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1 · SNAPSHOT

Patellar Dislocation / Patellofemoral Instability body chart — Illustrative, not diagnostic. Canva body chart for Patellar Dislocation / Patellofemoral Instability.

Common in adolescents and young athletes.

Illness script in one line: a teenager or young adult whose knee "gave way" or "went out" on a twisting or decelerating movement — often with the kneecap visibly displaced laterally or a description of it "popping back in" — followed by rapid swelling and fear of it happening again.

Caseload frequency: you will see this on a general outpatient or sports caseload, and you will see the second presentation more often than the first.

The first dislocation is a decision point, not an event

This is the organising idea. What you are managing is not the dislocation. It is the probability of the next one.

Read further: epidemiology and natural history of acute patellar dislocation [1], incidence and risk factors of primary dislocation [2]. The direction that matters: recurrence is common enough to be the central clinical question, and the risk is highest in the young.

And the risk factors stack. Read further: risk factors in recurrent patellofemoral instability [3], combined prevalences of anatomic factors associated with recurrence [4], morphology and anatomic risk factors in first-time traumatic lateral dislocation [5]. A paper on combined prevalences exists, and that is the point: one factor is a risk, three is a different conversation.

What you are actually deciding	Not
How likely is the next one?	"How swollen is it?"
Is this knee shaped in a way that predisposes it?	"Is the VMO weak?"
Does this need a surgical opinion now, or after a proper trial?	"How many weeks of rehab?"

A student who leaves this page with one thing should leave with that reframe.

2 · SE — THE SUBJECTIVE PATTERN (the 70%)

Main problem

"My kneecap went out." — or, more often, "my knee gave way and something moved".

Establish first whether this was a patellar dislocation at all, because "gave way" is the same word patients use for an ACL rupture, a meniscal lock and a pain-inhibited quadriceps.

What they describe	What it points to
"It went out to the side and I pushed it back"	Patellar dislocation. Close to diagnostic
"Someone straightened my leg and it went back in"	Patellar dislocation, reduced by extension
"A pop, then it swelled up within an hour, and I couldn't continue"	Could be either — ACL or patella. Section 3
"It locks and I can't straighten it"	Meniscal, or a loose body. Section 4

Body chart

Anterior knee, and expect medial tenderness. Ask them to point: medial patellar border and the medial femoral epicondyle region is the pattern; lateral joint line and lateral femoral condyle tenderness matters too, because that is where the two bones hit each other on the way through.

Behaviour

Aggs: twisting, cutting, decelerating, landing, stairs, squatting, kneeling; anything that puts the knee into flexion under rotation; and — importantly — the anticipation of those movements.
Eases: extension, a brace or tape, avoiding pivoting.

Ask about apprehension explicitly, and in their words: do you trust it? Fear of recurrence is a legitimate clinical target here, not a soft finding.

History

First time or not? The whole page turns on this.
Mechanism — contact or non-contact, twisting, landing.
How was it reduced, and by whom?
Was there imaging in the emergency department, and what did it say? Section 4.
Age and skeletal maturity. Read further: traumatic patellar instability in the paediatric patient [6], evaluation and management in paediatric and adolescent athletes [7]. Section 4.
Has the other knee ever done it? Ask, always.
Family history of hypermobility, or a knee that has always felt loose.
Sport, level, and what they are trying to get back to.

Special / screening questions

Immediate, tense swelling within an hour? Section 4.
True locking or an inability to fully extend? Section 4.
Any catching or a sensation of something loose? Section 4.
Are they skeletally immature? Section 4.

Assessing this region? Download the Knee assessment template →

3 · HYPOTHESIS RANKING

Pattern	The one discriminating feature
Lateral patellar dislocation / patellofemoral instability	A visible lateral displacement or a description of it going out and back, medial patellar and medial epicondyle tenderness, apprehension on lateral glide.
ACL rupture	A pop with immediate haemarthrosis and a giving-way on pivoting, without the patella being described as moving. Same age group, same mechanism family. Its own page — test for it.
Osteochondral fracture / loose body	True mechanical locking, catching, or an inability to fully extend after the dislocation. Section 4.
Meniscal tear	Joint-line tenderness, locking, and a twisting mechanism without patellar displacement. Its own page.
Patellofemoral pain	Pain without an instability event. Different problem, different page — and applying its programme unchanged here is a mistake.
Patellar tendinopathy	Localised inferior pole pain with jumping load, no giving way. Its own page.
Generalised hypermobility / connective tissue	Multiple joints, bilateral, a long history of things "going out". Changes the prognosis conversation.

The discriminator that does most of the work: did the patella move, or did the knee? And if you cannot get a clear answer, test for both.

4 · RED FLAGS — DON'T MISS THIS

Free forever. Never gated.

1. Osteochondral fracture — the thing you cannot sit on

When the patella dislocates laterally and relocates, the medial patellar facet and the lateral femoral condyle strike each other. That can take a piece of cartilage and bone off.

Read further: cartilage lesions and early osteoarthritis after patellar dislocation [8], MRI findings after acute dislocation in children [9].

What should make you escalate:

A tense haemarthrosis that came up within an hour.
True mechanical locking, or a springy block to extension.
Catching, or a sense of something loose moving in the joint.
An inability to weight-bear.

Action: this is an imaging question and a surgical opinion, and it is time-sensitive — a loose fragment is more fixable early. Do not start a strengthening programme in a knee that is locking.

2. The knee that isn't a patella problem

Same age, same mechanism family: a pop, immediate swelling, giving way on pivoting. Examine the ACL and the menisci on every one of these, and do not let a confident patellar history stop you testing. Both can happen in the same injury.

3. The skeletally immature knee

Read further: traumatic patellar instability in the paediatric patient [6], evaluation and management in paediatric and adolescent athletes [7], MRI findings after acute dislocation in children (Wilson et al. 2013).

This is predominantly an adolescent condition, and an open physis changes both the surgical options and the injury pattern. A skeletally immature knee gets a paediatric orthopaedic opinion, not improvised adult reasoning — and adolescents are also the group in whom recurrence risk is highest, which raises the stakes on getting the first episode right.

4. The recurrent dislocator who has never had an opinion

Someone on their third or fourth dislocation who has never seen a surgeon is not a rehabilitation problem you have not tried hard enough on. Read further: risk factors in recurrent instability (Hiemstra et al. 2017), combined prevalences of anatomic factors (Steensen et al. 2015). You cannot strengthen a trochlea.

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Twelve slides on this pattern: what you'll hear, what to examine, what to do. Free with an account.

Guideline anchor

No Australian guideline and no clinical practice guideline of any kind.

The anchors are syntheses of the primary-dislocation question: a systematic review and quantitative synthesis of treatment of primary acute patellar dislocation (Longo et al. 2017, PMID 28107220), a systematic review and meta-analysis of surgical versus conservative treatment of primary patellar dislocation (Saccomanno et al. 2016, PMID 26202017) and an updated meta-analysis of the same comparison (Yao et al. 2015, PMID 25218834). The physiotherapy anchors are a review of nonoperative treatment of patellar instability (Dixit et al. 2017, PMID 28459749) and a randomised controlled trial of rehabilitation following first-time patellar dislocation (Smith et al. 2015, PMID 25921095).

PubMed Source

None of these is a clinical practice guideline. They are systematic reviews, meta-analyses, a narrative review of nonoperative treatment and one randomised trial of rehabilitation.

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The evidence summary is for members

Verified diagnostic accuracy, where the evidence stands and what it doesn't settle. Free with an account.

Sources · 20

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Every source on this page resolves and title-verifies against PubMed. Newest first.

2004Fithian et al. (2004). Epidemiology and natural history of acute patellar dislocation. The American journal of sports medicine, 32(5), 1114-21. https://doi.org/10.1177/0363546503260788
2008Sillanpää et al. (2008). Incidence and risk factors of acute traumatic primary patellar dislocation. Medicine and science in sports and exercise, 40(4), 606-11. https://doi.org/10.1249/MSS.0b013e318160740f
2017Hiemstra et al. (2017). Assessment of demographic and pathoanatomic risk factors in recurrent patellofemoral instability. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA, 25(12), 3849-3855. https://doi.org/10.1007/s00167-016-4346-0
2015Steensen et al. (2015). The prevalence and combined prevalences of anatomic factors associated with recurrent patellar dislocation: a magnetic resonance imaging study. The American journal of sports medicine, 43(4), 921-7. https://doi.org/10.1177/0363546514563904
2017Askenberger et al. (2017). Morphology and Anatomic Patellar Instability Risk Factors in First-Time Traumatic Lateral Patellar Dislocations: A Prospective Magnetic Resonance Imaging Study in Skeletally Immature Children. The American journal of sports medicine, 45(1), 50-58. https://doi.org/10.1177/0363546516663498
2017DeFroda et al. (2017). Diagnosis and Management of Traumatic Patellar Instability in the Pediatric Patient. Orthopedics, 40(5), e749-e757. https://doi.org/10.3928/01477447-20170602-04
2015Khormaee et al. (2015). Evaluation and management of patellar instability in pediatric and adolescent athletes. Sports health, 7(2), 115-23. https://doi.org/10.1177/1941738114543073
2012Vollnberg et al. (2012). Prevalence of cartilage lesions and early osteoarthritis in patients with patellar dislocation. European radiology, 22(11), 2347-56. https://doi.org/10.1007/s00330-012-2493-3
2013Wilson et al. (2013). Magnetic Resonance Imaging Findings After Acute Patellar Dislocation in Children. Orthopaedic journal of sports medicine, 1(6), 2325967113512460. https://doi.org/10.1177/2325967113512460
2017Longo et al. (2017). Treatment of Primary Acute Patellar Dislocation: Systematic Review and Quantitative Synthesis of the Literature. Clinical journal of sport medicine : official journal of the Canadian Academy of Sport Medicine, 27(6), 511-523. https://doi.org/10.1097/JSM.0000000000000410
2016Saccomanno et al. (2016). Surgical versus conservative treatment of primary patellar dislocation. A systematic review and meta-analysis. International orthopaedics, 40(11), 2277-2287. https://doi.org/10.1007/s00264-015-2856-x
2015Yao et al. (2015). Comparison operative and conservative management for primary patellar dislocation: an up-to-date meta-analysis. European journal of orthopaedic surgery & traumatology : orthopedie traumatologie, 25(4), 783-8. https://doi.org/10.1007/s00590-014-1523-z
2012Sillanpää & Mäenpää (2012). First-time patellar dislocation: surgery or conservative treatment?. Sports medicine and arthroscopy review, 20(3), 128-35. https://doi.org/10.1097/JSA.0b013e318256bbe5
2010Smith et al. (2010). Immobilization Regime Following Lateral Patellar Dislocation: A Systematic Review and Meta-Analysis of the Current Evidence Base. European journal of trauma and emergency surgery : official publication of the European Trauma Society, 36(4), 353-60. https://doi.org/10.1007/s00068-010-9165-2
2011Smith et al. (2011). A national survey of the physiotherapy management of patients following first-time patellar dislocation. Physiotherapy, 97(4), 327-38. https://doi.org/10.1016/j.physio.2011.01.003
2015Smith et al. (2015). Rehabilitation following first-time patellar dislocation: a randomised controlled trial of purported vastus medialis obliquus muscle versus general quadriceps strengthening exercises. The Knee, 22(4), 313-20. https://doi.org/10.1016/j.knee.2015.03.013
2017Dixit & Deu (2017). Nonoperative Treatment of Patellar Instability. Sports medicine and arthroscopy review, 25(2), 72-77. https://doi.org/10.1097/JSA.0000000000000149
2016Buchanan et al. (2016). CURRENT CONCEPTS IN THE TREATMENT OF GROSS PATELLOFEMORAL INSTABILITY. International journal of sports physical therapy, 11(6), 867-876. PubMed 27904790
2014Respizzi & Cavallin (2014). First patellar dislocation: from conservative treatment to return to sport. Joints, 2(3), 141-5. https://doi.org/10.11138/jts/2014.2.3.141
2017Manske & Prohaska (2017). REHABILITATION FOLLOWING MEDIAL PATELLOFEMORAL LIGAMENT RECONSTRUCTION FOR PATELLAR INSTABILITY. International journal of sports physical therapy, 12(3), 494-511. PubMed 28593102

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