Effect Of Tibial Tubercle Transfer Surgery On Patellofemoral Pressure: A Biomechanical Study In Human Cadaveric Knees

Objective: Tibial tubercle transfer is a commonly used operation fororthopedic and sports trauma disease in clinical and applies to the patientswith abnormal tibial tubercle position. For patients with tibial tubercle transferoperation, one of the most important problem is the location of tibial tubercle,within the moving distance is insufficient or excessive all cannot achieve thetreatment function, and the scholars also did not have a unified standard.Therefore this study will discuss the pressure relationship between the tibialtubercle position and patellofemoral joint and find the best tibial tubercleposition which can get the equal pressure between the medial and lateral of thepatellofemoral joint. In clinical, the evaluation index mainly includes Q angleand TTTG distance. Scholars hold different points of view for the accuracyand clinical significance of these two evaluation standard. On the basis ofbiomechanical test, this study will discuss the the Q Angle and TTTG distancein diagnosis, treatment and prognosis of recurrent patellar dislocation and theclinical significance in the choice of operation scheme.Method: Eight human cadaveric knees were included in this study. Therewas no ligament damage, apparent joint deformity and osteoarthritis in everyknee specimen. The femur and tibia were cut approximately20cm from thejoint line. The surrounding skin and muscles were removed to expose thebones, and the fibula was then rigidly fixed to the tibia with a cortical screw.Firstly, we measure the TTTG distance. It is obtained by superimposingcomputed tomography (CT) images of the summit of the TG coronal (cutwhere the femoral notch resembles a roman arch) and the TT in a fullextended knee. The deepest point of the TG and the highest point of the tibialtuberosity are projected perpendicularly on the line tangent to the posteriorcondyles. The distance between these points is defined as the TT-TG.Then fixed knee specimens, the femur is fixed to an adjustable knee joint holder, thelower end of the tibia was connected to control knee flexion. We did the tibialtubercle osteotomy, and fixed the tibial tubercle at the position which theTTTG distance is0mm with screws, then we measured the Q-angle. The kneewas adjusted at the flexion of30°, along the patellar capsule, we put theTekscan pressure sensors on the In the lateral surface of patellofemoral jointand load50N on the femoral quadriceps tendon, lasts2minutes, recordedpressure value through the computer. The Tekscan pressure sensors wereremovedafter the removal of load when we finished the measurement. Thenthe knee was fixed at60°,90°,120°respectively, and repeated the experimentprocess. Afterwards, we made the TTTG distance was5mm,10mm,15mm,20mm,25mm respectively and repeated the experiment process. Thekinematic data from this study were analyzed using the SNK-q and Linearregression correlation (SPSS13.0, SPSS Inc., USA). Significance was set atp<0.05.Results: When the knee flexion was30°, the lateral pressure ofpatellofemoral joint increased with the increase of TTTG distance. There wereno significant differences（P>0.05）among the groups which the TTTGdistance was0mm,5mm,10mm, but with TTTG distance=15mm and20mm,25mm three groups comparison, difference have statistical significance (P <0.05). when TTTG distance=15mm,20mm,25mm compared betweengroups, there was no statistically significant difference (P>0.05), prompted thelateral pressure of patellofemoral joint have obvious change when TTTGdistance>10mm, especially within the range of10mm to15mm, thepatellofemoral joint lateral pressure increases rapidly. The medial pressure ofpatellofemoral joint decreased with the increase of TTTG distance. There wereno significant differences（P>0.05）among the groups which the TTTGdistance was0mm,5mm, but with TTTG distance=10mm,15mm,20mm and25mm four groups comparison, difference have statistical significance (P <0.05). When TTTG distance=10mm,15mm,20mm and25mm comparedbetween groups, there was no statistically significant difference (P>0.05), prompted the medial pressure of patellofemoral joint have obvious changewhen TTTG distance <10mm.When the knee flexion was60°,90°,120°respectively, the results was same, that is when TTTG distance between5mm-10mm, the optimal pressure of the lateral and medial of patellofemoraljoint can be obtained. In addition, through to analyse the linear regressioncorrelation between average Q angle and TTTG distance (P <0.05), indicatingthat the linear correlation exists between the Q angle and TTTG distance. Butthree knee specimens exsited patellar dislocation when TTTG distance was25mm, and the Q angle decreased. Although the linear correlation existsbetween the Q angle and TTTG distance, but when TTTG distance is too large,the two losing this relationship due to the influence of the mobility of patella.Conclusions: Through biomechanical experiment, with the increase ofTTTG distance the lateral pressure of patellofemoral joint increase gradually,and the medial pressure decreases gradually, and when TTTG distancebetween5mm-10mm, the patellofemoral joint pressure can achieve theoptimal value. Q angle is difficult to make accurate judgments to the patientswith patellofemoral joint convolution relationship, it just represents the stressdistribution of the patella. TTTG distance does not represent the position ofthe patella and its numerical value will not be affected by patellar mobile,therefore, TTTG distance as a diagnosis of patellofemoral joint convolutionrelationship or index of patellar offshoring degree is more accurately than Qangle.