Retrospective Study Comparing Two Materials Commonly Used in the LFS Technique for CCLR

Introduction

Cranial cruciate ligament rupture (CCLR) is the most common orthopedic injury causing hind limb lameness encountered in canine patients and is the most common cause of degenerative joint disease (DJD) in the stifle of adult dogs.^1–3 Deterioration of the extracellular matrix of the cranial cruciate ligament leads to either partial or complete CCLR with subsequent stifle instability and DJD.^1,2,4 This degenerative process is supported by the finding that most animals diagnosed with CCLR are > 5 yr of age.^1–4 The severity of the degenerative changes in the stifle joint caused by this disease are directly linked to body size, with animals > 15 kg showing the most changes.¹ A number of surgical procedures have been described with the goal of stabilizing the stifle, including intracapsular ligament replacement, extracapsular suture techniques, fibular head transposition, tibial plateau leveling osteotomy, and tibial tuberosity advancement.^2,3 Unfortunately, none of the listed procedures can either completely restore the original biomechanics of the stifle joint or reverse the progression of DJD.^3,5

The lateral fabellar suture (LFS) technique, one of the extracapsular repair methods, has been advocated for the surgical treatment of CCLR in animals. A good to excellent clinical outcome has been reported in 77–82% of cases that underwent LFS surgery.^3,6 In 1970, DeAngelis and Lau originally described the placement of an extra-articular suture around the lateral fabella that was then anchored to the patellar ligament, but that procedure has evolved and several modifications have been reported.^1,7 One of those modifications involves passing the suture around the lateral fabella and through either one or two bone tunnels created in the tibial tuberosity (rather than attaching the suture to the patellar ligament).⁶ Another modification is the use of bone anchors to allow suture placement in the most isometric point in the stifle joint.^3,8,9 In addition, several different techniques for knot tying, including clamped square knots, slip knots, or self-locking knots, have been evaluated in search for a knot that resists elongation and slippage.^10–14 A metal crimper used for loop fixation instead of a hand-tied knot has been advocated to help maintain initial suture tension and stiffness, decrease loop elongation, and prevent a large suture mass resulting in overlying soft tissue irritation.^3,10,11,15 Additionally, various LFS loop configurations have been compared, showing that double loop, single strand constructs (e.g., the interlocking loop configuration) have significantly higher tensile strength than other constructs.¹⁶ The LFS technique continues to evolve so that early postoperative stability can be achieved, resulting in early return of limb function.¹⁵

Many suture materials, including stainless steel, monofilament nylon leader line (NLL), fishing lines, multifilament nonabsorbable suture material, and polyblend polyethylene sutures have been investigated to identify a superior material (in terms of strength and elongation resistance) to use in the LFS procedure.^3,15,17–25 Unfortunately, all of those materials have been shown to fail at some point postoperatively.¹⁵ That failure can occur through several mechanisms, including premature suture stretching, alterations in attachment points, or entrapment of soft tissues intraoperatively resulting in loosening.¹⁵ The goal is to have suture failure occur after the body has been able to form adequate periarticular fibrosis surrounding the suture material, maintaining stifle stability after the suture ultimately fails.¹⁵ Suture failure before that process has occurred results in continued stifle instability and patient morbidity.¹⁵

The ideal suture material is thought to have constant strength, be biologically inert, aseptic, easily to handle, inexpensive, have excellent knot security and compactness, and have the ability to withstand both cyclical and tensile loading.^15,21,25 Several suture materials have been tested in a quest to find a superior material. Stainless steel was found to have a 20% failure rate by 3 wk postoperatively and an 80% failure rate by 6 wk postoperatively.¹⁸ NLL has been determined to be stronger and stiffer compared with fishing lines, but NLL requires additional throws to secure the knots.³ Multifilament nonabsorbable sutures are more likely to house bacteria compared with monofilament sutures, leading to infection and draining tracts.³ To date, an ideal suture material has yet to be identified.

Over the last several years, a new generation of suture materials have been created and evaluated for strength and resistance to elongation. A variety of the newer commercial materials^a–c are nonabsorbable, multifilament, polyblend polyethylene orthopedic sutures that are stronger, stiffer, and undergo less elongation than similarly sized monofilament sutures, such as NLL.^{15,19,23,25,26} In particular, one of the newer materials (FW) is a nonabsorbable polyblend suture material with an ultrahigh molecular weight multifilament polyethylene core surrounded by a polyester and polyethylene braided jacket.^19,21,24,25 That design resists elongation and creates a greater area and noncircular cross-section compared to either an equally sized circular silicone-coated braided polyester suture^d and nonabsorbable monofilament polypropylene suture^e.^19,21 FW is reportedly 10% stronger than the nonabsorbable monofilament polypropylene suture and 25% stronger than the silicone-coated braided polyester suture.²¹ Compared with an equally sized nonabsorbable multistranded braided polyester suture^f used in human medicine, FW displayed superior resistance to abrasion when placed through a bone anchor eyelet and had between 5 and 51 times more mean number of cycles to failure.²⁰ Those findings suggest that the abrasion resistance demonstrated by FW was sufficient to eliminate concern over weakening of the suture at the point where it passed through the bone anchor eyelet.²⁰ The abrasion resistance was also confirmed by Wüst et al. (2006) who reported that FW was more resistant than other polyblend polyethylene sutures.²⁰ Wright et al. (2006) also evaluated several suture materials and measured load to failure (LTF) and ultimate tensile strength (UTS) of both undamaged suture and suture after it had been cut with a razor blade.²⁴ That group also tested the undamaged and damaged suture when used in conjunction with a bone anchor.²⁴ That study found that undamaged FW had the highest LTF and UTS compared with the other sutures, and damaged FW had a significantly higher LTF and UTS than the other tested sutures.²⁴ For the bone anchor test, both damaged and undamaged FW had the highest LTF than the other tested sutures as well.²⁴ They also found that suture stiffness was not significantly affected when cut.²⁴

One disadvantage of FW is that although knots were more secure than knots of another commercial suture material^f, the FW knots were significantly bulkier.^22,25 Wüst et al. (2006) evaluated knot security between several polyblend polyethylene suture materials and found that an additional two throws were needed compared with polyester suture material, resulting in a total of six single throws.²³ Another disadvantage was that FW had significantly more knot slippage compared with several other suture materials.²⁵

The purpose of this study was to compare the short-term outcome of dogs undergoing LFS using either FW or NLL for treatment of either partial or complete CCLR. To the authors’ knowledge, there are no studies comparing the clinical use of FW and NLL for surgical correction of CCLR using the LFS procedure, and this is the first study to compare those two materials in clinical cases.

Materials and Methods

Medical records of all dogs admitted to the authors’ hospital between June 2009 and June 2010 for either a partial or complete CCLR performed using the LFS technique were reviewed. All cases had complete physical and neurologic examinations performed, and standard mediolateral and caudocranial radiographs of the affected stifle were obtained. The diagnosis of CCLR was based on history, physical examination (positive tibial compression test, cranial drawer sign, and pain on extension of the stifle), radiography (cranial tibial translation and evidence of joint effusion within the stifle joint), and confirmed by exploration of the stifle joint via lateral arthrotomy. Cases were included in the study if the CCLR was repaired with either FW or NLL. Dogs were excluded from the study if they did not undergo surgical correction, were not treated using the LFS technique, if there was evidence of other ligament damage present within the stifle (i.e., collateral ligament or caudal cruciate ligament injury), if there was no follow-up information available, and if the medical record was incomplete.

The following information from the medical records was recorded: age, sex, weight and body condition score (BCS), breed, affected limb, partial or complete CCLR, intact or torn medial meniscus, length of follow-up, type of suture material and number of strands used, method of securing the suture (i.e., a hand-tied knot versus crimp clamp), and if a bone anchor was used. If a follow-up examination was not performed at the authors’ hospital, the referring veterinarians were contacted to ascertain outcome. A successful surgery was defined as a stifle that was determined to be stable postoperatively and during follow-up examinations. A failure was defined as a procedure that did not result in adequate stifle stability at any point postoperatively, resulting in either marked stifle instability or partial instability with marked lameness. Instability was defined as a positive cranial drawer sign and/or a positive tibial compression test in the operated stifle. A stifle was considered to have marked instability when > 5 mm of movement was elicited in the stifle during a cranial drawer test/tibial compression test. Partial instability was defined as between 2 mm and 5 mm of movement during a cranial drawer test/tibial compression test. A dog was deemed to have marked lameness when they were either nonweight bearing or toe-touching lame on the operated limb.

Results

As summarized in Table 1, stabilization of CCLR using the LFS technique was performed on 16 dogs (19 procedures). Dogs ranged in age from 2 yr to 12 yr (mean, 6.5 yr), and 8 of 16 (50%) of the dogs were female. Mean body weight was 12.8 kg (range, 4–32 kg), and 4 of the dogs weighed >15 kg. Based on a standard BCS ranging from 1–5, 4 dogs were considered in ideal body condition (a BCS of 3 was considered ideal) and 12 were considered overweight (BCS > 3). Breeds represented included the bichon frise (n = 2), Yorkshire terrier (n = 2), and one each of the following breeds: cocker spaniel (n = 1), West Highland white terrier, miniature schnauzer, Labrador retriever, pug, beagle, chow chow, Scottish terrier, Irish water spaniel, keeshond, Pembroke Welsh corgi, and Australian blue terrier.

Table 1 Description of the Study Population and Summary of LFS Outcomes

*

Bilateral CCLRs. The stifles were repaired at separate times.

†

Case that had a failed repair that was later modified via the lateral fabellar suture (LFS) technique.

§

Case that had a failed repair that was later modified via the lateral fabellar suture (LFS) technique.

#, pound; CCLR, cranial cruciate ligament rupture; CM, castrated male; FW, a commercial polyblend polyethylene orthopedic suture material; LFS, lateral fabellar suture; M, male; N/A, not applicable; NLL, monofilament nylon leader line; SF, spayed female.

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Overall, 8 of the 19 surgeries were performed on the left stifle. One dog was diagnosed with bilateral CCLRs that were repaired at separate times. Five dogs had the stabilizations fail, and 3 of those dogs needed to have the stabilizations modified. A complete CCLR was diagnosed in 17 of 19 (89.5%) dogs during exploratory arthrotomy, leaving 2 of 19 (10.5%) dogs diagnosed with partial CCLRs. The medial meniscus was intact in 13 of 19 (68.4%) of the dogs. Mean follow-up time was 3.2 mo (range, 1–16 mo). One dog died of unrelated causes 10 mo postoperatively.

In 5 of the 19 dogs (26.3%), the stifles were stabilized using FW. Of those, 3 of 19 (15.8%) stifles were stabilized using two strands of FW passed around the femoral fabellar ligament, under the patellar ligament, through a single hole drilled in the tibial tuberosity, and tied using the recommended 5–6 throws. The remaining two stifles had FW passed through a bone anchor placed in the lateral femoral condyle, under the patellar ligament, through a single hole drilled in the tibial tuberosity, and tied using the recommended 5–6 throws. In 8 of 19 (42.1%) stifles, two strands of NLL were passed around the femoral fabellar ligament, under the patellar ligament, through a single hole drilled in the tibial tuberosity, and tied using square knots. In 3 of 19 (15.8%) stifles, one strand of NLL was passed around the femoral fabellar ligament, under the patellar ligament, through a single hole drilled in the tibial tuberosity, and tied using square knots. In 2 of 19 (10.5%) stifles, one strand of NLL was passed around the femoral fabellar ligament, under the patellar ligament, through a single hole drilled in the tibial tuberosity, and crimped using a crimp-clamp system. One of those cases used 80 pound test NLL size and a crimp size that corresponded to the suture size. The second case used 50 pound test NLL size and a crimp size that corresponded to 40 pound test NLL size. In the remaining stifle, two strands of NLL were passed around the femoral fabellar ligament, under the patellar ligament, through a single hole drilled in the tibial tuberosity, and crimped using a crimp-clamp system with a crimp size matched to the size of the suture. One case needed a medial imbrication suture placed in addition to the LFS procedure using two strands of NLL to correct a concurrent lateral patellar luxation. NLL size was selected based on the weight of the dog, where the test strength was approaching twice the weight of the dog in pounds. No. 2 FW was used in all of the cases included in this study based on the previously reported recommendation of using No. 2 FW for all animals weighing < 35 kg.¹⁵

Three stabilizations needed revision. One of those dogs underwent LFS using FW that had been passed around the femoral fabellar ligament and tied, but failed 2 wk postoperatively. That dog became acutely lame 2 wk after surgery and a follow-up orthopedic examination revealed marked stifle instability and pain on manipulation. The decision was made to reoperate on the stifle to determine the cause of the deterioration. During the second surgery, the suture was observed to have pulled through the femoral fabellar ligament. This was corrected using FW passed through a bone anchor. Four wk after the second surgery, there was a “slight” cranial drawer noted on re-evaluation, but stifle stability was considered adequate. The second failed case had one strand of 80 pound test NLL that had been crimped with a crimp size matched to the size of the suture that failed 4 wk postoperatively. The mode of failure was not recorded. This case was corrected using one strand of 40 pound test NLL passed around the femoral fabellar ligament and tied using square knots. That dog was fitted for a custom orthotic brace postoperatively to be worn thereafter. The third failed case originally had FW passed around the femoral fabellar ligament that failed 12 wk postoperatively. That dog underwent physical rehabilitation at the authors’ hospital’s rehabilitation facility and was fitted for a custom commercial orthotic brace 5 mo postoperatively. Results were deemed unacceptable after 2 mo of brace augmentation so the stifle was stabilized by means of a tibial plateau leveling osteotomy procedure 7 mo after the LFS procedure. At that time, it was determined that the suture had pulled through the femoral fabellar ligament. Mean time to diagnosed failure was 6 wk (range, 2–12 wk). One of the four dogs (25%) weighing > 15 kg had a stabilization that failed (one of the cases where FW had been passed around the femoral fabellar ligament and tied). Three of the five failures occurred in dogs that were considered overweight.

All of the stabilizations that had FW passed around the femoral fabellar ligament and tied ultimately failed. One of the three stifles that were stabilized using the crimped NLL failed. One of the eight stifles that were stabilized using two strands of NLL passed around the femoral fabellar ligament and tied ultimately failed. Of the three stifles that were stabilized a second time, two were repaired using LFS, and all of those cases continued to have some degree of laxity postoperatively. Overall, 5 of 19 (26.3%) of the stabilizations failed, but if the stabilizations that involved FW being passed around the femoral fabellar ligament were removed from analysis, only 2 of 16 (12.5%) of the stabilizations failed.

The χ² test showed that FW was significantly more likely to fail compared with NLL (P = 0.0379). The odds ratio estimate found that FW was 14.667 times more likely to fail than NLL. Further, FW was 6 times more likely to fail compared with one strand of NLL and 32 times more likely to fail than two strands of NLL.

Discussion

This retrospective study evaluated clinical cases diagnosed with CCLR that were treated using the LFS technique with either FW or NLL. All surgeries were performed within a 12 mo period to evaluate only one group of surgeons and residents to limit surgeon variability in the results.

Several epidemiologic factors were recorded in the current study. The median age of diagnosis in the current study population was 6.5 yr. This is in agreement with the current literature that states that dogs suffer from CCLR when they are between 5 yr and 7 yr of age.^1–4 The average age for the dogs undergoing LFS with FW was 4 yr (range, 2–7 yr), and the average age for dogs undergoing LFS with NLL was 7.4 yr (range, 4–12 yr). Both the FW and the NLL populations were roughly equal in weight distribution.

In the current study, 75% of the included cases were considered overweight. Studies performed in the past reported as many as 71% of dogs with CCLR were overweight.²⁷ Of the five cases that failed in the current study, three were considered overweight. This finding is in agreement with the study performed by Casale and McCarthy (2009) that identified a high body weight to be a significant risk factor in the development of postoperative complications.⁶ The overall complication rate reported in that study was 17.4%.⁶ That complication rate was lower than in the current study, in which the overall complication rate was 26.3%. Once the failed FW repairs were removed, the complication rate decreased to 10.5%, which was lower than reported by Casale and McCarthy (2009).⁶ In the authors’ institution, NLL size was selected based on the weight of the dog, where the test strength approached twice the weight of the dog in pounds. If the dog undergoing LFS was overweight, the next highest pound test NLL size that equaled twice the dog’s weight in pounds was selected in an attempt to compensate for this risk factor. For example, if an overweight dog that weighed 20 pounds was undergoing the procedure, 60 pound NLL was used instead of 40 pound NLL.

Conclusions about breed predisposition cannot be made due to the small sample population. Also, the authors’ hospital commonly recommends that if the animal weighs > 15 kg, either a tibial plateau leveling osteotomy or tibial tuberosity advancement procedure should be performed instead of a LFS. Thus, the results reported in this study likely show an overrepresentation of smaller breed dogs. That said, 4 of the 16 cases weighed > 15 kg and only 1 of those failed following LFS. Therefore, in this study, being a large-breed dog did not make failure of the extracapsular technique more likely, but this could be a type II error.

Concurrent medial meniscal injury reportedly occurs in approximately 50% of dogs sustaining a CCLR.^1,6 It has also been said that with CCLR chronicity and complete CCLR versus a partial rupture, the frequency of meniscal damage increases and can be up to 80%.² Only 31.6% of the dogs reported in the current study had a torn medial meniscus requiring excision, which was similar to the study performed by Casale and McCarthy (2009) that found concurrent meniscal injury in 37.5% of the cases.⁶ This low incidence of meniscal injury may be due to owners recognizing their dog’s lameness and seeking surgical treatment earlier, rather than either treating conservatively or not at all. With earlier surgical intervention, the amount of time between the CCLR and the LFS may not have been an adequate amount of time to allow enough insult to the medial meniscus requiring excision. Another cause may be due to the fact that meniscal injuries may be difficult to visualize grossly.^2,28

The results of this study revealed that overall, the success rate of the LFS repair in this population was 73.7%, which was lower than the previously reported 77–82%.⁶ Once the FW failures were removed, the success rate of the LFS procedure was 89.5%, which was higher than reported.⁶ Statistically, it was found that FW passed around the femoral fabellar ligament was significantly more likely to fail compared with NLL.

Because all FW failures were due to the suture pulling through the femoral fabellar ligament, the authors’ hospital now uses a bone anchor when employing FW rather than passing it around the femoral fabellar ligament. The use of metal anchors for FW implantation is similar to the materials used during the tightrope procedure. When metal anchors were used in two of the included cases, the stifles were either stable or had minimal laxity postoperatively. Those results are in agreement with Guénégo et al. (2007) who evaluated bone anchors placed in the lateral femoral condyle during a modified LFS procedure.³ They found that 91% of the dogs were considered sound at both a walk and trot postoperatively.³ Burkhart et al. (1997) evaluated human patients that underwent treatment of shoulder injuries and demonstrated that the primary mode of failure during tendon repairs was the suture pulling through the tendon.²⁹ The findings of the current study are in agreement with the results of Burkhart et al. (1997) and add to the ongoing debate as to whether the increased stiffness of new polyblend polyethylene sutures lead to the suture cutting through the soft tissues.²⁹ To date, no complications have been identified using FW passed through a bone anchor during the LFS procedure in the authors’ hospital.

One of the cases that failed had an ideal body weight. That 12 kg dog had one strand of 80 pound test NLL crimped. The larger NLL could have contributed to the failure due to the suture cutting through the femoral fabellar ligament, inadequate crimping of the larger sized crimp, or because the animal may have been overly active during the postoperative period. It should be noted that those suggestions are only speculations because the mode of failure was not recorded.

Several limitations of the current study exist that can be attributed to its retrospective nature. There was a small number of cases, and there was the possibility of incomplete information in the medical record such as underreporting of complications including stifle instability, failure of the referring veterinarian to report complications or stifle instability. Several factors in this study were subjective, such as BCS and amount of laxity. In addition, the amount of variation in the LFS procedure and physical examinations due to individual surgeon discretion could have occurred, and there was a lack of knowledge regarding the degree of owner compliance in terms of postoperative cage confinement, performance of physical rehabilitation, or follow-up care. Finally, all pertinent physical and orthopedic examination findings may not have been recorded. Further studies are needed to evaluate a larger number of cases employing FW placed through a bone anchor compared with NLL in dogs treated with LFS.

Conclusion

CCLR is a common condition resulting in hind limb lameness and DJD in canine patients. The LFS technique is a popular procedure used for surgical treatment of CCLR. In this study, FW was significantly more likely to fail compared with NLL (P = 0.0379). FW was 6 times more likely to fail versus one strand of NLL and 32 times more likely to fail than two strands of NLL. Because all FW failures were due to the suture pulling through the femoral fabellar ligament, the authors’ hospital now uses a bone anchor positioned in the lateral femoral condyle rather than passing FW around the femoral fabellar ligament. Using this modification in clinical cases, stifles were either stable or had minimal laxity postoperatively. Future studies evaluating FW that is passed through a bone anchor versus NLL for a larger number of patients with LFS are needed.