I. Surgical Approach
A. Anterior skin incision
1. Total knee arthroplasty (TKA) traditionally has been performed through an anterior midline incision.
2. This approach minimizes risk to neurovascular structures.
B. Medial parapatellar approach
1. This approach uses the classic deep exposure technique, used for both primary and revision TKA.
2. Extensile exposure allows for easy patellar eversion and excellent visualization of the entire femoral and tibial anatomy.
3. Technique
a. A curved or straight incision can be used.
b. The deep arthrotomy can originate in the medial aspect of the quadriceps tendon and curve along the border of and directly over the patellar bone or through the anteromedial knee capsule before finishing at the tibial anterior cortex.
c. Insall advocated the use of a straight arthrotomy, where the quadriceps expansion is directly dissected off the patella with the periosteum.
d. Some authors have argued that the parapatellar approaches may be inferior because they require incision into the quadriceps tendon.
4. Relative contraindication—previous lateral parapatellar arthrotomy.
C. Midvastus approach
1. Technique
a. The midvastus approach spares the quadriceps tendon from incision and relies on carrying the proximal portion of the arthrotomy up into the muscle belly of the vastus medialis along the line and direction of its fibers (
Figure 1).
b. This portion of the arthrotomy is performed in line with the fibers of the muscle belly itself.
c. The patella is commonly subluxated instead of everted.
2. Advantages
a. The vastus medialis insertion onto the medial border of the quadriceps tendon is not disrupted (
Figure 2).
b. This technique may allow for rapid restoration of extensor mechanism function (accelerated rehabilitation).
c. Patellar tracking is improved compared with the classic medial parapatellar approach.
[Figure 1. Schematic representation of the incisions (dashed line) for the midvastus arthrotomy. Note that the dissection is carried between the fibers of the vastus medialis. The quadriceps muscle is not incised.]
[Figure 2. Schematic representations comparing the medial peripatellar (A), subvastus (B), and midvastus (C) approaches.]
[
Figure 3. Schematic representations showing blunt dissection of the vastus medialis off the septum (A) and deep arthrotomy (B) for subvastus exposure.]
3. Relative contraindications
a. Hypertrophic arthritis
b. Obesity
c. Range of motion (ROM) <80°
d. Previous high tibial osteotomy
D. Subvastus approach
1. Surgical technique—With this approach, initially described in 1929, the quadriceps tendon is spared as the muscle belly of the vastus medialis is lifted off the intermuscular septum (Figure 3).
2. Advantages
a. The patellar vascularity is completely preserved, which may minimize patella fractures, prosthesis loosening, and anterior knee pain.
b. The extensor mechanism is kept intact, which may result in less postoperative pain and preserved extensor mechanism strength.
c. The patella can be subluxated or everted.
d. The need for lateral retinacular release is minimized.
3. Relative contraindications
a. Revision TKA
b. Obesity
c. Previous high tibial osteotomy
d. Previous parapatellar arthrotomy
e. Extremely muscular quadriceps
E. Mini-incision
1. Technique
a. Several minimally invasive approaches have been described. With these approaches, not only is the quadriceps tendon spared, but the vastus medialis is neither incised nor dissected off of the septum.
b. Some of these techniques do not use an anterior incision, and they require special instrumentation and resection blocks.
c. These approaches are technically demanding and are associated with significant learning curves and risk of complications.
d. The evolutionary features of minimally invasive TKA are described in
Table 1.
2. Results
a. Some results reported in the literature suggest that these minimally invasive techniques allow more rapid recovery.
b. Long-term data do not exist to confirm that the early benefits seen with these approaches translate into improved long-term function or survival.
F. Lateral approach
1. Indications—The lateral approach is advocated for fixed preoperative valgus deformity.
2. Technique
a. A lateral skin incision is used.
b. The arthrotomy originates proximally along the lateral border of the quadriceps tendon and extends distally 1 to 2 cm lateral to the patellar border and along the medial border of the Gerdy tubercle.
c. When indicated, iliotibial band release is performed with appropriate protection of the peroneal nerve.
d. The fat pad and capsule are mobilized to provide an adequate soft-tissue envelope for closure.
e. The extensor mechanism is translocated laterally with gradual peel of the lateral 50% of the patellar tendon.
[Table 1. Evolutionary Features of Minimally Invasive Total Knee Arthroplasty]
f. When indicated, a posterior lateral release is performed.
g. Arthrotomy closure is performed.
3. Advantages
a. The lateral approach avoids the need for a lateral release.
b. It allows for a more direct approach to the pathologic lateral anatomy with an extensive lateral retinacular release.
c. It also allows for medial displacement of the extensor mechanism, internal rotation of the tibia, and further exposure of the posterolateral corner.
d. Vascularity is preserved. (The medial blood supply is not violated.)
e. Optimal tracking is achieved because the retained extensor mechanism has an inherent self-centering tendency.
4. Disadvantages
a. The lateral approach is technically demanding.
b. The exposure is less familiar than the medial exposure.
c. Medial eversion and displacement of the extensor mechanism is more difficult.
II. Fixation
A. Overview—Data from 10-year follow-up studies support the use of either a cemented or a cementless technique.
B. Cemented fixation
1. Cemented fixation is the gold standard for TKA across all indications.
2. Optimization of cementing techniques has allowed for reliable and durable fixation for all three components (patella, femur, tibia).
3. Meticulous technique is critical.
a. The cement is prepared with vacuum suction and centrifugation.
b. Cancellous bone is cleaned with pulsatile lavage and drying at the time of implantation. Drying can be augmented with intraosseous suction or negative pressure intrusion into the proximal tibia.
c. Critical attention to details allows for adequate cement penetration and minimizes interruption of the bone-implant-cement interface.
C. Cementless fixation
1. Cementless fixation has not had the success in TKA that has been seen in total hip arthroplasty, despite many attempts to perfect this technique in hopes of avoiding the need for cement fixation.
2. Implant designs have varied in ingrowth surfaces, types of adjunctive fixation, and extent of adjunctive fixation.
3. Complications
a. The biggest challenges involve the patellar and tibial components, with pain and positive bone scan with lucency (assume tibial fibrous union) reported.
b. The most common late complication is osteolysis.
4. When the following key requirements are met, survival of cementless TKA rivals the long-term success seen with a cemented technique.
a. Optimal porous coating
b. Stem design that enhances stability
c. Meticulous surgical technique
d. Irrigation of bone cuts to avoid thermal necrosis
e. Some type of adjunctive (peripheral) fixation (screws or pegs)
5. Improvement in fixation technology will likely achieve more predictable outcomes for cementless TKA.
[
Figure 4. Schematic representations comparing classic (A) and anatomic (B) techniques for bone resection for TKA.]
III. Bone Resection
A. Classic technique—The most commonly used technique uses a 5° to 7° (depending on body habitus) valgus femoral cut and a neutral tibial cut.
B. Anatomic technique—This technique uses a 9° valgus femoral cut and a 3° varus tibial cut (Figure 4).
IV. Ligament Balancing
A. Overview
1. The goal of ligament balancing is to achieve equal and symmetric fixation and extension gaps.
2. Balance may be different in flexion and extension because the posterior capsule and hamstring tendons contribute to medial-lateral stability in full extension, whereas they are lax during flexion.
B. Ligament balancing considerations for various conditions
1. Varus deformity
a. Most of the ligament balancing required for a varus deformity occurs at the time of exposure-controlled posteromedial release.
b. The medial side is tight, and therefore subperiosteal medial release or stripping of the medial side will help with balancing.
c. It is critical to remove femoral and tibial osteophytes and then the meniscus with its capsular attachment, followed by release of the deep medial collateral ligament (MCL), release of the posteromedial corner, the attachment of the semimembranosus, and sequential subperiosteal elevation of the superficial MCL (at the pes anserine region), avoiding complete release.
d. Release of the posterior cruciate ligament (PCL) is rarely indicated.
e. Selective division of the MCL or epicondylar osteotomy has also been used.
2. Valgus deformity
a. The surgeon must be careful not to perform an overly aggressive medial release during the exposure.
b. The medial structures may be attenuated and lax.
c. Significant valgus deformities will require
i. Osteophyte resection
ii. Lateral capsule release off the tibia
iii. Iliotibial band release if tight in extension (either Z-type release or release off the Gerdy tubercle)
iv. Popliteus release if tight in flexion
v. Lateral collateral ligament release (Use of constrained device should be considered when severe valgus deformity with incompetent MCL is present.)
3. Although there have been many descriptions of the correct order and sequence for anatomic release, the overriding concern is to make sure that all tight structures are adequately released to allow for adequate balancing.
4. In valgus deformities >15°, the iliotibial band and popliteus may have to be released. This is often done through a selective internal release of tight lateral structures and with a tensioning device in place.
5. When correcting combined valgus deformity with flexion contracture, the risk of peroneal nerve palsy is a concern.
C. Flexion contracture
1. Overview
a. In patients with fixed flexion contractures, shortened posterior soft tissues prevent full extension.
b. Most flexion contractures are treated using appropriate capsular and soft-tissue releases.
c. Data are mixed as to whether a flexion deformity after implantation can improve with time.
2. Technique
a. Normal posterior capsular recess is recreated by stripping the adherent capsule proximally off of the femur after posterior condylar resection.
b. Posterior osteophytes are removed.
c. The tendinous origins of the gastrocnemius are released.
3. Additional bone also can be resected from the distal femur in concert with collateral ligament balancing to enlarge the extension gap. Resecting too much bone can lead to varus-valgus flexion instability despite stability in extension (tension band effect), in which instance, it may advisable to consider the use of a constrained implant or possibly a hinged implant.
D. Flexion and extension mismatches
1.
Table 2 shows factors to be considered when balancing flexion and extension gaps.
2. Sagittal plane balancing
a. If tight in extension and flexion, a symmetric gap is present, and more proximal tibia should be cut.
b. If extension is acceptable and flexion is loose, an asymmetric gap is present and too much of the posterior femur was cut. Therefore, the size of the femoral component should be increased up to the next (anterior to posterior) size, and the posterior gap should be filled with cement or metal augmentation.
c. If extension is tight and flexion is acceptable, an asymmetric gap is present and either not enough of the posterior capsule was released or not enough of the distal femur was cut. Therefore, the posterior capsule should be released and more bone should be removed from the distal femur in 1- to 2-mm increments.
d. If extension is acceptable and flexion is tight, an asymmetric gap is present, the tibial bone cut has no posterior slope, and either not enough posterior bone was cut or—if a PCL-retaining implant is used—the PCL is scarred and too tight. Therefore, the size of the femoral component should be decreased (anterior to posterior) to the next smaller size, the PCL should be recessed, and the posterior slope of the tibia should be assessed and recut if the slope is anterior.
e. If extension is loose and flexion is acceptable, an asymmetric gap is present and either too
[Table 2. Balancing Flexion and Extension Gaps]
|
much of the distal femur was cut or the anteroposterior size of the implant is too big. Therefore, distal femoral augmentation should be performed, a smaller size (anteroposterior) femoral component should be used, and a thicker tibial polyethylene inset should be used to address the tight flexion gap. |
E. Articular constraint options
1. Unconstrained
a. Posterior cruciate-retaining TKA
i. Advantages
(a) Minimizes flexion instability (taut PCL in flexion prevents anterior translation).
(b) Preserves femoral roll-back (posterior shift of the femoral tibial contact point as the knee flexes)
(c) Preservation of roll-back may improve flexion.
ii. Disadvantages
(a) Roll-back is actually a combination of roll and slide (no anterior cruciate ligament).
(b) Polyethylene must be flat to allow roll-back—leads to increased contact stresses and sliding wear.
b. Posterior cruciate-substituting TKA
i. Should be used in patients with previous patellectomy, inflammatory arthritis, previous PCL injury, or excessive release of PCL that occurs during surgery
ii. Polyethylene post and cam between femoral condyles produces mechanical roll-back in flexion.
iii. Can also use a highly congruent liner with build-up of the anterior lip (allows for use of a femoral component without a box or cam)
iv. Advantages
(a) Improved flexion and mechanical rollback
(b) Congruent articulation can be used to reduce contact stresses.
v. Disadvantages
(a) Knee balancing must be carefully addressed to avoid flexion instability and dislocation.
(b) Boxed implants can require extensive bone resection in the region of the notch depending on design.
2. Constrained nonhinged
a. Advantages—Increased varus-valgus support.
b. Disadvantages
i. Increased polyethylene-bone interface stress
ii. Stems advised
3. Constrained hinged
a. Advantages—Maximal internal constraint.
b. Disadvantages
i. Potentially restricted ROM
ii. High degree of bone stress interface
iii. Stems required
V. Unicompartmental Knee Arthroplasty
A. General/indications
1. Unicompartmental knee arthroplasty has been a controversial procedure since its introduction 30 years ago.
2. The indications tend to vary widely.
3. It can be considered as an alternative to TKA and osteotomy when degenerative arthritis involves only one compartment.
4. Traditionally, unicompartmental knee arthroplasty has been reserved for older, lower-demand, thin patients with unicompartmental disease.
5. Data suggest that only 6% of patients meet the early criteria for ideal candidates for this procedure.
a. Noninflammatory arthritis
b. <10° varus and <5° valgus
c. Intact anterior cruciate ligament
d. ≥90° flexion
e. No evidence of mediolateral subluxation
f. Flexion deformity <15°
g. Correctable deformity
h. Stress radiographs demonstrating no collapse of opposite compartment
i. Patellofemoral cartilage changes grade III or lower and asymptomatic
j. <90 kg in weight
6. Age and weight have remained the most controversial criteria.
7. Until recently, unicompartmental knee arthroplasty was performed in only 5% of patients for whom knee arthroplasty was indicated.
8. There have been efforts to expand the indications for this procedure to include younger patients as well as patients with moderate involvement of the compartments not being resurfaced.
9. There are advantages for two distinct patient populations
a. Middle-aged patients (alternative to osteotomy)
i. Higher initial success rate
ii. Fewer early complications
iii. More acceptable cosmetic appearance
iv. Longer-lasting result
v. Easier conversion to TKA
b. Octogenarians (expected to outlive the implant)
i. Faster recovery
ii. Less blood loss
iii. Less medical morbidity
iv. Less expensive procedure
B. Technique
1. Overcorrection should be avoided (the mechanical axis should be undercorrected by 2° to 3°).
2. Peripheral and notch osteophytes are removed.
3. Minimal bone is resected.
4. Extensive releases are avoided.
5. Edge loading is avoided.
6. Appropriate mediolateral placement is achieved to prevent tibial spine impingement.
7. Varus tibial cut is avoided to prevent implant loosening.
8. To prevent tibial plateau stress fracture due to high medial stresses, caution should be used when placing proximal tibial guide pins.
C. Results
1. First-decade results from studies published from the late 1980s to the early 1990s are highlighted in
Table 3.
a. Ten-year survival rates range from 87.4% to 96%.
b. The standard for failure rate in the first decade is 1%.
2. Second-decade results are also highlighted in Table 3.
a. A rapid decline in survivorship is noted.
b. Fifteen-year survival rates range from 79% to 90%.
3. Causes of late failure
a. Opposite compartment degeneration
b. Component loosening
c. Polyethylene wear
D. Mobile-bearing unicompartmental knee arthroplasty
1. Meniscal bearing designs exist that allow increased conformity and contact without constraint, which can lead to significant decrease in wear.
2. Excellent survivorship has been demonstrated with these prostheses in some series out to the second decade.
3. The procedure is technically demanding, and the bearings can dislocate.
VI. Surgical Technique for Primary TKA
A. Indications
1. To relieve pain caused by severe arthritis
[Table 3. Long-Term Results of Unicompartmental Knee Arthroplasty Outcome Studies]
2. Cartilage space loss confirmed on radiographs
3. Younger patients with multiple joints affected
4. Severe patellofemoral arthritis
5. Severe pain from pseudogout and chondrocalcinosis
6. Severe progressive deformity
7. Nonsurgical treatment exhausted (Nonsteroidal anti-inflammatory drugs, injections, activity modification, use of assistive device for ambulation)
B. Contraindications
1. Infection
2. Incompetent extensor mechanism
3. Compromised vascularity
4. Recurvatum deformity secondary to muscular weakness
5. Local neurologic disruption affecting musculature about the knee
6. Presence of a painless, well-functioning arthrodesis
C. Posterior-stabilized TKA versus cruciate-retaining TKA
1. Numerous studies compare posterior-stabilized TKA and cruciate-retaining TKA.
2. Successful long-term results are attained with both techniques.
3. Advocates of posterior-stabilized TKA believe that this is a more forgiving approach and therefore more predictable.
4. Surgeons who spare the PCL and use a cruciate-retaining implant believe in the benefit of preserving the anatomy and therefore allowing for more idealized kinematic function.
D. Mobile-bearing TKA
1. Allows motion at the interface between the undersurface of the tibial polyethylene and the top surface of the tibial base plate.
2. Advocates believe it allows for increased ROM, lower polyethylene stresses, and a more idealized kinematic knee function.
3. Increasing conformity of tibial liner implants reduces polyethylene stress but increases stress at the tibial fixation interfaces.
4. A theoretical advantage for mobile-bearing TKA is that the articular surface of the implant can be congruent over the entire ROM without increasing constraint.
a. This leads to lower contact stresses as a result of increasing contact area.
b. Some authors believe lower contact stresses will translate into a lower incidence of osteolysis.
5. Data do not exist to show whether these apparent advantages with regard to contact stresses actually translate into decreased wear and osteolysis in vivo.
E. High-flexion TKA
1. Cultural differences exist regarding the ideal amount of natural knee flexion. Some of these differences are the driving force behind the high-flexion TKA prostheses.
2. The reported ROM for TKA has varied between 100° and 110°.
3. Modifications in femoral component design as well as tibial articular geometry have allowed for larger total arcs of motion (135° to 155°).
a. Thickening of the posterior condyle to allow continuation of the posterior condylar axis
b. Utilization of a minus size to allow for optimal gap balancing, chamfering of the femoral condyle to avoid impingement of the PCL, and chamfering of the posterior aspect of the tibial liner (
Figure 5)
c. Recession of the anterior surface of the liner to allow room for the patellar tendon during deep flexion
4. Despite TKA implant design, preoperative ROM remains the most consistent predictor of postoperative ROM. It is unlikely that implant design modifications can change this association.
F. Results
1. Survival rates for total condylar prostheses range from 91% to 96% at 14- to 15-year follow-up.
2. Newer prosthetic designs must match these results for survival.
a. The survival rate for cemented PCL-retaining TKA ranges from 96% to 97% at 10- to 12-year follow-up.
[Figure 5. Photographs showing prosthesis design modification to allow for high flexion. The minus size, between the standard size and the size below, allows for fine tuning of the soft-tissue balancing.]
b. The survival rate for cemented PCL-substituting TKA is 97% at 10-year follow-up and 94% at 13-year follow-up.
c. The survival rate for cementless TKA ranges from 95% to 97% at 10- to 12-year follow-up.
VII. Patellofemoral Joint
A. Resurfacing versus not resurfacing
1. Data support both resurfacing and not resurfacing the patella at the time of TKA.
2. Some data suggest an increased incidence of anterior knee pain postoperatively when the patella is not resurfaced.
3. Data conclusively show that survival of the patellar
[
Figure 6. Schematic representation of the patellar blood supply. SG = supreme genicular artery, MSG = medial superior genicular artery, MIG = medial inferior genicular artery, LSG = lateral superior genicular artery, APP = ascending parapatellar artery, OPP = oblique prepatellar artery, LIG = lateral inferior genicular artery, TIP = transverse infrapatellar artery, ATR = anterior tibial recurrent artery.]
component is inferior to the survival seen for the tibial and femoral components.
4. Poor results have been attributed to several factors.
a. Inferior prosthetic design (metal-backed patellar components)
i. High failure rate
ii. Poor ingrowth
iii. Peg failure
iv. Dissociation of polyethylene
v. Component fracture
b. Suboptimal surgical technique
i. Asymmetric resection
ii. Overstuffing the patellofemoral joint
iii. Excessive patellar resection
5. Complication rates have been lowered to 0 to 4% with improved technique that focuses on several factors.
a. Equal facet thickness
b. Maintaining the native patellar height
c. Good patellofemoral tracking
d. Exercising care to maintain the vascular supply to the patella
6. Patients who can be considered for an unresurfaced patella
a. Young
b. Thin
c. Noninflammatory arthritis
d. Well-preserved patellar cartilage
e. Ideal patellar tracking
f. Limited anterior knee pain
7. Critical to use a femoral component with a design that accommodates the native patella
B. Patellar blood supply
1. The patella is a sesamoid bone.
2. The patella has an extraosseous blood supply and an intraosseous blood supply.
a. Extraosseous blood supply consists of an anastomotic ring that encircles the patella itself. This ring receives contribution from all of the geniculates (Figure 6).
b. Intraosseous blood supply is damaged during resurfacing, which is why other approaches to TKA have been advocated over the medial parapatellar approach.
C. Patellectomy
1. Patellectomy has been used to treat severe isolated patellofemoral arthritis.
2. Experimental data suggest a 25% to 60% reduction in extension power following patellar resection.
a. There may also be a significant increase in tibiofemoral joint reaction forces.
b. A significant increase in tibiofemoral joint reaction forces may explain the high incidence of arthrosis in the medial and lateral compartments following patellectomy.
3. If TKA is to be performed after a patellectomy, a posterior-stabilized component should be selected.
4. The results of TKA in patients who also undergo patellectomy have generally been less successful when compared with patients in whom the patella is not compromised.
D. Rotational malalignment
1. Patellar maltracking must be avoided when performing TKA.
2. Most common complications in TKA involve abnormal patellar tracking.
3. Surgeons must avoid an increased Q angle (the angle formed by the intersection of the extensor mechanism axis above the patella with the axis of the patellar tendon) to avoid increased lateral patellar subluxation forces.
4. Femoral component internal rotation should be avoided because it causes lateral patellar tilt and a net increase in the Q angle.
5. The femoral component should be placed in 3° of external rotation to the neutral axis to maintain symmetric flexion gap.
a. The line perpendicular to the AP axis is the neutral rotational axis.
b. The epicondylar axis is usually slightly externally rotated to the neutral axis; component should be placed parallel to this.
c. The line externally rotated 3° to 5° to the posterior condylar axis is the neutral axis.
6. The femoral component should be biased to a lateralized position because medialization places the trochlear groove in a medial position and increases the Q angle.
7. The midpoint of the tibial component should align over the medial third of the tibial tubercle, and care should be taken to avoid an internally rotated position and err toward external rotation.
8. Internal rotation of the tibia results in external rotation of the tubercle and increases the Q angle.
9. The patella should be placed medially and superiorly on the undersurface of the patella.
VIII. Patellofemoral Arthroplasty
A. Indications
1. Isolated patellofemoral osteoarthritis
2. Posttraumatic arthrosis
3. Severe chondrosis (Outerbridge grade IV)
4. Failed nonsurgical treatment
5. Patients who are symptomatic with prolonged sitting, stair or hill ambulation, or squatting
B. Contraindications
1. Inflammatory arthritis
2. Chondrocalcinosis with involvement of the menisci or tibiofemoral chondral surfaces
3. Patients with unrealistic expectations
4. Severe patellar maltracking or malalignment (a realignment procedure is required in concert with or before arthroplasty)
C. Results
1. Most series report 85% good to excellent results.
2. Failures are associated with uncorrected alignment issues and progression of tibiofemoral arthritis (25% at 15-year follow-up in one study).
3. Some series report higher failure and revision rates as well as poorer functional outcomes, which appear to be correlated to implant design.
4. Cemented trochlear and all-polyethylene components are not associated with a high rate of loosening; appropriate patient selection should result in predictable outcomes.
IX. Complications
A. Instability
1. Symptomatic instability occurs in 1% to 2% of patients undergoing TKA.
2. Instability accounts for 10% to 20% of all TKA revisions.
3. Instability occurs in the mediolateral (axial instability) and the anteroposterior (flexion instability) planes.
4. Several factors contribute to instability.
a. Ligament imbalance
b. Component malalignment or failure
c. Implant design
d. Mediolateral instability (symmetric or asymmetric)
e. Bone loss from overresection of femur
f. Bone loss from femoral or tibial component loosening
g. Soft-tissue laxity of collateral ligaments
h. Connective tissue disorders (rheumatoid arthritis, Ehlers-Danlos)
i. Inaccurate bone resection
j. Collateral ligament imbalance (underrelease, overrelease, traumatic disruption)
5. Axial instability
a. If symmetric (flexion and extension), a thicker tibial liner can be used.
[
Table 4. Factors Affecting Neurovascular Injury Following TKA]
b. If asymmetric, then augmentation and component revision is required.
6. Flexion instability occurs when the flexion gap is larger than the extension gap.
a. It can occur with anteriorization and downsizing of femoral component.
b. It can result in posterior dislocation (0.15% of TKAs with posterior-stabilized prosthesis).
c. Instability can occur with PCL-retaining designs as well.
d. PCL-retaining TKAs should be revised to posterior-stabilized TKAs.
e. Posterior-stabilized TKAs need to be revised if dislocation is recurrent; results are variable.
B. Heterotopic ossification
1. Heterotopic ossification can occur following TKA.
2. It's incidence is not the same as is seen following total hip arthroplasty.
3. It is generally believed to be the result of periosteal stripping.
4. Some surgeons have suggested that excessive dissection of the anterior femur can result in the development of heterotopic ossification just proximal to the anterior flange of the femoral component. This may have implications for ROM if scarring of the extensor mechanism occurs as a secondary result.
5. It is also critical to be aware that periprosthetic heterotopic ossification may be an indicator of indolent infection.
C. Vascular injury
1. The incidence of vascular injury following TKA is quite low.
2. A vascular examination should be performed and documented before the procedure.
3. It is critical to avoid sharp dissection in the posterior compartment of the knee.
4. Posterior retractor placement must also be performed carefully and should be biased to a medial position away from the popliteal artery; this artery has been shown to lie 9 mm posterior to the posterior cortex of the tibia at 90° of flexion.
5. It is worthwhile to release the tourniquet after the bony cuts are made.
6. If arterial injury is suspected, the tourniquet must be dropped to check the artery.
7. Popliteal injury can lead to acute ischemia, compartment syndrome, and potential amputation.
D. Nerve palsy
1. The incidence of nerve injury following TKA has been reported to be 0.3%.
2. In patients with severe valgus deformities, the rate of peroneal nerve injury increases to 3% to 4%.
3. Severe flexion contracture of >60° occurs in 8% to 10% of patients.
4. The risk factors that seem to increase the incidence of nerve palsy are listed in Table 4.
5. If a peroneal nerve palsy is suspected following TKA, the patient's leg should be immediately flexed and all compressive dressings should be removed.
6. Initial management should include the use of an ankle-foot orthosis.
7. If dorsiflexion does not recover, a late decompression of the nerve or muscle transfer can be considered.
E. Wound complications
1. Systemic factors
a. Type II diabetes mellitus
b. Vascular disease
c. Rheumatoid arthritis
d. Medications
e. Tobacco use
f. Nutritional status
g. Albumin <3.5 g/dL
h. Total lymphocyte count <1,500/uL
i. Perioperative anemia
j. Obesity
2. Local factors
a. Previous incisions
i. The most acceptable medial incision should be used.
ii. Skin bridges >5 to 6 cm should be used.
iii. Care should be taken to avoid crossing old incisions at angles <60°.
b. Deformity
c. Skin adhesions secondary to surgery or trauma
d. Local blood supply
3. Technique
a. Length of incision
b. Large subcutaneous skin flaps
c. Preservation of subcutaneous fat layer
d. Optimizing arthroplasty techniques
4. Several postoperative factors can help prevent wound complications.
a. Hematoma should be avoided.
b. Knee flexion past 40° in the first 3 to 4 days should be avoided.
c. Nasal oxygen should be used in at-risk patients in the first 24 to 48 hours postoperatively.
d. Tissue expanders should be used preoperatively to facilitate incision healing postoperatively.
e. When wound drainage (greater than 4 days) and/or failure occurs, aggressive surgical management is important to avoid putting the implant at risk for deep periprosthetic infection.
F. Stiffness
1. To prevent stiffness, it is critical to follow patients closely during the early postoperative period to determine whether further intervention, such as a manipulation under anesthesia, might be required.
2. Patient factors
a. Preoperative ROM
i. Body habitus
ii. Female
iii. Extreme varus
iv. Young
v. Limited intraoperative extension
b. Postoperative ROM
i. Patient compliance
ii. Pain tolerance
3. Technical factors
a. Postoperative ROM
i. Overstuffing the patellofemoral joint
ii. Mismatched gaps
iii. Inaccurate balancing
iv. Component malposition
v. Oversized components
vi. Joint line elevation
vii. Excessive tightening of the extensor mechanism at closure
b. Postoperative complications
i. Infection
ii. Delayed wound healing
iii. Hemarthrosis
iv. Component failure
v. Periprosthetic fracture
vi. Complex regional pain syndrome
vii. Heterotopic ossification (severe)
4. When patients present with <90° of motion in the first 6 weeks following surgery, manipulation should be considered if progressive improvement is not demonstrated.
a. This should be performed carefully because overly aggressive manipulation can result in fracture or injury to the extensor mechanism.
b. Manipulation is associated with greater risk and lower benefit when performed >3 months after surgery.
5. Late knee stiffness and a thrombosis may require open procedures, such as scar excision, quadricepsplasty, and even revision of components.
Top Testing Facts
1. Care should be taken to avoid placing the tibial component in internal rotation to avoid undesired increases in the Q angle.
2. The patellar component should be placed in a medial and superior position.
3. PCL failure should be considered in a well-functioning PCL-retaining TKA that starts to demonstrate instability, hyperextension, and recurrent effusion.
4. Correction of a gap-balancing mismatch requires equalization of the flexion and extension gap.
5. Successful cementless fixation requires adjunctive peripheral fixation (eg, pegs and screws).
6. Modes of failure in unicompartmental TKA include opposite compartment degeneration, component loosening, and polyethylene wear.
7. Excellent survival outcomes exist for cruciate-retaining and cruciate-substituting TKA designs.
8. The femoral component should be lateralized, parallel to the neutral rotational axis, and externally rotated 3° to 5° to the posterior condylar axis.
9. Patellofemoral arthroplasty should not be performed in patients with extensor mechanism maltracking or malalignment.
10. If a peroneal nerve palsy is suspected following TKA, the patient's leg should be immediately flexed and all compressive dressings should be removed.
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