Patellofemoral Osteoarthritis

Original Editor - User Name Top Contributors - Mandy Roscher, Kim Jackson, Shanshika Maddumage, Simisola Ajeyalemi, Rachael Lowe, Wanda van Niekerk and Lucinda hampton

Introduction

OA of the knee is commonly diagnosed. Tibiofemoral (TF) OA is more commonly focused on as compared to Patellofemoral (PF) OA. PF OA, however, is very prevalent with up to 25% of people having signs of Patellofemoral joint OA and up to 40% of these people have isolated PF OA.(11) 

Definition 

PF OA occurs at the patella femoral joint. 

Diagnosis 

To date there are no specific diagnostic criteria to formally diagnose PF OA. A combination of clinical signs and symptoms as well as radiographic information from X-rays and MRIs is used to diagnose PF OA. 

Clinical Features

·     Anterior knee pain(especially on loading activities eg stair climbing)- this is normally the major finding in PF OA. 

·     Knee crepitus 

·     Swelling

·     Pain on PFJ compression

·     Stiffness after sitting

·     Valgus knee deformity

·     Reduced Quadricep Strength

It is important to note that pain may not necessarily be originating from the PF joint itself but can also be from surrounding structures such as the fat pad, ligaments, bursae, muscles etc (course notes)

Imaging

Xray and MRI can both be used to diagnose PF OA. It is important to note that findings on radiological investigations do not always correlate to clinical symptoms and it has been found that in certain individuals who have positive findings on X-ray or MRI do not have any knee pain or other symptoms of PF OA. 

X-ray

X-ray is most commonly performed in the diagnosis of PF OA. In TF OA the Kellgren and Lawrence (KL) Grading system is used however there is no standardised scoring system for PF OA. In research the KL grading system has been used to score PF OA but it has not been validated for this purpose. 

A skyline view is most appropriate to adequately view the PFJ. The presence of osteophtes as well as joint space narrowing confirms the clinical findings for PF OA. 

The X-ray can also be used to interpret the morphology of the PFJ such as the shape of the trochlear where a shallow trochlear has been associated with PF OA. 

MRI 

MRIs Findings such as cartilage lesions, osteophytes and bone marrow lesions (LINK) at the PFJ can be used in the diagnosis of PF OA. There is no formal diagnostic criteria at present to diagnose PFJ on MRI

PF OA and TF OA

PF OA and TF OA can be found in isolation or in combination. There does seem to be a relationship between the 2 and having either is a risk factor for developing the other. The PFJ is often the first joint to present with symptoms (11) (1). It is still unsure as to whether PF OA will always progress to combined OA (11)

Outcome Measures

At present there are no evidence based patient reported outcome measures specifically for PF OA. The KOOS and WOMAC can be used but they are outcomes focused on general knee OA and not specific for PF OA. Performance tests such as the Timed Up and Go can be used in a PF OA population. However this test may not be appropriate in early stages of PF OA as it may not challenge the joint enough. 

Risk Factors

Abnormal Joint Alignment

Patellofemoral as well as tibiofemoral alignment has been implicated in PF OA and treatment targeted at correcting imbalances may be helpful to treat symptoms and prevent progression of the condition.

Patellofemoral alignment

The following alignment patterns of the patella have been shown to be a potential risk factor for PF OA. (8)

(PICTURE OF PATELLA POSITION)

1.    Lateral translation

2.    Lateral tilt

3.    Proximal translation (Patella alta) – 

A recent study conducted in 2019 by Macri et al used MRI to confirm that those 3 patella positions are commonly found in patients presenting with PF OA. 

These alignment problems are commonly found in patients with PFJ pain and it is hypothesised that by correcting these alignment issues the progression to PF OA could possibly be prevented. This is currently still a theory and has not been proven. 

Patella’s that are positioned higher (increased proximal translation have been associated with worse PF OA symptoms. This could potentially due to a lack of stability as there is more time that the patella is not snug in the trochlear. 

Tibiofemoral Alignment

Varus and valgus angles at the knee can affect the PFJ. Lateral PF OA is more commonly seen in knees with valgus deformities and medial PF OA in varus deformities.(6) It appears that in general valgus deformities target the PFJ more. Isolated PF OA is more commonly found in knees with valgus and combined PF and TF OA as well as isolated TF OA is more commonly found in knees with varus deformities (REF).

Abnormal Trochlear Morphology

A shallow trochlear is a risk factor for the development of PF OA (6). Multiple studies have shown that the more severe PF OA patients present with shallow trochlear. They often have increased osteophytes, greater joint space narrowing and more cartilage loss as compared to people with deeper trochlear. (6) 

Abnormal Kinetics and Kinematics 

Decreased quadricep strength has been shown to be a significant risk factor in PFJ symptoms and development of PF OA. (6) 

Proximal muscles at the hip have been implicated in PF OA such as gluteus medius, minimus and lower hip abductors. (6)

Teng et al (2015) found that progression of PF OA is related to increased peak knee flexion in the terminal stance of gait (Knee Flexion Moment During the Second Half of the Stance Phase of Gait Is Associated With the Progression of Osteoarthritis of the Patellofemoral) 

Patients with tight hip flexors or those that lack hip extension due to joint stiffness may need to increase knee flexion to forwardly translate foot. As well as those with reduced dorsiflexion due to tight calf muscles or ankle siffness.  (course notes) Treatments targeted to correct these biomechanical faults may reduce progression of PF OA.

Altered joint alignment as discussed above is often not a structural problem and can be caused by muscular imbalances. For example weak quadricep muscles may influence the lateral translation or tilt of the patella, a long patella ligament may cause an increased proximal translation of the patella and weak hip abductors can also lead to increased femoral internal rotation and abduction leading to altered patellofemoral alignment. (6)

BMI

Adults that suffer from PF pain tend to have a higher BMI (7). And those with PF OA have a much greater BMI than control. 

There is a debate of is this finding because PF Pain leads to decreased activity and as such BMI increases? Or, is the actual adipose tissue produces adipokines and creates an inflammatory environment that contributes to joint degeneration. 

Increased load from an increased BMI has also been proposed as a pain mechanism and cause of PF OA. However OA is more commonly found in non-weight bearing joints of obese people as well and these joints do not have the increased load due to BMI.(7)

Obese individuals with knee OA were found to have an elevated interleukin-6 and this may contribute to the inflammatory profile that accelerates cartilage degeneration. It has not yet been researched as to whether a reduction in BMI can ultimately change symptoms and radiological findings in PF OA. 

Treatment

Management in PF OA cannot be a “one size fits all” approach. Patients need to be subgrouped and bespoke treatment plans created to address their particular risk factors and biomechanical faults. 

Taping and Bracing

The goal of taping and bracing is to potentially affect the joint alignment. Callaghan et al (2015) determined in their RCT that wearing a Q-brace for 6 weeks alters the volume of bone marrow lesions as well as pain for people with PF OA. (Callaghan article) The Q brace does alter patella position as well as improve patella contact with the femur trochlea (6). Taping the patella has also shown to be effective but its mechanism of action is uncertain and has not been studied to date (6).

PICTURE OF Q BRACE

Exercise

Exercise continues to be the recommended treatment in osteoarthritis in general. In PF OA targeted exercises based on individual patients assessment would be best practice to manage symptoms and prevent further degeneration. There is limited evidence on exercise in PF OA specifically. (6)

Surgical

Patella resurfacing has been suggested as a surgical option in the treatment of PF OA. There has been 1 study to date and this did not show any difference between the intervention and control group (6)