Orthopedic Examination Question Patellar Instability Decoded
Key Takeaway
This article provides essential research regarding Orthopedic Examination Question Patellar Instability Decoded. For an examination question patellar instability, assessment involves a detailed history and clinical exam. Key investigations include lateral and axial radiographs for patellar tilt/height and trochlear depth, MRI for articular lesions and MPFL integrity, and CT for femoral anteversion, tibial torsion, and TT-TG distance. Risk factors like trochlear dysplasia are crucial for diagnosis.
You are presented with this patient who has a history of recurrent patellar instability. What are the key clinical and radiographic findings you need to look for, and how would you classify the severity of her trochlear dysplasia?
Candidate: I would examine the patient for the J-sign, patellar hypermobility, and assess the Q-angle. Radiographically, I need to check for patella alta using the Insall-Salvati ratio, measure the TT-TG distance on axial CT, and classify the trochlea using the Dejour classification system. In this specific image, I am assessing for the presence of a crossover sign or supratrochlear spur.
Candidates often focus solely on the "MPFL reconstruction" solution without discussing the underlying bony alignment. Failing to define the TT-TG distance or correctly identifying the Dejour Type (e.g., missing the "crossover sign" which is pathognomonic for severe dysplasia) is a common failure point.
The candidate should structure the answer by addressing three pillars: 1. Clinical Stability: Mention the J-sign, patellar glide, and apprehension test. 2. Radiographic Parameters: Explicitly mention Insall-Salvati (>1.2 = alta), TT-TG (>20mm = pathological), and the Dejour classification (Type A-D). 3. Surgical Planning: Emphasize that in the presence of severe trochlear dysplasia (Dejour C/D) and increased TT-TG, an MPFL reconstruction alone is insufficient and likely to fail; a combined approach (Trochleoplasty + TTO + MPFL) is the gold standard.
Following a successful MPFL reconstruction, the patient returns at 6 months with persistent anterior knee pain and discomfort during deep flexion, but no further dislocations. How do you investigate this, and what is your leading differential?
Candidate: I would investigate for potential over-tensioning of the graft. I would perform a physical exam checking for restricted passive patellar excursion and imaging to ensure the graft was placed at the correct femoral insertion point (Schottle's point). My leading differential is graft over-constraint causing increased patellofemoral contact pressures.
Candidates often suggest "re-operation" or "revision" too quickly without confirming the diagnosis. They may also ignore the possibility of secondary chondral damage sustained during the original injury.
The "Gold Standard" response highlights: 1. Clinical suspicion: Suspect over-constraint due to non-isometric graft placement or excessive tensioning. 2. Verification: Use lateral radiographs to assess for graft tunnel position (Schottle’s point) and perform a clinical comparison of medial/lateral patellar glide. 3. Management: Recommend conservative therapy (physiotherapy/ROM focus) first, and only consider revision surgery (graft release or repositioning) if there is clear evidence of patellofemoral articular overload on MRI/arthroscopy.
