This study evaluated 141 patients with patellar pathology to determine if the tibial tubercle-trochlear groove (TT-TG) distance measured on MRI corresponds to measurements on CT scans. They also examined the relationship between the TT-TG distance and the tibial tubercle-posterior cruciate ligament (TT-PCL) distance. They found poor agreement between TT-TG measurements on MRI versus CT. The TT-PCL distance measures true tibial tubercle lateralization while the TT-TG reflects lateralization and knee joint rotation. Patients can be grouped based on their TT-TG and TT-PCL distances which may help explain outcomes after tibial tubercle surgery.

1. The Radiological Work Up Of Patients With
Patellar Femoral Pathology: Should The TT-TG
Distance Be Measured On MRI And What Is Its
Relationship To The TT-PCL Distance?
C Anley1, G Morris1, A Saithna1, S James2, M Snow1
1 Arthroscopy Division, The Royal Orthopaedic Hospital, Birmingham, UK
2 Radiology Department, The Royal Orthopaedic Hospital, Birmingham, UK

2. Disclosures
The authors have no financial
conflicts related to this poster to
disclose

3. TT-TG Measurement
Tibial tubercle-Trochlear
groove (TT-TG) traditionally
radiographic measure to
determine lateralisation of TT
TT-TG > 20mm on CT surgical
intervention
Varies with knee flexion and
difficult in trochlea dysplasia
Dejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar instability: an anatomic radiographic study.
Knee Surg Sports Traumatol Arthrosc. 1994;2(1):19-26

4. TT-PCL Measurement
TT-PCL is the mediolateral
distance between the
midpoint of the insertion of
the patellar tendon and the
medial border of the
posterior cruciate ligament
Measured parallel to the
dorsal tibia condylar line
Normal: 24 mm
dTCL: Dorsal tibia condylar line
PCL: Posterior cruciate ligament;
TT-PCL: Tibial tubercle-Posterior
Cruciate Ligament distance
Seitlinger G, Scheurecker G, Hogler R, Labey L, Innocenti B, Hofmann S. Tibial tubercle-posterior cruciate ligament
distance: a new measurement to define the position of the tibial tubercle in patients with patella dislocation.
Am J Sports Med. 2012;40(5):1119-1125
TT-PCL

5. Objective
Radiographic study to:
1. Review whether TT-TG on CT and MRI are
interchangeable
2. Establish if there is a correlation between TT
lateralisation as indicated by TT-TG and TT-PCL

6. Methods
141 scans (108F 33M) with patellar pathology and both
MRI and CT scan, were identified on the hospital PACS
system. Ave age: 28.5 yrs (10-59, SD ±11.13 yrs)
TT-TG, TT-PCL and Knee Joint Rotation were measured
independently by two fellowship trained orthopaedic
surgeons according to the methods used by Seitlinger et
al and Shoettle
Thirty measurements where repeated on a separate
occasion to allow for an assessment of the intrarater
reliability

7. Results: TT-PCL
Mean TT-PCL: 20.32mm
(10.11-32.01, SD: ± 3.45mm)
Excellent (> 0.75) inter- and intraobserver
agreement
14% (20/141) TT-PCL > 24 mm of which
55% (11/20) had TT-TG >20mm on CT
31% (44/141) TT-TG > 20mm on CT of which
25% (11/44) had TT-PCL >24mm

8. Results: TT-TG CT vs MRI
Interobserver and
intraobserver agreement
was considered excellent
(> 0.75) for both MRI and
CT (0.98 and 0.97)
ICC for each rater
comparing the two
imaging modalities was
only fair (0.54 and 0.48)
Measurements are not
interchangeable between
the two modalities
CT MRI
Mean 17.72mm 13.56mm
Mean difference: 4.16mm
Range 6.97-31.33mm 2-30.04mm
SD ±5.15 ±6.07
P value p<0.001

9. Results
Based on the TT-TG and TT-PCL measurements,
4 groups of patients can be established.
When comparing knee joint rotation (KJR)
between groups, we noted that an increased TT-
TG may result from either true lateralisation of
the TT, an increased knee joint rotation or a
combination of both.

10. Results: TG and PCL
TG <20mm
PCL<24mm
TG<20mm
PCL>24mm
TG>20mm
PCL<24mm
TG>20mm
PCL>24mm
Number (%) 88 (62.4%) 9 (6.4%) 33 (23.4%) 11 (7.8%)
Mean TG
Mean PCL
15.04
18.92
15.06
25.92
23.22
20.82
25.42
25.88
SD TG
SD PCL
±3.12
±2.66
±3.55
±2.42
±2.77
±2.27
±3.99
±1.75
CT KJA 6.8 6.7 12.5 10.3
P < 0.05

11. Conclusion
Commonly accepted values for the TT-TG
distance cannot be used interchangeably
between CT and MRI and a TT-TG >20mm
measured on MRI should not be used as an
indication for surgery

12. Conclusion
The TT-PCL measurement is a measure of true
lateralisation of the tibial tubercle while the TT-
TG is an amalgamated measure of true
lateralisation and KJR.
The clinical relevance of these different groups
requires further investigation and may explain
the poor results in some patients following tibial
tubercle transfers.

13. References
Dejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar
instability: an anatomic radiographic study. Knee Surg Sports Traumatol
Arthrosc. 1994;2(1):19-26
Seitlinger G, Scheurecker G, Hogler R, Labey L, Innocenti B, Hofmann S.
Tibial tubercle-posterior cruciate ligament distance: a new measurement
to define the position of the tibial tubercle in patients with patella
dislocation. Am J Sports Med. 2012;40(5):1119-1125
Schoettle PB, Zanetti M, Seifert B, Pfirrmann CW, Fucentese SF, Romero J.
The tibial tuberosity–trochlear groove distance: a comparative study
between CT and MRI scanning. Knee. 2006;13:26-31.