Patellar instability-can the TT-TG distance be measured clinically?

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Radiology

Background:

• The tibial tubercle-trochlear groove (TT-TG) distance is crucial for diagnosing and treating patellar instability.
• Accurate measurement of TT-TG distance is essential for surgical planning, particularly for tibial tubercle transfer procedures.

Purpose of the Study:

• To evaluate the efficacy of a simple string-based method for measuring TT-TG distance in an outpatient setting.
• To compare the accuracy of this non-invasive technique with Magnetic Resonance Imaging (MRI) findings.

Main Methods:

• A string-based technique was used to measure TT-TG distance in 24 knees of patients scheduled for patellar realignment surgery.
• Measurements were taken with the knee at 90 degrees flexion and in extension.
• Results were compared with TT-TG distances obtained from MRI scans.

Main Results:

• In 90 degrees knee flexion, visual assessment showed the tibial tubercle aligning with the trochlear groove in both stable and unstable knees, rendering this position unhelpful for diagnosis.
• In the extended knee position, the string method failed to identify the significant TT-TG distance observed on MRI in objectively unstable knees.
• Visual inspection alone is insufficient for accurately assessing TT-TG distance and guiding surgical decisions.

Conclusions:

• The string measurement technique is unreliable for assessing TT-TG distance in the outpatient setting.
• Accurate assessment of TT-TG distance, particularly in cases of suspected patellar instability, requires advanced imaging like MRI.
• MRI is recommended prior to considering medial tibial tubercle transfer to ensure appropriate surgical intervention.