Correlation Between Merchant's Standard Q Angle and TT-TG Distance.

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Radiology

Background:

• The standard Q angle (SQA) was developed to improve the reliability of clinical quadriceps angle (Q angle) measurements.
• Assessing Q angle is crucial for diagnosing and managing knee conditions.

Purpose of the Study:

• To investigate the correlation between the standard Q angle (SQA) and tibial tubercle-trochlear groove (TT-TG) distance.
• To compare this correlation in awake versus anesthetized patients with recurrent patellar instability.

Main Methods:

• A cross-sectional study included 47 patients (94 knees) with recurrent patellar instability.
• Standard Q angle (SQA) and computed tomography (CT) scans were used to measure TT-TG distance, Caton-Deschamps index (CDI), and lateral trochlear inclination (LTI).
• Measurements were taken both in the clinic (awake) and in the operating room (anesthetized).

Main Results:

• A significant correlation between SQA and TT-TG distance was observed in anesthetized patients (R² = 0.15).
• This correlation strengthened in anesthetized patients with normal patellar height (CDI < 1.2) and normal lateral trochlear inclination (LTI > 11°) (R² = 0.57).
• Correlations were weak or nonsignificant in awake patients and those with anatomic risk factors.

Conclusions:

• The SQA shows a strong positive correlation with TT-TG distance in anesthetized patients with normal knee anatomy.
• The SQA's utility is limited in awake patients or those with predisposing anatomic factors for patellar instability.
• Anesthesia may enhance the reliability of SQA measurements for assessing patellar instability.