Patellofemoral osteoarthritis (Knee cap arthritis)

Ross Hauser, MD

Typically, when someone reaches out to us about their knee pain and degenerative arthritis, they tell us of the many problems their knee MRI picked up including bone on bone knees and thin or no cartilage. Their MRI may suggest little or no cartilage between the thighbone and the shinbone under the kneecap. Some people may have meniscus damage some people may have little meniscus damage. There may be swelling under the knee cap and the development of bone spurs on the patella itself. Their knee ligaments may show no signs of damage, but the MRI typically cannot pick up weakness or looseness in the knee ligaments, only more obvious tears. The same can be said of the patella tendon and the quadricep tendons.

Whole knee problems

Sometimes a patient will write of a history of patella dislocation in one of both knees. Many will tell us that these dislocations occurred in their younger careers as school or academy athletes. They will also reveal a history of arthroscopic surgeries with limited successes and eventually a recommendation for a knee cap replacement. Some will have the surgery, others will opt for physical therapy and a continuation of conservative care options.

For some people, the problem will start when they had surgery for another knee problem. They may have had a meniscus surgery or other arthroscopic repair. Following the surgery they had anterior or front of the knee pain. Eventually they received a diagnosis of arthritis, and/or fibromyalgia, and/or patellofemoral pain syndrome.

In some people the focus falls explicitly on the patellofemoral joint, the joint between the back of the knee cap and the groove of the thigh bone and the disappearance of the cartilage of this joint. While in others, the three compartments of the knee, the medial inner surface between thigh and shin bones, the lateral outer surface between thigh and shin bones, and behind the knee cap will suffer from significant cartilage loss and be diagnosed as tricompartmental arthritis.

Patellofemoral osteoarthritis conservative care treatments

If you suffer from patellofemoral osteoarthritis you probably have you own history and continuance of resting, anti-inflammatory medications, physical therapy, patellar braces, corticosteroid injections, and hyaluronic acid and other injections for knee osteoarthritis. Ultimately your knee pain progressed and now you are looking for surgical options or surgical alternatives.

What are we seeing in the image below?

Ultrasound evidence of patellofemoral knee compartment osteoarthritis. The kneecap (patella) and the femur form a joint called the patellofemoral joint. The top or upper part of the image shows mild arthritis in patella femoral joint. Measurements of the trochlear articular cartilage with taken (see measurements). The lower bottom image shows severe osteoarthritis in the patellofemoral joint where no cartridge was resent. Measurements were difficult to obtain because of the significant decrease in trochlear articular cartilage.

Ultrasound evidence of patellofemoral knee compartment osteoarthritis

Postoperative anterior knee pain following knee replacements and patella resurfacing

A September 2022 paper in The Journal of arthroplasty (1) examined why patients had front of the knee pain following a primary unilateral total knee replacement with a posterior-stabilized prosthesis and patellar resurfacing.

In looking for answers the researchers write: “Factors related to postoperative anterior knee pain and its impact on patient outcomes are poorly understood.” To help discover these answers this study included 506 patients who had undergone elective primary unilateral total knee replacement with a posterior-stabilized prosthesis and patellar resurfacing. Outcome measures prior to and 12 months after total knee replacement included self-reported anterior knee pain, knee function, and quality of life.”

  • Prevalence of anterior knee pain was 72% prior to and 15% following total knee replacement.
  • Patients who had preoperative anterior knee pain had twice the risk of experiencing anterior knee pain after total knee replacement than patients who did not have preoperative anterior knee pain.
  • Conclusion: One in seven patients reported anterior knee pain 12 months following posterior-stabilized and patella-resurfaced total knee replacement. Suspected cause: The presence of preoperative anterior knee pain

Do not resurface normal patella during knee replacement

A September 2022 study in the journal Clinics in orthopedic surgery (3) looked at forty-three patients who underwent bilateral primary total knee replacement with patellar resurfacing on one side only. The researchers resurfaced normal patellae as well as damaged patellae routinely with the belief this would help patients long-term. What they found was the the patella resurfacing in a non-damaged patella was not that helpful. They concluded: “It is advisable not to perform resurfacing on normal patellae. However, in order to apply this result to damaged patellae, comparative studies between resurfaced patellae and damaged patellae are needed.”

Comparing patellofemoral replacement with total knee replacement in patients with isolated patellofemoral osteoarthritis

In this September 2022 paper published in the Journal clinical orthopaedics and related research (5) followed up on a previous 2-year outcome study comparing patellofemoral replacement and total knee replacement for isolated patellofemoral osteoarthritis. The researchers had found advantages of patellofemoral replacement over total knee replacement for range of motion and various aspects of knee-related quality of life as assessed by patient-reported outcomes at two year follow-up. When follow-up was extended to six years the researchers examined contradictory evidence that patellofemoral replacement revision rates from 2 to 6 years increased after surgery at a time when annual total knee replacement revision rates are decreasing, which suggests rapidly deteriorating knee function in patients who have undergone patellofemoral replacement. The researchers questioned this and suggested that their tests showed two-year outcomes did not deteriorate during the subsequent four years. They write: “Patients who underwent patellofemoral replacement had a better quality of life throughout the postoperative years based on several of the knee-specific outcome (self-report patient surveys).” However, they also note: “Our findings cannot explain the rapid deterioration of results implied by the high revision rates observed in implant registers (the high revision rates observed in other studies), and it is necessary to question indications for the primary procedure and subsequent revision when patellofemoral replacement is in general use. Our data do not suggest that there is an inherent problem with patellofemoral replacement implant type as otherwise suggested by (other studies).”

In other words, this research did not see the same problems with high revision rates and implant failures seen in other studies. So the question, is patellofemoral replacement better than total knee replacement in patients with isolated patellofemoral osteoarthritis? Remains.

Patellofemoral Osteoarthritis and Patella Alta

A September 2022 study in The journal of knee surgery (4) looked at the connection between patella alta (a high riding knee cap in relationship to the rest of the knee), suggested that patella alta is commonly found in patients with patellofemoral osteoarthritis and that patellofemoral joint replacement can decrease patellar height.

Matrix-induced autologous chondrocyte implantation (MACI)

An October 2022 paper in the International orthopaedics (2) investigated outcomes in cartilage repair and its preventative factors in patellofemoral osteoarthritis patients at a three year follow-up after matrix-induced autologous chondrocyte implantation (MACI). This study included 32 patients who underwent matrix-induced autologous chondrocyte implantation (MACI). The researchers found that MACI can lead to significant pain relief and restoration of knee joint function, and good quality cartilage repair tissue was a protective factor against patellofemoral osteoarthritis at the three year follow-up.

When a patella is too far gone and needs an orthopedic consult

Knee x-ray showing chondromalacia patella and bone spur. This is the knee of a 66 year-old woman who was diagnosed with knee osteoarthritis associated with chronic pain and a grinding sensation under the kneecap. Patient had two previous knee surgeries. She was getting minimal improvement from Prolotherapy treatments, To assess her situation, an x-ray was ordered. The x-ray revealed minimal joint space under her kneecap consistent with chondromalacia patella and the grinding sensation she experienced. Notice also the hook bone spur offer patella. Because of the abnormality of the bone spur, continuing Prolotherapy was not the best treatment option for her and despite two previous surgeries, she needed an orthopedic consult.


1 Silva DD, Webster KE, Feller JA, McClelland JA. Anterior Knee Pain Following Primary Unilateral Total Knee Arthroplasty With Posterior-Stabilized Prosthesis and Patellar Resurfacing: Prevalence and Clinical Implications. The Journal of Arthroplasty. 2022 Sep 5. [Google Scholar]
2 Lyu J, Geng H, Zhu W, Li D, Chen K, Ye H, Xia J. Correlation between the quality of cartilage repair tissue and patellofemoral osteoarthritis after matrix-induced autologous chondrocyte implantation at three-year follow-up: a cross-sectional study. International Orthopaedics. 2022 Oct 5:1-8. [Google Scholar]
3 Ko YI, Yang JH, Choi CH. Comparison of Clinical Outcomes after Total Knee Arthroplasty with and without Patellar Resurfacing in the Same Patients. Clinics in Orthopedic Surgery. 2022 Jan 14;14. [Google Scholar]
4 Lee H, Fletcher C, Hartwell M, Strickland SM. Effect of Patellofemoral Arthroplasty on Patellar Height in Patients with Patellofemoral Osteoarthritis. The Journal of Knee Surgery. 2022 Sep 1. [Google Scholar]
5 Odgaard A, Kappel A, Madsen F, Kristensen PW, Stephensen S, Attarzadeh AP. Patellofemoral Arthroplasty Results in Better Time-weighted Patient-reported Outcomes After 6 Years than TKA: A Randomized Controlled Trial. Clinical orthopaedics and related research. [Google Scholar]




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