CONCEPTS UNDERLINING BALANCING IN TKA pptx

CONCEPTS UNDERLINING BALANCING IN TKA

Wui K. Chung FRACS


Good balance is essential for the effective pain-free and durable function of a TKA. It is important to
recognize that knee balance is not simply a function of soft-tissue balance. Balance of the knee joint
following TKA is influenced by,
1. Component size, level and alignment and related bone surgery
2. Articular geometry
3. Soft-tissue envelope

ERRORS OF KNEE BALANCE
There are innumerable ways to commit errors of knee balancing. Major errors may result in loss of
motion, pain, instability, loosening or early wear of the prosthesis. The main categories of errors are
• Component malalignment
• Errors of patellar resurfacing
• Alteration of joint level
• Errors of soft-tissue balancing
• Errors of Flexion-Extension space balancing
Less severe errors may result in more subtle problems such as recurrent effusion, post-activity aches,
and less than satisfactory range of motion.
Some common errors of knee balancing are less recognized eg.
• Extension loss – occurs frequently. To avoid this error the surgeon should aim to obtain 3
degrees of extension with the components in place. If only zero degrees of extension is
obtained during surgery, there is a strong likelihood that a flexion deformity will ensue. Post-
operative pain resulting in quadriceps inhibition and hamstring spasm if unattended will also
result in development of a fixed flexion contracture
• Flexion laxity – is a common error that is not recognized adequately by many practitioners.
Laxity in extension is readily appreciated as patients with the problem suffer obvious
instability. Mild flexion laxity may not cause instability symptoms but causes recurrent

activity-related effusion, post-activity pains and increased wear rate. Flexion laxity often
results from over-zealous soft-tissue release.
• Over-zealous soft-tissue release – in the effort to fully expose the knee joint during surgery,
surgeons often perform excessive soft-tissue releases. Release of most soft-tissue structures
of the knee joint lead to greater expansion of the flexion space than of the extension space.
Flexion-extension space discrepancy results from such error. Radical soft-tissue releases also
cause more post-operative bleeding and pain, which may lead to poor post-operative range of
motion.

METHODS OF TKA
There are two well-established methods to perform TKA.
1. The Independent Bone Cut
2. Flexion (Tibial) First Methods.
Both methods have identifiable advantages and disadvantages.

The Independent Bone Cut Method is perhaps the more popular method. This is the method
popularized by Freeman-Insall. The surgical sequence in this method being
1. Femoral bone cuts according to prescription
2. Tibial bone cut according to prescription
3. Flexion-Extension space balancing
Technique
The tibia is osteotomized conventionally – perpendicular to the long frontal axis of the tibia and to
remove a prescribed amount of tibia bone. The femoral component is set at a level and rotational
alignment according to a predetermined criterion. Femoral rotation is generally set according to the
Trans-Epicondylar axis or the Whiteside line according to the surgeon’s preference and the amount
of bone removed from the distal and posterior femur is matched to the thickness of prosthetic
replacement. Soft-tissue balancing is performed subsequent to bone surgery to obtain a rectangular
and equal flexion-extension spaces.
Disadvantages
This method suffers from the following disadvantages,

1. The amount of femoral external rotation is set arbitrarily and may not reflect correctly the
native femoral rotation. There is frequently more femoral rotation in patients with
osteoarthritis compared with normal non-arthritic joints.
2. The epicondylar landmarks are not easily identified and it has been reported that the rate of
surgical error is high even in specialist centers.
Olcott & Scott CORR 1999 – range +11 degrees and -
4 degrees
3. Soft-tissue releases to achieve collateral balance tend to increase flexion space more readily
than extension space, potentially creating problems with equalization of flexion-extension
gaps. Over expansion of the flexion requires the surgeon to resect more distal femur to
increase the extension space to match the flexion space. This leads to an elevation of the joint
level.

The Flexion (Tibial) First Method
was popularized with the introduction of the LCS knee and continues to enjoy popular use. In this
method the tibia is resected first and then a measured rectangular flexion space is created under
distraction of the flexion space. The femoral bone cuts are set parallel to the cut tibial surface. Thus
in this method the rotational alignment of the femoral component is not pre-determined and is
dependent on the soft-tissue balance. After creation of a measured and rectangular flexion space, an
equal extension space is created to match the flexion gap.
Advantages and Disadvantages
Soft-tissue release in this method tends to be more selective and limited compared with the former
method. There are however some disadvantages with this method as well.
1. Femoral rotational alignment being responsive to soft-tissue balance is also subject to errors
created by the soft-tissue work
2. Femoral condyle hypoplasia not uncommonly encountered in lateral compartment arthritis
presents may present difficulty assessing the amount of soft-tissue release
3. Overzealous soft-tissue release during the flexion phase of the operation may demand greater
amount of bone to be removed from the distal femur during the extension phase of the
operation. Joint level alteration is not uncommon using this method.

Extension First Method
This presentation introduces a less well-known method of performing TKA by an Extension First
approach. The author was stimulated to evolve this method by,
1. Knowledge that with few exceptions, the release of ligaments and tendons about the knee
leads to greater expansion of flexion space than extension space
2. The relative difficulty of correcting flexion contracture compared with tightness of flexion
space
3. The frequency of joint level alteration caused by use of conventional methods
The essential steps involved in this method being,
1. Standard paramedial arthrotomy, meniscectomies, anterior subluxation of tibia, removal of
marginal osteophytes.
2. Resection of ACL +/- PCL according to the type of implant selected.
3. Early correction of deformity - Limited, selective soft-tissue release to correct
malalignment of the Mechanical Axis in extension – performed under manual traction with
care being taken to avoid over-correction.

4. Osteotomy of proximal tibia in standard fashion removing prescribed amount of bone from
the less worn tibia condyle.
5. Distal femoral osteotomy performed under tension. Measured extension space created,
factoring in the Femoral Valgus Angle and relation of distal femoral cut to the Frontal
Epicondylar Axis (Mechanical Axis). The extension space created is thus rectangular and of
a dimension to accommodate the anticipated thickness of tibial and femoral implants.














6. The knee is flexed to 90 degrees and a tensioner or spacer applied. The rotational position of
the femur is checked against known axes such as the Trans-epicondylar Axis and Whiteside
line. Minor adjustment may be required with selective soft-tissue release to ensure adequate
external rotation – the aim being to set the Epicondylar Axis (or the Whiteside Line)
parallel to the cut tibial surface. A measured amount of posterior femoral bone is then
removed to create a flexion space than is rectangular and equal to the extension space.

This method of performing a TKA has in our experience resulted in effective correction of
flexion contractures without significant alteration of joint level or flexion laxity.
The author has observed that the Frontal Trans-Epicondylar Axis bears a consistent relationship
with the Mechanical Axis of the femur, being perpendicular to this axis in the vast majority of
patients. Applying this observation, the author is able to select the correct femoral valgus angle
for resection of the distal femur without use of an intra-medullary rod.


FUNDAMENTALS OF KNEE BALANCING
The aims in TKA are simply to
• To correct deviation of the Mechanical Axis and to centre the axis to the centre of the
knee joint
• Create a knee joint plane that is perpendicular to the Mechanical Axis
• Osteotomize the tibial perpendicular to its’ Anatomical Axis – the native tibia surface and
knee joint plane (frontal) is tilted in slight (average 3 degrees) varus. By convention
during TKA the tibia is cut perpendicular to the tibia axis – this alters the native knee
joint plane. In order to maintain parallel relationship between the femoral component and
the tibia component at 90 degrees of knee flexion, the femoral component needs to be
externally rotated an extra 3 degrees. For this reason the posterior condylar axis, which
parallels the native tibia surface cannot be used to set the femoral component – an extra 3
degrees of external rotation is required if this axis is used for reference during TKA.
Studies have shown that the Trans-epicondylar and the Whiteside line corresponds quite
well to the required amount of rotation for the femoral component
• Reproduce the correct joint level – It is necessary to understand that there is the Tibial
Joint Level and the Femoral Joint Level. When the knee is properly balanced the 2 joint
levels coincide. There are numerous suggestions about how best to assess joint level
during TKA.

1. Meniscal line – where identifiable the meniscal line is a ready and accurate
indication of the joint level
2. Tibial Joint level – is about 10mm proximal to the tip of the fibular head
3. Femoral Joint level – approximately 25mm below the lateral epicondyle and
30mm below the medial epicondyle

BASIC BONE CUTS
Although there is anything up to a dozen bone cuts during TKA, there are only 3 basic cuts.
1. Tibia cut – affects flexion and extension space equally
2. Distal femoral cut – affects extension space only
3. Posterior femoral cut – affects flexion space only
Knowledge of this is essential for effective balancing of the knee as bone cuts may be varied to deal
with flexion/extension space issues.

REPLACING WHAT IS REMOVED – Importance of knowing the knee system in use
For most standard TKA the aim is to removed from the less worn condyle an amount of bone equal
to the thickness of the prosthetic component. This rule is modified in certain situations to correct
deformities that cannot be fully corrected by soft-tissue release. For example additional amount of
bone may be removed from the distal femur to correct a fixed flexion deformity. Each millimetre of
additional distal femur resection will correct 4 degrees of fixed flexion.
Recognizing this principle it is thus important that surgeons performing TKA be completely familiar
with specifications of the knee system they are using.
THE PFC-SIGMA specifications
With the Sigma fixed bearing system the required extension space is 1mm greater than the required
flexion space. This rule holds true for all sizes up to size 5. Thus the minimum extension space
required is 17mm (9mm distal femur + 8mm tibial thickness) and the minimum flexion space is
16mm (8mm posterior femur + 8mm tibial thickness). The thinnest tibial implant for the PFC-RP is
10mm which follows that the smallest extension space required is 18mm and the flexion space
17mm.
Minimum Space PFC-Sigma

Using 8mm insert
•
9 + 8 = 17mm distally
•
8 + 8 = 16mm posteriorly
KNOWING THE COMPONENT
SPECIFICATIONS
PFC-Sigma
PFC Tibial Component
•
Tray thickness = 2mm
•
8mm insert = 2 + 6mm


ABOUT COMPONENT ROTATION
Incorrect femoral or tibial component rotation affect knee balance and result in patellar instability
and increased wear rate of the polyethylene insert.
FEMORAL ROTATION
The aim is to set the femoral component parallel to the tibia component when the knee is at 90
degrees flexion (discussed in the section above). Provided the tibia osteotomy is correct and the
collateral ligament balance satisfactory, then the Trans-epicondylar Axis (or the Whiteside Axis)
should be parallel to the cut tibia surface. The correct identification of the TEA and the WA can
present difficulties. The WA may be difficult to identify if
1. the femoral sulcus is shallow due to lateral condylar attrition or hypoplasia
2. osteophytes formation in the intercondylar notch. Care should thus be taken to remove the
osteophytes in order that the roof the notch may be clearly identified
Mistakes are often made with location of the TEA. The lateral epicondyle is relatively easy to
identify as it is a distinct bony prominence. The point to be used for the TEA is the highest part of
the bone prominence and this is best located by running a finger proximal-distally on the bone. The

point medially is more difficult to identify and there is debate about the best bone point to use.
Berger et al identified 2 points
1. The Anatomical Medial Epicondyle – represented by the bone prominence on which the
superficial medial collateral ligament originates
2. The Surgical Medial Epicondyle – represented by the sulcus from which the deep medial
collateral ligament takes origin. He recommends use of this landmark to set the femoral
rotation
The practical difficulty during surgery is to identify the most prominent point of the medial
epicondyle as this epicondyle unlike the lateral epicondyle does not rise to a peak. Rather the medial
epicondyle resembles an inverted cashew nut without a raised peak. During TKA the author seeks
the sulcus of the medial epicondyle by following the deep medial collateral ligament to its origin
and uses a point 1mm above the sulcus as the landmark for the TEA.




DEALING WITH BONE DEFORMITY
Severe varus or valgus deformities may be associated with significant condylar bone loss
particularly on the tibia side of the joint. It is a common and undesirable practice to perform the tibia
osteotomy at the lowest level of the bone defect. This leads t a number of potential problems.
1. Component size mismatch - the tibial implant size may end up smaller than the femoral
component size. Although most manufacturers advise that the femoral and tibial component
may be a size up or down, one should be aware that size mismatch can adversely affect the
quality of articular contact. It is best to avoid a mismatch of sizes.
2. A low tibial resection may result in impingement of the tibial tray against the fibular head
The preferred technique is thus to build-up rather than resect down.
•
Too much bone removed
•
Lateral joint pain

•
Component mismatch


GUIDELINES TO SOFT-TISSUE BALANCING
Surgeons not infrequently carry out excessive amount of soft-tissue release during surgical exposure
and balancing of the knee. Such over-zealous release may result in
• Over expansion of the flexion space which in turn demand further bone resection or soft-
tissue surgery to increase the extension space in order to create a “balanced” situation
• Joint instability
• Post-operative bleed and pain
• More scarring and loss of motion
Care should be taken to be selective about the soft-tissue structures to release and to titrate the
amount of release to the degree of correction required.
USE OF TENSIONING DEVICE
Although there is potential value in the use of a tensioning device, it is far more important that the
surgeon assess joint space and tissue tension under similar conditions. It is a very common error,
whether using spacer blocks or tensioners, for surgeons to perform the evaluation in flexion with the
weight of the thigh on the knee whilst performing the evaluation in extension without the same
weight on the knee. The weight of the thigh should be eliminated during the examination in flexion
for the testing to be accurate.

FLEXION-EXTENSION SPACE BALANCING
Achieving rectangular and equal flexion / extension space is a fundamental requirement for
successful TKA. Some helpful points to register in this regard are,
1. FIXED FLEXION - It is more difficult correcting a fixed flexion deformity than it is to
correct tightness in flexion because release of most soft-tissue structures in and about the
knee leads to greater expansion of the flexion space than the extension space. Mild flexion
deformity can be corrected by posterior capsular release. Moderate and severe deformity
requires additional amount of distal femoral resection. Very severe fixed flexion deformity of

more than 50 degrees should be managed with caution because of the stretch risk of injury to
the Lateral Popliteal Nerve. Most cases can be managed by
• Radical posterior capsular release
• Release of Gastrocnemius at insertions
• Additional resection of distal femur
• Knee splintage at 50% correction and serial adjustment as permitted by function of
Lateral Popliteal Nerve over a period of 7-10 days to minimize risk of nerve palsy

2. LIMITATION OF FLEXION – is relatively easier to correct. It is essentially to first identify
the anatomical factors causing the limitation of motion eg. Osteophytes, notch occlusion,
capsular/ligamentous contracture, quadriceps contracture etc. In general such joints should be
treated with a PS TKA as excision of the PCL substantially increases flexion space.
A useful algorithm is
• Comprehensive posterior and intercondylar osteophyte removal
• Ensure 4-6 degrees of posterior slope to the tibia osteotomy
• Avoid patellar over-stuffing
• Downsize femoral component or use “Hi-Flex” design with reduce posterior condylar
radius if that is available
• Multi-puncture quadriceplasty for muscle contracture
• Epicondylar osteotomy to release collateral contracture

3. VARUS DEFORMITY – The amount of surgery necessary to correct this deformity vary
according to the stiffness of the deformity and can be judged by how well the deformity
corrects with passive testing. Mild varus deformity of less than 5-6 degrees is generally
corrected by the standard medial capsular release required for exposure of the knee joint and
subluxation of the tibia. Moderate deformity of up to 12 degrees will usually require release
of the semi-membranosus tendon at its insertion on the posteromedial condyle of the tibia.
Additionally some cases require partial release of the deep medial collateral ligament.
Correction of the deformity should be assessed with the knee in extension as well as flexion.
Persistent varus deformity in flexion is usually associated with tightness of the mid and

anterior portion of the deep MCL and only this portion of the ligament require release. Varus
deformity in extension is usually associated with tightness of the posterior portion of the
ligament. The author prefers selective and careful titration of ligament release using the
multi-puncture method. A tensioner is useful for this method of selective release and one
should be cautious to increase distraction in graduated and careful steps so as to avoid over-
release. Over release of collateral ligaments are a very difficult complication to treat.
Severe varus deformity of more than 12 degrees may require release of the superficial MCL.
The author prefers release of this ligament by osteotomy of the medial epicondyle to
releasing the ligament at its distal attachment, as this method provides more control and
avoids the problem of over-release.
Severe varus deformity is often associated with bone loss of the posterior portion of the
medial tibial condyle. The bone defect can be managed by autologous bone graft or metal
augment (older patient).

4. VALGUS DEFORMITY – there is no agreement amongst practitioners about the best
method to correct the valgus. The author prefers using the paralateral approach for moderate
and severe deformity and finds the approach suitable for applicable for most patients with the
exception of the obese. It is necessary in the preoperative examination to determine if the
deformity is
• Present in extension, flexion or in flexion as well extension
• Correctable or not to passive stress – tight or loose deformity
This information arms the surgeon with knowledge about the soft-tissue structures that are
likely to require attention during the TKA.
Deformity in extension is generally correctable by simple release of the Ilio-tibial band (the
author preferring to perform the release at the insertion at the Gerdi tubercle). Deformity in
flexion is usually associated with bone loss and the majority are “loose” deformity. The
algorithm for treatment is
• Mild (<10 degrees) – release ITB, lateral capsular release
• Moderate (10-20) – release ITB, Posterolateral capsule (multi-puncture supra-
Popliteus tendon technique). PS TKA recommended.

• Severe (>20) – Popliteus tendon, lateral epicondyle osteotomy
Care should be taken before a decision is made t release the Popliteus tendon as the action
will result in quite dramatic expansion of the flexion space. In the author’s experience the
need for Popliteus tendon release is uncommon.
Correction of major valgus deformity is associated with a significant incidence of Lateral
Popliteal Nerve injury.

5. UNSTABLE JOINTS – Major collateral ligament instability presenting for TKA may be due
to bone loss or ligament incompetence. The former is managed by management of the bone
loss and little additional ligament surgery is required. Instability due to ligament
incompetence may be treated by
• Ligament advancement or augmentation (the author recommends the former)
• Use of constrain prosthesis – TC3 or SROM rotating hinge depending on the degree
of instability
“MINOR MISTAKES” THAT ARE UNFORGIVING
It is not possible even amongst the most skilled surgeons to perform every operation to perfection.
Mistakes are made, though some are more harmful than others. There are few “minor” technical
errors that tend to cause significant symptoms. Some of these technical pitfalls are discussed below.
1. Component malrotation – Internal rotation of the femoral component is poorly tolerated and
the risk of consequent patella dislocation is high. Internal rotation of the tibial component is
better tolerated especially when using a mobile bearing device.
2. Component overhang – Lateral overhang particularly of the tibia component is poorly
tolerated. In my experience patients with more than 2mm of lateral overhang of the tibial
component tend to suffer from soft-tissue impingement symptoms. This error is made usually
when the surgeon endeavours to provide full cover of the cut tibial surface by using a larger
than necessary tibial tray. 80% of good host bone contact is all that is necessary to provide a
stable platform for fixation of the prosthesis and there is no need to fully cover the cut
surface. Although there is value in lateralizing the tibia and femoral component in order to
benefit patella tracking, care must be taken to avoid lateralizing beyond the bone edge.
3. Lateral placement of patella component – the articular centre of the native patella is medial

of the anatomical centre because the lateral facet normally accounts for 60% of the articular
surface. Thus when positioning the patella component, the prosthesis should be centred about
5mm medial to the mid-point of the cut patella surface. The plane of the patella osteotomy is
also an important consideration. Studies have shown that oblique osteotomy of the patella is
associated with higher loosening rate of the prosthesis. To achieve a horizontal cut of the
patella it is necessary to resect more of the medial facet than lateral facet.
4. Tibial Osteotomy error – the most common error of tibial osteotomy is the varus osteotomy.
This is usually the result of displacement of the tibial cutting block by the patella tendon. It is
well documented that error of more than 3 degrees is associated with higher incidence of
tibial component loosening. When such error is committed in the obese patient the margin of
error is even smaller.
5. Patella tendon avulsion – this is a dreadful complication that can occur early or late. It is
caused by traction on the patella tendon insertion when exposing a tight knee. The
complication may be avoided by adopting one of these techniques,
• Avoid eversion of the patella till femoral and tibia bone resections are completed
• Adequate resection of the fat pad – which contributes substantially to reducing
tension of the patella tendon. This is particularly so when performing revision
surgery.
• Quadriceps snip
• Protective pin inserted through patella tendon insertion – this popular method is
unlikely to be helpful