summary Bipartite Patella is a congenital knee condition caused by the failure of the patella to fuse and is often an incidental finding on radiographs. Diagnosis is confirmed radiographically with most commonly an unfused patella at the superolateral pole. Treatment is observation and most often does not require treatment as the condition is typically asymptomatic. Epidemiology Incidence 2-3% of the population Demographics no notable sex predilection Anatomic location most often found in the superolateral region (Type III) bilateral in 50% Etiology Etiology Normal patella variant representing a failure of fusion often confused with patella fractures Pathophysiology considered a developmental variation of ossification painful bipartite patella following injury direct or indirect injury results in disruption of the fibrocartilaginous zone between the main patella and accessory fragment fibrocartilaginous zone cannot heal by bony union, resulting in persistent pain lack of arterial penetration from patella to osteochondral fragment vastus lateralis contributes to traction force in fragment separation and nonunion Associated conditions nail-patella syndrome patella fracture compared with patella fractures, bipartite patellas: are located superolaterally have smooth, rounded borders may have similar findings on contralateral knee radiographs (50%) Anatomy Osteology the patella is the largest sesamoid bone arises from a single ossific nucleus ossification males at 4-5 years old females at 3 years old accessory ossification center appears between 8-12 years separate fragment attached to patella by fibrocartilaginous tissue Function fulcrum for the quadriceps protects the knee joint articular cartilage of patella is thickest in body (up to 1cm) enhances lubrication of the knee see complete knee biomechanics Blood supply blood supply to patella is predominantly from distal to proximal 6 arteries contribute from popliteal artery superior lateral geniculate artery superior medial geniculate artery inferior lateral geniculate artery inferior medial geniculate artery from superficial femoral artery supreme geniculate artery from anterior tibial artery anterior tibial recurrent artery Classification Saupe Classification Type Incidence Location Type I 5% Inferior pole Type II 20% Lateral margin Type III 75% Superolateral pole Presentation Symptoms most are asymptomatic and discovered incidentally only 2% become symptomatic anterior knee pain from direct trauma (e.g. fall, kick to the knee) indirect trauma or overuse injuries (e.g. cycling, hill climbing) aggravated by squatting, jumping, climbing stairs giving way Physical exam localized tenderness over accessory fragment (typically superolateral patella) hematoma quad inhibition unusual patella prominence or palpable defect larger than normal patella Imaging Radiographs recommended views AP knee radiograph best view to visualize bipartite patella skyline view prone position (non-weight-bearing) squatting position (weight-bearing) may show displacement of the accessory fragment consider radiographs of the contralateral knee for comparison findings smooth edges (helps differentiate from fracture) weight-bearing skyline (squatting) view demonstrates increased separation of fragments compared with non-weight views (prone) 50% have bilateral bipartite patella MRI indications assessment of painful bipartite patella to determine if pain is attributable to the bipartite patella findings edema around the fragment may indicate that it is the cause of symptomatic knee pain Bone scan indications equivocal radiographs with high suspicion for symptomatic bipartite patella findings increased uptake along superolateral aspect utility somewhat controversial CT scan will clearly demonstrate fragment, but does not demonstrate edema Studies Histology interposed tissue between accessory and main fragment composed of fibrocartilage > fibrous > hyaline cartilage avascular adjacent bone scalloped surface with numerous osteoclasts well-vascularized Treatment Nonoperative rest, immobilization, NSAIDS, and physical therapy indications generally, non-operative, symptomatic management is indicated for bipartite patella for at least 6 months modalities rest and restriction of sports activities NSAIDs isometric quadriceps strengthening exercises immobilization with the knee braced in 30° of flexion local corticosteroid injections non-operative management may be less successful in younger, athletic patients, possibly due to non-compliance Operative open excision of the accessory fragment indications failed nonoperative treatment >6 months or in cases of a displaced fragment requiring reduction, direct trauma resulting in the onset of pain, or significant impairment in daily activities most common treatment technique, typically good results may lead to poor results if large, articular fragment due to patellofemoral incongruity arthroscopic excision thought to lead to expedited recovery and avoids disrupting the quad tendon limited evidence to support but good results in case reports lateral retinacular release indications superolateral fragment (to remove the traction force of the vastus lateralis on the fragment) vastus lateralis release (subperiosteal) indications superolateral fragment to avoid long lateral retinacular release open vs arthroscopic quicker recovery and less effusion noted in arthroscopic patients ORIF indications for large fragments limited support in the literature, controversial Complications Patellofemoral maltracking due to excision of a large fragment or lateral retinacular release may lead to patellofemoral degenerative changes Effusion may require arthrocentesis following fragment excision Persistent knee pain may see following lateral retinacular release Quadriceps weakness Osteonecrosis