TTTG (tibial tuberosity–trochlear groove) distance measures how far the tibial tubercle is shifted laterally relative to the femoral trochlear groove on axial imaging; normal values are ≤10 mm and ≥20 mm is considered pathological.
What is a TT-TG?
TT-TG (tibial tuberosity–trochlear groove) is the transverse distance on an axial CT or MRI between the deepest point of the trochlear groove and the center of the tibial tuberosity, used to quantify patellar maltracking.
Surgeons rely on this measurement to figure out if procedures like tibial tubercle transfer (TTT) could help stabilize a patella that keeps dislocating or sliding out of place.
How do you measure TTTG?
TTTG is measured on axial CT or MRI slices by drawing a line through the posterior femoral condyles, then marking the trochlear groove and tibial tuberosity; the distance between these two points is the TT-TG.
Radiologists use specialized musculoskeletal software to keep things consistent—if two observers disagree by more than 1 mm, that’s usually considered acceptable in clinical practice.
What is an abnormal TT-TG distance?
TT-TG ≥20 mm is considered pathological and typically warrants surgical correction in patients with patellar instability, whereas values ≤10 mm are normal.
Some research suggests that TT-TG >15 mm means physical therapy alone probably won’t cut it, which helps surgeons decide when to operate.
What is TTT knee surgery?
TTT (tibial tubercle transfer) is an open osteotomy procedure that moves the tibial tuberosity medially or anteriorly to improve patellar tracking, often combined with medial reefing or trochleoplasty.
After surgery, expect about six weeks of limited weight-bearing and rehab focused on strengthening the vastus medialis obliquus while keeping swelling under control.
What causes increased Q angle?
An increased Q angle is most often driven by femoral anteversion, external tibial torsion, or a laterally positioned tibial tubercle, which laterally displaces the patellar tendon vector.
Other factors like knock-knees, a high-riding patella, or loose ligaments can also play a role—fixing these helps prevent the problem from coming back.
Is patella a ratio?
The Insall–Salvati ratio compares patellar tendon length to patellar length on a 30° flexed lateral X-ray; normal values are 0.8–1.2, with <1.0 indicating baja and >1.2 alta.
Always check these measurements on properly aligned X-rays—rotational errors can mess up the results.
What is a Trochleoplasty?
A trochleoplasty is an open osteochondral procedure that deepens or reshapes the trochlear groove to prevent recurrent patellar dislocations, performed under general anesthesia.
This surgery is usually reserved for cases with a severely shallow or flat groove that keeps causing dislocations, even after soft-tissue fixes.
Is patella alta painful?
Patella alta predisposes to instability events that damage the patellofemoral cartilage, leading to anterior knee pain, swelling, and eventual osteoarthritis.
Patients often describe a sudden “giving-way” feeling and tenderness right in front of the knee—over time, this maltracking wears out the joint faster.
How is Trochlear depth measured?
Trochlear depth is calculated by subtracting the deepest trochlear groove distance from the mean anteroposterior height of the medial and lateral femoral condyles on an axial CT slice.
If the groove is too shallow—less than 1 mm deep—it’s a red flag for dysplasia and higher dislocation risk, which helps guide surgery choices.
What is the normal TT TG distance?
The normal TT-TG distance is 10 mm or less on axial CT or MRI in asymptomatic individuals; values >15 mm correlate with patellofemoral instability.
Surgeons use this cutoff to decide whether soft-tissue procedures will work or if they need to realign the bone.
What is the femoral trochlea?
The femoral trochlea is the cartilaginous groove on the anterior distal femur formed by medial and lateral ridges that articulates with the patella, guiding its motion during flexion.
When this groove is too shallow or bulges outward—a condition called dysplasia—it becomes a major risk factor for the patella popping out repeatedly.
How do you measure patella alta?
Patella alta is measured using the Caton–Deschamps index, which compares the length of the patellar articular surface to the distance from the distal patellar articular margin to the anterosuperior tibial plateau on a lateral X-ray; normal is 0.6–1.3.
Anything above 1.3 suggests a high-riding patella, which raises the risk of dislocation and messes with how the joint moves.
How long does TTT surgery take?
A TTT procedure typically takes 60–90 minutes under general or spinal anesthesia, including time for fluoroscopic confirmation of correction.
Plan on two to six weeks of protected walking and gradual strengthening to get your quad control back after surgery.
What is a osteotomy procedure?
An osteotomy is a bone-cutting procedure that reshapes or realigns a malaligned joint surface to offload damaged cartilage or correct angular deformity, commonly performed around the knee.
For example, a high tibial osteotomy shifts weight off the worn inner knee compartment in early arthritis caused by bow-leggedness.
What is a lateral release knee surgery?
A lateral release is an arthroscopic procedure that incises the lateral retinaculum to allow medialization of the patella into the trochlear groove, performed through three small portals.
Often, surgeons pair this with medial patellofemoral ligament reconstruction when patients have repeated dislocations and a tight lateral side.
