What anatomy is essential to know for a total knee replacement?

Essential Anatomy for Total Knee Replacement

Understanding the anatomical structures and biomechanical relationships of the knee is critical for successful total knee arthroplasty (TKA) to minimize morbidity and mortality and optimize quality of life outcomes.

Bony Anatomy

• Femoral Component:

  • Distal femur with medial and lateral condyles
  • Intercondylar notch
  • Anterior and posterior aspects of condyles (crucial for component sizing)
  • Trochlear groove (for patellofemoral tracking)

• Tibial Component:

  • Tibial plateau with medial and lateral compartments
  • Tibial tubercle (reference point for rotational alignment)
  • Proximal tibia anatomy (for proper component positioning)
  • Mechanical axis alignment (for weight-bearing distribution)

• Patella:

  • Articular surface (for resurfacing decisions)
  • Thickness (to avoid overstuffing the patellofemoral joint)

Soft Tissue Structures

• Ligaments:

  • Collateral ligaments (MCL and LCL) - critical for varus/valgus stability
  • Cruciate ligaments (ACL and PCL) - decisions on preservation vs. sacrifice affect implant selection 1
  • Extensor mechanism (quadriceps tendon, patellar tendon) - essential for knee function

• Joint Capsule:

  • Posterior capsule - important for flexion gap balancing
  • Medial and lateral retinacular structures - affect patellar tracking

• Neurovascular Structures:

  • Popliteal artery and vein (posterior aspect)
  • Peroneal nerve (lateral aspect) - at risk during lateral releases
  • Saphenous nerve (medial aspect)

Biomechanical Considerations

• Alignment Parameters:

  • Mechanical axis (hip-knee-ankle alignment)
  • Anatomic axis of femur and tibia
  • Joint line position (restoration critical for proper function)
  • Rotational alignment of components (affects patellar tracking)

• Balance Considerations:

  • Flexion-extension gap balance
  • Medial-lateral ligament balance
  • Patellofemoral tracking

Imaging Anatomy

• Radiographic Assessment:

  • Full-length (hip-to-ankle) weight-bearing views for mechanical axis assessment 1
  • AP, lateral, and axial views to evaluate all compartments
  • Patellofemoral alignment on axial views 1

• Advanced Imaging:

  • CT for assessment of rotational alignment and component positioning 1
  • MRI with metal artifact reduction techniques for evaluation of soft tissues and occult fractures 1

Surgical Approach Considerations

• Anatomical Landmarks:
  • Tibial tubercle (reference for midline incision)
  • Patella (for arthrotomy)
  • Femoral epicondyles (reference for femoral component rotation)
  • Whiteside's line (anteroposterior axis of distal femur)
  • Posterior condylar axis

Common Pitfalls and Complications

• Component Malpositioning:

  • Rotational malalignment leading to patellofemoral issues
  • Coronal malalignment affecting weight distribution and implant longevity
  • Sagittal malalignment affecting range of motion

• Soft Tissue Management:

  • Inadequate ligament balancing leading to instability
  • Excessive soft tissue release causing instability
  • Insufficient release causing stiffness and limited range of motion

• Bone Preparation:

  • Excessive tibial resection (should be no more than 5-8mm from medial subchondral bone)
  • Improper femoral sizing affecting flexion stability
  • Failure to address bony defects appropriately

Postoperative Assessment

• Radiographic Evaluation:

  • Component position and alignment
  • Periprosthetic lucency and osteolysis
  • Evidence of loosening or fracture 1

• Clinical Evaluation:

  • Stability assessment (varus/valgus, anterior/posterior)
  • Range of motion
  • Patellofemoral tracking

By thoroughly understanding these anatomical considerations, surgeons can optimize TKA outcomes, minimize complications, and improve patient quality of life following surgery.