Combined PCL instabilities cannot be identified using posterior stress radiographs in external or internalrotation: A cadaveric study

Briese T, Riemer R, Deichsel A, Peez C, Herbst E, Glasbrenner J, Raschke MJ, Kittl C

Abstract

Purpose: Posterior stress radiography is recommended to identify isolatedor combined posterior cruciate ligament (PCL) deficiencies. The posteriordrawer in internal (IR) or external rotation (ER) helps to differentiatebetween these combined instabilities. The purpose of this study was toevaluate posterior stress radiography (PSR) in isolated and combined PCLdeficiency with IR and ER compared to PSR in neutral rotation (NR) fordiagnosing combined PCL instabilities.Methods: Six paired fresh‐frozen human cadaveric legs (n = 12) weremounted in a Telos device for PSR. The tibia was rotated using anattached foot apparatus capable of rotating the foot 30° internally and ex-ternally. A posterior tibial load of 15 kp (147.1 N) was applied to the tibialtubercle at 90° knee flexion, and a lateral radiograph was obtained. Thiswas repeated with the foot in 30° IR and ER. The PCL, posterolateralcomplex (PLC), and posteromedial complex (PMC) were sectioned in sixknees, while the PMC was sectioned before the PLC in the other six knees.Posterior tibial displacement (PTD) was measured radiographically. Statis-tical analysis was performed using a two‐way ANOVA and a mixed modelwith Bonferroni correction, and the significance was set at p < 0.05. Fur-thermore, intra‐ and interobserver reliability was determined.Results: Cutting the PCL significantly increased the radiographic PTD by9.8 ± 1.8 mm (side‐to‐side difference compared to the intact state of theknee, n = 12; p < 0.001). This further increased to 12.2 ± 2.3 mm (n = 6;p < 0.01) with an additional PLC deficiency and to 15.4 ± 3.4 mm (n = 6;p < 0.05) with an additional PMC deficiency. A combined PLC and PMCdeficiency resulted in an increase of the PTD to 15.9 ± 4.5 mm (n = 12;p < 0.01). In the PCL/PLC deficient state, ER did not demonstrate a higherPTD, compared to the NR and IR posterior drawer. In the PCL/PMC defi-cient state in IR, PTD was 1.6 ± 0.7 mm (p < 0.01) higher compared to NR and 3.2 ± 1.9 mm (p < 0.05) higher compared to ER. We showed excellentintra‐ and interobserver reliability (0.987–0.997).Conclusion: Combined PCL instabilities resulted in a significant increase inposterior tibial displacement in posterior stress radiographs. However, PSRin IR or ER was unable to differentiate between these combined instabilities.Based on our data, additional stress radiographs in rotation are unlikely toprovide any diagnostic benefit in the clinical setting.Level of Evidence: There is no level of evidence as this study was anexperimental laboratory study.