Patellar instability is the tendency of the kneecap (patella) to displace laterally out of the trochlear groove, either partially (subluxation) or completely (dislocation). It can occur as a single traumatic event or as a recurrent pattern driven by anatomic predispositions. Dr. Chudik developed a tunnelless anatomic medial patellofemoral ligament (MPFL) reconstruction technique that addresses the specific anatomic factors driving recurrent dislocation.
What Is Patellar Instability?
The patella normally tracks in the trochlear groove, a shallow V-shaped channel on the front of the femur. Several structures keep the patella centered in the groove: the trochlear depth itself, the quadriceps pulling from above, the patellar tendon anchoring below, and a complex of soft-tissue stabilizers. The medial patellofemoral ligament (MPFL) is the primary restraint against lateral patellar displacement, contributing approximately 50 to 60 percent of the total restraint.
During a dislocation event, the patella displaces laterally out of the groove, typically tearing the MPFL in the process. In many cases the patella spontaneously reduces back into the groove as the knee straightens. The dislocation can also cause cartilage injury on the undersurface of the patella and on the lateral femoral condyle where they contact each other during displacement.
Patellar instability is driven by a combination of factors:
- Trochlear dysplasia: a shallow or abnormally shaped trochlear groove
- Patella alta: a patella that sits too high, above the trochlear groove in early flexion
- Increased tibial tubercle to trochlear groove distance (TT-TG): a lateralized pull from the patellar tendon
- Generalized ligamentous laxity
- Valgus lower extremity alignment
Causes and Risk Factors
- Non-contact twisting injury with the knee in slight flexion (the most common mechanism)
- Direct blow to the medial aspect of the knee
- Anatomic predispositions listed above, especially in patients with recurrent instability
- Female sex, particularly in adolescence
- Adolescent or young adult age at first dislocation is associated with a higher recurrence rate
- Family history of patellar instability
Symptoms
- Visible lateral displacement of the kneecap at the time of dislocation
- Pain and immediate swelling after the event
- Sensation that the knee gave way or buckled
- Difficulty bearing weight or bending the knee after the event
- Recurrent episodes with decreasing energy required to trigger dislocation
- Sense of instability, apprehension, or catching with specific knee positions
Diagnosis
Dr. Chudik’s evaluation includes the mechanism of the dislocation, the history of prior episodes, and any family history of instability. Physical examination includes the apprehension test, J-sign (lateral deviation of the patella during active extension), patellar glide, and assessment of alignment and ligamentous laxity. X-rays including sunrise and lateral views evaluate patellar position and trochlear shape. MRI characterizes the MPFL tear, cartilage damage, and loose bodies. CT or MRI is used to measure TT-TG distance and assess trochlear dysplasia when surgical planning requires it. The Westmont office has on-site high-field MRI and X-ray.
Treatment
Non-surgical treatment is appropriate for first-time dislocators without significant cartilage damage or loose bodies and for patients without major anatomic predispositions. It involves brief immobilization for comfort, a targeted physical therapy program for quadriceps strengthening (especially the vastus medialis obliquus), core and hip strengthening, neuromuscular retraining, and patellar bracing during return to activity.
Surgery is indicated for recurrent dislocations, for first-time dislocators with significant cartilage damage or loose bodies, and for patients with major anatomic predispositions that drive recurrence. Dr. Chudik performs:
- MPFL reconstruction using a tendon graft, the most common procedure for recurrent instability. Dr. Chudik developed an anatomic tunnelless MPFL reconstruction technique that reconstructs the ligament without drilling tunnels across the patella, reducing the risk of patellar fracture and preserving bone stock.
- Tibial tubercle osteotomy for cases with significantly elevated TT-TG distance
- Trochleoplasty in selected cases with severe trochlear dysplasia
- Cartilage repair or removal of loose bodies at the same procedure when indicated
Recovery and Outcomes
Recovery after MPFL reconstruction typically includes progressive range of motion starting within days, weight-bearing in a brace for four to six weeks, progressive strengthening over three months, and return to sport at four to six months. Recovery after combined procedures (tibial tubercle osteotomy) follows a longer timeline of six to nine months before return to sport.
Outcomes after anatomic MPFL reconstruction are very good in appropriately selected patients. Recurrence rates are low when the underlying anatomic factors are addressed. In cases where MPFL reconstruction alone is performed without addressing a significantly abnormal TT-TG or trochlear dysplasia, recurrence rates are higher.
When to See Dr. Chudik
Schedule an evaluation after any patellar dislocation, after recurrent episodes of the knee giving way or the kneecap shifting, or if prior treatment has not resolved instability symptoms. Call 630-324-0402 or request an appointment online.