Cortical Screw Post Femoral Fixation Using Whipstitches, Fabric Loop, or Endobutton: The Universal Salvage

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Chapter 32 Cortical Screw Post Femoral Fixation Using Whipstitches, Fabric Loop, or Endobutton

The Universal Salvage

Chadwick C. Prodromos

Background

Importance

We believe that every surgeon performing anterior cruciate ligament reconstruction (ACLR) would benefit by being able to perform at least one of the variants of cortical screw post femoral fixation described here. Although probably not their primary techniques, they are the universal “bail-out” methods for rescuing more exotic and complicated single-incision techniques gone awry on the femoral side. The ability to troubleshoot is arguably the most important skill a surgeon can possess, and these techniques not only troubleshoot all other femoral methods (and all grafts), but they also can be accomplished with materials that are present in every orthopaedic surgical suite.

History

Whipstitch cortical screw post was perhaps the most popular method of soft tissue ACL graft fixation when two-incision methods were commonly used. There are many reports of high stability using this method.¹^–⁶ However, the advent of the Endobutton and then the various cross-pins that did not require a formal second incision relegated the two-incision method to a secondary role. More recently it has become apparent that a second incision for outside-in drilling can facilitate the lower femoral tunnel placement that is now recognized as biomechanically preferable, and more two-incision methods are now being described.

Biomechanics

The technique uses rigid cortical bone for anchorage. This has been shown to be the most important factor in producing high-stiffness fixation.⁷ The stiffness is reduced slightly by the length of the construct, but the rigidity of the cortical bone⁷ has been shown to more than compensate. A fabric or suture interface has been associated with high-stability ACLR,⁸^–¹¹ as have whipstitches if properly implanted.¹²^–¹⁴ Both are described here in conjunction with cortical screw post fixation.

Advantages

We no longer use the femoral screw post through a second incision as a primary method because we have had success using the one-incision Endobutton method. However, we still believe that the two-incision technique has a number of advantages.

1 It is useful in revision cases where single-incision techniques may be problematic or impossible.

2 It is useful in difficult primary cases, particularly those with small distal femora resulting in short femoral tunnels as a backup to single-incision techniques if the surgeon blows out the back wall.

3 It allows odd-numbered strand grafts such as triple semitendinosus (3ST), 3ST/1 gracilis (Gr), and 3ST/2Gr,² grafts that cannot be looped as a quadruple graft with the use of cross-pins.

4 We believe that due to the small learning curve, it is a more reliable method than some complicated single-incision techniques for the surgeon who performs a small volume of ACL reconstructions.

5 It allows the most precise proximal-distal positioning of the graft in the tunnels and knee of any method. This is useful with shorter grafts where malposition in the proximal-distal direction may result in too little graft length in one of the tunnels.

6 No other fixation method has resulted in higher stability rates.²

7 Most importantly, as mentioned earlier, it can troubleshoot any problem that occurs with a femoral fixation device, femoral tunnel, or femoral graft.

The only disadvantage to this technique is that it requires a second incision. However, this disadvantage is usually primarily in the mind of the surgeon. We, and others, have never found the use of a small second incision to be of concern to the patient (see Chapter 49). Furthermore, the incision does not need to be large. Some may dislike the fact that a nonbioabsorbable and nonradiolucent screw remains in the patient. However, we have never seen one of these screws back out, nor have we ever seen one bother the patient² because the screw sits flush on cortical bone under a thick muscular layer. Plus, because they are metadiaphyseal, they are far enough from the joint to not interfere with subsequent magnetic resonance images (MRIs).

Surgical Technique

Materials

A standard 6.5-mm, two-thirds threaded cortical screw with a smooth washer is usually used. ACL tibial fixation posts can also be used as follows: There are two 4.5-mm screws without washers with which we are familiar, one made by Smith & Nephew (Andover, MA) and one by Arthrex (Naples, FL). If these washerless screws are used, the screw must be slightly angled away from the femoral tunnel to prevent suture or fabric loop slippage. Linvatec (Largo, FL) has a good 6.5-mm screw, which is used with a washer. Arthrex also has a 6.5-mm screw that is used with a washer, but it uses a smaller (2.5-mm) hex screwdriver. In the past we had occasional instances of breakage of the smaller screwdriver when it encountered high torque with the large screw.

Whipstitches should be put in using either standard #5 braided, nonabsorbable polyester sutures such as Ethibond (Ethicon, Somerville, NJ), Tevdek (SybronEndo, Orange, CA), or Mersilene (Ethicon) or one of the newer stronger #2 sutures such as Fiberwire (Arthrex) or Ultrabraid (Smith & Nephew). The surgeon may also pass a 5- or 6-mm Dacron tape through a quadruple graft and tie it around the cortical screw instead of using whipstitches. A 2- or 3-mm tape is not strong enough. The best loop, however, is the fabric loop that is attached to the Endobutton-CL, which comes in 5-mm increments with 15 mm being the smallest.

Incision

The lateral femoral incision should be made with the knee flexed. The posterior border of the lateral femoral condyle should be palpated and the incision made over the middle of the lateral femoral metaphysis at the flare of the condyle. In a lean patient this incision is about 2 cm long. It will need to be larger in larger patients. The iliotibial band is longitudinally split, and the lateral femoral metaphysis is exposed.

Femoral Screw Insertion Technique

The femoral screws should be inserted unicortically as with tibial screw posts for three reasons.

1 As mentioned earlier, we have never had one back out, so bicortical insertion is unnecessary.

2 They are cancellous screws, and if they are inserted bicortically, they may be impossible to remove later if needed.

3 Also, they can toggle if they are tied under tension before final tightening, with the tip moving slightly away from the predrilled hole in the opposite cortex. This may make it impossible for the tip of the screw to enter this hole at final tightening, resulting in the screw remaining proud and potentially irritating the patient. Unicortical insertion prevents this problem.

Attaching the Graft to the Femoral Post

There are four methods by which this may be successfully accomplished, all of which we have used. We prefer number four. Numbers one and four require an Endobutton-CL to be available. If it is not available, then method two or three may be used, and both are very satisfactory.

1 Endobutton-CL Fabric Loop Passed around the Femoral Post

This is the most difficult technique for properly positioning the graft, but it does have the advantage of being the only technique of the four described that does not require the tying of knots for those who perceive a knot as a possible weak link (which we have not found it to be). The femoral tunnel should be drilled in the appropriate location by an inside-out or outside-in technique. The 3.2-mm drill bit for the femoral screw should be drilled a distance of at least 1.5 cm from the femoral tunnel. This will result in at least a 1-cm bone bridge between the femoral tunnel and the screw when the 6.5-mm cancellous screw and smooth washer are screwed in. The screw should be angled slightly away from the femoral tunnel to further prevent the loop from slipping over the washer and screw. The two-thirds threaded screw should be advanced until all threads are buried into the femur, leaving only smooth screw shank exposed.

At the back table or Mayo stand, the graft should be placed through the Endobutton-CL loop and then #5 braided nonabsorbable sutures passed through the Endobutton eyelets. These sutures are used to pass the construct through the knee and out of the femoral tunnel into plain view. The loop is passed over the screw head and washer, and the screw is tightened down. The Endobutton will lie between the screw and the femoral tunnel and will not interfere with fixation.

The length of the loop should be calculated in advance to allow the graft to sit where desired in the knee in a proximal-distal direction. This must take into account the size of the bone bridge between the shank of the screw and the opening of the femoral tunnel as well as the diameter of the screw. Added to this should be the amount of length the surgeon wishes the graft to be recessed within the femoral tunnel from its outer opening. The graft should be clearly marked circumferentially before implantation at a distance of 2 cm from each end with a marking pen. As long as these marks are not visible arthroscopically the surgeon can be sure there is at least 2 cm of graft in each tunnel. The graft should also be marked with a 3-O or 4-O, violet-colored, absorbable monofilament suture that is used to tie the strands together in the middle of the graft. This suture serves the dual purpose of preventing the graft from sliding along the loop when tensioning and tibial fixation are carried out and also allows the surgeon a visible guide point for what should be the approximate intraarticular midpoint of the graft.

With a long 2ST/2Gr graft this method is highly satisfactory because there is enough length to have more graft than is needed in each tunnel; usually 3 cm in each tunnel is a reasonable goal. If the measurements are off slightly after the graft is tightened down, the graft does not need to be adjusted. If the end result is too little graft in one of the tunnels by the surgeon’s standards, then the graft can be withdrawn out the tibial tunnel and passed through again using a shorter or longer Endobutton-CL loop. With the shorter 4ST graft this method is still usually satisfactory but requires more precision. A minimal length of 15 mm of graft in the tunnels appears to be adequate.^15,¹⁶

2 Fabric Tape Tied Around the Femoral Post

If a Dacron tape was used to pass the graft up into the tibial tunnel and out the femoral tunnel, it should be discarded, as it may be frayed, and a new tape should be used for fixation. The surgeon should watch the intraarticular portion of the graft on the video screen, with the assistant holding the arthroscope as the surgeon ties the 5- or 6-mm Dacron tape around the post. The tape ends should be passed once around the shank of the screw, crossed around the opposite side of the shank, and then brought back to the near side of the screw for tying.

By this means the surgeon controls the proximal-distal position of the graft. The tape is tied to a length that will provide optimal lengths of tissue in each tunnel. Before the surgeon ties, the assistant should exert mild tension on the tibial end of the graft to remove gross slack from the graft, which further ensures proper positioning. The screw and washer should then be finally tightened. The graft should be marked with both a marking pin and a cross-suture near the proposed femoral aperture, as described previously.

3 Whipstitch Technique

In this technique the four-strand graft, if it is used, may be made into four single strands of graft of equal length. #2 braided, nonabsorbable whipstitches are then woven into each of the eight ends as described in Chapter 42.

It is of paramount importance that all the sutures are woven in very tightly with strong tension after every pass or every other pass of the suture to maximally tighten the weave so that no tightening of the weave will occur later. Again, the graft should be marked with both a marker and suture, as in method 1. The sutures are then tied, two by two, around a cancellous screw and washer (Fig. 32-1) as follows: Each double suture strand is brought up to the smooth screw shank and crossed around the far side of the screw. These ends are then pulled back and tied two by two, such that the knot is on the graft side of the screw for the first two graft limbs. The process is repeated for the other two graft limbs. This will result in two knots in the femoral post. It is important to keep track of which sutures correspond to which graft segment either by using different color sutures or marking or knotting the suture ends before passing the graft segments.

Fig. 32-1 A and B, Two-thirds threaded femoral cancellous screw and washer used as fixation post for whipstitches from four-strand hamstring graft tied around it.

4 Graft Passed Through the Endobutton-CL Loop and Sutures Used to Tie the Endobutton to the Femoral Post

This is our preferred technique. Rather than tying a fabric loop around a cancellous screw, the surgeon can pass the graft through a short Endobutton loop and then pass a #5 braided nonabsorbable suture through each end of the Endobutton. These sutures can then be used to tie the Endobutton (and hence the loop and graft) to the screw as described in the previous paragraph. We prefer this technique if the Endobutton-CL is available because of the known strength of the fabric loop attached to the Endobutton. It also obviates the need to put whipstitches in the femoral end. Generally the surgeon will prefer to use the shortest loop, which is 15 mm. The Endobutton will be closely juxtaposed to the screw (Fig. 32-2) but is sufficiently low in profile to allow secure attachment to the screw without being in the way. A washer should be used on the screw.

Fig. 32-2 A and B, Sutures through the Endobutton eyelets are tied around the femoral screw post. The graft is looped through the Endobutton-CL fabric loop.

Again, the graft should be marked with both a marker and suture as in method 1.

Fixating Single Strands of Graft and Odd Numbers of Strands

Double-length strands that are looped over a femoral fixation device are now the mainstay of autograft and allograft ACL soft tissue femoral fixation. However, single strands may also be used in combination with double strands or other single strands to fashion a variety of grafts. The goal is to have a graft of sufficient strength to provide good stability using the available tissue. Reports of excellent stability now exist for three-, four-, five-, six-, and eight-strand grafts (see Chapter 17). These variegated grafts may be used with any of the four fixation methods described earlier. For an added single strand of graft, whipstitches of braided #2 nonabsorbable suture should be implanted. Then the two ends can be tied one to one either around the Endobutton-CL fabric loop (methods 1 and 4), the Dacron tape (method 2), or the femoral screw itself (method 3).

Radiography

We use C-arm fluoroscopy after the screw is tightened down to document its satisfactory position. Fluoroscopy is not needed during implantation. We have never found a screw to be intraarticular or otherwise malpositioned. The screw will generally lie in the distal femoral metaphysis, but it can be placed adjacent to wherever the femoral tunnel emerges on the external femoral surface.

The Femoral Post Technique Can Salvage the Following Situations

1 Lateral cortex blowout with Endobutton fixation: Conversion is easy, and the Endobutton can still be used for fixation by taking advantage of the fabric loop.

2 Proximal tunnel wall blowout: This is not a problem for femoral cortical suspensory fixation such as the Endobutton or EZLoc but is a problem for interference fixation. It is easily remedied with the femoral post technique, as a circumferential bone tunnel is not required. It is, however, important that the graft be pulled distalward against the distal tunnel wall and the screw be inserted distal to the exit area of the femoral tunnel. This will compress the graft against the distal wall. If the screw is put in proximal to the exit area of the femoral tunnel, the graft could potentially be pulled out of the femoral tunnel, as this tunnel is now really a “notch” and not a tunnel.

3 Revision surgery in which a new proximal tunnel partially overlaps with the old more distal tunnel: The surgeon may need to bone graft the old tunnel in this case. However, a semicircular notch in the femur (indenting in from the over-the-top position) can often be created lower down on the femur, which will produce a very biomechanically sound graft and save the patient both the pain of a bone graft and a second procedure. This tunnel may tighten a little more than usual toward extension, which should be taken into account when tensioning.

4 Fixation device breakage: The breakage or lack of availability of another device should allow conversion to one of the previously described techniques.

5 Harvesting a short semitendinosus or gracilis: If one tendon is cut too short during harvest to use as a loop (i.e., less than 14 cm) but the other tendon is at least 21 cm, then the longer tendon can be tripled and combined with the shorter tendon as a single strand as described earlier (i.e., the surgeon can use either a 3ST/1Gr or 1ST/3Gr). Both of these grafts are strong enough to substitute for the torn ACL, especially the 3ST/1Gr (in fact, 3ST alone should be sufficient). Because some femoral fixation systems would have difficulty with these grafts, the surgeon may use femoral screw post fixation instead, thus obviating the need to make an unplanned switch to allograft, which might otherwise be necessary.

Conclusions

1 Stability: Femoral post fixation provides unsurpassed stability.

2 Morbidity: Morbidity is minimal. The use of a second incision is necessitated; however, this is usually well tolerated by patients. Screw removal is virtually never necessary.

3 Ease of use: The method is straightforward and uses techniques familiar to every surgeon. If whipstitches are used, they must be inserted carefully and tightened maximally.

4 Equipment: Although the Endobutton-CL is useful, it is certainly not necessary. Every operating suite will have a 6.5-mm, partially threaded screw and smooth washer and #5 braided nonabsorbable sutures, and probably 5- or 6-mm Dacron tape as well. Also, 4.5-mm cancellous screws with washer can be used with care.

5 The universal salvage: In the increasingly complex world of ACLR in which high-tech techniques can go awry, it is a great comfort to have the ability to perform this technique, which can salvage virtually any ACLR-related problem on the femoral side.

1 Prodromos CC, Joyce BT. Five-strand hamstring ACL reconstruction: a new technique with better long-term stability than four-strand. Presented at the 2006 meeting of the Mid-America Orthopaedic Association, San Antonio, TX, April, 2006. 2006.

2 Prodromos CC, Joyce BT. Five-strand hamstring ACL reconstruction: a new technique with better long-term stability than four-strand. Presented at the 2006 meeting of the Arthroscopy Association of North America, Hollywood, FL, May, 2006. 2006.

3 Goradia VK, Grana WA. A comparison of outcomes at 2 to 6 years after acute and chronic anterior cruciate ligament reconstructions using hamstring tendon grafts. Arthroscopy. 2001;17:383-392.

4 Howell SM, Deutsch ML. Comparison of endoscopic and two-incision techniques for reconstructing a torn anterior cruciate ligament using hamstring tendons. Arthroscopy. 1999;15:594-606.

5 Hamada M, Shino K, Horibe S, et al. Preoperative anterior knee laxity did not influence postoperative stability restored by anterior cruciate ligament reconstruction. Arthroscopy. 2000;16:477-482.

6 Maeda A, Shino K, Horibe S, et al. Anterior cruciate ligament reconstruction with multistranded autogenous semitendinosus tendon. Am J Sports Med. 1996;24:504-509.

7 To JT, Howell SM, Hull ML. Contributions of femoral fixation methods to the stiffness of anterior cruciate ligament replacements at implantation. Arthroscopy. 1999;15:379-387.

8 Prodromos CC, Han YS, Keller BL, et al. Stability of hamstring anterior cruciate ligament reconstruction at two- to eight-year follow-up. Arthroscopy. 2005;21:138-146.

9 Cooley VJ, Deffner KT, Rosenberg TD. Quadrupled semitendinosus anterior cruciate ligament reconstruction: 5-year results in patients without meniscus loss. Arthroscopy. 2001;17:795-800.

10 Gobbi A, Mahajan S, Zanazzo M, et al. Patellar tendon versus quadrupled bone-semitendinosus anterior cruciate ligament reconstruction: a prospective clinical investigation in athletes. Arthroscopy. 2003;19:592-601.

11 Gobbi A, Tuy B, Mahajan S, et al. Quadrupled bone-semitendinosus anterior cruciate ligament reconstruction: a clinical investigation in a group of athletes. Arthroscopy. 2003;19:691-699.

12 Feller JA, Webster KE. A randomized comparison of patellar tendon and hamstring tendon anterior cruciate ligament reconstruction. Am J Sports Med. 2003;31:564-573.

13 Howell SM, Deutsch ML. Comparison of endoscopic and two-incision techniques for reconstructing a torn anterior cruciate ligament using hamstring tendons. Arthroscopy. 1999;15:594-606.

14 Goradia VK, Grana WA. A comparison of outcomes at 2 to 6 years after acute and chronic anterior cruciate ligament reconstructions using hamstring tendon grafts. Arthroscopy. 2001;17:383-392.

15 Zantop T, Brucker P, Bell K, et al. The effect of tunnel-graft length on the primary and secondary stability in ACL reconstruction: a study in a goat model. Presented at the 2006 meeting of the European Society of Sports Traumatology, Knee Surgery, and Arthroscopy,Innsbruck, Australia, May, 2006. 2006.

16 Yamazaki S, Yasuda K, Tomita F, et al. The effect of intraosseous graft length on tendon-bone healing in anterior cruciate ligament reconstruction using flexor tendon. Knee Surg Sports Traumatol Arthrosc. 2006;14:1086-1093.

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