SHould You TransFer the Tubercle?

For patients with recurrent lateral patellofemoral instability, a medial patellofemoral ligament reconstruction (MPFL-R) consistently provides significant improvements in symptoms, quality of life, and return to sport. During an MPFL-R the surgeon will place a soft tissue graft from the medial patella to the femur. The graft used to create the new MPFL can be autograft (usually hamstring tendon) or allograft.

The tibial tubercle osteotomy (TTO) is a procedure designed to change the vector of the pull of the quadricep muscles by moving the insertion point of the patellar tendon. This is achieved by transferring the tendon with a block of bone to allow for consistent and reliable healing. The TTO is a versatile procedure that can move the patellar tendon insertion medially, anteriorly, or distally, or a combination of these directions. It can be used to correct a lateralized tibial tubercle or patella alta.

Despite the association of an increased TT-TG distance with patellofemoral instability, it has been difficult to demonstrate a correlation with patient outcomes after patellar stabilisation surgery. In addition, studies have been unable to correlate the pre-operative presence of patella alta with clinical outcomes after MPFL-R.

This randomized clinical pilot trial will randomly allocate patients with lateral patellofemoral instability and an elevated TT-TG distance with or without patella alta ato receive either an isolated MPFL-R or an MPFL-R in combination with a correcting TTO (medializing, distalizing, or a combination of both).

Patients will be followed for two years post-operative with subjective outcome measures and objective clinical and functional testing.

The study groups will be:

• Isolated MPFL-R
• MPFL-R with a TTO

The primary outcome measures will be:

• Number of study patients recruited
• Adherence to the study protocol (number of protocol deviations)
• Follow-up completion rates of study patients at a minimum of 12 months post-operative

Secondary outcome measures include the Banff Patellar Instability Instrument 2.0 (BPII 2.0), functional testing, clinical assessment, complications, re-dislocation rate, post-operative pain scores, patient satisfaction, and patient-reported outcome scores.

If feasibility is demonstrated via this Pilot RCT, a larger RCT will be designed to answer important questions on how to optimize outcomes and limit morbidity after MPFL-R.

Inclusion criteria

• Age 13-30 years
• Symptomatic recurrent lateral patellofemoral instability
• TT-TG ≥15mm measured on MRI or ≥18mm on CT scan
• Closed physes (confirmed on knee x-rays)

Exclusion criteria

• Caton-Deschamps ratio ≥ 1.4 on lateral radiographs
• Femoral anteversion ≥ 25 degrees on diagnostic imaging rotational profile
• Tibial external rotation ≥ 45 degrees on diagnostic imaging rotational profile
• High-grade trochlear dysplasia requiring trochleoplasty
• Significant osteoarthritis on skyline plain imaging (Kellgren Lawrence grade ≥ 2)
• A chondral lesion of the patellofemoral joint that is undergoing a cartilage restoration procedure.
• Unable to complete computer-based outcome questionnaires
• Pregnant (at time of surgery)