Upping your lateral suture game

Lateral suture stabilization is a time-tested treatment for cranial cruciate ligament (CCL) rupture in dogs. Although tibial plateau leveling osteotomy (TPLO) and other osteotomy procedures are considered the gold-standard treatment for most patients, a lateral suture can also produce good results, especially with proper case selection. The lateral suture procedure is a more affordable option for owners and a less complex procedure that may be more accessible to general practitioner surgeons. However, a few critical steps are key to increasing the likelihood of success.

Stifle exploration

A thorough stifle exploration via arthrotomy or arthroscopy is crucial for the successful treatment of CCL rupture. Most surgeons treating with a lateral suture will opt for a lateral parapatellar approach. The CCL is evaluated first, confirming the diagnosis. In dogs with a complete CCL tear, debridement of the torn ligament will facilitate visualization of other intra-articular structures.

A partially torn CCL presents more of a challenge for meniscal evaluation. Leaving a partially intact CCL in place has been associated with better long-term joint health in dogs receiving TPLO, including improved cartilage scoring on second-look arthroscopy.¹ However, a thorough evaluation of the menisci is difficult when performing an arthrotomy in a joint with a partially intact CCL. I prefer to assess the remaining ligament as “competent” or “incompetent.” Competent ligaments have substantial remaining structure, often with at least 50% of the original ligament intact.

A slender instrument such as a ball-end probe or a neuro hook is very useful for palpating the CCL as well as the menisci. Incompetent partial tears have fewer intact fibers, which may be stretched, allowing some cranial drawer movement. I debride incompetent partial tears to better assess the menisci but typically leave competent tears intact, with the assumption that significant meniscal injury is much less likely in those cases.

Meniscal treatment

Meniscal injury is quite common in dogs with CCL rupture. Dogs with meniscal tears tend to be more lame preoperatively and inadequate treatment of these tears will lead to an unsuccessful outcome, even if stifle stability is achieved. Additionally, late meniscal injury is a diagnostic differential for dogs with recurrent or persistent lameness after stifle stabilization surgery.

Knowledge of normal meniscal anatomy and of meniscal injury patterns is critical to successful meniscal treatment. Although thorough assessment and probing of both menisci are warranted, a bucket-handle tear of the caudal horn of the medial meniscus is the most common injury. Proper access to the caudal horn of the medial meniscus is often not possible without either distracting the stifle or cranially displacing the proximal tibia. Here are 3 methods that I use:

• Apply a Senn retractor to the infrapatellar fat pad, applying cranial traction on the proximal tibia to “pull it into drawer,” allowing visualization of the caudal joint. This tends to work best in small patients with a large degree of stifle laxity (Figure 1).

Figure 1. Stifle arthrotomy with Gelpi retracting the patellar ligament, Senn retractor on the infrapatellar fat pad, and probe used to palpate intra-articular structures.

• Use a thrust lever instrument to hook the caudal aspect of the proximal tibia while levering against the distal femur. This instrument can be a slender thrust lever (my preference), a mini Hohmann retractor, or a curved hemostat appropriately sized for the patient (Figure 2).

Figure 2. Stifle arthrotomy with Gelpi retracting the patellar ligament. A thrust lever is inserted in the stifle, with the tip hooked caudal to the tibial plateau and the shaft of the instrument levering against the femoral condyles, causing cranial translation of the tibia.

• Use a self-retaining retractor to distract the femur and tibia. This can be a standard Gelpi retractor (my preference) or specialized stifle distractor. Place the tips of the retractor in the fossa of the origin of the CCL proximally and in the cranial intermeniscal ligament distally. Then, open the retractor carefully, distracting the femur and the tibia. Gentle stifle extension will increase the amount of distraction and allow better visualization in some cases. Do not perform forceful extension or flexion of the stifle while the retractor is in place; serious injury could result. This technique is most helpful in medium- to large-breed dogs (Figure 3).

Figure 3. Stifle arthrotomy with Gelpi retracting the patellar ligament. The larger Gelpi is being used as a stifle retractor, with the proximal tip in the cruciate fossa and the distal tip in the cranial intermeniscal ligament.

Once the caudal joint is visualized, palpate the caudal meniscotibial ligament with a hook. Normal laxity of this ligament allows slight cranial translation of the caudal horn with traction, but significant translation (more than about 2-3 mm) suggests a meniscal tear, even if it is not immediately evident.

Treatment of a meniscal tear should completely remove the damaged portion of the meniscus but spare all uninjured meniscus. Complete medial meniscectomy is rarely indicated in these cases. Depending on the extent of injury, caudal horn meniscectomy or partial meniscectomy should be performed. Other than the instrument used for stifle distraction or tibial translation, required instruments include a probe (as described above), scalpel (#11, #15, or #64 blade), and mosquito hemostats. Kocher hemostats are preferred, if available, to provide a better grip on the torn meniscus.

Hook the meniscotibial ligament of the torn caudal portion of the meniscus with a probe and transect it. Once this transection is complete, the most axial part of the torn meniscus can be grasped with a hemostat and manipulated. Use the blade to excise the torn meniscus from the intact meniscus abaxially. Use the probe to palpate any remaining caudal meniscotibial ligament. Not uncommonly, multiple meniscal tears are present and must be treated. Once no further meniscal tissue is pulled cranially by traction on the meniscotibial ligament, or if the entire caudal pole of the meniscus has been removed, meniscal resection is complete.

Lateral suture stabilization

Many variations of the lateral suture procedure exist, but the most common involves the use of monofilament nylon leader line placed around the femoral-fabellar ligament, under the patellar tendon from lateral to medial, through a tibial tunnel from medial to lateral, and then tied or crimped laterally. If monofilament nylon leader line is chosen, be sure to select the appropriate suture size. This monofilament is rated in pounds, and this rating should correlate roughly to the bodyweight of the dog. For example, 40-lb test monofilament is typically selected for a 40-lb dog. Commonly available sizes are 20, 40, 60, 80, and 100 lb. When between sizes, I usually round up to the next heaviest suture. The leader line can be purchased with either a single or double strand with a swaged needle, which allows for easier suture passage. Alternatively, a length of sterile leader line is loaded onto an appropriate-sized cruciate needle.

Leader line can be tied or crimped. Crimps are commercially available for 40-, 80-, and 100-lb suture. When used with a ratcheting tension device, crimps allow greater control over suture tension. Crimped knots are also less likely to allow suture loosening over time and are less bulky.² If crimps are not available or if hand-knotting is elected, strategies for tensioning the knot include using a sliding half-hitch (my preference) or a square knot with an assistant to clamp the first throw to hold tension while the second throw is placed.

Once an intra-articular assessment is complete, lavage the joint and close the joint capsule. The lateral retinacular fascia is not closed at this time and must be dissected free of the joint capsule to allow adequate exposure of the lateral fabella. Typically, a double strand of leader line is passed, either with a length of line loaded through a cruciate needle with equal resultant strands or with a swaged needle with double strands. Place the suture from proximal to distal around the femoral-fabellar ligament, axial to the fabella, and adjacent to the femur. Pass the suture as deeply as possible; tension on the suture should meet strong resistance and move the fabella.

Next, pass the suture from lateral to medial deep to the patellar ligament, in the region of the infrapatellar fat pad. In this region, the suture will not be intra-articular. A bone tunnel is created in the proximal tibia. The position of this bone tunnel is key to the success of the procedure; it should be placed relatively caudally and proximally. Create the bone tunnel with a pin and Jacobs chuck, or a drill bit just large enough to allow passage of 2 strands of suture. Elevate the cranial tibial muscle and retract it caudally. Pass the pin or drill bit from lateral to medial, just cranial to the long digital extensor tendon, and 5 to 10 mm distal to the joint. Cut the needle from the suture and guide the sutures from medial to lateral through the bone tunnel using a large hypodermic needle (16-18 gauge). Tie or crimp each suture so they have similar tension. Proper suture tension should eliminate cranial drawer but still allow normal stifle range of motion. Finally, perform routine closure of retinacular fascia, subcutaneous tissues, and skin.

Success with lateral suture stabilization is possible with excellent meniscal visualization and treatment, a well-placed tibial bone tunnel, and secure suture knots or crimps. Having a few relatively inexpensive instruments helps the surgeon perform these key steps successfully and efficiently.

References

1. Hulse D, Beale B, Kerwin S. Second look arthroscopic findings after tibial plateau leveling osteotomy. Vet Surg. 2010;39(3):350-354. doi:10.1111/j.1532-950X.2010.00676.x
2. Anderson CC III, Tomlinson JL, Daly WR, Carson WL, Payne JT, Wagner-Mann CC. Biomechanical evaluation of a crimp clamp system for loop fixation of monofilament nylon leader material used for stabilization of the canine stifle joint. Vet Surg. 1998;27(6):533-539. doi:10.1111/j.1532-950x.1998.tb00528.x

Jason Syrcle, DVM, DACVS-SA, is associate professor of clinical small animal orthopedic surgery in the Department of Clinical Sciences & Advanced Medicine, and chief of Small Animal Surgery at the Matthew J. Ryan Veterinary Hospital at the University of Pennsylvania School of Veterinary Medicine in Philadelphia.