,
and use of dycem

32. AVOID HIGH SHEAR STRESS
 Spreading the stresses in space.
 Rounding sharp edges and keeping pressures low.
 Reduce the peak levels by spreading them out in time.
 Avoid repetitive stresses.