What is the definition of a bipartite patella?

Definition of Bipartite Patella

Bipartite patella is a developmental anomaly that forms when incomplete patellar ossification leaves a residual fibrocartilaginous synchondrosis between ossification centers. This condition results from the failure of secondary ossification centers to fuse during development 1.

Characteristics

• Anatomical Feature: A patella with two distinct parts separated by a fibrocartilaginous synchondrosis
• Location: Most commonly found at the superolateral quadrant of the patella (approximately 97% of cases) 2
• Prevalence: Relatively rare developmental variation of the knee cap
• Distinction from Fracture: Must be differentiated from an acute patellar fracture, which has different management implications

Classification

Bipartite patella is typically classified based on the location of the unfused fragment:

• Type I: Lower pole fragment
• Type II: Lateral fragment (most common)
• Type III: Superolateral fragment

Clinical Significance

• Symptomatology: Usually asymptomatic and discovered incidentally on imaging studies
• Pain Mechanism: When symptomatic, pain typically results from repetitive traction forces across the synchondrosis, most commonly presenting in adolescence 1
• Risk Factors for Symptoms:
  • Adolescent age group (symptomatic occurrence is statistically higher in younger patients) 2
  • Participation in competitive sports
  • Direct trauma or overuse injury 3

Diagnostic Imaging

• Radiographs: Usually the first imaging modality used

  • Can distinguish bipartite patella from fractures in most cases
  • Axial radiographs demonstrate the degree of patellar tilt or subluxation 4
  • Weight-bearing axial radiographs provide better assessment of patellofemoral kinematics 4

• MRI: Useful for confirming diagnosis and assessing for associated edema

  • Can detect edema around the synchondrosis, which may indicate symptomatic bipartite patella
  • Allows measurement of fragment height and distance between fragment and patella 2
  • Helps differentiate between bipartite patella and acute fracture

• Bone Scan: May show increased uptake in symptomatic cases

  • Less dramatic uptake in stress fractures compared to acute fractures
  • A negative bone scan with an indeterminate linear lucency on radiographs suggests sesamoid bipartition 4

Clinical Implications

• Management: Most cases are asymptomatic and require no treatment

• When Symptomatic:

  • Initial management typically includes rest, physical therapy, cryotherapy, and anti-inflammatory medications
  • Surgical intervention (10% of cases) may be considered for persistent symptoms, particularly in competitive athletes 1
  • Surgical options include fragment excision, lateral release, fragment fixation, or synchondrosis drilling 1

• Prognosis:

  • Most patients improve with conservative management
  • After surgical treatment, patients typically return to sports in approximately 2-3 months 1, 3
  • Approximately 15% risk of persistent or recurrent symptoms requiring reoperation after surgical treatment 1

Bipartite patella should be considered in the differential diagnosis of anterior knee pain, particularly in adolescent athletes, and appropriate imaging studies should be obtained to confirm the diagnosis and guide management decisions.