Patellar Dislocation: What You Need to Know
Patellar dislocations (kneecap dislocations) make up around 2–3% of all knee injuries. They tend to happen in younger, active people, particularly teenagers and those in their 20s. Females in their adolescent years are most commonly affected.
If not managed properly, a patellar dislocation can lead to ongoing issues such as instability, repeated dislocations or subluxations (partial slips), pain, and difficulty returning to sport. Most first-time dislocations happen during sport or activity, either from a twisting movement or from a direct blow to the knee. In this post, I’ll run through what actually happens when the kneecap dislocates, what we look for clinically, and how these injuries are best managed.
A Quick Look at the Anatomy
The kneecap sits in a groove at the end of the thigh bone (the trochlear groove). Its stability comes from a mix of bony shape, ligament support, and muscular control. The medial patellofemoral ligament (MPFL) is the key soft tissue restraint stopping the kneecap from slipping sideways. Other structures like the medial retinaculum and nearby ligaments also play a supporting role.
Why Do Patellar Dislocations Happen?
Some people have structural or biomechanical factors that put them at higher risk, including:
Trochlear dysplasia - a shallow groove for the patella to sit in
Patella alta - a high-riding kneecap
Patellar tilt or abnormal alignment
Large Q-angle, knock knees or increased femoral rotation
Generalised hypermobility or ligament laxity
Even with these factors, most dislocations still occur with a specific injury.
Mechanism of Injury
In most cases, the kneecap dislocates laterally (outwards). The classic story is a twisting or pivoting movement when the knee is close to straight, such as cutting, changing direction, or landing awkwardly. Patients often describe hearing or feeling a “pop,” followed by pain, swelling, and the knee giving way.
Medial dislocations (inwards) are extremely rare and usually only happen after surgery.
Early Management
Reduction: Many kneecaps will relocate by themselves, but sometimes they need gentle assistance in the emergency department.
Imaging: X-rays are used to check for fractures and positioning, while MRI gives more detail about soft tissue damage and cartilage injury.
Common associated findings include bone bruising, cartilage damage, ligament tearing (especially MPFL), or loose fragments in the joint.
Treatment - Surgical vs Non-Surgical
There’s ongoing debate about whether surgery is better than conservative (non-surgical) management for first-time dislocations. Current research suggests:
Both approaches can give good outcomes.
Re-dislocation rates are a little higher without surgery, but return-to-sport and function can be similar.
Surgery is more strongly considered when there’s significant cartilage damage, fractures, or repeated dislocations.
Surgical options include repairing or reconstructing the MPFL, removing or fixing cartilage fragments, or in some cases bony realignment procedures if anatomy is a major factor.
Conservative management usually starts with a short period in a brace, pain management, and then early physiotherapy to restore movement, strength, and confidence.
Physiotherapy & Rehab
Rehab is critical whether surgery is performed or not. The goals are to:
Restore range of motion and confidence in movement
Build strength in the quadriceps (especially the whole group, not just VMO) and hip muscles
Improve balance, control, and proprioception
Progress through sport-specific drills
Towards the end of rehab, we mimic the demands of the person’s sport — things like cutting, change of direction, landing, and uneven surfaces.
There’s no exact timeline for return to sport, so we use criteria-based progression. This means athletes must demonstrate strength, control, and readiness (both physical and psychological) before getting back to competition.
Return to Sport Criteria
Some of the key benchmarks we look for include:
Full or near-full range of motion
No swelling or pain
Symmetry in hop and strength tests (at least 90% compared to the other leg)
Good quality movement on single leg tasks, jumps, and agility drills
Confidence in the knee and no fear of re-injury
Psychological readiness is often the final hurdle, it’s very common for people to feel hesitant even when their knee is physically ready. Open discussion and gradual exposure to sport-specific drills help with this.
Key Takeaways
Patellar dislocations are common in young, active people, most often from a twisting injury.
Imaging is important to rule out fractures and assess ligament or cartilage damage.
Surgery isn’t always required, but may be needed in cases with fractures, significant soft tissue injury, or repeated dislocations.
Physiotherapy plays a huge role in getting strength, stability, and confidence back.
Safe return to sport is based on meeting functional criteria, not just on time passing.
If you’ve recently had a patellar dislocation, or you’re dealing with ongoing kneecap instability, the right management and rehab make all the difference. Our physio team can guide you through each stage, from reducing pain and swelling, to rebuilding strength and confidence, and ultimately getting you back to the activities you enjoy. Book an appointment with us today to start your recovery on the right track.