Dr Noyes discusses the problems that can be faced when arthrofibrosis pulls the kneecap too low in the joint.

First published by Dr Noyes in 2008, and reviewed August 2023 by Dr Sheila Strover (Clinical Editor)


Patella infera refers to a condition in which the patellar tendon shortens and the patella is pulled downwards on the tibia, as is shown in the two x-rays below.

It is also referred to as 'patella baja'

patella inferanormal patella

The left hand x-ray is of a patient’s knee before an anterior cruciate ligament reconstruction and meniscus repair that were performed at another orthopaedic Center. The patella is in the normal position. The right x-ray is of the same knee just 4 weeks following surgery after the patient was referred to our Center with significant quadriceps atrophy and limited knee motion and patellar mobility. You can see that the patella has dropped significantly.

[Noyes FR, Barber-Westin SD: Chapter 41: Prevention and treatment of knee arthrofibrosis. This article was published in Noyes’ Knee Disorders: Surgery, Rehabilitation, Clinical Outcomes, Noyes FR, Barber-Westin SD (eds.), pp. 1053-1095, Copyright Saunders, 2009.]

Patella infera may occur due to many reasons, such as poor rehabilitation following knee surgery; a fracture in the femur, tibial plateau, or patella; rupture of the quadriceps muscle; or as a result of reflex sympathetic dystrophy or complex regional pain syndrome.


Early signs and symptoms of patella infera are:

  • Pain with quadriceps contraction
  • Poor, inadequate contraction
  • Soft tissue swelling, edema
  • Joint stiffness, limited motion
  • Decreased patellar mobility, peripatellar contracture
  • Decreased tension in the patellar tendon


To prevent patella infera, steps to prevent arthrofibrosis are taken before and after surgery. The patient is instructed preoperatively on the importance of achieving a voluntary quadriceps contraction as soon as possible after surgery, which is expected to occur by the second postoperative day. Patellar mobility is assessed weekly by the therapist to detect any early contracture.

Serial lateral radiographs are taken to detect any decrease in patellar height for patients demonstrating limited patellar mobility or in whom an early arthrofibrotic response is detected. The height of the patella is measured as shown below.

[Noyes FR, Barber-Westin SD: Chapter 41: Prevention and treatment of knee arthrofibrosis. This article was published in Noyes’ Knee Disorders: Surgery, Rehabilitation, Clinical Outcomes, Noyes FR, Barber-Westin SD (eds.), pp. 1053-1095, Copyright Saunders, 2009.]

measuring the patella

On the left image, the numerator (line segment A) is the distance between the most ventral (anterosuperior) rim of the tibial plateau and the lowest end of the patellar articular surface. The denominator (line segment B) is the maximum length of the patellar articular surface. An alternative numerator (line segment C) locates the tibial reference point on the middle of the tibial plateau. The patellar vertical-height ratio equals A/B or C/B. Right, the numerator (A) is the superior most aspect of the trochlear cartilage that is in contact with line segment B. The denominator (line segment B) is the maximum length of the articular patellar surface. Using this method, the mean index is 32 + 12%, greater than 50% is a patellar infera, and less than 12% is a patella alta.


Treating Early Patella Infera

If a transient (or early) patella infera condition is detected, it can usually be resolved through supervised rehabilitation and an arthroscopic release of contracted tissues. Emphasis is placed on regaining normal knee motion, patellar mobility, and quadriceps muscle strength. Joint effusions are aspirated as required to promote full voluntary quadriceps contractions Knee motion and patellar mobilization exercises are performed 4-6 times daily. Electrical muscle stimulation and biofeedback are used to promote strong quadriceps contractions. Strenuous exercises are avoided that might aggravate the inflammatory condition. Oral corticosteroids may be considered if non-steroidal anti-inflammatory medications are not successful in resolving joint swelling.

If an early patella infera goes unrecognized or untreated for a few months, it then becomes established and is much more difficult to treat.


Treating Chronic Patella Infera

Patients with chronic, established patella infera required more extensive treatment methods in an attempt to restore the normal height of the patella. Established patella infera results from a cascade of events:

  • Quadriceps weakness - Initially inhibited by the pain, the quadriceps becomes weak and wasted.
  • Contracted peripatellar retinacular tissue - As part of the capsular thickening, the fibrous structures at the sides of the patella become thickened and contracted.
  • Chronic patellar entrapment - The patella becomes immobile, and unable to be moved from side to side or up and down.
  • Quadriceps contracture - In response to disuse, the quadriceps tendon above the patella contracts.
  • Fibrosis of the patellar tendon - Below the kneecap, the patellar tendon gets involved itself in developing abnormal fibrous tissue, and the deep and superficial infrapatellar bursae scar up.
  • Scarring of the infrapatellar fat pad - The process extends to the fat pad.
  • Chondrification and calcification of the capsule, fat pad and surrounding tissues - Fibrous tissue starts to change even further, turning partly into cartilage and calcifying like bone.
  • Infrapatellar contracture syndrome - The whole block of tissues below the patella contract.
  • Permanent shortening of the patellar tendon - The fibrous tissue in the patellar tendon contracts permanently.
  • Patellar infera - The patella is pulled downwards towards the tibia.
  • Patellofemoral arthrosis - The softened joint surfaces between patella and underlying groove of the femur disintegrate.


The patella infera condition is classified into one of two types based on the damage to the articular cartilage. Several years ago, we described a group of patients who had severe damage to the undersurface of the kneecap and in these cases, the surgical option of lengthening the patellar tendon to correct the position of the kneecap was not of benefit. In these patients, we remove the scar tissue and restore the retinaculum to help alleviate some of the pain, but they realize they are gradually going to wear out their kneecap and require a knee replacement.

There is a second form of patella infera where a young patient has lost (for example) 50 percent of the length of the tendon and still has relatively normal articular cartilage. Here, you want to protect the joint and restore the patella to a normal position. In these rare cases, there are two ways to accomplish this goal. One procedure is referred to as a DeLee osteotomy –the tibial tubercle is removed and advanced proximally, which is a good way to restore the patella to its normal congruity with the femur. The second option is to lengthen the patella tendon – which is a little bit more difficult to do, but is the best way to restore the patella to its normal position because we are not moving the tibial tubercle.

Before any surgery is considered, the patient must re-establish quadriceps muscle function to avoid a quadriceps shutdown after the surgical procedure. Then, the contracted and scarred tissues are removed either by arthroscopic or open surgery. This is followed by a number of months of intensive supervised physical therapy. This protocol helps many patients, especially those who are willing to live with some functional limitations, understanding that an eventual knee arthroplasty procedure may be required.

z-plasty x-rays

[Noyes FR, Barber-Westin SD: Chapter 41: Prevention and treatment of knee arthrofibrosis. This article was published in Noyes’ Knee Disorders: Surgery, Rehabilitation, Clinical Outcomes, Noyes FR, Barber-Westin SD (eds.), pp. 1053-1095, Copyright Saunders, 2009.]

For those rare cases where patellar tendon lengthening is indicated, the procedure is done at this point. If possible, the patient’s patellar tendon undergoes a z-plasty lengthening and then is augmented with a graft made from the patient’s semitendinosus and gracilis tendons.

In the worst cases, the patellar tendon is essentially non-existent and a second graft (usually an allograft) must be used along with the STG to create a new tendon. These major operative procedures require at least 6 months of rehabilitation to obtain the best recovery possible.

Fortunately, established patella infera is now a rare problem. I have only seen a few cases in the last two years, so it is our hope that the education of medical professionals has helped to eliminate this potential disastrous condition.


J. Zeichen A1, M. van Griensven A1, I. Albers A1, P. Lobenhoffer A1, U. Bosch . Immunohistochemical localization of collagen VI in arthrofibrosis. Archives of Orthopaedic and Trauma Surgery. 1999;119 (5-6):315-318

Noyes FR, Wojtys EM: The early recognition diagnosis and treatment of the patella infera syndrome. In Tullos HE (ed.): Instructional Course Lectures. Rosemont, IL: AAOS, 1991: pp. 233-246.

Noyes FR, Wojtys EM, Marshall MT: The early diagnosis and treatment of developmental patella infera syndrome. Clin Orthop Rel Res 265: 241-252, 1991.

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