Primary indication: end-stage degenerative osteoarthritis (primary, posttraumatic, secondary to avascular necrosis, osteochondritis, or sepsis).

Additional indications include inflammatory arthropathies, osteonecrosis, tumor, and fracture.

Contraindications: preexisting sepsis or infections (including osteomyelitis) either at knee or distant site and severe vascular disease.

Plain radiographs of the knee should include weight-bearing anteroposterior (AP), lateral (at 30° of flexion), PA flexed (or alternatively a tunnel view), and merchant views of the involved knee, as well as a long-leg hip-to-ankle standing AP radiograph of both limbs to assess asymmetry and mechanical and anatomic limb axes.

AP and lateral plain radiographs of the hips may be indicated in the context of symptoms of groin pain, stiffness, or limited range of motion or may be indicated for severe knee pain with normal knee radiographs.

Magnetic resonance imaging (MRI) may be indicated to evaluate meniscal and ligament integrity.

The purpose of preoperative templating is to assist the surgeon in selecting an appropriate implant design and size of the femoral and tibial component, as well as assess the patient’s deformity and mechanical versus anatomic axis.

Tibiofemoral angles: Assess the degree of malalignment and/or deformity using a standing AP radiograph:

The goal is to template for placing the tibial component at 90° to the anatomic-mechanical axis to model the normal joint line during the gait cycle.

Total knee replacement: The two most common implant designs are the posterior stabilized (PS) and cruciate retaining (CR). Meta-analyses have shown no difference in implant type with regard to postoperative extension angle, patient satisfaction, complications (such as anterior knee pain), short- and long-term knee society outcomes (pain and function), as well as similar prosthesis survivorship. The most significance difference between the two implant designs is the greater flexion angle and increased range of motion in the PS design as compared to the CR design.

Cemented: A static fixation without osseointegration potential that provides immediate mechanical stability in the acute postoperative period. Cemented implants are indicated for patients with poor bone quality.

Non-cemented: Biologic interface between the native bone and the implant. A non-cemented implant may be indicated in patients with adequate bone quality. Two non-cemented implant options include hydroxyapatite coating or high-porosity trabecular metal, which function by encouraging bony ingrowth at the implant-bone interface. Traditionally, non-cemented components had a high failure rate, especially on the tibial side.

Hybrid fixation: The femoral (or tibial) component is cementless, while the tibial (or femoral) and patellar components are cemented.

Arterial injury: The prevalence of arterial injury following TKA is 0.03–0.17 % and most commonly involves the popliteal artery. The major risk factor is preexisting peripheral arterial disease, and the risk is compounded by the use of a tourniquet during the procedure.

Arthrofibrosis: Stiffness after TKA, also termed arthrofibrosis, prevalence ranges in the literature from 1 to 25 %. Proposed risk factors include poor preoperative range of motion, previous operations, diabetes, depression, and poor patient education; perioperative, surgeon technique and operative time; and postoperative, infection and poor pain control and patient compliance with physiotherapy.

Aseptic loosening: Aseptic loosening is one of the most common reasons for revision TKA and is best diagnosed by radiographic presence of radiolucent lines around the components, periprosthetic fractures, and changes in component positions in successive radiographs.

Mortality: Incidence of mortality has been reported as 0.2 % at 20 days and 1.6 % at 1 year postoperative. Independent predictors of mortality include increased patient age, diabetes, and simultaneous bilateral TKA.

Peroneal nerve injury: The prevalence of common peroneal nerve palsy is 0.3–9.5 %, although these numbers are thought to be underestimates of the true prevalence given the wide spectrum of nerve injury presentations. Controversy surrounds proposed risk factors, but some are thought to be younger age, higher body mass index, preoperative valgus deformity, preoperative flexion contracture, and duration of perioperative tourniquet use.

Restore near-neutral mechanical coronal alignment to the lower extremity.

Mechanical axis should pass through the central 1/3 of the knee.

Minimize Q angle.

Standing AP, flexed PA (the Rosenberg view), hip-to-knee standing alignment, and merchant and lateral radiographs of bilateral knees.

Identify medial or lateral joint space gapping (can be a sign of collateral ligament insufficiency), subluxation of femur on the tibia (on AP and/or lateral), and bone defects.

Anticipate the need for ligament releases to balance the knee and/or ↑ prosthetic constraint for MCL/LCL incompetence.

Standing full-length radiographs (AP and lateral) assist in determining femoral valgus cut angle if femoral or tibial deformity is present or in very tall (>190 cm) or short (<152 cm) patients.

Excessive preoperative deformity and femoral bowing ↑ risk of postoperative malalignment.

Merchant view evaluates patellofemoral articulation and articular congruence (patellar tilt).

Preoperative patellar tilt predicts risk of postoperative tilt.

Mechanical axis of limb passes from center of femoral head to center of ankle (i.e., center of plafond).

Normally passes through central 1/3 to slightly medial of knee joint; if passes medial 1/3 = varus alignment; if passes lateral 1/3 = valgus alignment.

Quantified by mechanical axis deviation (MAD), measured as perpendicular distance from center of knee to mechanical axis of the limb:

Anatomic tibiofemoral angle formed by line bisecting femoral diaphysis and a second line bisecting tibial diaphysis; normal angle: 5–7° valgus.

Mechanical tibiofemoral angle formed by mechanical axes of femur and tibia (see below); normal angle: 1 ± 2° varus.

Postoperative neutral mechanical axis permits even load distribution across medial and lateral condyles of prosthesis.

Anatomic axis of femur (AAF) defined by a line bisecting femoral diaphysis.

Mechanical axis of femur (MAF) defined by line from center of femoral head to intersection of anatomic axis and intercondylar notch.

Valgus cut angle (VCA) defined as difference between AAF and MAF; normal angle: ~6°.

Template VCA on standing full-length AP radiograph.

VCA perpendicular to mechanical axis of femur and limb.

Since proximal femoral offset does not vary significantly from patient to patient, VCA tends to vary with patient height; tall patients require VCA <5°; short patients require VCA >7°.

Consider VCA of 3° in valgus knees to “overcorrect” alignment; however, this is surgeon preference rather than an accepted rule.

Anatomic axis of tibia (AAT) defined by line that bisects tibial diaphysis.

Determines entry point for tibial intramedullary cutting guide.

Normal tibia in 2–3° of anatomic varus.

Mechanical axis of tibia (MAT) defined by line from center of tibia plateau to center of ankle; usually coincident with AAT, unless tibial deformity.

Proximal tibia cut should be perpendicular to mechanical axis of tibia.

>3° of tibial component varus risks early implant failure, usually through medial plateau bone collapse.

>8° of femoral component valgus contributes to early implant failure.

Historically superior implant survivorship and patient satisfaction for neutral to slightly valgus limb alignment (between 2.5° and 7.4° of anatomic valgus).

Recent literature questions whether modern implant survivorship is improved for TKA aligned ±3° from neutral (0°).

Excessive preoperative malalignment (>8° of varus or >11° of valgus) has ↑ risk of failure; can be incompletely mitigated by postoperative neutral alignment.

Soft tissue balance is also key factor in load distribution across prosthesis and for implant survival.

Q angle is defined as angle between line from anterior-superior iliac spine (ASIS) to center of patella (axis of quadriceps) and second line from center of patella to tibial tuberosity (axis of patellar tendon).

Normal angle: 11 ± 7°.

Varies with patient height; greater in short patients; less in tall patients.

Larger Q angles ↑ lateral subluxation forces on the patella; risk for pain, mechanical symptoms, accelerated wear, and dislocation.

“Balanced knee”:

Coronal plane balancing → correcting varus/valgus deformity

Sagittal plane balancing → correcting (equalizing) flexion/extension gap

Gap balancing technique → Bony resection on the tibia and femur is determined by the intraoperative tension of the ligaments.

Measured resection technique → Bony resection on the tibia and femur is made first, and the ligaments are balanced depending on the bony resection.

Coronal plane imbalance: Medial or lateral ligamentous complexes become tight and/or stretched depending on deformity.

Sagittal plane imbalance: Often caused by a progressive flexion contracture deformity from a tight posterior capsule, tight hamstrings, or large posterior osteophytes; improper intraoperative tibial and femoral bone resection can lead to intraoperative sagittal plane imbalance.

Standard AP, lateral, merchant views + the Rosenberg view (45° flexion PA view)

Bilateral long-leg standing axis films to assess overall limb alignment

Coronal Balancing

Sagittal Balancing

Correction of severe combined deformity of valgus + flexion contracture can lead to peroneal nerve palsy from over-lengthening a previously contracted nerve:

Posterior release can lead to popliteal artery injury.

A flexion contracture present postoperatively, which was corrected intraoperatively, is often due to tight hamstring tendons.

Not balancing flexion gap (if left too loose) in a posterior-stabilized (PS) knee can lead to cam-post dislocation, resulting in a posterior knee dislocation .

Coronal plane instability (varus/valgus) – can be treated with a constrained prosthesis with a thicker post.

Anteroposterior instability with an incompetent extensor mechanism – requires a hinge-type prosthesis with extensor mechanism reconstruction.

Global knee instability requires a hinge-type prosthesis.