This document discusses instability after total knee arthroplasty (TKA). It begins by outlining the goals and basic principles of TKA. It then describes the bone cuts made during TKA and emphasizes that resection of the proximal tibia influences both flexion and extension gaps. The document discusses various causes of instability after TKA including improper bone cuts, soft tissue imbalance, and component malpositioning. It provides details on managing different types of instability such as instability in extension, flexion, and mid-flexion. Prevention of instability through proper bone cuts and soft tissue balancing is emphasized.

1. INSTABILITY IN TKR..!!
DR RISHI RAM POUDEL
DR RISHIRAJ
PROF R.MALHOTRA

2. Total Knee Arthoplasty..!!!
Aims:
• Restoration of mechanical
axis
• Restoration of joint line
• Balance soft tissues
• Equalize flexion &
extension gaps
• Restore patellofemoral
alignment & mechanics

3. 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

4. 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

5. Bone cuts in TKA..!!! Distal femoral cut
Intramedullary jig in
desired valgus angle
Femoral cutting guide Distal femoral cut

6. Bone cuts in TKA..!!
Proximal tibial bone cut
Extramedulaary cutting guide Resected tibial bone

7. 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 gap
Larger size recommended in posterior referencing to avoid anterior notching of femur

8. Bone cuts in TKA..!!
Rotation of femoral
component
Antero-posterior femoral cuts
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

9. Bone cuts in TKA..!!
Antero-posterior femoral cuts
Transepicondylar axis: key reference for rotation of femoral component

10. Bone cuts in TKA..!!
Antero-posterior femoral cuts
Trans-epicondylar axis Femoral sizing jig

11. Bone cuts in TKA..!!
Antero-posterior femoral cuts
Headless pins in 3º external rotation Angels wing to estimate level of cut

12. 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

13. Bone cuts in TKA..!!
Antero-posterior femoral cuts
Anterior femoral cut Posterior condylar cuts

14. Rectangular flexion & extension
gaps..!!

15. Flexion & extension gaps…!!
Flexion gap & extension gaps should be rectangular & equal

16. Balancing the gaps..!!
Preoperative Planning to prevent instability in Total Knee Arthoplasty :OCNA
volume 32.number 4.October 2001

17. BALANCING THE GAPS..!!

18. BALANCING THE GAPS..!!

19. 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

20. 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

21. TKR Failure..!!
1.Aseptic loosening
2.Instability
3.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

22. Leading causes for failure: INFECTION (38%) & INSTABILITY (27%)
Malalignment & Instability are major causes of early failue ,
therefore ligamentous balancing & appropiate alignment are paramount
in performing the surgery..!!

24. Instability after TKA…!!
Tibio-femoral instability
Patellar instability
Instability in extension Instability in flexion
Symmetric Assymetric
Mid-flexion Antero-posterior

25. 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

26. 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

27. 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

28. 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

29. Radiographs…!!
1. AP,Lateral & Sky-line views
2. Scannogram B/L Lower Limbs
3. NCCT knee

30. Extension Instability..!!
Symmetric
• Uncommon
• Components don’t
fill space.
Asymmetric
• Common
• One side is not
balanced
correctly.

31. Extension instability..!!
Potential instability corrected by using thicker tibial insert
symmetric
Sebastein Paratte ,Mark W Pagnano:Instability After Total Knee Arthoplasty
JBJS vol 90 A.No 1.January 2008

32. 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

33. Extension instability..!!
assymetric
Undercorrection of fixed angular deformity ,out of fear of creating
instability in opposite direction…!!
Inadequate release

34. Medial release for varus knees..!!

35. Medial release for varus knee..!
Periosteal stripping of medial structures while maintaining continuous soft tissue sleeve

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

37. 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..!!

38. 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”

39. 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..!

40. MCL Augmentation with hamstring tendon..!!
The hamstring tendon can be run through a drill hole to the femur & tied over a button

43. Use of increased constraint contributes
to favorable outcome
Treatment without increased constraint
were associated with residual instability
requiring revision

44. PS KNEES
FLEXION INSTABILITY..!!
DSF or” jump distance”:distance needed
for cam to ride over the post before
dislocating.

45. FLEXION INSTABILITY..!!
PS KNEES
Most common activity leading
dislocation is marked knee
flexion plus a varus
stress(putting ankle of
operated limb on contralateral
knee)

46. PS KNEES
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:closed
reduction ,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.

47. FLEXION INSTABILITY
without dislocation:
• Sense of instability
without giving away
• Difficulty ascending &
descending stairs
• Recurrent knee effusions
• Peri-retinacular
tenderness
• Excessive anterior
translation
PS KNEES
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

48. 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

49. FLEXION INSTABILITY..!!
Treatment
Non-operative :poor results
Operative :conversion to Posterior
Stabilized implant design with focus on
balancing flexion-extension gaps
CR KNEES

50. 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..

51. Mid-flexion instability..!!
Prevention:
Address pre-op flexion contracture with
posterior capsule release & removal of
osteophytes while minimizing excess distal
femoral resection

52. Preventing mid-flexion
instability…!!
Flexion gap>>extension gap Posterior release

53. 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

54. Hyperextension..!!

55. Hyper-extension..!!
Krackow & Weiss collateral transfer.
Moving femoral origins
of MCL & LCL proximally
& posteriorly creates a
tightening action during
full extension of the
knee

56. Hyper-extension..!!
“HINGED TKR”

57. Patellar instability..!!
Etiology..
• Internal rotation &
medialisation of femoral
component
• Internal rotation malalignment
of 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

58. 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 TKA
J Arthosplasty 11:507-511,1996
Engh GA ,Parks NL,Ammeen DJ:Influence of surgical approach in lateral retinacular release in TKA
ClinOrthop 236:44-51,1988

59. Patellar instability..!!
IR femoral component: lateral patellar tilt & tendency to track laterally

60. Patellar instability..!!
Medialisation of femoral component has similar effect to that of internal
rotation on lateral patellar tracking

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

62. Patellar instability..!!
Resection of more bone from medial facet is necessary to obtain
symmetric patellar cut parallel to anterior surface

63. Patellar instability..!!
Overstuffing of patellofemoral joint tightens the lateral retinaculum
increasing risk of lateral patellar tracking

64. Patellar instability..!!
Medialisation of patellar component
allows patellar button to be centralised
in the trochlear groove

65. No thumbs technique..!!
Patella should track in the trochlear groove & medial facet should
be in touch with femoral prosthesis throughout the ROM

66. Patellar instability..!!
• Peri-patellar pain & limited flexion without
symptoms of frank instability
• Usually pain has been present since surgery
different from pain before surgery

67. Radiology..!!
Laterally subluxated patella in
merchant view

68. Radiology..!!
Femoral component evaluation..!!
Berger et al:Rotational instability & malrotation after TKA
OCNA vol 32.No 4.October 2001

69. Radiology..!!
Relation between tibial
component axis & tibial
tubercle orientation
(normal:18 degrees)
Berger et al:Rotational instability & malrotation after TKA
OCNA vol 32.No 4.October 2001

70. Combined component rotation & patellar
complications..!!
Berger et al:Rotational instability & malrotation after TKA OCNA vol
32.No 4.October 2001

71. Management…!
• Non-surgical measures :unsucessful
(strengthening VMO,Bracing)
In absence of component malposition:Lateral retinacular
release 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..!!

72. Principles of revision TKA ..!!
Robert B.Bourne ,H.A rawford:Principles of revision total knee arthoplasty
OCNA vol 29.No 2.April 1998

73. Prevention is better than
cure..!!
“Preventing instability during primary
surgery saves the revision surgery”..!!

74. Thank You..!!!!!