Miller-Total knee Flashcards
Review the AAOS guidelines for knee OA treatment
Review osteotomy treatments
Best indication
•
Young active patient, generally younger than 45 years, and
•
Occupation precludes the use of prosthetic joint replacement owing to significant implant loading and cycles (i.e., high-load, high-stress type occupation)
□
Most likely to succeed when disease affects predominantly one compartment
□
For varus knee malalignment
•
Treatment is valgus-producing proximal tibial osteotomy
•
Reason: problem is usually due to proximal tibial varus.
•
Goal of surgery: correct the deforming problem
•
Osteotomy goal: maintains joint line of knee perpendicular to mechanical axis of leg
•
Mechanical axis of leg defined as center of hip through center of knee to center of ankle
□
For valgus knee malalignment
•
Treatment is varus-producing supracondylar femoral osteotomy
•
Reason: problem typically is result of lateral femoral condylar hypoplasia.
•
Goal of surgery: correct the deforming problem
•
Osteotomy goal: maintain joint line of knee perpendicular to the mechanical axis of leg
□
Valgus-producing tibial osteotomy (for varus knee deformity)
•
Selection criteria
•
Clinical examination and radiographs show that other two compartments are free of arthritis.
•
Clinical pain is isolated to medial knee compartment.
•
Patient is physiologically young and has an occupation or activity level that makes prosthetic arthroplasty less appropriate
•
Contraindications
•
Inflammatory arthritis
•
Lack of flexion—minimum of 90 degrees needed
•
Flexion contracture more than 10 degrees
•
Ligament instability
•
Especially varus thrust gait (this indicates abnormal lateral compartment ligament/capsular stretch-out)
•
Femoral-tibial subluxation more than 1 cm (viewed on AP radiograph)
•
Note: ACL deficiency acceptable if all other criteria are met
•
Medial compartment bone loss
•
Lateral compartment joint narrowing
•
Detected by valgus stress radiograph
•
Osteotomy less successful in following conditions
•
Smoking
•
Age 60 years or older
•
Varus deformity of 10 degrees or more
•
There is just not enough bone to remove to correct deformity.
•
Concomitant arthritis in other compartments
•
Main problems
•
Closed-wedge technique
•
Patella baja deformity (most common)
•
Patella baja results in loss of knee flexion
•
Loss of tibial posterior slope
•
Open-wedge technique
•
Patella baja deformity (also most common)
•
Nonunion
•
Loss of valgus correction (i.e., collapse of open wedge)
□
Varus-producing femoral osteotomy (for valgus knee deformity)
•
Selection criteria
•
Valgus deformity of 12 degrees or greater
•
Clinical pain isolated to lateral knee compartment
•
Clinical examination and radiographs show medial knee compartment free of arthritis.
•
Patellofemoral joint should also be free of arthritis, but minimally symptomatic patellofemoral disease is acceptable (reduction of Q angle improves patellofemoral mechanics and reduces pain).
•
Patient is physiologically young and has an occupation or activity level that makes prosthetic arthroplasty less appropriate.
•
Contraindications
•
Inflammatory arthritis
•
Prior medial meniscectomy
•
Lack of flexion—minimum of 90 degrees needed
•
Flexion contracture more than 10 degrees
•
Ligament instability
•
Especially valgus thrust gait (this indicates abnormal medial compartment ligament/capsular stretch-out)
•
Femoral-tibial subluxation seen on AP radiograph
•
Medial compartment joint narrowing
•
Detected by varus stress radiograph
•
Age older than 65—relative contraindication
•
Osteoporosis—relative contraindication
•
Main problems
•
Nonunion
•
Loss of varus correction
•
Seen more often in patients with osteopenia/osteoporosis
•
Residual patellofemoral maltracking may require a lateral retinacular release.
•
Osteotomy technique (for femoral osteotomy)
•
Crescentric dome preferred
•
This osteotomy produces the least bone displacement.
•
Allows for femoral stem with TKA
Review unicompartment treatments of the knee
Utilized for patients in whom arthritis predominantly affects one compartment of knee
□
The most common UKA, by far, is medial compartment replacement
□
Advantages of UKA (medial or lateral) over TKA and knee osteotomy
•
Quicker recovery
•
Fewer short-term complications
•
Shorter hospital stay with less postoperative pain
•
Better knee function than with TKA
•
ACL is preserved as it is in TKA
□
Results
•
High rate of short-term to mid-term satisfaction
•
However, long-term survivorship is not comparable to that with TKA when measured by revision rates.
□
Contraindications
•
Inflammatory arthritis
•
Significant fixed deformity
•
Deformity must be correctable on clinical exam (e.g., resting varus attitude must be correctable to normal valgus)
•
Previous meniscectomy in opposite compartment
•
ACL-deficient knee
•
ACL deficiency is an absolute contraindication to a mobile-bearing UKA
•
Mobile-bearing UKA is utilized only for medial compartment replacement
•
Flexion contracture less than 10 degrees
•
Tricompartmental arthritis
□
Selection criteria—important:
•
Pain must be localized to the compartment being replaced
•
Medial knee pain signifies medial compartment disease
•
Lateral knee pain signifies lateral compartment disease
•
Anterior knee pain signifies patellofemoral compartment disease
•
Diffuse or global pain signifies tricompartmental disease
□
Surgical technique
•
Overcorrection must be avoided.
•
Overcorrection puts increased load on unresurfaced compartment.
•
Can result in early revision owing to accelerated progression of arthritis
•
For medial UKA, correction to 1–5 degrees of clinical valgus
□
Complications unique to UKA
•
Stress fracture of tibia (never femur)
•
Associated with heavy weight and high and early postoperative activity level
•
Typical presentation: pain-free interval (usually 4–6 weeks), then spontaneous acute onset of pain with weight-bearing activity
•
Aspiration of knee reveals blood
•
Treatment
•
If tibial fixation stable
•
Relative rest and limited weight bearing
•
If tibial fixation compromised
•
Revision of tibial implant with or without ORIF of the medial tibia
•
Conversion to TKA with tibial stem support when medial bone is compromised
□
Failure mechanisms
•
Overcorrection at time of surgery
•
Risk is disease progression in opposite compartment
•
Pain localized to arthritic compartment
•
Undercorrection at time of surgery
•
Risk is implant overload with subsequent failure due to accelerated polyethylene wear/failure, osteolysis, and/or mechanical loosening
•
Implant subsidence
•
Tibial side only
•
Due to weak metaphyseal bone; factors:
•
The deeper the tibial cut, the weaker the metaphyseal bone
•
Undercoverage—preference is to place tibial implant on host rim bone, which is stronger.
•
Osteoporosis
•
Patellar impingement upon femoral implant causing pain
•
Related to implant design and surgical technique
•
Pain is localized anteriorly
•
Requires revision to TKA
•
Arthritis progression in other compartments (i.e., natural progression of disease)
•
Pain in other knee compartments
•
Requires revision to TKA
▪
Isolated patellofemoral arthritis
□
TKA (not patellofemoral arthroplasty) is recommended choice in older patients (≥50 years)
•
Superior functional results than those of patellectomy and patellofemoral arthroplasty
□
Lateral retinacular release commonly required with isolated patellofemoral arthritis
•
Reason: maltracking is usually the cause of isolated patellofemoral arthritis
▪
TKA: see next section
Review the end cuts on TKA
Goal of end cuts is to restore neutral mechanical alignment of the limb.
•
Neutral mechanical alignment is defined as a line from hip head center, through knee center, to ankle center
□
Preoperative analysis of femur (review of full-length radiographs) is used to determine the following (Fig. 5.67):
•
Anatomic axis of femur (AAF)
•
A line that bisects the medullary canal of the femur
•
The AAF, drawn to the distal end of the femur, determines entry point for the femoral medullary guide rod for the cutting jigs
•
Mechanical axis of femur (MAF)
•
A line from center of distal femur (entry point hole) to center of femoral head
•
Significance—distal femur is cut perpendicular to MAF.
•
Allows even mechanical loading to knee implant
•
Valgus cut angle
•
Defined as angle between AAF and MAF
•
Intramedullary guide rod is placed into femur (this defines AAF).
•
Distal femoral cut jig is assembled to intramedullary guide rod.
•
Surgeon selects valgus cut angle (typically between 4 and 7 degrees).
•
Distal femur should end up being perpendicular to MAF.
•
Valgus cut angle should always be measured in tall and short patients (Fig. 5.68).
•
Hip offset remains relatively constant.
•
Femur length, therefore, has more influence on valgus cut angle.
□
Preoperative analysis of tibia (review of full-length AP radiograph) is used to determine the following (Fig. 5.69):
•
Anatomic axis of tibia (AAT)
•
A line that bisects the medullary canal of the tibia
•
The AAT, drawn through the proximal tibia, determines the entry point for the tibial medullary guide.
•
Both intramedullary and extramedullary cutting jigs for the proximal tibial end cut are acceptable techniques.
•
Mechanical axis of tibia (MAT)
•
A line from center of proximal tibia (entry point hole) to the center of ankle
•
Significance—proximal tibia is cut perpendicular to MAT.
•
Allows even mechanical loading to knee implant
•
Tibial cut angle
•
Defined as angle between AAT and MAT
•
Intramedullary guide technique
•
Intramedullary guide is placed into tibia.
•
Proximal tibia cut jig is assembled to intramedullary guide.
•
Surgeon selects tibial cut angle (usually 0 degrees).
•
Proximal tibia should end up being cut perpendicular to MAT.
•
Extramedullary guide technique
•
The extramedullary guide technique is placed over the anterior tibia. A jig distally holds guide centered over ankle. A proximal jig holds guide centered over proximal tibia (landmark is medial one-third of tibial tubercle).
•
Surgeon selects tibial cut angle.
•
In most cases the AAT and MAT are coincident. Therefore tibial cut angle is zero.
•
When there is a tibial deformity (e.g., fracture or bowing deformity), the AAT and MAT are divergent. The tibial cut angle is then carefully measured and selected to provide a proximal tibial end cut perpendicular to MAT.
Review the sagital plane gap deformity guide
Review the sequence of release for medial deformity
Convex side is lateral—loose
□
Concave side is medial—medial compartment release needed
□
Medial compartment release in sequence
•
Osteophytes
•
Deep medial collateral ligament (also known as meniscal tibial ligament)
•
Includes medial knee capsule
•
Posterior medial corner
•
Capsule
•
Semimembranosus
lateral release sequence
Lateral compartment release in sequence
•
Osteophytes
•
Lateral capsule
•
Iliotibial band—key structure
Release for lateral extension tightness
•
Popliteus—key structure
•
Tight in flexion
•
Release for lateral flexion tightness
•
Release of popliteus off anterior portion of lateral epicondyle (Fig. 5.72)
•
Note: the inadvertent cut of a noncontracted popliteus tendon does not significantly affect the static stability of the knee.
•
Lateral collateral ligament (LCL)—last
review extra-articular bone deformity
General rules
•
The closer the extraarticular coronal bone deformity is to the knee joint, the greater the mechanical malalignment at the joint line.
•
For any given magnitude, the farther a deformity is from the knee, the smaller the intraarticular bone cut needed to correct the mechanical alignment.
•
An extraarticular deformity within the distal one-fourth of the femur or proximal one-fourth of the tibia is the most difficult to correct if bone cuts are made only at the knee joint. Reasons:
•
Large bone resections required may compromise ligament attachment sites.
•
Large bone resections adversely affect implant sizing, fitting, and rotational alignment.
•
Extreme releases required to balance the knee often render the ligament incompetent (Fig. 5.73).
•
McPherson one-fourth rule: when coronal deformity is within the distal one-fourth of the femur or proximal one-fourth of the tibia and the deformity is 20 degrees or more, the recommended treatment is:
•
Concomitant osteotomy and TKA
•
Closing wedge osteotomy preferred
•
Diaphyseal press fit stem with splines recommended
•
Provides rotational stability and obviates the need for additional fixation at osteotomy site
treatments for flexion deformity
Concave side is posterior—posterior knee release required
▪
Posterior knee release procedure—in sequence is:
□
Osteophytes
□
Posterior capsule
□
Gastrocnemius muscle origin
▪
Posterior releases are performed with the knee flexed (generally at 90 degrees of flexion).
□
Less danger to popliteal artery
Criteria for diagnosing a periprosthethic joint infection
Review the total knee prothesthic designs
Designs are categorized according to an increasing level of mechanical constraint in knee system.
□
Least constrained
•
Cruciate-retaining TKA—remove ACL and keep PCL
•
Cruciate-sacrificing TKA—remove ACL and PCL
•
Both used for straightforward primary TKA
□
Constrained
•
Constrained nonhinged TKA
•
Used for complex primary or revision TKA
□
Highly constrained
•
Hinge TKA
•
Used for complex revision TKA
Review Cruciate Retaining Knee implant
PCL helps provide flexion gap stability.
□
PCL tension influences femoral prosthetic rollback.
•
Rollback is defined as the progressive posterior change in femoral-tibial contact point as the knee moves into flexion.
□
Generally, cruciate-retaining implants have more flat PE inserts to accommodate for flexion rollback.
▪
Advantages
□
Bone conserving
□
More consistent joint line restoration
•
Keeping PCL keeps flexion gap smaller
▪
Disadvantages
□
Harder to balance with severe deformities
•
Cruciate-retaining implants should be avoided if
•
Varus more than 10 degrees
•
Valgus more than 15 degrees
□
PCL balance is critical for long-term bearing wear
•
A tight PCL in flexion causes increased PE wear
•
PCL in flexion must be balanced.
•
Lift-off must be avoided (Fig. 5.80).
•
PCL can be released off femur or tibia.
•
PCL balance is sometimes hard to assess intraoperatively.
•
PCL balance is sometimes hard to achieve—over-release of PCL is common.
•
Excess recession (i.e., release) can result in late failure caused by flexion instability and repetitive subluxation
•
Flexion instability is characterized by
•
Knee effusion
•
Chronic pain
•
Inability to climb stairs with reciprocal gait
•
Inability to arise from low chair
•
Knee buckling
□
Late rupture of PCL with resultant instability
•
PE particle debris can cause osteolysis and result in disruption of PCL from bony attachments
•
Traumatic fall onto flexed knee can cause rupture.
□
Paradoxical forward sliding as knee flexes
•
With ACL removed, knee kinematics are drastically altered.
•
Prosthetic knee does not roll back like native knee.
•
As knee flexes, there is paradoxical forward-sliding movement, which causes sliding wear on PE insert.
•
Sliding wear causes significant PE wear.
Review cruciate sparing TKR implant
Spine and cam mechanism in the posterior aspect of the knee
•
Also called posterior stabilized knee
□
An extended anterior PE lip with a concomitant smaller posterior lip
•
Also called anterior stabilized knee
▪
Posterior stabilized primary TKA design
□
Description (Fig. 5.81)
•
A cam connects between the two posterior femoral condyles.
•
The cam engages a tibial PE post during flexion.
•
The cam and post control rollback.
•
Generally, posterior stabilized implants have more dished (i.e., congruent) PE inserts.
□
Advantages
•
Easier balancing in severe coronal deformities (i.e., varus/valgus) because both ACL and PCL are removed
•
Controlled flexion kinematics with spine and cam, less sliding wear
□
Disadvantages
•
Femoral cam jump (Fig. 5.82)
•
Occurs when flexion gap is left too loose
•
Mechanism of cam jump
•
Varus or valgus stress when knee is flexed
•
Patient usually lying in bed or sitting on floor
•
Flexion gap opens up, and femoral cam rotates in front of post and then comes to rest in front of tibial post.
•
Closed reduction maneuver
•
With use of anesthesia, knee is positioned at 90 degrees of flexion off the table (dependent dangle)
•
An anterior drawer maneuver is performed
•
Clunk will be felt as knee is reduced.
•
Ultimate solution requires knee revision to address loose flexion gap
•
Causes of loose flexion gap
•
Overrelease of contracted popliteus
•
Inadvertently occurs also with saw blade
•
Overrelease of anterior portion of superficial MCL
•
Anterior translation of femoral component
•
Anterior translation increases flexion gap space
•
Patella clunk syndrome
•
Scar tissue (descriptively, a nodule of scar) superior to patella gets caught in box as knee moves from flexion into extension.
•
Scar catches in box, then releases with a clunk.
•
Clunk occurs in range between 30 and 45 degrees.
•
Treatment is removal of suprapatellar scar nodule (Fig. 5.83).
•
Arthroscopic removal is acceptable.
•
Miniarthrotomy is also acceptable.
•
Preventive treatment (Fig. 5.84)
•
Synovectomy and débridement of all scar from quadriceps tendon at time of TKA
•
Risk factors that cause patellar clunk are related to factors that increasequadriceps force. These include:
•
Small patella implant (decreased extensor offset)
•
Thin total patella height (decreased extensor offset)
•
Short patella tendon (patella baja)
•
Increased posterior condylar offset (patella pulled lower down)
•
A result of PCL removal requiring an increase in the AP femoral size to fill the increased flexion gap
•
Tibial post wear and breakage
•
Tibial post is an additional PE surface that can wear and enhance risk for osteolysis.
•
Aseptic loosening and osteolysis are correlated with tibial post wear and damage.
•
If the knee hyperextends, the edge of the femoral box can impinge on the anterior tibial post (Fig. 5.85).
•
Causes anterior post damage and fatigue
•
Causes increased PE wear and osteolysis
•
Anterior tibial post wear occurs when TKA components are in net hyperextension, such as with
•
Flexion of femoral component on distal femur
•
Excess tibial posterior slope
•
Knee hyperextension (i.e., loose extension gap)
•
Anterior translation of tibial component on tibia (i.e., placing tibial implant toward front of tibia rather than placing on posterior tibial rim)
•
Anterior translation of femoral component has no effect on anterior tibial post impingement.
•
Additional bone is removed from middle of distal femur.
•
Bone removed can be substantial in a small knee.
•
Flexion gap is bigger
•
Flexion gap opens up when PCL is removed.
•
To balance the extension gap, additional distal femur bone is removed in a posterior stabilized TKA.
•
Consequence of additional distal femoral bone removal
•
Joint line elevation with possible baja deformity
•
The maximum joint line elevation allowed in primary TKA is 8 mm so as to maintain knee ligament kinematics.
•
Ensures proper kinematic function and stability of collateral ligaments.
□
PS TKA must be used in following situations
•
Patellectomy
•
Cruciate-retaining knee with a flat PE is prone to anterior subluxation when patella is absent.
•
Inflammatory arthritis
•
PCL is at risk for rupture with erosive disease process
•
Trauma with PCL rupture or attenuation
Review anterior stabilizing TKA implant
A cruciate-retaining femoral component is used.
The PCL is removed (or highly recessed).
•
Tibial insert is a highly congruent bearing with a raised anterior PE lip and a smaller posterior lip.
•
No mechanism for rollback
•
Anterior lip resists anterior translation.
□
Advantages
•
Easier balancing in severe deformities (i.e., varus/valgus)
•
Bone conserving—no box cut needed
•
Operative versatility
•
Switch to posterior stabilized system not required if PCL is lost or overreleased.
•
Regulated flexion kinematics
•
High congruency limits sliding wear
•
Knee flexion is achieved by
•
Posterior placement of tibial knee flexion center; this is called posterior offset center of rotation.
•
Placement of tibial component with native posterior slope; femur is less likely to impinge upon posterior tibia in flexion.
□
Disadvantages
•
Increased PE surface area
•
Increases risk for greater PE wear debris and osteolysis
•
Minimal rollback
•
Surgical technique must be adjusted to attain high flexion.
•
Posterior translation of tibial component on tibia, when possible; this will place tibial center of rotation more posteriorly.
•
Recreation of native tibial posterior slope.
•
Flexion gap laxity causes rotational instability and pain
•
A loose flexion gap will cause instability usually in midflexion and full flexion.
•
Mechanism of midflexion instability
•
Varus or valgus stress when knee is flexed (between 50 and 90 degrees)
•
Patient usually lying in bed or sitting on floor
•
Flexion gap opens up and tibia rotates anteriorly. This creates a subluxing event, but knee usually does not lock up.
•
Patient experiences pain when climbing stairs with reciprocal gait, arising from a chair, or negotiating uneven surfaces; it is usually associated with a knee effusion.
•
Treatment requires revision to address loose flexion gap.
Review tibial rotating platform
The tibial PE bearing rotates on a polished metal tibial baseplate.
□
The rotating platform can be used with both anterior stabilized (high congruent) and posterior stabilized TKA designs.
□
The PCL is removed when a tibial rotating platform is used.
▪
Advantages
□
Better articular conformity through entire knee range
•
Theoretically less PE wear
□
Equivalent in survivorship to fixed-bearing knee, but not superior
•
Wear and osteolysis still seen
▪
Disadvantages
□
Bearing spinout (Fig. 5.88)
•
Occurs when flexion gap is left too loose
•
Mechanism of spinout
•
Varus or valgus stress when knee is flexed
•
Patient usually lying in bed or sitting on floor
•
Flexion gap opens up, and tibia rotates behind femur.
•
Femur then comes to rest in front of tibial PE bearing and locks into spinout position.
•
Closed reduction maneuver
•
With use of anesthesia, knee is positioned at 90 degrees of flexion off the side of the table (dependent dangle).
•
Tibial bearing is manipulated by digital palpation and pressure into reduced position.
•
Ultimate solution requires knee revision to address loose flexion gap.
TKA techniques to avoid patella maltracking
Reduction of excess valgus
□
Valgus deformity must be corrected to a neutral mechanical alignment—always.
□
Severe valgus deformities that require radical ligamentous releases can be adequately managed with sophisticated revision-style prosthetic systems.
▪
Component positioning
□
Patellar maltracking—causes
•
Internal rotation of
•
Femoral component
•
Tibial component
•
Medialization of
•
Femoral component
•
Tibial component
▪
Femoral component rotation
□
Femoral component should never be internally rotated.
Review the technique for internal rotation of the tibia component
why do you set 3-5 degrees of external rotation cut on the femur?
Review the 5 established techniques to address femoral rotation:
