RigidLoop Femoral Fixation Techniques

Introduction

The RigidLoop (RL) Cortical Fixation System was developed by Depuy Mitek to provide a strong, reliable, and easy to use method of soft tissue femoral graft fixation. The fixation system shares some similarities in usage and design to the Smith and Nephew Endobutton (Memphis, Tennessee), and provides strength and minimizes laxity in the graft through its continuous preloaded loop design and titanium implant. Compared with available adjustable loop devices, the primary advantage of fixed loop devices is the capacity for tactile feedback upon button seating through the femoral cortex, confirming adequate placement, and also the higher load to failure when compared with adjustable loop devices.

Biomechanics

When utilizing a soft tissue graft for anterior cruciate ligament (ACL) reconstruction, achieving rigid fixation while minimizing stretch and graft loosening are imperative. Adjustable loop devices have been shown to at times lengthen, causing concern in the immediate perioperative period with rehabilitation. Maintaining graft length and providing stable fixation are critical in the first 3–6 months of the postoperative period while the graft is still incorporating, and the surgical fixation provides the majority of stability. Recent published literature has suggested that adjustable loop devices may be susceptible to loop lengthening after initial tensioning.

Biomechanically, RL has demonstrated increased strength and stiffness compared with similar fixed loop devices, while again providing minimal displacement through cyclical loading ( Table 66.1 ). Selecting a suspensory fixation device that will minimize lengthening allows the initial set tension of the ACL to be more reliably maintained.

TABLE 66.1

Comparison of Biomechanical Properties of Femoral Suspensory Devices

	Cyclic Displacement (mm)	Ultimate Strength (N)	Stiffness (N/mm)
20-mm RigidLoop	0.68 ± 0.03	2136 ± 93	594.0 ± 21.3
20-mm Endobutton	0.59 ± 0.03	1405 ± 112	448.5 ± 22.4
20-mm TightRope	1.36 ± 0.24	790 ± 97	729.6 ± 74.8

From Spenciner DB, Gustafson A. RigidLoop cortical fixation system, EndoButton CL Ultra, and Tightrope: a comparison of mechanical properties. Depuy Synth Mitek Sport Med . 2013:13–14.

One of the technical benefits over the adjustable loop devices is the tactile feedback provided by the twin suture design. Once passed through the lateral femoral cortex, the surgeon can manipulate the device by pulling on the two passing sutures in sequence to feel the device toggle on the lateral femoral cortex, providing tactile feedback that appropriate deployment of the instrument has occurred. Confirmation of successful deployment through tactile feedback obviates the need for fluoroscopy, arthroscopic examination of soft tissues, or graft failure due to deployment in the vastus lateralis or other soft tissues.

Biomechanics

When utilizing a soft tissue graft for anterior cruciate ligament (ACL) reconstruction, achieving rigid fixation while minimizing stretch and graft loosening are imperative. Adjustable loop devices have been shown to at times lengthen, causing concern in the immediate perioperative period with rehabilitation. Maintaining graft length and providing stable fixation are critical in the first 3–6 months of the postoperative period while the graft is still incorporating, and the surgical fixation provides the majority of stability. Recent published literature has suggested that adjustable loop devices may be susceptible to loop lengthening after initial tensioning.

Biomechanically, RL has demonstrated increased strength and stiffness compared with similar fixed loop devices, while again providing minimal displacement through cyclical loading ( Table 66.1 ). Selecting a suspensory fixation device that will minimize lengthening allows the initial set tension of the ACL to be more reliably maintained.

TABLE 66.1

Comparison of Biomechanical Properties of Femoral Suspensory Devices

	Cyclic Displacement (mm)	Ultimate Strength (N)	Stiffness (N/mm)
20-mm RigidLoop	0.68 ± 0.03	2136 ± 93	594.0 ± 21.3
20-mm Endobutton	0.59 ± 0.03	1405 ± 112	448.5 ± 22.4
20-mm TightRope	1.36 ± 0.24	790 ± 97	729.6 ± 74.8

From Spenciner DB, Gustafson A. RigidLoop cortical fixation system, EndoButton CL Ultra, and Tightrope: a comparison of mechanical properties. Depuy Synth Mitek Sport Med . 2013:13–14.

One of the technical benefits over the adjustable loop devices is the tactile feedback provided by the twin suture design. Once passed through the lateral femoral cortex, the surgeon can manipulate the device by pulling on the two passing sutures in sequence to feel the device toggle on the lateral femoral cortex, providing tactile feedback that appropriate deployment of the instrument has occurred. Confirmation of successful deployment through tactile feedback obviates the need for fluoroscopy, arthroscopic examination of soft tissues, or graft failure due to deployment in the vastus lateralis or other soft tissues.

Procedure

Materials

RL is a cortical femoral suspension system that utilizes a titanium implant that provides a suspensory fit from the lateral femoral cortex without requiring a separate incision on the thigh. The instrument is passed from within the knee using a series of passing sutures. RL is available in various loop sizes, from 15 mm to 60 mm, to accommodate various size patients and graft combinations. The metal portion of the device that provides fixation is 12 mm for all of the continuous loop sizes. If the femoral cortex is reamed to a diameter of greater than 6 mm, the RL XL device must be used. It can be attached to the standard implant, expanding the size of the device to accommodate tunnel sizes of 6–10 mm. The system utilizes a 2.5-mm passing pin and a proprietary cannulated drill 4.5 mm in diameter. Various diameter cannulated reamers are available, which can be selected based on the graft size. The instrument tray provides depth gauge options as well to aid in appropriate sizing.

Preparation and Setup

A quadrupled hamstring graft is prepared cutting the length to 19 cm typically with a goal for a minimum 8.5 mm graft diameter. If this is not achieved the authors will bring a fifth limb of graft at 9.5 cm of semitendinosus up to tie directly to the button or augment with an allograft to achieve at least 8.5 mm total diameter.

Notchplasty

The author utilizes a minimal notchplasty to improve visualization to enable accurate anatomic femoral tunnel placement. Our preference is to typically drill an anatomic femoral tunnel using the lateral viewing portal, and in this case a small (3 mm) notchplasty will allow for clearer visualization of anatomic landmarks. The remnant ACL stump is removed, utilizing a shaver device as well as a radiofrequency ablator initially, from both its tibial and femoral attachments. Soft tissue is then removed from the lateral wall of the notch until the posterior edge of the notch is easily visualized and able to be probed. Once soft tissues are cleared appropriately, a high-speed burr is used to remove 3 mm of bone in an anterior to posterior systematic fashion from the lateral wall of the notch. Avoiding divots and providing a smooth lateral wall aids in decision making for tunnel placement. Adequate visualization of this position is essential in appropriate tunnel placement “low and posterior” in the notch. Care should be taken to débride the resident’s ridge to avoid anterior placement of the femoral tunnel, which should reference the true posterior aspect of the notch, or the over-the-top position.

Femoral Tunnel Drilling

Our preference is to drill the femoral tunnel using an anteromedial (AM) portal technique. This allows for unconstrained, anatomic placement of the femoral tunnel. After completion of a minimal notchplasty, we will typically mark the center of the ACL footprint with a microfracture awl and confirm placement from both the AM and anterolateral portals ( Fig. 66.1 ).