Patella alta describes a situation in which the position of patella is high. It may might be idiopathic meaning that is occurs from unknown cause or it could result secondary to a condition such as patellar tendon rupture. It may also occur due to spastic cerebral palsy. Several conditions are associated with patella alta and they include knee joint effusion, recurrent dislocation of patella, and idiopathic retropatellar pain.
What is patella?
Patella is also referred to as kneecap or kneepan, and it is a thick, circular triangle-shaped bone articulating with the thighbone or femur. It covers and protects the frontal articular surface of knee joint. Patella sits at the frontal part of knee and plays the role of a fulcrum where it helps increase the moment arm of quadriceps muscles at the anterior of the knee thereby increasing the power and efficiency of knee extension.
It also helps in guiding the extensor mechanism ensuring that it is aligned in the middle of front part of knee. The back of patella has a layer of articular cartilage that offers a contact surface thereby ensuring low friction and reduction in wear. The shape of patella is obscure, and the number and direction of the different soft tissue attachments including tendons, muscles, ligaments, and retinaculae are also complex.
When the patella sits too high, it is called patella alta but when it sits too low, it is called patella baja or patella infera. A high riding patella or patella alta is a variation in anatomical alignment of the patella or kneecap in relation to the surrounding bones.
Causes of patella alta
Although patella alta is not considered hereditary, it might occur due to an overgrowth of patellar tendon in puberty thereby resulting in high riding patella. Other conditions, which are associated with patella alta are such as recurrent patella subluxation, patellar dislocation, poliomyelitis, cerebral palsy, and chondromalacia of patella.
It may also be associated with patellar ligament rapture, femoral osteomyelitis, Sinding-Larsen-Johansson disease, and Osgood-Schlatter disease. Patients with cerebral palsy may show patella alta and prepatellar bursitis due to crawling. In cerebral palsy, patella alta features a lengthened and higher positioned patella because of chronic spasms.
It is quite difficult to clinically assess the exact position and height of patella in relation to deeper structures of knee by its look or feel at the front of knee. X-rays are performed, though the reports also don’t give much about appearance of knee. Therefore, for proper analysis, a knee specialist has to actually have a look at the images and not just the reports in order to make a detailed assessment.
When the patella sits too highly, it is likely to cause patellar instability and increased contact pressure on frontal surface of patella. When a patient is in a standing position, an examiner positions himself or herself on the side of a patient and assesses for a camel back sign on knee. In patients with patella alta, a camel back sign is usually observed.
The first hump represents the high positioned patella while the second hump represents infrapatellar fat pad or the infrapatellar bursa. In a sitting position, a normal patellae is directed towards the frontal part of knee but in case of patella alta, it is appears directed upwards.
Complications associated with patella alta
When a person has patella alta, there is increased chances of having patellar instability. When patella sits too high, it only engages in trochlear groove sometimes later in flexion arc when the knee is bent greater than the normal degrees, which are usually between 20 to 30 degrees. What this means is that the patella is likely to be less stable for much of the time.
In addition to that, since in patella alta, the patellar tendon is longer, it means that it has a greater windscreen wiper action or effect. The longer the patellar tendon, the more it is likely to move side-to-side, which makes it unstable. A high riding patella puts pressure on kneecap, something that may result in anterior knee pain, increased wear and tear, and articular cartilage damage on back of patella. This may eventually lead to patellofemoral arthritis.
Treatment of patella alta
People with patella alta experience gait instability and pain. The treatment helps allow for normal function of knee and relieve the discomforts. Conservative treatments include manual griding, patella taping, ice packs, weight loss, and sleeves for knees. Physical therapy such as closed chain strengthening and other exercises may also help bring the patellar to its position.
Surgery may be opted to bring back the patella to its position. A surgery procedure referred to as tibial tuberosity advancement osteotomy is the most commonly applied in correcting this deformity of the kneecap position. When surgery is performed, the knee movement is restricted and one may remain in knee splints or braces for about 6 weeks following the surgery.