2. History
• 19th century
– interposition of soft tissues for reconstruction of articular
surfaces
• 1950s
– Walldius designs first hinged knee replacement
• 1970
– Guepar develops a new hinged prosthesis based on design
by Walldius that increases motion and decreases bone
loss
• ~1973
– "total condylar prosthesis" is introduced which is first to
resurface all three compartments (PCL sacrificing)
4. Constraint
– varus-valgus and flexion-extension stability in the face
of ligamentous laxity or bone loss
– ligamentous laxity or severe bone loss, standard
cruciate-retaining or posterior-stabilized implants may
not provide stability
– least constrained to most constrained
• cruciate-retaining
• posterior-stabilized (cruciate-substituting)
• varus-valgus constrained (non-hinged)
• rotating-hinge
5. Femoral rollback
– the posterior translation the femur with progressive flexion
• importance
– improves quadriceps function and range of knee flexion by preventing
posterior impingement during deep flexion
• biomechanics
– rollback in the native knee is controlled by the ACL and PCL
• 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
6. Cruciate-Retaining (CR)
– minimally constrained prosthesis that depends on an
intact PCL to provide stability in flexion
• Indications
– arthritis with minimal bone loss, minimal soft tissue
laxity, and an intact PCL
– varus deformity < 10 degrees
– valgus deformity < 15 degrees
• Radiographs
– radiographs won't show box in the central portion of
the femoral component as PS knees have (see PS knee
radiographs)
7. Cruciate-Retaining (CR)
• Advantages
– avoids tibial post-cam impingement/dislocation that may
occur in PS knees
– more closely resembles normal knee kinematics
(controversial)
– less distal femur needs to be cut than in a PS knee
– improved proprioception with preservation of native PCL
• Disadvantages
– tight PCL may cause accelerated polyethylene wear
– loose or ruptured PCL may lead to flexion instability and
subluxation
8. Posterior Stabilized (PS)
– femoral component contains a cam that engages the tibial
polyethylene post during flexion
– polyethylene inserts are more congruent, or deeply "dished"
• Indications
– previous patellectomy
• reduces risk of potential anteroposterior instability in setting of a
weak extensor mechanism
– inflammatory arthritis
• inflammatory arthritis may lead to late PCL rupture
– deficient or absent PCL
• Radiographs
– lateral radiograph will show the outline of the cam, or box, in
the femoral component
9. Posterior Stabilized (PS)
• Advantages
– easier to balance a knee with absent PCL
– arguably more range of motion
– easier surgical exposure
• Disadvantages
– cam jump
• mechanism
– with loose flexion gap, or in hyperextension, the cam can rotate over the post and
dislocate
• treatment
– initial
» closed reduction by performing an anterior drawer maneuver
– final
» revision to address loose flexion gap
– tibial post polyethylene wear
– patellar "clunk" syndrome
• mechanism
– scar tissue gets caught in box as knee moves into extension
• treatment
– arthroscopic versus open resection of scar tissue
– additional bone is cut from distal femur to balance extension gap
10. Constrained Nonhinged Design
– constrained prosthesis without axle connecting tibial and
femoral components (nonhinged)
– large tibial post and deep femoral box provide
• varus/valgus stability
• rotational stability
• Indications
– LCL attenuation or deficiency
– MCL attenuation or deficiency
– flexion gap laxity
– moderate bone loss in the setting of neuropathic
arthropathy
• Radiographs
11. Constrained Nonhinged Design
• Advantages
– prosthesis allows stability in the face of soft tissue
(ligamentous) or bony deficiency
• Disadvantages
– more femoral bone resection
• necessary to accommodate large box
– aseptic loosening
• as a result of increased constraint
12. Constrained Hinged Design
– most constrained prosthesis with linked femoral and tibial
components (hinged)
– tibial bearing rotates around a yoke on the tibial platform
(rotating hinge)
• decreases overall level of constraint
• Indications
– global ligamentous deficiency
– hyperextension instability
• seen in polio or tumor resections
– resection for tumor
– massive bone loss in the setting of a neuropathic joint
• Radiographs
13. Constrained Hinged Design
• Advantages
– prosthesis allows stability in the face of soft tissue
(ligamentous) or bony deficiency
• Disadvantages
– aseptic loosening
• as a result of increased constraint
• large amount of bone resection required
14. Mobile Bearing Design
– minimally constrained prosthesis where the polyethylene can rotate on the
tibial baseplate
– PCL is removed at time of surgery
• Indications
– young, active patients (relative indication)
• Advantages
– theoretically reduces polyethylene wear
• increased contact area reduces pressures placed on polyethylene (pressure=force/area)
• Disadvantages
– bearing spin-out
• mechanism
– occurs as a result of a loose flexion gap
– tibia rotates behind femur
• treatment
– initial
» closed reduction
– final
» revision to address loose flexion gap
15. All-polyethylene base plates
– tibial plate is a solid block of polyethylene as opposed
to a metal tray with a poly insert.
• Advantages
– less expensive
– decreased rates of osteolysis
• Disadvantages
– loose modular flexibility
• Outcomes
– studies show equivalent functional
outcomes with decreaed cost
