What Is Patella Dislocation?

So you’ve dislocated your patella (knee cap). What does that mean and what do you do now? This article will describe the different types of patella dislocation, including the signs, symptoms, and risk factors, as well as give a brief overview of how it is diagnosed and treated.  

Introduction

A patella dislocation is when the patella (knee cap) moves out of the groove of the knee joint. Most commonly it dislocates laterally (where the knee cap moves to the outside of the leg), but it can dislocate in other directions also. Your patella is incredibly important for the normal function of your knee, which will be explained in more detail below.

Anatomy of the knee

Your knee is made up of three bones; your thigh bone (femur), your shin bone (tibia) and your knee cap (patella). The knee joint allows bending (flexion) and straightening (extension), with a small amount of rotational movements (called medial and lateral rotation). As you bend and straighten your knee, the patella moves up and down a groove in the femur called the trochlear groove. A complex network of ligaments and tendons holds the patella within this groove, with just enough stretch to allow the normal movement of the knee.

The patella has an important role in the movement and stability of the knee. Firstly, it acts as a central point for the quadriceps and patella tendons, much like a pulley.¹ It also supports the function of the quadriceps muscles and stops the soft tissues from rubbing on the bone underneath which could create friction and damage the ligaments and tendons. Finally, it assists with the overall stability of the knee joint.¹

Definition of patella dislocation

Dislocation, in medical terms, refers to bones in one of your joints being moved out of its normal place. So in the case of the patella, it is where the kneecap is moved out of the groove that it usually moves up and down in when you bend and straighten your knee. When this happens, your knee will lock, as the pulley system is no longer working. It can also cause the soft tissues (e.g. muscles, ligaments, tendons, and blood vessels) to be injured, which can be painful.

Whilst it isn’t entirely clear what causes a patella to dislocate, it can commonly occur when either:²

• There is a sudden twist when your knee is slightly bent and the quadriceps are contracted^2,3, e.g., twisting when landing from a jump
• There is a direct impact to the knee²

Types of patella dislocation

In about 90% of cases, the patella dislocates laterally.⁴ This is when the knee cap moves from the groove in the femur to the outside of the leg, and can cause injury to one of the ligaments. 

The patella can dislocate medially (to the inside of the leg), but this is far more rare and likely because of congenital conditions or quadriceps atrophy.⁶ The patella can also dislocate superiorly (upwards), but this is almost always in elderly patients who hyperextend their knee.⁶ In very rare cases, the patella can separate from some of the soft tissue it sits in and twist so that it faces the wrong way.⁷

You may also hear of subluxation of the patella. This is where the patella moves partially out of the trochlea groove. It’s most commonly associated with people who have previously dislocated their patella. In most instances, the patella will return to its normal position by itself.⁸ 

Risk factors

The following are risk factors for a first-time lateral patella dislocation:

• Young people between the ages of 10 to 20 years⁵ 
• Sporting or dancing activities (55-72% of all cases)⁴ 
• People who have general ligament laxity may experience a slightly higher occurrence; however, it is more likely that they will have recurrent subluxations rather than full dislocations⁶ 

You are at risk of recurrent patella dislocations if:

• You have previously had a patella dislocation⁹
• Some anatomical factors such as a shallow trochlea groove (trochlea dysplasia) or a patella that runs higher than usual (patella alta)⁶
• Some genetic conditions such as Marfan Syndrome or Ehler’s Danlos⁶
• Muscle imbalance, such as a weak vastus medialis, which can cause the patella to track abnormally⁶

Symptoms of patella dislocation

Symptoms of an acute patella dislocation include:

• An audible pop or snap
• An obvious change in the position of the knee cap
• Severe pain
• Rapid swelling
• Bruising at the knee
• A feeling like the knee will ‘give way’ on you
• An inability to bend or straighten the knee
• An inability to walk

Your symptoms may vary depending on the type and severity of dislocation. It will depend on several things, including what structures around the patella have been affected, e.g., ligaments, nerves, and blood vessels. Until your patella is relocated, you will not be able to use the leg normally.

If your patella relocates itself, you may find that your pain levels are reduced and you can move your knee more. You should still seek advice from a healthcare provider, as they will be able to fully assess the knee to check if there have been any injuries to the ligaments and other structures around the patella.

Diagnosis

Your healthcare provider will be able to diagnose a patella dislocation by sight if it is still dislocated. They will ask you questions about what happened and physically look at the knee. In most cases this will be enough to diagnose a dislocation; however, they may refer to for imaging, such as an X-ray or MRI, to look for any other injuries to the ligaments, cartilage, or a fracture.

Treatment options

If you suspect that you have dislocated your patella, you should call for assistance from your healthcare provider immediately. In the UK, the NHS advises that you should call 999 if your patella is dislocated or 111 if you think the patella is subluxed or has relocated itself. It is important to contact your healthcare provider even if you have managed to relocate the patella as they will want to check for any other injuries.

Initial management

Your healthcare provider may provide you with some medication to reduce your pain whilst they relocate the patella. Once the patella has been relocated, you will be given advice that follows the ‘POLICE’ principle:

• Protect: emphasises the importance of avoiding further injury. You may be given a brace to help support the knee
• Optimally load: your healthcare provider will advise how much weight you should put through the leg. They may give you crutches to help reduce the stress on the knee
• Ice: you may find applying ice to the knee for 15 minutes every couple of hours helps to reduce your pain and some swelling. Do not put ice directly on the skin as this can cause an ice burn
• Compression: this helps to limit the swelling around the knee. Use a stretchy bandage that wraps from the bottom of the knee to the top
• Elevation: this helps to reduce swelling by using gravity to move it away from the affected area

Non-surgical treatment

The majority of first-time dislocations will be managed conservatively (i.e. without surgery), as long as there are no other injuries such as a fracture.^6,10 This may include:

• A brace to support the knee
• Crutches to reduce the load on the knee
• NSAIDs to help reduce pain and swelling
• Physiotherapy referral to provide advice and exercises

Surgical treatment options

There is still debate around surgery in first-time dislocations.⁶ Surgical management will be considered if:

• A first-time dislocation has an associated fracture or loose body
• MRI scan reveals an injury to the ligament attached to the patella
• Subluxed patella
• Failure to improve with conservative non-surgical treatment
• Recurrent dislocations

Rehabilitation and recovery

Rehabilitation under the direction of a Physiotherapist is vital to the recovery of good knee function. The physiotherapist will provide advice and exercises to help facilitate the healing of the soft tissue around the knee and strengthen the vastus medialis (one of the quadriceps muscles). If these are inadequately rehabilitated, then the chances of re-dislocation are higher.⁶

If this is the first time you have dislocated your patella, you are likely to recover in 6-12 weeks if treated conservatively. If you have recurrent dislocations and have been recommended surgery, this timeline may increase.

Prevention strategies

Accidents are hard to prevent, and genetics even more so, but there are several things you can do to try to reduce the chance of a patella dislocation:

• Strength and conditioning of leg muscles. We know that muscle atrophy or muscle imbalance can contribute to a patella dislocation. Strengthening all the leg muscles will be important to achieve good balance
• Stretching. If some muscles are tighter than others, then it can pull the patella slightly out of its normal tracking. Make sure you stretch your leg muscles, especially your quadriceps to help reduce the chances of this happening
• Proper warm-up. We know that a large proportion of patella dislocations occur during sporting activities, so conducting a proper warm-up will ensure your body is ready for the activity it is about to perform
• Protective gear. If you have had recurrent dislocations, you may be advised by a healthcare professional to wear a brace or protective strapping on your knee during particular activities

Complications and recurrence

Sometimes when a patella dislocates, it can injure some of the structures surrounding it. Some complications can include⁶:

• A fracture of the patella or part of the bone of your femur or tibia
• Deteriorated cartilage that can contribute to degenerative arthritis 
• The risk of recurrence 

Summary

A patella dislocation is where the patella moves out of its normal groove in the knee. Symptoms include an audible pop, pain, difficulty moving the knee or walking, immediate swelling and bruising. The majority of dislocations are laterally and are managed conservatively and you can expect to be back to normal within 6-12 weeks of injury. If you have had recurrent dislocations, you may be a candidate for surgery where the rehabilitation timelines may be longer. If you think you have dislocated your patella, you must seek medical advice so that you can get a proper diagnosis and treatment.