Total Knee Arthroplasty Mechanical Alignment Restores the Anatomy - - PowerPoint PPT Presentation

Orthopaedic Institute

Total Knee Arthroplasty

Mechanical Alignment Restores the Anatomy and Function

Giles R. Scuderi, MD

Disclosures

 Consultant and

Royalties

 Zimmer Biomet

 Consultant

 Medtronic  Convatec  Pacira  Merz Pharmaceuticals

 Research Support

 Pacira

• Society BOD
• Op Walk USA

 Book Royalties

 Elsevier  Springer  Thieme  World Scientific

The Varus Knee Spectrum of Pathology

The Valgus Knee Spectrum of Pathology

Successful TKA

• Long standing surgical principles:
• Soft tissue balance
• Bone resection
• Component alignment
• Component fixation

TKA: Surgical Technique

Anatomic Resection Classical Resection

Total Knee Arthroplasty

• Soft tissue technique
• Bone preparation technique
• Achieve neutral mechanical axis
• Conventional instruments
• Computer Navigation
• Patient specific instruments (PSI)
• Goal
• Lower limb alignment should be within 3° of neutral mechanical

alignment

Berend, et al: CORR 428, 2004 D’Lima, et al: CORR 392, 2001 Fang, et al: J Arthroplasty 24, 2009 Werner, et al: J Biomech 38, 2005 Bellemans: Orthop 34, 2011

Total Knee Arthroplasty

Restore mechanical axis

• Center hip-knee-ankle
• Femur
• Mechanical – anatomic angle 6° valgus
• Tibia
• Mechanical – anatomic angle 0° (neutral)

Appropriate Bone Resection Soft tissue balance

• Ligament release

Patella tracking

Classic Method of Bone Resection

Neutral Mechanical Alignment

• Better functional outcome at 1 year when coronal

alignment within 3° neutral

• International Knee Society Score
• SF 12
• Knee Society Score

Choong, et al: J Arthroplasty 24, 2009 Longstaff, et al: J Arthoplasty 24, 2009

Alignment and Failure Rate

Lower failure rate when restore mechanical alignment

Ritter, et al: JBJS 93(A) 17, 2011

Impact of Mal-Alignment

• Component mal-alignment in the presence of acceptable

knee alignment

• Radiographic analysis and retrieval analysis
• Tibial component varus
• Medial compartment wear
• Total wear
• Tibial tray subsidence
• Varus mal-alignment as low as 3°
• associated with accelerated wear,

even if overall limb alignment is ideal Srivastava, et al: Knee 19(5), 2011 Collier, et al: JBJS 89A, 2007

Outcome of Total Knee Arthroplasty

It’s Not Just the Coronal Alignment

• Effect of sagittal alignment
• Femur
• Tibia
• Axial rotation
• Femur
• Tibia
• Soft Tissue Balance

Not Just the Coronal Alignment

• Sagittal Position: Risk factors for failure
• Flexion of the femoral component >3°
• Tibial slope > 7° or < 0°

Kim, et al: Int Orthop 38, 2014

Femoral Component Rotation

• AP axis to Epicondylar axis: 90.33° ± 2.44°
• AP axis to Posterior Condyles: 93.08° ± 2.71°
• Epicondylar axis to Posterior Condyles: 3.6° ± 2.02°

Poilvache et al: CORR 331, 1996

Correlation Between Condylar Lift-off and Femoral Component Alignment

CT scan with fluoroscopic analysis

• Supports Epicondylar Axis
• Lift-off less frequent
• Lift-off of less magnitude

Insall, Scuderi et al: CORR 403, 2002 Scuderi, Insall: Am. J. Knee 13, 2000 Olcott, Scott: CORR 367, 1999 Poilvache et al: CORR 331, 1996

Consequence of Internal Rotation

• f the Femoral Component
• Patella instability
• Limited Motion
• Arthrofibrosis
• Lateral flexion laxity
• Instability
• Less favorable clinical
• utcomes

Romero et al: J. Arthroplasty 22(2), 2007 Boldt et al: Int. Orthop 30(5), 2006

Axial Position of Tibia

• Component Malposition
• Internal rotation of the tibial

component

• Causes tibia to externally rotate

during flexion

• Increases Q-angle

Tibial Component Rotation

Matsuda et al: Am. J. Knee Surg: 14(3), 2001

Anatomic Tibial Component

• No longer need to sacrifice coverage to get the proper

rotation

Combined Femoral and Tibial Rotation

Internal Rotattion External Rotattion

Berger et al: CORR 356, 1998

Patella Dislocation & Failure Normal Tilt Subluxation

Balancing the Knee

• TKA is a soft tissue operation
• “Every knee has its own soft tissue identity”
• Understand the infuence of supporting ligaments
• Anterior fibers influence flexion
• Posterior fibers influence extension
• Release of the PCL with preferentially increase the flexion

gap

Baldini, Scuderi, et al: J Knee Surg 2004

Soft Tissue Balance in TKA

• Every knee has its own soft tissue identity
• Deformity may or may not be correctable
• Gradual soft tissue release
• Goal: Equal and symmetrical flexion and extension gaps

Neutral Mechanical Alignment and Classic Bone Resection remain the Gold Standard

• Sufficient supporting data
• Clinical and functional outcomes
• Durability
• Safe Zone
• 0° (SD 3°)
• Best survival

30 years old

Alignment: Hitting the Target

iASSIST™ Surgical Expertise Conventional Instruments

Mechanical vs Anatomic Alignment

• Impact of human error in bone resection
• Computer navigation outliers
• 9% tibiofemoral alignment
• 4.9% femoral components
• 4% tibial components
• Compromises
• Aiming for a “slight degree of varus” requires acceptance of 3° of

intended varus in addition to potential error of 3° - 4° of varus, resulting in unacceptable alignment. Mason, et al: J Arthroplasty 22, 2007 Abdel, et al: JBJS 96B, 2014 Lombardi, Ortho 34, 2011

“…until additional data can be generated to more accurately determine the ideal post-operative limb alignment in individual patients, a neutral mechanical axis remains a reasonable target and should be considered as the standard for comparison if other alignment targets are introduced…”

Parratte, et al: JBJS 92A, 2010

TWO FINAL COMMENTS

Mechanical Alignment

• Most Recent Supporting Information
• Tibial component varus increased implant migration with lateral

liftoff

• RSA analysis of cemented PS TKA at minimum of 10 years
• In vivo RSA measurement showed greater wear with varus aligned

limbs

• Despite polyethylene material, retrieval study showed more medial

wear

• Mechanical alignment still the target
• 20 year survival and function
• Alternate alignment strategies must prove safety and efficacy

MacDonald, et al: The Knee Society Members Meeting, Sept 2017 Naudie: The Knee Society Members Meeting, Sept 2017 Wright, et al: The Knee Society Members Meeting, Sept 2017 Abdel, et al: The Knee Society Members Meeting, Sept 2017

Mechanical Alignment

Revision TKA

“THOU SHALL NOT VARUS”