Instability in TKR

INSTABILITY IN TKR..!!

DR RISHI RAM POUDEL

DR RISHIRAJ

PROF R.MALHOTRA

Total Knee Arthoplasty..!!!

Aims:

• Restoration of mechanical axis

• Restoration of joint line

• Balance soft tissues

• Equalize flexion & extension gaps

• Restore patellofemoralalignment & mechanics

Basic principles..!!

• Tibiofemoral alignment should be restored to 6±2º of anatomic valgus

Coronal plane: femur in 5-10 degrees of valgus

tibia resected at 90±2º in relation to

tibial shaft axis

Sagittal plane: femoral component in 0-10º of flexion

tibial component neutral or 5º posterior slope

Rectangular & equal flexion & extension gaps

Bone cuts in TKA..!!!

• Resection of proximal tibia influences both FLEXION & EXTENSION gaps

• Resection of distal femur selectively influences the EXTENSION gap

• Resection of posterior femur selectively influences the FLEXION gap

• Resection of anterior femur influences both FLEXION gap & PATELLOFEMORAL JOINT

Bone cuts in TKA..!!! Distal femoral cut

Intramedullary jig in desired valgus angle

Femoral cutting guide Distal femoral cut

Bone cuts in TKA..!!Proximal tibial bone cut

Extramedulaary cutting guide Resected tibial bone

Bone cuts in TKA..!!

Femoral sizing:

Antero-posterior femoral cuts

Posterior referencing Anterior referencing

If sizing falls into “between “ sizes:Smaller size recommended in anterior referencing to avoid over-stuffiing of flexion gapLarger size recommended in posterior referencing to avoid anterior notching of femur

Bone cuts in TKA..!!Rotation of femoral component


Epicondylar axis is 3º externally rotated to Posterior condylar axis

Whiteside’s line perpendicular to Epicondylar axis

In valgus knees posterior condylar axis distorted by dysplastic lateral femoral condyle

Relation between epicondylar axis & whiteside’s line remains constant

Bone cuts in TKA..!!Antero-posterior femoral cuts

Transepicondylar axis: key reference for rotation of femoral component

Bone cuts in TKA..!!


Trans-epicondylar axis Femoral sizing jig


Headless pins in 3º external rotation Angels wing to estimate level of cut

Why usual 3 º external rotation??

Because tibial resections are performed perpendicular to long axis—not the normal 3º medial inclination of the medial plateau—externally rotated femoral component is necessary to ensure balanced flexion-extension gaps

Internal rotation of femoral component has higher rates of patellar mal-tracking & subluxation


Anterior femoral cut Posterior condylar cuts

Rectangular flexion & extension gaps..!!

Flexion & extension gaps…!!

Flexion gap & extension gaps should be rectangular & equal

Balancing the gaps..!!

Preoperative Planning to prevent instability in Total Knee Arthoplasty :OCNA volume 32.number 4.October 2001

BALANCING THE GAPS..!!

JOINT LINE LEVEL..!!!

Normal joint line Lowered joint line Elevated joint line

Correct joint line level should be maintained to ensure good patellar tracking & collateral ligament symmetry

JOINT LINE LEVEL..!!

Properly placed joint-line should be:

10 mm from lower pole of patella

approximately 30 mm distal to medial femoral epicondyle

25 mm distal to lateral epicondyle

10-15 mm proximal to fibular head

TKR Failure..!!

1.Aseptic loosening

2.Instability3.Structural failure of implant

4.Sepsis

5.Extensor mechanism rupture

6.Stiffness

7.Peri-prosthetic fracture

8.Undiagnosed Pain

Little attention directed towards instability despite it being a cause of failure and reason for revision in 10-22 percent cases

Leading causes for failure: INFECTION (38%) & INSTABILITY (27%)

Malalignment & Instability are major causes of early failue ,therefore ligamentous balancing & appropiate alignment are paramountin performing the surgery..!!

Instability after TKA…!!

Tibio-femoral instability

Instability in extension Instability in flexion

Symmetric AssymetricMid-flexion Antero-posterior

Patellar instability

Approach to "instability”..!!

“Patient’s report of instability is not a diagnosis..!!”

Causes of buckling & giving away:

1. Pain

2. Fixed flexion contracture

3. Quadriceps weakness

4. Patellar dislocation

Kelly G. Vince ,Ayesha Abdeen ,Tanzo sugimori:The unstable total knee arthoplasty causes and cures: The journal of Arthoplasty vol.21 No.4 suppl.1 2006

Approach..!!

Presentation:

Gross instability: FRANK DISLOCATION

Subtle mechanical instability:

1. Vague complaints of anterior knee pain

2. Recurrent effusions

3. Soft tissue tenderness to palpation

4. Difficulty starting ambulation after being seated

Approach…!!

History:

1. Original diagnosis precipitating knee replacement

2. Pre-operative deformity or contracture

3. Type of prosthesis

4. Specifics of operative procedure

5. Post-operative rehabilitation program

6. Any trauma to knee after surgery

Approach..!!

Physical examination:

1. Generalised ligamentous laxity

2. Gait (varus or valgus thrust)

3. Anteroposterior & varus-valgus stability in extension,30 degrees of flexion & 90 degree of flexion

4 .Patellar tracking & intregity of extensor mechanism

Radiographs…!!

1. AP,Lateral & Sky-line views

2. Scannogram B/L Lower Limbs

3. NCCT knee

Extension Instability..!!

Symmetric

• Uncommon

• Components don’t fill space.

Asymmetric

• Common

• One side is not balanced correctly.

Extension instability..!!

Potential instability corrected by using thicker tibial insert

symmetric

Sebastein Paratte ,Mark W Pagnano:Instability After Total Knee ArthoplastyJBJS vol 90 A.No 1.January 2008

Extension instability..!!symmetric

Using thicker tibial insert will elevate the joint line with tight flexion space,midflexion instability and patella baja

Solution:distal femoral augments

Undercorrection of fixed angular deformity ,out of fear of creating instability in opposite direction…!!

Extension instability..!!assymetric

Inadequate release

Medial release for varus knees..!!

Medial release for varus knee..!

Periosteal stripping of medial structures while maintaining continuous soft tissue sleeve

Needle puncturing is new,effective,and safe technique for correction of MCL tightness in varus knees

Lateral release for valgus knees..!!

“Inside-out” technique..

Sequence:

1.Removal of lateral osteophytes

2.Placement of lamina spreader to assist gap tightness

3.PCL release completely from femur

4.Postero-lateral capsule release intra-articularly with electrocautery

5.ITB lengthening with “pie-crust” technique

6.Popliteus release if still tight laterally The depth of surgical blade kept at <5mm

to avoid peroneal nerve injury..!!

Lateral release..is it over-released??

With trial prosthesis in place ,limb in ‘figure-4’ position..!!

“If dislocation: thicker or more constrained tibial insert to be used”

Iatrogenic collateral injury..!!

During proximal tibial resection & vigorous varus-valgus stability testing..!

1.Surgical re-approximation of ligament with use of krackow-pattern sutures.

2.Augmentation with hamstring tendon

3. Constrained condylar implant to add stability..!

MCL Augmentation with hamstring tendon..!!

The hamstring tendon can be run through a drill hole to the femur & tied over a button

Use of increased constraint contributes to favorable outcome

Treatment without increased constraint were associated with residual instability requiring revision

FLEXION INSTABILITY..!!PS KNEES

DSF or” jump distance”:distance needed for cam to ride over the post before dislocating.

FLEXION INSTABILITY..!!PS KNEES

Most common activity leading dislocation is marked knee flexion plus a varusstress(putting ankle of operated limb on contralateral knee)

FLEXION INSTABILITY..!!• Loose flexion gap

associated with LCL laxity

At risk: who had correction of large valgus deformity & regained knee flexion with aggressive rehabilitation

1st dislocation:closedreduction ,trial of bracing & avoiding activity leading to dislocation

Recurrent dislocation:

1.Thicker insert(if room in extension space)

2. Constrained condylar implant

The new construct to be checked in fig-4 position.

PS KNEES

• Sense of instability without giving away

• Difficulty ascending & descending stairs

• Recurrent knee effusions

• Peri-retinaculartenderness

• Excessive anterior translation

8 out of 10 patients of symptomatic flexion instability treated with revision arthoplasty.

1.Obtaining balanced flexion-extension gaps

2.Careful attention in filling flexion space with larger femoral component & posterior femoral augments

FLEXION INSTABILITYwithout dislocation:

PS KNEES

FLEXION INSTABILITY..!!

Causes:

1.Excess flexion gap:undersized femoral component & excessive tibial slope

2.PCL failure

3.Posteromedial polyethylene wear

Symptoms & signs:

1.Sense of instability without giving away

2.Recurrent knee effusion

3.Posterior sag sign

4.Tenderness over pes-anserinus region & retinaculum

CR KNEES

Treatment

Non-operative :poor results

Operative :conversion to Posterior Stabilized implant design with focus on balancing flexion-extension gaps

FLEXION INSTABILITY..!!CR KNEES

Mid flexion instability..!!!

• Relatively newly described problem

• When large distal femoral cut is made to address pre-op flexion contracture

• In full extension posterior capsule will provide varus-valgus stability. With knee past 30º flexion posterior capsule is no longer taut ,collaterals will be loose due to elevation of joint line & instability results..

Mid-flexion instability..!!

Prevention:

Address pre-op flexion contracture with posterior capsule release & removal of osteophytes while minimizing excess distal femoral resection

Preventing mid-flexion instability…!!

Flexion gap>>extension gap Posterior release

Hyperextension..!!

Hyperextension after TKA is very difficult to correct

Best management is “Prevention”

Recurvatum :

1.Severe valgus deformity with ITB contracture :RA

2.Neuromuscular disease:Polio

3.Collateral instability may lead to recurvatum post-operatively

Hyperextension..!!

Hyper-extension..!!

Krackow & Weiss collateral transfer.

Moving femoral origins of MCL & LCL proximally & posteriorly creates a tightening action during full extension of the knee

“HINGED TKR”

Hyper-extension..!!

Patellar instability..!!Etiology..

• Internal rotation & medialisation of femoral component

• Internal rotation malalignmentof tibial component

• Lateralisation of patellar button & faulty patellar resection

• Overall alignment of >10 degree valgus or femoral component in >7 degree valgus

Leading cause for revision surgery

Surprisingly, often the most neglected part of a TKA surgery!!!

Michael Malo,Kelly G. Vince :The unstable patella after TKA,etiology ,prevention & management:J Am acad Orthop Surg 2003;11:364-371

Patellar instability…!!

Medial parapatellar Subvastus Midvastus

Requirement for lateral retinacular release significantly low in subvastus & midvastus approach

Bindeglass DF ,Cohen JL:patellar tilt & subluxation following subvastus & parapatellar approach in TKAJ Arthosplasty 11:507-511,1996Engh GA ,Parks NL,Ammeen DJ:Influence of surgical approach in lateral retinacular release in TKA ClinOrthop 236:44-51,1988

Patellar instability..!!

IR femoral component: lateral patellar tilt & tendency to track laterally


Medialisation of femoral component has similar effect to that of internal rotation on lateral patellar tracking


Internal rotation of tibial component forces tibia into external rotation during flexion increasing the Q angle , leading to lateral patellar tracking &subluxation


Resection of more bone from medial facet is necessary to obtain symmetric patellar cut parallel to anterior surface


Overstuffing of patellofemoral joint tightens the lateral retinaculum increasing risk of lateral patellar tracking


Medialisation of patellar component allows patellar button to be centralisedin the trochlear groove

No thumbs technique..!!

Patella should track in the trochlear groove & medial facet should be in touch with femoral prosthesis throughout the ROM


• Peri-patellar pain & limited flexion without symptoms of frank instability

• Usually pain has been present since surgery different from pain before surgery

Radiology..!!

Laterally subluxated patella in merchant view

Radiology..!!Femoral component evaluation..!!

Berger et al:Rotational instability & malrotation after TKAOCNA vol 32.No 4.October 2001

Radiology..!!

Relation between tibialcomponent axis & tibialtubercle orientation

(normal:18 degrees)

Berger et al:Rotational instability & malrotation after TKAOCNA vol 32.No 4.October 2001

Berger et al:Rotational instability & malrotation after TKA OCNA vol32.No 4.October 2001

Combined component rotation & patellar complications..!!

Management…!

• Non-surgical measures :unsucessful

(strengthening VMO,Bracing)

In absence of component malposition:Lateral retinacularrelease with or without VMO advancement & medial plication

Osteotomy & medial displacement of tibial tubercle

(feared complications: patellar tendon rupture & non union of osteotomy)

When substantial malposition of components revision of components is the procedure of choice..!!

Principles of revision TKA ..!!

Robert B.Bourne ,H.A rawford:Principles of revision total knee arthoplastyOCNA vol 29.No 2.April 1998

Prevention is better than cure..!!

“Preventing instability during primary surgery saves the revision surgery”..!!

Thank You..!!!!!

Instability in TKR

Health & Medicine

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