Patellofemoral joint (PFJ) pain is a common, often chronic, aching pain behind or around the kneecap, frequently called "runner's knee". It occurs when the kneecap does not glide smoothly over the thigh bone, often due to muscle weakness or overuse. It makes sitting for long periods, climbing stairs, or kneeling painful.

Symptomatic knee osteoarthritis (OA) is a common, long-term condition where the protective cartilage in the knee joint wears away, causing the bones to rub together, leading to daily pain and stiffness. In simple terms, it is a "wear-and-tear" disease of the entire joint that makes walking, climbing stairs, or bending the knee difficult.

The PFJ is where the patella (kneecap) meets the femoral trochlea (front part of the lower thigh bone) at the front of the knee. Patellar tracking refers to the movement of the patella that begins to engage in the distal femoral trochlear groove (smooth, U-shaped groove at the bottom of the thigh bone).

By doing this study, we hope to advance clinical knowledge of the PTJ features in a more natural position by using weight-bearing computed tomography (WBCT) images while the leg is straight and slightly bent. Determining links between specific knee symptoms and the PTJ structure on WBCT images could enable providers to effectively target the underlying causes and to develop targeted treatments.

The patellofemoral joint (PFJ) is the articulation where the patella meets the femoral trochlea at the front of the knee. Patellar tracking refers to the movement of the patella that begins to engage in the distal femoral trochlear groove.

The proposed research will advance clinical knowledge of patellofemoral joint features in a more physiological position by using weight-bearing computed tomography (WBCT) images at 0° and 20° of knee flexion. Determining associations between specific knee symptoms and patellofemoral joint structural metrics on WBCT images could enable providers to effectively target the underlying causes and to develop targeted treatments.

PFJ features have become a significant area of interest, and numerous studies have been conducted to understand morphological characteristics, as it is the most common site associated with many knee symptoms and is a frequent location of early knee osteoarthritis (OA). There is growing evidence indicating that patellofemoral OA contributes to knee pain and functional limitations independent of tibiofemoral OA, and that the etiology and management may differ. A key factor in the risk profile for PFJ dysfunction may be malalignment of the patella with the femoral trochlea and subsequent abnormal tracking in the groove, leading to abnormal loading and wear of PFJ subchondral bone, microtearing of the lateral retinaculum, or irritation of the synovium, one of the most painful structures in the knee.

Quantifying patellofemoral alignment is an important aspect in assessing knee health, particularly in conditions that affect the PFJ, such as patellar instability, OA, or patellofemoral pain syndrome. There is no consensus on PFJ imaging position, knee flexion angle, joint position (e.g. stabilized or free), weight-bearing status, or beam angulation. However, the introduction of weight-bearing CT (WBCT) provides the ability to acquire 3D imaging of the PFJ under functionally loaded conditions. Using WBCT offers a unique advantage in this context because it allows for the evaluation of the knee in a loaded position, closely simulating the conditions under which the joint normally operates during activities like walking, running, and jumping, and under conditions in which the PFJ is symptomatic.

WBCT provides a three-dimensional view of the patellofemoral joint, allowing for the accurate measurement of various alignment parameters. These measurements may include the TT-TG, reTFR, patellar tilt angle, patellar height, and congruence angle. By analyzing these parameters, clinicians can gain insights into the alignment and positioning of the patella relative to the femur and the tibia.

Rationale:

WBCT can give us a better understanding of the patellofemoral joint in a loaded configuration in which the joint normally works during activities like walking, running, and jumping. This three-dimensional view will allow us to measure alignment parameters in a more functional position. This imaging technique is particularly valuable because it demonstrates the influence of factors such as muscle contractions or soft tissue conditions, the lack of which may distort results in non-weight-bearing assessments. Determining the extent to which these parameters are associated with knee symptoms will help to guide treatment decisions and improve clinical outcomes for patients with knee disorders.

Inclusion Criteria:

• Age ≥ 18
• Knee pain, falling into either of the two groups, i.e., PFJ pain (pain only in the anterior region of the knee) or symptomatic knee OA (pain in any other area of the knee, including the anterior region)

Exclusion Criteria:

• Bilateral total knee arthroplasty
• Pregnant
• Unable to stand safely for 2 minutes with support
• Any condition that the investigator identifies as inappropriate for participation (e.g., unable to participant in consent process, unsafe to stand on WBCT platform, etc.)

Voluntary participants who consented to be contacted for research