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Tibial plateau leveling osteotomy--part 2.

689 P art 1 of this series dealt with the history and theory behind the development of the tibial plateau leveling osteotomy (TPLO). At the heart of this theory is the cranial to caudal tibial plateau downward slope or angle and the role it plays in producing the cranial thrust of the proximal extremity of the tibia (cranial tibial thrust) when a stifle with a deficient cranial cruciate ligament ([CCL] deficient stifle) is weight-bearing. Much recent research has concentrated on the angle of the tibial plateau: Its significance, its measurement, and its role in the etiology of CCL rupture. The first problem is that measurement of the tibial plateau angle is not as repeatable and consistent as one would like. Significant variations in tibial plateau slope measurement can occur, if less than perfect lateral stifle radiographs are obtained or if radiographic reference points are not precisely identified and marked. Most disconcerting is that significant variation in slope measurement has been documented among different individuals, even when they may be well experienced in the measurement procedure (1,2). Obviously, variation in slope measurement can importantly affect the surgical procedure, but there is no current evidence to link measurement inconsistency with negative surgical outcome. One of Barclay Slocum’s early theories was that CCL rupture was more likely to occur in dogs with a greater tibial plateau slope. On this point, the current data is somewhat conflicting. While a significant difference has been demonstrated in the mean tibial plateau slope between a breed noted to be CCL-rupture “resistant” (greyhound) and the “poster breed” for CCL rupture (Labrador retriever) (3), the Labradors with CCL rupture actually had slightly lesser angles than did the Labradors without CCL rupture (3). In another survey, no significant difference was found between the tibial plateau slope in Labradors with CCL rupture and those without (4). In yet another interesting “angle” on this debate, the tibial plateau slope of dogs with ruptured CCL was compared with the mean slope of large dogs, 11 y and older, without stifle lesions: Dogs with normal stifles that were older than 11 y were unlikely to develop CCL rupture; thus, they represented a low-risk population. Their tibial plateau angles were significantly less than those dogs with CCL ruptures (5). And what does one make of the observation that standing lateral radiographs show the standing tibial plateau angle does not vary significantly from 0 degrees, regardless of the breed (3)? In other words, regardless of the tibial plateau angle, most dogs seem to stand in such a way that the tibial plateau is nearly parallel to the ground. But does that make the concept of cranial tibial thrust during locomotion in the CCL-deficient stifle any less valid? If relatively greater tibial plateau angles predispose to CCL rupture in some dogs, might one consider prophylatic TPLO? The current state of knowledge would fall far short of supporting such a recommendation, except in the case of partial CCL rupture, where it appears that TPLO may prevent complete rupture (6). Along with accounts of TPLO success rates and theories on why and how the procedure works, there are reports that describe complications and complication rates. Two major reports in the last year produced several key conclusions (7,8). Complication rates (20.6% and 28% of 253 and 397 TPLOs, respectively) were high in comparison with other CCL repair procedures. This was due in large part to the fact that TPLO is a demanding and invasive surgical procedure. “Major” complications, however, defined as infections, loose or broken implants, fractures of the tibial tuberosity or fibula, or complications requiring a second surgery or ongoing treatment, were not significantly greater than those that have been reported for other CCL repair procedures (8). Complications in addition to those listed include intraarticular placement of screws; hemorrhage; and incisional complications, such as swelling, bruising, wound breakdown, seromas, and hematomas. Two complications that have commonly been identified are medial meniscal damage subsequent to surgery, for which the meniscal release procedure is now advised, and patellar tendon desmitis (7,8). The TPLO produces a tibial tuberosity that is separated from the main portion of the proximal extremity of the tibia. The placing of the insertion of the patellar tendon “on an island” in this manner inevitably produces thickening of the patellar tendon and occasionally causes lameness. Three factors were linked specifically to the complication rate in TPLO patients: 1) Greater numbers of complications were seen in dogs where bilateral TPLOs were done during the same general anesthetic (7); 2) performing an arthrotomy at the same time as a TPLO has been associated with a higher complication rate (8) (while some surgeons prefer to do an arthrotomy to visualize Animal Clinic of Regina, 1800 Garnet Street, Regina, Saskatchewan S4T 2Z2. ORTHOPEDICS ORTHOPÉDIE