Patellar Instability
What is the Anatomy and Function of the Patella?
The patella (kneecap) is a bone located at the front of the knee joint. It sits within the quadriceps tendon and glides within a groove at the end of the femur (thigh bone) called the trochlear groove.
The patella plays several key roles:
Improves leverage of the quadriceps muscle, increasing the efficiency of knee extension (straightening the leg).
Guides motion of the quadriceps and helps maintain proper alignment of the knee during activity.
The stability of the patella depends on a combination of:
Bony anatomy (depth and shape of the trochlear groove)
Soft tissue restraints such as the medial patellofemoral ligament (MPFL) and retinaculum
Dynamic muscle control via the quadriceps
Bony alignment of the lower extremity
Disruption in any of these factors can lead to patellar instability or dislocation.
How Do Patella Dislocations Occur?
Patellar dislocation most commonly occurs when the kneecap moves out of its normal position, usually laterally (to the outer side) of the knee.
Typical causes and mechanisms include:
A twisting injury to the knee or an awkward landing from a jump.
A direct blow to the inner side of the knee forcing the patella outward.
Anatomical predispositions, including:
Shallow trochlear groove (trochlear dysplasia)
High-riding patella (patella alta)
Rotational and limb alignment bony deformities
Generalized ligamentous laxity (hyperflexibility)
Patients often describe a sudden “pop” followed by immediate pain, swelling, and difficulty bending or walking. The patella may spontaneously reduce (move back into place) or require manual relocation.
How Do You Diagnose Patellar Instability?
Diagnosis is based on a combination of clinical history, examination and imaging.
Clinical Assessment:
History: First-time or recurrent dislocation and mechanism of injury.
Symptoms: Pain around the kneecap, swelling, instability, and a feeling that the knee may “give way.”
Physical examination:
Tenderness over the inner patellar border or MPFL region.
The patient becomes anxious or resists when the kneecap is pushed laterally.
Assessment of patella instability risk factors, such as rotational deformity of the extremity, ligament laxity, and a superiorly stationed patella.
Imaging:
X-rays: To identify fractures, patellar height (patella alta), limb alignment, or trochlear dysplasia.
MRI: The best tool to assess damage to the MPFL, cartilage injuries/loose bodies, bone bruising, or loose fragments after dislocation.
CT scan (if needed): To evaluate the bone alignment of the femur and tibia
What are the Long-Term Consequences of Patella Dislocations and Recurrent Instability?
If patellar instability is not properly treated, long-term consequences can include:
Recurrent dislocations or subluxations (partial dislocations).
Cartilage damage on the patella or trochlear groove, causing progressive arthritis and knee pain.
Formation of loose bodies in the joint can cause aggressive arthritic changes to the knee joint.
Quadriceps weakness and altered gait mechanics due to chronic instability or apprehension.
What are the Indications for Conservative Management of Patella Instability?
Conservative (non-surgical) treatment is often appropriate, particularly after a first-time dislocation or when structural alignment is normal.
Indications include:
First-time patellar dislocation without large osteochondral (cartilage/bone) fragments and minimal anatomic risk factors.
Low-demand or elderly patients
Patients who are committed to rehabilitation.
Conservative management typically includes:
Immobilization or bracing for 2–3 weeks allows for soft tissue healing, reduces swelling, and improves pain.
Physiotherapy to restore strength and control, focusing on:
Quadriceps strengthening
Core and hip stability
Proprioception and balance training
Gradual return to sport once pain-free and strength is restored (usually around 6–12 weeks).
What are the Indications for Surgical Management of Patellar Instability?
Surgery may be required when there is recurrent instability, cartilage loose bodies, or significant structural abnormality.
Indications include:
Recurrent dislocations or chronic instability, especially after failed conservative management.
Large osteochondral fractures or loose fragments identified on MRI.
Underlying anatomical abnormalities, such as:
Trochlear dysplasia (shallow groove)
Patella alta (high-riding kneecap)
Tibial tubercle malalignment (excessive lateral pull)
Rotational/alignment abnormalities of the limb
High-demand athletes who require predictable recovery for returning to sport
Surgical procedures are tailored to the individual’s anatomy and may include:
MPFL reconstruction – taking a tendon graft to restore the main ligament soft-tissue restraint to prevent lateral dislocation.
Tibial tubercle osteotomy (TTO) – realigning the attachment of the patella tendon, improving how the patella tracks within the trochlea.
Trochleoplasty – deepening the trochlear groove in cases of severe dysplasia.
Arthroscopic removal or fixation of cartilage or bone fragments if present.
Tibial/Femoral Osteotomy- realign the femur or tibia to improve tracking of the patella
Surgical treatment aims to restore stability, prevent recurrent dislocation, and protect the cartilage from further damage.
