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CLINICAL RESEARCH

Is Primary Arthroscopic Repair Using the Pulley Technique an Effective Treatment for Partial Proximal ACL Tears?

Liao, Weixiong PhD; Zhang, Qiang PhD

Author Information
Clinical Orthopaedics and Related Research: May 2020 - Volume 478 - Issue 5 - p 1031-1045
doi: 10.1097/CORR.0000000000001118

Abstract

Introduction

During the past century, primary ACL repair with an open procedure was in wide use [37]. However, because this technique’s outcomes have been inconsistent, the use of ACL reconstruction has increased recently [6, 18, 22, 31, 32, 34, 35]. This method has yielded more-predictable results and is in wide use for treating all ACL tear types. On the other hand, there are disadvantages to reconstruction, such as loss of proprioception, physeal disruption, donor-site morbidity, graft-associated infection, and potential problems with revision surgery. Therefore, recent attention has focused on ACL preservation using primary arthroscopic repair [1, 8, 9, 36]. Currently, advanced imaging, surgical techniques, instrumentation, and hardware allow surgeons to identify the ACL injury pattern preoperatively with MRI, confirm the diagnosis with arthroscopy, and perform primary repair with a biomechanically sound construct.

However, the fact that it is possible to perform primary direct repair in some patients does not mean that surgeons ought to do so. There are several unanswered questions and concerns about this approach. Partial ACL tears may evolve into complete tears because the blood supply is interrupted [28], and nonoperative management often provides unsatisfactory results for this tear type, especially in very active patients [16, 20]. When symptomatic knee instability develops, the patient may be a candidate for surgical treatment [7], including thermal modification [21], single-bundle reconstruction [23], and primary repair [13]. Because thermal modification adversely affects collagen tensile stiffness [7], and because of the concerns associated with reconstruction (it is a much larger intervention than primary repair), we believed that primary arthroscopic repair using the pulley technique, which is commonly used for repairing the rotator cuff in patients with partial proximal ACL tears, deserves further inquiry in carefully selected patients. This technique maximizes cuff-to-bone compression along suture anchors and provides extremely secure fixation in the medial aspect of the footprint [4, 11]. But to our knowledge, this approach has not been studied in primary arthroscopic ACL repair.

We therefore asked: (1) Does primary arthroscopic repair using the pulley technique result in satisfactory ROM (a functional ROM with a flexion contracture of 30° or less), knee stability, and functional scores in patients with partial proximal ACL tears? (2) What complications are associated with primary arthroscopic repair using the pulley technique in patients with partial proximal ACL tears?

Patients and Methods

Study Design and Setting

We performed this retrospective case series study after obtaining approval from our ethical review committee and consent from the patients. As it is a non-randomized series rather than a prospective study, selection bias might have arisen from unblinded surgeons and patients. The STROBE study diagram shows the flowchart of patient selection (Fig. 1). Between January 2014 and March 2016, 183 patients with ACL injuries were treated with arthroscopic surgery by the senior surgeon at our institution (QZ). We treated 23 patients surgically who had partial proximal ACL tears and excellent tissue quality (defined as a remnant with mild interstitial tearing and the ability to hold sutures). All patients meeting those two criteria were treated using primary arthroscopic repair using the pulley technique. During that period, this represented 13% (23 of 183) of the patients we treated surgically for ACL tears. We only included unilateral partial proximal ACL tears and excluded bilateral tears. Of these 23 patients, two were lost to follow-up before 2 years postoperative and 21 were analyzed at a mean (range) follow-up duration of 36 months (25-49).

F1
Fig. 1:
The STROBE study diagram shows the flowchart of patient selection.

Participants

Patients were excluded if they had other ACL tear types and/or insufficient tissue quality (defined as a severely torn remnant that was not strong enough to hold sutures) and thus underwent conversion to ACL reconstruction (n = 118, including 39 complete proximal ACL tears located in the most-proximal 10% of the ligament. When performing primary ACL repair in the acute phase, if we found a type III or IV tear intraoperatively, we performed early ACL reconstruction rather than wait 3 weeks, despite the potential complications. Other exclusion criteria were multi-ligamentous injuries (more than two ligaments involved) (n = 15) or substantial arthrosis (chondromalacia greater than Outerbridge Grade 3) (n = 27).

The indications for primary arthroscopic ACL repair were preoperative clinical instability (abnormal anterior drawer tests and/or Lachman test findings), type I partial proximal ACL tear identified on a preoperative MR image (Fig. 2) or confirmed with arthroscopy (Fig. 3), and excellent tissue quality characterized by a remnant with mild interstitial tearing and the ability to hold sutures. A Type I partial proximal ACL tear occurs when part of the most-proximal 10% of the ACL is avulsed [39], and the rest of the proximal end is still intact and attached to the femoral wall [19]. This tear type has the possibility of reapproximating the torn distal remnant to the femoral footprint.

F2
Fig. 2A-F:
Preoperative T2-weighted MR images show a partial proximal ACL tear with a mostly normal-appearing distal ligament in two different patients. (A) Sagittal, (B) coronal, and (C) axial MR images of the left knee of Patient 2 are shown here. The (D) sagittal, (E) coronal, and (F) axial MR images of the right knee of Patient 20 are also shown. The arrows indicate the injured part of the ACL.
F3
Fig. 3A-F:
Arthroscopic images and schematic drawings show three different types of partial proximal ACL tears. (A) A partial proximal tear in the anteromedial and posterolateral bundles of the left knee of Patient 12 was confirmed with arthroscopy. (B) A partial proximal tear in the anteromedial bundle of the right knee of Patient 15 was confirmed with arthroscopy. (C) A partial proximal tear in the posterolateral bundle of the right knee of Patient 1 was confirmed with arthroscopy. Schematic drawings show that (D) five patients had partial proximal tears in both the anteromedial and posterolateral bundles, (E) 10 had partial proximal tears in the anteromedial bundle, and (F) six had partial proximal tears in the posterolateral bundle. The red shading indicates the femoral footprint of the native ACL, which was oblong and extended from the lateral intercondylar ridge anteriorly to the articular cartilage posteriorly. A ridge separated the anteromedial and posterolateral regions of the femoral footprint of the native ACL. The circles indicate the injured areas.

Description of Experiment, Treatment, or Surgery

Surgical Technique

The patient was placed in the supine position, and the operated leg was prepared and draped in the standard fashion for knee arthroscopy. Anteromedial and anterolateral portals were created. A general inspection of the knee was performed to confirm the presence of a partial proximal ACL tear and excellent tissue quality and to determine whether attempting primary repair would be reasonable. The femoral footprint was prepared with a shaver or burr to induce bleeding. Subsequently, an accessory anterior portal was created at the inferomedial margin of the patella under direct visualization as a viewing portal. A malleable Passport cannula (Arthrex, Naples, FL, USA) was placed in the anteromedial portal to facilitate suture passage and management, as well as ligament repair.

A double-pulley technique was performed when a proximal tear was involved in both the anteromedial and posterolateral bundles of the ACL [4, 11]. Two 3.5-mm nonabsorbable Twinfix suture anchors (Smith & Nephew Endoscopy, Andover, MA, USA) doubly loaded with Number 2 Ultrabraid sutures (Smith & Nephew Endoscopy) were placed in the femoral footprint through the anteromedial portal (Fig. 4A). The first anchor was placed in the origin of the anteromedial bundle of the native ACL’s footprint with the knee in 90° of flexion. The second anchor was placed in the origin of the posterolateral bundle of the native ACL’s footprint with the knee in approximately 110° to 115° of flexion to adjust the angle of approach and avoid perforating the posterior condyle. Two strands of a single suture from each anchor were separately passed through the ACL with a FastPass Scorpion (Arthrex), producing four points of fixation in the ligament with a ligament bridge between them (Fig. 4B). A suture strand from each anchor was retrieved through the anteromedial portal and manually tied into a two-strand-overhand locking knot over a metal rod [41]. The two free suture strands were pulled to transport the knot over the ligament bridge, thus tensioning the ACL remnant back up to the femoral footprint (Fig. 4C). Then, the two free suture strands were tied into a multiple-throw square knot with a knot pusher (Arthrex) (Fig. 4D). Subsequently, simple stitching was performed of the two suture strands of the other suture from each anchor [3]. A suture strand was passed through the ACL and the other was left wrapped around its proximal avulsed end. Then, the two suture strands were tied into a Samsung Medical Center knot to overlock the ligament stump that was not fixed using the pulley technique (Fig. 4E). The knee position in tensioning is at 90° of flexion to minimize gap formation between the repaired ligament and the femoral footprint. The final construct comprised a double-mattress-suture configuration and two simple-suture configurations to compress the ACL remnant against the femoral footprint (Fig. 4F) [3]. The schematic drawings (Fig. 5A-F) show the procedures of double-pulley technique.

F4
Fig. 4A-F:
The double-pulley technique was performed using arthroscopy on the left knee of Patient 2. (A) Two 3.5-mm nonabsorbable Twinfix suture anchors doubly loaded with number 2 Ultrabraid (Smith & Nephew Endoscopy, Andover, MA, USA) sutures were placed in the femoral footprint. (B) Two strands of a single suture from each anchor were separately passed through the ACL with a FastPass Scorpion (Arthrex, Naples, FL, USA). (C) The two free suture strands were pulled to transport the two-strand-overhand locking knot over the ligament bridge. (D) The two free suture strands were tied into a multiple-throw square knot with a knot pusher. (E) Simple stitching was performed for two strands of the other suture from each anchor to overlock the ligament stump that was not fixed using the pulley technique. (F) The final construct comprised a double-mattress-sutures configuration and two simple-suture configurations to compress the ACL remnant against the femoral footprint.
F5
Fig. 5A-F:
This schema shows the double-pulley technique. (A) Two 3.5-mm nonabsorbable Twinfix suture anchors doubly loaded with number 2 Ultrabraid (Smith & Nephew Endoscopy, Andover, MA, USA) sutures were placed in the femoral footprint. (B) Two strands of a single suture from each anchor were separately passed through the ACL with a FastPass Scorpion (Arthrex, Naples, FL, USA). (C) The two free suture strands were pulled to transport the two-strand-overhand locking knot over the ligament bridge. (D) The two free suture strands were tied into a multiple-throw square knot with a knot pusher. (E) Simple stitching was performed for two strands of the other suture from each anchor to overlock the ligament stump that was not fixed using the pulley technique. (F) The final construct comprised a double-mattress-sutures configuration and two simple-suture configurations to compress the ACL remnant against the femoral footprint.

A single-pulley technique was performed when a proximal tear was involved in a single ACL bundle (Fig. 6A). A 3.5-mm nonabsorbable Twinfix suture anchor (Smith & Nephew Endoscopy, Andover, MA, USA) doubly loaded with number 2 Ultrabraid sutures (Smith & Nephew Endoscopy) was placed in the origin of the avulsed bundle of the native ACL’s footprint in the same fashion as was used in the double-pulley technique (Fig. 6B). Four suture strands from the anchor were separately passed through the ACL with a FastPass Scorpion (Arthrex), producing four points of fixation in the ligament (Fig. 6C). A strand from each suture was retrieved and manually tied into a two-strand-overhand locking knot [41]. The two free suture strands were pulled to transport the knot over the ligament bridge (Fig. 6D). Then, the two free suture strands were tied into a multiple-throw square knot with a knot pusher (Arthrex) (Fig. 6E). The knee position in tensioning is at 90° of flexion to minimize gap formation between the repaired ligament and the femoral footprint. The final construct comprised two sutures overlying the ACL remnant in a double-mattress-sutures configuration (Fig. 6F). The schematic drawings (Fig. 7A-F) show the procedures of single-pulley technique.

F6
Fig. 6A-F:
The single-pulley technique was performed using arthroscopy on the right knee of Patient 20. (A) A proximal tear in the anteromedial bundle of the ACL was verified by probing. (B) A 3.5-mm nonabsorbable Twinfix suture anchor doubly loaded with number 2 Ultrabraid (Smith & Nephew Endoscopy, Andover, MA, USA) sutures was placed in the origin of the anteromedial bundle of the native ACL’s footprint. (C) Four suture strands from the anchor were separately passed through the ACL with a FastPass Scorpion (Arthrex, Naples, FL, USA). (D) The two free suture strands were pulled to transport the two-strand-overhand locking knot over the ligament bridge. (E) The two free suture strands were tied into a multiple-throw square knot with a knot pusher. (F) The final construct comprised two sutures overlying the ACL remnant in a double-mattress-sutures configuration.
F7
Fig. 7:
This schema shows the single-pulley technique. (A) A proximal tear in a single bundle of the ACL was verified by probing. (B) A 3.5-mm nonabsorbable Twinfix suture anchor doubly loaded with Number 2 Ultrabraid (Smith & Nephew Endoscopy, Andover, MA, USA) sutures was placed in the origin of the avulsed bundle of the native ACL footprint. (C) Four suture strands from the anchor were separately passed through the ACL with a FastPass Scorpion (Arthrex, Naples, FL, USA). (D) The two free suture strands were pulled to transport the two-strand-overhand locking knot over the ligament bridge. (E) The two free suture strands were tied into a multiple-throw square knot with a knot pusher. (F) The final construct comprised two sutures overlying the ACL remnant in a double-mattress-sutures configuration.

After the repair was complete, the ACL remnant had excellent tension and stiffness, which was verified by probing. ROM exercises confirmed anatomic positioning without impingement, and an examination of manual laxity showed minimal translation with a firm endpoint on Lachman’s test intraoperatively. Radiographs taken immediately postoperatively were used to assess the implant position.

Aftercare

The involved knee was placed in a hinged knee brace with 30° of ROM for the first week postoperatively. The brace was then adjusted to increase ROM by 30° every week and to 90° of knee flexion at the third week postoperatively. Full ROM with the brace unlocked was allowed at 1 month postoperatively. Weightbearing was avoided for the first 2 weeks postoperatively. Partial weightbearing with crutches and full weightbearing were initiated at 2 and 4 weeks, respectively. The brace was removed and patients were encouraged to return to activities of daily living or light work 3 months after surgery. Patients were advised that they could return to non-contact sports such as jogging, swimming, or cycling when they were able to run 500 meters without pain or swelling and had nearly full ROM and quadriceps strength equal to the strength of the contralateral side, which were often achieved by 6 months after surgery. Patients were permitted to return to contact sports such as basketball or soccer at 12 months postoperatively. Isometric quadriceps exercises were performed throughout the early rehabilitation stage to prevent disuse atrophy.

Variables, Outcome Measures, Data Sources, and Bias

Data were obtained from medical records and operative notes. Postoperative assessments were performed regularly on an outpatient basis (at 6 weeks, 3 months, 6 months, and 12 months postoperatively and at the last follow-up examination), and the results of the last follow-up examination were analyzed. ROM to the maximum point was measured with a universal goniometer. Knee stability was evaluated with the anterior drawer test and Lachman test. Functional outcomes were assessed using Lysholm, Tegner activity, IKDC subjective scores. AP and lateral plain radiographs were used to evaluate the position and displacement of the implant. All clinical assessments were conducted by an independent observer (WL).

Statistical Analysis, Study Size

The statistical analysis was performed with SPSS version 17.0 (SPSS, Chicago, IL, USA). Data are expressed as the mean ± SD. A paired t-test was used to compare preoperative and postoperative scores, whereas qualitative data were compared using a chi-square test. Statistical significance was set at p < 0.05.

Demographics, Description of Study Population

There were 16 males and five females, with a mean (range) age of 32 years (17-56). The right knee was involved in 12 patients and the left knee was involved in nine. The injury mechanisms were 17 sports injuries, three traffic collisions, and one fall. The mean (range) delay from injury to surgery was 24 days (10-87). Seven patients had concomitant injuries, including two mild chondromalacias and five meniscus tears (Table 1). Radiographs showed that suture anchors were properly placed in the origin of the native femoral footprint without perforating the posterior condyle immediately after surgery, and no substantial implant displacement had occurred by the time of the last follow-up examination (Fig. 8A-D).

T1
Table 1.:
Demographic characteristics of the patients
F8
Fig. 8A-D:
Radiographs of two different patients at the last follow-up examination show that suture anchors were properly placed in the origin of the native femoral footprint without perforating the posterior condyle, and no substantial implant displacement occurred. These (A) AP and (B) lateral plain radiographs are of Patient 2’s the left knee. These (C) AP and (D) lateral plain radiographs are of Patient 20’s the right knee.

Results

At the last follow-up examination, all patients achieved full extension and only one patient lacked full flexion, with a flexion contracture of 10°. Twenty patients had no instability on the anterior drawer test and Lachman examination findings, and one patient had a 1 + anterior drawer test score. Before surgery, 13 of 21 patients had a positive anterior drawer test; this improved at latest follow-up to 1 of 21 (p < 0.001). Before surgery, 8 of 21 patients had a positive Lachman test; this improved at latest follow-up to 0 of 21 (p = 0.002). The mean Lysholm score improved from a mean ± SD of 71 ± 9 before surgery to 94 ± 6 (mean difference 23 points [95% CI 20 to 25]; p < 0.001) at latest follow-up. The mean IKDC subjective score improved from a mean ± SD of 64 ± 10 before surgery to 86 ± 11 (mean difference 22 points [95% CI 20 to 25]; p < 0.001) at latest follow-up. Though Tegner activity score decreased in three patients, we found no difference in the Tegner scores from before surgery to latest follow-up (6.3 ± 1.2 versus 6.1 ± 1.2, mean difference 0.2 [95% CI 0.0 to 0.5]; p = 0.056) (Table 2).

T2
Table 2.:
Clinical outcomes of the patients

One patient re-ruptured his ACL 2 months after surgery in military training during an obstacle race. This patient was treated with a quadriceps-strengthening program. His subjective scores were only fair (the Lysholm score improved from 70 before surgery to 90 at latest follow-up, and the IKDC subjective score improved from 64 before surgery to 72 at latest follow-up), and he had a decrease in his Tegner score (from 7 to 6) at the most recent follow-up examination. No complications such as infection, thrombosis, stiffness, patellofemoral pain, or implant failure were found in any patients.

Discussion

Open primary ACL repair was abandoned because of a high risk of recurrent instability [6,18, 22, 31, 32, 34, 35], but we believe that perhaps this decision was premature. Several problems with open primary repair lead to its abandonment. Because of limitations to diagnostic technology, patients with all tear types were at one time treated with primary repair, regardless of the ACL tear type and tissue quality. Better results were seen with careful patient selection, specifically considering the injury pattern (proximal tear) and tissue quality [32]. Additionally, arthrotomy rather than arthroscopic approaches may have contributed to greater morbidity (in particular knee stiffness) after open primary repair; arthroscopic surgery now is an option for this surgical technique [8]. Finally, contemporary fixation modes and materials, such as suture anchors and non-absorbable sutures, may achieve more direct tensioning of the repaired ligament to the femoral wall than fixation modes and materials that were used in the past [9, 36]. Modern diagnostic tools allow better patient selection, and contemporary arthroscopic techniques that allow more secure tendon-to-bone reattachment caused us to believe that perhaps this procedure—which seems smaller than ACL reconstruction and which has been explored in only a few studies [1, 8, 9, 36]—deserved another look. Specifically, we wanted to explore the pulley technique, which has been used with some success in rotator repair surgery [4, 11, 24, 29]. The application of pulley technique in the treatment of partial but not complete tears is the novelty of our study. We found that patients with partial proximal ACL tears who undergo primary arthroscopic repair using the pulley technique can achieve excellent knee stability and outcomes scores in the short term.

This study had a number of limitations. First, it is a non-randomized series rather than a prospective study, and selection bias might have arisen from unblinded surgeons and patients. The findings of this work may apply to patients with partial proximal ACL tears, but may not apply to those who do not meet the prespecified criteria. During the study period, all patients who met the prespecified criteria received this approach. Second, there are concerns for assessment bias based on our study design; the fact that patients and surgeon knew what was done tends to inflate the outcomes scores, and this should be considered as these findings are interpreted. Future studies using randomization and blinding can mitigate both selection and assessment bias. Third, we recommend creating an accessory anterior portal at the inferomedial margin of patella rather than the usual medial accessory portal to obtain a better view of the femoral footprint and facilitate the operation. Especially in the placement of the second anchor, a better view of the femoral footprint can be obtained via this accessory anterior portal when the knee was flexed to approximately 110° to 115°, so as to facilitate adjusting the angle of approach and to avoid perforating the posterior condyle. This technique carries a risk of patellar tendon injury during creation of the accessory anterior portal at the inferomedial border of the patella; we suggest that surgeons avoid this, as we did, by using a longitudinal incision instead of a transverse incision, and by placing this portal very carefully. Fourth, there are no objective methods to quantify the tissue quality and the possibility of reapproximating, and these were subjectively assessed according to the surgeon’s intraoperative judgement. Objective criteria to quantify the tissue quality and the gap between the torn distal remnant and the femoral footprint may be helpful to minimize the bias. Fifth, the concomitant meniscal injury might influence the postoperative results. However, we did not exclude those with concomitant meniscal injuries for this can further decrease the sample size of this study. Additionally, the concomitant meniscal injuries were mild in most patients and might have little influence on the postoperative results. Sixth, knee stability was evaluated with subjective test findings, and a more objective assessment with a KT-1000 arthrometer was not performed in this study; this raises the concern for assessment bias and overestimation of the benefits of the operation in question. Future studies should use blinded assessors. Seventh, because MRI is more expensive than radiographs, some participants were unwilling to undergo MRI; in these patients, we could only use radiographs to evaluate implant position and displacement. It is necessary to evaluate the ACL healing using MRI in the future follow-up to verify healing. Finally, there are also concerns for transfer bias (follow-up not sufficiently long, and two patients were missing) in our study. Patients lost to follow-up may have had complications or reoperations, but there were only two of them. Furthermore, despite the promising short-term clinical outcomes of our study, longer-term follow-up is necessary to identify whether clinical outcomes deteriorate.

Stability and Outcomes Scores

In our study, 95% of the patients had a clinically stable knee with negative anterior drawer tests and Lachman test findings at the last follow-up examination, and 100%, 90%, and 90% of these patients’ scores met the minimal clinically important difference for the Lysholm score, modified Cincinnati score, and IKDC subjective score, respectively [14]. These promising outcomes are in accordance with those described by DiFelice and van der List [8] and DiFelice et al. [9], who reported that 91% of patients with proximal ACL tears treated with primary arthroscopic repair had stable knees, excellent patient-reported outcomes, and high return-to-activity levels in the short-term and mid-term. Likewise, Jonkergouw et al. [17] demonstrated that arthroscopic primary repair had resulted in good objective and subjective outcomes at 3.2-year follow-up in a carefully selected population, and the role of additional internal bracing is possibly beneficial. Heusdens et al. [15] described that patients with an acute proximal ACL rupture treated with the Independent Suture Tape Reinforcement repair technique demonstrated improvements in the Knee Injury and Osteoarthritis Outcome Score, VAS pain scale, Veterans RAND 12 Item Health Survey physical score as well as a decrease of the Marx activity scale compared with preoperative scores at 2-year follow-up. Achtnich et al. [1] showed that proximal refixation of the ACL using knotless suture anchors and microfracturing restored knee stability and resulted in comparable functional outcomes to a control group treated with single-bundle ACL reconstruction. Tear location seems to be a critical predictor of the success of primary repair. Proximal tears can be repaired and lead to femur healing [38, 40]. Additionally, 90% of tears in the most proximal 10% of the ACL can be treated with primary arthroscopic repair [39]. In our study, only patients with partial proximal ACL tears and preoperative clinical instability (abnormal anterior drawer tests and/or Lachman test findings) underwent primary repair. Healing of the ACL midsubstance is limited because the synovial fluid washes away fibrin clots that are necessary for healing [25, 30]. In contrast, the proximal part of the ACL has a substantial healing capacity similar to that of the medial collateral ligament because of stable clot formation [26, 27]. This explains how the ACL reattaches to the posterior cruciate ligament and how proximal tears heal [5, 33], reminding us that the knee should be thoroughly inspected to avoid overlooking hidden lesions, especially in patients with a partial proximal ACL tear. Primary repair for complete ACL tears should be performed acutely, preferably within a few days, because resorption always occurs as early as 2 weeks after injury, making repair impossible [2]. Nevertheless, the acuity of surgery was not the most important determinant of surgery for patients with partial proximal tears who were enrolled in the current study; in these patients, there was less resorption and contracture of the ACL and the torn distal remnant was more likely to be reapproximated toward the femoral footprint, despite a considerable delay until surgery compared with patients with complete proximal tears. This may explain why the interval from injury to surgery varied widely in our study. The fixation mode we applied in primary arthroscopic repair is called the pulley technique because the suture anchor eyelets are used like pulleys to bring the knots down onto the tissue. This technique is commonly used in rotator cuff repair [4, 11]; it has not been applied in ACL repair before. It maximizes cuff-to-bone compression along the suture anchors and provides extremely secure fixation in the medial aspect of the footprint [4, 11]. A biomechanical study [29] showed that the ultimate tensile strength for the double-pulley technique was approximately 248 N in pig models. Similarly, in a cadaveric study, Mazzocca et al. [24] demonstrated that the ultimate load to failure for suture anchor repair was approximately 256 N to 305 N. Combined with the strain provided by the uninjured part of the ACL, the tensile strength of the repaired ligament is competent for weightbearing and non-weightbearing exercises after surgery, during which the strain on the ACL was estimated to be approximately 150 N or less [10]. In the pulley technique, suture strands were extracorporeally tied as a two-strand-overhand locking knot, a novel surgical knot designed by Zhao et al. [41], who proved that the two-strand-overhand locking knot had a substantially lower unraveling rate and greater holding strength than the other surgical knot configurations, regardless of the suture’s material. Additionally, the ligament stump that is not fixed using the pulley technique can be attached to the bony bed of the femoral footprint through a supplementary simple stitch. This improves the healing potential by minimizing gap formation and maximizing the contact area, which is an advantage of this knotted technique versus a knotless one. Another advantage is that the stitching point can be adjusted intraoperatively according to the proximally torn ACL tissue quality to avoid excessive tension of the repaired ligament. However, the disadvantage is that it may introduce knot burden in the intercondylar notch. Future comparative trials will be helpful to delineate the relative merits of knotted versus knotless fixation. The arthroscopic nature of this technique and its intrinsic characteristics not only maximally leverages technologic advances to the benefit of patients, but also exponentially decreases the morbidity of the procedure. If a revision procedure is indicated, it is performed in a manner similar to primary ACL reconstruction.

Re-rupture and Complications

The flexion deficit and clinical failure in two patients were attributed to poor adherence to the rehabilitation protocol rather than any technical variables. The first patient, a 56-year-old non-military woman, was unwilling to initiate early ROM during the postoperative rehabilitation program for fear of pain and reinjury, leading to flexion restriction. On the contrary, the military patients always performed an overactive rehabilitation protocol to return to duty as soon as possible, which was more likely to result in ACL re-rupture rather than flexion deficit. The second patient, a 20-year-old soldier, removed the brace and returned to military training only 1 month after surgery. The stability of his knee deteriorated when he experienced an atraumatic pop during an obstacle race at approximately 2 months postoperatively. Subsequently, he underwent nonoperative treatment with a proper quadriceps strengthening program and modified his activities to adapt to these exercises, as shown objectively by the decrease in the patient’s Tegner score, despite fair subjective scores. Likewise, DiFelice et al. [9] reported that 9% of patients (1 of 11) re-ruptured their ACL while descending stairs 3 months after primary repair. Heusdens et al. [15] demonstrated that 5% of patients (2 of 42) reported an ACL re-rupture after ACL repair with Independent Suture Tape Reinforcement. Nevertheless, Gagliardi et al. [12] showed that failure risk was increased in the ACL repair with suture ligament augmentation (50%) relative to ACL reconstruction with quadriceps tendon-patellar bone autograft (5%) among adolescent patients. The average Tegner score before surgery was 6.3 in this study, which is lower than the score in most ACL studies [8, 9]. This could be explained by the fact that the procedure was initially performed in patients with relatively lower demands. However, the three patients with the highest preoperative Tegner scores still had the same activity level at the last follow-up examination, whereas the other three patients decreased their activity level on their own volition in case of reinjury, with no important difference between preoperative and postoperative Tegner scores. Even patients with stable, pain-free knees may choose to refrain from athletics for reasons unrelated or only peripherally related to their surgery, such as lack of trust in the operative knee (regardless of perceived stability), fear of reinjury, and changing life circumstances. Tegner activity score mainly informs us on what patients do after surgery, not what they are capable of doing. However, further study is necessary to find whether the decrease of Tegner activity score is related to the surgery.

Conclusions

Primary arthroscopic repair using the pulley technique can achieve short-term clinical success in a carefully selected (the selection process includes first identifying the ACL injury pattern preoperatively with MRI, confirming the diagnosis under arthroscopy, and deciding whether to perform an intraoperative repair) subset of patients with partial proximal ACL tears and excellent tissue quality (defined as a remnant with mild interstitial tearing and the ability to hold sutures). Despite the promising clinical outcomes of our study, this technique should not be widely adopted unless it has been compared directly with ACL reconstruction, so future studies should be conducted to compare the clinical outcomes between this technique and ACL reconstruction, and longer-term follow-up is necessary to identify whether there is deterioration in the clinical outcomes.

Acknowledgments

We thank Can Huang MD, of the Chinese PLA General Hospital, for her assistance in the collection of patients’ clinical data. We also thank Yang Liu MD, of the Chinese PLA General Hospital, for his assistance in the acquisition of images under arthroscopy.

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