TKA Axial Alignment - Recon (2024)

Updated: Jul 30 2024

Douglas Dennis MD

TKA Axial Alignment

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  • Introduction

    • Important consideration

      • pre-op planning

      • component insertion

      • ligament balancing

      • prosthetic design selection

    • Normal anatomy

      • distal femur is ~9 degrees of valgus (anatomic axis compared to joint line)

        • 5-7 deg valgus of femur refers to difference of anatomic axis to mechanical axis

      • proximal tibia is 2-3 degrees of varus (anatomic axis to joint line)

    • Technical goals

      • restore mechanical alignment (mechanical alignment of 0°)

      • restore joint line ( allows proper function of preserved ligaments. e.g., pcl)

      • balanced ligaments (correct flexion and extension gaps)

      • maintain normal Q angle (ensures proper patellar femoral tacking)

    • Mechanical axis of Limb

      • axis from center of femoral head to center of ankle

  • Preoperative Evaluation

    • Radiographs

      • standing AP and lateral of knee

        • to evaluate for

          • joint space narrowing

          • collateral ligament insufficiency

            • lateral gapping in varus & medial gapping in valgus deformities

          • subluxation of femur on tibia

          • bone defects

      • standing full-length radiographs (AP and Lateral)

        • are indicated to determine an accurate valgus cut angle when the patient has

          • femoral or tibial deformity

          • very tall or short stature

      • extension and flexion laterals

      • sunrise view

  • Femoral Alignment

    • Anatomic axis femur (AAF)

      • a line that bisects the medullary canal of the femur

      • determines entry point of femoral medullary guide rod

      • intramedullary femoral guide goes down anatomic axis of the femur

    • Mechanical axis femur

      • defined by line connecting center of femoral head to point where anatomic axis meets intercondylar notch

      • obtaining a neutral mechanical axis allows even load sharing between the medial and lateral condyles of a knee prosthesis

    • Valgus cut angle (~5-7° from AAF )

      • difference between AAF and MAF

      • perpendicular to mechanical axis

      • jig measures 6 degrees from femoral guide (anatomic axis)

      • will vary if people are very tall (VCA < 5°) or very short (VCA > 7°)

      • can measure on a standing full length AP x-ray

  • Tibial alignment

    • Anatomic axis of tibia (AAT)

      • a line that bisects medullary canal

      • tibia medullary guide (internal or external) runs parallel to it

      • determines entry point for tibial medullary guide rod

    • Mechanical axis of tibia

      • line from center of proximal tibia to center of talus

      • proximal tibia is cut perpendicular to mechanical axis of tibia

      • usually mechanical axis and anatomic axis of tibia are coincident and therefore you can usually can cut the proximal tibia perpendicular to anatomic axis (an axis determined by an intramedullary jig)

      • if there is a tibia deformity and the mechanical and anatomic axis are not the same, then the proximal tibia must be cut perpendicular to the mechanical axis (therefore an extramedullary tibial guide must be used)

  • Patellofemoral Alignment

    • Q angle

      • Abnormal patellar tracking, although not the most serious, is the most common complication of TKA.

      • The most important variable in proper patellar tracking is preservation of a normal Q angle (11 +/- 7°)

        • the Q angle is defined as angle between axis of extensor mechanism (ASIS to center of patella) and axis of patellar tendon(center of patella to tibial tuberosity)

      • Any increase in the Q angle will lead to increased lateral subluxation forces on the patella relative to the trochlear groove, which can lead to pain and mechanical symptoms, accelerated wear, and even dislocation.

        • It is critical to avoid techniques that lead to an increased Q angle. Common errors include:

          • internal rotation of the femoral prosthesis

          • medialization of the femoral component

          • internal rotation of the tibial prosthesis

          • placing the patellar prosthesis lateral on the patella

      • Q angle management in TKA

  • Joint Line Preservation

    • Goal is to restore the joint line by inserting a prosthesis that is the same thickness as the bone and cartilage that was removed

      • this preserves appropriate ligament tension

      • if there are bone defects they must be addressed so the joint line is not jeopardized

      • elevating the joint line (> 8mm leads to motion problems) and can lead to

        • mid-flexion instability

        • patellofemoral tracking problems

        • an "equivalent" to patella baja

        • never elevate joint line in a valgus knee until after balancing to obtain full extension

      • lowering joint line can lead to

        • lack of full extension

        • flexion instability

Technique Guide TKA - Parapatellar Approach Derek T. Bernstein Stephen Incavo Recon - High Tibial Osteotomy
Technique Guide TKA - Varus Knee with Anterior Referencing and Gap Balancing Technique Derek T. Bernstein Stephen Incavo Recon - TKA Axial Alignment

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FAQs

What is the normal alignment of the knee joint? ›

Normal knee alignment

In general the normal knee joint alignment is 2°–3° of varus compared with the mechanical axis although healthy non-arthritic patients may have different values. In fact obesity, activity and muscle strength, all play a crucial role in the development of arthritis also with a perfect aligned knee.

What is the normal axis of the knee joint? ›

The normal tibial joint angle (TJA) is 2 to 3° varus to the mechanical axis of the tibia (equivalent to the tibial shaft axis (Figure 5.3-B). Smaller numbers are typically used when describing these terms (e.g., a 3° varus TJA vs. a medial TJA of 87°).

What is the alignment of the knee replacement? ›

Kinematic alignment (KA) is a technique for total knee arthroplasty that aims to reconstruct patient-specific limb alignment and knee biomechanics based on the pre-arthritic kinematic axes of the patient's femur.

What is the most common indication for TKA revision? ›

If an artificial joint becomes infected, it may become stiff and painful. The implant may begin to lose its attachment to the bone. Even if the implant remains properly fixed to the bone, pain, swelling, and drainage from the infection usually make revision surgery necessary.

What is abnormal alignment of the knee? ›

Knock knees can cause the kneecaps to be off-center, which increases pressure and pain in the front of the knee. Knock knee alignment places high stresses on the outside (lateral side) of the knee, causing additional knee pain. These stresses often lead to knee arthritis.

How do you know if your knee is out of alignment? ›

Symptoms may include: Knee stiffness. Grinding or clicking sounds when the knee is extended. Knee giving out unexpectedly.

What is normal to axis? ›

Each of the 4 quadrants represents 90° and an axis type (eg, 0° to +90° is a normal axis; +90° to 180° is RAD; 0° to -90° is LAD; and -90° degrees to 180 degrees is an extreme axis). Therefore, if leads I and aVF are positive, the axis falls within the normal range.

What is an abnormal knee angle? ›

Positive sign: Normal Q angle score for females is between 13-18° and in males is between 12-15°, with values greater than and lesser these are considered abnormal and may indicate the patient is at risk of developing chondromalacia patellae, patella alta or mal-tracking of the patella.In a research by Clienger et al, ...

Can a knee replacement go out of alignment? ›

Instability may be the result of increased soft-tissue laxity (looseness), or improper positioning or alignment of the prosthesis. The soft tissues, including the ligaments around the knee, may stretch out after surgery and no longer provide the support that the knee needs.

What is functional alignment in TKA? ›

The principle of functional alignment TKA is to restore pre-arthritic alignment and achieve balanced flexion–extension gaps and equal mediolateral soft tissue tension by adjusting bone resections within some limit and/or minimum soft tissue release with robotic-assisted technology [46].

Can you change knee alignment? ›

An osteotomy is a surgical procedure used to alter the alignment of the leg to change the loading pattern of the knee. A cut is made in the tibia (shin bone)and then the cut is opened or closed to change the axis of that bone.

What is the newest alternative to knee replacement? ›

A BioKnee® is a knee replacement alternative. It combines three key procedures that rebuild, regenerate, or biologically replace the damaged parts of the knee using donor tissues, a patient's own healing response, and growth factors.

Which knee arthroplasty has the highest revision rate? ›

Unicompartmental knee arthroplasty (UKA) has higher revision rates than total knee arthroplasty (TKA). As revision of UKA may be less technically demanding than revision TKA, UKA patients with poor functional outcomes may be more likely to be offered revision than TKA patients with similar outcomes.

Why does my knee still hurt 2 years after knee replacement? ›

Ongoing pain after knee replacement is complex and can be related to different factors. Factors known to be associated with ongoing pain include inflammation, infection, nerve damage, incorrect positioning of the replacement joint, and depression.

How straight should knees be? ›

Knees should be “soft” and not locked. Locking your knees forces the pelvis and chest to be pushed out, which causes undo stress on the lower back. It is also difficult to maintain proper balance in an unnatural posture. The pelvis should be in a neutral position, with the sternum facing straight ahead.

How should your knees be positioned? ›

You should adjust your chair high and sit toward the front of the seat pan with your knees dropped much lower than your thighs with an open trunk to thigh angle. You should sit with your low back straight and your trunk held near erect- not bent forward.

What is a neutral alignment of the knee? ›

Mechanical alignment of the knee requires that the tibial and femoral cuts be perpendicular to the mechanical axis of each bone in the coronal plane. The neutral mechanical alignment is described as a hip-knee-ankle acute angle of 0° ± 3 [1,3].

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