Accuracy of Tibial Osteotomy Placement Using 2 Different Tibial Plateau Leveling Osteotomy Jigs

Accuracy of Tibial Osteotomy Placement Using 2Different Tibial Plateau Leveling Osteotomy JigsChristopher J. Tan1, BVSc, MACVSc, Diplomate ECVS, Mary Sarah Bergh2, DVM, MS, Diplomate ACVS& ACVSMR, Mark A. Schembri3, BVSc, MACVSc, MPH,and Kenneth A. Johnson1, MVSc, PhD, FACVSc, Diplomate ACVS & ECVS1 University Veterinary Teaching Hospital, University of Sydney, Sydney, Australia ,2 Department of Veterinary Clinical Sciences, College ofVeterinary Medicine, Iowa State University, Ames, Iowa and 3 Harvard School of Public Health, Harvard University, Boston, Massachusetts

Corresponding AuthorDr. Christopher J. Tan, BVSc, MACVSc,Diplomate ECVS, University VeterinaryTeaching Hospital Sydney, Evelyn WilliamsBuilding B10, Faculty of Veterinary Science,University of Sydney, Sydney, NSW 2006,Australia.E‐mail: [email protected]

Submitted October 2012Accepted February 2013

DOI:10.1111/j.1532-950X.2014.12173.x

Objective: To report the accuracy of osteotomy position in dogs undergoing tibialplateau leveling osteotomy (TPLO) and to evaluate the effect of 2 different TPLO jigand saw systems on tibial osteotomy position.Study Design: Retrospective case series.Animals: Dogs (n¼ 124; 134 TPLO).Methods: Medical records (2004–2005; 2008–2011) and stifle radiographs of 2groups of dogs that had TPLO to treat cranial cruciate ligament disease were reviewed.One group had a TPLO performed using an alignment jig system alone (Slocum group),whilst in the other group, an alignment jig system combined with a saw guide (Synthesgroup) was used. Postoperative radiographs were examined and the distance anddirection of the centroid of the osteotomy was compared to the intended osteotomyposition.Results: The absolute distance of eccentricity (DOE) in the Slocum group(5.6� 2.5mm) was significantly greater than that of the Synthes group(3.4� 1.8mm; P<.01). DOE was caudal and distal in 79% of cases.Conclusions: Most tibial osteotomies were centered at a point distal and caudal to theintended osteotomy position. Use of a TPLO system with a saw guide was associatedwith more accurate placement of the osteotomy and more accurate leveling of the tibialplateau.

Cranial cruciate ligament (CCL) rupture is one of the mostcommon causes of lameness in the dog, resulting in jointinstability, and progressive osteoarthritis.1 One of thecommonly used surgical techniques described to managethis disorder is the tibial plateau leveling osteotomy (TPLO),2

which involves alteration of the tibial plateau angle (TPA)to eliminate cranial tibial thrust during weight bearing.3,4

Cadaveric studies have demonstrated that reduction of theTPA to 6.5� 0.9° eliminates cranial tibial thrust, whereas anyfurther reduction in TPAwill increase the magnitude of caudaltibial thrust, which is counteracted by the caudal cruciateligament.3

Alteration of TPA by TPLO requires preoperativedetermination of the TPA, cylindrical osteotomy of theproximal tibia, rotation of the tibial plateau segment, andstabilization with a plate and screws.2 The position and radiusof the cylindrical osteotomy are planned from the preoperative

mediolateral radiographic projection. Initially, it was recom-mended by Slocum and Slocum2 that the centroid of theosteotomy be placed at a point overlying the femoral condyles.This was based on an assumption that this approximates thecenter of motion of the stifle; however, the canine stifle is not asimple hinge joint, and as such, it undergoes substantialtranslation during flexion. Therefore, the center of motion ofthe stifle is identified as an arc over the femoral condyles ratherthan a single point.5 Subsequent studies have demonstrated theimportance of placing the centroid of the osteotomy at the mostproximal point of the tibial long axis, which lies on the tibialplateau slope midway between the 2 intercondylar tubercles.6

Geometric analysis6 and cadaveric studies7 have shown thatfailure to position the centroid of the cylindrical osteotomyover this point results in translation of the proximal tibialfragment and imprecise alteration to TPA. Furthermore,inaccurate positioning and orientation of the osteotomy caninduce angular limb deformity8 and increase the risk of tibialtuberosity fracture.9

Despite the emphasis placed on accurate preoperativeplanning, to our knowledge, there are no published reports thatdocument the actual osteotomy position in relation to theintended position in a series of clinical TPLO cases.

Work performed at the University Veterinary Teaching Hospital,University of Sydney, Australia and the College of VeterinaryMedicine, The Ohio State University, Columbus, OH.Presented in part at the ACVSc (Surgery Chapter) meeting, GoldCoast, Australia, June 2009 and the ECVS annual scientificmeeting, Helsinki, Finland July 2010.

Veterinary Surgery 43 (2014) 525–533 © Copyright 2014 by The American College of Veterinary Surgeons 525

Custom cutting guides and jigs are designed to improvethe accuracy of osteotomies and these are commonly used inhuman and canine orthopedic procedures, such as total kneereplacement and tibial osteotomy.10–14 Cutting guides areclassified as being either a slotted type cutting guide, in whichthe blade is placed through a slot in the guide or an open guide,where the blade is placed against the surface of the guide.Although the use of cutting guides improves the accuracy ofosteotomies,15 inaccuracies are still common and these mayinfluence surgical outcome.13

Our purpose was to compare the intended osteotomyposition with the actual osteotomy position in a series of dogsthat had TPLO using 1 of 2 types of osteotomy jigs; 1 grouphad TPLO using an alignment jig system alone, and 1 group,an alignment jig system combined with a saw guide. Wehypothesized that TPLO performed with a jig system thatincorporated a saw guide would result in more accurate andprecise osteotomy positioning. It was also hypothesized that amore accurate osteotomy placement would be associated withmore accurate reduction of the TPA.

MATERIALS AND METHODS

Case Selection

Medical records of consecutive dogs with CCL rupture that hadTPLO using an alignment jig (Slocum Enterprises, Eugene,OR) between March 2004 and November 2005 at The OhioState University, Veterinary Medical Center were identifiedthrough the hospital’s surgical database. These dogs wereclassified as the “Slocum group.”

Medical records of consecutive dogs with CCL rupturethat had TPLO performedwith an alignment jig incorporating asaw guide (Synthes, Inc., Paoli, PA) from August 2008 toNovember 2011 at the University of Sydney, VeterinaryTeaching Hospital were identified through the hospital’ssurgical database. These dogs were classified as the “Synthesgroup.”

For both groups, data on age, breed, gender, weight atsurgery, and affected limb, and radius of the saw were retrievedand recorded.

Inclusion Criteria

Dogs were included if a clinical diagnosis of complete orpartial CCL rupture had been made at the time of examinationand the rupture was subsequently treated with TPLO using acylindrical TPLO saw with a radius of 24, 27, or 30mm.Additionally, only dogs in which the osteotomy was stabilizedwith either a 3.5mm standard TPLO bone plate (SlocumEnterprises) or a 3.5mm locking TPLO plate (Synthes, Inc.)were included. Additional inclusion criteria were the availabil-ity of complete medical records and correctly positionedimmediate postoperative radiographic projections. Radio-graphs were considered correctly positioned if there was�2mm separation of the superimposed femoral condyles.16

Dogs were excluded if any other type of TPLO plate, or double

bone plates were used for stabilization of the osteotomy orthere had been a concurrent surgical procedure such as femoralcorrective osteotomy performed.

Preoperative Planning

Preoperative radiographs were obtained for TPLO planningfor all dogs. The mediolateral radiographic projection of thestifle was collimated to include the hock and the TPA wasmeasured.17 For the Slocum group, acetate sheets with circulartemplates were laid over the radiographic film and used toselect the saw size and osteotomy position. For the Synthesgroup, computed radiography and a digital templating system(Sound‐Eklin, Carlsbad, CA) was used to select saw size andosteotomy position.

The aim was to ensure that saw size and osteotomyplacement resulted in a remaining tibial tuberosity width>1 cm or >25% of the craniocaudal tibial width at the mostcranial portion of the osteotomy. The centroid of the osteotomywas positioned on the tibial plateau slope, midway betweenthe 2 intercondylar tubercles.6 Additionally, the intendedosteotomy was positioned to ensure there was adequate bonestock for plate application.

Three distances were measured to allow transposition ofthe surgical plan to the intraoperative field (Fig 1). D1 wasdefined as the distance from the insertion of the patellar tendonto the proposed osteotomy, when measured perpendicular tothe cranial aspect of the tibial crest. D2 was defined as thedistance from the insertion of the patellar tendon to theproposed osteotomy, whenmeasured along the proximal aspectof the tibia. D3 was defined as the distance from the tibialplateau, at the midpoint of the intercondylar tubercles,measured to the proposed osteotomy at the point where itintersects the caudal tibial cortex. The D3 measurement wouldbe equivalent to the radius of the saw to be used.

Surgical Procedure

A medial surgical approach to the proximal aspect of the tibiawas made and a caudomedial arthrotomy performed to inspectthe caudal region of the medial meniscus.18 Hemimeniscec-tomy was performed and the caudal portion of the medialmeniscus removed if any medial meniscal pathology wasidentified at surgery. The caudomedial arthrotomy allows onlylimited observation of the intra‐articular structures of the stiflebut was used because of the increased sensitivity in thedetection of medial meniscal tears when compared to acraniomedial arthrotomy in stable stifles.19 A 3mm diameterEllis pin was inserted 5mm distal to the tibial plateau, justcaudal to the medial collateral ligament. After initialattachment of the proximal arm of the TPLO jig to theproximal pin, a 2nd identical pin was inserted into the distal endof the tibial diaphysis.

D1, D2, and D3were measured on the medial cortex of thetibia intraoperatively and the positions marked with electro-cautery. For D3, a hypodermic needle was inserted through themedial collateral ligament midway along the tibial plateau in anattempt to identify a point, which would lie directly medial to

526 Veterinary Surgery 43 (2014) 525–533 © Copyright 2014 by The American College of Veterinary Surgeons

Accuracy of Tibial Osteotomy Placement Tan et al.

the intercondylar tubercles. These measurements were used toplan the position of the osteotomy.

For the Slocum group, a biradial TPLO saw (SlocumEnterprises), the size of which had been predetermined fromthe preoperative radiographs, was used to create the osteotomyafter attachment of an alignment jig (Slocum Enterprises) andthe measurements D1–3 marked as described above. After theTPLO saw had penetrated the cis cortex, the blade wasremoved and the fragments were marked with the intendeddistance of rotation that was calculated using a TPLO chart(Slocum Enterprises). This chart determines the distancerequired to create a postoperative TPA of 5° based upon the sawsize and the measured preoperative TPA. After completion ofthe osteotomy, a 3mm diameter negatively profiled pin wasplaced in a craniocaudal direction through the plateau segment,and this was used to rotate the plateau segment until the pre‐placed marks were aligned. A 1.6 or 2.0mm Kirschner wirewas then inserted through the proximal part of the tibialtuberosity and into the tibial metaphysis to temporarilymaintain the reduction of the osteotomy. The osteotomy wasdefinitively stabilized with a 3.5mm TPLO plate (SlocumEnterprises) that had been contoured to the proximomedialtibia and 3.5mm cortical bone screws.

For the Synthes guide group, a TPLO jig (Synthes, Inc.)was attached to the pins and a saw guide (Synthes, Inc.) wasattached to the jig and positioned so that the edge of the guidewas positioned along the proposed osteotomy (Fig 2). ATPLOsaw (Synthes, Inc.), the size of which had been predeterminedfrom preoperative radiographs, was used to start the osteotomy.Similar to the Slocum group, after the TPLO saw hadpenetrated the cis cortex, the fragments were marked with thedesired distance of rotation. The saw guide was then removedbefore completing the osteotomy. The fragment was rotatedand temporarily secured with a 1.6mm Kirschner wire. Theosteotomy was definitively stabilized with a precontoured 6hole 3.5mm locking TPLO plate (Synthes, Inc.) using 3locking head screws proximally and 3.5mm cortical bonescrews distally.20 In some cases, the distal end of the plate wascontoured to the proximomedial aspect of the tibia.

Radiographic Assessment

Immediate postoperative radiographic projections of the stiflewere obtained with the dog anesthetized. The beam wascentered over the stifle but collimated to include the talocruraljoint.

All radiographic measurements were made by 1 observer(C.T.) using a digital workstation (Efilm, Merge Healthcare,Chicago, IL) and software (Sound‐Eklin). Magnification of theimages allowed for accurate identification of all landmarksused in the study. The digital format of radiographic imageswas obtained by either scanning of radiographic films or directuse of digital radiography and storage in DICOM format.Calibration was performed on the digital workstation by usingeither the TPLO plate of known dimensions as an internalstandard for calibration (Slocum group) or a 10 cm calibratedrod placed alongside the limb at the height of the stifle duringradiography (Synthes group).

Figure 2 The saw guide used in this study is attached to the SynthesTPLO jig and positioned so the edge of the saw guide overlies theproposed osteotomy. The guide is attached to the Synthes TPLO jigusing a bolt that can be positioned in 4 different holes in the jig arm,while the proximal jig pin is positioned through the guide in 1 of 3 slots,allowing accurate alignment of the guide with the intended osteotomy.This image was reproduced with the permission of Synthes, Inc. (WestChester, PA).Figure 1 Preoperative measurements performed on the mediolateral

radiograph using a circular digital template. The centroid of the circulartemplate was positioned on the tibial plateau slopemidway between theintercondylar tubercles. The size of the template (saw size) was selectedto ensure the remaining tibial tuberosity width was >1 cm or >25% ofthe craniocaudal width of the tibia. The distance from the insertion ofthe patellar tendon to the intended osteotomy was measuredperpendicular to the cranial aspect of the tibial crest (D1) and alongthe proximal border of the tibia (D2). The distance D3 is equal to theradius of the selected saw and is measured from the tibial plateaumidway between the intercondylar tubercles to the caudal border of theproximal tibia.


Tan et al. Accuracy of Tibial Osteotomy Placement

The long axis of the tibia was marked on each radiographby drawing a line through the center of the talus and midpointof the 2 intercondylar tubercles on the tibial plateau.21 Theintended centroid of the osteotomy (ICO) was identified as theintersection of the tibial long axis and the tibial plateau midwaybetween the intercondylar tubercles. A circular template wasselected to match the radius of the saw used intraoperatively.The template was digitally overlain so that the curvature of thetemplate aligned with the curvature of the osteotomy. Thecenter of circular template was identified and this was termedthe actual centroid of the osteotomy (ACO). The distancebetween the intended and the ACO was measured digitally andtermed the distance of eccentricity (DOE; Fig 3). The directionof eccentricity was also recorded by using the tibial long axis asa reference line and the ACO was classified as eithercranioproximal, caudoproximal, craniodistal, or caudodistalto the ICO. To evaluate the precision (reproducibility) of theosteotomies in each group, a point termed the center of thecluster (CC) was identified for both the Slocum and the Synthesgroups. This point was calculated using the x and y co‐ordinates of the ACO data points, with the axes crossing at theICO. The CC point was the median value of the x co‐ordinatesand y co‐ordinates for each group. The distance from the CC

point to each ACO was then calculated to assess osteotomyprecision.

Postoperative tibial plateau angle (TPA) was measuredfrom the postoperative mediolateral projection using the samemethods used for measurement of preoperative TPA.21

Statistical Analysis

Descriptive statistics were calculated for the signalment (age,weight, sex, and breed) of both groups. Sex and surgical side ofthe 2 groups were compared using a Fisher’s exact test and theMann–Whitney U test was used to compare weight and agebetween the 2 groups. A Kruskal Wallis test was used tocompare the Slocum and Synthes groups based on the sizes ofsaws used during the procedures. DOE between groups wascompared using the Mann–Whitney U test. Multivariate linearregression analysis was also used to identify independentcorrelates of DOE. To generate the multivariate models,univariate variables with a P�.4 were entered as covariates.Values of P�.05 were considered significant.

To evaluate the variation in distance of the ACO from theCC point within the 2 groups, the data were first tested fornormality and subsequently, a Levene’s test was used tocompare variability in the data between groups as a measure forosteotomy precision. To investigate the effect of time, andsurgeon experience on DOE, a sub‐analysis of both groupswere performed. DOE of the first half (chronologically) andsecond half of each group was compared using a Mann–Whitney U test. To evaluate postoperative TPA, the deviationof this value from 5° was calculated for each surgery and theMann–Whitney U test was used to compare groups. Inaddition, a multivariate linear regression was performed as forthe DOE. All analyses were performed using commerciallyavailable software programs (Minitab, State College, PA andStata, College Station, TX).

RESULTS

The initial hospital database search identified 443 TPLOprocedures in the Slocum group and 115 TPLO surgeries in theSynthes group. Reasons for exclusion included the use ofdouble plates, smaller saw sizes and plates and concurrentsurgical procedures. After evaluation of the medical recordsand radiographic images, 87 TPLO procedures met theinclusion criteria for inclusion in the Slocum group (84dogs), and 47 in the Synthes group (40 dogs).

For the Slocum group the most common breeds were theLabrador (n¼ 28), mixed breed (n¼ 20) and Golden Retriever(n¼ 9), whereas the most common breeds in the Synthes groupwere Rottweiler (n¼ 8), Labrador (n¼ 5), Golden Retriever(n¼ 5), andmixed breed dogs (n¼ 4). The differences betweenthe sex distribution in the 2 groups was significant (P¼.01),but differences for weight and age were not significant.

One board certified surgeon (K.A.J.) performed all TPLOin the Synthes group, whereas 3 board certified surgeons,including K.A.J., performed TPLO in the Slocum group. All

Figure 3 Postoperative radiographic assessment involved identifyingthe tibial long axis (solid line) and creating a perpendicular line (dottedline), which intersected with the tibial long axis at the intended centroidof the osteotomy. A circular template of identical radius to that usedsurgically was positioned so the actual centroid of the osteotomy (crosshairs) could be located. The distance of eccentricity (double headedarrow) was then measured in addition to the direction of eccentricity.



surgeons were experienced with the procedure at the time ofperforming surgery on dogs in this study.

In the Slocum group (n¼ 87), 39 TPLO were performedon the left stifle and 48 on the right stifle. The saw sizes usedwere, 24mm (71 surgeries) and 30mm (16 surgeries).

For dogs in the Synthes group (n¼ 47), 26 TPLO wereperformed on the left stifle and 21 on the right stifle. The sawsizes used in this group were 24 mm (31), 27 mm (9), and30 mm (7). The differences between groups for side of surgeryand saw sizes used were not significant (Table 1).

Mean DOE, without regard to direction, was significantlygreater in the Slocum group (5.6� 2.5mm) than for theSynthes group (3.4� 1.8mm; P<.01).

DOE was caudodistal in 74/87 of the Slocum group and32/47 of the Synthes group such that the ACO was locatedcaudal and distal to the ICO (Fig 4).

Table 1 Descriptive Data for the Slocum and Synthes Groups

Slocum Group Synthes Group

Total number of stifles 87 47Sex (male/female) 37/50 31/16�

Operated limb (left/right) 39/48 26/21Mean�SD age (years) 5.4� 2.6 6.4� 3.3Mean�SD weight (kg) 37.9� 8.9 38.5� 9.6Mean�SD Distance of

eccentricity (mm)5.6� 2.5 3.4� 1.8�

Range of distance ofeccentricity (mm)

1–15 0–7

Mean�SD deviation ofpostoperative TPA from 5° (°)

3.2� 2.4 2.4� 2.3�

�Significant difference.

Figure 4 Distance and direction of eccentricity for both the Synthes group (black circle) and Slocum group (red circle). The y‐axis represents the tibiallong axis, whereas the x‐axis is perpendicular to this. The lines intersect at the intended centroid of the osteotomy, a point on the tibial plateau midwaybetween the intercondylar tubercles. Each data point represents the actual centroid of the osteotomy in relation to the intended location.



The CC point for the Slocum group was located 3.8mmcaudal and 2.4mm distal to the ICO. The CC point for theSynthes group was located 2.1mm caudal and 0.5mm distal tothe ICO. When comparing the distribution of data pointsaround the CC point, there was no difference (P¼.09) betweenthe Slocum and Synthes group.

For the Slocum group, there was no difference in the DOEbetween the first half and second half of cases (P¼.29).Similarly, for the Synthes group, there was no difference inDOE between the first and second half of cases (P¼.43).

Mean deviation of the postoperative TPA from theintended 5° for the Slocum group (3.2� 2.4°) was significantlygreater than for the Synthes group (2.4� 2.1°; P¼.05; Fig 5).However, multivariate analysis did not identify weight, sex,side of surgery, DOE, or saw size as significantly influencingpostoperative TPA deviation from the intended TPA of 5°.

DISCUSSION

A surgeon’s ability to precisely position the osteotomy for aTPLO surgery can potentially influence postoperative out-come. We found that TPLO performed with a jig system thatincorporates a saw guide was associated with a more accurateosteotomy placement compared with the preoperativelyplanned position. With respect to precision observed in bothgroups, there was a trend toward less variability in the Synthesgroup; however, this difference did not reach significance(P¼.09).

Accurate placement of the osteotomy during TPLO reliesupon both accurate translation of the preoperative plan to theintraoperative field and the creation of an osteotomy preciselyat the intended location. In both groups of dogs, a similarmethod of preoperative planning and translation to the surgicalfield was used so that the accuracy of the osteotomy in thesedogs is more likely to reflect the method used for performing

the osteotomy than differences in planning. Although it hasbeen suggested that the osteotomy position in TPLO tends to bedistally located,7 there are no published reports to ourknowledge that document the postoperative position of theosteotomy in a series of clinical cases. The DOE we foundsuggests caudal and distal deviation is by far the most common,with the ACO located caudally and distally in over 79% ofcases (Fig 4). The reason for this distribution is not clear butmay be because of the presence of the proximal jig pin,inadvertently leading the surgeon to center the osteotomy atthis location (distal and caudal to the intercondylar tubercles)rather than at the ICO. Alternatively, there may be a tendencyfor the surgeon to center the osteotomy distally rather thanproximally to ensure there is adequate bone stock to allowappropriate stabilization with a bone plate.

We elected to exclude dogs in which double plates wereused because the surgeon may have been influenced to relocatethe osteotomy to maintain adequate bone stock in the proximalfragment. Although the 2 different plates we used have similaroverall dimensions, the design of the proximal part of eachplate is different.Whereas the screw holes of the SlocumTPLOplate are oval and will accept cortical bone screws, theprecontoured Synthes TPLO plate has round, threaded holesproximally that are designed to accepting either locking screwsor cortical bone screws. The most distal hole in the proximalfragment is located further distally in the Slocum plate whencompared to the Synthes plate. This difference in holedistribution, along with the use of locking screws in ananatomically precontoured plate may have provided thesurgeon with more confidence to position the osteotomy inthe optimal position in the Synthes group.

Our results do not suggest that it is the saw guide alonewhich results in improved accuracy of the osteotomy duringTPLO but rather the use of a TPLO system that includes a sawguide that results in more accurate osteotomy placement. Thedifferent TPLO saws may also have some influence onaccuracy of osteotomy placement. The Slocum TPLO saw hasa patented biradial design23 that is thickest in the central portionof the saw and tapers toward both ends. It is designed toproduce 2 osteotomy surfaces of the same radius that fittogether perfectly. The curvilinear saw produced by Synthes isthinner and has a uniform thickness across its width. Thecutting performance of these 2 designs have been shown tovary in efficiency and durability,24 with the Synthes saw shownto be more efficient in cutting and the Slocum saw moredurable. A saw of uniform width was also shown to generateless heat than a Slocum biradial saw.25 The saw design andsharpness may have influenced the accuracy of osteotomyposition because of the tendency of the blade to “walk” oncethe oscillation begins. The type of oscillating saw driving theTPLO blade was not recorded in this study but it is possible thatit may have also influenced the degree of “walking” of theblade over the smooth cortical bone surface as each saw is helddifferently.

Translocation of the proximal bone fragment duringTPLOmight be influenced by saw blade design and the methodof plate fixation. In this report, translation of the proximal bonefragment will result in a slight shift of the ICO, from which the

Figure 5 Postoperative TPA for both groups in this study. The solidhorizontal line at 5° represents the intended postoperative TPA. Althoughthe two groups are significantly different, the DOE was not a significantfactor in determining the postoperative TPA.



DOE is measured. The thicker blade of the Slocum saw willremove a greater kerf of bone compared with the thinnerSynthes blade and may have increased the distance oftranslation after osteotomy stabilization. Similarly, the use ofcompression screws and the different plate designs may alsohave resulted in variations in translation.

The improved accuracy of osteotomy placement in theSynthes groupmay be related to the ability to carefully positionthe saw guide, using measurements made from preoperativeradiographs in addition to the ability to stabilize the oscillatingsaw when the osteotomy is initiated. In human kneereplacement surgery, the use of an open guide has beenassociated with fewer cutting errors when compared toprocedures performed with the use of slotted cutting guides.13

It was proposed that the thicker and stiffer saws that could beused with the open guides helped reduce any errors inorientation of the osteotomy. Comparisons between freehandcutting and use of customized cutting guides in both human andveterinary surgery have concluded that more accurateosteotomies can be performed when a saw guide is used.11,15,26

The use of the saw guide is contingent upon the use of aTPLO jig to position and stabilize the saw guide. Recentstudies have questioned the use of any TPLO jig at all duringsurgery, suggesting that application of the jig may addunnecessary time to the procedure without improvingresults.27,28 However, It has been suggested that the use of aSynthes TPLO jig and saw guide results in a more anatomicallyaccurate osteotomywhen compared with a SlocumTPLO jig instudies of plastic bone and cadaveric specimens.29 Accurateosteotomy orientation is important in avoiding inadvertentinduction of angular limb deformities.8

A detrimental effect of a poorly positioned osteotomy isfracture of the tibial tuberosity, a well reported complicationafter TPLO, with an incidence of 3–9%.22,34‐36 Risk factors fortibial tuberosity fractures include bilateral simultaneous TPLOsurgeries and a tibial tuberosity width of <1 cm.9 The tibialtuberosity width that remains after TPLO is a direct result ofsaw size and osteotomy placement. Transposing the carefullymeasured preoperative plan into the intraoperative field,allowing for accurate osteotomy placement, is essential toensure adequate tibial tuberosity width is maintained, thereforereducing the risk of tibial tuberosity fracture. The absence oftibial tuberosity fractures in these cases may reflect thedirection of inaccuracy observed. As most osteotomies werecentered caudal to the ICO, the remaining tibial tuberositywidth would have been wider than planned and therefore, theinaccuracy reported here would not have increased thepropensity for the tibial tuberosity to fracture.

Kowaleski and McCarthy6 demonstrated the importanceof osteotomy position in a mathematical model of the TPLOprocedure. The proximal point of the tibial long axis is locatedwithin the osteotomized proximal fragment, which will berotated during the surgery. Failure to center the osteotomy onthe tibial plateau midway between the intercondylar tubercleswill result in translation of the tubercles and therefore create ashift in the tibial long axis, which will in turn, result in apostoperative TPA that may be greater or less than the intendedangle depending on the direction of eccentricity of the

osteotomy. More specifically, a cranially or distally centeredosteotomy results in a postoperative TPA up to 4° greater thanintended as a result of tibial long axis shift. Biomechanically,distally centered osteotomies were less effective in eliminatingcranial tibial thrust in cadaveric models.7 However, theimportance of TPA on functional outcome has been ques-tioned. Robinson et al.30 did not find a significant relationshipbetween postoperative TPA and ground reaction forces inLabradors that had TPLO and with a resultant postoperativeTPA in the range of 0°–14°. Because of the complexity of thecanine stifle joint, it is likely that TPA is simply one of manyfactors that influence the clinical outcome of dogs treated byTPLO for management of CCL rupture.

As the 2nd hypothesis of this study, the deviation of thepostoperative TPA from the intended 5° was comparedbetween groups. Dogs within the Synthes guide group hadsignificantly less variation in postoperative TPA from theintended 5° when compared with dogs in the Slocum group;however, multivariate analysis showed no variable measured,including DOE, was significantly associated with thisdifference. We would suspect this lack of association of anyone variable reflects the fact that the postoperative TPA isinfluenced by a large number or variables, including degree offragment rotation, osteotomy placement, and loss of reductionduring plate application. A possible explanation for thedifference in postoperative TPA between groups may be theuse of 2 different plate designs. TPLO locking plates, as used inthe Synthes group, have been shown to maintain reductionmore effectively than conventional screws and non‐lockingTPLO plates, as used in dogs of the Slocum group.31

As with any retrospective study, there are a number oflimitations in this study. Firstly, although the technique ofpreoperative planning and transposition of the plan to theintraoperative field was similar between groups, we acknowl-edge that the effect of different surgeons may have alsoinfluenced these results. The order of screw placement,decision to use screws in the loaded or neutral position andthe angle of screw insertion could not be standardized and istherefore a confounding factor that must be considered whencomparing the 2 groups. Despite all surgeons being experi-enced with TPLO, we elected to compare 2 time periods withineach group to investigate the influence of time on accuracy ofosteotomy placement. The learning curve effect is wellrecognized in veterinary surgery32 and as the cases wereconsecutive and not concurrent, there is the potential thatimproved accuracy may have been related to improvement inthe surgeons’ technical skills rather than the jig systems used.However, when we compared the DOE of the first versus thesecond half of dogs within each group, no significant differencewas detected. This result is consistent with a procedureperformed by a surgeon experienced with that particulartechnique.

Secondly, radiographic image acquisition also variedbetween the 2 groups with the Synthes group having allradiographs and planning procedures performed using com-puted radiography and digital templating, whereas dogs in theSlocum group had radiographic film and acetate templatesused. Digital radiographs have been shown to have potential



benefits as magnification can allow for more accurateidentification of landmarks.17

In the initial preoperative radiographs, dogs in the Slocumgroup had no calibration performed to account for radio-graphic magnification before preoperative planning com-menced. In contrast, the digital radiographs from dogs in theSynthes group were all calibrated before preoperativemeasurements, which may have allowed for more accuratepreoperative planning. Magnification increases�1% for every1 cm that the bone is elevated off the radiographic plate33 andalthough magnification for the mediolateral stifle projection isgenerally <5%, it must be acknowledged as a source ofvariation between groups.

Thirdly, all observations were conducted by the sameobserver (C.T.) who was not blinded to group because the useof different plates distinguished groups and could not beobscured because of the measurement required in these cases.Although the repeatability of themeasurement of TPA has beenquestioned, the landmarks used in the accuracy of osteotomycomponent of this study (center of the talus, intercondylartubercles, and the osteotomy line) were easily identified.

Whenmeasuring TPA, the caudal edge of the tibial plateauis consistently reported to be the most difficult landmark toidentify because of proliferative osseous changes associatedwith osteoarthritis.21 The postoperative TPA is not onlyaffected by the distance and direction of eccentricity but also bythe measured preoperative TPA, degree of rotation, andmovement of the proximal fragment that may occur duringplate application.31 It would therefore be difficult to concludefrom this study that more accurate osteotomy placement alonewill result in more precise alteration to the TPA in all clinicalcases.

In this study, we documented that the ACO may deviatefrom the ICO by up to 15mm despite preoperative planning.Our findings suggest that, compared to the Slocum TPLOsystem, the use of the Synthes TPLO system, which comprisesthe TPLO jig, saw guide, saw, and precontoured locking plate,was associated with more accurate osteotomy placement,which may allow for more precise alteration to TPA.

DISCLOSURE

Dr. KA Johnson was a member of the AOVET expert group(VEEG) that developed the combined saw guide and jig incollaboration with Synthes Vet. Some of the instrumentationused for this study was provided by Synthes Vet. Dr. Johnsondid not receive any financial rewards or royalties from anycommercial organization. Otherwise, the authors report nofinancial or other conflicts of interest related to this report.

REFERENCES

1. Innes JF, Barr ARS: Clinical natural history of the postsurgicalcruciate deficient canine stifle joint: year 1. J Small Anim Pract1998;39:325–332

2. Slocum B, Slocum TD: Tibial plateau leveling osteotomy forrepair of cranial cruciate ligament rupture in the canine. Vet ClinNorth Am Small Anim Pract 1993;23:777–795

3. Warzee CC, Dejardin LM, Arnoczky SP, et al: Effect of tibialplateau leveling on cranial and caudal tibial thrusts in caninecranial cruciate‐deficient stifles: an in vitro experimental study. VetSurg 2001;30:278–286

4. Reif U, Hulse DA, Hauptman JG: Effect of tibial plateau levelingon stability of the canine cranial cruciate‐deficient stifle joint: an invitro study. Vet Surg 2002;32:147–154

5. Ireland WP, Rogers J, Myers RK: Location of the instantaneouscenter of joint rotation in the normal canine stifle. Am J Vet Res1986;47:837–840

6. Kowaleski MP, McCarthy RJ: Geometric analysis evaluating theeffect of tibial plateau leveling osteotomy position onpostoperative tibial plateau slope. Vet Comp Orthop Traumatol2004;17:30–34

7. Kowaleski MP, Apelt D, Mattoon JS, et al: The effect of tibialplateau leveling osteotomy position on cranial tibial subluxation:an in vitro study. Vet Surg 2005;34:332–336

8. Wheeler JL, Cross AR, Gingrich W: In vitro effects of osteotomyangle and osteotomy reduction on tibial angulation and rotationduring the tibial plateau‐leveling osteotomy procedure. Vet Surg2003;32:371–377

9. Bergh MS, Rajala‐Schultz P, Johnson KA: Risk factors for tibialtuberosity fracture after tibial plateau leveling osteotomy in dogs.Vet Surg 2008;37:374–382

10. Liska WD, Doyle ND: Canine total knee replacement: surgicaltechnique and one‐year outcome. Vet Surg 2009;38:568–582

11. Marcellin‐Little DJ, Harrysson OLA, Cansizoglu O: In vitroevaluation of a custom cutting jig and custom plate for canine tibialplateau leveling. Am J Vet Res 2008;69:961–966

12. Bruce WI, Rose A, Tuke J, et al: Evaluation of the triple tibialosteotomy. A new technique for the management of the caninecruciate‐deficient stifle. Vet Comp Orthop Traumatol2007;20:159–168

13. Yau WP, Chiu KY: Cutting errors in total knee replacement:assessment by computer assisted surgery. Knee Surg SportsTraumatol Arthrosc 2008;16:670–673

14. Conzemius M: Nonconstrained elbow replacement in dogs. VetSurg 2009;38:279–284

15. Tigani D, Del Baldo A, Trentani P, et al: Closed‐wedge tibialosteotomy: conventional technique versus a new system ofcompression‐dynamic fixation. Orthopedics 2002;25:1265–1268

16. Grierson J, Sanders M, Guitan J, et al: Comparison of anatomicaltibial plateau angle versus observer measurement from lateralradiographs in dogs. Vet Comp Orthop Traumatol 2005;4:215–219

17. Serwa D, Lorinson K, Lorinson D, et al: Comparison ofconventional and digital measurements of tibial plateau angle indogs. J Am Vet Med Assoc 2009;234:622–624

18. Piermattei DL, Johnson KA: An atlas of surgical approaches tothe bones and joints of the dog and cat (ed 4). Philadelphia, PA,Saunders, 2004

19. Pozzi A, Hildreth BA III, Rajala‐Schultz PJ: Comparison ofarthroscopy and arthrotomy for diagnosis of medial meniscalpathology: an ex vivo study. Vet Surg 2008;37:749–755



20. Windolf M, Leitner M, Schwieger K, et al: Accuracy of fragmentpositioning after TPLO and effect on biomechanical stability.Vet Surg 2008;37:366–373

21. Fettig AA, RandWM, Sato AF, et al: Observer variability of tibialplateau slope measurement in 40 dogs with cranial cruciateligament‐deficient stifle joints. Vet Surg 2003;32:471–478

22. Stauffer KD, Tuttle TA, Elkins AD, et al: Complicationsassociated with 696 tibial plateau leveling osteotomies (2001–2003). J Am Anim Hosp Assoc 2006;42:44–50

23. Slocum B: Biradial saw blade. US Patent Class 606/82 and n.4955888

24. Farrell M, Mathieson A, Chung P, et al: In vitro performancetesting of two arcuate oscillating saw blades designed for useduring tibial plateau leveling osteotomy. Vet Surg 2011;40:694–707

25. Bachelez A, Martinez SA: Heat generation by two different sawblades used for tibial plateau leveling osteotomies. J Am AnimHosp Assoc 2012;48:83–88

26. Hibi H, Ueda M: A technique for ensuring accurate bone cuts inthe intraoral vertical ramus osteotomy. J Oral Maxillofac Surg1995;53:1480–1481

27. Bell JC, Ness MG: Does use of a jig influence the precision oftibial plateau leveling osteotomy surgery? Vet Surg 2007;36:228–233

28. Schmerbach KI, Konrad C, Boeltzig M, et al: In vitro comparisonof tibial plateau leveling osteotomywith and without use of a tibialplateau leveling jig. Vet Surg 2007;36:156–163

29. Burton NJ, Wallace AM: Evaluation of cut accuracy and ciscortical damage for tibial plateau leveling osteotomy performed

with and without the aid of a novel saw guide: an in vitro study.Vet Surg 2013;42:28–37

30. Robinson DA, Mason DR, Evans R, et al: The effect of tibialplateau angle on ground reaction forces 4–17 months after tibialplateau leveling osteotomy in Labrador Retrievers. Vet Surg2006;35:294–299

31. Leitner M, Pearce SG, Windolf M, et al: Comparison oflocking and conventional screws for maintenance of tibialplateau positioning and biomechanical stability after locking tibialplateau leveling osteotomy plate fixation. Vet Surg 2008;37:357–365

32. Freeman L, Rahmani EY, Burgess RCF, et al: Evaluation of thelearning curve for natural orifice transluminal endoscopic surgery:bilateral ovariectomy in dogs. Vet Surg 2011;40:140–150

33. Conn KS, Clarke MT, Hallett JP: A simple guide to determinethe magnification of radiographs and to improve the accuracy ofpreoperative templating. J Bone Joint Surg Br 2002;84B:269–272

34. Priddy NH, Tomlinson JL, Dodam JR, et al: Complicationswith and owner assessment of the outcome of tibial plateauleveling osteotomy for treatment of cranial cruciate ligamentrupture in dogs: 193 cases (1997–2001). J Am Vet Med Assoc2003;222:1726–1732

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

36. Kergosien DH, Barnhart MD, Kees CE, et al: Radiographic andclinical changes of the tibial tuberosity after tibial plateau levelingosteotomy. Vet Surg 2004;33:468–474



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Accuracy of Tibial Osteotomy Placement Using 2 Different Tibial Plateau Leveling Osteotomy Jigs