What Is It?
A primary patellar dislocation occurs when the kneecap (patella) slips out of its normal groove on the thigh bone (femur), usually toward the outer (lateral) side.
This type of injury is often sudden and can be quite alarming, particularly for athletes or active individuals.
When the patella dislocates, it typically causes injury to the surrounding soft tissues that are responsible for stabilising the kneecap and keeping it tracking correctly during movement.
Structures Commonly Injured
A patellar dislocation doesn’t just involve the kneecap itself. It often affects several important stabilising structures around the knee:
- Medial Patellofemoral Ligament (MPFL): the main restraint preventing the patella from sliding laterally, often partially or completely torn.
- Medial Retinaculum: a soft tissue layer that reinforces patellar stability and supports proper tracking.
- Cartilage and Bone: bruising or small osteochondral fragments may occur on the patella or femoral condyle.
- Medial Collateral Ligament (MCL): may be mildly sprained due to valgus loading at the time of injury.
Understanding which structures are involved is important, as it helps guide both diagnosis and rehabilitation planning.
How Does It Happen (Mechanism of Injury)?
Primary patellar dislocations most commonly occur during dynamic movements, particularly in sport.
Typical mechanisms include:
- Twisting or pivoting on a planted foot
- Landing awkwardly after a jump
- Contact or collision from the side of the knee (valgus force)
- These injuries are commonly seen in sports such as netball, AFL, basketball, and soccer, where rapid changes in direction and jumping are frequent.
There are also several predisposing factors that can increase the risk of dislocation:
- A shallow trochlear groove
- Patella alta (a high-riding kneecap)
- Joint hypermobility
- Weak hip and thigh muscles
- Poor neuromuscular control during cutting or landing
These factors can affect how well the patella is supported and controlled during movement.
Typical Signs and Symptoms
Following a dislocation, symptoms are usually immediate and noticeable. Common signs include:
- Sudden pain and swelling, often within the first hour
- A feeling of the kneecap ‘shifting’ or ‘popping out’
- Difficulty walking or straightening the knee
- A sensation of instability or ‘giving way’
- Tenderness along the inner (medial) aspect of the patella
These symptoms can vary in severity depending on the extent of the injury.
Diagnosis
Diagnosis of a primary patellar dislocation is based on a combination of clinical assessment and imaging.
- History and physical examination are key in identifying the mechanism and symptoms
- A positive Patellar Apprehension Test may indicate instability
- X-ray is used to rule out fractures and assess patella height and alignment
- MRI helps confirm MPFL injury, detect bone bruising, and identify structural risk factors
Early and accurate diagnosis ensures appropriate management and reduces the risk of recurrence.
Physiotherapy Management
Rehabilitation following a patellar dislocation is typically structured in phases, with each stage building on the previous one.
Early Stage
Goals: Protect injured tissues, reduce swelling, restore early motion, and maintain quadriceps activation.
- Brace: Patella-stabilising brace (limit flexion >30° for 2–3 weeks)
- Crutches: Weight-bearing as tolerated
- Exercises:
- Gentle ROM (0–30° progressing to 60° by week 2)
- Quadriceps activation (inner range quads, straight leg raises)
- Hip and core strengthening
- Swelling control (ice, compression, elevation)
Most individuals regain normal walking within 2–4 weeks.
Mid Stage
Goals: Restore full range of motion, strength, and dynamic control.
- Gradual strengthening (mini squats, step-ups, leg press 0–60°)
- Stationary bike and low-impact cardiovascular exercise
- Balance and neuromuscular control drills
- Begin light jogging once pain-free, swelling has resolved, and strength reaches ≥70–80% of the other leg
Late Stage
Goals: Build power, agility, and confidence for return to sport.
- Jump and landing retraining (plyometrics)
- Direction-change drills
- Strength symmetry testing
- Gradual return to sport and team training
- Continued use of bracing or taping for confidence early in return
Return to sport typically occurs between 12–20 weeks, depending on the individual, sport demands, and progression through rehab.
Return-to-Play (RTP) Criteria
Before returning to sport, it’s important that key benchmarks are achieved to reduce the risk of re-injury:
- Ability to run, jump, and hop pain-free
- No swelling or feelings of instability
- Greater than 90% strength and hop symmetry
- Confidence performing sport-specific drills
- Psychological readiness, including low fear of reinjury
Prevention & Long Term Care
Ongoing management plays a key role in reducing recurrence risk.
- Continue hip, quadriceps, and core strengthening
- Maintain ankle flexibility and good landing mechanics
- Include neuromuscular training in all pre-season programs
- Reassess if instability or ‘giving way’ persists
- Consider bracing or taping during early return to high-risk sports
Key Research Insights
Current research highlights several important considerations for managing primary patellar dislocations:
- Early rehabilitation with movement and muscle activation promotes better outcomes (Parikh et al., 2024)
- Bracing for 3–4 weeks combined with early range of motion may reduce recurrence risk (Honkonen et al., 2022)
- Neuromuscular and landing control exercises play a key role in preventing re-injury (Hopper et al., 2017)
- Psychological readiness and adequate sleep are important factors in recovery and injury prevention (Ardern et al., 2014; Copenhaver & Diamond, 2017)
References
- Ardern CL et al. Psychological readiness and return to sport after ACL reconstruction. Br J Sports Med. 2014.
- Bahr R, Krosshaug T. Understanding injury mechanisms: a key component of preventing injuries in sport. Br J Sports Med. 2005.
- Belcher S et al. ACL injury mechanisms in elite netball players. Sports Biomech. 2024.
- Brukner P, Khan K. Clinical Sports Medicine. 5th ed. McGraw-Hill, 2017.
- Christensen TC et al. Risk factors and time to recurrent patellar dislocation. Am J Sports Med. 2017.
- Finlayson CJ et al. Consensus-Based Guidelines for Management of First-Time Patellar Dislocation in Adolescents. J Pediatr Orthop. 2024.
- Flores GW et al. Conservative management following patellar dislocation: a systematic review. J Orthop Surg Res. 2023.
- Honkonen EE et al. Patella-stabilizing vs neoprene brace after first-time patellar dislocation. Am J Sports Med. 2022.
- Hopper AJ et al. Neuromuscular training in young female netballers. Front Physiol. 2017.
- Hsu CJ et al. MPFL Reconstruction: From Rehabilitation to Return to Sport. Int J Sports Phys Ther. 2025.
- Huber C et al. Properties and Function of the Medial Patellofemoral Ligament: A Systematic Review. Am J Sports Med. 2020.
- Lampros RE, Tanaka MJ. Return to Play Considerations After Patellar Instability. Curr Rev Musculoskelet Med. 2022.
- McCarthy MI et al. Evaluating Patellar Instability Risk Factors. Clin Sports Med. 2022.
- Moiz M et al. Clinical outcomes after nonoperative management of lateral patellar dislocations. Orthop J Sports Med. 2018.
- Parikh SN et al. Consensus agreement: Return to play 2–4 months for primary patellar dislocation. J Pediatr Orthop. 2024.
- Copenhaver EA, Diamond AB. Sleep and athletic performance, injury, and recovery in youth athletes. Pediatr Ann. 2017.