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Patellofemoral Osteoarthritis

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

Introduction

Osteoarthritis (OA) of the knee is a commonly diagnosed condition. Radiographic patellofemoral osteoarthritis (PFOA) is observed in 64–69% of individuals experiencing chronic knee pain. Radiographic tibiofemoral osteoarthritis (TFOA) is present in 44–45% of these patients.[1] [2]

Tibiofemoral OA tends to be more focused on in research and management than PF OA. However, PF OA contributes to a significant proportion of patients' symptoms and functional impairments and should be addressed. Patellofemoral Pain Syndrome is thought to be a precursor to PF OA, but longitudinal studies have yet to prove this.

[3]


Diagnosis 

There are no specific diagnostic criteria for PF OA. It is diagnosed using a combination of clinical signs and symptoms, radiographic information from X-rays, and MRIs. 

Clinical Features

  • Anterior knee pain (especially on loading activities, eg stair climbing) - this is usually the significant finding in PF OA. 
  • Knee crepitus 
  • Swelling
  • Pain on Patellofemoral joint (PFJ) compression
  • Stiffness after sitting
  • Valgus knee deformity
  • Reduced Quadriceps Strength

It is important to note that pain may not originate from the PF joint itself. The surrounding structures, such as the fat pad, ligaments, bursae, muscles, etc, can also contribute to symptoms. [4][5]

Imaging

X-ray and MRI can both be used to diagnose PF OA. It is important to note that findings on radiological investigations do not always correlate with clinical symptoms. It has been found that in certain individuals who have positive findings on X-ray or MRI, have any knee pain or other symptoms of PF OA.[4] 

X-ray

X-ray is most commonly used to diagnose 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 has not been validated. 

A skyline view is most appropriate to view the PFJ. The presence of osteophytes and joint space narrowing confirms the clinical findings for PF OA. 

X-rays can 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 

MRI findings such as cartilage lesions, osteophytes and bone marrow lesions at the PFJ can be used to diagnose PF OA. There are no formal diagnostic criteria at present to diagnose PFJ on MRI [4]

Patellofemoral Osteoarthritis and Tibiofemoral Osteoarthritis

PF OA and TF OA can be found in isolation or in combination. There does seem to be a relationship between the two, and having either PF or TF OA is a risk factor for developing the other. The PFJ is often the first joint to present with symptoms. [4] It is still unclear as to whether PF OA will always progress to combined OA.[1]

Outcome Measures

Currently, there are no evidence-based patient-reported outcome measures specifically for PF OA. The KOOS (Knee injury and Osteoarthritis outcome scores) [6] 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 the early stages of PF OA as it may not challenge the joint enough.[1] 

Risk Factors

Abnormal Joint Alignment

Patellofemoral and tibiofemoral alignment have been implicated in PF OA. Treatment that corrects imbalances may help treat symptoms and prevent the progression of the condition.

Patellofemoral alignment

The following alignment patterns of the patella are a potential risk factor for PF OA. [7]

  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 three patella positions are commonly found in patients presenting with PF OA.[7] 

These alignment problems are commonly found in patients with PFJ pain. It is hypothesised that correcting these alignment issues could possibly prevent the progression to PF OA. However, this is still a theory and has not been proven. 

Patellas that are positioned higher (increased proximal translation) have been associated with worse PF OA symptoms. This could potentially be 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.[8] Generally, valgus deformities target the PFJ more. Isolated PF OA is more commonly found in knees with valgus. Combined PF and TF OA, as well as isolated TF OA, are more commonly found in knees with varus deformities. [7]

Abnormal Trochlear Morphology

A shallow trochlear is a risk factor for the development of PF OA. [8] 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.[8] 

Abnormal Biomechanics

Patellofemoral osteoarthritis (PFOA) occurs when the patellofemoral joint's articular cartilage cannot adapt to excessive loads from abnormal biomechanics. This leads to increased stress, often on the lateral patellar facet, wearing down the articular surface, and ultimately deteriorating the joint.[9]

Abnormal Kinetics and Kinematics 

"Small changes in alignment and stability can alter patellofemoral joint stresses."[9]

Decreased quadriceps strength is a significant risk factor in PFJ symptoms and development of PF OA.[4] Weakness or dysfunction in the proximal muscles at the hip have been implicated in PF OA such as gluteus medius, minimus and lower hip abductors.[4]

Teng et al (2015) found that progression of PF OA is related to increased peak knee flexion in the terminal stance of gait.[10] 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 stiffness.[5] Treatments targeted to correct these biomechanical faults may slow the progression of PF OA.

Altered joint alignment, as discussed above, is often not a structural problem and is 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. Weak hip abductors can also lead to increased femoral internal rotation and abduction, leading to altered patellofemoral alignment.[8]

Body Mass Index

Adults who suffer from PF pain tend to have a higher BMI. [11] Those with PF OA have a much greater body mass index (BMI) than controls. [11]

There is a debate about the association between BMI and PF OA.[12] Is this finding because PF Pain leads to decreased activity, and as such, BMI increases? Or, is it that the 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 an increased load due to BMI.[11] 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. Research has not yet been conducted on whether a reduction in BMI can ultimately change symptoms and radiological findings in PF OA.

Sex

Isolated patellofemoral osteoarthritis (PF OA) is more prevalent in women, who also report greater knee pain and disability compared to men. This suggests that the features of PF OA, as well as the biomechanical risk factors for patellofemoral pain, are sex-dependent.[13][12]

Treatment

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

Taping and Bracing

The goal of patellar taping and bracing is to 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.[14] The Q brace alters patella position and improves patella contact with the trochlea. [4] Taping the patella has also been shown to be effective, but its mechanism of action is uncertain and has not been studied to date. [4] However, a recent systematic review with meta-analysis by Souto and colleagues[15] concluded that " knee taping, (.....) and knee brace do not offer additional benefits to exercise alone."[15]

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[4]; however, it has been suggested that improving the function of the vastus medialis oblique (VMO) muscle in patients with patellofemoral disorders reduces the pressure applied on the lateral cartilage within the patellofemoral joint, thus helping to reduce symptoms. [16]

A systematic review of the effectiveness of exercise therapy in patients with knee osteoarthritis by Kitagawa et al., [17]concluded that exercise therapy can be used as a conservative approach; however, the evidence is inadequate.[17]

Surgical

Patella resurfacing has been suggested as a surgical option in treating PF OA. There has been 1 study to date, which did not show any difference between the intervention and control groups. [4]

References

  1. ↑ 1.0 1.1 1.2 Lankhorst NE, Damen J, Oei EH, Verhaar JA, Kloppenburg M, Bierma-Zeinstra SM, van Middelkoop M. Incidence, prevalence, natural course and prognosis of patellofemoral osteoarthritis: the Cohort Hip and Cohort Knee study. Osteoarthritis and cartilage. 2017 May 1;25(5):647-53.
  2. ↑ Hill JR, Oei EH, Crossley KM, Menz HB, Macri EM, Smith MD, Wyndow N, Maclachlan LR, Ross MH, Collins NJ. Classification approaches used to grade radiographic patellofemoral osteoarthritis: a scoping review. Osteoarthritis Imaging. 2025 Mar 1;5(1):100258.
  3. ↑ Patellofemoral joint Arthritis Indications for Treatment by Dr. S. Hayasaka. Available from:https://www.youtube.com/watch?v=zKrzvjfkkpg&ab_channel=OrthofracsAOA
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 van Middelkoop M, Bennell KL, Callaghan MJ, Collins NJ, Conaghan PG, Crossley KM, Eijkenboom JJ, van der Heijden RA, Hinman RS, Hunter DJ, Meuffels DE. International patellofemoral osteoarthritis consortium: consensus statement on the diagnosis, burden, outcome measures, prognosis, risk factors and treatment. In Seminars in arthritis and rheumatism 2018 Apr 1 (Vol. 47, No. 5, pp. 666-675). WB Saunders.
  5. ↑ 5.0 5.1 Robertson C. Patellofemoral Osteoarthritis Course Slides. Plus. 2019
  6. ↑ Crossley KM, Macri EM, Cowan SM, Collins NJ, Roos EM. The patellofemoral pain and osteoarthritis subscale of the KOOS (KOOS-PF): development and validation using the COSMIN checklist. British journal of sports medicine. 2018 Sep 1;52(17):1130-6.
  7. ↑ 7.0 7.1 7.2 Macri EM, d'Entremont AG, Crossley KM, Hart HF, Forster BB, Wilson DR, Ratzlaff CR, Goldsmith CH, Khan KM. Alignment differs between patellofemoral osteoarthritis cases and matched controls: An upright 3D MRI study. Journal of Orthopaedic Research®. 2019 Mar;37(3):640-8.
  8. ↑ 8.0 8.1 8.2 8.3 Macri EM, Stefanik JJ, Khan KK, Crossley KM. Is tibiofemoral or patellofemoral alignment or trochlear morphology associated with patellofemoral osteoarthritis? A systematic review. Arthritis care & research. 2016 Oct;68(10):1453-70.
  9. ↑ 9.0 9.1 Arias C, Lustig S. Physiopathology of patello-femoral osteoarthritis: current concepts. J ISAKOS. 2024 Aug;9(4):806-813.
  10. ↑ Teng HL, MacLeod TD, Link TM, Majumdar S, Souza RB. Higher knee flexion moment during the second half of the stance phase of gait is associated with the progression of osteoarthritis of the patellofemoral joint on magnetic resonance imaging. Journal of orthopaedic & sports physical therapy. 2015 Sep;45(9):656-64.
  11. ↑ 11.0 11.1 11.2 Hart HF, Barton CJ, Khan KM, Riel H, Crossley KM. Is body mass index associated with patellofemoral pain and osteoarthritis? A systematic review and meta-regression and analysis. Br J Sports Med. 2017 May 1;51(10):781-90.
  12. ↑ 12.0 12.1 Zhao J, Liu J, Han J, Wan X, Xu W, Zhang Z, Xu Y. Analysis of Risk Factors on Patellofemoral Osteoarthritis: Distribution Characteristics and Radiographic Parameters of Patellofemoral Joint. Orthop Surg. 2024 Dec;16(12):3151-3161.
  13. ↑ King MG, Ackland DC, Hart HF, Schache AG, Sritharan P, Pandy MG, Crossley KM. Walking biomechanics in women with patellofemoral osteoarthritis differ compared to men with and women without patellofemoral osteoarthritis. Braz J Phys Ther. 2024 Nov-Dec;28(6):101132.
  14. ↑ Callaghan MJ, Parkes MJ, Hutchinson CE, Gait AD, Forsythe LM, Marjanovic EJ, Lunt M, Felson DT. A randomised trial of a brace for patellofemoral osteoarthritis targeting knee pain and bone marrow lesions. Annals of the rheumatic diseases. 2015 Jun 1;74(6):1164-70.
  15. ↑ 15.0 15.1 Souto LR, De Oliveira Silva D, Pazzinatto MF, Siqueira MS, Moreira RFC, Serrão FV. Are adjunct treatments effective in improving pain and function when added to exercise therapy in people with patellofemoral pain? A systematic review with meta-analysis and appraisal of the quality of interventions. Br J Sports Med. 2024 Jul 1;58(14):792-804.
  16. ↑ Adel J, Koura G, Hamada HA, El Borady AA, El-Habashy H, Balbaa AE, Saab IM. Squatting versus squatting with hip adduction in management of patellofemoral osteoarthritis: A randomised controlled trial. Journal of back and musculoskeletal rehabilitation. 2019 Jan 1;32(3):463-70.
  17. ↑ 17.0 17.1 Kitagawa T, Isaji Y, Sasaki D, Onishi K, Hayashi M, Okuyama W. Effectiveness of exercise therapy in patients with knee osteoarthritis: an overview of systematic reviews. BMJ Open. 2025 Jul 16;15(7):e093163.
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