## 2 Materials and Methods  
Our retrospective analysis included 44 patients who underwent BPTB ACL reconstruction in our hospital between December 2011 and March 2015. There were 23 males and 21 females. The mean age of patients was 28 years old (range 13-73). There were 18 right and 26 left knees. At the time of final evaluation (96 weeks postoperatively), all patients, except one, were stable on clinical evaluation. This patient with ACL graft complete injury had a traumatic secondary graft failure. The rehabilitation protocol was the same for all patients. The only difference was weight-bearing immediately after the surgery, and this factor was also evaluated separately in this study. One group of patients had full weight-bearing immediately after the surgery. The second group had no weight bearing for the first three weeks after the surgery. A brief description of the rehabilitation protocol is presented in Table 1.  
MRI was performed in all patients postoperatively at 2, 6, 12, 18, 24, 36, 48, 72, and 96 weeks. MRI images were obtained using a 1.5 tesla GE Signa HDxt scanner with an 8-channel knee coil. Full, routine MRI protocol for ACL assessment included axial and sagittal PDWI (Proton Density Weighted Images), axial FSE STIR (Fast Spin Echo Short Tau Inversion Recovery), DWI (Diffusion Weighted Images), and T2 Mapping sequences. Signal intensity was measured manually using the regions of interest (ROI) tool with a diameter of 3 mm on axial and sagittal PDWI sequences (Table 2). To measure ACL graft signal intensity, we used the method previously described by [PERSON] et al. [9], [PERSON] et al. [10] and [PERSON] et al. [11], by calculating signal-to-noise quotient (SNQ, Equation (1)):  
\[\text{SNQ}=\frac{\text{Signal of ACL graft }-\text{Signal of PCL}}{\text{Signal of background}} \tag{1}\] \begin{table}
\begin{tabular}{c c c} \hline \hline
**Time** & **Rehabilitation Protocol** & **GROUP 1—Full Weight Bearing** & **GROUP 2—No Weight Bearing after the** \\  & **Allowed Immediately after the Surgery** & **Surgery for 3 Weeks** \\ \hline Days 1–7 & Pain and swelling control & \\ \hline \hline \end{tabular} \begin{tabular}{c} Care for the dressing \\ \end{tabular} \begin{tabular}{c} Early range of motion exercises \\ \end{tabular} \
\begin{tabular}{c} Manual therapy \\ \end{tabular}
\begin{tabular}{c} Quadriceps femoris muscle (QF) activation + hamstrings cocontraction exercises \\ Full weight bearing as tolerated \\ \end{tabular} No weight bearing for 3 weeks  
\begin{tabular}{c} Weeks 2–6 \\ \end{tabular} Gradual increase of range of motion (ROM) 0–100  
\begin{tabular}{c} Hamstrings cocontraction exercises \\ \end{tabular} \begin{tabular}{c} Close kinetic chain QF exercises \\ Simple priorioception exercises \\ \end{tabular} \begin{tabular}{c} Pelvic stabilization exercises \\ \end{tabular} \
\begin{tabular}{c} Scars mobilisation \\ \end{tabular}
\begin{tabular}{c} Weeks 6–12 \\ \end{tabular} Progression of above mentioned exercises  
Months 3–6 & Gradual implementation of open kinetic chain exercises \\ \hline \hline Months 6–12 & Targeted exercices to eliminated any side-to-side differences in muscle strength \\ \hline \hline Introducing a bike \\ \hline \hline \end{tabular} \begin{tabular}{c} Prioprioception exercises \\ \end{tabular} \
\begin{tabular}{c} Introducing jogging \\ \end{tabular}
\begin{tabular}{c} Regaining proper biomechanics \\ \end{tabular}
\end{table} 
Table 1: Brief description of rehabilitation protocol. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **ax PDWI** & **sag PDWI** \\ \hline TR (ms) & 2800 & 2800 \\ \hline TE (ms) & 35 & 35 \\ \hline Slice thickness (mm) & 2 & 2 \\ \hline Intersection gap (mm) & 2 & 2 \\ \hline FOV (cm) & \(16\times 16\) & \(16\times 16\) \\ \hline Matrix & \(512\times 256\) & \(512\times 256\) \\ \hline Flip angle & 90 & 90 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Magnetic resonance imaging (MRI) parameters. We wanted to evaluate which measurements (sagittal or axial plane) are more reliable for predicting ACL graft insufficiency.