Clinical Picture

• Age 14 – patellar dislocation with hemarthrosis: an acute hemarthrosis at the time of a first dislocation is a strong indicator that an osteochondral fracture occurred (usually of the medial patellar facet or lateral femoral condyle) as the patella sheared back across the trochlea on reduction - Campbell's Operative Orthopaedics.
• Age 19 – a further "fracture": likely another osteochondral or patellar fracture from a subsequent dislocation/subluxation episode, each of which causes progressive cartilage loss.
• Age 25 – recurrent anterior knee pain, worse with exertion, weight-bearing, and stair climbing, with transient ease on squatting.

Most likely cause

• Repeated dislocation episodes tear the medial patellofemoral ligament and shear cartilage off the patella/trochlea, producing loose fragments and exposed subchondral bone (chondromalacia patellae) - Campbell's Operative Orthopaedics, Miller's Review of Orthopaedics.
• Pain from patellofemoral cartilage lesions is load- and flexion-angle dependent: stair climbing, prolonged standing, and rising from sitting load the patellofemoral joint in the mid-flexion range (20-50°) where damaged cartilage is under maximal contact stress - Rheumatology, 2-Vol Set, "Anterior Knee Pain" and Textbook of Family Medicine, "Patellofemoral Syndrome."
• The described temporary relief on deep squatting is a recognized quirk of chondromalacia: in deep flexion the contact area shifts proximally on the patella (toward the quadriceps tendon facet), which is often relatively spared compared with the classic lesion sites, so symptoms can paradoxically ease compared to the mid-range loading of stair use.
• PubMed evidence confirms osteochondral fractures are common after patellar dislocation and are a major driver of recurrent symptoms and later degenerative change (Khan et al., JAAOS Global Res Rev 2021, PMID 34860734; Uimonen et al., OJSM 2021, PMID 33553448).

Differential causes to work through in this patient

1. Chondromalacia patellae / patellofemoral osteoarthritis (most likely, given the trauma history) - retropatellar grinding, positive patellar apprehension/grind test, joint space narrowing or patellar facet irregularity on imaging.
2. Loose intra-articular body - a retained osteochondral fragment from either injury can cause intermittent locking, effusion, and pain with weight-bearing; often needs MRI/CT to identify.
3. Recurrent patellar subluxation/instability itself (without fixed cartilage damage) - "giving way," apprehension on lateral patellar pressure, possible trochlear dysplasia or patella alta as an underlying predisposing factor - Campbell's Operative Orthopaedics, "PATELLA."
4. Associated meniscal tear - dislocation and fracture events can concurrently injure the menisci; joint line tenderness, McMurray's sign.
5. Osteochondritis dissecans of the femoral condyle/patella - can coexist with or mimic post-traumatic chondral injury.
6. Malunion or intra-articular step-off from the prior patellar fracture - if the 19-year fracture involved the patella itself and healed with incongruity, this alone can produce patellofemoral overload pain.
7. Secondary quadriceps weakness/patellar maltracking from years of pain avoidance, perpetuating the cycle of instability and cartilage overload.

What would confirm the diagnosis

• Plain radiographs (skyline/Merchant view) for patellar tilt, subluxation, trochlear dysplasia, or old fracture fragments.
• MRI to assess cartilage thickness/signal (chondromalacia grading), look for loose bodies, meniscal integrity, and MPFL status.
• Clinical tests: patellar apprehension test, patellar grind (Clarke's) test, effusion assessment.

A note on recent evidence

Correlating the MRI Report with the Case

• Non-united osteochondral fracture with two small fragments involving the medial patella, specifically at the site of medial retinaculum attachment
• Stretching and mild altered signal of the medial retinaculum at its patellar insertion - description of "p/o partial healing" (i.e., partial healing after a tear)
• Mild joint effusion
• Patellar articular cartilage was normal at that time - no chondromalacia, cruciates/collaterals/menisci all normal, no synovitis

What this changes/confirms

1. The fragments never united. A symptomatic ununited osteochondral fragment at the medial patella, still tethered to a stretched retinaculum, is a durable mechanical pain generator on its own - it can catch, produce point tenderness medially, and generate an effusion with loading, independent of any generalized cartilage disease.
2. Cartilage was still normal in 2019. This tells us her chondromalacia/patellofemoral arthritis (if present now) is not long-standing - it would have developed over the following years, likely driven by continued patellar instability from the never-fully-competent medial retinaculum.

Revised explanation for her current (age 25) symptoms

• Chronic medial patellofemoral ligament/retinaculum insufficiency - the "stretching" seen on the 2019 scan never fully tightened back to normal tension, so the patella likely still tracks slightly laterally under load, especially in the 20-50° flexion range used in stair climbing and prolonged weight-bearing.
• The nonunited osteochondral fragment(s) at the medial facet act as a chronic irritant - loading in extension/mid-flexion (standing, stairs) puts tension through the retinaculum and micromotion across the fracture line, reproducing pain; deep squatting can transiently relieve this because in high flexion the quadriceps centralizes the patella in the trochlear groove and shifts contact proximally away from the medial fragment, reducing shear at the nonunion site.
• Secondary patellofemoral chondromalacia/early osteoarthritis has probably developed over the 6-7 years since this scan, given ongoing instability - this needs to be confirmed on a repeat MRI now, since her 2019 cartilage was normal but continued malalignment is the classic pathway to chondral wear - Rheumatology, 2-Vol Set, "Classification of Chondromalacia Patellae"; Rockwood and Green's Fractures in Adults, "Acute Patellar Dislocations."
• Persistent mild effusion on the old scan also fits a joint that is mechanically irritated rather than quiescent.

Practical next step

• Whether the osteochondral fragments have displaced, resorbed, or remain in situ
• Current status/laxity of the medial retinaculum and MPFL (grading instability)
• Whether patellofemoral cartilage (previously normal) now shows chondromalacia or early arthritic change
• Patellar tracking/tilt and any trochlear dysplasia predisposing to recurrence

Adding "Giving Way" and Rare Locking to the Picture

Occasional giving way

Rare locking

1. A loose osteochondral body - her 2019 MRI already documented two small non-united fracture fragments at the medial patella. An ununited fragment can migrate slightly within the joint and intermittently wedge between the patella and the femoral condyle or lodge in the joint recess, blocking terminal extension until it disengages - S Das, A Manual on Clinical Surgery, "Loose Bodies of the Knee Joint"; Campbell's Operative Orthopaedics notes explicitly that "an osteocartilaginous loose body... can cause locking," and this must be distinguished from a meniscal bucket-handle tear.
2. A meniscal tear - given the trauma history, a meniscal tear (medial or lateral) cannot be excluded even though her 2019 scan reported normal menisci; a new tear could have occurred since then, especially with ongoing instability altering joint mechanics.

Updated working diagnosis

• Recurrent activity-related anterior knee pain (retinacular traction + fragment micromotion)
• Intermittent giving way (retinaculum/MPFL insufficiency, patella subluxating laterally)
• Rare true locking (the loose fragment or, less likely, a new meniscal tear transiently blocking extension)
• Likely evolving secondary patellofemoral chondromalacia/early osteoarthritis (cartilage was normal in 2019 but 6-7 years of instability make this probable now)

Differential still to exclude on repeat imaging/exam

Recommended next step

Integrating the New History: Longstanding Crepitus + Non-Contact Twisting Mechanism

Childhood cracking/crepitus on squatting during dance

• Trochlear dysplasia (shallow or dysplastic femoral trochlear groove) - the patella tracks slightly abnormally even before any dislocation, producing crepitus/clicking with deep flexion activities like squatting, and is one of the strongest anatomical risk factors for a first dislocation and for recurrence - Miller's Review of Orthopaedics, "Patellar instability... etiology can be multifactorial."
• Generalized ligamentous laxity/joint hypermobility - dancers often have above-average joint flexibility, and constitutional ligamentous laxity is explicitly listed as a predisposing factor for patellar instability in Campbell's Operative Orthopaedics and Miller's Review. A recent systematic review directly examined this link (Heighes et al., J Orthop 2024, PMID 38784948) and found generalized joint hypermobility is significantly associated with patellofemoral instability and recurrent dislocation.
• Patella alta or maltracking - also produces crepitus/clunking specifically in the squat-to-stand transition, as the patella engages and disengages the trochlear groove.

Mechanism of the first dislocation - twirling

Updated integrated picture

1. Constitutional predisposition (likely trochlear dysplasia and/or generalized ligamentous laxity, consistent with lifelong dance flexibility and childhood patellofemoral crepitus)
2. First dislocation at age 14 during a twisting/pivoting dance movement, with hemarthrosis, causing a medial patellar osteochondral avulsion fracture at the MPFL/retinaculum attachment (as confirmed on her 2019 MRI, seen as a non-united fragment years later)
3. Second fracture event around 18-19 years, most likely a recurrent dislocation episode, further stretching an already-compromised medial retinaculum, which is why the 2019 MRI showed a retinaculum that was "stretched" and only "partially healed"
4. Current age 25: chronic patellofemoral instability (occasional giving way), a persistent symptomatic loose/non-united osteochondral fragment (rare true locking), and activity-related anterior knee pain from a combination of retinacular insufficiency, fragment micromotion, and probable evolving patellofemoral chondromalacia/early arthritis

Why this matters clinically

• Predisposing factors must be assessed and quantified on current imaging: trochlear dysplasia (Dejour classification), patellar height (Caton-Deschamps/Insall-Salvati index), tibial tubercle-trochlear groove (TT-TG) distance, and patellar tilt - not just the fragment and retinaculum.
• A formal hypermobility assessment (Beighton score) is worth doing given the dance history and childhood crepitus - if she scores high, this supports a diagnosis of generalized joint hypermobility (or a hypermobility spectrum disorder) as a contributing systemic factor, which would also inform rehabilitation strategy (more emphasis on dynamic neuromuscular control/VMO strengthening since passive ligamentous restraint is less reliable).
• Isolated MPFL reconstruction or fragment excision alone may not be sufficient if significant trochlear dysplasia or patella alta is found - these would need to be addressed (e.g., trochleoplasty or tibial tubercle osteotomy) to meaningfully reduce recurrence risk, per the risk-factor-based surgical algorithms in Campbell's Operative Orthopaedics and the JBJS predictive model (Ling et al. 2021, PMID 33787553).