Optimal exposure algorithm in revision total knee arthroplasty (RTKA)
2.2.1 Skin Incision
We must use the previous incision, avoiding close parallel incisions and skin bridges of >7 cm and an angle >60° to the old incision to avoid skin necrosis [1]. If there are multiple surgical scars, we will select the most recent scar, the one with the most lateral and vertical orientation (given the vascularization of the skin originates in the medial part of the knee). If there are fistulas, they should be removed together with the skin incision and all the way to the joint capsule.
If there are wide and immobile scars, a plastic surgery consultation is recommended. It is also important to note that the cutaneous blood supply travels from deep to superficial. Hence, a full thickness skin flap must be created and medial dissection performed in a subfascial plane, avoiding large lateral flaps. We use atraumatic retractors and avoid excessive skin retraction. Polyethylene extraction together with hyperflexion and external rotation of the knee also will decrease tension in the soft tissues. Additional skin techniques can be used with soft tissue expansion prior to RTKA [2].
2.2.2 Arthrotomy
We typically start with a long, standard medial parapatellar approach. A subvastus approach in RTKA is not recommended due to the difficulty of moving the patella laterally. After the arthrotomy, we perform a release of the intra-articular scar and synovectomy to increase knee flexion. We release the suprapatellar pouch and the medial and lateral gutters. We also release peripatellar adhesions and the upper edge of the anterior tibial tuberosity (TT). If there is significant tension in the patellar tendon, we perform an early lateral release from the inside out from the lateral aspect of the patella to the lateral aspect of the patella tendon to the TT. Patellar subluxation is usually adequate, and eversion is not needed; a surgical pitfall is to place a fixation pin in the medial insertion of the patellar tendon to prevent lateral avulsion. We perform an extensile medial tibial subperiosteal release (superficial medial collateral ligament, pes anserinus, posteromedial capsule, and semimembranosus insertion) to allow external rotation of the tibia and lateralization of the TT. If the extensor mechanism is adhered to the distal femur, a release is performed with complete elevation of the quadriceps mechanism. Avulsion of the patellar tendon can compromise knee function drastically and must be avoided; therefore, if tension persists, we will consider more extensile approaches to ensure adequate exposure.
2.2.3 Extensile Exposures
If the mobility of the knee is 70° or less, an extensile exposure is necessary. There are three classical techniques: proximal V-Y quadricepsplasty, quadriceps snip, and TT osteotomy (at the distal level).
The V-Y quadricepsplasty technique consists of sectioning the quadriceps tendon in an inverted V. Wound closure will be done in an inverted Y to lengthen the tendon and allow better flexion. Another alternative is the modified Insall technique, continuing the medial parapatellar incision of the quadriceps tendon in a 45° direction toward the superolateral angle of the patella. Patients often have an extensor lag that affects quadriceps strength and changes the postoperative rehabilitation protocol. There is a risk of avascular necrosis of the patella if we injure the superior lateral geniculate artery. Our preference is the quadriceps snip technique because it is quick, easy, and there is no need to modify the postoperative rehabilitation protocol. It consists of extending the medial parapatellar approach through the quadriceps tendon with an angle of 45° toward the vastus lateralis. It is performed from distal-medial to proximal-lateral. It is an easy technique and with similar results to the classical medial arthrotomy in terms of strength and postoperative range of motion [3].
TT osteotomy is another alternative in RTKA. We use it when adequate exposure is not achieved after a quadriceps snip, if access to the tibial intramedullary canal is needed to remove a long-stemmed cemented tibial component, or when there is arthrofibrosis or patella baja. Typically, the bone fragment must be long (at least 6 cm is recommended) with the coronal osteotomy made from the medial side. If it is very long, there is a risk of tibial diaphysis fracture, and if it is short, we may have fixation problems. Proximally, the thickness should be approximately 1 cm for exposure of a stiff knee tapering distally to approximately 5 mm; if performed to aid in removal of a long-stemmed cemented tibial component, it should be thicker to allow better access to the tibial canal. It can be performed with an osteotome or oscillating saw, leaving a lateral periosteal and soft tissue hinge. To avoid the risk of diaphyseal fracture, we can perform a distal osteotomy, and to avoid proximal migration of the fragment, we can perform a proximal osteotomy to create steps of about 5 mm of tibial bone between the osteotomy and the proximal tibia. The fragment can be fixed with wires (three small drill holes are made in the lateral aspect of the bony fragment and three holes in the medial tibia approximately 1 cm posterior to the edge of the osteotomy and slightly distal) or at least two screws (to avoid possible fracture of the osteotomy fragment and placed into the tibial cortex in a divergent manner to avoid the tibial stem).
The tibial stems should bypass the distal part of the osteotomy by at least 2 cortical diameters to reduce the risk of fracture.
(a) V-Y quadricepsplasty technique; (b) quadriceps snip technique; (c) lateral radiographs showing reduction of the tibial tuberosity (TT) osteotomy with wire fixation of the osteotomy fragment
Extensive femoral peel, complete subperiosteal peel of the femur, including origins of collateral ligaments.
Medial epicondylar osteotomy.
“Banana peel” patellar tendon off TT, leaving a lateral soft tissue hinge.
2.3 Component Removal
The position, rotation, and alignment of the components should be assessed before component removal, with any deficiencies addressed and improved afterward. Component removal should be preplanned in a systematic fashion to prevent complications.
The objective is implant removal with bone stock preservation (preserving the intact cortical rims), avoiding fractures or diaphyseal perforation and soft tissue (ligaments, tendons, and capsule) injuries.
Instruments required for interface disruption in revision total knee arthroplasty (RTKA)
Hand tools | Power tools |
|---|---|
Osteotomes set (flexible and rigid, straight, curved, and angled) | Oscillating saw (section polyethylene) |
Gigli saw | High speed burrs (section metal, intramedullary cement) |
Disimpaction punches | Drills and trephines |
Component extractors (universal and prosthesis specific) |
The technique to remove a TKA is more invasive when it is uncemented. The removal of constrained prostheses with intramedullary stems is more difficult than the removal of condylar implants. In general, both are more invasive for the femur than for the tibia. We must avoid damaging the underlying bone during component extraction.
2.3.1 Polyethylene
The surgeon must know which implant is in place and also its polyethylene block system, because manufacturer-specific tools for extraction may be required.
The polyethylene tibial insert is removed first to facilitate exposure of the TKA and the knee flexion. The removal of the polyethylene insert is usually easy and can be performed with the tip of a standard Hohmann retractor inserted between the polyethylene and the tibial component and pulling the polyethylene forward and upward.
To remove a monobloc or an all-polyethylene tibial component, it is separated from the tibial surface by sectioning the pegs or the stem.
2.3.2 Cemented Femoral Components
Cemented femoral components are rarely loose; aggressive maneuvers to remove well-fixed implants should be avoided due to the risk of iatrogenic femoral shaft fracture, condyle fracture, or bony avulsion.
We recommended circumferentially releasing the periphery of the distal femur to achieve adequate exposure and then proceed to remove the component. Initially, we divide the peripheral prothesis-cement interface with rigid osteotomes or an oscillating saw, always progressing to the central portions of the prothesis-cement interface parallel to the femoral component to avoid cutting into the bone. First, the anterior femoral component from medial to lateral and proximal to distal, later the anterior chamfer and the distal femur; an alternative is to use a Gigli saw inserted from the top of the trochlea and advanced distally to the box or the pegs. Then continue to the posterior chamfer and posterior condyle, taking care not to damage the collateral ligaments and soft tissues. Angled osteotomes are used to work from “inside out” in the femoral box.
Removal of the femoral component using direct impaction in the proximal part (a). Alternatively, a manufacturer-specific extractor may be used (b)
The femoral component’s undersurface is inspected to assess the amount of iatrogenic damage: (a) undersurface showing minimal bone loss; (b) undersurface showing significant bone loss
2.3.3 Cemented Tibial Components
The tibial component is next. Tibial exposure is improved by moving it anteriorly, externally rotating it and releasing of the semimembranosus and the posterior capsule. For safe removal, 360° exposure of the tibial component is necessary. Cemented tibial components are removed by using the same principles as the femoral component; osteotomes or an oscillating saw are used to cut beneath and parallel to the component, first on the anteromedial area and then on the posteromedial area, which is the most difficult. Then we advance around the keel or pegs. Later, we continue to the lateral side, which is more dangerous, taking care not to damage the patellar tendon. We must be careful in the posterolateral area to avoid bone stock loss during the removal. A Gigli saw can be used in the posterolateral area.
(a) Use a manufacturer-specific extractor to lift the baseplate off the tibial bone. Alternatively, try direct impaction under the anteromedial area of the implant, or use the “stacked osteotomes” technique. Finally, we remove the cement under direct vision (b)
2.3.4 Press-Fit Components
Removal of a porous-coated prosthesis can be difficult, especially when it has pegs designed for bone ingrowth. If the component cannot be removed with a specific or universal extractor, the union between the peg and the bone must be loosened. We can make a window in the femur (in the lateral walls of the intercondylar notch or in the condyles) and in the tibia (at a point as close as possible to the peg). Alternatively, we can use a microsagittal saw parallel to the tibial component to separate the metal backed from the pegs. It can be done freehand or using the tibial resection block with an extramedullary guide (maintaining the direction during the cut of the pegs). During metal cutting, the rest of the knee should be covered with compresses to prevent the introduction of metal debris, which could cause metallosis and/or synovitis.
2.3.5 Patellar Component
Patellar revision can be avoided if the patellar component is undamaged, well-fixed, well-positioned, and compatible with the revision implant and in cases of aseptic RTKA. Appropriate patellar tracking is paramount to a successful revision. The majority of patellar components are cemented all-polyethylene implants; we use the oscillating saw to cut between the cement and the component interface and section the peg-patellar component junction. The pegs and residual cement are then removed with a high-speed burr or a drill bit. Metal-backed and cementless components are more difficult to remove. A high-speed diamond-edged saw is then necessary. In order not to fracture the patella, lever movement of the component with osteotomes should be avoided.
2.3.6 Long-Stemmed Components
More and more often, revision prostheses are removed in which long stems have been used to achieve stability. We have learned the techniques of extraction of the stems from the extraction of femoral stems during revision total hip prostheses. In cases with a well-fixed stem component, we must make a window to liberate the stem using straight or curved osteotomes. At level of the femur, we create an anterior window using an oscillating saw or the combination of drill hole and an osteotome; the window must be 10–15 mm wide and almost as long as the stem. At the tibia, we will make a TT osteotomy. The window is then fixed with wires or metallic cables. To prevent a stress riser, it is necessary to bypass the osteotomy with a stemmed revision implant in which the stem extends beyond the window by at least 2 cortical diameters.
2.4 Joint Reconstruction
The goals of RTKA are the following: achieve good alignment, restore the joint stability, and achieve a well-balanced revision construct with optimal fixation and minimized constraint.
2.4.1 Balancing
The adjustments made on the femoral side can affect the knee in flexion or extension, whereas adjustments on the tibial side will affect both. Reconstruction is performed using a three-step method: (1) recreate the flat tibial surface, (2) recreate the femur and rebuild the flexion space, and (3) rebuild the extension space [5].
2.4.1.1 Recreate the Tibia
The first step is to build a tibial base to facilitate gap balancing, because any change on the tibial side affects the flexion and extension gaps. We must create a flat surface perpendicular to the mechanical axis. The flat tibial surface should be close to the original height of the tibia. Often, only one condyle is intact, and it will be used for referencing. Treatment of tibia bone loss depends on its severity and consists of cement, metal augmentation, modular cones, structural allograft, and proximal tibia replacement. To ensure the tibial component is in the proper rotation, we will use the TT and the anteromedial aspect of the tibia as reference points.
2.4.1.2 Recreate the Femur
The flexion gap should be evaluated. Femoral component sizing influences the flexion space by restoring the anteroposterior (AP) dimensions and the posterior condylar offset of the femur. Assess the femoral size from previous procedures or use the opposite side as a template. Posterior bone loss occurs almost always, so templating intraoperatively runs the risk of undersizing the femoral component. The epicondylar width of the femur also helps us select the appropriate femoral size. If we select an excessively small femoral component, there will be a failure to restore the posterior femoral offset, and it will compromise flexion stability. In general, in RTKA there is an asymmetric flexion gap, so an oversized femoral component can be used to balance the knee. Correct rotation of the femoral component is important for knee kinematics and patellar tracking. We determine the rotation with the transepicondylar axis. Generally, there is bone loss in the posterolateral condyle that requires augmentation to achieve correct rotation of the femoral component. In case of severe bone loss affecting the epicondyle, the tibial platform is used as a reference point for the rotation of the femoral component with the knee at 90° flexion.
2.4.1.3 Rebuild the Extension Gap
Next, the knee should be brought to full extension to evaluate the extension gap. The distal femur position is key to restoring the distance from the joint line, distally and posteriorly. The distance from the epicondyles to the posterior joint line is similar to that of the distal joint line and is useful to confirm the correct size of the femoral component. It is important to restore the natural joint line in revision surgery, because the joint line is always more distal than it first appears.
There are various landmarks that can be used intraoperatively to assess whether the distal joint line has been restored: a prior meniscal scar, an average of 15 mm proximal to the fibular head, 25 mm from the lateral epicondyle, and 30 mm from the medial epicondyle and 32 mm proximal to the TT.
Elevation of the joint line occurs when the bone lost from the distal femur is not reconstructed and the defect is addressed by thickening the tibial insert. Use a thicker polyethylene than in primary TKA only if you have removed more bone from the tibia; in most cases, the polyethylene thickness should be between 10 and 15 mm. Polyethylene >15 mm correlates significantly with joint line elevation, worsens the clinical outcome, and reminds us that thicker distal femoral augments, instead of thicker polyethylene inserts, should be used to restore the defects and the joint line [6]. Flexion and extension gaps must be equal and symmetric. We must release tight structures in the concavity.
2.4.2 Management of Bone Loss
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