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 login to view 2 more bullets Associated conditions nail-patella syndrome patella fracture compared with patella fractures, bipartite patellas: login to view 3 more bullets 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 login to view 1 more bullet 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 login to view 4 more bullets from superficial femoral artery login to view 1 more bullet from anterior tibial artery login to view 1 more bullet 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 login to view 3 more bullets 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 login to view 1 more bullet skyline view login to view 3 more bullets 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 login to view 1 more bullet modalities login to view 5 more bullets non-operative management may be less successful in younger, athletic patients, possibly due to non-compliance Operative open excision of the accessory fragment indications login to view 1 more bullet most common treatment technique, typically good results login to view 1 more bullet 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 login to view 1 more bullet vastus lateralis release (subperiosteal) indications login to view 2 more bullets open vs arthroscopic login to view 1 more bullet ORIF indications login to view 2 more bullets 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