Paper 22: Coexistence of knee hyperextension and steeper posterior tibial slope increases the risk of graft failure after anterior cruciate ligament reconstruction

Objectives: Anterior cruciate ligament reconstruction (ACLR) is widely performed to restore knee stability, but graft failure remains a serious complication, with reported rates of 2.8–19.3%. Several risk factors have been reported, including younger age, high activity level, tunnel malposition, steeper posterior tibial slope (PTS), graft choice or diameter, and generalized joint laxity. Although these factors have been consistently identified as an independent risk factor, little is known about the impact of the coexistence of these risk factors. There might be a cumulative effect when risk factors coexist. Thus, the purpose of the present study was (1) to investigate independent risk factors for graft failure after ACLR using hamstring autograft and (2) to further investigate whether the coexistence of risk factors cumulatively increase the risk of graft failure.
Methods: The present retrospective study included 341 ACL-injured patients (172 males, 169 females; mean age 26.4 ± 12.7 years [mean ± SD]) who underwent primary ACLR using hamstring autograft at a single institution, with a minimum follow-up of one year. Patients with multi-ligament injuries, concomitant osteotomies, bone–patellar tendon–bone or quadriceps tendon grafts, additional lateral extra-articular procedures, or absence of preoperative radiographs were excluded. Clinical variables included age, sex, body mass index (BMI), pre-injury Tegner Activity Scale (pre-TAS), and pivot-shift test grade under general anesthesia. Knee hyperextension was defined as ≥5° of extension in the ACL-injured knee under general anesthesia. PTS was measured on lateral knee radiographs as shown in Figure 1. Graft failure was defined as re-rupture diagnosed by clinical examination, requiring or scheduled for revision ACLR. Surgical variables included graft type (single-bundle [SB] or double-bundle [DB] reconstruction), presence of medial/lateral meniscal injury, and the corresponding management (none, repair, or excision).
For statistical analysis, univariate comparisons were made between the failure and non-failure groups. Variables that were statistically significant in univariate analysis were entered into Cox proportional hazards model to identify independent predictors of graft failure. Receiver operating characteristic (ROC) analysis was performed to determine the cutoff value for PTS, and Cox proportional hazards model was further used to assess hazard ratio (HR) of each risk factor as well as combined hazard effect of several risk factors on graft failure.
Results: Graft failure occurred in 31 patients (9.1%) at a mean of 1.7 years postoperatively. Patients with graft failure were younger (20.5 ± 8.8 vs 27.0 ± 12.9), had higher pre-TAS (8.1 ± 1.5 vs 7.0 ± 1.9), more frequent knee hyperextension ≥5° (32.3% vs 11.3%, p<0.01), and steeper PTS (12.7° ± 3.3 vs 10.9° ± 2.6, p<0.01) compared with the non-failure group. Medial meniscal injuries were more common (19.4% vs 39.0%) in the non-failure group. No significant differences were found in sex, BMI, lateral meniscal injuries, or treatment of meniscal injuries (Table 1).
Multivariate analysis using the Cox proportional hazards model identified higher pre-TAS (HR 1.4, 95% CI 1.1–1.8), knee hyperextension ≥5° (HR 5.9, 95% CI 2.5–13.9), and increased PTS (HR 1.4, 95% CI 1.2–1.5) as independent predictors of graft failure (Table 2). ROC analysis demonstrated an optimal cut-off value of 11.8° for PTS (AUC 0.66; sensitivity 65%, specificity 68%).
When stratified according to the presence of risk factors, graft failure rates were 2.8% with neither factor, 15.2% with hyperextension only, 13.4% with PTS ≥11.8° only, and 41.7% when both were present, as shown in Table 3 (HR 16.2, 95% CI 3.7–71), indicating a substantial increase in risk of graft failure when two factors coexist.
Conclusions: Younger age, knee hyperextension, and steeper PTS were independent predictors of graft failure after ACLR with hamstring autograft. Furthermore, coexistence of knee hyperextension and steeper PTS, though uncommon, was associated with a remarkably increased risk of graft failure, indicating a cumulative effect. The novelty of the present study was that the coexistence of two risk factors (knee hyperextension and steeper PTS) significantly increased the risk of graft failure compared to the patients with one risk factor, suggesting the importance of preoperative assessment of knee hyperextension and PTS. The present findings also suggest that additional procedures such as lateral extra-articular augmentation may need to be considered at the time of ACL reconstruction in these high-risk patients in order to reduce the risk of graft failure.