Tibial plateau leveling osteotomy--is it really more effective (Proceedings)

‘‘Rupture of the cranial cruciate ligament is seen for the most part in active jumpers, and especially in those individuals (dogs) having the defect in conformation where the sti?e and tarsus are carried in over- extension. The absence of the normal ?exion angle of these joints in the standing position appears to be a predisposing cause. Fixation (immobilization) for from three to six weeks will in most cases result in a recovery that at least approximates perfection as far as function is concerned.''–Erwin Schroeder 1939

Background

CCL injury is one of the most common injuries encountered by veterinarians, and is by far the most common cause of lameness of the sti?e joint1. Early surgical stabilization is generally recommended, particularly in dogs weighing more than 15kg, because poor results are reported for most dogs that undergo non-operative management2. The Wall Street Journal recently reported that the incidence of cruciate ligament surgery in dogs actually exceeds that in humans in the USA, and the estimated repair costs of these surgeries was about 1.23 billion dollars in 20033. Despite these staggering numbers it was recently demonstrated that not a single surgical technique consistently returns dogs to normal function4.

Management of CCL injury by stabilization of the sti?e with a lateral fabellotibial suture (LSS) has been performed for over 30 years, and is generally considered to be quick, affordable, and safe. Problems with implant reaction and infection were initially reported to be common, but dogs in these early studies had been implanted with multi?lament suture of questionable sterility from cassettes. Implant loosening continues to be an issue, but problems have decreased with recent identi?cation and utilization of more isometric attachment sites5.

It is often suggested that the great majority of dogs weighing less than 20 kg will return to near normal function after LSS, but larger and more athletic dogs will only have a fair outcome. Despite common usage of this surgical procedure for more than a third of a century, neither of these assumptions has ever been veri?ed in a controlled clinical study. In fact, the only quantitative data available suggests that in at least one large breed dog (the Labrador retriever), animals will obtain a very respectable 95 percent of normal weight bearing by six months after surgery6.

History of TPLO

Tibial plateau leveling osteotomy (TPLO) was first described by Dr. Barclay Slocum about 18 years ago7. Originally both the procedure and implants required to perform the procedure were patented. Surgeons had to be certified to perform TPLO, and were required to sign a waiver agreeing not to teach it to others. When patent rights expired a number of years ago, the procedure became much more widely available. Recently, TPLO seems to have taken on a life of its own, with instrument companies ?ocking to the fray to produce new implants of every shape, size, and color. Popularity of this technique has now increased to the point that in some hospitals it is the most commonly performed treatment for CCL injury in all sized dogs and even cats.

TPLO Theory

The key to understanding TPLO is in recognizing the forces generated in the stifle during locomotion.  When a dog bears weight, ground reaction forces and extensor muscle forces generate compressive forces on the articular surface of the tibia (figure 1). Because the tibial plateau is sloped caudally (line AC is not parallel to line AB), shear is created which tends to drive the femur caudally and the tibia cranially (large arrows). This “cranial tibial thrust” (CTT) is proportional to the caudal slope of the tibial plateau (?BAC), and is restrained by the cranial cruciate ligament in the normal knee.

The intent of TPLO is to level the tibial plateau (make line AC parallel to line AB) such that cranial tibial thrust is neutralized even in the cruciate deficient knee. After TPLO, when the patient bears weight, the tibia does not tend to slide forward, so a CCL is not required.

TPLO Procedure

TPLO essentially involves making a circular osteotomy in the proximal portion of the tibia just below the knee, rotating the osteotomy into a new position determined by preoperative radiographs, and repairing the osteotomy with a specially designed metal plate and screws (figure 2,3). The technique utilizes an arc shaped saw blade and osteotomy jig to accomplish rotation of the articular surface of the proximal tibia.

TPLO can be performed with or without arthrotomy for “early” partial cranial cruciate ligament tears. Opening the joint in every case allows the surgeon to explore for abnormalities not possible to detect on physical examination, but studies have indicated fewer complications and earlier recovery if the joint is not explored. Instrumentation is presently available to perform TPLO on any sized dog, or even cats.

TPLO is best performed with an assistant, and can easily be done in 60-90 minutes with experience. There is a substantial learning curve, and initial procedures may take several hours to perform correctly. It has been reported that bilateral TPLO can be performed at the same surgical episode, but this option may result in an increase risk of complications, and is not recommended.

Functional Outcome in Dogs with TPLO

Initial subjective evaluations of dogs with TPLO suggested very encouraging results. Dr. Slocum indicated 94% of dogs will have excellent or good results, where excellent is defined as indistinguishable from normal, and good is defined as some slight abnormality such as a crooked sit, but the animal is pain free and can still perform all functions7. In a limited prospective clinical trial comparing 15 dogs with lateral suture stabilization to 15 dogs with TPLO, TPLO compared very favorably in the first 6 months after surgery8. Most if not all surgeons performing TPLO suggest very good clinical outcomes.

Despite an almost universal consensus among surgeons that TPLO is a good procedure, there is not a single piece of scientific evidence to support the belief that it is clinically superior. Conzemius examined peak vertical force values in dogs 2 and 6 months after surgery with intra-capsular stabilization (ICS), lateral suture stabilization (LSS), and TPLO techniques6. No significant difference was detected between dogs that received TPLO or LSS, whereas both groups performed better than dogs with ICS repairs. Only 11% of dogs with TPLO, and 15% of dogs with LSS were indistinguishable from normal controls on a force plate.

In a separate study, peak vertical forces were compared in 65 dogs after either TPLO or LSS up to 24 months after surgery9. Results indicated no significant difference between groups at any time interval.

I have always argued that a major limitation of each of these studies is that the dogs were walked over the force plate after rest, and perhaps a significant difference would have been detected after a period of exercise. It is also possible that differences in the two groups would have been noticed with longer follow-up. Despite these study limitations, it is clear that contrary to the statements of many veterinary surgeons, TPLO is certainly not markedly superior in clinical outcome to the less expensive, less risky, and more easily performed LSS.

Development of osteoarthritis after TPLO

Several studies have evaluated the progression of osteoarthritis (OA) after TPLO with conflicting results9,10. It is clear that OA progresses after TPLO, but some studies suggest that the rate of progression is less than LSS while others indicate no significant difference. In any case, level of OA correlates poorly with clinical outcome in dogs with CCL injury11.

Complications After TPLO

Tibial plateau leveling osteotomy (TPLO) is a highly detailed and technical procedure that requires significant surgical expertise and a regular caseload to develop and maintain surgeon proficiency. Because of increased surgical time, increased surgical dissection, the addition of an osteotomy and a metallic implant, the potential for increased complications exists.

The overall complication rate after TPLO is reported to be from 15% to 34%, with a second surgery required to manage the complication in from 5% to 9% of cases12,13,14. In comparison, complications are recorded in about 16% of LSS procedures, with an expected re-operation rate of 4%15. Although most complications after TPLO are suggested to be minor or easily correctible, this is not always the case. Infection rate after TPLO is about 6.0% and implant loosening or failure is also reported with some frequency.

Surgical Decision Making

The advent of TPLO has caused tremendous debate among veterinary surgeons with regard to which surgical procedure is most appropriate for which dog, especially in dogs over about 20kg. There are surgeons in the United States that recommend TPLO as the best option for essentially every dog, and others that never recommend TPLO. Owners are faced with a multitude of information sources and opinions ranging from their private practitioner, referral surgeon, and university teaching hospital to breeders, neighbors, and friends. In addition Internet searches are frequent. The following guidelines may be helpful in surgical decision-making:

1.        TPLO is best suited for large, young, athletic dogs where the difference between      85% and 95% of normal may be appreciated. Field trial dogs, hunting dogs, and show dogs may be excellent candidates. In my opinion, improved outcome compared to traditional methods is subjectively obtained in 50-75% of these patients.

2.        There is little evidence to support TPLO surgery in very small dogs or cats.

3.        TPLO may be particularly indicated in dogs with very steep tibial plateau slopes (>30 degrees).

4.        Traditional surgical techniques provide a fair to good outcome in most dogs, and can be offered as a reasonable alternative in any patient.

5.        TPLO is expected to be associated with a least some increased risk of complications, and a definite increase in cost. Owners should not choose TPLO if they cannot afford the risk of a problem requiring increased financial investment.

6.        At least 33% of dogs (and close to 75% in some breeds) will tear their opposite CCL within several years of the first. Owners should be apprised of this possibility during decision-making. Some owners may feel that if two injured legs are likely, every attempt should be made to get the best possible outcome, and opt for TPLO surgery. Alternately, financial considerations may dictate choice of a traditional surgical technique.

References

Ness MG, Abercromby RH, May RH, et al. A survey of orthopaedic conditions in small animal veterinary practice in Britain. Vet Comp Orthoped Traumatol 1996;9:43-52.

Vasseur PB. Clinical results following nonoperative management for rupture of the cranial cruciate ligament in dogs. Vet Surg 1984;13:243-246

Helliker K. This joint problem makes dogs, owners, weak in the knees. Wall Street Journal 2006:A1.

Aragon CL, Budsberg SC. Applications of evidence based medicine: cranial cruciate ligament repair in the dog. Vet Surg 2005;34:93-98.

Roe SC, Kue J, Gemma J. Isometry of potential suture attachment sites for the cranial cruciate ligament deficient canine stifle. Vet Surg 2008;21:215-220.

Conzemius MG, Evans RB, Besancon MF et al. Effect of surgical technique on limb function after surgery for rupture of the cranial cruciate ligament in dogs. J Am Vet Med Assoc 2005;226:232-236.

Slocum B, Devine T. Tibial plateau leveling osteotomy for repair of cranial cruciate ligament rupture in the canine. Vet Clin North Am 1993;23:777-795.

Schwarz PD. tibial plateau leveling osteotomy: A prospective clinical comparative study. Proc Ninth Annual Amer Coll Vet Surg Symposium 1999;379-380.

Au KK, Gordon-Evans WJ, Dunning D. et al. comparison of short- and long-term function and radiographic osteoarthrosis in dogs after postoperative physical rehabilitation and tibial plateau leveling osteotomy or lateral fabellar suture stabilization. Vet Surg 2010;39:173-180.

Lazar TP, Berry CR, Dehaan JJ, et al. Long-term comparison of tibial plateau leveling osteotomy versus extracapsular stabilization for cranial cruciate ligament rupture in the dog. Vet Surg 2005;34:133-141.

Gordon WJ, Conzemius MG, Riedesel E, et al. The relationship between limb function and radiographic osteoarthrosis in dogs with stifle osteoarthrosis. Vet Surg 2003;32:451-454.

Pacchiana PD, Morris E, Gillings SL, et al. Surgical and postoperative complications associated with tibial plateau leveling osteotomy in dogs with cranial cruciate ligament rupture: 397 cases (1998-2001). J Am Vet Med Assoc 2003;222:184-193.

Priddy NH, Tomlinson JL, Dodam JR, et al. Complications with and owner assessment of the outcome of tibial plateau leveling osteotomy for treatment of cranial cruciate ligament rupture in dogs: 193 cases (1997-2001). J Am Vet Med Assoc 2003;222:1726-1732.

Fitzpatrick N, Solano MA. Predictive variables for complications after TPLO with stifle inspection by arthrotomy in1000 consecutive dogs. Vet Surg 2010;39:460-474.

Casale SA, McCarthy RJ. Complications associated with lateral fabellotibial suture surgery for cranial cruciate ligament injury in dogs 363 cases (1997-2005). J Am Vet Med Assoc 2009;234:229-235.