Purpose

Residual posterior sagging may occur after posterior cruciate ligament (PCL) reconstruction (PCLR), yet when it mainly occurs is not fully understood. This study aimed to elucidate sequential changes in radiographic posterior tibial translation (PTT) through PCLR.

Methods

Radiographic findings from 22 patients who underwent bi-socket double-bundle PCLR for isolated grade II or III PCL injury from January 2007 to December 2016 with at least two years of follow-up (mean: 4.5 years; range: 2–12 years) were retrospectively investigated. On lateral radiographs with gravity sag views, PTT (side-to-side difference of the tibiofemoral relationship) was serially measured preoperatively and immediately, three and six months, and one and two or more years postoperatively. Risk factors for residual posterior sagging, indicating the PTT was 5 mm or more (grade = II) at two or more years postoperatively, were also investigated using a multivariable logistic regression analysis.

Results

The PTT was 10.1 ± 2.3 mm preoperatively, then was reduced significantly to -0.8 ± 1.2 mm immediately after surgery (P < 0.001). Subsequently, the PTT was significantly increased by 5.2 ± 2.6 mm up to 4.1 ± 2.7 mm at three months postoperatively (P < 0.001). Then, no significant changes at six months (4.1 ± 2.5 mm), one year (4.4 ± 2.1 mm), and two or more years (4.4 ± 1.9 mm) postoperatively were observed.Seven cases of residual PTT with grade II at two or more years after PCLR were identified, whereas no patient underwent revision PCLR due to subjective recurrent instability and no instance of grade III injury persisted to the final follow-up. PTTs with residual posterior sagging were significantly larger than those without residual posterior sagging at all time points except for immediately postoperatively [preoperatively, 9.1 ± 1.6 vs. 12.2 ± 2.2 mm (P < 0.001); immediately postoperatively, -0.8 ± 1.3 vs. -0.8 ± 0.8 mm (P = 0.950); three months postoperatively, 2.7 ± 1.6 vs. 7.0 ± 1.8 mm (P < 0.001); and two or more years postoperatively, 3.4 ± 1.0 vs. 6.6 ± 1.4 mm (P < 0.001)]. Multivariate logistic regression analysis showed preoperative grade III injury was independently associated with residual posterior sagging (odds ratio: 26.809; 95% confidence interval: 2.037–282.672; P < 0.001). Meanwhile, the receiver operating characteristic analysis highlighted a cutoff value of 12.64 mm for the preoperative PTT as the optimal threshold for differentiating the two groups with and without residual posterior sagging (sensitivity: 71.4%; specificity: 100.0%)

Conclusion

The initially reduced postoperative PTT significantly increased within three months with conventional rehabilitation protocols but no progression was observed up to 4.5 years after PCLR. Preoperative grade III injury was independently associated with residual posterior sagging. Therefore, we recommend that clinicians consider the preoperative PTT as a risk factor for postoperative residual posterior sagging and take meticulous care, especially in the early postoperative period, to protect the transplanted PCL graft even if the PTT could be reduced immediately after PCLR.