Patella alta, commonly referred to as a high-riding kneecap, is an orthopedic condition where the patella sits in an abnormally high position relative to the femur. This altered position disrupts the biomechanics of the patellofemoral joint, the articulation between the kneecap and the femoral groove. Treatment generally begins with non-surgical methods, but this article explores the specific criteria determining when surgical intervention is required.
Understanding Patella Alta and Associated Symptoms
The patella normally tracks within the trochlear groove of the femur, especially as the knee bends. When the patella is positioned too high, it fails to properly engage with this groove during the initial degrees of knee flexion. This results in incorrect kneecap tracking, often causing mechanical dysfunction.
Patients frequently experience chronic anterior knee pain, often termed patellofemoral pain syndrome. This discomfort is aggravated by activities that require deep bending, such as squatting, climbing stairs, or prolonged sitting. The primary concern, however, is instability, which manifests as the knee “giving out,” or an actual patellar subluxation or dislocation.
Because the high-riding patella does not sit correctly in the femoral groove, it is highly mobile and prone to shifting out of place. This instability can be recurrent, leading to repeated episodes of partial or full kneecap dislocation. Improper tracking over time also causes increased pressure and friction on the joint surfaces, leading to a grinding or popping sensation known as crepitus.
Conservative Management Approaches
Management for patella alta starts with a structured non-operative approach aimed at addressing muscle imbalances that contribute to poor patellar tracking. Physical therapy is the cornerstone of this treatment, focusing on strengthening the muscles around the hip and knee. Strengthening the quadriceps, particularly the vastus medialis obliquus (VMO), helps pull the patella into a more stable position.
The physical therapy program incorporates exercises to strengthen the hip abductors and external rotators, which help control leg alignment during movement. Activity modification is necessary to reduce painful loading on the joint, often requiring a temporary reduction in high-impact activities like running or jumping. Taping or bracing the knee may be used to improve patellar stability and increase the contact area between the kneecap and the femur.
In addition to physical therapy, non-steroidal anti-inflammatory drugs (NSAIDs) can be used to manage the associated pain and inflammation. These conservative measures are designed to improve muscle control and reduce symptoms, often allowing patients to avoid surgery entirely. The goal is to restore normal function by maximizing the stability provided by the surrounding soft tissues.
The Tipping Point: Indications for Surgical Intervention
Surgery is considered only after a prolonged attempt at conservative management has failed to provide adequate relief, typically defined as a structured program lasting six months or more. This failure means the patient continues to experience debilitating pain or persistent and recurrent patellar instability. Surgery is reserved for cases where the underlying anatomical abnormality cannot be compensated for by physical rehabilitation alone.
Objective evidence of patella alta severity must be documented through specialized imaging before surgical planning begins. Radiographic measurements quantify the kneecap’s height, using the Insall-Salvati ratio (ISI) and the Caton-Deschamps index (CDI) as the most common metrics. Patella alta is generally diagnosed when the ISI is greater than 1.2 or the CDI exceeds 1.2 to 1.3, confirming the anatomical malposition.
Recurrent patellar dislocation or subluxation unresponsive to non-operative methods is the most persuasive indication for surgery. This instability carries a high risk of damaging the cartilage; patella alta is a known risk factor, present in up to 30% of patients with recurrent instability. The mechanical instability must be clearly linked to the high patellar position as the primary cause of dysfunction.
Evidence of progressive degenerative changes in the joint, such as early-onset cartilage wear or chondromalacia, can also push the decision toward surgical correction. The reduced contact area caused by the high patella concentrates forces on a smaller part of the joint surface, accelerating wear. Surgical intervention is necessary to prevent further joint damage and the eventual progression toward severe patellofemoral osteoarthritis.
Surgical Techniques to Correct Patella Alta
The primary surgical procedure for correcting patella alta is a Tibial Tubercle Osteotomy (TTO) with a distalization component. This procedure directly addresses the anatomical problem by repositioning the attachment point of the patellar tendon on the tibia. The tibial tubercle, a bony prominence where the tendon attaches, is carefully cut and detached from the rest of the tibia.
Once detached, the bone fragment is moved downward, or distalized, to lower the patella into a more anatomically correct position within the trochlear groove. The precise amount of distalization is calculated pre-operatively using the radiographic indices, with the surgical goal typically aiming for a post-operative CDI between 1.0 and 1.2. The repositioned bone fragment is then secured with screws to allow for proper healing.
When patellar instability is a significant concern, TTO distalization is frequently combined with other procedures to enhance joint stability. A common secondary procedure is a Medial Patellofemoral Ligament (MPFL) reconstruction, which uses a tendon graft to replace the primary soft-tissue restraint against lateral dislocation. The surgeon may also medialize the tibial tubercle (move it slightly inward) in addition to lowering it, to further improve tracking within the groove.