Chapter 38 Anterior Cruciate Ligament Reconstruction Utilizing the Rigidfix for Femoral-Sided Fixation

Background

Graft selection for anterior cruciate ligament (ACL) reconstruction has been debated in the literature.¹ Historically, the debate has been regarding the use of soft tissue grafts secondary to increased laxity as compared with patellar tendon autografts.² The point of concern occurred at the site of graft fixation with soft tissue grafts, and the issues were “suspensory” fixation and creep with cyclical loading. Improved fixation techniques have largely eliminated the historical differences in laxity comparing quadrupled hamstring tendon with bone–patellar tendon–bone (BPTB) autografts.³ It has been well documented in recent literature that the two graft types have similar success rates.⁴^–⁶ Some potential advantages of soft tissue grafts include decreased kneeling pain, decreased patellar tendonitis, lower risk of postoperative patella fracture, and improved cosmesis with a smaller incision for harvest.¹

The patellar tendon graft, with bone plugs on each end, has classically been fixed with a metal interference screw in the tibia and femur with near-aperture fixation. This fixation was sufficiently rigid to prevent significant graft slippage or creep. The patellar tendon graft became the gold standard by which all other grafts and graft fixation systems were compared.¹ Despite the increased laxity with hamstring tendon reconstructions, this technique gained popularity as patients complained of significant anterior knee and kneeling pain with patellar tendon autografts. The potential for patellar fracture also exists. Hamstring tendon autografts have less morbidity, although they do demonstrate some permanent hamstring weakness at high flexion angles.⁷ The clinical significance of this weakness remains unclear.

A quadrupled hamstring tendon graft has two significant biomechanical advantages. First, quadrupled hamstring grafts have a larger cross-sectional area when compared with patellar tendon grafts.⁷ The larger cross-sectional area results in more collagen and thus a stronger graft. The ultimate tensile strength of a quadrupled hamstring autograft is 4140N with a stiffness of 807 N/mm. This is compared to the patellar graft at 2977N and 455 N/mm, respectively. The native ACL has been tested at 2160N and 242 N/mm, respectively.¹ Second, hamstring tendon grafts require smaller bone tunnels than do grafts with bone plugs. These grafts heal circumferentially to the tunnel wall if the interference screw is eliminated. These advantages fueled the search for better soft tissue graft fixation devices.

The historical poor performance of soft tissue grafts cannot be compared with today’s graft fixation. Initial studies compared doubled hamstring tendons to patellar tendons. A quadrupled soft tissue graft is the optimal choice when hamstring tendons are used. Studies of soft tissue graft fixation preceded the use of transfixion devices. Kousa et al ⁸ tested the pullout strength of the soft tissue fixation devices that are currently most used for hamstring grafts. On the femoral side, the Bone Mulch Screw (Arthotek, Warsaw, IN) (1112N), Endobutton-CL (Smith & Nephew, Endoscopy Division, Andover, MA) (1086N), and Rigidfix (Depuy Mitek, Westwood, MA) (868N) systems had the best fixation for soft tissue grafts.⁸ These were significantly stronger than patellar tendons fixed with an endoscopic interference screw (588N). On the tibial side, the fixation is much more secure. The IntraFix (Depuy Mitek) (1332N) and WasherLoc (Arthrotek) (975N) both had higher pullout strengths than a patellar tendon bone plug fixed with a metal interference screw (758N, 9- × 30-mm screw). Interference screws for soft tissue grafts are weaker, with pullout strengths from 201N to 665N depending on the system.⁸

The improved fixation systems for hamstring tendons, combined with strength and stiffness superior to the native ACL, make this an attractive graft option. One must challenge any concept of a BPTB autograft as the gold standard. Patient factors and desires and the surgeon’s preference should dictate which graft is chosen. Surgeons completing ACL reconstructions should be well versed in both techniques. Allograft reconstruction offers an additional soft tissue option. For those surgeons or patients desiring an allograft source, the tibialis anterior tendon has an ultimate tensile strength of 4122N and is an attractive alternative.⁹ We also use the technique described here when an allograft tibialis is selected.

Surgical Technique

Patients undergoing ACL reconstruction are treated in the outpatient surgical suite. General anesthesia is combined with the intraarticular injection of a local anesthetic containing epinephrine to obviate the need for a tourniquet. The leg holder is positioned in as proximal a position on the thigh as possible so as to allow more than 100 degrees of flexion during graft tunnel preparation and graft passage if necessary. A well-padded tourniquet is placed on the upper thigh. It is not routinely inflated during the procedure in order to minimize quadriceps inhibition postoperatively. An examination under anesthesia is performed prior to final positioning.

The knee is initially prepped with povidone-iodine (Betadine) and injected with 60 mL of 1% lidocaine with epinephrine (1:100,000). The injection is performed laterally adjacent to the superior lateral portion of the patella. During the injection, a fluid wave should be visualized medially, which ensures that a fat pad injection has not occurred. The hemostatic effect would largely be lost with a fat pad injection. The knee is then prepped and draped with standard arthroscopy drapes.

Surgical landmarks are identified and marked on the skin, including the superior border of the pes anserine tendons. This is palpable in most patients, but when not palpable, the middle of the tibial tubercle can be used to estimate its location. An oblique, skin-fold incision is used for graft harvest. This incision parallels the gracilis tendon. This incision is approximately 3 cm in length and is centered over the anterior border of the medial collateral ligament (Fig. 38-1). This is generally 4 to 5 cm medial to the tibial tubercle. Both arthroscopic portals and the harvest incision are injected with 5 to 10 mL of 1% lidocaine with epinephrine for the hemostatic effect.¹⁰

Fig. 38-1 Preparing the skin incision for graft harvest. An oblique incision allows for easy harvest visualization, tunnel preparation, and a good cosmetic result.

After the skin incision is made and subcutaneous soft tissues mobilized, the intersection of the anterior border of the medial collateral and the superior border of the sartorius fascia is marked with electrocautery (Fig. 38-2). The main advantage of this starting point is that it allows a relatively horizontal femoral tunnel in the coronal plane when the femoral tunnel is drilled through the tibial tunnel. Vertical grafts in the coronal plane have been associated with increased anterior laxity and functional instability. In order to locate this landmark later in the procedure, the electrocautery is used to make a cruciform periosteal incision that exposes enough of the tibia for the tibial tunnel drill site. The hamstring tendons are harvested after identifying the gracilis and semitendinosus tendons. It is our preference to used a closed loop tendon stripper to remove the tendons after freeing all palpable slips to the gastrocnemius and dissecting the tendon off the tibia, including Sharpey fibers.