Toggle-Rod Fixation for Management of Coxofemoral Luxation- Technique and Tips

The following instructions are intended to be used as a quick reference. More detailed information is included with purchase.

Michael F. Flynn, DVM, Diplomate ACVS
Mt. Hood Veterinary Specialists
Gresham, Oregon
(Dr. Flynn is one of the original researchers of the toggle rod)

Indications/Advantages

Can be utilized in any case of coxofemoral luxation to stabilize the hip after open reduction, but is ideally suited to those polytrauma patients in which there are multiple limb injuries requiring that the patient to be able to bear weight on the reduced hip immediately postop. This would also apply to other cases in which placement of an Ehmer sling postop would be either difficult or impossible, such as in the presence of open wounds or in male dogs where a belly band would be impractical. The procedure in theory is more physiologic than some other methods in that it mimics the normal anatomy of the hip joint by reconstructing a round ligament (ligament of the head of the femur) suture prosthesis. Toggle-rod fixation is best suited for craniodorsal/dorsal luxations rather than for ventral luxations, not because it won't work in the latter cases, but rather because the dorsal joint capsule is usually intact in ventrally luxated hips. Therefore, simple open reduction combined with use of hobbles to prevent abduction is usually sufficient to manage ventral luxations (avulsion fractures of the greater trochanter often occur in combination with ventral luxations, and should be stabilized by tension band fixation).

Contraindications for use of toggle-rod fixation would include pre-existing hip dysplasia in a trauma patient, poor hip conformation leading to spontaneous luxation/subluxation in patients with no history of significant trauma, avulsion fractures of the femoral head, and acetabular fracture. To reiterate the point regarding hip conformation, this method is not intended to be used in dysplastic hips. Ultimately, the long-term success of the procedure depends on there being a normal hip conformation to begin with, one that is conducive to maintaining reduction had there not been a traumatic incident. A toggle-rod repair performed in a patient with a shallow/subluxating hip conformation is doomed to failure. Take-home message: pick your patients wisely.

Approach:

I use a caudal approach to the hip in preference to a craniolateral approach for several reasons (see Piermattei - Surgical Approaches to the Bones and Joints of the Dog and Cat). First, with craniodorsal hip luxation a craniolateral approach requires that the femoral head be distracted distally and caudally to visualize the acetabulum. This necessitates overcoming significant gluteal muscle contraction in the opposite direction, and can make for very difficult and frustrating retraction and visability. A dorsal approach by trochanteric osteotomy provides very good visualization, but is technically more difficult and subsequent repair of the osteotomy by tension band fixation places the suture prosthesis at risk for being cut by the k-wires as they are driven down the femoral shaft. The osteotomy also tends to interfere with the transverse bone tunnel that may be utilized to secure the suture laterally. With the caudal approach, the hip is naturally retracted craniodorsally by virtue of it being luxated, thereby providing excellent access to and visualization of the acetabulum with minimal additional retraction. If the external rotator tendon (combined tendons of internal obturator and gemelli muscles) insertion on the femur at the trochanteric fossa is intact, you will need to perform a tenotomy here to gain access to the acetabulum. However not uncommonly this tendon is already ruptured as a result of the trauma, in which case the approach is almost made for you.

Acetabular Preparation:

Open the joint capsule further if necessary to allow complete visualization of the acetabulum - orient the incision in such a way that will leave sufficient capsule tissue on either side, thereby allowing easy and secure suture closure later if possible (i.e., don't make the job more difficult for yourself later). Completely remove remnants of the round ligament (RL) (I like to use a #11 blade). This is very important. Any significant amount of RL remaining will interfere with subsequent placement of the toggle rod (see below). Drill a bone tunnel thru the medial wall centered in the acetabular fossa, using a 3.2 mm drill bit. Take care not to allow the drill bit to extend too far into the pelvic canal when drilling, to protect against potential rectal perforation or sciatic nerve injury. Pass a length of suture material thru the eye of the toggle rod. I prefer Mason hard nylon, but braided polyester suture can also be used (e.g., 1 or 2 strands of #5 Ethibond or Mersilene). If you are using nylon, it should specifically be "hard" nylon material, which is much more resistant to abrasion than conventional nylon. Also, if you are securing the suture on the lateral cortex using a crimp sleeve (see below), I would use the Mason nylon specifically sized and manufactured for SECUROS for that purpose because this should provide the most secure crimp (owing to uniform diameter throughout). The crimp sleeves are available for use with 80 lb test and 40 lb test nylon. The toggle rod can accommodate a single strand of Mason hard nylon as large as 80# test. Load the toggle rod onto the insertion tool and fold the suture back along the grooves of the toggle. Hold the suture in this position by sliding an O-ring over the toggle and onto the insertion tool, pinning the suture between the O-ring and sides of the insertion tool. Insert the end of the toggle into the acetabular bone tunnel as deeply as it will go. Then, while pressing the insertion tool firmly into the fossa with one hand, depress the plunger with the other hand to advance the toggle thru the tunnel to the medial side. It is very important to keep the insertion tool pressed firmly into the fossa while the plunger is depressed. Otherwise, the insertion tool will be pushed up and out of the fossa rather than the toggle being inserted thru the bone tunnel. It is also important to have removed all of the round ligament from the fossa. Any remaining RL that is interposed between the fossa and the tip of the insertion tool will in effect shorten the depth to which the toggle is inserted when the plunger is advanced, thereby risking the possibility that the toggle will not be able to turn effectively and lock onto the other side of the medial cortex. WHILE CONTINUING TO HOLD THE PLUNGER IN PLACE, gently tug on the suture strands a few times to dislodge the toggle and cause it to rotate 90 degrees and seat on the medial cortex, but do not yet pull hard on the suture. Remove the insertion device gently and insert the tips of a pair of closed Kelly hemostats thru the bone tunnel as deeply as they will go easily. Rotate the hemostats 90 degrees clockwise and then 90 degrees counterclockwise. This is to ensure that the toggle has been pushed completely thru the tunnel to the other side. While continuing to hold the hemostats in place in the tunnel, pull firmly upward on both ends of the suture to ensure that the toggle has securely engaged on the medial side of the cortex. Remove the hemostats. You should at this point literally be able to lift the pelvis upward, although you do not need this degree of force to determine if proper placement has been achieved.

Femoral Head/Neck Preparation

Internally rotate the femur until you can visualize the femoral head caudally. Using a #11 blade, carefully remove any remnants of the RL attached to the fovea capitis, being careful not to damage the surrounding articular cartilage. Using a .062" k-wire, drill a small starter hole in the femoral head directly centered on the fovea (previous attachment of the RL). Drill only 2-3 mm deep. This starter hole is to allow you to place the tip of the femoral head aiming device precisely where it should be without having it slip during subsequent drilling. Place the tip of the aiming device into the starter hole in the femoral head as described, and externally rotate the femur back to a relatively neutral position while maintaining tension on the tip of the aiming device to prevent it from dislodging. The location on the lateral femoral cortex at which the bone tunnel is to begin is at a point several mm cranial to the crest of the third trochanter, at a level distally roughly even with the lesser trochanter medially. A common mistake is to start this bone tunnel too far proximally. It is helpful to have identified the desired starting point on the lateral cortex before placing the aiming device. Elevate enough vastus lateralis muscle cranially from the crest of the third trochanter at the selected level to provide a clear view of the bone to be drilled. Predrilling a small starter hole with a .062" k-wire or small Steinmann pin will help prevent the drill bit used later from "walking" during the actual drilling of the femoral neck bone tunnel. Position the drill sleeve of the aiming device on the desired point (starter hole) on the lateral femoral cortex and tighten the sleeve. In larger dogs, drill the femoral head/neck tunnel using a 3.2 drill bit. In medium/small dogs or cats, I use an appropriately sized drill sleeve insert to drill a narrower bone tunnel in the femoral neck with a smaller drill bit (2.5 mm for medium dogs; 2.0 mm for cats and small dogs, depending on size of suture being used). For small-medium sized patients, SECUROS also has available a long, 2.4 mm diameter drill bit and drill sleeve that is compatible with the current aiming device, available for use with both their external fixator system as well as the coxofemoral luxation system, and this is probably the simplest way to accomplish drilling the smaller tunnel when indicated. Remove the aiming device. Internally rotate the femur again to expose the fovea capitis. Pass the suture ends thru the bone tunnel at the fovea and back out thru the lateral cortex. This can be accomplished in several ways. If using nylon, the suture is stiff enough to allow passage by simply pushing each end of the suture back thru the tunnel. If using limp braided polyester, you will need to pass the strand(s) using the SECUROS suture passer, but this is only possible if you have drilled a 3.2 mm tunnel. If using braided polyester with narrower bone tunnels, you will need to pass the suture using a wire loop made of 22 ga. wire passed from lateral to medial in similar fashion as the SECUROS suture passer. Reduce the hip while pulling firmly on the suture to keep it taut.

Securing the Suture Prosthesis to the Femur

The suture can be secured laterally in several ways:

1) Because I am typically using nylon, I secure the suture by using a crimp sleeve (very difficult to tie knots in hard nylon). Drill a transverse bone tunnel in the lateral femoral cortex from caudal to cranial at a point approximately 1.5 - 2 cm proximal to where the suture tunnel exits (see illustration in Brinker, Flo, Peirmattei). Tunnel the end of one of the suture strands under the vastus lateralis muscle cranially and proximally between the femoral neck tunnel and the cranial end of the transverse bone tunnel. Pass this end of the suture thru the transverse tunnel from cranial to caudal. Then pass this and the other end of the suture thru an appropriately-sized crimp sleeve in opposite directions. This places the crimp sleeve on the caudal aspect of the bone of the greater trochanter, where it is easily accessible to crimp, and will not impinge on muscle. Clamp a pair of mosquito forceps to the suture on either side of the crimp sleeve and apply tension to the suture using the SECUROS tensioning device (available separately or with the SECUROS cruciate repair system). Test the range of motion as described below to determine if the tension is correct. Adjust as necessary. When satisfied, apply 3 crimps to the sleeve using the SECUROS crimping tool.

2) If using braided polyester, I simply pass one end of the suture thru the eye of a second toggle rod and tie a knot with the toggle rod locked against the lateral cortex. Technically, a polypropylene button could be used for this, but I find the toggle rod provides a much lower profile and less interference with soft tissues.

3) If using braided polyester, you could also pass the suture thru a transverse bone tunnel as in Method 1 and tie the ends.

Determining How Tightly to Tie the Suture:

It is extremely important NOT to over-tighten the suture. This is the single biggest mistake to make. The suture should only be tightened enough to maintain hip reduction while preserving relatively normal range of motion to the hip. In a normal hip, there will be several mm of mediolateral translation of the femoral head in and out of the acetabulum possible when the capsular vacuum effect is released. This should be preserved. Before the suture is crimped or tied, test the tightness of the reduction as follows: 1) Test for presence of Ortolani sign/laxity - there should be little or no subluxation. If negative, then you now need to make sure it is not too tight (step 2, etc.). If positive, then you need to tighten further before proceeding. 2) Test for mediolateral translation by grasping the greater trochanter and lifting upward, or simply grasping the thigh and lifting upward while keeping the femur parallel to the table. There should be a few mm of laxity present. 3) Take the hip thru a range of motion in flexion/extension, adduction/abduction, and internal/external rotation. There should be relatively normal ranges of motion without allowing overt subluxation; however, neither should there be overt tightness or decreased range of motion in any direction. Do not crimp or tie the suture until you are satisfied with the degree of tension. You will be surprised at how little tension really needs to be placed on the suture - you should not have the impression that you are socking the femoral head tightly into the acetabulum. Making the hip too tight risks causing either premature failure of the suture prosthesis or pressure-induced chondromalacia of the articular cartilage.

Once you have secured the suture, perform whatever capsule repair is possible with the tissues available, and close (you will need to reattach the external rotator tendon insertion if you tenotomized it, or try to reattach it if it was previously ruptured/avulsed). Document proper positioning of the toggle rod with postoperative radiographs.

Aftercare:

If the patient will not be required to ambulate on the operated leg immediately postop, then you could consider enhancing security of the repair by placing the limb in an Ehmer sling or tibial sling for 10-14 days. The patient should be absolutely confined to a small room or large cage or crate for 6 weeks, with activity restricted to brief leash walks only long enough to eliminate. At 6 week recheck, if the hip is still reduced the patient can be allowed a gradual return to activity by progressively lengthening leash walks over one month thereafter.