Choosing cruciate rupture repair methods (Proceedings)

Cranial cruciate ligament rupture is a common cause of hindlimb lameness in dogs and is seen in cats as well.  Patients can be managed without surgery with exercise restrictions, body weight management and pain medications.  However, a better prognosis is achieved when the patients are less than 15 kg.  Also, the presence of a meniscal tear or concurrent patellar luxation makes medical management less successful. 

When surgical stabilization is opted for, the veterinarian is faced with a plethora of options.  The key is to find the balance of what the surgeon is comfortable with and what the best option is for the patient.  If the best possible option is chosen by the veterinarian but they do not have the training or experience to perform the procedure correctly, the potential complications can be disastrous.  The fact that several options are available to address the same surgical problem indicates that no one procedure is perfect for all cases and all situations.  Being current on the options and the data published is necessary to make the most educated decisions for your patients. 

There are innumerable intraarticular repair methods in the literature and the theory behind these is the basis for human ACL repair.  However, due to the degenerative nature of CCLR in dogs, these techniques have fallen out of favor.  Intracapsular techniques are degraded by the inflammatory mediators seen in stifles with osteoarthritis (OA).  The result is an unstable surgical repair and a lower level of function due to lameness with progressive OA.  Long term outcomes with intracapsular repair are not as good as extracapsular techniques.  However, if this is the procedure you are most comfortable with, and the owner will not accept referral to a surgeon, than this may be the “best” option for that patient. 

The original extracapsular prosthetic stabilization has gone through many revisions and adjustments since its inception in 1966.  The current technique is usually a lateral circumfabellar-tibial suture.  Bone anchors can be used on the femur instead of around the fabella if preferred.  The tibial suture is typically passed through a tibial bone tunnel located at the level of the long digital extensor tendon groove. 

Sutures can be tied or crimped.  Nylon leader, monofilament or braided sutures are currently used, while stainless steel is no longer recommended due to cycling failure.  The type of knot thrown can affect structural strength of some suture materials.  For instance a surgeon's throw may weaken knot security, but a square knot where the first throw is clamped to maintain tension while the rest of the knot is tied has not shown to weaken a number of suture materials.  Crimps are available for use with specific prosthetic materials but are not interchangeable with sizes or types of sutures. 

Crimp placement requires addition equipment and slippage is found to occur in 8% of cases.  However crimp placement has less elongation and more stiffness than a clamped square knot.  The loop configuration of the prosthetic material has also been shown to influence performance.  But in most cases, the tension of the suture is not conserved for longer than six to eight weeks after surgery.  Most commonly the strength is lost through elongation or rupture.  Despite positive clinical results, these techniques do not achieve normalization of stifle biomechanics to the cruciate deficient stifle and may not be the best option especially for large or overweight dogs.

Isometry and a stiffer prosthesis are the potential benefits of the TightRope CCL®.  The FiberTape (Arthrex Vet Systems) used in the system has shown significantly greater stiffness and ultimate load to failure forces. However this puts the joint at risk if the prosthesis is over-tightened or if poor isometry is created with inaccurate bone tunnels.  In a recent study the TightRope CCL® resulted in outcomes similar to that of the TPLO (Tibial Plateau Leveling Osteotomy).  A multicenter study has shown 94% of dogs having good to excellent outcomes with a 9% major complication rate including implant failure, infection, and meniscal tear. 

The TPLO surgery has historically been promoted for use in active large breed dogs or dogs with excessive tibial plateau slope.  Several studies have found similar results six months postoperatively when comparing the extracapsular suture and the TPLO.  However, the extracapsular dogs tended to be lighter and begin physical rehabilitation earlier than the TPLO group.  It is possible that larger dogs treated with a lateral suture may have had a worse outcome.  Clinically the TPLO dogs are believed to bear more weight sooner while the extracapsular dogs hold the leg up for 1-2 weeks.  The TPLO surgery involves specialized equipment and is described as having a steep learning curve. 

Utilizing arthroscopy or a mini-arthrotomy is proposed to minimize patient discomfort over the arthrotomy used with the lateral suture technique. Complication rates with the TPLO are lower with unilateral or staged procedures ranging from 12-21%.  A less specialized version of the TPLO is the Cranial Closing Wedge (CCW) which also lessons the tibial slope to negate tibial thrust, but also alters the mechanical axis of the tibia with a forward shift.  This changes the biomechanics of the tibia and may change weight distribution on the menisci.  The technique utilizes a saw but does not require a specialized bone plate.  It can be combined with the TPLO in cases with excessive (greater than 30°) tibial slope.     

The Tibial Tuberosity Advancement (TTA) is a newer procedure that eliminates cranial tibial thrust.  The mechanics place the patellar tendon force perpendicular to the weight-bearing force through the stifle.  A bone graft appears to be beneficial for speeding the healing of the boney defect created.  Specialized equipment is required but the procedure is technically less challenging and perhaps faster than the TPLO.  Long term studies show similarities between the TPLO and TTA, although the TTA appears to take longer to heal the osteotomy and cannot be used in cases with excessive tibial slope.  Implant designs are still changing with regards to fork design and available cage sizes for advancement.  The overall complication rate for TTA ranges from 25-59%, including minor complications. 

All of the osteotomy techniques require strict confinement while the bone heals.  This may be a deciding factor between techniques in ill mannered dogs or outdoor-only animals.  While physical rehabilitation is started early in all dogs, the postoperative care for the osteotomy dogs can be weeks to month longer than the lateral suture technique.  However, early return to function is vital for joint health, and to rebuild muscle mass and regain lost bone density.  Service or therapy dogs who are kept in a controlled manner will likely benefit from the quick return to weight bearing of the osteotomy procedures, with their daily activities being as controlled and calm as most rehabilitation programs. 

The existence of so many variations on the same surgical problem has shown no concrete superior method for treating our veterinary patients exists to date.  Research is ongoing to illustrate the pros and cons of the newer techniques to determine the best options.  Kinematic and objective controlled multi-center prospective trials are needed.  But patient needs and variation in fibrosis, activity level, meniscal damage and age along with owner financial constraints will all play into the decision of the “right” treatment modality.