Indications

• Proper rotational alignment of the prosthetic components is an important factor to achieve successful functional outcome and durability in total knee arthroplasty (TKA).

• It has been suggested that the most common cause of revision TKA is error in surgical technique.

• Small changes in component positioning can lead to substantially worse postoperative performance.

• Malrotation of the femoral and/or tibial component has been associated with complications including:

  • Patellar tilt, subluxation, fracture, accelerated wear, and loosening.

  • Altered kinematics leading to accelerated topside polyethylene wear, post wear on posterior-stabilized designs, and backside wear.

  • Laxity or stiffness secondary to imbalanced flexion and extension gaps.

    Treatment Options

    • Several methods of rotational alignment for the femoral and tibial components are frequently used during TKA, often in combination.

    • Femoral component techniques:

      • Whiteside’s line (the transtrochlear axis or anteroposterior axis)

      • The transepicondylar axis

      • Three degrees of external rotation off the posterior condyles

      • Soft tissue tensioning to yield flexion gap symmetry

    • Tibial component techniques:

      • Anatomic (used with an asymmetric tray)

      • Relative to the posterior tibial cortex

      • Relative to the junction between the medial and central third of the tibial tubercle

      • Relative to the femoral component rotation with the knee in full extension

    • Computer navigation assistance to determine femoral and tibial rotation based upon landmarks for mechanical and rotational axes.

     

    Examination/Imaging

• Assessment of overall limb alignment can assist with anticipating potential difficulties in obtaining proper rotational position of components intraoperatively.

  • Severe varus or valgus alignment may indicate bony deficiencies that can alter landmarks for rotation on both the femoral and tibial sides of the joint.

  • Collateral ligament laxity or tightness may affect flexion and extension gaps, requiring soft tissue release and/or adjustment of component rotation to compensate for soft tissue imbalance.

• Full-length standing films allow for preoperative templating of the mechanical axis of the femur and tibia. This allows for anticipation of the relative proportion of medial and lateral bone cuts in extension to attain a neutral mechanical axis (Fig. 1A and 1B).

  • A decreased amount of distal lateral femoral condyle will be cut with a valgus alignment to attain a neutral (90°) mechanical axis (see Fig. 1A).

  • A decreased amount of medial tibial plateau will be cut with a varus knee to establish a neutral (90°) mechanical axis for the tibia (see Fig. 1B).

     

    Methods of Rotational Alignment

     

     

     

     

     

    55

     

    A

     

    B

    FIGURE 1

     

     

    Methods of Rotational Alignment

     

  • The distal femoral condyles will be cut without a “bridge” of bone from the trochlea on the valgus knee because of the lateral condylar and trochlear deficiency. The distal femoral condylar cuts on the varus knee will have connecting bone from the trochlea.

• Full-length standing films allow for templating based upon the mechanical axis from the center of the femoral head and the center of the ankle. Using the anatomic axis on short-knee films introduces increased error in measurement due to parallax.

• A standing posteroanterior Rosenberg view (taken at 45° of knee flexion), when compared with traditional standing views of bilateral knees, can help identify hypoplastic posterior femoral condyles, particularly in valgus knees (Fig. 2A and 2B).

   

   

   

   

  56

   

  A

   

   

   

  B

  FIGURE 2

   

   

  P EARLS

  • Placing the footrest at the widest part of the gastrocnemius muscle will usually be the optimal level.

     

  • For stiff knees that flex less than 90°, the footrest should be placed in its usual position to allow for foot support after the knee flexes following quadriceps mechanism mobilization and soft tissue release.

   

  Methods of Rotational Alignment

   

  Surgical Anatomy

  • See “Portals/Exposures.”

    Positioning

  • Supine positioning on a standard, level operating table.

  • A footrest placed at the proximal third of the tibia will allow for controlled, sustained flexion of approximately 90–100° (Fig. 3A). When the knee is hyperflexed, the footrest will prevent the foot from sliding down the table (Fig. 3B).

  • A bump can be placed under the greater trochanter of the ipsilateral hip to maintain the leg in neutral rotation during the surgery.

   

   

   

   

  57

   

  A

   

   

   

  B

  FIGURE 3

   

   

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  Methods of Rotational Alignment

   

  FIGURE 4

   

   

  P ITFALLS

  • A trochanteric bump that is too large will internally rotate the leg in flexion and extension, which can lead to erroneous assessment of rotation.

   

  • Alternatively, a side post can be placed at the level of the tourniquet to maintain the leg in neutral rotation, as well as support the leg while flexed. This can assist during visualization of the distal femoral rotation or tibial shaft from the end of the table without requiring an assistant, as well as with positioning the leg reproducibly with repeated flexion and extension (Fig. 4).

    Portals/Exposures

  • Many surgical exposures exist for TKA, including the medial parapatellar, midvastus, and subvastus, depending on the position of the arthrotomy.

  • Full-size, or standard, exposures allow for better visualization of landmarks that are traditionally used to determine femoral and tibial rotation.

  • For the femoral side, these include (Fig. 5A and 5B):

    • Anterior femoral trochlear sulcus or patellar groove

    • Medial and lateral epicondyles

    • Posterior femoral condyles

  • For the tibial side, these include (Fig. 6A and 6B):

    • Tibial tubercle: junction of medial and central thirds

    • Patellar tendon edge

    • Posterior tibial cortex

• Limited or minimally invasive exposures can limit visualization of many of these landmarks and can present challenges for proper component positioning (Fig. 7).

• Patellar eversion versus subluxation can also limit visualization.

Lateral epicondylar

Posterior femoral condyles

prominence Patellar groove Medial sulcus

Methods of Rotational Alignment

A B

FIGURE 5

Junction of central and medial third of tibial tubercle

Border of patellar tendon

Medial border of tibial tubercle

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A B

FIGURE 6

FIGURE 7

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Methods of Rotational Alignment

Procedure 1: Determining Proper Femoral Component Rotational Alignment

• At least four ways have been proposed to determine proper femoral component rotational alignment.

  • Whiteside’s line (the transtrochlear axis or anteroposterior axis)

     

    P EARLS

    • Rationale for empirical 3° of external rotation:

       

      • Neutral femoral rotational alignment and a 3° varus tibial cut (anatomic) results in a symmetric flexion gap.

         

      • Neutral femoral rotational alignment and a neutral (90°) tibial cut results in an asymmetric flexion gap that is tight medially.

         

      • Three degrees of external rotation of the femoral component alignment results in restoration of a symmetric flexion gap.

     

  • The transepicondylar axis

  • Three degrees of external rotation off the posterior condyles

  • Soft tissue tensioning to yield flexion gap symmetry

    Method 1

• After adequate exposure, the deepest part of the patellar trochlear groove is identified and marked with the electrocautery or a marking pen.

  • Commercial tools are available to mark a perpendicular line, delineating the true anteroposterior (AP) axis (Whiteside’s line) (Fig. 8).

  • The AP axis based on Whiteside’s line has been shown to consistently approximate 4° of external rotation relative to the posterior condylar surfaces.

• The surgical transepicondylar axis is identified and marked by drawing a line to connect the lateral epicondylar prominence and the sulcus of the medial epicondyle (Fig. 9; see also Fig. 5A).

  Instrumentation/ Implantation

  • Different alignment jigs have different capabilities and mechanisms for setting the cutting guide to the proper amount of external rotation. Anticipation of variability in the bony anatomy based upon the preoperative deformity will allow for proper adjustment unique to each system to create a symmetric flexion gap.

   

  • The transepicondylar axis is usually parallel to

    Whiteside’s line.

     

• The sizing and rotational alignment jig is placed. In this system, the rotational reference is based on the posterior condylar axis of the posterior condyles, so care must be taken to anticipate malrotation based upon bony deformity.

  • Varus knees with preoperative tibia vara often have a relatively elongated medial femoral condyle, which will place the jig into too much internal rotation. To adjust for this, any remaining cartilage can be removed from the medial posterior condylar surface (Fig. 10).

     

     

     

     

     

    Methods of Rotational Alignment

     

     

     

     

     

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    FIGURE 8

     

    FIGURE 9

     

    FIGURE 10

     

     

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    Controversies

    • Studies comparing these different techniques show each have advantages and disadvantages for accurate and reproducible femoral component rotation. One study suggests any single method carries at least a 10% chance of creating a flexion space asymmetry. If possible, more than one of these techniques should be used simultaneously to minimize malrotation.

     

    Methods of Rotational Alignment

     

  • Valgus knees often have a relatively hypoplastic lateral femoral condyle, which will also place the jig into too much internal rotation. To adjust for this, the jig can be placed in “extra” external rotation, leaving the lateral foot of the jig off of the lateral posterior condyle by 1–2 mm (Fig. 11).

• The jig is adjusted for the proper-size femur, and the pins are placed in 3° of external rotation empirically (upper hole medially, lower hole laterally) (Fig. 12).

• The jig is removed and the position of the pins is examined relative to the marked AP axis line and transepicondylar axis line. In this case, anticipation and adjustment for too much internal rotation based on the posterior condylar axis was correct, and the pins are exactly on the line (Fig. 13).

  Method 2

• Soft tissue tension must be taken into consideration when assessing flexion gap symmetry.

  • Bone cuts based upon anatomic landmarks such as the transepicondylar axis or Whiteside’s line are approximations based upon reproducible bony anatomy. They do not take into consideration differences between medial and lateral ligament tension.

  • Lateral or medial joint laxity can be addressed either by adjusting the rotation of the bone cuts or by soft tissue releases.

• Two laminar spreaders are placed medially and laterally at equal tension to open the flexion space based upon the relative soft tissue tightness of both compartments.

• The extramedullary tibial alignment guide is used to assess for ligament tension relative to the position of femoral rotation by elevating it to the level of the femoral pins (Fig. 14).

   

   

   

   

   

  Methods of Rotational Alignment

   

  Lateral foot of jig with

  gap to increase external rotation

   

  FIGURE 11

   

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  FIGURE 12

   

   

   

  FIGURE 13 FIGURE 14

   

   

  P EARLS

  • A navicular gouge works well to adjust the pinhole positions. It can be tapped into the new location and will displace the bone from the new position to fill the defect at the original pinhole (see Fig. 16B).

     

    P ITFALLS

  • When using the tibial extramedullary cutting guide to assess the flexion gap symmetry on the femur, care should be taken to set the guide to the same position in which it will be used to cut the tibia. If changes are made and the tibia is cut in more varus or valgus, an asymmetric flexion gap will result.

  • If the femoral component is flush with the anterior cortex, care must be taken when lowering the lateral pinhole to create more external rotation, as this can cause the anterior cortex to be notched.

   

  Methods of Rotational Alignment

   

• The position of the pins is examined relative to the tibial cutting guide (Fig. 15A and 15B).

  • The placement of the pins based upon bony landmarks is internally rotated when the soft tissues are tensioned (see Fig. 15A).

• The rotation of the femoral cutting guide can be adjusted by moving the medial pinhole upward or the lateral pinhole downward (Fig. 16A and 16B).

  • For varus knees, the medial pinhole is usually moved upward to loosen a tight medial flexion space.

  • For valgus knees, the lateral pinhole is usually moved downward to tighten the lateral flexion space due to the hypoplastic lateral condyle.

     

     

     

    64

     

     

    P ITFALLS

    • Because the tibia is cut first, and the flexion gap is based upon the tibial cut, error in varus or valgus will propagate to error in femoral rotation. Care must be taken to make a correct neutral tibial cut before the flexion space is established.

     

    A Note internal rotation

     

    Lateral

    of pinholes relative to tibial alignment guide

     

    Medial

    B

     

     

    FIGURE 15

     

     

     

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    Methods of Rotational Alignment

     

    A

     

     

     

    Lateral

     

    Navicular gouge elevating medial hole to increase external rotation

     

    Medial

     

     

    B

    FIGURE 16

    Transepicondylar axis

     

     

    • Adjusting the femoral cutting guide rotation based upon tissue tension will decrease the amount of soft tissue release necessary to balance the flexion gap. However, the femoral rotation may often be closer to 5–7° of external rotation relative to the posterior condylar axis (see Fig. 16A).

       

      66

       

      Methods of Rotational Alignment

       

      Method 3

• With many muscle-sparing or minimally invasive exposures, the techniques above can be difficult to apply, given less exposure of landmarks and less room for placement of alignment jigs (see Fig. 7).

• A balanced gap technique with a tensiometer can be used to adjust for femoral rotation and gap symmetry given less bony exposure.

  • This technique is similar in theory to the use of laminar spreaders to create a symmetric, soft tissue–balanced flexion gap.

• The distal femoral cut and tibial cut are made in standard fashion to establish the extension gap and neutral mechanical axis.

  • A block spacer can be used to measure the extension gap (Fig. 17).

• The tensiometer is then applied in flexion. The tension is increased in the medial and lateral compartments until equal tension is measured for a symmetric flexion gap (Fig. 18A and 18B). Note the increased excursion in the lateral compartment to attain the same tension as the medial compartment. This will effectively increase the external rotation of the femoral component to create a symmetric flexion gap based upon the soft tissue tension.

• The tensiometer allows placement of a cutting jig adjusted to create a flexion space equal to the size of the spacer block placed in extension, independent of the rotation of the femoral cuts. This will create equal, rectangular flexion and extension gaps.

   

  P EARLS

  • If the tibial guide is pinned in place with zero posterior slope, and then the posterior slope is added, tension is created at the pin-jig interface, which adds stability to the jig while cutting.

     

  • The tibial guide is usually set to engage the ankle 3–6 mm medial of center, as the center of the talus is usually medial to the line bisecting the distance between the malleoli. This will align the extramedullary guide with the tibial shaft and prevent a varus tibial cut.

   

  Procedure 2: Determining Proper Tibial Component Rotational Alignment

• Several ways have been proposed to determine proper rotational alignment for the tibial component:

  • Anatomic (used with an asymmetric tray)

  • Relative to the posterior tibial cortex

  • Relative to the junction between the medial and central third of the tibial tubercle

  • Relative to the femoral component rotation with the knee in full extension

• After obtaining sufficient exposure, the tibial tubercle is identified and marked at the junction of the medial and central third (see Fig. 6B).

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Methods of Rotational Alignment

FIGURE 17

Transepicondylar axis

Lateral collateral ligament

Increased external rotation based on tensiometer relative to

anatomic axes

Lateral (fibula)

Whiteside line

Medial collateral ligament

Level of tibial plateau

Medial (tibia)

Same tension

A B

FIGURE 18

68

• With a symmetric baseplate design, if the tibia is properly sized and externally rotated, the posterolateral tibial plateau should be entirely covered by the tibial baseplate. The posteromedial plateau will often be slightly uncovered, and the anteromedial cortex should be congruent with the edge of the baseplate (no overhang) (see Fig. 22).

   

  P ITFALLS

• When the tibial guide is set to cut the posterior slope, it is important to maintain the proper rotation centered on the tibia. If the guide is rotated externally, the slope will be cut posteromedially. If the guide is rotated internally, the slope will be cut posterolaterally. This will create a varus or valgus malalignment, respectively.

Methods of Rotational Alignment

• The extramedullary tibial guide is set to make a neutral cut (perpendicular to the tibial shaft), and pinned in place centered on the mark (Fig. 19).

• After the trial components have been placed, including proper femoral rotational alignment, the knee is brought into extension. With the handle attached to the tibial trial component, the tibial plate is rotated to match the rotation of the femoral component, maintaining the patient’s foot in a neutral position (Fig. 20).

• The handle is then removed, and the position is marked on the tibia (Fig. 21).

• The trial components are removed and the knee is then flexed. The tray is placed at the marked position and pinned (Fig. 22).

  • The position of the tray relative to the tibial tubercle can be examined at this point. The tray will usually be centered at the junction of the medial and central third of the tibial tubercle.

• The overall position of the tibial tray should not be internally rotated relative to the tibial tubercle.

  • This can cause increased stresses at the component-polyethylene interfaces, particularly in conforming designs.

  • With increased lateral positioning of the tibial tubercle, the Q angle will be increased, leading to patellofemoral complications.

• Tibial components that have a rotating platform (RP) can theoretically allow more flexibility when placing the tibial baseplate.

  • The rotating polyethylene adjusts for any rotational mismatch between the tibial baseplate and the femur by rotating to match the femoral rotation.

  • This decompresses stresses encountered by conforming, malrotated, fixed-bearing components.

  • This allows more freedom to maximize the tibial bone coverage with the metal plate through rotation.

  • If the rotation of an RP tibial baseplate is placed appropriately, the polyethylene may not rotate much. However, patients with altered anatomy may benefit from the rotational capability of the RP tibial components.

  • In Figure 23, a tibial baseplate has been placed at the medial third of the tibial tubercle, but with approximately 10° of rotation between the baseplate and polyethylene.

   

   

   

  69

   

   

   

  Methods of Rotational Alignment

   

  FIGURE 20

  FIGURE 19

   

   

   

  FIGURE 21 FIGURE 22

   

   

   

  FIGURE 23

   

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  Methods of Rotational Alignment

   

  Postoperative Care and Expected Outcomes

• Proper rotation of the femoral and tibial components is important for successful outcome in TKA.

• Function and durability can be related to proper surgical technique, particularly with regard to the placement of the components.

• Many techniques exist to determine proper component position, each with advantages and disadvantages.

• Use of multiple techniques based upon the patient anatomy, surgical approach, and specifics of the implant design will help minimize component malposition.

Evidence

Akagi M, Mori S, Nishimura S, Nishimura A, Asano T, Hamanishi C. Variability of extraarticular tibial rotation references for total knee arthroplasty. Clin Orthop Relat Res. 2005;(436):172-6.

This study compared the variability of the tibial AP axis with the variability of the transmalleolar axis and the second metatarsus bone axis for extra-articular rotational reference axes of the tibia. A new technique of determining the tibial AP axis by a line from the middle of the posterior cruciate ligament and the medial edge of the patellar tendon is described.

Arima J, Whiteside LA, McCarthy DS, White SE. Femoral rotational alignment based on the anteroposterior axis in total knee arthroplasty in a valgus knee. J Bone Joint Surg Am. 1995;77:1331-4.

This study compared the interobserver reliability for identification of the AP axis, the posterior condylar axis, and the transepicondylar axis in 30 cadaveric femora. The AP axis consistently approximated 4° of external rotation relative to the posterior condylar surfaces.

Berger RA, Rubash HE, Seel MJ, Thompson WH, Crossett LS. Determining the rotational alignment of the femoral component in total knee arthroplasty using the epicondylar axis. Clin Orthop Relat Res. 1993;(286):40-7.

This study examined 75 cadaveric femora to define the surgical epicondylar axis as the line connecting the lateral epicondylar prominence and the medial sulcus of the medial epicondyle. The posterior condylar angle was defined as the angle subtended by the surgical epicondylar axis and the posterior condylar line.

Huddleston JI, Scott RD, Wimberley DW. Determination of neutral tibial rotational alignment in rotating platform TKA. Clin Orthop Relat Res. 2005;(440):101-6.

This study quantified rotational alignment in 109 primary rotating platform TKAs. Five percent of patients had a neutral tibial axis with a mean divergence of greater than 10° from the medial border of the tibial tubercle. (Level II-3 evidence [diagnostic study])

Katz MA, Beck TD, Sliber JS, Seldes RM, Lotke PA. Determining femoral rotational alignment in total knee arthroplasty: reliability of techniques. J Arthroplasty 2001;16:301-5.

This study examined the reliability of identification of the transepicondylar axis, AP axis, and balanced flexion gap tension line in eight fresh frozen cadaver knees by three independent observers. The balanced flexion gap technique showed more accuracy and reliability in determining femoral rotational alignment in relationship to the flexion-extension axis.

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Methods of Rotational Alignment

Miller MC, Berger RA, Petrella AJ, Karmas A, Rubash HE. Optimizing femoral component rotation in total knee arthroplasty. Clin Orthop Relat Res.

2001;(392):38-45.

This study examined three-dimensional kinematics of TKAs performed in 11 cadaveric knees using a multiaxial transducer and Oxford knee simulator. Femoral component rotation parallel to the epicondylar axis resulted in the most normal patellar tracking and minimized tibiofemoral wear motion and instability.

Olcott CW, Scott RD. A comparison of 4 intraoperative methods to determine femoral component rotation during total knee arthroplasty. J Arthroplasty 2000;15:22-6.

This study examined the femoral alignment necessary to create a rectangular flexion in 100 TKAs. The transepicondylar axis most consistently re-created a balanced flexion space. However, any single method carried a 10% chance of creating a flexion space asymmetry.

Siston RA, Patel JJ, Goodman SB, Delp SL, Giori NJ. The variability of femoral rotational alignment in total knee arthroplasty. J Bone Joint Surg Am. 2005;87:2276-80.

This study examined the variability of five alignment techniques, including one computer-assisted technique, to determine femoral rotational alignment in 10 cadeveric specimens. No technique was identified as superior to the others, including the computer navigation system.

Siston RA, Goodman SB, Patel JJ, Delp SL, Giori NJ. The high variability of tibial rotational alignment in total knee arthroplasty. Clin Orthop Relat Res.

2006;(452):65-9.

This study evaluated the precision of computer-assisted rotational alignment techniques for tibial component alignment by 11 surgeons in 10 cadaveric specimens. Navigation systems that establish rotational alignment by identifying anatomic landmarks were not more reliable than traditional instrumentation. (Level I evidence [diagnostic study])

Whiteside LA, Arima J. The anteroposterior axis for femoral rotational alignment in valgus total knee arthroplasty. Clin Orthop Relat Res. 1995;(321):168-72.

This study compared 46 valgus TKAs using the posterior femoral condyles as landmarks for rotational alignment with 107 valgus TKAs using the AP axis for alignment. The rates of tibial tubercle osteotomy and late patellar instability were significantly greater in the posterior femoral condylar axis group.