**9. Consideration about surgical technique**

We think that to improve an already successful procedure, as TKR was well demonstrated to be, we need to look at small details.

In the debate between PS versus CR-TKR, the main reason in favor of PCL sacrifice is that balancing a joint with an intact PCL could be very difficult, especially in case of drastic deformities as severe fixed flexion, varus or valgus angulations more than 20° or considerable joint subluxation: but in these cases, we think that probably PS implant is not the solution since should be preferable the use of a more constrained implant.

We think that the ability of the surgeon is critical to obtain a good CR replacement; technical difficulties lead to a longer learning curve, but using some tips and having cleared all basic science considerations explored in the previous paragraphs, you can achieve good results even in the most difficult cases.

Taking these points into account, the first element to consider is that the goal of the procedure is both to place the TKA in neutral mechanical alignment and to obtain a knee stable in all range of movement. In CR-TKR, the main criticism of the process is the preservation of the PCL and consequent balance of the spaces.

Performing a CR-TKR, the main criticism of the surgical technique is that the distal attachment of the PCL is vulnerable to injury during the tibial resection; the distal attachment of the PCL is located posterior and distal to the tibial plateau, so the application of a protective device on the front is really useful to safeguard it; however, excessive bone resection from the proximal tibia (i.e., greater than 1 cm) or a large posteriorly sloped cut may anyway jeopardize the tibial attachment of the PCL and it has been demonstrated that a pin of minimum 1.7 mm of length ensures a larger margin of safety [25]. In addition, the creation of a bone island with the incision of the posterior cortex is really useful to avoid the avulsion of the ligament during the removal of the plateau.

The second element is that in order to accurately balance the joint, the surgeon can remove less bone from the distal femur (typically matching the thickness of the femoral implant which should be chosen to reproduce the A-P size of the back of native femoral condyles) in comparison to what would be done for a PS TKR (**Figure 7**); due to the retention of the PCL in a CR-TKR, the flexion gap will remain smaller (in a range of 1.8–4.8 mm) than what would be created for a PS implant; therefore, the goal is to keep the extension gap small as well [15].

The third element is about the slope of the tibial cut: posterior slope opens the flexion space and this helps to obtain flexion without PCL recession. Therefore, a modest posterior slope (typically matching the patient's native slope within the range of 3–7°) may help to reduce tension on the PCL and this may facilitate knee flexion. If the extension gap is asymmetrical, it is necessary to perform a ligamentous release in order to obtain a symmetric space, and the gap size finally should be verified with a spacer block. Reflecting on the solution to achieve a symmetrical space in the flexion gap, it is really important to consider what type of instrument we are using: if we get the restoration of a neutral mechanical alignment in extension through the use of an intramedullary device for the femur and an external guide for the tibia, in our experience, the best instrument that helps us to get the correct rotation of femur in flexion is the flexion spacer by Biomet; in fact, it is always referred to the tibial osteotomy (that regardless of surgeon accuracy should be 1° or 2° in valgus or varus deviation) and allows us to reach a parallel cut even in case of a severe lateral condyle hypoplasia thanks to its multiple choice in asymmetrical components (1°, 3°, 4°, 5°, 6°, 8°). Once rotation is obtained, the following step is to determine the depth of the flexion gap. Not only does the flexion gap need to be rectangular (indication of rotation), but it also needs to obtain the same size of the extension gap. Through the use of the flexion spacer, the normal posterior condyle offset is recreated. Then, the depth of the anterior cut is not measured directly but rather determined by the size of the 4-in-1 cutting jig; it may be too shallow (this will cause overstuffing of the patellofemoral joint) or it may be too deep (this will cause notching) [26].

When the desired balancing and gaps are achieved, the femoral, tibial, and insert trial components of the correct size are inserted; we check the maximum extension and flexion and then stability and the patellar tracking in the full range of movement; usually, we do not perform

Once the tibial stem hole is created and the preparation procedure is completed, we perform a wash of the joint and then insert definitive cemented components and the polyethylene bear-

We think that to improve an already successful procedure, as TKR was well demonstrated to

In the debate between PS versus CR-TKR, the main reason in favor of PCL sacrifice is that balancing a joint with an intact PCL could be very difficult, especially in case of drastic deformities as severe fixed flexion, varus or valgus angulations more than 20° or considerable joint subluxation: but in these cases, we think that probably PS implant is not the solution since

We think that the ability of the surgeon is critical to obtain a good CR replacement; technical difficulties lead to a longer learning curve, but using some tips and having cleared all basic science considerations explored in the previous paragraphs, you can achieve good results

Taking these points into account, the first element to consider is that the goal of the procedure is both to place the TKA in neutral mechanical alignment and to obtain a knee stable in all range of movement. In CR-TKR, the main criticism of the process is the preservation of the

Performing a CR-TKR, the main criticism of the surgical technique is that the distal attachment of the PCL is vulnerable to injury during the tibial resection; the distal attachment of the PCL is located posterior and distal to the tibial plateau, so the application of a protective device on the front is really useful to safeguard it; however, excessive bone resection from the proximal tibia (i.e., greater than 1 cm) or a large posteriorly sloped cut may anyway jeopardize the tibial attachment of the PCL and it has been demonstrated that a pin of minimum 1.7 mm of length ensures a larger margin of safety [25]. In addition, the creation of a bone island with the incision of the posterior cortex is really useful to avoid the avulsion of the liga-

The second element is that in order to accurately balance the joint, the surgeon can remove less bone from the distal femur (typically matching the thickness of the femoral implant which should be chosen to reproduce the A-P size of the back of native femoral condyles) in comparison to what would be done for a PS TKR (**Figure 7**); due to the retention of the PCL in a CR-TKR, the flexion gap will remain smaller (in a range of 1.8–4.8 mm) than what would be created for a PS implant; therefore, the goal is to keep the extension gap small as well [15].

patellar resurfacing [24] but just remove osteophytes.

**9. Consideration about surgical technique**

should be preferable the use of a more constrained implant.

ing of the previously evaluated size.

34 Primary Total Knee Arthroplasty

be, we need to look at small details.

even in the most difficult cases.

PCL and consequent balance of the spaces.

ment during the removal of the plateau.

Nevertheless, problems can occur once that bone cuts are performed and trial components are inserted.

A slightly lax PCL is preferable to one that is excessively tight, but an overly lax PCL can result in functional disability secondary to flexion instability. Balance of the PCL should be assessed after correction of any varus or valgus ligamentous imbalance. An excessively tight PCL will result in anterior translation of the tibia from beneath the femur, anterior lift-off of the trial polyethylene from the tibia tray in flexion, and/or displacement of the femoral component in flexion. A useful test of the relative balance of the PCL is the so-called POLO (for PullOut, LiftOff) test introduced by Dr. Richard Scott. In this test, a trial reduction is done with a stemless tibial trial and a curved tibial insert. The PullOut portion of the test is done at 90° of flexion and confirms that the PCL is not too loose if the tibial insert cannot be subluxed (pulled out) anteriorly from beneath the femur. The LiftOff portion is done while putting the knee through a range of motion up to 120° and ensuring that the tibial insert does not look open (lift-off) in flexion, indicating that the PCL is too tight. Scott postulates that if the PCL is not too loose and not too tight, then it must be just right [1].

If the PCL is excessively tight, the tension can be decreased by several techniques. Increased tibial bone resection is only appropriate if the knee is tight in both flexion and extension. If the knee is tight only in flexion, increasing tibial bone resection will leave the knee lax in extension, resulting in symptomatic instability due to hyperextension or excessive varus-valgus play. If the knee is tight only in flexion, the posterior slope of the tibial cut should be assessed. The tibia normally has a 3 to 7°degree posterior slope. The amount of posterior slope cut on the tibia will be dependent on the prosthetic design. Some implants have an inherent posterior slope in the articular geometry and will require less posterior slope than knees with a flat geometry in the sagittal plane. Increasing posterior slope for the tibial resection will relax the PCL. Posterior tibial slope typically should not exceed 10° to avoid risk of injury to the tibial attachment of the PCL. Posterior cruciate recession consists of selective release of the anterior fibers of the PCL from their tibial attachment. Release of the anterior 10–20% of the PCL can often help achieve the correct soft tissue balance. If greater than 75% of the PCL is released, some feel a PCL-substituting prosthesis should be considered. The concern in those cases is that the remaining 25% of the PCL fibers may rupture later with activity, leading to flexion instability. If the PCL is released or absent, the tibial tray should be more conforming because rollback does not occur. Hence, the surgeon should match the constraints of the soft tissue with the inherent constraints of the knee system being used [1].

A knee that is tighter in flexion requires one or a combination of maneuvers that include PCL release, downsloping the tibial resection, downsizing the femoral component, or additional tibial resection with distal advancement of the femoral component. A knee that is tighter in extension is usually corrected merely by added distal femoral resection [1].
