# The Influence of Bone Bruises on Bone Tunnel Enlargement Regarding ACL Rupture
## 4 Discussion
This study provides novel data characterizing the relationship between the size of the bone tunnel after ACLR and BBs--information that is critical for improving treatment strategies for ACL rerupture. In our study, there were no relationships between the size of the BB and the time from injury to the MRI evaluation. Previous studies [40; 41; 42; 43; 44; 45] concluded that there is no consensus on the mean time after which BBs resolve after ACL tears. Bone contusions evolve over time from those showing acute, high-intensity signals to symptom resolution. [PERSON] et al. [46], based on MR images in a group of 98 patients, indicated that bone contusions resolve within average of six weeks after injury. [PERSON] et al. [47] reported that in acute knee injuries, BBs occurred in 53% of patients, and bone changes persisted in the fourth and twelfth months of follow-up in 69% and 12% of patients, respectively. On the other hand, a prospective study [45] showed that the BB volume can initially increase within the first six weeks after injury. Such a situation may be related to the extent of the injury, the size of the contusion, and other accompanying injuries, which also affect the extent of the injury. In most recent study, [PERSON] et al. quantified the number of bone contusions and their locations observed on MRI scans of noncontact ACL-injured knee acquired within six weeks of injury [48]. They detected bone contusions in 135 of 136 patients. In our study, the mean time from injury to the MRI examination in the STGR group was 10 days (SD = 9 days), and the mean time from injury to surgery was 50 days (SD = 43 days). Hence, in some patients, BBs might resolve to some extent until ACLR is performed, particularly when the knee joint operation is postponed by the patient for personal reasons. Therefore, we divided the STGR group into three relatively homogeneous subgroups regarding the time from injury to ACLR and analyzed the most abundant subgroup B (n = 15). This process caused an increase in the correlation coefficients. The long-term effects of ACLR can be objectively observed by MR imaging, including the assessment of possible BTE, which may cause loosening of the graft inside the bone tunnel, mechanical failure, and, as a result, the loss of the expected effect of the operation on the stability of the knee. Bone tunnel widening occurs predominantly within the first three months following ACLR. Most changes in the size of the femoral and tibial tunnels occur within the first six weeks after surgery [49]. The BTE etiology is multifactorial, including biomechanical components linked to grafts collected from both the patellar tendon (bone-tendon-bone method, BTB) and hamstrings, suggesting that more cases of BTE occur in patients with hamstring grafts [50]. On the other hand, [PERSON] and [PERSON] studied fixation techniques and concluded that the position of the fixation sites and the type of fixation device are the main factors affecting the development of BTE [51]. In recent years, determining the best place to position tunnels has been discussed. Studies have shown that transtibial tunnel techniques result in a nonanatomic position of the femoral tunnel [52]. The transtibial drilling method has been increasingly replaced by the anatomic femoral tunnel method, providing translational and tensioning patterns similar to those of the native ACL and increased rotational stability [53; 54]. Additionally, it has been observed that originally small tunnels are more likely to exhibit an advanced enlargement process than are originally large tunnels drilled during surgery [1]. The mean tibial BTE was significantly and inversely dependent on the original tibial bone tunnel diameter, with a correlation coefficient of \(-0.55\) per unit (\(7\,\mathrm{mm}=+1.93\,\mathrm{mm}\), \(8\,\mathrm{mm}=+1.43\,\mathrm{mm}\), \(9\,\mathrm{mm}=0.83\,\mathrm{mm}\), \(p=0.007\)). Thus, every additional increase (mm) in the diameter of the original tibial bone tunnel reduces the extent of tunnel widening by \(0.55\,\mathrm{mm}\).