Managing cruciate disease–Where are we now? (Proceedings)

A controversy exists in the veterinary field as to which surgical technique is the best to repair a dog's knee that has a cranial cruciate ligament (CrCL) injury. There are many accepted surgical techniques described (over 40 different methods) to correct the CrCL-deficient joint. Results of all of these different surgical repairs indicate a reported success rate of approximately 90% (good to excellent function), regardless of the surgical technique used. A smaller number of these surgical techniques are more commonly in use today with published success rates approaching 95%. The biggest change-to-date is the trend to perform the "functional stabilization techniques" or "geometric stabilization techniques", such as the TPLO or TTA, which have become the most frequently performed procedures in referral institutions – including at Tufts University, where they are the most common surgical techniques we perform.

Adding to this controversy, however, is that currently there is no documented evidence (published scientific reports) of any superiority to any one of these surgical techniques over the long-term, and the specific technique chosen primarily depends upon individual surgeon preference (ACVS survey 1999). There has, however, been much anecdotal evidence (supported by a small unpublished clinical pilot study at Tufts) that there may be a quicker recovery (return to full function) in a shorter period of time with the functional techniques (TPLO or TTA). The rapid return to function is the primary reason that these latter techniques are more frequently performed at Tufts. In addition, there is anecdotal evidence from owner reports (not scientific data) that dogs with these techniques do better, interpreted as retuning to work (hunting, field trials), better than dogs with the historical techniques (extracapsular and intra-articular stabilizations).

The primary surgical techniques in use today by most veterinary surgeons involve some form of the lateral suture stabilization and the osteotomy techniques. The intra-articular replacements have apparently lost popularity, but an argument can be made that this area has not been adequately evaluated, and perhaps it is the future of repair in veterinary medicine; currently, it is the technique of choice in humans.

Extracapsular stabilization (lateral suture/imbrication)

The lateral suture stabilization procedure was first introduced in 1970. There have been numerous modifications of the original procedure, but the basic premise of the procedure remains unchanged, i.e., an extra-articular constraint on the lateral side of the joint that prevents cranial tibial subluxation. Continued success is predicated on the development of periarticular fibrous connective tissue to stabilize the joint long-term. The original description that remains most popular is passing this extra-articular restraint from the lateral fabella to a point on the tibial tuberosity (through 1-2 bone tunnels). A newer technique (Cook 2008) recently has been proposed as a further improvement, the TightRope® (Arthrex Vet Systems; Frechen, Germany), whereby the points of suture anchorage are postulated to be placed at isometric positions; secondly, the material used (FiberWire®, FiberTape®; Arthrex Vet Systems) has been shown to have significantly superior strength compared to previously utilized suture materials.

The major advantages proposed for this method of stabilization include its simplicity and ease of the surgical technique, short operative time, good results, low complication rate and low cost. Some of the proposed disadvantages of anchoring this suture have been with regard to the non-isometric positioning of the lateral fabella and bone tunnel(s) in the tibial tuberosity. This concept originally was investigated in an experimental study (Hulse 2006) that attempted to define the preferred points of attachment for such a lateral suture. This led to a number of procedures in which the points of attached were secured with bone anchors; however, suture breakage became an issue (at the anchor/suture interface). The TightRope® procedure addressed the latter issue by devising a technique whereby the points of attachment at these sites were bone tunnels rather than anchors at these same points. In addition, as previously noted, the material used was significantly stronger than previous suture materials. Finally, this technique has been advocated as a minimally invasive method whereby the suture can be applied essentially through stab incisions. This technique has been proposed to be a significant improvement in the application of lateral suture stabilization.

There is no question that this technique remains the most simple of the group discussed. Operative times have generally been reported to be <1 hr, and results reported to be good or excellent in 85-93% of the cases. Complications have been reported <20%, with re-operation in <8%. Cost is minimal – simply the suture material, or the addition of ~7-17€ if a crimp-clamp system is utilized (nylon suture material). The costs do increase for the suture material when performing a variety of the Arthrex System CrCL repair techniques: FiberWire® ~23€ [Canine CrCL Repair Kit], FiberWire® with corkscrew anchor [Canine CrCL Repair Anchor System] ~300€, TightRope® (FiberTape® ~145€; in addition, there is some additional expense for technique-specific implants for the TightRope® technique: scissors, guidewire, cannulated drill, suture tensioner – estimated 400€). There is no comparable data for the TightRope® procedure; however, one small preliminary short-term study indicates a complication rate of 12.5% (Cook 2010). The recommendations for this technique have included the bigger/heavier dogs, this despite any longer-term data, and recent published reports that the lateral suture stabilization (standard suture technique) has increased complications in both younger (more active) and heavier dogs (Casale 2009).

The primary issues with this technique are multiple. Is there truly an isometric point that is extra-articular? Despite the study's (unpublished, Hulse 2006) indications that there are preferential suture locations, this data is not consistent with a more recent published study (Roe 2008); furthermore, these points cannot be accounted for uniformly in all dogs, i.e., differing conformations between the femurs and tibias. This information also appears to be borne out by a more recent study evaluating attachment sites and suture tension (Fischer 2010). Also somewhat rhetorically, if in fact there exists such an isometric position outside the joint, what anatomic structure does it mimic? The only true isometric position at the joint is in its center, either the CrCL or caudal cruciate ligament (CaCL), and even these structures are not a single fiber, but are composed of millions of strands. Based upon this fact alone, it is not surprising that instability recurs in the joint, as a result of stretching of the implant that attempts to mimic the CrCL – or creep into the soft tissues, breakage, or loss of the anchor point. Furthermore, placement of this suture is not functional, as it minimizes internal rotation (the normal screw-home mechanism that allows internal rotation with stifle joint flexion) and turns the stifle joint into a simple hinge. Finally, this technique also does not address issues related to angular deformities (e.g., tibial varus or valgus, increased tibial plateau angle) should they also be present.

Osteotomy techniques (tplo, tta)

The TPLO was introduced ~1998, and the TTA ~2003. There has been much anecdotal evidence presented that these techniques are comparable, and offer a better alternative to the lateral suture stabilization procedures. Both of these techniques [and others: cranial closing wedge osteotomy (CCWO), triple tibial osteotomy (TTO), etc.] all provide stifle joint stability by altering the stifle joint anatomy, attempting to take advantage of the forces present to intrinsically neutralize cranial tibial thrust. Although their premise (proposed mechanisms of action) may appear to be different, there is evidence to suggest that they all are effective based upon a single mechanism, re: alteration of the patellar tendon angle, which alters the tibiofemoral shear forces, i.e., elimination of the cranial tibiofemoral shear force in stifle joint extension.

The major advantages proposed are that these techniques can be used in the most active (athletic) dogs of large size with good to excellent results (that population of dogs with the greatest number of complications with a lateral suture stabilization). Additionally, there are many anecdotal reports that with these techniques the recovery is very quick, and that postoperative weight-bearing is not unusual within the first 24 hr after surgery. Finally, there is additional anecdotal evidence that this group of athletic dogs perform close to their pre-injury status (hunting, field trial, etc.), which has not been the case historically with other techniques.

The difference between the TPLO and TTA may indicate that the TTA corrects the cranial tibiofemoral shear force closer to the neutral point as compared to the TPLO. This may have some ramifications on the status of the CaCL, which becomes the primary stabilizer to the joint postoperatively. There have not been, however, and clinical reports of untoward effects on the CaCL despite experimental findings that support this claim. The TTA also appears to decrease retropatellar pressure and also (presumably) other joint contact pressures, and patellar tendon force. The implications here may affect the postoperative findings, e.g., of patellar tendonitis postoperatively in TPLOs (reported incidence ~80%) and meniscal injuries, as the TTA appears to better return intra-articular contact pressure to normal. Once again, however, there have not been clinical reports demonstrating these possible negative effects despite experimental findings that support these claims. As an adjunct, there is much controversy regarding the menisci, and whether – despite the experimental results – the menisci should be preserved or a meniscal release be performed. It appears that meniscal injury can occur after either of these techniques, but the true incidence reported remains quite variable.

Both the TPLO and TTA are complex procedures, requiring appropriate preoperative planning and accurate execution of the details of the procedure. As originally described, TPLO is a relatively invasive procedure where there is abundant circumferential dissection of the entire proximal aspect of the tibia, and a greater potential for injuring some vital structures around the joint. There also are a number of surgical technical errors that can occur with TPLO. Anecdotally, TTA is considered by many to be a much simpler procedure than the TPLO. Similar comments regarding soft tissue dissection and limited coverage in the area of the proximal tibia may be made for the TTA; however, the surgical dissection is confined to cranial portion of the bone; therefore, it has been suggested that there is a much more limited possibility for iatrogenic surgical injury with TTA. It may be argued that despite TTA also being a relatively complex procedure, there are fewer unrecognized pitfalls that may result in postoperative problems. Regardless, much of this is supposition as there are no reports of objective comparisons of the two surgical techniques comparing these factors and their possible effects.

There are a few published reports that document the complication rate of TPLO (comprising a total of 1772 cases), reporting an overall complication rate of 26.3%. A re-operation rate was reported in ~ <10% of the cases. Similarly, published reports that document the complication rate of TTA (249 total cases) report an overall major complication rate of 12.3-38.0%. A re-operation rate of 11.3-14.0% was reported. The only unifying similarity in all studies is that they represent early experience with both techniques. The majority of the complications appeared to be the result of technical errors, underscoring the technical difficulty of the procedures. At this time, review of the early results and complications of both the TPLO and TTA indicate that their outcomes are very similar. There are no published clinical reports that compare the techniques, much less the complications and outcomes with experienced surgeons that might allow a direct comparison of the techniques and their outcome.

The osteotomy techniques require a great deal of surgical expertise, and also necessitate a good working knowledge of fracture fixation principles in that plate fixation is required. Not only are there increased costs pertaining to increased surgical time, but also implant costs. In general, for an average large breed dog, the implant costs for a TTA are ~180€, whereas for a TPLO they are ~100-250€ depending upon which implant manufacturer is selected and whether locking screw fixation is applied.

The major disadvantages of these techniques include their technical difficulty – as an experienced surgeon is desired (although this does not always equate to a good result). Furthermore, there is an increased overall cost compared to, for example, the [standard] lateral suture technique, where an ~40% greater cost is present. Neither technique address all of the issues previously noted (e.g., angular deformities of tibial varus or valgus, increased tibial plateau angle), but both of these procedures can be so modified to address these issues. The TPLO is a more versatile technique compared to the TTA whereby these anatomic abnormalities may be addressed more easily with the osteotomy being performed. Even under these conditions, however, this may not be a simple procedure. Alternatively, the TTA is well suited to address simultaneous patellar luxation (and patellar Alta or Baja) as the osteotomy may be transposed medial/lateral or proximal/distal simultaneously with the advancement.

Intra-articular stabilization

This procedure was first popularized by Paatsama, using fascia lata as a replacement for the CrCL in dogs. Many modifications were performed [with skin, various tendons and ligaments (patellar tendon)]. The technique gained greater popularity/usage in 1979 after Arnoczky reported using the medial one third of the patella tendon and fascia lata, which was passed over-the-top of the lateral femoral condyle. This popularity was not long-lived as despite a revascularization and remodeling (~20 wks) of this autograft, mechanical stability did not always return to normal. In addition, this was a technically demanding procedure to perform as originally described using the patellar tendon; the latter resulted in various modifications using only fascia, but the disadvantage was lower graft strength. Various ligament augmentation devices have been suggested to address this issue, but were not met with success. Regardless of the method, and despite anecdotal reports of good success, there are no published reports of long-term outcome of these techniques. This is compounded by a relatively recent clinical study compared the intra-articular, extra-articular and tibial osteotomy stabilizations, with inferior results for the intra-articular technique (Conzemius 2005). This technique no longer appears to be routinely applied in dogs.

Prosthetic grafts (e.g., Gore-Tex, Dacron, etc.) also have been tried in the dog, but have been associated with high complication and failure rates. Not only are there issue with revascularization and restitution of mechanical integrity over time, but issues regarding immediate postoperative fixation. The latter must minimize graft motion and resist slippage. Placement in an isometric position also must be considered. The over-the-top position (lateral femoral condyle) proximally, and cranial on the tibial tuberosity distally appear to be most appropriate positions; however, a bone tunnel at the insertion of the CrCL also has been proposed as the more anatomic position. There currently is debate about a proximal femoral tunnel as preferred to the over-the-top position in dogs, as the former position is standardized in humans. The bone-ligament-bone preparation has traditionally been accepted as the gold standard (Hospodar 2009). It must be recognized that in the dog historical investigations have indicated that the femoral tunnel technique has a high failure rate when compared to the over-the-top (OTT) position (Montgomery 1998). The femoral condyle in the dog has greater flare than in humans, which makes finding the appropriate location of the femoral tunnel more difficult. This assessment was the initial rationale of the OTT procedure as originally described in the dog, i.e., less variability of the graft placement (Arnoczky 1979). It also was demonstrated that the OTT position of the graft resulted in no change to the instant-center-of-motion of the joint through varying degrees of flexion/extension (Arnoczky 1977).

There are many issues that need to be addressed, but intuitively, if the CrCL could be replaced it would function in the identical manner of the native CrCL, which theoretically would ameliorate the postoperative issues with the meniscus and presumably the lack of development of osteoarthritis, which ultimately is considered the "gold standard" of success – and which currently does not exist in any of the techniques currently in use. Unfortunately, this area of investigation in the dog has received little attention.

The ideal prosthetic has yet to be developed, but there is renewed interest because of technological advances in materials design. Perhaps one of the newer modalities – biologic scaffolds – holds some promise (e.g., silk scaffolds) (Richmond 2010). In this scenario, the scaffold retains sufficient mechanical strength immediately after implantation such that mechanical integrity is immediately restored, and over time the scaffold is replaced by fibrous ingrowth that gradually replaces the graft while maintaining its integrity, i.e., the remodeling process allows a simultaneous increase in strength of the native tissue at the same rate of decline of the strength of the resorbable graft. This approach may be the future of treatment for the CrCL deficient stifle joint, either as a stand-alone device or a ligament augmentation device.

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