orthopedic presentation about total knee joint replacement describing everything you need to know about this subject.

1. Total knee arthroplasty
By
Ahmed Shafik MD.

2. Anatomy of the knee

3. femur
Medial and lateral condyles
• Convex ,asymmetric
• Medial larger than lateral

4. tibia
• Tibial platateau
• Medial: convave
• Lateral: convex
• Medial 50% of lateral

5. Indications for total knee replacement
• Knee arthritis
• Primary:
osteoarthritis
• Secondary:
Traumatic
Rheumatoid
Other types of arthropathy as psoriasis etc…

6. Who is candidate for TKR
• Quality of life severely affected
• Pain at rest
• Restriction of ordinary activities
• Evidence of significant radiographic changes of the knee

7. When do I have to do TKR
• Young patients who have limited function
• Progressive deformity
• Failure of other treatment modalities
• T K R should be done before the patient experiences severe decrease
in ROM, deformity, contracture, joint instability or muscle atrophy

8. Technical goals of T K R
• The restoration of mechanical alignment.
• Preservation (restoration) of the joint line, balancing ligaments.
• Maintaining or restoring a normal Q angle.

9. Knee biomechanics
The knee is comprised of 2 joints
• tibiofemoral joint
• patellofemoral joint

10. Patellofemoral joint
Function
• transmits tensile forces generated by the
quadriceps to the patellar tendon
• increases lever arm of the extensor mechanism
• patellectomy decreases extension force by 30%
Motion
• "sliding" articulation
• patella moves 7cm caudally during full flexion
• maximum contact between femur and patella is
at 45 degrees of flexion

11. Stability
• passive restraints to lateral subluxation
1. medial patellofemoral ligament
2. medial patellomeniscal ligament
3. medial retinaculum
• dynamic restraint
quadriceps muscles

12. Q angle
• definition
line drawn from the anterior superior iliac spine --> middle of patella -->
tibial tuberosity (13-18 degrees)

13. Tibiofemoral joint
instant center of rotation (femoral rollback)
• definition
point at which the joint surfaces are in direct contact
• relevance
posterior rollback :as the knee flexes, the instant center of rotation on the femur moves posteriorly
allows for increased knee flexion by avoiding impingement
"screw home" mechanism
• definition
tibial externally rotates 5 degrees in the last 15 degrees of extension
• cause
medial tibial plateau articular surface is longer than lateral tibial plateau
• relevance
"locks" knee decreasing the work performed by the quadriceps while standing

14. Stability
• varus stress
lateral collateral ligament
• valgus stress
superficial portion of medial collateral ligament
• anterior translation
anterior cruciate ligament
• posterior translation
posterior cruciate ligament
• external rotation
posterolateral corner is the primary stabilizer of external
tibial rotation

15. Prothesis design
Different Designs
• unconstrained
posterior-cruciate retaining (CR)
posterior-cruciate substituting (PS)
• constrained
nonhinged
hinged
• fixed versus mobile bearing
• unicompartmental

16. Concepts of prothetic design
• Femoral rollback

17. design implications
both PCL retaining and PCL substituting designs
allow for femoral rollback
• PCL retaining:
native PCL promotes posterior displacement of
femoral condyles similar to a native knee.
• PCL substituting:
• tibial post contacts the femoral cam causing
posterior displacement of the femur.

18. Constraint
definition
• the ability of a prosthesis to provide varus-valgus and flexion-extension
stability
• design implications
in order of least constrained to most constrained
• PCL-retaining
• PCL-substituting
• varus-valgus constrained non-hinged (LCCK)
• rotating-hinge

19. Modularity
definition
• the ability to augment a standard prosthesis to balance soft tissues
and/or restore bone loss
options include
• metal tibial baseplate with modular polyethylene insert
• metal augmentation for bone loss
• modular femoral and tibial stems

20. • Fixation
options include
• cemented
• cementless

21. designs
Cruciate retaining (CR)
depends on an intact PCL to
provide stability
Disadvantages
• tight PCL may
cause accelerated
polyethylene wear .
• loose or ruptured PCL may
lead to flexion instability and
subluxation

22. Posterior stabilized (PCL sacrifice)
slightly more constrained
femoral component contains a cam that engages
the tibial polyethylene post.
polyethylene inserts are more congruent, or
deeply "dished"
Disadvantages
cam jump
with loose flexion gap, or in hyperextension, the
cam can rotate over the post and dislocate
treatment
• closed reduction by performing an anterior
drawer maneuver
• revision to address loose flexion gap
tibial post polyethylene wear

23. patellar "clunk" syndrome
• mechanism
scar tissue gets caught in box as knee moves
into extension
• treatment
arthroscopic versus open resection of scar
tissue

24. Constrained non-hinged design
large tibial post and deep femoral box
• LCL or MCL attenuation or deficiency
• flexion gap laxity
• moderate bone loss
Disadvantages
• more femoral bone resection
• aseptic loosening

25. Constrained hinged design
linked femoral and tibial components (hinged)
• global ligamentous deficiency
• hyperextension instability (polio)
• resection for tumor
• massive bone loss in the setting of a neuropathic
joint
• aseptic loosening is very high

26. Mobile bearing design
• polyethylene can rotate on the tibial baseplate
• theoretically reduces polyethylene wear
• Disadvantage:
bearing spin-out

27. All polyethylene base plate
Tibial plate is a solid block of polyethylene
Disadvantage : lose modular flexibility

28. Unicompartmental knee arthroplasty
Fixed-bearing or mobile-bearing
Advantage compared to TKA:
• faster rehabilitation
• smaller incision
• less blood loss
• less expensive
• preservation of normal kinematics
retaining ACL, PCL and other compartments

29. Indications:
• controversial
• as an alternative to total knee arthroplasty or
osteotomy for unicompartmental disease
• classicaly reserved for older (>60), lower-demand,
and thin (<80 kg) patients
• 6% of patient's meet the above criteria with no
contraindications
• new effort to expand indications to include younger
patients and patients with more moderate arthrosis

30. Contraindications
• inflammatory arthritis
• ACL deficiency
• fixed varus deformity > 10 degrees
• fixed valgus deformity >5 degrees
• restricted motion
• flexion deformity of > 5-10°
• previous meniscectomy in other compartment
• tricompartmental arthritis (diffuse or global pain)
Results:
• Mobile-bearing: 15-year survivorship reported at 93%
• revision rates are worse than total knee revision rates

31. Surgical approaches
• medial parapatellar
• midvastus
• subvastus
• minimally invasive

32. MECHANICAL ALIGNMENT OF TKA
• pre-op planning
• component insertion
• ligament balancing
• prosthetic design selection

33. pre-op planning:
standing AP and lateral of knee to evaluate for:
• joint space narrowing
• collateral ligament insufficiency
• subluxation of femur on tibia
• bone defects

34. pre-op planning:
standing full-length radiographs (SCANOGRAM)
• femoral or tibial deformity
• very tall or short stature
extension and flexion laterals
sunrise view

35. Femoral component alignment
Valgus cut angle(~5-7° from AAF )
• difference between AAF and MAF
• perpendicular to mechanical axis
• jig measures 6 degrees from
femoral guide (anatomic axis)
• will vary if people are very tall
(VCA < 5°) or very short (VCA > 7°)

36. Tibial component alignment
Anatomic axis of tibia (AAT)
• a line that bisects medullary canal
Mechanical axis of tibia
• line from center of proximal tibia to center of
talus
• you can usually can cut the proximal tibia
perpendicular to anatomic axis (an axis
determined by an intramedullary jig)
• In tibial deformity the mechanical and anatomic
axis are not the same (extramedullary tibial
guide must be used)

37. Coronal plane balancing
Varus deformity:
medial side is tight, lateral side stretched.
Medial release (in order)
1. Medial Osteophyte Removal
2. Deep MCL and capsule Release
3. Release Posteromedial Corner and Semimembranosis (Especially If There Is An
Associated Flexion Contracture)
4. Pie Crust Superficial MCL (Favor Use Of 18 Gauge Needle)
5. Complete Superficial MCL Release / Pes Anserinus
Destabilizes Medial Flexion Gap / Consider A Constrained Prosthesis
Differential release:
posterior oblique portion (release if tight in extension)
anterior portion (release if tight in flexion)

38. Valgus deformity:
lateral side is tight, medial side stretched.
lateral release (in order)
1. osteophytes
2. posterolateral capsule
3. iliotibial band if tight in extension
4. pie crust or release off Gerdy's tubercle
5. popliteus if tight in flexion
6. LCL if tight in both flexion and extension
• if LCL & Popliteus require release, flexion gap stability is lost so consider
constrained prosthesis

39. Flexion deformity
Posterior release order
• 1) posterior femoral & posterior tibial osteophytes
• 2) posterior capsule
• 3) additional resection of distal femur
• 4) gastronemius muscles (medial and lateral)
• All releases are performed with knee at 90 degrees of flexion
• You do not want to address a contracture by removing more tibia as this will
change the joint line and lead to patella alta

40. Sagittal plane (gap) balancing

41. Patellofemoral alignment
• the most common complication of TKA
• an increase in the Q angle will lead to:
an increased lateral subluxation forces on the patella relative to the trochlear
groove
pain, mechanical symptoms, accelerated wear, and even dislocation.