What is the medical term for excessive movement of the patella (kneecap) on examination?

Patellar Hypermobility: Medical Terminology and Clinical Significance

The medical term for excessive movement of the patella on examination is "patellar hypermobility." This condition is a significant risk factor for patellofemoral instability and can lead to complications such as patellar subluxation or dislocation.

Understanding Patellar Hypermobility

Patellar hypermobility refers to abnormal mobility of the patella that exceeds normal physiological limits. This condition:

• Is characterized by excessive lateral movement of the patella when manual pressure is applied during physical examination 1
• Can be associated with patellofemoral instability, which has an incidence of 1% to 12% after total knee arthroplasty 1
• Is often linked to imbalance in the extensor mechanism, which may be caused by excessive tightness of the lateral retinaculum, component malrotation, or valgus alignment of the extensor retinaculum 1

Clinical Assessment of Patellar Hypermobility

When evaluating patellar mobility, several examination techniques can be employed:

• The Moving Patellar Apprehension Test is highly sensitive (100%) and specific (88.4%) for diagnosing patellar instability related to hypermobility 2
• Axial radiographs can demonstrate the degree of patellar tilt or subluxation 1
• Weight-bearing axial radiographs are recommended to better assess patellofemoral kinematics 1
• CT is the modality most commonly used for measuring axial malrotation of a knee prosthesis when evaluating component rotation that may affect patellar alignment 1

Clinical Significance and Complications

Patellar hypermobility has important clinical implications:

• It is a strong risk factor for patellar instability and dislocation 3, 4
• Patients with generalized joint laxity have six times higher prevalence of patellar dislocation compared to those without (64.4% vs 10.9%) 3
• Transverse patellar fractures are associated with patellar maltracking, which can result from hypermobility 1
• Patellar complications after total knee arthroplasty occur in approximately 3.6% of cases 1

Management Considerations

When treating patients with patellar hypermobility:

• Lateral release alone has no role in treating hyperlax patellofemoral joints as it adds additional laxity to an already unstable system 5
• Medial patellofemoral ligament (MPFL) reconstruction can improve function in patients with hypermobility, though outcomes may be less favorable than in non-hypermobile patients 6
• Patients with Ehlers-Danlos Syndrome (a condition associated with hypermobility) have a 19.1% failure rate following MPFL reconstruction 3
• Identification of at-risk groups with hypermobility may aid in prevention of dislocations and guide appropriate treatment planning 3

Imaging Considerations

For diagnostic evaluation of patellar hypermobility:

• Radiographs are usually satisfactory for assessment of patellar complications and can guide treatment 1
• CT with metal artifact reduction techniques may be useful for detecting patellar complications in patients with prostheses 1
• MRI with metal artifact reduction techniques can also be used to evaluate patellar complications 1
• Bone scans, nuclear medicine studies, and FDG-PET/CT are not typically used for assessment of patellar complications 1

Understanding patellar hypermobility is essential for proper diagnosis and management of patients with patellofemoral disorders, particularly those at risk for instability or who have undergone knee arthroplasty.