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Patella Problems and Injuries

Anatomy and Function of the Knee

Before you start, it will be very helpful to review our article on knee anatomy to better understand the anatomy of the knee, where the patella (knee cap) is located, and how the knee functions.

Anatomy and Function of the Patella

The patella, or kneecap, is the circular and more mobile bone that exists on the front of the knee.  The patella is part of the extensor mechanism of the leg; a major stabilizer of the knee and the primary extensor of the knee (i.e. straightens the knee). The extensor mechanism is composed of the quadriceps, the quadriceps tendon, patella and patellar tendon, and their associated soft tissues. The patella gives mechanical advantage to the quadriceps muscle and enables it to more powerfully straighten out the knee.

In order for the patella to track up and down normally within the patellofemoral groove (formed by the medial and lateral condyles of the femur), there has to be a balanced pull from both the lateral (outside) and medial (inside) sides of the patella. This balance is achieved by the overall alignment of the leg and the associated soft tissues around the knee. Importantly, a patella that stays centered within the patellofemoral groove throughout the knee’s full range of motion is a well-functioning patella.

The underside of the patella is covered with the thickest amount of articular cartilage found anywhere in the body. Articular cartilage is a smooth and spongy covering that is found on almost all joint surfaces. This slippery surface helps the patella glide within the patellofemoral groove of the femur as the knee goes through motion.

How The Patella Causes Knee Pain

People can develop knee pain when the cartilage under the patella begins to wear and tear. This results in softening of the cartilage (called chondromalacia patellae). Chondromalacia can develop for numerous reasons. Age (generalized wear and tear — similar to putting a lot of mileage on a car), trauma, or muscle imbalances around the knee can all contribute to the development of chondromalacia.

A very common knee problem is when the patella moves slightly abnormally as the knee bends or straightens. This happens because of an underlying muscle or structural imbalance around the knee. Normally the patella moves centrally within the patellofemoral groove — a path controlled by the quadriceps muscle and the patellar tendon.  Abnormal movement can cause wear and tear to the cartilage.

These aforementioned structural imbalances can exist if there are variations in the anatomy of the bones in the thigh or leg or due to increases in the Q-angle — the angle created between a line through the center of the quadriceps tendon and a line through the center of the patellar tendon. With an increased angle, the patella naturally wants to be pulled outwards out of the patellofemoral groove as the knee goes through range of motion. Women tend to have a greater angle than men.

Another structural variation that can contribute to knee issues is when the the lateral (outer) femoral condyle is smaller than normal. This forms the lateral “bunker” of the patello-femoral groove which keeps the patella tracking within the groove. If the femoral condyle is too small, this bunker may be non-existent. Consequently, the patella will have a tendency to slip out of the groove.

Abnormal mechanics of the patellofemoral joint can lead to altered pressures on the patellar cartilage which can lead to early chondromalacia and arthritis. It is also increases the risk of injury to the knee e.g. patellar dislocation.

Symptoms Of Patellar Problems

Bones of the knee joint

Depending on the underlying problem, symptoms vary.  For instance, people with chondromalacia patellae may experience vague knee pain that is hard to localize. Pain is commonly associated with walking down stairs or hills, keeping the knee bent for long periods of time (i.e. prolonged sitting), or while kneeling. The knee may even feel as though it wants to gives out on occasion, but this is a reflex response to pain and not an indication of instability in the knee. Finally, you may feel that your knee grinds or pops when squatting or going up and down stairs. This occurs with motion as the normally smooth surfaces of the patella and femur become roughened and rub against one another.

Patellar instability can occur after a patellar dislocation.  After the first dislocation, it may continue to want to dislocate, making it hard for you to trust your knee.

How Are Patella Problems Diagnosed

Diagnosis begins with a complete history i.e. your story regarding your knee pain, how it started, and what types of activities aggravate it.  Your physician will examine you while standing, sitting, and/or lying down. Strength of the muscles around the knee will be tested. X-rays will likely be performed by your primary care doctor prior to visiting with an orthopedic surgeon. An x-ray helps doctors better understand the alignment of your knee and if there is any evidence of any bone issues like fractures or  underlying arthritis.

If symptoms persist, however, a MRI scan may be needed to look more closely at the knee to see what might be causing your symptoms. Ultimately, if surgery is warranted, knee arthroscopy will additionally allow for the identification of any problems that were not seen on X-rays.

What Are The Treatments For Patella Problems

For the most common patellar problems, symptoms improve with a short period of rest, anti-inflammatory medication and physical therapy. Physical therapy typically consists of exercises to strengthen the muscles around the knee. Additionally, the therapists will work with you to improve upon your flexibility. Both of these factors will allow for a more well-balanced and a better functioning knee.

For instance, with chondromalacia patellae, usually the Vastus Medialis Obliqus (VMO) muscle is targeted for strengthening. While helps for improved mechanics of the patellofemoral joint.

If anti-inflammatory medications and physical therapy fail to address your issue. Depending on your underlying problem, your doctor may recommend a steroid injection. With a steroid injection, a strong anti-inflammatory is injected into the joint space.

If non-surgical treatments fail to improve your condition, surgery may be warranted. For instance, with patellar instability, the patella has a tendency to want to dislocate laterally (outwards). Usually this is due to a structural problem with your knee. A lateral release may be performed to improve the sliding mechanics of the patella — specifically, to ensure that it stays centered in the patellofemoral groove with motion. In a lateral release, the tight lateral ligaments on the outside of the patella are cut to allow the patella to move towards the center of the femoral groove.

Depending on the severity of your malalignment, the medial (inner) aspect of the patella may also need to be reinforced to further ensure that the patella stays centered with knee motion.  This latter surgery is called a MPFL (medial patello-femoral ligament) reconstruction.

In very severe cases where the patella keeps dislocating, the attachment of the patellar tendon on the tibia may also have to be moved. Once the surgery heals, the patella will track centrally within the patellar groove, reducing pressure on the articular cartilage.


  1. My knee has always had problems with it buckling. Usually it hurts for a few days and then I’m fine until it happens again. I make sure not to do squats, lunges, running, etc. so that I won’t strain my knee. Lately, however, I’ve been abl to move my patella in and out of place without pain. Kind of like flexing a muscle. I’m not rly sure wat to do-if u know, pls help

  2. Patricia Ojeda says

    Our daughter fell and shattered her kneecap. She had surgery but the kneecap could not be completely re-constructed because pieces were missing. It has been almost a year and she cannot put any weight on that foot. She recently had an MRI that determined that due to the surgery and injury her foot mechanism has now been altered and she cannot stand on that foot. Is there anything that she can do to repair or replace the kneecap and get the leg and foot in proper alignment so that she can walk again. She is 64 Years of age and prior to the injury she was very mobile.

  3. I was in a car accident 28 years ago. Fractured my right femur, right pelvis, pubic bones, tailbone, peroneal nerve palsy, both lungs collapsed and traumatic head injury. The nerve damage caused ultra sensitivity from knee down and drop foot. Myfoot felt like it was in a pan of boiling water for years. Anything that touched it exacerbated the pain, socks, shoes, water, blankets, even the air. I was in the hospital for 2 months. In the hospital, I held my foot in my arms up to my chest to keep anything from brushing against it. I’m not sure why I was allowed to do this. My femur healed malrotated 90° and my tendons and ligaments behind my knee shortened so I couldn’t straighten my leg. My pelvis, pubic bones and tailbone all healed misaligned . I was in a wheelchair for over 2 years before they did the corrective surgery to straighten my femur, but they didn’t correct the rest. 16 months on crutches, another year back in my wheelchair, 14 months on crutches. Early 1997, I was upright with a foot brace. Within a few months, the knee pain started. The inside of my knee hurt with every step. If I layed down on my left side, it felt like my bones were pinching ligament. On my right, it felt like it was separating. I have seen dozens of doctors, orthopedics, endocrinologists, neurologists. I have had over a dozen MRIs, multiple CT scans, atleast 20 cortisone shots, 3 arthroscopic surgeries, several dozen arthritis meds, anti-inflammatories, muscle relaxants, pain killers, nearly 100 needle aspirations….none of it has helped. Now, the cartilage is completely worn away. It hurts to walk, sit, stand and lie down. I slide my foot when I’m walking to keep my knee from separating when it comes off the ground. I was scheduled for a total knee replacement but they cancelled it when my doctor actually looked at my knee without xrays. I have an 8° femoral neck anteversion, my knee is externally rotated over 35° but my tibia and foot are straight. I wish someone had answers. I’m tired of being a big pharma guinea pig. Thoughts?

  4. MaryAnn Fox says

    Hi, I broke my left knee cap 20 years ago. I never had any problems until recently when I sprain my LCL ligament On my right knee. I had to use crutches for almost three months therefore my left knee took all my weight. So now, whenever I’m getting up, walking up a hill or walking for a long period of time it really hurts. Can just three months of over using my left knee cause so much damage that now it hurts on the daily? My doctor said it’s because I lost my muscles around the knee that’s why it is hurting. I’m wondering what kind of exercises I should do to strengthen the muscles around my left knee. Can’t do squats they cause more pain. Thank you!

  5. Sergei simon says

    Hi Doctor
    My daughter was born with a deformed patella ( where our knee cap is in its right place, hers is slightly a little higher), which cause her not to be able to straighten the leg At all, so she’s walking with a limp. Can surgery be done

  6. Angela Younger says

    My doctor I went to told me my joints in knees look good but my knee caps are worn out and rubbing against bone and I should lose weight to see if that helps cause he couldn’t do anything.

  7. I have noticed for a while that when I walk it feels like my knee cap has slid down. My mother has taken me to a physio and we’ve had an X-ray and nothing has shown up. Could this maybe be whats causing the pain?

  8. James grooms says

    My knee has popped out the times in the past two months. If I get on my knees at work to plumb a sink or anything it pops out. When in get up I can’t walk. I got to bend it back and forth then it pops back into place. What is going on? I’m 44 and never had any knee problems.

  9. My knee cap can move up and down + left and right.. I don’t know if it’s broken or if it’s just normal.. and when i stand up, i can move it up without touching it. Please give me some advice. Thank you.

  10. Years ago I was playing a 2-on-2 game of street basketball. I was driving to the hoop for a lay-up, getting by this kid, he then kicked my left knee out on purpose and my patella/kneecap was completely dislocated.

    So I am on the ground in excruciating pain and everyone is freaked out because they have never seen an injury like that before. So I go to try and adjust my leg and there was a loud POP. My kneecap slid back in place and surprisingly felt OK. I could move it and all. I even refused the ambulance when it had arrived because I thought I was OK. Til the swelling began to kick in….

    So of course I wound up in the hospital because my knee swelled up to the size of a volleyball. They just gave me 1 Vicodin with no prescription for more, which sucked. They also just gave me a knee splint, and some papers about the R.I.C.E healing method (Rest Ice Compression Elevation).

    I was completely immobilized for 3 weeks. Since I didn’t have meds for the pain, the healing time was one of the absolutely most painful periods of my life!

    3 weeks later I thought I was good enough to move around as long as I wore a brace. One day, I was getting ready to leave the house and out of nowhere the loud POP sound came, and down to the ground I went. So I wasn’t fully functional after 3 weeks, and it took about 6 months for the swelling to subside and make my knee not look slightly deformed any more.

    Years later now, I notice my knee still tries to slide out of place. If I tweak it bad enough it will almost try to slide out all the way. It just happened to me yesterday. It hurt so bad, now I have some pain and swelling on the inside of my knee. It hurts when I crouch and turn corners mostly.

    My question is, since this is a chronic problem (14 years later after initial injury) does this constitute needing surgery ?

  11. Hey! I see some stories of people saying ‘’ I went to the doc and he said he can’t do anything for me” if you honestly think it’s bad go and see someone els!!

    My doc told me that and I just left it. When I would bend down my right knee would grind not crack it would make a loud 1second grinding sound. After 9months seeing him I jumped onto a small stage and dislocated my right knee. I needed surgery and had loose bone fragments and cartilage. Got a latteral release done and have level 4 (highest) wear and tear on kneecap. It’s been 2 months swine surgery and still not back on track. Keeps getting stiff after being on in for 3+ hrs and starts to hurt after 5hrs. Hurts when I try and lift it up while the leg is straight. Still going back to the doctor every month per his request.
    I’m 26 haven’t had a if sports life.

    Always get a second opinion

  12. what can I do for the patella against shin bone

  13. My dr said to give up running and cycle to build up the quads. To balance the muscles

  14. MAULIK PARIKH says

    I am facing, the problem, exaclty the way it is written out here. it looks like my story, word to word. I am 46yrs and am a long distance runner and a tri-athelete. as said here, the medicines do give a relief but not a cure. it seems, the strength of the muscles surrounding and attached to my patella is unequal and not properly structured, may be because of impropermuscle development on account of my long distance activity. i fear a surgery, as i feel it might disturb the natural setup of my knee design, and would not be able to run again. the pain is bearable but resting without any daily workout, over this last 4months is a big agony.

    if anybody can direct me to the correct ailment, i would be deeply obliged

  15. My left. Knee keep pop and cracker a lot I went the doc I did threpy for it it didn’t help made it worst go back my doc he want me to MRI I did that after he told me that he can’t do anything for me I’m reading this and sound like it can be fix I’m a running I can’t run anymore I’m 37 years old

  16. hello
    dr. i had my kneecap operation before 2yrs, my kneecap is removed as it was broken into 5pieces. but till now i m not able to walk properly. i can only band my leg to 15degree.
    i really want to be like a normal boy i want to live my life normally like others. please help me. please tell me what should i do to get the movement!!
    i m going in depression day by day. please help me!!

  17. My Dr said that I may have burst a cushion in my knee but he wanted the x-ray and ultrasound back before speculating on options. When I was 39 weeks pregnant I had a fall and protected my belly by landing on my left knee. The knee was very swollen and bruised immediately after the fall. The knee is still swollen after 6 weeks as past since the injury happened. Does a knee cushion repair its self or does it need medical intervention?

  18. Regarding patella knee problems what sort of exercises should be conducted to help or elevate this problem?
    Thank you

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