Framing Patellar Instability: From Diagnosis to the Treatment of the First Episode

Framing Patellar Instability: From Diagnosis to the Treatment of the First Episode

Maggioni DM, Giorgino R, Messina C, Albano D, Peretti GM, Mangiavini L. Framing Patellar Instability: From Diagnosis to the Treatment of the First Episode. J Pers Med. 2023 Aug 2;13(8):1225. doi: 10.3390/jpm13081225. PMID: 37623475; PMCID: PMC10456090.

This is the editor's interpretation of a paper published in the orthopaedic literature in 2023 - our attempt to make relevant medical articles accessible to lay readers. If you wish to read the original just click through the link above.

The authors begin by highlighting that disorders relating to the patellofemoral joint can be classified into three types:

• objective patellar instability

• potential patellar instability

• patellofemoral pain syndrome

1. In objective patellar instability, there has already been a dislocation event

   and it is possible to identify one or more of the principle factors for instability -
   • trochlear dysplasia
   • increased TT-TG distance
   • patella alta

   (in other words the groove is abnormal, the patella is too high or the sideways forces on the patella are too great).

   The paper explains how these anatomical problems make the patellofemoral joint susceptible to both objective and potential instability,

2. In potential patellar instability, the patient has never experienced an actual dislocation event but has strong feelings that the patella generally does not feel stable,

   and it is possible to identify one or more of the principle factors for instability -
   • trochlear dysplasia
   • increased TT-TG distance
   • patella alta

3. In patellofemoral pain syndrome, the overwhelming issue is one of pain relating to the kneecap,and there is no history of any dislocation nor any feelings of instability,

   and imaging does not reveal any of the principle factors for instability.

The authors explain that , even though a dislocation may have reduced when the patient is first seen, objective imaging evidence of a dislocation event having taken place may still be present, and include bone bruises, osteochondral fractures, and rupture of the MPFL ligament.

In the investigational workup after such an event, besides the identification of the principle contributing factors, a number of secondary contributing factors may also be identified -

• varus/valgus malalignment of the knee
• genu recurvatum
• torsional malalignment
• patellar dysplasia
• abnormal pronation of the subtalar joint in the foot

Peer-reviewed papers

• Quotes from this paper:

  "....While the principal factors of instability must be detected via an accurate instrumental evaluation (MRI or CT scan), the secondary factors of instability can initially be assessed clinically...."

  Once identified clinically, any "....torsional malalignment of the lower extremities, such as increased femoral anteversion or increased internal torsion of the distal femur, can be better defined via specific imaging evaluation (CT scan)....."

  "....Patellar dysplasia....can be assessed on an axial view of radiographs of the patella....."

Quick links

• Femoral anteversion

• Femoral torsion

End of links

The authors also recommend to include in the examination an evaluation of the J-sign and the patellar apprehension test.