The Effect of Posterior Draw During Graft Fixation of Anterior Cruciate Ligament Reconstruction

Background: We think reduction forced toward the posterior side during graft xation could be helpful in reducing the side-to-side difference (STSD) after ACL reconstruction. The purpose of our study was to compare the clinical and radiological outcomes of graft xation with or without a posterior draw during anterior cruciate ligament (ACL) reconstruction surgery. Methods: Among 110 patients who underwent primary arthroscopic ACL reconstruction between January 2017 and August 2020, 76 patients underwent surgery without a posterior draw (non-draw group) and 34 patients underwent ACL reconstruction with posterior draw (draw group). Results of the Lachman test, pivot-shift test, Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index, Lysholm score, International Knee Documentation Committee (IKDC) subjective score, and STSD on stress radiography were compared between the two groups. Results: The postoperative WOMAC index, Lysholm score, and IKDC subjective score were similar with the draw group. Postoperative STSD (non-draw group vs draw group, 2.4 ± 2.2 vs 2.0 ± 2.2, P = 0.319) and change of STSD (preoperative STSD vs postoperative STSD, 3.5 ± 3.5 vs 4.3 ± 4.4, P = 0.295) were not superior in the draw group. Conclusion: Graft xation with a posterior draw was not helpful in enhancing postoperative stability during ACL reconstruction. Postoperative clinical outcomes were also not superior in the draw group. Study design: Level III, retrospective comparative study.


Introduction
Anterior cruciate ligament (ACL) tears are a common orthopedic injury that most frequently affect young and active patients. [24] For those interested in returning to high-level athletic competitions, ACL reconstruction is widely performed with satisfactory results. [23] The anatomical ACL reconstruction allowed us to obtain accurate restoration of native ACL positioning and biomechanical characteristics. [1; 8; 17] However, some patients had poor outcomes with residual instability after surgery.[6; 11; 21] Numerous factors were associated with stability after ACL reconstruction, including graft selection, tunnel position, and extra-articular structure injury (ex. anterolateral ligament). [12; 14; 20] Among them optimal xation is one of the important factors for successful reconstruction. [7; 13] Optimal xation of soft tissue grafts in ACL reconstruction, including graft selection, optimal tension, xative method (aperture xation vs. suspensory xation), and knee exion angle during xation remains a controversial topic.[9; 13; 26] Almekinders et al. [3] had rst reported the concept of static anterior tibial subluxation after ACL injury, and the abnormal static relationship between the femur and tibia with the knee in extension. Subsequently, several studies investigated the static anterior tibial subluxation after ACL injury.[2; 4; 20; 25] Therefore, we think reduction forced toward the posterior side during graft xation could be helpful in reducing the side-to-side difference (STSD) after ACL reconstruction. [22] (Fig. 1) This study aimed to compare the clinical and radiological outcomes of graft xation with or without a posterior draw. We hypothesized that graft xation with a posterior draw would reduce postoperative STSD following ACL reconstruction.

Patients
This was a retrospective study of enrolled patients who underwent primary arthroscopic ACL reconstruction between January 2017 and August 2020 at our institution. The inclusion criteria were: 1) ACL total rupture, diagnosed by magnetic resonance imaging and arthroscopic examination, 2) performed arthroscopic ACL reconstruction, and 3) a follow-up period of more than 12 months. The exclusion criteria were as follows: 1) osteoarthritic changes in the injured knee, 2) multiple-ligament reconstruction, or 3) contralateral knee ACL reconstruction history. A total of 110 patients was enrolled in this study. Patients were divided into two groups: those who underwent graft xation with posterior draw (draw group) and those who underwent graft xation without posterior draw (non-draw group). Among the 110 patients, 76 patients were in the non-draw group and 34 in the draw group. The study protocol was approved by our institutional review board (ISPAIK 2021-09-019)

Surgical Procedures
The operations were performed by two fellowship-trained surgeons (J.H.C. and S.S.L.). One surgeon preferred the posterior draw of the tibia during graft xation, while the other surgeon did not. The remaining surgical procedures were similar. All patients were able to select the graft type (autograft or allograft) after su cient explanation. The hamstring tendon was harvested, and a 4-strand double-loop single-bundle graft was inserted in reconstruction with an autograft. If patients opted for an allograft, the allogenous tibialis anterior tendon was used for ACL reconstruction. A mixed graft was used when the diameter of the harvested autograft was too small for application.
Portal formation and arthroscopic examinations were performed in the standard manner. Combined meniscal tears were also evaluated. The femoral tunnel was formed using trans anteromedial portal method. [15] The center of the anatomical footprint was marked with a microfracture awl (ConMed [Linvatec]), after removal of the ACL remnant tissue. A 2.4 mm guide pin was inserted with the knee fully exed, then a 4.5 mm EndoButton drill (Smith & Nephew) was used to drill through the far cortex. After measuring the femoral tunnel length, the femoral tunnel was formed using a cannulated reamer. To form the tibial tunnel, a guide wire was inserted from the medial tibial cortex to the footprint of the ACL using a Pinn-ACL guide (Linvatec), and the tibial tunnel was created using a cannulated reamer. The EndoButton drill (Smith & Nephew) was used for femoral side graft xation. After the graft was passed, the position of the EndoButton was checked using C-arm uoroscopy. Tensioner was routinely used to check the initial tension (target: 25 N). Hybrid xation, which combined intra-tunnel aperture and extracortical suspensory xation, was used for tibial side xation.[7; 26] The posterior draw force was applied when tibial aperture xation was performed in the draw group, and draw force was not applied in the non-draw group. (Fig. 2) Partial weight-bearing walking with crutches was allowed for the initial 4 weeks after reconstruction surgery, and full weight-bearing walking was permitted at 6 weeks. Range of motion (ROM) exercise was started 2 days after surgery and reached 120° of knee exion by 4 weeks. Straight-leg raises, quadriceps sets, and ankle pump exercises were started on the rst postoperative day, closed kinetic chain exercise was initiated 2 weeks postoperatively, and return to sports was allowed after 9 months, depending on the patient's condition.

or 3 (gross).[16]
Preoperative and postoperative telos stress radiography (15 kg on the tibia at 20° of knee exion) was evaluated to measure STSD. (Fig. 3) Anterior tibial translation was investigated from the radiographs by measuring the distance from the posterior margin of the tibial condyle to the femoral condyles. STSD was de ned as the difference between the anterior tibial translations of both knees. The STSD was evaluated by two independent orthopedic surgeons (SHC and BHK) specializing in ACL reconstruction, who did not participate in the current study, to verify interobserver reliability. The intraobserver reliability was checked by having the observers repeat the same measurements 6 weeks later. Intra-class correlation coe cients (ICCs) were used for inter-and intra-observer reliability assessments.
Preoperative and postoperative outcomes were compared, and all outcomes were compared between the draw and non-draw groups.

Statistical analysis
The Shapiro-Wilk test was used to evaluate the normality of the distribution. A paired t-test was used to compare the preoperative and postoperative outcomes. To compare the demographic data and preoperative and postoperative outcomes between both groups, Student's t-test or the Mann-Whitney U test was used for continuous variables, whereas the chi-squared test or Fisher's exact test was used for categorical variables. Statistical signi cance was set at p <0.05. All data was analyzed using SPSS version 27.0 (IBM Corp., Armonk, NY, USA). In our study, 76 and 34 knees were allocated to the non-draw and draw groups, respectively. It would be 99% power to detect a difference of at 1 mm in the mean STSD with a standard deviation of 1 mm in a previous study (α = 0.05). [15]

Results
The inter -and intra-observer ICC of the STSD showed good agreement with respect to the reliability of the radiographic measurement (>0.80). The demographic data are presented in Table 1.

Discussion
The principal nding of the current study is that the posterior draw force is not helpful in enhancing postoperative stability during ACL graft xation. Moreover, the postoperative clinical outcomes were similar in the groups.
Almekinders et al. [3] had rst described abnormal tibiofemoral positioning after an ACL injury. They suggested that untreated ACL ruptures result in irreducible anterior tibial subluxation, and this phenomenon was especially evident in patients with failed ACL reconstruction on plain radiographs.
McDonald et al. [20] investigated tibiofemoral subluxation after ACL tears in more detail using magnetic resonance imaging. In their study, patients were divided into four experimental cohorts according to their ACL status: intact ACL, acute ACL disruption (within 2 months of an ACL tear), chronic ACL disruption (more than 12 months after an ACL tear), and failed ACL reconstruction. The study demonstrated signi cantly increased medial and lateral compartment subluxation in patients with chronic ACL disruption than in those with normal knees; however, patients with acute ACL tears did not show signi cant subluxation. In the current study, the mean time from injury to surgery was 9.2 and 7.2 weeks in the non-draw and draw groups, respectively. Therefore, in our study, it was too early for the tibiofemoral subluxation to have occurred. We think there would be no signi cant postoperative STSD difference between the two groups because subluxation did not occur. To identify the e cacy of posterior draw force during ACL graft xation in patients with tibiofemoral subluxation, further investigations with a revised ACL reconstruction cohort or chronic ACL de ciency cohort is necessary.
Mae et al. [19] had conducted a cadaveric investigation with respect to graft tension during ACL reconstruction. They suggested that the tibia moved proximally and posteriorly during tensioning in the graft xation stage. After graft xation, the proximal and posterior tibial forces caused the tibia to move proximally and posteriorly. We believe that our results support the hypothesis of the previous study. Adequate graft tensioning causes the tibia to move posteriorly; therefore, intentional posterior draw is not necessary during ACL graft xation.
This study has some limitations. First, factors, such as xation method, graft selection, and tunnel position, could be confounding factors for postoperative stability. However, two fellowship-trained surgeons performed the same surgical procedure, except for the posterior draw force during graft xation. Moreover, demographic data and preoperative data were similar between both groups; therefore, it was su cient to determine the effect of posterior draw on postoperative stability after ACL reconstruction. Second, follow-up was relatively short and, therefore, survival analysis or long-term results could not be fully evaluated. Third, this was a retrospective study, which has inherent limitations and biases. Fourth, the posterior draw force was applied manually. Therefore, a constant force would not have been applied to the patients in the draw group, which could be a bias in interpreting the results.

Conclusion
Graft xation with a posterior draw is not helpful in enhancing the postoperative stability during ACL reconstruction. Postoperative clinical outcomes were also not superior in the draw group.

Declarations
Con ict of interest: