Patellar Instability
Background
The patella, or kneecap, normally glides within a groove at the front of the thighbone as the knee bends and straightens. Patellar instability occurs when the kneecap slips partly out of that groove, called a subluxation, or comes completely out, called a dislocation. It usually moves toward the outside of the knee.
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A dislocation can injure the medial patellofemoral ligament (MPFL), a ligament on the inside of the knee that helps keep the kneecap in place. The shape of the groove, the position of the kneecap, and how the kneecap tracks can also contribute to instability. Some patients have one dislocation, while others experience repeated episodes.
Symptoms
Patients with patellar instability may experience:
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A feeling that the kneecap has shifted or popped out of place
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Pain and swelling after a dislocation
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Difficulty bending the knee or bearing weight
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A sense that the kneecap might slip out during activity
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Apprehension when twisting, changing direction, or straightening the knee
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Repeated episodes of the kneecap slipping or dislocating
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A dislocation can also damage the cartilage on the kneecap or thighbone. A loose piece of cartilage or bone may cause catching or locking.
Diagnosis
Diagnosis begins with a discussion of the first episode, any previous dislocations, and what movements make the knee feel unstable. The examination assesses swelling, knee motion, kneecap tracking, and the feeling of instability when the kneecap is gently moved.
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X-rays show the position and shape of the kneecap and its groove. An MRI helps assess the MPFL, cartilage, and any loose fragments after a dislocation. Imaging also helps identify features that may increase the risk of another episode and guide treatment.
Treament Options
Treatment depends on whether this is a first dislocation or a repeated problem, whether cartilage was injured, and the factors contributing to the kneecap’s movement.
Nonoperative Treatment
After a first dislocation without a significant cartilage injury, treatment often begins with a brace when appropriate and physical therapy. Rehabilitation focuses on restoring motion, reducing swelling, strengthening the quadriceps and hip muscles, and improving control during activity.
Some patients regain confidence and return to sports without surgery. Continued instability or additional dislocations may lead to a discussion about surgical treatment.
MPFL Reconstruction
For patients with repeated instability, MPFL reconstruction may be recommended. The injured ligament is replaced with a tendon graft to help keep the kneecap centered as the knee moves. The graft may come from the patient or from a donor.
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MPFL reconstruction addresses the damaged soft tissue restraint. The rest of the treatment plan depends on the patient’s anatomy and whether other factors are causing the kneecap to track toward the outside of the knee.
Tibial Tubercle Osteotomy
The tibial tubercle is the area of bone below the knee where the patellar tendon attaches. In some patients, its position contributes to poor kneecap tracking. A tibial tubercle osteotomy, or TTO, repositions this piece of bone to improve the pull on the kneecap. It is then secured while the bone heals.
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TTO may be performed along with MPFL reconstruction when the kneecap sits too high or its tracking needs to be corrected. It is selected based on the overall examination and imaging, rather than one measurement alone. Because the bone must heal, recovery may be more restrictive than after an isolated MPFL reconstruction.
Return to Sport
Return to sport follows a gradual progression from restoring knee motion and strength to running, jumping, cutting, and sport specific practice. After a first dislocation treated without surgery, some patients return within two to four months.
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After MPFL reconstruction, return commonly takes around six to eight months. Adding a TTO may extend recovery while the bone heals.
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Full clearance depends on stable kneecap tracking, minimal swelling, restored strength, and confidence during the movements required for the patient’s sport.