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Flashcards in Miller-Total knee Deck (33)
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1

Review the AAOS guidelines for knee OA treatment

2

Review osteotomy treatments

Best indication

Young active patient, generally younger than 45 years, and

Occupation precludes the use of prosthetic joint replacement owing to significant implant loading and cycles (i.e., high-load, high-stress type occupation)

Most likely to succeed when disease affects predominantly one compartment

For varus knee malalignment

Treatment is valgus-producing proximal tibial osteotomy

Reason: problem is usually due to proximal tibial varus.

Goal of surgery: correct the deforming problem

Osteotomy goal: maintains joint line of knee perpendicular to mechanical axis of leg

Mechanical axis of leg defined as center of hip through center of knee to center of ankle

For valgus knee malalignment

Treatment is varus-producing supracondylar femoral osteotomy

Reason: problem typically is result of lateral femoral condylar hypoplasia.

Goal of surgery: correct the deforming problem

Osteotomy goal: maintain joint line of knee perpendicular to the mechanical axis of leg

Valgus-producing tibial osteotomy (for varus knee deformity)

Selection criteria

Clinical examination and radiographs show that other two compartments are free of arthritis.

Clinical pain is isolated to medial knee compartment.

Patient is physiologically young and has an occupation or activity level that makes prosthetic arthroplasty less appropriate

Contraindications

Inflammatory arthritis

Lack of flexion—minimum of 90 degrees needed

Flexion contracture more than 10 degrees

Ligament instability

Especially varus thrust gait (this indicates abnormal lateral compartment ligament/capsular stretch-out)

Femoral-tibial subluxation more than 1 cm (viewed on AP radiograph)

Note: ACL deficiency acceptable if all other criteria are met

Medial compartment bone loss

Lateral compartment joint narrowing

Detected by valgus stress radiograph

Osteotomy less successful in following conditions

Smoking

Age 60 years or older

Varus deformity of 10 degrees or more

There is just not enough bone to remove to correct deformity.

Concomitant arthritis in other compartments

Main problems

Closed-wedge technique

Patella baja deformity (most common)

Patella baja results in loss of knee flexion

Loss of tibial posterior slope

Open-wedge technique

Patella baja deformity (also most common)

Nonunion

Loss of valgus correction (i.e., collapse of open wedge)

Varus-producing femoral osteotomy (for valgus knee deformity)

Selection criteria

Valgus deformity of 12 degrees or greater

Clinical pain isolated to lateral knee compartment

Clinical examination and radiographs show medial knee compartment free of arthritis.

Patellofemoral joint should also be free of arthritis, but minimally symptomatic patellofemoral disease is acceptable (reduction of Q angle improves patellofemoral mechanics and reduces pain).

Patient is physiologically young and has an occupation or activity level that makes prosthetic arthroplasty less appropriate.

Contraindications

Inflammatory arthritis

Prior medial meniscectomy

Lack of flexion—minimum of 90 degrees needed

Flexion contracture more than 10 degrees

Ligament instability

Especially valgus thrust gait (this indicates abnormal medial compartment ligament/capsular stretch-out)

Femoral-tibial subluxation seen on AP radiograph

Medial compartment joint narrowing

Detected by varus stress radiograph

Age older than 65—relative contraindication

Osteoporosis—relative contraindication

Main problems

Nonunion

Loss of varus correction

Seen more often in patients with osteopenia/osteoporosis

Residual patellofemoral maltracking may require a lateral retinacular release.

Osteotomy technique (for femoral osteotomy)

Crescentric dome preferred

This osteotomy produces the least bone displacement.

Allows for femoral stem with TKA

3

Review unicompartment treatments of the knee

Utilized for patients in whom arthritis predominantly affects one compartment of knee

The most common UKA, by far, is medial compartment replacement

Advantages of UKA (medial or lateral) over TKA and knee osteotomy

Quicker recovery

Fewer short-term complications

Shorter hospital stay with less postoperative pain

Better knee function than with TKA

ACL is preserved as it is in TKA

Results

High rate of short-term to mid-term satisfaction

However, long-term survivorship is not comparable to that with TKA when measured by revision rates.

Contraindications

Inflammatory arthritis

Significant fixed deformity

Deformity must be correctable on clinical exam (e.g., resting varus attitude must be correctable to normal valgus)

Previous meniscectomy in opposite compartment

ACL-deficient knee

ACL deficiency is an absolute contraindication to a mobile-bearing UKA

Mobile-bearing UKA is utilized only for medial compartment replacement

Flexion contracture less than 10 degrees

Tricompartmental arthritis

Selection criteria—important:

Pain must be localized to the compartment being replaced

Medial knee pain signifies medial compartment disease

Lateral knee pain signifies lateral compartment disease

Anterior knee pain signifies patellofemoral compartment disease

Diffuse or global pain signifies tricompartmental disease

Surgical technique

Overcorrection must be avoided.

Overcorrection puts increased load on unresurfaced compartment.

Can result in early revision owing to accelerated progression of arthritis

For medial UKA, correction to 1–5 degrees of clinical valgus

Complications unique to UKA

Stress fracture of tibia (never femur)

Associated with heavy weight and high and early postoperative activity level

Typical presentation: pain-free interval (usually 4–6 weeks), then spontaneous acute onset of pain with weight-bearing activity

Aspiration of knee reveals blood

Treatment

If tibial fixation stable

Relative rest and limited weight bearing

If tibial fixation compromised

Revision of tibial implant with or without ORIF of the medial tibia

Conversion to TKA with tibial stem support when medial bone is compromised

Failure mechanisms

Overcorrection at time of surgery

Risk is disease progression in opposite compartment

Pain localized to arthritic compartment

Undercorrection at time of surgery

Risk is implant overload with subsequent failure due to accelerated polyethylene wear/failure, osteolysis, and/or mechanical loosening

Implant subsidence

Tibial side only

Due to weak metaphyseal bone; factors:

The deeper the tibial cut, the weaker the metaphyseal bone

Undercoverage—preference is to place tibial implant on host rim bone, which is stronger.

Osteoporosis

Patellar impingement upon femoral implant causing pain

Related to implant design and surgical technique

Pain is localized anteriorly

Requires revision to TKA

Arthritis progression in other compartments (i.e., natural progression of disease)

Pain in other knee compartments

Requires revision to TKA

Isolated patellofemoral arthritis

TKA (not patellofemoral arthroplasty) is recommended choice in older patients (≥50 years)

Superior functional results than those of patellectomy and patellofemoral arthroplasty

Lateral retinacular release commonly required with isolated patellofemoral arthritis

Reason: maltracking is usually the cause of isolated patellofemoral arthritis

TKA: see next section

4

Review the end cuts on TKA

Goal of end cuts is to restore neutral mechanical alignment of the limb.

Neutral mechanical alignment is defined as a line from hip head center, through knee center, to ankle center

Preoperative analysis of femur (review of full-length radiographs) is used to determine the following (Fig. 5.67):

Anatomic axis of femur (AAF)

A line that bisects the medullary canal of the femur

The AAF, drawn to the distal end of the femur, determines entry point for the femoral medullary guide rod for the cutting jigs

Mechanical axis of femur (MAF)

A line from center of distal femur (entry point hole) to center of femoral head

Significance—distal femur is cut perpendicular to MAF.

Allows even mechanical loading to knee implant

Valgus cut angle

Defined as angle between AAF and MAF

Intramedullary guide rod is placed into femur (this defines AAF).

Distal femoral cut jig is assembled to intramedullary guide rod.

Surgeon selects valgus cut angle (typically between 4 and 7 degrees).

Distal femur should end up being perpendicular to MAF.

Valgus cut angle should always be measured in tall and short patients (Fig. 5.68).

Hip offset remains relatively constant.

Femur length, therefore, has more influence on valgus cut angle.

Preoperative analysis of tibia (review of full-length AP radiograph) is used to determine the following (Fig. 5.69):

Anatomic axis of tibia (AAT)

A line that bisects the medullary canal of the tibia

The AAT, drawn through the proximal tibia, determines the entry point for the tibial medullary guide.

Both intramedullary and extramedullary cutting jigs for the proximal tibial end cut are acceptable techniques.

Mechanical axis of tibia (MAT)

A line from center of proximal tibia (entry point hole) to the center of ankle

Significance—proximal tibia is cut perpendicular to MAT.

Allows even mechanical loading to knee implant

Tibial cut angle

Defined as angle between AAT and MAT

Intramedullary guide technique

Intramedullary guide is placed into tibia.

Proximal tibia cut jig is assembled to intramedullary guide.

Surgeon selects tibial cut angle (usually 0 degrees).

Proximal tibia should end up being cut perpendicular to MAT.

Extramedullary guide technique

The extramedullary guide technique is placed over the anterior tibia. A jig distally holds guide centered over ankle. A proximal jig holds guide centered over proximal tibia (landmark is medial one-third of tibial tubercle).

Surgeon selects tibial cut angle.

In most cases the AAT and MAT are coincident. Therefore tibial cut angle is zero.

When there is a tibial deformity (e.g., fracture or bowing deformity), the AAT and MAT are divergent. The tibial cut angle is then carefully measured and selected to provide a proximal tibial end cut perpendicular to MAT.

5

Review the sagital plane gap deformity guide

6

Review the sequence of release for medial deformity

Convex side is lateral—loose

Concave side is medial—medial compartment release needed

Medial compartment release in sequence

Osteophytes

Deep medial collateral ligament (also known as meniscal tibial ligament)

Includes medial knee capsule

Posterior medial corner

Capsule

Semimembranosus

7

lateral release sequence

Lateral compartment release in sequence

Osteophytes

Lateral capsule

Iliotibial band—key structure

 

 

Release for lateral extension tightness

Popliteus—key structure

Tight in flexion

Release for lateral flexion tightness

Release of popliteus off anterior portion of lateral epicondyle (Fig. 5.72)

Note: the inadvertent cut of a noncontracted popliteus tendon does not significantly affect the static stability of the knee.

Lateral collateral ligament (LCL)—last

8

review extra-articular bone deformity

General rules

The closer the extraarticular coronal bone deformity is to the knee joint, the greater the mechanical malalignment at the joint line.

For any given magnitude, the farther a deformity is from the knee, the smaller the intraarticular bone cut needed to correct the mechanical alignment.

An extraarticular deformity within the distal one-fourth of the femur or proximal one-fourth of the tibia is the most difficult to correct if bone cuts are made only at the knee joint. Reasons:

Large bone resections required may compromise ligament attachment sites.

Large bone resections adversely affect implant sizing, fitting, and rotational alignment.

Extreme releases required to balance the knee often render the ligament incompetent (Fig. 5.73).

McPherson one-fourth rule: when coronal deformity is within the distal one-fourth of the femur or proximal one-fourth of the tibia and the deformity is 20 degrees or more, the recommended treatment is:

Concomitant osteotomy and TKA

Closing wedge osteotomy preferred

Diaphyseal press fit stem with splines recommended

Provides rotational stability and obviates the need for additional fixation at osteotomy site

9

treatments for flexion deformity

Concave side is posterior—posterior knee release required

Posterior knee release procedure—in sequence is:

Osteophytes

Posterior capsule

Gastrocnemius muscle origin

Posterior releases are performed with the knee flexed (generally at 90 degrees of flexion).

Less danger to popliteal artery

10

Criteria for diagnosing a periprosthethic joint infection

11

Review the total knee prothesthic designs

Designs are categorized according to an increasing level of mechanical constraint in knee system.

Least constrained

Cruciate-retaining TKA—remove ACL and keep PCL

Cruciate-sacrificing TKA—remove ACL and PCL

Both used for straightforward primary TKA

Constrained

Constrained nonhinged TKA

Used for complex primary or revision TKA

Highly constrained

Hinge TKA

Used for complex revision TKA

12

Review Cruciate Retaining Knee implant

PCL helps provide flexion gap stability.

PCL tension influences femoral prosthetic rollback.

Rollback is defined as the progressive posterior change in femoral-tibial contact point as the knee moves into flexion.

Generally, cruciate-retaining implants have more flat PE inserts to accommodate for flexion rollback.

Advantages

Bone conserving

More consistent joint line restoration

Keeping PCL keeps flexion gap smaller

Disadvantages

Harder to balance with severe deformities

Cruciate-retaining implants should be avoided if

Varus more than 10 degrees

Valgus more than 15 degrees

PCL balance is critical for long-term bearing wear

A tight PCL in flexion causes increased PE wear

PCL in flexion must be balanced.

Lift-off must be avoided (Fig. 5.80).

PCL can be released off femur or tibia.

PCL balance is sometimes hard to assess intraoperatively.

PCL balance is sometimes hard to achieve—over-release of PCL is common.

Excess recession (i.e., release) can result in late failure caused by flexion instability and repetitive subluxation

Flexion instability is characterized by

Knee effusion

Chronic pain

Inability to climb stairs with reciprocal gait

Inability to arise from low chair

Knee buckling

Late rupture of PCL with resultant instability

PE particle debris can cause osteolysis and result in disruption of PCL from bony attachments

Traumatic fall onto flexed knee can cause rupture.

Paradoxical forward sliding as knee flexes

With ACL removed, knee kinematics are drastically altered.

Prosthetic knee does not roll back like native knee.

As knee flexes, there is paradoxical forward-sliding movement, which causes sliding wear on PE insert.

Sliding wear causes significant PE wear.

13

Review cruciate sparing TKR implant

Spine and cam mechanism in the posterior aspect of the knee

Also called posterior stabilized knee

An extended anterior PE lip with a concomitant smaller posterior lip

Also called anterior stabilized knee

Posterior stabilized primary TKA design

Description (Fig. 5.81)

A cam connects between the two posterior femoral condyles.

The cam engages a tibial PE post during flexion.

The cam and post control rollback.

Generally, posterior stabilized implants have more dished (i.e., congruent) PE inserts.

Advantages

Easier balancing in severe coronal deformities (i.e., varus/valgus) because both ACL and PCL are removed

Controlled flexion kinematics with spine and cam, less sliding wear

Disadvantages

Femoral cam jump (Fig. 5.82)

Occurs when flexion gap is left too loose

Mechanism of cam jump

Varus or valgus stress when knee is flexed

Patient usually lying in bed or sitting on floor

Flexion gap opens up, and femoral cam rotates in front of post and then comes to rest in front of tibial post.

Closed reduction maneuver

With use of anesthesia, knee is positioned at 90 degrees of flexion off the table (dependent dangle)

An anterior drawer maneuver is performed

Clunk will be felt as knee is reduced.

Ultimate solution requires knee revision to address loose flexion gap

Causes of loose flexion gap

Overrelease of contracted popliteus

Inadvertently occurs also with saw blade

Overrelease of anterior portion of superficial MCL

Anterior translation of femoral component

Anterior translation increases flexion gap space

Patella clunk syndrome

Scar tissue (descriptively, a nodule of scar) superior to patella gets caught in box as knee moves from flexion into extension.

Scar catches in box, then releases with a clunk.

Clunk occurs in range between 30 and 45 degrees.

Treatment is removal of suprapatellar scar nodule (Fig. 5.83).

Arthroscopic removal is acceptable.

Miniarthrotomy is also acceptable.

Preventive treatment (Fig. 5.84)

Synovectomy and débridement of all scar from quadriceps tendon at time of TKA

Risk factors that cause patellar clunk are related to factors that increasequadriceps force. These include:

Small patella implant (decreased extensor offset)

Thin total patella height (decreased extensor offset)

Short patella tendon (patella baja)

Increased posterior condylar offset (patella pulled lower down)

A result of PCL removal requiring an increase in the AP femoral size to fill the increased flexion gap

Tibial post wear and breakage

Tibial post is an additional PE surface that can wear and enhance risk for osteolysis.

Aseptic loosening and osteolysis are correlated with tibial post wear and damage.

If the knee hyperextends, the edge of the femoral box can impinge on the anterior tibial post (Fig. 5.85).

Causes anterior post damage and fatigue

Causes increased PE wear and osteolysis

Anterior tibial post wear occurs when TKA components are in net hyperextension, such as with

Flexion of femoral component on distal femur

Excess tibial posterior slope

Knee hyperextension (i.e., loose extension gap)

Anterior translation of tibial component on tibia (i.e., placing tibial implant toward front of tibia rather than placing on posterior tibial rim)

Anterior translation of femoral component has no effect on anterior tibial post impingement.

Additional bone is removed from middle of distal femur.

Bone removed can be substantial in a small knee.

Flexion gap is bigger

Flexion gap opens up when PCL is removed.

To balance the extension gap, additional distal femur bone is removed in a posterior stabilized TKA.

Consequence of additional distal femoral bone removal

Joint line elevation with possible baja deformity

The maximum joint line elevation allowed in primary TKA is 8 mm so as to maintain knee ligament kinematics.

Ensures proper kinematic function and stability of collateral ligaments.

PS TKA must be used in following situations

Patellectomy

Cruciate-retaining knee with a flat PE is prone to anterior subluxation when patella is absent.

Inflammatory arthritis

PCL is at risk for rupture with erosive disease process

Trauma with PCL rupture or attenuation

14

Review anterior stabilizing TKA implant

A cruciate-retaining femoral component is used.

 

The PCL is removed (or highly recessed).

Tibial insert is a highly congruent bearing with a raised anterior PE lip and a smaller posterior lip.

No mechanism for rollback

Anterior lip resists anterior translation.

Advantages

Easier balancing in severe deformities (i.e., varus/valgus)

Bone conserving—no box cut needed

Operative versatility

Switch to posterior stabilized system not required if PCL is lost or overreleased.

Regulated flexion kinematics

High congruency limits sliding wear

Knee flexion is achieved by

Posterior placement of tibial knee flexion center; this is called posterior offset center of rotation.

Placement of tibial component with native posterior slope; femur is less likely to impinge upon posterior tibia in flexion.

Disadvantages

Increased PE surface area

Increases risk for greater PE wear debris and osteolysis

Minimal rollback

Surgical technique must be adjusted to attain high flexion.

Posterior translation of tibial component on tibia, when possible; this will place tibial center of rotation more posteriorly.

Recreation of native tibial posterior slope.

Flexion gap laxity causes rotational instability and pain

A loose flexion gap will cause instability usually in midflexion and full flexion.

Mechanism of midflexion instability

Varus or valgus stress when knee is flexed (between 50 and 90 degrees)

Patient usually lying in bed or sitting on floor

Flexion gap opens up and tibia rotates anteriorly. This creates a subluxing event, but knee usually does not lock up.

Patient experiences pain when climbing stairs with reciprocal gait, arising from a chair, or negotiating uneven surfaces; it is usually associated with a knee effusion.

Treatment requires revision to address loose flexion gap.

15

Review tibial rotating platform

The tibial PE bearing rotates on a polished metal tibial baseplate.

The rotating platform can be used with both anterior stabilized (high congruent) and posterior stabilized TKA designs.

The PCL is removed when a tibial rotating platform is used.

Advantages

Better articular conformity through entire knee range

Theoretically less PE wear

Equivalent in survivorship to fixed-bearing knee, but not superior

Wear and osteolysis still seen

Disadvantages

Bearing spinout (Fig. 5.88)

Occurs when flexion gap is left too loose

Mechanism of spinout

Varus or valgus stress when knee is flexed

Patient usually lying in bed or sitting on floor

Flexion gap opens up, and tibia rotates behind femur.

Femur then comes to rest in front of tibial PE bearing and locks into spinout position.

Closed reduction maneuver

With use of anesthesia, knee is positioned at 90 degrees of flexion off the side of the table (dependent dangle).

Tibial bearing is manipulated by digital palpation and pressure into reduced position.

Ultimate solution requires knee revision to address loose flexion gap.

16

Review all poly insert

Implant is nonmodular

Implant is cemented

Economical (compared with metal tray–modular PE combo)

Wear rate and aseptic loosening rates are similar to those of modular tibial implant.

Disadvantages

Cementing an APT is technically harder to perform.

“Forcing” the APT in place during cementing process can change balance of knee by damaging soft tissues.

Failure mechanisms

Bending of PE implant at periphery, as there is no underlying metal to support cantilever bend forces

PE implant bends, causing cement to crack. Implant then becomes loose.

17

What are the indications for a hinged prothesis?

This is absolute indication for hinge.

Hyperextension conditions include

Postpolio knee or spina bifida

Increased knee extension forces to lock and hold knee in extension during gait, eventually causing posterior capsule to stretch out

Erosion of posterior capsular attachments to bone as a result of

Advanced bony osteolysis

Autoimmune disease states (particularly rheumatoid arthritis)

Native knee removal

Tumor

High-energy fracture with communication

Massive infection

18

TKA techniques to avoid patella maltracking

Reduction of excess valgus

Valgus deformity must be corrected to a neutral mechanical alignment—always.

Severe valgus deformities that require radical ligamentous releases can be adequately managed with sophisticated revision-style prosthetic systems.

Component positioning

Patellar maltracking—causes

Internal rotation of

Femoral component

Tibial component

Medialization of

Femoral component

Tibial component

Femoral component rotation

Femoral component should never be internally rotated.

19

Review the technique for internal rotation of the tibia component

20

why do you set 3-5 degrees of external rotation cut on the femur?

21

Review the 5 established techniques to address femoral rotation:

22

Review implant medialization

femoral implant should be lateralized

tibial implant should be lateralized

patella component may be medialized

23

what is the pre-op evaluation for a TKA revision?

Revision of a painful TKA without identification of a specific cause of pain is likely to have a poor outcome.

First, pain must be determined as having either an intrinsic intraarticular source or an extrinsic source.

Extrinsic sources of knee pain

Referred pain from the hip

Most common missed diagnosis

Hip pain typically refers to anterior-medial knee region (distal branch of obturator nerve).

Referred pain from the spine

Typically L3 nerve root

Extraarticular at the knee

Allodynia—chronic regional pain syndrome

Local superficial neuroma

Intrinsic sources of knee pain

Mechanical loosening

Osteolysis with PE debris synovitis

Malposition and/or malalignment of implants

Instability

Infection

Typically, presentation is constant global pain with abnormal infection biomarkers and positive aspiration findings.

PJI is currently the number one reason for revision within the first 2 years of primary TKA.

Hypersensitivity—rare

Typically, constant global pain with normal infection laboratory results and negative aspiration findings.

Most common metal ion involved in knee hypersensitivity is nickel.

Intraarticular aspiration

WBC count greater than 3000 cells/μL raises suspicion for a chronic PJI.

Intraarticular lidocaine challenge

Administration of at least 15 mL of lidocaine or 50/50 mixture of lidocaine/bupivacaine

Relief of more than 90% of pain constitutes a positive result.

Indicates that pain emanates primarily from within the knee joint

Radiographs

Smooth radiolucent lines around cement mantle and metallic implants suggest aseptic loosening.

Stem tilt to side of medullary canal with an outer cortical periosteal reaction suggests aseptic loosening.

CT

Evaluation for rotational malalignment of implants

Posterior condylar axis of metallic femoral condyles should be compared with epicondylar axis.

Posterior condylar axis should be parallel or slightly externally rotated in relation to epicondylar axis.

Internal rotation of femoral implant is a known cause of flexion gap imbalance.

Tibial implant axis should lie over medial third of tibial tubercle.

A tibial implant axis lying medial to tibial tubercle indicates malalignment (i.e., relative increase of tibial tubercle external rotation).

24

review the surgical technique for a revision TKA:

The prior incision should be used instead of a new incision made.

Reason: a “skin bridge” can necrose from devascularization.

If a second incision is required, the minimum distance between incisions is 7 cm.

If two or more longitudinal incisions are present in the anterior knee, the most lateral incision should be chosen for revision.

Reason: blood supply for the anterior knee skin comes from medial side of distal thigh and knee.

Difficult exposure sequence

Extended proximal arthrotomy

To most proximal end of quadriceps tendon

External rotation of tibial bone from soft tissue envelope

Subperiosteal dissection of soft tissues from medial tibial tubercle all the way around to posterior-medial corner of knee

Release of posterior-medial corner structures and, if needed, posterior tibial capsule

Lateral knee débridement

Removal of scar from patella, tendon, and lateral gutter

Gradual eversion of patella as tibia is externally rotated

Lateral retinacular release—only if needed

Quadriceps tendon snip (usually 2 cm)

Transverse snip at most proximal region

Snip will not cause quadriceps dysfunction or lag

Tibial tubercle osteotomy

Used as last resort

Best indication is for a stiff TKA (<90 degrees flexion) with patella baja deformity.

Implant System

Comprehensive revision system must be available.

Revision surgery is often unpredictable.

Constrained tibial insert option is a must.

Stems and metallic augmentations are required.

25

can you just change out the poly in a TKA revision?

Modular Bearing Change for Premature Excessive Wear

Most current tibial PE bearings should last at least 13–15 years with an average patient wear scenario in a well-balanced knee.

Failure of a PE bearing within 5–7 years is premature and indicates a problem with knee balance and/or alignment.

Failure rate of isolated modular bearing change for excessive premature PE failure is 30%–40%.

Reasons for premature failure

Unappreciated malalignment

Poor knee balancing in either coronal or sagittal plane

Isolated modular bearing change in this scenario is not recommended.

26

review the workflow sequence of a revision TKA

Workflow sequence

First—implant removal

Second—joint line restoration with tibial implant

Joint line is generally 1.5 cm superior to top of fibular head.

Failure to restore joint line will result in diminished knee flexion.

Third—femur restoration

Extension gap restored first

Surgeon must ensure that patella is in appropriate position (i.e., no baja or alta).

Restoration of flexion gap

Gap balance fine tuned.

Fourth—adjustment of femoral and tibial implant rotation for best patellar tracking

Fifth—selection of constraint

The least constraint needed for stable knee function should be used.

Sixth—assessment of patellar tracking

Large lateral retinacular release should be avoided if possible. Lateral superior genicular artery should not be cut.

Segmental defect femur or tibia

Metadiaphyseal trabecular cones are preferred solution to provide prosthetic support (Fig. 5.92).

Trabecular cones have predictable osteointegration to host bone.

Revision TKA—Patella

Isolated patella component failure usually indicates subtle malalignment in patellar tracking.

Higher failure rate for isolated patellar revision

Full revision should be considered.

A mechanically loose patellar component can cause significant patellar bone loss.

For revision to another patellar component, bone thickness must be at least 12 mm, and there must be enough bone to support PE pegs within bone.

If bone is inadequate for revision resurfacing

Débridement of patellar implant with bone retention is acceptable

Patellectomy is recommended for bony fragmentation.

27

Patella resurfacing vs non-resurfacing

Between the two techniques, neither method has been established as superior.

Overall, patellar resurfacing has a lower risk of reoperation than nonresurfacing.

Absolute indication for patellar resurfacing is autoimmune inflammatory arthritis.

Problems with resurfaced patella

Patella component loosening

Due to maltracking

Due to osteolysis

Patella clunk and crunch

Clunk occurs when suprapatellar scar tissue gets entrapped within the posterior stabilized box as the knee comes from flexion into extension.

Clunk is unique to posterior stabilized design.

Patellar crunch occurs when scar accumulates around patellar component, creating a crunching noise as the knee comes from flexion to extension.

Patella fracture

Reason: bone cut too thin

Minimum thickness for patella is 13 mm.

Avascular necrosis of patella with fragmentation

Reason: peripatellar devascularization due to lateral retinacular release

Disruption of lateral superior geniculate artery

Problems with nonresurfaced patella

Anterior knee pain

Incidence increases over time.

Articular cartilage wears away, and there is point loading upon patellar bone.

Results of secondary resurfacing are variable.

Pain relief not predictable

Criteria for patellar nonresurfacing

Noninflammatory arthritis

Lower activity level

No dysplasia or maltracking

No baja

Requirements for patellar nonresurfacing

Anatomic femoral component

V-shaped trochlea groove to match native patella

Deep trochlear groove to prevent overstuffing of patellar gap

Circumferential denervation of patella with electrocautery

28

review the operative techniques to address patella baja

Operative solutions to reduce baja in TKA

Superior placement of patellar component

Use of smaller patellar dome placed superiorly on patella

Trimming/tapering of inferior bone to reduce flexion impingement

Useful for mild baja deformity

Lower joint line—sophisticated technique (Figs. 5.103 and 5.104)

29

review the measures to avoid catastrophic poly wear

PE thickness at least 8 mm (for traditional PE)

Congruent bearing design

High contact area

Low contact load

Sliding wear on tibia minimized

PCL substitution or

PCL accepting prosthesis

PCL is used as a static stabilizer only (seen with anterior stabilized knee).

Direct compression–molded PE bearing

No machining of articular surface

Inert PE irradiation

γ-Irradiation sterilization in an oxygen-free environment

Quality packaging to minimize on-the-shelf oxidation

Packaging must keep oxygen from diffusing back into PE through it

Oxygen scavengers embedded in PE material

Reduces effect of in vivo oxidation

Vitamin E is currently the most commonly added antioxidant.

30

review factors contributing to advanced poly wear:

 

"The Perfect Storm"

Metal-backed tibial baseplate with bone-conserving tibial bone cut

Thin PE, 5 mm

Flat bearing design in coronal plane

Low contact area (a line)

High contact load

PCL retention with flat PE insert

High sliding wear

Ram bar PE with calcium stearate additive

Fusion defects in PE

γ-Irradiation sterilization in air (i.e., oxygen)

Weakening of mechanical properties of PE

Machined PE surface

Cutting-tool stretch effect upon PE