Abstract
Growing participation in youth athletics has resulted in increased numbers of anterior cruciate ligament (ACL) injuries in skeletally immature patients. Use of autogenous graft material has been associated with improved graft survival. However, pediatric patients sometimes possess hamstring tendons that produce smaller-diameter grafts than those prepared with adult autogenous materials. Smaller-diameter grafts may predispose younger patients to graft failure. We describe a technique that increases the diameter of the ACL construct through the use of an 8-strand autologous hamstring tendon graft. The 8-strand ACL autograft is commonly used in all-inside ACL reconstruction surgery.
Reconstruction of the anterior cruciate ligament (ACL) in skeletally immature patients presents distinct challenges from that in the adult population. Whereas autograft ACL constructs can lead to donor-site morbidity, studies have shown improved graft strength and reduced revision rates, making autograft tissue favored in pediatric populations.1, 2, 3, 4, 5 The presence of open physes typically precludes the use of the bone–patellar tendon–bone autograft in favor of a hamstring construct. Smaller patients, however, sometimes produce thinner final graft sizes because of smaller hamstring tendons.6, 7, 8, 9 Because a smaller-diameter graft size is associated with increased need for revision ACL surgery,9 maximizing graft thickness is essential. We describe a technique for preparing an 8-strand hamstring autograft that maximizes the diameter of the ACL construct while maintaining sufficient length for tibial and femoral fixation.
Technique
The semitendinosus and gracilis tendons are harvested on the medial side of the proximal tibia by the surgeon's preferred technique. On the graft preparation table, the muscle at the proximal aspect of the tendons is cleared. The length of harvested tendon needed is dependent on the reconstruction technique used. To perform a transphyseal technique in patients with closing physes, the graft length used is between 26 and 28 cm to yield a graft length of 6.5 to 7 cm. To perform an all-epiphyseal technique in a pediatric patient with wide open physes, the total length of harvested tendon should be approximately 20 cm to yield a final graft length of 5 cm. The graft is prepared for an all-inside ACL reconstruction technique with button fixation on the distal femur and proximal tibia. We describe the graft preparation technique in this report and in Video 1.
Equipment
The following equipment is used for this technique: looped sutures (ACL TightRope RT and TightRope ABS; Arthrex, Naples, FL); high-strength looped suture (No. 2 FiberLoop with straight needle and No. 2 FiberWire; Arthrex); and a Graft Prep station (Arthrex) (Fig 1).
Fig 1.
A graft preparation station facilitates preparation and tensioning of the 8-strand anterior cruciate ligament autograft construct.
Graft Station Preparation
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1.
The femoral-side looped suture with button attached (TightRope RT) and the tibial-side looped suture (TightRope ABS) are seated in each tensioner attachment (Fig 2A).
-
2.
A suture is passed through the TightRope ABS loop, which is later used to pull the ABS through the tibial socket (Fig 2B).
Fig 2.
Each end of the graft preparation station is pictured in detail. (A) The femoral-side TightRope RT and the tibial-side TightRope ABS are seated in each tensioner attachment. (B) A suture is passed through the TightRope ABS loop (arrow), which is later used to pull the ABS through the tibial socket.
Preparation of Initial 4-Strand Construct
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1.
The muscle attached to both the semitendinosus and gracilis tendons is removed, and the length of the semitendinosus and gracilis is measured (Fig 3).
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2.
The semitendinosus and gracilis tendons are each passed through the TightRope ABS suture loop and folded with equal length and even tension. Each strand is marked 1.5 cm from the free end (Fig 4A).
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3.
The 4-strand end is whipstitched with a high-strength suture (Arthrex SpeedWhip technique with No. 2 FiberLoop) for whipstitching of the grafts with approximately 5 throws under equal tension for all strands (Fig 4B).
Fig 3.
To clean the harvested semitendinosus and gracilis tendons for graft preparation, the muscle around the tendon is removed and the length of graft tissue is measured. To perform a transphyseal technique in patients with closing physes, the graft length used is between 26 and 28 cm to yield a graft length of 6.5 to 7 cm. To perform an all-epiphyseal technique in a pediatric patient with wide open physes, the total length of harvested tendon should be approximately 20 cm to yield a final graft length of 5 cm.
Fig 4.
(A) After overlaying of the gracilis and semitendinosus tendons, they are loaded and looped in linkage with the TightRope ABS and marked 1.5 cm from the free end (arrow). (B) The 4-strand end is whipstitched together with No. 2 FiberLoop (arrow).
Preparation of Final 8-Strand Construct
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1.
The midportion of the 4-strand construct is folded through the ACL TightRope RT suture loop with equal length.
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2.
The whipstitched end of the 4-strand construct is tied over the TightRope ABS suture loop. The straight needle is used to pass each of the 2 whipstitch sutures through the tendon and around the TightRope ABS loop. The ends of the whipstitched sutures are tied over the TightRope ABS with equal tension (Fig 5A).
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3.
The graft is tensioned to 15 lb (Fig 5B).
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4.
A mark is placed at 1 cm and 1.5 cm from each end of the graft (Fig 6A). By use of a total of 4 interrupted FiberWire sutures, each of these 4 stitches is passed through each of the 8 strands of tendon at the marked ends of the strands. The suture free limb is passed obliquely through each of the 8 strands and then wrapped once around the entire bundle, creating a self-reinforcing suture noose. The suture free limb is then passed perpendicular to the previous passage, and the knot is tied on the inside of the graft (Fig 6B). Graft thickness is evaluated at both the femoral and tibial sides for guidance in tunnel placement (Fig 6C). Both graft sizing blocks are left in place for approximately 5 to 10 minutes to place circumferential compression on the graft. Such compression reduces the amount of required bone removed when creating ACL bone tunnels within the limited space available for pediatric patients.10
Fig 5.
(A) The graft is folded through the TightRope RT (at the other end of the graft preparation station). The 4-strand end is secured back upstream and folded into the elbow of the graft formed at the TightRope ABS end (arrow). (B) In this case, the 8-strand graft length is 5 cm.
Fig 6.
(A) Four suture places are marked on the graft: 2 on the tibial side (solid arrows) and 2 on the femoral side (open arrows). (B) By use of a total of 4 interrupted FiberWire sutures, each of these 4 stitches is passed through each of the 8 strands of tendon, and the suture free limb is wrapped once around the bundles, creating a self-reinforcing suture noose. (C) The final diameter of each side is determined for preparation of the bone tunnel. In this case, the thickness of the femoral side is 9.0 mm (solid arrow).
Graft Fixation
The 8-strand ACL autograft can be used in both transphyseal and all-epiphyseal reconstruction techniques. An all-inside retrodrilling technique (GraftLink; Arthrex) is used. In brief, a retrodrill (FlipCutter; Arthrex) is used to create separate femoral and tibial sockets. Graft passing is achieved using high-strength suture (FiberStick; Arthrex) passed through each socket. Once passed into and through the femoral socket, the TightRope RT is fixed onto the lateral femoral cortex. The TightRope ABS loop is similarly passed into the tibial socket (Fig 7). Finally, a TightRope ABS Button (Arthrex) is fastened to the TightRope ABS loop to secure the distal end of the graft at the proximal tibia.
Fig 7.
The GraftLink (Arthrex) technique is used in 8-strand anterior cruciate ligament autograft fixation. Devices for passing both ends of the 8-strand anterior cruciate ligament graft are seen traversing the cannula. The TightRope RT will be passed into the femoral socket, whereas the TightRope ABS will be passed into the tibial socket. A TightRope ABS Button is fastened to the TightRope ABS loop to secure the distal end of the graft at the proximal tibia.
Postoperative Rehabilitation
Use of the 8-strand ACL graft does not necessitate modification of standard postoperative rehabilitation protocols used for ACL reconstruction in children and adolescents. A suggested postoperative rehabilitation protocol is provided in Table 1.
Table 1.
Example of 9-Month Postoperative Rehabilitation Goals in Pediatric Anterior Cruciate Ligament Reconstruction
| Postoperative Time Frame | Goals and Activities |
|---|---|
| Weeks 0-1 | Ambulation/brace use: toe-touch weight bearing |
| Weeks 2-4 | Maintain knee flexion |
| Promote knee flexion | |
| 90° by end of week 2 | |
| 130° by end of week 4 | |
| Weeks 4-12 | Normalize gait |
| Full knee range of motion | |
| Enhance proprioception/balance | |
| Improve cardiovascular conditioning | |
| Weeks 12-16 | Continue strength, endurance, and proprioception progression |
| Incremental running progression | |
| Bilateral jumping | |
| Weeks 16-24 | Begin gradual and progressive sport-specific activities |
| Months 6-9 | Prepare athlete for unrestricted return to sport progression |
| Improve neuromuscular control and dynamic stability |
Discussion
Younger age, higher activity level, and decreased autograft size are all factors that predispose younger patients to failure of ACL reconstruction.4, 9, 11 Because hamstring graft diameter is related to a patient's height, mass, and age,7 success of ACL reconstruction in young, skeletally immature patients relies on additional efforts to prepare a large-diameter ACL autograft. Graft size may also be a concern in adult female patients and persons of short stature. Magnussen et al.9 noted increased ACL graft survival rates for young patients with graft diameters equal to or greater than 8 mm. We have previously described a technique for preparing a 5-strand hamstring graft, which increased graft thickness over the traditional hamstring graft by 1 to 1.5 mm,6 although ensuring equal tension among the 3 semitendinosus strands is more technically challenging. When performing the 8-strand autograft technique, equal tension is applied to both the semitendinosus and gracilis muscles, mitigating the technical challenge previously encountered. Using the described technique, we have noted a graft diameter increase of 2 to 4 mm over the traditional 4-strand hamstring graft. In addition, use of the 8-strand hamstring autograft achieves sufficient graft diameter to improve stability while eliminating the need for the use of allograft materials. Moreover, the increased number of strands increases the amount of collagen that can be placed within the construct. One disadvantage is that the procedure is more technically challenging because more steps are required than for either a 4-strand or 5-strand graft.
Whereas graft thickness contributes to graft survival, so too does graft length. For an all-inside reconstruction technique, a maximum graft length of 70 to 75 mm after tensioning is used as a general guideline.12 However, data are lacking regarding minimum graft length necessary to ensure tendon-bone healing. Zhao et al.13 reported successful outcomes using an 8-strand hamstring technique during double-bundle ACL reconstruction, in which a minimum intra-articular length of 18 mm was noted. In our technique, with a harvested tendon exceeding 260 to 280 mm, the final graft length is expected to be approximately 65 to 70 mm. In the all-epiphyseal technique, with a harvested tendon exceeding 200 mm, the final graft length is expected to be approximately 50 mm. The graft is then distributed with an intra-articular length of 20 mm and at least 15 mm on both tibial and femoral tunnels to allow for sufficient graft length within the tunnels (Tables 2 and 3).
Table 2.
Pearls and Pitfalls of 8-Strand Graft for ACL Reconstruction Surgery
| Pearls |
| Ensure the patient has sufficient starting total graft length to yield an adequate final construct length. |
| Overlay the thicker end of the semitendinosus with the thinner end of the gracilis to minimize variability in graft diameter. |
| Ensure the TightRope RT remains mobile after stitching the graft ends together. |
| When securing graft circumferentially with suture, dock forceps into the graft board to separate the strands. |
| Pitfalls |
| Failure to harvest sufficient starting total graft length |
| Stitching TightRope RT into ACL autograft |
| Failure to place adequate tension on graft |
ACL, anterior cruciate ligament.
Table 3.
Advantages and Disadvantages of 8-Strand Graft in ACL Reconstruction Surgery
| Advantages |
| Increases diameter of ACL autograft to improve stability |
| Eliminates need for use of allograft materials |
| Increases amount of collagen placed in construct |
| Disadvantages |
| More technically challenging |
| Slightly more time-consuming graft preparation |
ACL, anterior cruciate ligament.
The 8-strand hamstring autograft technique offers a viable option for preparing an ACL graft construct with only autogenous materials. The described technique is a variation of the graft preparation technique for the existing all-inside ACL reconstruction with 4-strand semitendinosus autograft. The 8-strand graft construct is ideally suited for ACL reconstruction in pediatric patients and smaller patients to maximize graft diameter and minimize the need to supplement with allograft tissue.
Footnotes
The authors report that they have no conflicts of interest in the authorship and publication of this article.
Supplementary Data
Eight-strand anterior cruciate ligament autograft preparation technique using harvested semitendinosus and gracilis tendons. A 4-strand construct is initially created by overlaying the tendons together and folding over the TightRope ABS suture loop. The free ends of the 4-strand construct are whipstitched, folded into the elbow of the opposite side, and sutured in place. Circumferential sutures are placed at 1 cm and 1.5 cm from each end of the graft construct.
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Associated Data
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Supplementary Materials
Eight-strand anterior cruciate ligament autograft preparation technique using harvested semitendinosus and gracilis tendons. A 4-strand construct is initially created by overlaying the tendons together and folding over the TightRope ABS suture loop. The free ends of the 4-strand construct are whipstitched, folded into the elbow of the opposite side, and sutured in place. Circumferential sutures are placed at 1 cm and 1.5 cm from each end of the graft construct.