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Using the TTTG Measurement to Determine Surgical Management of Patellofemoral Instability

Using the TTTG Measurement to Determine Surgical Management of Patellofemoral Instability

Megan Diack, MBCHB, MRCSI, MCh, IRELAND Orla Hennessy, MB BaO BCh, MCh, IRELAND Diane Bergin, Prof., IRELAND Fintan J. Shannon, FRCS (Tr/Orth), IRELAND

University Hospital Galway, Galway, Galway, IRELAND

2021 Congress   ePoster Presentation     rating (1)


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Sports Medicine

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Summary: Using a Tibial Tuberosity to Trochlear Groove (TTTG) measurment of more or less than 18mm can determine the successful use of either an isolated Tibial Tubercle Osteotomy or Medial Patellofemoral Ligament (MPFL) reconstruction, respectively.


Patellofemoral instability (PFI) is a common orthopaedic condition that most often affects adolescents and young adults. Patients with patellar instability often experience disabling symptoms which can limit their daily activities and adversely affect their quality of life. Despite its prevalence the management of this condition is complex and remains highly variable.
The aim of this study was to investigate the clinical and functional outcome of a cohort of patients with recurrent PFI that were surgically managed based on a simple binary algorithm and to determine if the Tibial Tuberosity to Trochlear Groove (TTTG) offset measurement alone, could be reliably used to direct surgical management of PFI toward either an isolated tibial tubercle osteotomy or an MPFL Reconstruction.

Materials And Methods

All Patients who had undergone surgical management of recurrent PFI under the senior author were identified. Patients with greater than one surgical procedure at index surgery, skeletally immature, and those with patellofemoral arthropathy and/or fixed lateral subluxations were excluded. Patient demographics, history, radiology parameters (TTTG measure, trochlear dysplasia, patellar height) and surgical management were tabulated.
All suitable patients were contacted. Persistent or recurrent instability, patient satisfaction and return to preferred activities were recorded. Patient reported outcomes were determined using the IKDC (International Knee Documentation Committee) Subjective Knee Form. Multivariant statistical analysis was performed.


Forty-eight patients were deemed eligible for review. The male-to-female ratio was 2:3 with an average age of 26 years (range 14 - 47).
There was a positive correlation between TTTG measurements of more/less 18mm and the successful isolated use of a tibial tubercle osteotomy or MPFL reconstruction, respectively. 16 patients (33%) with a TTTG <18mm that were managed with an isolated MPFL reconstruction had an average IKDC outcome score of 82% (range 53 - 93%). 24 patients (50%) with a TTTG >=18mm were managed with an isolated tibial tubercle osteotomy procedure and had an average IKDC outcome score of 78% (range 57 - 99%). The remaining 8 patients (17%) did not follow the algorithm, 40% of these resulted in an IKDC score of below 60%, conversely validating our hypothesis. There were only 3 cases (6%) that experienced recurrent dislocation post-operatively. Overall a patient satisfaction rate of 90% was reported.


A simple binary algorithm using the TTTG measurement was successfully used to determine a safe surgical management solution for patients with recurrent PFI. We achieved high patient satisfaction rates and post-operative IKDC scores.
We believe that there is a limited role for combined procedures. Trochleoplasty and femoral osteotomies should be reserved for failed primary surgical management, severe dysplasia and gross maltracking.