Your knee creaks and hurts and it gets worse going up or down stairs, getting up after sitting a while, and when keeping the knee bent. Don’t even bother trying to squat. Sound familiar? You could be experiencing a condition called patellofemoral arthritis. Never heard of it? The authors of this article provide an in-depth review — everything you ever wanted to know about patellofemoral arthritis.
The patella (kneecap) is the moveable bone on the front of the knee. The underside of the patella is covered with articular cartilage, the smooth, slippery covering found on joint surfaces. This covering helps the patella glide (or track) in a special groove on the femur(thighbone). This groove is called the trochlear or femoral groove.
Patellofemoral arthritis occurs when there is a loss of the articular cartilage on the back of the patella and/or in the femoral groove. Wear and tear on the patella can occur anywhere but most often, the lateral edge (side away from the other knee) gets overloaded first. Experts think a slight tilt or malalignment of force contributes to the development of this problem.
Because the knee is in the middle of the leg, any changes in alignment from the pelvis down to the foot can create patellofemoral problems. The quadriceps muscle along the front of the thigh helps control the patella so it stays within its groove. If the quadriceps is weak for any reason, a muscle imbalance can occur. When this happens, the uneven pull of the quadriceps muscle may cause the patella to move more to one side than the other. This in turn causes more pressure on the articular cartilage on one side than the other. In time, this pressure can damage the articular cartilage.
Weakness of the muscles around the hip can also indirectly affect the patella and can lead to patellofemoral joint pain. Weakness of the muscles that pull the hip out and away from the other leg, the hip abductor muscles, can lead to imbalances to the alignment of the entire leg – including the knee joint and the muscle balance of the muscles around the knee. This causes abnormal tracking of the patella within the femoral groove and eventually pain around the patella.
Treatment for this problem has not been very successful in the past. But new understanding of the biomechanics (anatomy and function) of the joint have opened up new management techniques. The first step is to see a physical therapist. The therapist will design a therapy program to restore full, balanced strength and function of the hip and knee muscles.
Activity modification will be required. Avoiding stairs, squatting, jumping, and biking can reduce the load on the patellofemoral joint. Weight loss is always advised for anyone who is overweight. Reducing the stress, pressure, and load on the joint can be very helpful. Medications such as pain relievers and antiinflammatories may be prescribed. Occasionally, the use of steroid or hyaluronic injections is beneficial.
Some patients find relief from pain using a patellar unloading sleeve (a slip on neoprene support). Bracing or taping may also be helpful but studies are lacking in providing evidence that these measures really make a difference. Often, a combination of these nonsurgical treatment approaches works the best.
But, if after three to six months, there’s been no improvement, then some patients may be candidates for surgery. What can the surgeon do? Well, there are a variety of techniques that can be used. Which one is best differs for each patient and depends on the underlying cause of the condition.
In some cases, it’s just a matter of removing any bone spurs and smoothing the edges of the patella. Other patients benefit from the release of the lateral retinaculum. This is a fibrous band of connective tissue along the outside edge of the patella. When it gets bound down or tethered, it can create uneven pull and a restraint to the natural up and down movement of the patella.
If there are holes in the articular cartilage called defects, it may be possible to repair the damage. A newer technique called autologous chondrocyte implantation (ACI) has had favorable results. Normal, healthy cartilage is removed from a nonweight-bearing portion of the knee joint. The cells are taken to a lab where they are used to grow more cells. The cells are then transplanted back into the patient to fill up the hole.
Cartilage implantation has worked well for smoothing out the surface of the knee joint. It may not be as successful along the back of the patella. There are two main reasons for failure of this technique. The first is abnormal tracking of the patella. If the patella is not riding up and down in the center of the femoral groove, the same problem will develop again. Anything contributing to the malalignment of the patella must be addressed along with chondrocyte implantation.
Secondly, resurfacing the patella may be successful but the patellofemoral joint takes quite a beating everyday. There is a lot of pressure and load on the surface of the patella. The mechanics of gliding up and down over the femur put a much greater demand on patellar articular cartilage than even on the knee joint itself. The implantation may not be able to hold up under such rigorous conditions.
Other procedures that may help alleviate pressure from the patellofemoral include tibial tubercle transfer, patellectomy (remove the patella), and patellofemoral arthroplasty (replace the patella). The authors describe the indications and use for each of these operations.
Tibial tubercle transfer refers to the removal and relocation of the bump of bone called the tibial tubercle. This is the insertion point for the quadriceps muscle. The idea in transferring this area of bone is to change the pull of the quadriceps muscle on the patella and thereby reduce the load on the arthritic patella. The surgeon must plan this procedure carefully, using the results of X-rays, MRIs, and arthroscopy to determine what type of incision to use, where to make the incision, and how far to move the tubercle.
Treatment of patellofemoral problems is difficult. Disabling knee pain and patellofemoral breakdown may not respond to any of these limited surgical interventions. Sometimes it’s necessary to remove the patella completely. This is considered a more radical approach but it’s a simple and safe procedure that works. The down side is that the patient is left with a big loss in knee extension strength.
One alternative to just a patellectomy alone is a patellar replacement. A screw-on patellar shell is used to replace the patella once it is removed. Early efforts at patellofemoral replacement resulted in as many failures as successes. Newer designs and 3-D technology for designing the implant to fit the patient have improved overall results.
If all efforts fail to improve symptoms, motion, and function, then a total knee replacement (TKR) may be the final choice. This procedure is not advised for younger patients but reserved for older adults. Because of the abnormal alignment and mechanics that led to the patellofemoral arthritis in the first place, surgeons must approach a total knee replacement carefully. Imbalances must be corrected during the procedure to ensure optimal results.
What does the future hold for patients who develop patellofemoral arthritis in the years ahead? The hope is to identify contributing factors early enough to prevent this problem from developing. Short of that, restoring damaged cartilage is the focus of a new area of study called orthobiologics. And for those who end up with a patellar or full knee replacement, improved implant designs and surgical techniques will continue to provide satisfactory pain relief and restored knee function.