Primary Total Knee Arthroplasty

Jatinder S. LuthraMS DNB MRCS

Historic Evolution

• 19th century – Soft tissue interposition

• 1950 Walldius Hinged knee replacement

• 1960 MacIntosh & McKeever Acrylic tibialplateau

• 1973 – Total condylar prosthesis

Prosthetic Design

• Femoral rollback

– Posterior translation femur with flexion

– Controlled by PCL

– Improves Quad function and knee flexion

Prosthetic Design

Modularity

• Augmentation of standard prosthesis

Metal base plate + Poly

Metal augment - bone loss

Femoral/ tibial stem

Prosthetic Design

• Constraint

– Ability of prosthesis to provide varus – valgus and flexion –extension stability in presence of ligamentous laxity / bone loss

Prosthetic Design

• Cruciate retaining prosthesis (CR)

• Cruciate sacrificing prosthesis (CS)

• Varus – valgus constrained

• Hinged prosthesis

• Total condylar Prosthesis

Prosthetic DesignCruciate retaining

• Intact PCLVarus def. < 10 Valgus def. < 15

• Advantage1. Avoid post cam impingement/ dislocation2. More closely resembles knee kinematics3. Bone preserving4. Improved proprioception

• Disadvantage1. Tight PCL – Increased poly wear2. Rupture PCL – flexion instability

Prosthetic DesignCruciate stabilized

• Cam and post mechanism• Insert more congruent / dished

AdvantagesEasier to balance kneeMore range of motion

DisadvantagesCam jumpPost wearPatellar clunk syndromeAdditional cut from distal femur

ABSOLUTE INDICATION•Previous patellectomy

•Inflammatory arthritis

•Deficient PCL

Cruciate sacrifice / retain - Evidence

• PS increased ROM –No functional improvement

• No difference in ROM between PS and CR

• PCL does not work in CR knees

• Increased wear Ps knee – cam & post

Cochrane review – No difference in function whether cruciate retained

or sacrificed

Prosthetic DesignSemiconstrained design

• No axle connecting tibia and femur

• Large tibial post and deep femoral box

• Varus / valgus stability• Rotational stability

More femoral resectionEarly loosening – increased

constrained

INDICATIONSMCL/ LCL attenuationFlexion gap instability

Prosthetic DesignConstrained Hinged design

• Linked femoral and tibial components

• Tibial bearing rotates around yoke

Aseptic loosening

Large amount bone resection

INDICATIONGlobal ligamentousdeficiencyHyperextension instability

Prosthetic DesignMobile Bearing Design

• Poly Rotates over tibialbase plate

• Reduced poly wear

• Bearing spin out

Fixed Bearing or mobile bearing -Evidence

• No advantage of mobile bearing over fixed bearing

• Increased wear in undersurface of mobile bearing

Prosthetic DesignHi flex design

• Cultural / pt expectation

• Cut more posterior condyle

Preop flexion - most significant - Gatha etal 2008No difference in ROM - Mehin JBJS 2010

No difference in ROM Sumino Int Ortho 2010

Radiographs

• Standing Ap & Lateral

• Sunrise – Merchant view

• Hip to ankle x- rays

– Bony deformity

– Short stature ( < 150 cm)

– Very tall ( > 190 cm)

Radiographs

• Femoral and tibial cut

• Position of femoral canal entry

• Bone defects

• Joint subluxation

• Ligament stretch out – Varus Thrust

• Ligament release

• Constraint needed

Approaches

• Multiple incision –choose lateral incision

• Previous transverse incision – cross at right angles

ApproachesMedial parapatellar approach

• Most common

• Surgeon are familiar

Lateral parapatellar approach

• Valgus knee

• Allows access to lateral side

• Technically demanding

• Medial patellar eversiondifficult

Midvastus approach

• Spares VMO insertion

• Advantages

Accelerated rehab.

Improved patellar tracking

• Disadvantages

Less extensile

Difficult in obese & flex contracture

Subvastus approach

• Vastus medialis lifted off Lateral intermuscularseptum

• AdvantagesIntact quadPreserved vascularity of

patella

• DisadvantageLeast extensileDenervation of VMO possible

Extensile Exposure

• Quad snip

• VY turndown

• Tibial Tubercle osteotomy

Technical Goals

• Restore mechanical alignment

• Restore joint line

• Balanced ligaments

• Normal Q angle

Femoral Cut

• Valgus cut angle

• AAF – MAF

• Between 5 – 7 deg

• Intramedullary guide

Tibial Cut

• Angle between AAT –MAT

• Tibial cut angle- Zero

• Tibial deformity – cut perpendicular to MAT

• Intra or extramedullaryguide

Joint line preservation

• Inserting prosthesis prosthesis same size as removed bone and cartilage

• Elevate joint line –mid flexion instabilityAbnormal patellofemoral trackingEquivalent to Patella Baja

• Lowering joint lineLack of full extension

Knee Balancing

• Balance in Coronal and saggital plane

• Concave side –ligaments contracted –release

• Convex side – ligaments stretched – Fill gap

Varus Knees

HenriK Schroeder – Boesch – Ligament balancing in TKR

Grade 1 release

Grade 2 release

Grade 2A

Grade 2 release

• Grade 2B release

Posterior part tight in

extension

Anterior part tight in flexion

Grade 3 release

• Grade 2A + 2B

Grade 4 release

Valgus deformity

• Osteophytes

• Lateral capsule

• Iliotibial band - Tight in extension

• Popliteus – Tight in flexion

• LCL

Pie crusting

Flexion contracture

• Osteophytes

• Posterior capsule

• Gastrocnemius ( Medial and lateral head)

• Inreased distal femoral cut

Sagital plane balancing

• Mc Pherson’s rule

Symmetric gap – address tibia

Asymmetric gap – address femur

Tight in Extension Tight in flexion

Symmetric gap Cut more tibia

Loose in Extension Loose in Flexion

Symmetric gap•Thicker poly •Tibial Metal augmentation

Extension good

Loose in flexionAsymmetric gap

1. Increase size femoral component

2. Translate femoral component posterior

3. Use thicker poly and readdress as tight extension gap

Extension TightFlexion Good

Asymmetric Gap1. Cut more

distal femur

2. Release posterior capsule

Extension GoodFlexion Tight

Asymmetric gap

1. Decreasefemoral component size

2. Recess PCL

3. Check slope of tibia

Extension LooseFlexion Good

Asymmetric gap1. Distal femoral

augmentation

2. Decrease femoral component size and thicker poly

Patellofemoral alignment

• Most common complication

• Maintain Q angle

• Proper component rotation

• Maintain normal patellofemoral tension

• Maintain Q angle

Avoid

1. Int rotn fem component

2. Medial fem component

3. Int rotn tibia

4. Patella prosthesis lateral

Femoral component rotation

• Ap Axis ( whiteside line)

• Transepicondylar axis

• Post condylar axis

• Tibial alignment axis

• Gap balance

Tibial component

• Int rotn tibia –increased Q angle

Patellar component

• Centre or medialized

• Avoid lateralizing

• Increases Q angle and cause patella maltracking

Patella Baja

• Patellar component superior

• Lower joint line

• Transfer tibial tubercle cephalad

• Patellectomy

Patella resurfacing vs non resurfacing

• Resurfacing

– Component loosening

– Clunk

– Fracture

– AVN

• Non resurfacing

– Anterior knee pain

– May require second resurfacing

Patellar resurfacing Vs non resurfacing - Evidence

• Metal backed patella higher complications

• Patellar replacement does not guranteepainless Patellofemoral joint

• No significant benefit of patellar replacement

Complication

• Femoral notch

Saw cuts into anterior femoral cortex

Increases chance of periprosthetic fracture

Femoral stem extension

Complication

• Peroneal Nerve palsy ( .3 to 2 %)

Pre op Flexion and Valgus defTourniquete time > 120 min.Epidural anaesthesia post opAberrant retractor placement

EMG & NCV at 3 months

Nerve decompression at 3 months

Complication

• Vascular complication ( <.17% - .2%)

• Risk factor

– Sharp dissection

– Posterior retractor placement

– Pre existing vascular disease

– Immediate vascular repair

Complications

• Extensor mechanism rupture ( .17% - 2.5% )

– Direct repair with suture - < 30 % avulsion

– Primary repair and augment with graft

– Allograft repair

Complications

• Stiffness

– Flexion contracture 10 – 15 % deg

– Flexion < 90 deg

• Treatment

– Manipulation under Anaesthesia

– Arthroscopic lysis of adhesion

– Revision TKR

Complications

• Hypersensitivity

Rare ( nickel)

• Patch testing

• Lymphocyte transformation test

• Revise to non allergic metal prosthesis

Summary

• Choose correct pt

• Plan properly

• Adequate exposure

• Follow principles to align and balance knee

• Meticulous closure

Hope for the best because 20 % of pt. with well performed TKR are not happy !!

THANK YOU