Ebook A beginner ’s guide to total knee replacement: Part 2

Instruments for Primary Total Knee Replacement

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10
Instruments for Primary
Total Knee Replacement

I

rrespective of the implant design or brand, the instruments
achieve exactly the same goals, namely:
1. Cutting the lower femur in a few degrees valgus and parallel
to the floor.
2. Cutting the upper tibia neutral to floor mediolaterally but with
a slight posterior slope.
3. Ensuring a proper rotational alignment during anterior,
posterior and chamfer cuts of distal femur.
4. The surface and taper cuts of distal femur should exactly
match the undersurface of the femoral component.
5. Adequate trials for checking all cuts and releases before
implantation.
6. Instrumentation to ensure that gaps in flexion and extension
are equal.

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CHARNLEY FEMORAL BROACH

The intramedullary broach and alignment rod is available in different
combinations from the simplest to the most complicated. This is the
first instrument used and locates the long axis of the femur. The rod
should be inserted deep enough into the medulla to catch the isthmus
to ensure that a wrong axial identification is avoided. The distal
femoral cutting guide is attached to this block.


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DISTAL FEMORAL CUTTING ASSEMBLY

Various designs of distal cutting blocks achieve the same purpose
with minor technical variations in the instrumentation.


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EACH SYSTEM PROVIDES A VALGUS CUT

Each instrument can provide valgus cuts from 3° to 7° in small
increments to tailor the cut according to the patient.

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BLOCK DESIGNS VARY

These blocks can vary from simple Freeman and Insall designs (top
and bottom) to the complex fourth generation magnetic snap-on
jigs.


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THE UPPER TIBIAL CUTTING GUIDE

The upper tibial cutting guides too come in various designs. They cut
7 mm of upper tibia with a slight posterior slope.


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STATIC GAP EVALUATION DEVICES. THEY CANNOT MEASURE MIDFLEXION GAPS

The gap balancing can be either static or dynamic. Static balancers
are just spacers of different thicknesses which are tried in flexion and

extension to ensure that the knee is neither too tight nor too wobbly.


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DYNAMIC GAP BALANCING INSTRUMENTS

The dynamic gap balancers expand the gap with a turn screw and
even mid-range gaps can be measured. Long-term success of a
knee depends on proper gap balancing and equalization of tension
in all quadrants.


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FEMORAL COMPONENT SIZE MEASURING

Each implant design has its own femoral size template. It is useful to
have a metal scale to correctly measure the cut dimensions and
ensure that the right size implant is used.


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THE FOUR-IN-ONE CUTTING BLOCK, COMMON TO ALMOST ALL
DESIGNS

The four-in-one cutting blocks do the anterior, posterior, anterior
chamfer and posterior chamfer cuts.


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THE FOUR-IN-ONE CUTTING BLOCK, COMMON TO ALMOST ALL
DESIGNS

Each design is different, but they are all based on the same scientific
principles and produce the same end result. The one in blue is a light
titanium cutting block designed by me in 1994.


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TIBIAL SIZERS

Tibial sizers match the implant and differ from company to company.


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BOX CUTTERS ARE NEEDED IF A CRUCIATE SCARIFYING DESIGN
IS USED

In case a posterior cruciate ligament scarifying design is used, a box
cut is needed; each implant design has its own box device.


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CS AND CR IMPLANTS HAVE THEIR OWN TRIALS

Femoral trials are available in many sizes and designs depending
on the manufacturer.


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COSTLIER DESIGNS HAVE A LARGER INVENTORY WITH MINIMAL
SIZE AND THICKNESS INCREMENTS

Early generation knees had universal (common left/right) femoral
components in 3 or 4 sizes. Modern knees have 10 left and 10 right
femoral components each in CR and CS designs.

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TIBIAL TRIALS IN VARIOUS SIZES AND THICKNESSES

Each set comes with its own tibial trials, some in 1 mm difference,
others in 2, 3 and 5 mm differences. Separate trials exist for CS and
CR designs.


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TIBIAL TRIALS IN VARIOUS SIZES AND THICKNESSES

Some designs have pegs to convert CR trials to PS ones. Some have
as few as 4 thicknesses, while others have up to 9.


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TRIAL REDUCTION

Different designs and their trial reductions.

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THE TWO CLASSIC OLD DESIGNS

On top is Freeman Mark II and at bottom is IB I, both time-tested classic
gold standard designs.


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TIBIAL PREPARATION DEPENDS ON THE DESIGN

Tibial preparation depends upon type of implant, and includes
guides, drills and fin cutters.


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TIBIAL PREPARATION DEPENDS ON THE DESIGN

Other designs use box chisels or broaches to match the tibial metalback.

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Impactors for femur and tibia.


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Block pins, extractors, angle strips, and other nuts and bolts.


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11
Postoperative Treatment,
Mobilization and Physiotherapy

T

he patient is shifted to the ward. In case a spinal anaesthetic
is used, and for elderly patients with a history of prostatic
or urinary symptoms, it is usual to catheterize in the theatre
itself.
On the first postoperative day, the catheter is removed. If the
patient has a good pain threshold, one can make him stand.

Walking with a walking frame is started on day two and weight
bearing is allowed up to pain tolerance.

Patient is mobilized with a walker early.
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Postoperative Treatment, Mobilization and Physiotherapy 277

Drain is removed on second or third day after it has stopped
collecting.
The bandages are loosened on the fifth day and knee flexion
is started. Using a smooth mica board with talcum powder on
it, the patient is encouraged to rub the heel on the board allowing
gradual flexion.

Knee flexion begins on the fifth day.