Things worth knowing about "Patellar instability"
Patellar instability describes the tendency of the kneecap to slip out of its normal groove, causing knee pain and reduced mobility. It commonly affects young, active individuals.
What is Patellar Instability?
Patellar instability is a condition in which the kneecap (patella) does not move smoothly within its groove on the thigh bone (trochlea of the femur). Instead of tracking evenly during bending and straightening of the knee, the kneecap tends to shift sideways – usually outward – or dislocate completely (patellar luxation). This may happen once or repeatedly and is more common in young, physically active individuals, with women being affected more frequently than men.
Causes
Patellar instability is usually the result of multiple anatomical and muscular factors:
- Anatomical abnormalities: A shallow or malformed groove in the thigh bone (trochlear dysplasia) is one of the most common underlying causes.
- High-riding kneecap (patella alta): The kneecap sits too high and has less bony guidance within the groove.
- Muscle imbalances: A weakened inner thigh muscle (vastus medialis obliquus) can allow the kneecap to be pulled outward.
- Ligament injury: The medial patellofemoral ligament (MPFL), which holds the kneecap in place on the inner side, may be stretched or torn.
- Leg alignment problems: Knock knees (genu valgum) or rotational deformities of the thigh or lower leg increase the risk.
- Trauma: A fall or direct impact can trigger an initial dislocation and damage the MPFL.
Symptoms
Symptoms of patellar instability can vary and may include:
- Pain at the front of the knee, especially when climbing stairs, squatting, or sitting with the knee bent
- A feeling that the knee is giving way or feels unstable
- Visible or noticeable sideways displacement of the kneecap
- Swelling of the knee following a dislocation
- Clicking, grinding, or popping sensations in the knee
- Avoidance of certain movements due to fear of dislocation
Diagnosis
Diagnosis is established through a combination of clinical examination and imaging:
- Clinical examination: The physician assesses the stability of the kneecap using the apprehension test, which triggers anxiety or resistance when the kneecap is pushed sideways, along with leg alignment assessment.
- X-ray: Evaluates kneecap position and bone structure.
- MRI (Magnetic Resonance Imaging): Provides detailed images of ligaments, cartilage, and any cartilage damage following dislocation.
- CT (Computed Tomography): Measures the TT-TG distance (tibial tubercle to trochlear groove), which is important for surgical planning.
Treatment
Conservative Treatment
After a first-time dislocation without significant associated injuries, conservative management is typically the first approach:
- Physiotherapy focused on strengthening the quadriceps muscle, particularly the vastus medialis obliquus
- Patellar taping or supportive knee braces to improve stability
- Anti-inflammatory medications (NSAIDs) for pain and swelling relief
- Gait training and neuromuscular coordination exercises
Surgical Treatment
When instability recurs (recurrent patellar dislocation) or significant anatomical abnormalities are present, surgery is often recommended:
- MPFL reconstruction: The medial patellofemoral ligament is reconstructed using a tendon graft – this is the most commonly performed procedure.
- Tibial tubercle osteotomy (TTT): The bony attachment point of the patellar tendon on the shin bone is repositioned to improve the tracking of the kneecap.
- Trochleoplasty: In cases of severe trochlear dysplasia, the groove is surgically deepened to provide better kneecap guidance.
Prognosis and Outlook
With appropriate treatment – whether conservative or surgical – most patients can achieve a stable knee and return to sports and daily activities. Without treatment, there is a significant risk of persistent instability and early cartilage damage (osteoarthritis). Long-term physiotherapy and muscular conditioning remain essential for maintaining knee stability.
References
- Migliorini F. et al. - Patellar Instability: A Systematic Review of the Diagnosis and Management. Journal of Orthopaedic Surgery and Research, 2021.
- Deutsche Gesellschaft für Orthopädie und Unfallchirurgie (DGOU) - Guidelines on the Treatment of Patellar Instability, 2022.
- Dejour D., Saggin P. - The sulcus deepening trochleoplasty -- the Lyon's procedure. International Orthopaedics, 2010.