RECONSTRUCTION 2023, Jan, 08 | 12:00 am

Tibial Component Alignment in Total Knee Arthroplasty: Intramedullary, Extramedullary, and Computer-Assisted Techniques

P ITFALLS

  • Results of each type of alignment are technique dependent, and familiarity with each will reduce component malposition. Each alignment technique has its own apparent pitfalls that must be recognized and compensated for during the procedure. Failure to realize these contraindications can result in postoperative alignment of greater than 3° of varus and valgus, which can lead to early failure of the knee replacement.

 

Tibial Component Alignment

 

Indications

  • Generally, patients requiring total knee arthroplasty have end-stage degenerative changes of the knee with subsequent intra- and/or extra-articular associated deformities.

  • Depending upon the deformity, there may be better indications for each of the different methods that can be utilized for obtaining proper tibial alignment: intramedullary, extramedullary and computer-assisted techniques.

    • Intramedullary indications: patients requiring stemmed components due to poor bone quality, severe bone loss necessitating stem support, or revision procedures requiring stems and augments with minimal extra-articular deformity.

      Controversies

      • Classically, intramedullary and extramedullary alignment both have had strong proponents. More recently, computer-assisted surgery has caused controversy about its merits. Principally, the question is whether the computer is accurate enough to justify the extra time required in surgery to merit its use. There are also concerns regarding extra holes placed in the tibia for the reference bases causing stress risers after surgery and subsequent periprosthetic fracture.

      • Transverse plane alignment of the tibial component has not been well described anatomically, and many

      described techniques exist with limited evidence basis.

       

    • Extramedullary indications: congenital, surgical, or posttraumatic deformity of the tibia in which use of intramedullary alignment rods may lead to tibial component malposition.

    • Computer-assisted indications: subject to availability of computer and related targeting equipment: correction of complex posttraumatic or postsurgical deformity, extra-articular deformity, or existing hardware making intramedullary alignment difficult.

  • All techniques may be used for primary total knee arthroplasty, where deformity or anatomic abnormality does not interfere with their use. Ultimately the surgeon should use the technique he or she finds most familiar and reproducible.

    Examination/Imaging

    Physical Examination

  • Limb deformity: is the knee in varus or valgus?

    • Location of the principle deformity: tibial or femoral sided?

    • Origin of the tibial deformity: intra-articular or extra-articular?

  • Flexion limit: less motion increases the difficulty of the exposure.

  • Extension limit: fixed flexion contracture or genu recurvatum?

  • Characteristics observed during the physical examination can then be verified by radiographic examination.

     

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    Tibial Component Alignment

     

    Radiographic Examination

    • Anteroposterior (Fig. 1A) and lateral (Fig. 1B) knee radiographs can identify deformity and hardware issues that may preclude certain tibial alignment techniques in the operating room.

    • A long-leg standing radiograph is taken to accurately determine deformity and whether it is intra- or extra-articular (Fig. 2). This aids in

      appreciating extra-articular deformity, which may preclude certain alignment techniques, and can aid in confirming an entry point for intramedullary instrumentation.

    • A lateral full-length tibial radiograph can be obtained if multiplanar deformity is present or suspected.

       

       

       

       

       

       

      A B

      FIGURE 1

       

       

      FIGURE 2

       

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      Tibial Component Alignment

       

      Surgical Anatomy

      • The tibial tubercle is the landmark utilized for transverse plane placement of the tibial baseplate (Fig. 3A).

    • Most implant systems and surgeons utilize the medial third of the tibial tubercle for a rotational landmark of the tibial baseplate.

    • Some surgeons use a free-floating technique in which the trial baseplate is free to rotate during trial component placement and, with the knee in full extension, the position of the baseplate is marked to re-create the foot progression angle.

      • The anterior tibial crest is utilized as a landmark during the extra-medullary alignment technique to make sure the alignment rod coincides with this landmark in the coronal plane and parallels it in the sagittal plane.

         

        P EARLS

        • All positioning requires the leg to be free to move through a range of motion throughout the procedure. This allows easy access for component alignment, gap balance, and range of motion throughout the procedure.

           

        • Positioning is supine with the table folded down at the knee to allow the leg to hang in a flexed position is useful for for patients with a hip fusion.

           

        • When draping, if the ankle and malleoli can be left relatively free from bulky layers of material, this will aid in visualization as well as registration for computer-assisted techniques.

           

          P ITFALLS

        • Failing to put a bump under the hip when the leg tends to externally rotate at the hip. The leg will tend to fall away from midline, requiring additional hands to stabilize it during the procedure unless the selected leg

        holder will also maintain neutral rotation of the leg.

         

      • The center of the talar dome on radiographs is utilized to determine the ankle center and mechanical alignment of the tibia.

      • The medial and lateral malleoli are utilized during computer-assisted navigation for registration points to determine the center of the ankle for alignment of the tibial cut during surgery.

      • The insertion of the posterior cruciate ligament, along with the medial third of the tibial tubercle, can aid in placement of the tibial baseplate in the proper position in the transverse plane (Fig. 3B and 3C). This line serves as a rotational axis to align the implant.

      • The patellar tendon insertion must be protected during determination of the tibial alignment and cutting of the proximal tibia.

        Positioning

      • Supine with leg holder to maintain the knee in flexed position (Fig. 4)

      • Supine with beanbag to aid assistant in holding the leg in a flexed position

       

      Tibial tubercle Anterior tibial crest

       

      Posterior cruciate ligament

       

       

      Patellar tendon

      B

       

       

       

      109

       

       

       

      Medial malleoli

       

       

      Tibial Component Alignment

       

      Lateral malleoli

       

      Talar dome

       

       

      A C

      FIGURE 3

       

       

       

       

      FIGURE 4

       

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      Equipment

      • There are a multitude of commercially available leg holders for total knee arthroplasty. When selecting one for use, consideration should be given to a leg holder that has minimal risk of contaminating the surgical field, as can occur with sterile drape punctures.

      • If using computer navigation, thought should be given to where the computer base should be positioned to give the best field of view during the operation. Most systems will provide an option to display the field of view to optimize the camera base position.

       

      Tibial Component Alignment

       

      Portals/Exposures

      • An anterior midline incision is most commonly utilized, but many variations are described. Medial and lateral parapatellar incisions may also be used depending on the planned deep approach (Fig. 5A).

    • Medial parapatellar arthrotomy is the most commonly used deep approach to the joint

      (Fig. 5B). There are many variations, including the subvastus, midvastus, and vastus intermedius approaches.

    • Lateral parapatellar arthrotomy may also be used. This approach has its greatest utility in knees with valgus deformity or in knees with multiple incisions anteriorly, in which it is desirable to use the most lateral approach.

  • Once the arthrotomy has been executed, excision or débridement of the infrapatellar fat pad and the anterior horns of the menisci is performed to

     

    P EARLS

    • After the arthrotomy is performed, visualization and capsular reflection are much easier after excising the anterior horns of the menisci and a portion of the infrapatellar fat pad. Elevating the capsule medially and laterally just distal to the osteophyte or 5 mm to or beyond the midcoronal line aids retractor placement.

       

    • Computer-assisted reference base placement needs to take into account the keel or stem length so that the pin position does not interfere with instruments or implantation of the tibial baseplate.

     

    visualize the tibial plateau. Subperiosteal lifting about the anterior and medial soft tissue sleeve of the tibia allows for external rotation and deliverance of the tibia anteriorly for better exposure (Fig. 5C).

  • For placement of computer navigation reference bases, the surgeon should take into account on which side of the operative table the computer-assisted camera will be based. This will assure that line of site is accessible during the surgery. It should be remembered that the leg will be in both flexion and extension during the procedure, and this needs to be taken into account for placement of the reference bases as well.

     

     

    P ITFALLS

    • Excessive elevation or faulty retractor placement can excessively release the medial collateral ligament, which may leave the knee loose. All ligaments should be protected with retractors during the tibial saw cut to prevent iatrogenic damage.

       

    • Placement of the computer-assisted reference bases too close to the joint line restricts cutting block or keel placement during the operation. Computer-assisted technique may have to

    be abandoned or restarted if this occurs.

     

     

    Instrumentation

    • Marking the skin incision in extension may cause the scar to be directly weight bearing in flexion for the kneeling patient. Marking the skin incision in flexion will help prevent this problem.

     

     

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    Controversies

    • Exposure of the knee is surgeon dependent, particularly with the advent of minimally invasive techniques. There are many proponents for several

    of the commonly described techniques. It is our feeling that the surgeon should be able to adequately visualize the procedure and then use the approach that gives the most reproducible results.

     

    Tibial Component Alignment

     

    A

     

     

     

    B

     

     

     

    C

    FIGURE 5

     

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    P EARLS

    • Preoperative radiographic delineation of the intramedullary canal axis on anteroposterior and lateral views can aid in determining where to drill the proximal tibia to open the intramedullary canal. This allows easier passage of the intramedullary guide rod and prevents excess varus or posterior slope.

       

      P ITFALLS

    • Failing to insert the intramedullary guide rod down to the physeal scar will decrease the accuracy of intramedullary alignment by allowing greater variability in its position.

       

    • Failing to verify the visual position of the intramedullary rod, thus not aligning it with the center of the ankle.

     

    Tibial Component Alignment

     

    Procedure

    Step 1: Intramedullary Alignment Technique

  • The surgeon’s preferred approach to the knee is performed, and the proximal tibia is exposed.

  • Distal femoral cuts are made, and menisci are excised to allow adequate visualization of the tibial plateau. If the femur is being cut first, then these cuts are made and the menisci are excised to allow adequate visualization of the proximal tibia.

  • The intramedullary canal of the tibia is opened with the appropriate drill just anterior to the root of the anterior cruciate ligament.

  • A “skinny” rod is passed down the intramedullary canal to verify central positioning of the opening hole in the proximal tibia.

  • An intramedullary alignment rod is then inserted down to the distal physeal scar, and a cutting guide is placed over the rod.

  • Visual inspection in both the coronal and sagittal planes of the rod is then conducted to verify that it is aligned with the center of the ankle.

    Instrumentation/ Implantation

    • An intramedullary starter drill is followed by the thin rod to verify alignment of the opening drill hole with the intramedullary axis. The intramedullary guide rod then

    follows on a T-handle with a jig on the rod that holds the cutting block for positioning.

     

  • The selected cutting block is then pinned into position in proper rotation of the medial third of the tibial tubercle and at the appropriate resection level (Fig. 6A and 6B).

  • Tibial resection is performed while protecting the patellar tendon, the collateral ligaments, and the posterior cruciate ligament if a cruciate-retaining knee is to be utilized.

     

     

    Controversies

    • Intramedullary referencing for tibial component position limits the ability of the surgeon to position the block. Some believe that this predisposes the cut to additional varus and posterior slope compared to other techniques.

     

     

     

    P EARLS

    • Utilization of multiple landmarks around the ankle will increase accuracy in the coronal plane. The over-the-top guide adds stability to the extramedullary alignment guide, allowing secure positioning of the block while it is pinned to the tibia.

     

    Step 2: Extramedullary Alignment Technique

  • The surgeon’s preferred approach to the knee is performed, and the proximal tibia is exposed.

  • Distal femoral cuts are made, and menisci are excised to allow adequate visualization of the tibial plateau.

 

 

 

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Tibial Component Alignment

 

A

 

P EARLS — cont’d

  • For patients with excessive internal tibial torsion, the external alignment rod will be lateral on the foot. Failure to properly externally rotate the tibial component will affect patellar tracking.

     

    P ITFALLS

  • Distal positioning of the extramedullary alignment guide based on the bones of the midfoot or forefoot will introduce more varus/valgus variability in the proximal tibial resection and should be avoided if possible. There is a tendency to introduce slight valgus alignment with this technique.

 

FIGURE 6

B

 

  • An extramedullary alignment guide is attached to the patient’s lower extremity.

  • The rod is then centered distally over the distal tibial crest, or the talar dome if palpable, or positioned

    at the medial middle-third junction between the malleoli.

  • Proximally, the rod is positioned over the medial middle-third junction of the tibial tubercle.

  • An over-the-top guide can be impacted into the tibial plateau at the base of the anterior cruciate ligament to aid with positioning of the cutting block.

  • The extramedullary alignment guide is then position to obtain the desired posterior slope in combination with the selected block (Fig. 7A and 7B).

  • The alignment guide should parallel the anterior crest of the tibia when no slope is required in the tibial resection or when the cutting block incorporates the desired posterior slope.

  • The selected cutting block is then pinned into position in proper rotation and at the appropriate resection level.

  • Tibial resection is performed while protecting the patellar tendon, the collateral ligaments, and the posterior cruciate ligament if a cruciate-retaining knee is to be utilized.

 

 

 

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Tibial Component Alignment

 

A B

Instrumentation/Implantation

  • Extramedullary alignment rod with attached ankle clamp and over-the-top guide if included in system

  • Jig to attach the cutting block to the guide and adjust the position of the distal aspect of the rod to the center of the ankle as well as the posterior slope of the cutting block

 

FIGURE 7

 

 

Controversies

  • Many surgeons believe that extramedullary alignment allows more complete positioning control compared to intramedullary, and gives the ability to bypass any intra-articular or extra-articular deformity that may be difficult to bypass with an intramedullary alignment rod.

 

 

P EARLS

  • Adequate exposure of the articular surfaces to allow a wide range of bony morphologic registration points to be obtained will improve accuracy of the computer alignment. The accuracy of the computer is entirely reliant on the registration points in the imageless systems commonly in use, and, if ever in doubt or if the reference base is loosened, then the registration should be repeated.

 

Step 3: Computer-Assisted Alignment Technique

  • The surgeon’s preferred approach to the knee is performed to allow tracker placement, and the proximal tibia is exposed.

  • Distal femoral and proximal tibial trackers are pinned to the bone in the surgeon’s preferred manner.

    • These may be placed within the incision or percutaneously, taking into account the positioning of the tracking camera to allow line of site during the procedure and throughout a range of positioning of the knee.

    • Figure 8 shows the location of computer navigation reference bases on the femur and tibia in full extension of the knee (Fig. 8A) and with the knee in flexion (Fig. 8B).

  • The infrapatellar fat pad and anterior horns of the menisci are excised as necessary to adequately visualize the articular surfaces of the knee.

 

 

 

 

P EARLS — cont’d

  • Reference base attachment points should be placed to decrease the stress riser in the tibia to prevent a periprosthetic fracture postoperatively. Placement in metaphyseal bone near the midcoronal region (near the neautral bending axis) of the tibia may be preferable.

     

    P ITFALLS

  • The malleoli of the ankle must be exposed for registration of points in the computer. Failing to leave the malleoli palpable during draping will decrease coronal and sagittal plane accuracy of component position.

     

  • If any question arises as to the validity of the alignment that is represented by the computer algorithm, the registration should be performed again.

     

  • The surgeon must know the system he or she is utilizing and how the center of the ankle is calculated from the registration landmarks. Some systems utilize a visual point along the malleolar axis, while others use a percentage of distance between the registered malleolar landmarks.

 

Tibial Component Alignment

 

A

 

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Instrumentation/ Implantation

  • Computer-assisted surgical system with associated guides

  • Distal femoral and proximal tibial tracker pins and trackers

  • Registration stylus and associated tracker

  • Adjustable cutting jigs and proximal tibial cutting block

  • Flat planar jig with reference base attachment for checking cut accuracy

 

B C

FIGURE 8

  • Registration of bone morphology is performed as directed by the software being utilized.

  • Bone cuts are sequentially made in the surgeon’s preferred order; more commonly, distal femoral cuts are performed prior to proximal tibial cuts.

  • The adjustable tibial cutting block is pinned through the jig holes in close approximation to the appropriate position as directed by the computer.

     

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    Controversies

    • Proponents of the computer-assisted surgery state that the increased accuracy afforded by the computer outweighs the extra time required to place the tracking pins and tracker and to perform the registration process. Component malposition outliers may also be reduced or potentially eliminated.

    • Newer custom disposable cutting blocks have now been introduced, but if they do not take into account the center of the ankle, then the surgeon should be aware that neutral alignment cannot be accurately determined.

     

    Tibial Component Alignment

     

  • The position of the tibial cutting block is fine-tuned through the jig position screws until the computer shows neutral alignment and the preoperatively selected slope. Location of the tibial reference base allows for standard extramedullary instrumentation to be utilized either by surgeon preference using a planar instrument to align the cutting block, or as a secondary check of alignment (Fig. 8C). The cutting block itself is then pinned in place.

  • Tibial resection is performed while protecting the patellar tendon, the collateral ligaments, and the posterior cruciate ligament if a cruciate-retaining knee is to be utilized.

  • The femoral tracker is then placed on a “flat” guide and the cut is verified with the computer. Many software systems will register the surgeon’s final selected cut to allow dynamic evaluation after insertion of components.

     

    P EARLS

    • Obtaining full extension after total knee arthroplasty, regardless of technique, requires diligence on the part of the patient. We instruct our patients to put a pillow or two under the heel to lift the leg in the air and allow the knee to “sag” under its own weight into full extension.

       

      P ITFALLS

    • Failing to diligently surveil the incision and the knee can potentially lead to catastrophic failure of the knee in the form of infection. We use a 7-day cutoff for any drainage from the knee. After this point in time, we wash out the knee and re-close the wound to prevent a deep wound infection.

     

    Postoperative Care and Expected Outcomes

  • Multiple clinical studies have reported on the advantages of alignment using computer navigation, but to date no difference in clinical outcome has been reported.

  • Total knee arthroplasty survivorship is approximately 90–94% at 10 years after surgery, on average.

 

 

Controversies

  • Duration and type of anticoagulation after total knee arthroplasty continues to be debated. There is growing evidence that the use of synthetic and fractionated heparinoids may increase postoperative wound complications and possibly infection rates.

 

 

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Tibial Component Alignment

 

Evidence

Bathis H, Perlick L, Tingart M, Luring C, Zurakowski D, Grifka J. Alignment in total knee arthroplasty: a comparison of computer-assisted surgery with the conventional technique. J Bone Joint Surg [Br]. 2004;86:682-7.

 

A prospective comparison of knee alignment was carried out. Eighty patients were placed in two different total knee arthroplasty (TKA) groups; one underwent TKA with computer assistance and the other with standard instruments. Postoperative long-leg standing radiographs showed that the mechanical axis of the leg was significantly better in the computer-assisted group (96%,  3°) compared with the conventional group (78%,  3°).

 

Denis K, Van Ham G, Bellemans J, Labey L, Sloten JV, Van Audekercke R, Van der Perre G, De Schutter J. How correctly does an intramedullary rod represent the longitudinal tibial axes? Clin Orthop Relat Res. 2002;(397):424-33.

 

This study investigated a robot-assisted procedure for preparing the tibia in TKA that utilized an intramedullary (IM) rod to register the tibia. In 18 cadaveric formalin-fixed tibias, the difference in orientation between the IM rod and several longitudinal tibial axes was analyzed. Three tibial axes and two IM rod insertion techniques were compared. A high standard deviation resulted, which indicated significant anatomic variation in specimens. The sagittal plane showed the highest degree of variability, while the frontal plane showed less than 2° of variation. The results of the two IM rod insertion techniques were not significantly different. The study did not assess the alignment after the tibial saw cut was made.

 

Ishii Y, Ohmori G, Bechtold JE, Gustilo RB. Extramedullary versus intramedullary alignment guides in total knee arthroplasty. Clin Orthop Relat Res. 1995;(318):167-75.

 

The authors prospectively compared intramedullary and extramedullary alignment for 100 consecutively operated knees. Postoperatively, long-leg standing radiographs were taken. No significant difference between the techniques was appreciated.

 

Mihalko WM, Krackow KA. Differences between extramedullary, intramedullary, and computer-aided surgery tibial alignment techniques for total knee arthroplasty.

J Knee Surg. 2006;19:33-6.

 

This study compares tibial alignment techniques to a computed tomography tibial alignment standard measure. The authors demonstrated improved overall accuracy with imageless computer navigation. Although non-navigated techniques demonstrated accuracy within very few degrees in any single plane, cumulatively across all planes the variability became significant.

 

Rottman SJ, Dvorkin M, Gold D.Extramedullary versus intramedullary tibial alignment guides for total knee arthroplasty. Orthopedics. 2005;28:1445-8.

 

This was a retrospective study evaluating intramedullary and extramedullary tibial alignment guides to determine differences in accuracy in 55 TKAs. Pre- and postoperative tibiofemoral angles, tibial component alignment angles, and femoral component alignment angles were all compared. A two-sample t-test revealed no statistical difference in alignment of the tibial component between the two methods.

 

Stockl B, Nogler M, Rosiek R, Fischer M, Krismer M, Kessler O. Navigation improves accuracy of rotational alignment in total knee arthroplasty. Clin Orthop Relat Res. 2004;(426):180-6.

 

Rotational alignment of TKA components was specifically evaluated. An optical navigation system was compared to conventional instrumentation between two groups of patients. Postoperative computed tomography showed superior postoperative alignment of the mechanical axis, posterior tibial slope, and rotational alignment.

 

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Tibial Component Alignment

 

Teter KE, Bregman D, Colwell CW Jr. Accuracy of intramedullary versus extramedullary tibial alignment cutting systems in total knee arthroplasty. Clin Orthop Relat Res.

1995;(321):106-10.

 

This review of over 300 TKAs showed that the differences in alignment between intramedullary and extramedullary techniques were insignificant in both the coronal and sagittal planes. Outliers in the intramedullary portion of the study were attributed to tibial bow and the inability to pass the intramedullary rod all the way down

the tibia.

 

Victor J, Hoste D. Image-based computer-assisted total knee arthroplasty leads to lower variability in coronal alignment. Clin Orthop Relat Res. 2004;(428):131-9.