Rupture of the cranial cruciate ligament causes instability of the stifle joint, lameness, and the development of osteoarthritis.1–5 Tibial tuberosity advancement is one of the most commonly used techniques for the dynamic repair of cranial cruciate ligament deficiency.6–12 The concept is based on the premise that the intra-articular force resulting from weight bearing is parallel to the patellar tendon.8,10 After rupture of the cranial cruciate ligament, TTA theoretically results in stabilization of the stifle joint during the stance phase by neutralizing cranial tibial thrust.6–8,10,13–15 Results of several ex vivo studies6,7,10,13–15 indicate that cranial tibial thrust is neutralized by advancing the tibial tuberosity to reduce the PTA to > 90° at a stifle joint extension angle of 135°.
Recently, a simplified TTA technique known as the MMT was described.16,17 By preserving the distal tibial crest attachment, the MMT requires fewer implants and makes the surgical procedure less complex.16–18 This procedure has garnered increasing interest among veterinary surgeons, and use of specific implant types has been investigated for this purpose.17,18
Preoperative planning methods for TTA and MMT procedures require the use of a mediolateral radiograph of the affected stifle joint at 135° extension,19–21 except for a method described by Ness22 to calculate advancement distance for use with a titanium-foam wedge in the MMT that relies on tibial anatomy alone. All described advancement determination methods require the identification of tibial plateau landmarks and PTA measurement, which can be determined by use of the tibial plateau method8,10 or the common tangent method.23 Preoperative measurements are made with the aim of subsequently reducing the PTA to the intended 90° during stance.6,8,10 Failure to decrease the PTA to 90° can lead to the persistence of femorotibial shear forces and lameness.6
Radiographic methods described for determination of the advancement distance for the tibial tuberosity include the conventional method used for classical TTA planning,8 a correction method,24 the tibial anatomy-based method for use with titanium foam wedges,22 and the modified TTA planning method.25 In the conventional method, the amount of advancement needed is measured along a line parallel to the tibial plateau slope.8 Because the tibial crest osteotomy differs between the classical TTA and the MMT, the displacement of the tibial tuberosity does not follow the same pattern for both procedures. In fact, no proximal displacement of the tibial crest is created during an MMT.8,24 Therefore, the methods described for the classical TTA might not be adapted to determine the required advancement when an MMT is planned. An alternative planning method, the correction method, was first described by Etchepareborde et al.24 The primary modification in this method, compared with the conventional TTA planning method, was that the amount of advancement needed was measured in a cranial direction perpendicular to the tibial mechanical axis, not along the line of the tibial plateau slope. Subsequently described methods22,25 also measure the amount of advancement needed in a cranial direction. The modified TTA planning method described by Kapler et al25 accounts for anticipated distal translation of the patella after advancement with an MMT. In this method, the line drawn perpendicular to the tibial slope is located approximately 3 mm distal to the proximal insertion of the patellar tendon along the patellar tendon axis.
The methods described by Etchepareborde et al,24 Ness,22 and Kapler et al25 should be more appropriate for planning surgery with the MMT than the conventional method. However, results of some studies25,26 indicate that these methods failed to consistently reduce the PTA to the intended 90°. Several factors could explain why previously described planning methods may fail to determine the true advancement distance required to achieve this goal. First, the advancement determined with each of the methods is measured in a cranial direction, perpendicular to the tibial mechanical axis or tibial crest.22,24,25 However, as the tibial crest is advanced in a curvilinear fashion relative to the osteotomy axis, reading the advancement perpendicular to the tibial mechanical axis or the tibial crest can be a source of error. Therefore, it may be more appropriate to determine the advancement along a line perpendicular to the planned osteotomy line, rather than to the tibial mechanical axis or tibial crest. Another source of error concerning these methods might be the discrepancy between the level of the advancement measurement and the level of advancement cage implant placement. In previously described methods, the advancement measurement is made at the level of the proximal aspect of the tibial tuberosity (at the distal insertion of the patellar tendon).8,22,24,25 Because the tibial crest is not proximally translated with the MMT, the advancement cage application is proximal to the level at which the advancement measurement is determined. Therefore, the advancement at the level of the tibial tuberosity is less than expected, which could explain why previously described methods did not consistently determine the true advancement. Additionally, accounting for anticipated distal translation of the patella after advancement might also be an important consideration in determining the true advancement. However, the anticipated distal translation distance of the patella after advancement used in the modified TTA planning method25 might not be appropriate; the true adjustment may be more or less than 3 mm.
Currently described advancement measurement methods do not take into account the osteotomy position and length, distal translation of the patella, and the level of advancement cage placement along the osteotomy site. The purpose of the study reported here was to assess the use of a new method accounting for these factors to determine the distance by which the tibial tuberosity should be advanced to achieve reduction of the PTA to 90° by means of the MMT in dogs. Evaluation goals included comparison of advancement measurements obtained by this method on radiographs of canine cadaver limbs with true advancement measurements determined after PTA reduction in the same limbs by use of the MMT in a previous study.26 We also sought to determine intraobserver and interobserver agreement for the advancement measurements obtained. We hypothesized that agreement between advancement measurements obtained for MMT planning with the new method and the true advancement measurements would be excellent.
Materials and Methods
Sample
Digital radiographsa of 24 canine stifle joints obtained in a previous study26 were reviewed. Briefly, both pelvic limbs had been collected by hemipelvectomy from the cadavers of 12 adult (> 1.5 years of age) medium-sized to large-breed dogs with a mean body weight of 26.1 kg (median, 25.5 kg; range, 17.3 to 37.8 kg). The dogs had been euthanized for reasons unrelated to orthopedic disease of the limbs and unrelated to the investigation. The quadriceps mechanism was simulated through use of a spring and a turnbuckle connected to the distal aspect of the quadriceps tendon and to the hemipelvis.6 Stifle joints were placed in true lateral position27,28 at an extension angle of 135 ± 1° as determined by use of so-called eminence landmarks,23 and the positions were maintained with a custom-made external skeletal fixator as described elsewhere.26,29 Mediolateral radiographs obtained for each stifle joint before and after PTA reduction with the MMT26 were used in the present study.
Radiographic measurements for PTA reduction planning
Measurements to calculate advancement distance for the tibial tuberosity were made on pretreatment radiographs. The PTA was measured by the tibial plateau method,8,10 and the tibial plateau angle was measured as described elsewehere.11 The tibial plateau was digitally marked with a line by a board-certified surgeon (TC). The positions of the osteotomy and the Maquet hole were determined on the same radiograph (Figure 1). The planned osteotomy was oriented from a point cranial to the medial tibial condyle to a point at a distance equivalent to 150% of the length of the tibial crest,30 which was defined as point O (site of the Maquet hole). Two distances (termed D1 and D2) were measured from point O; D1 was the distance from the most proximal part of the tibial crest to O, and D2 was the thickness of the cranial cortex of the tibia at the level of O. The length of the planned osteotomy was also measured. Distances D1 and D2 were measured only once for each stifle joint and were used for each reading session.
Representative pretreatment mediolateral radiograph of a stifle joint of a canine cadaver limb in a study to evaluate use of a new procedure to calculate the distance by which the tibial tuberosity should be advanced to reduce the PTA to 90° with the MMT. All joints were immobilized at 135° extension in the true lateral position; positioning was maintained with a custom external skeletal fixator. The planned osteotomy (yellow line) was oriented from a point immediately cranial to the medial tibial condyle to a point at a distance equivalent to 150% of the tibial crest length (TCL),30 which was defined as point O (site of the Maquet hole). Two distances were determined to report O on the tibiae (orange lines): D1 was the distance from the most proximal part of the tibial crest to O, and D2 was the thickness of the cranial cortex of the tibia at the level of O. The length of the planned osteotomy (OL) was also measured. The circle to the left of the joint represents the 25-mm-diameter radiographic reference positioned at the same level of the joint in each radiograph to allow the measurement of the anatomic structures and calculation of the radiographic magnification ratio.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
Representative pretreatment mediolateral radiograph of a stifle joint of a canine cadaver limb in a study to evaluate use of a new procedure to calculate the distance by which the tibial tuberosity should be advanced to reduce the PTA to 90° with the MMT. All joints were immobilized at 135° extension in the true lateral position; positioning was maintained with a custom external skeletal fixator. The planned osteotomy (yellow line) was oriented from a point immediately cranial to the medial tibial condyle to a point at a distance equivalent to 150% of the tibial crest length (TCL),30 which was defined as point O (site of the Maquet hole). Two distances were determined to report O on the tibiae (orange lines): D1 was the distance from the most proximal part of the tibial crest to O, and D2 was the thickness of the cranial cortex of the tibia at the level of O. The length of the planned osteotomy (OL) was also measured. The circle to the left of the joint represents the 25-mm-diameter radiographic reference positioned at the same level of the joint in each radiograph to allow the measurement of the anatomic structures and calculation of the radiographic magnification ratio.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
Representative pretreatment mediolateral radiograph of a stifle joint of a canine cadaver limb in a study to evaluate use of a new procedure to calculate the distance by which the tibial tuberosity should be advanced to reduce the PTA to 90° with the MMT. All joints were immobilized at 135° extension in the true lateral position; positioning was maintained with a custom external skeletal fixator. The planned osteotomy (yellow line) was oriented from a point immediately cranial to the medial tibial condyle to a point at a distance equivalent to 150% of the tibial crest length (TCL),30 which was defined as point O (site of the Maquet hole). Two distances were determined to report O on the tibiae (orange lines): D1 was the distance from the most proximal part of the tibial crest to O, and D2 was the thickness of the cranial cortex of the tibia at the level of O. The length of the planned osteotomy (OL) was also measured. The circle to the left of the joint represents the 25-mm-diameter radiographic reference positioned at the same level of the joint in each radiograph to allow the measurement of the anatomic structures and calculation of the radiographic magnification ratio.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
Advancement distance for the tibial tuberosity was calculated for each stifle joint with the following method. Similar to the conventional method for planning classical TTA,8–10 lines oriented to the patellar tendon and tibial plateau were drawn. A line drawn perpendicular to the tibial slope was initially located at the proximal insertion of the patellar tendon and was extended distally beyond the cranialmost point of the tibial tuberosity. First, the distance in the cranial direction between the point of the tibial tuberosity (distal insertion of the patellar tendon) and the line perpendicular to the tibial slope was determined along a line perpendicular to the planned osteotomy (Figure 2). This distance was termed a0. To account for anticipated distal translation of the patella after advancement of the tibial tuberosity, the origin of the line drawn perpendicular to the tibial slope was then successively located 3, 5, and 10 mm distal to the proximal insertion of the patellar tendon along the patellar tendon line, and the distance measurement between the point of the tibial tuberosity and this line was repeated to create measurements a3, a5, and a10, respectively. This methodology was called the osteotomy axis method.
Representative pretreatment mediolateral radiographs of a stifle joint (true lateral position; extension angle, 135°) of a canine cadaver showing measurement of 2 advancement distances (orange lines) for the tibial tuberosity. The advancements a0 (A) and a5 (B) were measured along a line perpendicular to the planned osteotomy, extending from the tibial tuberosity to a line perpendicular to the tibial plateau. The origin of the latter line was placed at the proximal insertion of the patellar tendon (A) for determination of the a0 measurement and 5 mm distal to the proximal insertion of the patellar tendon (B; purple line and arrow) for the a5 measurement. See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
Representative pretreatment mediolateral radiographs of a stifle joint (true lateral position; extension angle, 135°) of a canine cadaver showing measurement of 2 advancement distances (orange lines) for the tibial tuberosity. The advancements a0 (A) and a5 (B) were measured along a line perpendicular to the planned osteotomy, extending from the tibial tuberosity to a line perpendicular to the tibial plateau. The origin of the latter line was placed at the proximal insertion of the patellar tendon (A) for determination of the a0 measurement and 5 mm distal to the proximal insertion of the patellar tendon (B; purple line and arrow) for the a5 measurement. See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
Representative pretreatment mediolateral radiographs of a stifle joint (true lateral position; extension angle, 135°) of a canine cadaver showing measurement of 2 advancement distances (orange lines) for the tibial tuberosity. The advancements a0 (A) and a5 (B) were measured along a line perpendicular to the planned osteotomy, extending from the tibial tuberosity to a line perpendicular to the tibial plateau. The origin of the latter line was placed at the proximal insertion of the patellar tendon (A) for determination of the a0 measurement and 5 mm distal to the proximal insertion of the patellar tendon (B; purple line and arrow) for the a5 measurement. See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
To account for the advancement cage implant application level along the osteotomy site, a CPF was determined for each stifle joint (Figure 3). The distance (H; in millimeters) from the proximal extent of the planned osteotomy to the intersection point between the osteotomy axis and the line drawn perpendicular to the planned osteotomy at the level of the advancement measurement was determined. The CPF was calculated according to the following equation: CPF = (OL - 3) / (OL - H), where OL is the length of the planned osteotomy. The value 3 corresponded to the distance (in millimeters) of the cage application (proximal part of the implant) along the osteotomy site from the proximal margin of the tibial bone. The advancement measurements a0, a3, a5, and a10 obtained for each stifle joint with the osteotomy axis method were each multiplied by the CPF for the same joint, resulting in the adjusted advancement measurements A0, A3, A5, and A10, respectively (AX = aX • CPF, where X represents 0, 3, 5, or 10 on both sides of the equation [eg, A3 = a3 • CPF]). This was termed the osteotomy axis and cage position method.
Images depicting measurements used to account for advancement cage application level along the osteotomy site for dogs undergoing MMT. A—Illustration of the proximal aspect of the tibia with the tibial tuberosity advanced by use of the MMT. Measurements of the osteotomy length (OL) and wedge width in the osteotomy site at the level of the proximal part of the tibial tuberosity (a; unadjusted planning distance) are shown. A line is drawn perpendicular to the planned osteotomy and aligned with the proximal part of the tibial crest (green); the distance from this perpendicular line to the proximal extent of the osteotomy is indicated (H). The measurement for advancement at the level of cage application (A; adjusted planning distance) is equal to a • (OL – 3)/(OL – H), where 3 represents the distance (in millimeters) of the cage application (proximal part of the implant) along the osteotomy site from the proximal margin of the tibial bone in the present study. B—Representative pretreatment mediolateral radiograph of a stifle joint (true lateral position; extension angle, 135°) from a canine cadaver showing planning measurements used in calculation of the CPF (defined as [OL – 3]/[OL – H]). See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
Images depicting measurements used to account for advancement cage application level along the osteotomy site for dogs undergoing MMT. A—Illustration of the proximal aspect of the tibia with the tibial tuberosity advanced by use of the MMT. Measurements of the osteotomy length (OL) and wedge width in the osteotomy site at the level of the proximal part of the tibial tuberosity (a; unadjusted planning distance) are shown. A line is drawn perpendicular to the planned osteotomy and aligned with the proximal part of the tibial crest (green); the distance from this perpendicular line to the proximal extent of the osteotomy is indicated (H). The measurement for advancement at the level of cage application (A; adjusted planning distance) is equal to a • (OL – 3)/(OL – H), where 3 represents the distance (in millimeters) of the cage application (proximal part of the implant) along the osteotomy site from the proximal margin of the tibial bone in the present study. B—Representative pretreatment mediolateral radiograph of a stifle joint (true lateral position; extension angle, 135°) from a canine cadaver showing planning measurements used in calculation of the CPF (defined as [OL – 3]/[OL – H]). See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
Images depicting measurements used to account for advancement cage application level along the osteotomy site for dogs undergoing MMT. A—Illustration of the proximal aspect of the tibia with the tibial tuberosity advanced by use of the MMT. Measurements of the osteotomy length (OL) and wedge width in the osteotomy site at the level of the proximal part of the tibial tuberosity (a; unadjusted planning distance) are shown. A line is drawn perpendicular to the planned osteotomy and aligned with the proximal part of the tibial crest (green); the distance from this perpendicular line to the proximal extent of the osteotomy is indicated (H). The measurement for advancement at the level of cage application (A; adjusted planning distance) is equal to a • (OL – 3)/(OL – H), where 3 represents the distance (in millimeters) of the cage application (proximal part of the implant) along the osteotomy site from the proximal margin of the tibial bone in the present study. B—Representative pretreatment mediolateral radiograph of a stifle joint (true lateral position; extension angle, 135°) from a canine cadaver showing planning measurements used in calculation of the CPF (defined as [OL – 3]/[OL – H]). See Figure 1 for remainder of key.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
All measurements were performed with a digital radiographic viewing program.b Calibration was performed for each radiograph with a 25-mm diameter radiographic reference positioned at the same level of the joint to allow the measurement of the anatomic structures and calculate the radiographic magnification ratio.
One blinded observer (a second-year surgery resident [PP]) measured the advancements a0, a3, a5, and a10 for each stifle joint in a random order (assigned by use of a random number generator) on 3 separate occasions, with a ≥ 1-week interval between measurements, and 2 blinded observers (a board-certified surgeon [TC] and a first-year surgery resident [VL]) measured the a5 advancements in a random order on 3 separate occasions, with a ≥ 1-week interval between measurements. Because the methods for determining a0, a3, a5, and a10 measurements were similar, we chose to evaluate the intraobserver and interobserver variability for a5 measurements only. The same tibial plateau slope (line digitally marked on the preoperative radiograph) was used for each stifle joint for each of the readings to ensure that only the advancement measurement method variability was evaluated. The same 3 blinded observers measured the CPF in random order on 3 separate occasions, with a ≥ 1-week interval between measurements.
Determination of true advancement distances
True advancement measurements for the tibial tuberosity were determined for each stifle joint in a previous study.26 Briefly, the Maquet hole was drilled in a mediolateral direction at point O with D1 and D2 used to ensure location of this point was the same as that planned radiographically. The osteotomyc was performed with the MMT as described by Etchepareborde et al.16
A bone mark was made 3 mm below the proximal margin of the tibia at the caudal edge of the osteotomy with an osteotome. The mark was used to ensure consistency for advancement measurements. The tibial crest was advanced by turning a screw inserted in the tibial crest with the tip placed against a stainless steel stopper plate inserted into the osteotomy site6,26 until the PTA was 90 ± 0.1° on a mediolateral radiograph. To ensure use of the same tibial plateau landmarks, the tibial plateau slope marked on the radiograph obtained prior to the MMT was indicated on radiographs obtained after the procedure by digital superimposition. The advancement was measured perpendicular to the osteotomy line at the level of the previously described tibial bone mark with digital calipers (precision of 0.01 mm), and 0.6 mm was subtracted from the raw measurement to account for blade width. This measurement was deemed the true advancement distance. The same blinded observer (PP) measured the PTA with true advancement on posttreatment radiographs in random order on 3 separate occasions with a ≥ 1-week interval between measurements. Limb constructs were maintained until completion of the study and confirmation of an acceptable PTA (90 ± 0.1°). When the mean final PTA of the 3 series of measurements was not equal to that acceptable value, new radiographs were obtained to determine the true advancement distance.26
To evaluate the amount of patellar translation resulting from PTA reduction by use of the MMT, 1 blinded observer (PP) independently measured the patellar tendon length and the distance between pretreatment and posttreatment proximal insertion of the patellar tendon for each stifle joint in the present study. The measurements were performed on superimposed radiographs in random order on 3 separate occasions with a ≥ 1-week interval between measurements. The percentage distance of patellar translation along the patellar ligament was also calculated.
The position of the Maquet hole and the osteotomy length on the posttreatment radiographs were compared with the pretreatment planning measurements of D1 and D2 and osteotomy length, respectively. The median osteotomy length on the posttreatment radiographs was 60 mm (range, 42 to 73 mm), and the median D1 and D2 measurements were 45 mm (range, 33 to 58 mm) and 4 mm (range, 3 to 6 mm), respectively. On the basis of our clinical experience, we deemed a 5% margin of error between the planned and true osteotomy positions to be acceptable. Therefore, for comparison between desired and true advancement measurements, differences between the planned and true osteotomy length and D1 measurements were considered acceptable if < 3 and 2 mm (approximation of the 5% margin of error), respectively. Concerning D2, we chose to fix this difference to 1 mm, as a true 5% margin of error (0.2 mm) would be not clinically relevant.
Data analysis
Some data were not normally distributed (as assessed by the Shapiro-Wilk test). Therefore, results are presented as median, mean, IQR, and range. Advancement measurements for the tibial tuberosity and CPFs were subjected to statistical analysis. Agreement between the adjusted advancement and true advancement measurements was assessed with the Lin CCC.31–33 The CCC was calculated with 95% CIs and was used to determine agreement or repeatability according to the following scale: 1, perfect; ≥ 0.9 and < 1, excellent; ≥ 0.7 and < 0.9, good; ≥ 0.5 and < 0.7, moderate; and < 0.5, poor. Disagreement was further qualified by assessment of the precision (ρ) and accuracy (χa) factors; a perfect agreement is characterized by ρ = 1 and χa = 1.
Intraobserver, interobserver, and total agreement for a5 measurements and CPFs were assessed with intraobserver, interobserver, and total CCCs,34 which provide indices of agreement and measures of precision and accuracy. The closer these indices are to 1, the more perfect the agreement is. The scale used to determine the different levels of agreement was the same as that used for advancement measurements.
All calculations were performed with statistical software.d The Lin CCCs were calculated with software tools for analysis of epidemiological data.e
Results
Procedure planning measurements
The median PTA and tibial plateau angle in pretreatment radiographs were 102.7° (mean, 103.9°; IQR, 101.4° to 107.4°; range, 100.0° to 110.1°) and 23.5° (mean, 23.4°; IQR, 22.0° to 24.8°; range, 19.8° to 26.8°), respectively. Measurements for advancement of the tibial tuberosity determined with the osteotomy axis method (a0, a3, a5, and a10) were summarized (Table 1). Intraobserver, interobserver, and total agreements for a5 measurements were excellent (Table 2). The median CPF (a unitless value) was 1.22 (mean, 1.21; IQR, 1.18 to 1.24; range, 1.13 to 1.30). The intraobserver and interobserver agreements for the CPF measurements were good, and total agreement was 0.83. Intraobserver accuracy could not be calculated for the a5 measurements or for CPF; lack of convergence in the analysis for these variables could have been attributable to values close to 1. Adjusted advancement measurements (A0, A3, A5, and A10) made with the osteotomy axis and cage position method were reported (Table 3).
Unadjusted advancement measurements determined with the osteotomy axis method in a study to evaluate use of a new procedure to calculate the distance by which the tibial tuberosity should be advanced to reduce the PTA to 90° with the MMT in dogs.
| Advancement measurement | Median | Mean | IQR | Range |
|---|---|---|---|---|
| a0 (mm) | 12.7 | 12.8 | 10.4–14.3 | 8.1–18.5 |
| a3 (mm) | 12.0 | 12.0 | 9.8–13.5 | 7.6–17.4 |
| a5 (mm) | 11.5 | 11.4 | 9.2–12.8 | 7.3–16.3 |
| a10 (mm) | 10.4 | 10.3 | 8.5–11.4 | 6.7–14.8 |
Measurements were made on digital radiographs of 24 pelvic limbs from 12 canine cadavers prior to PTA reduction by means of the MMT. The a0 measurement was determined along a line perpendicular to the planned osteotomy and represented the distance in the cranial direction between the distal insertion of the patellar tendon on the tibia and a line perpendicular to the tibial plateau that extended from the proximal insertion of the patellar tendon past the cranialmost point of the tibial tuberosity. The same measurement was performed with the origin of the line perpendicular to the tibial plateau located 3, 5, and 10 mm distal to the proximal insertion of the patellar tendon along the patellar tendon line to obtain a3, a5, and a10 values as a means of accounting for anticipated distal translation of the patella after advancement of the tibial tuberosity. Measurements were determined in random order 3 times for each stifle by 1 blinded observer.
Concordance correlation coefficient, precision (ρ), and accuracy (χa) determinations for intraobserver, interobserver, and total agreement for measurement of the a5 distance for advancement of the tibial tuberosity on pretreatment radiographs and determination of the CPF for the same sample as in Table 1.
| Variable and agreement type | CCC (95% CI) | ρ (95% CI) | χa (95% CI) |
|---|---|---|---|
| a5 Measurement | |||
| Intraobserver | 0.96 (0.94–0.98) | 0.96 (0.95–0.97) | — |
| Interobserver | 0.96 (0.94–0.96) | 0.96 (0.95–0.97) | 0.96 (0.96–0.97) |
| Total | 0.95 (0.93–0.97) | 0.96 (0.95–0.97) | 0.99 (0.98–0.99) |
| CPF determination | |||
| Intraobserver | 0.86 (0.82–0.91) | 0.86 (0.82–0.91) | — |
| Interobserver | 0.89 (0.85–0.93) | 0.91 (0.87–0.94) | 0.99 (0.97–0.99) |
| Total | 0.83 (0.79–0.88) | 0.83 (0.80–0.87) | 0.98 (0.97–0.99) |
The CPF was calculated for each stifle joint as (OL – 3)/(OL – H), where OL is the length of the planned osteotomy, 3 is the distance (in millimeters) of advancement cage application along the osteotomy site from the proximal margin of the tibial bone, and H is the distance from the proximal extent of the planned osteotomy to an intersection point between the osteotomy axis and a line drawn perpendicular to the planned osteotomy at the level of the TTA distance measurement. The a5 measurements and CPFs were determined in random order on separate occasions by each of 3 blinded observers for assessment of agreement. Each individual performed measurements for each stifle joint in random order 3 times with a ≥ 1-week interval between readings. Levels of agreement were determined according to the following scale: 1, perfect; ≥ 0.9 and < 1, excellent; ≥ 0.7 and < 0.9, good; ≥ 0.5 and < 0.7, moderate; and < 0.5, poor.
— = The intraobserver accuracy for a5 and CPF measurements could not be determined. These values are calculated by iteration, and data did not converge for these variables.
Adjusted advancement distances determined on pretreatment radiographs with the osteotomy axis and cage position method for the same sample as in Table 1.
| Advancement measurement | Median | Mean | IQR | Range |
|---|---|---|---|---|
| A0 (mm) | 15.1 | 15.5 | 12.6–18.0 | 9.3–22.5 |
| A3 (mm) | 14.3 | 14.6 | 11.9–17.1 | 8.7–21.2 |
| A5 (mm) | 13.6 | 13.8 | 11.2–16.2 | 8.4–19.9 |
| A10 (mm) | 12.6 | 12.5 | 10.3–14.4 | 7.7–18.0 |
Advancement distances a0, a3, a5, and a10 obtained with the osteotomy axis method for each stifle joint were each multiplied by the CPF for that joint to create the adjusted advancement measurements A0, A3, A5, and A10, respectively.
True advancement measurements
The median true advancement for the tibial tuberosity was 13.5 mm (mean, 13.9 mm; IQR, 11.6 to 15.9 mm; range, 8.4 to 19.6 mm).26 Regarding the position of the Maquet hole, the differences between the planned and true D1 and D2 met the predetermined acceptance criteria of < 2 and < 1 mm, respectively, for each limb. The difference between the planned and true osteotomy length met the predefined acceptance criterion of < 3 mm for each limb.
Agreements between adjusted and true advancement measurements were good to excellent (Table 4). All of the adjusted advancement measurements with the line perpendicular to the tibial plateau placed 0 and 10 mm distal to the proximal insertion of the patellar tendon were subjectively greater and lesser than the true advancement measurements, respectively (Figure 4). Similarly, most of the adjusted advancement measurements with the line perpendicular to the tibial plateau placed 3 mm distal to the proximal insertion of the patellar tendon were greater than the true advancement measurements. The adjusted advancement measurements with the line perpendicular to the tibial plateau placed 5 mm distal to the proximal insertion of the patellar tendon had the best agreement with the true advancement measurements (CCC close to 1; Table 4). With a precision of 0.99 and an accuracy of 0.98, the osteotomy and cage position method with the line perpendicular to the tibial plateau located at this level was the most appropriate method evaluated for determination of the true advancement. The data points were close to the equality line on graphic analysis, and the difference between the slope for the data and the slope of the equality line was very small.
Scatterplots showing relationships between adjusted advancement measurements obtained with the osteotomy axis method and cage position method (A0, A3, A5, and A10) on radiographs for 24 stifle joints from 12 canine cadavers and true advancement measurements (TA) for the same stifle joints (A through D). True advancements were determined in a previous study.26 The line of equality (gray) represents perfect agreement between methods. Shorter distances between the data points and the equality line, whether above or below the line, indicate greater absolute agreement between methods. Smaller differences between the slopes of the sample data (blue line) and the equality line indicate greater consistency between methods.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
Scatterplots showing relationships between adjusted advancement measurements obtained with the osteotomy axis method and cage position method (A0, A3, A5, and A10) on radiographs for 24 stifle joints from 12 canine cadavers and true advancement measurements (TA) for the same stifle joints (A through D). True advancements were determined in a previous study.26 The line of equality (gray) represents perfect agreement between methods. Shorter distances between the data points and the equality line, whether above or below the line, indicate greater absolute agreement between methods. Smaller differences between the slopes of the sample data (blue line) and the equality line indicate greater consistency between methods.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
Scatterplots showing relationships between adjusted advancement measurements obtained with the osteotomy axis method and cage position method (A0, A3, A5, and A10) on radiographs for 24 stifle joints from 12 canine cadavers and true advancement measurements (TA) for the same stifle joints (A through D). True advancements were determined in a previous study.26 The line of equality (gray) represents perfect agreement between methods. Shorter distances between the data points and the equality line, whether above or below the line, indicate greater absolute agreement between methods. Smaller differences between the slopes of the sample data (blue line) and the equality line indicate greater consistency between methods.
Citation: American Journal of Veterinary Research 78, 4; 10.2460/ajvr.78.4.517
Concordance correlation coefficient, precision (ρ), and accuracy (χa) determinations for agreement between the adjusted advancement distances for the tibial tuberosity (A0, A3, A5, and A10) on pretreatment radiographs and true advancement measurements determined on posttreatment radiographs following PTA reduction to 90° with the MMT for the same sample as in Table 1.
| Comparison | CCC (95% CI) | ρ | χa |
|---|---|---|---|
| A0 vs true advancement | 0.83 (0.73–0.89) | 0.98 | 0.86 |
| A3 vs true advancement | 0.92 (0.88–0.94) | 0.99 | 0.96 |
| A5 vs true advancement | 0.96 (0.94–0.98) | 0.99 | 0.98 |
| A10 vs true advancement | 0.86 (0.77–0.91) | 0.99 | 0.89 |
True advancement measurements for the tibial tuberosity were determined for each stifle joint in a previous study.26 Advancement was adjusted until the PTA was 90 ± 0.1° on a mediolateral radiograph, and a blinded observer measured each PTA on posttreatment radiographs in random order on 3 separate occasions with a ≥ 1-week interval between measurements. If the mean final PTA was not within 1° of the predetermined 90°, the procedure was repeated. See Tables 2 and 3 for remainder of key.
The median patellar tendon length and patellar translation after MMT were 51.7 mm (mean, 51.8 mm; IQR, 48.9 to 53.9 mm; range, 42.6 to 61.2 mm) and 5.5 mm (mean, 5.6 mm; IQR, 4.9 to 6.2 mm; range, 3.2 to 8.1 mm). The median percentage distance of translation along the patellar ligament was 11.0% (mean, 10.2%; IQR, 9.2% to 13.1%; range, 5.6% to 16.6%).
Discussion
Preoperative measurements are among the most critical components of TTA by conventional methods or the MMT.30,35,36 Our results indicated that the new method described in the present study with the line perpendicular to the tibial plateau placed 5 mm distal to the proximal insertion of the patellar tendon resulted in planning measurements that were in close agreement with true advancement measurements after PTA reduction to 90 ± 1°, suggesting this is an excellent method to determine the amount of advancement required when an MMT is performed.
Several factors could explain why previously described methods seem to fail to determine the true advancement distance of the tibial tuberosity needed to achieve a PTA of 90° with the MMT. As mentioned before, advancement distance determined with the correction method,24 the modified TTA method,25 or the tibial anatomy-based method described by Ness22 is measured in a cranial direction, perpendicular to the tibial mechanical axis or tibial crest. However, clinically, the authors of the present study noticed that the osteotomy axis was rarely parallel to the tibial mechanical axis or tibial crest. As the tibial crest is advanced in a curvilinear fashion relative to the osteotomy, reading the advancement perpendicular to the tibial mechanical axis or tibial crest can be a source of error. We believe that it is more appropriate to determine the advancement along a line perpendicular to the planned osteotomy rather than the tibial mechanical axis. Thus, in the method described in the present study, the osteotomy position was planned by use of 2 distances (D1 and D2) as described for tibial plateau leveling osteotomy.37 Then, the advancement determination began with measuring the distance along a line perpendicular to the planned osteotomy axis from the proximal part of the tibial tuberosity to the line perpendicular to the tibial plateau (osteotomy axis method).
Current recommendations for advancement cage application indicate the implant should be placed at the proximal extent of the osteotomy but 2 to 5 mm distal to the proximal margin of the tibial bone.18,20 In previously described methods, however, the advancement measurement is made at the level of the proximal part of the tibial tuberosity. Because the tibial crest is not moved proximally with the MMT, the cage placement is proximal to the level of the advancement measurement. Therefore, the advancement at the level of the tibial tuberosity is less than expected, which would likely contribute to differences between the desired and actual distances. This error could be corrected by lowering the cage to the level of the tibial crest as described by Burns and Bourdieau38 for a modified TTA procedure used in large- or giant-breed dogs. However, without a cancellous bone block placed proximal to the cage to provide buttress support, this approach would dramatically increase the risk of tibial crest fracture.38 To account for the discrepancy between the level of the advancement measurement and the level of the cage application in the present study, a CPF was determined for each stifle joint, taking into account the cage application level along the osteotomy site, the osteotomy length, and the level of advancement measurement along the planned osteotomy. The CPF was calculated as (OL - 3) / (OL - H), where OL represented the osteotomy length and H represented the distance from the proximal extent of the planned osteotomy to an intersection point between the osteotomy axis and a line drawn perpendicular to the planned osteotomy at the level of the advancement measurement. The value 3 corresponded to the distance (in millimeters) of the cage application along the osteotomy site from the proximal margin of the tibial bone. We chose 3 mm as it is the value used at our institution; however, any other appropriate cage placement distance from the proximal margin can be used in this formula. We calculated the desired advancement (adjusted advancement distances) by multiplying the advancement distance obtained with the osteotomy axis method by CPF. On the basis of CCC determinations, the intraobserver and interobserver agreements of the CPF measurements were good.
Advancement of the tibial tuberosity in a curvilinear manner without proximal displacement induces a distal translation of the patella when the MMT is performed.25 In fact, the patella follows the direction of advancement of the tibial tuberosity, which is cranial and distal with this procedure. Similar to the modified TTA method,25 the method described in the present study also included steps to account for distal translation of the patella. The distance of the line drawn perpendicular to the tibial plateau slope to the proximal insertion of the patellar tendon is set to 3 mm in the modified TTA method.25 However, we observed a greater amount of distal patellar translation on most posttreatment mediolateral radiographs of stifle joints with PTAs of 90 ± 0.1° obtained in our previous study (where images used in the present study were obtained).26 Therefore, we chose to evaluate 4 configurations, with the line perpendicular to the tibial plateau successively placed at the proximal insertion of the patellar tendon (distance of 0 mm) and 3, 5, and 10 mm distal to this point along the patellar tendon axis. The values 0 and 3 were chosen on the basis of previously described methods,8,22,24,25 and the values 5 and 10 were included because of our findings in the previous study.26 We believed that the median distal patellar translation was close to 5 mm, but elected to include a higher value as well to evaluate its impact on the advancement measurements. According to our results, placing this line 5 mm distal to the proximal insertion of the patellar tendon along the patellar tendon axis provided the best agreement with true advancement measurements. These results were corroborated by the finding that the median patellar translation was 5.5 mm (range, 3.2 to 8.1 mm). However, these results should be considered with caution. Indeed, the appropriate distance may depend on the size of the dog and the patellar tendon length. The limbs studied were from cadavers of adult, medium-sized to large-breed dogs that weighed from 17.3 to 37.8 kg, and the median patellar tendon length was 51.7 mm (range, 42.6 to 61.2 mm). The appropriate distance may be shorter in small-breed dogs and larger in giant-breed dogs. This distance might also require adjustment according to the amount of advancement needed, with a shorter distance for small advancements and a larger distance for large advancements. Six stifle joints in the present study had an adjusted advancement ≥ 16 mm, and each had a patellar translation > 6 mm (range, 6.0 to 8.5 mm) and a percentage translation distance along the patellar ligament > 13.5% (range, 13.5 to 16.6). Some stifle joints with a lesser adjusted advancement (< 15 mm) had also a similar amount of patellar translation (> 6 mm); however, these stifle joints had a percentage translation distance along the patellar ligament < 13.5%. There appeared to be some correspondence between the amount of needed advancement and the percentage translation distance of the patella along its ligament; however, further studies are needed to investigate this.
In another study6 that used pelvic limbs from canine cadavers, neutralization of femorotibial shear forces occurred at a PTA of 90.3 ± 9°.6 Moreover, in a retrospective study of dogs that underwent unilateral or bilateral TTA, the mean postoperative PTA was 95°, and most patients had a clinically acceptable outcome.19 Additionally, results of a retrospective case series39 investigating the outcomes of 458 dogs following TTA indicated a mean postoperative PTA of 92 ± 2°, with high overall owner satisfaction in regard to clinical outcomes. Therefore, it is possible that underestimation of the required advancement distance may not have a clinical impact. However, another in vitro study15 determined that a PTA < 90° was required for stifle joint stability and that a PTA as low as 86° was required at higher limb loads (50% of body weight). Moreover, success (ie, postoperative PTA < 95°) rates reported in the study25 of dogs that underwent the MMT with preoperative measurements made by use of the modified TTA planning method and the tibial anatomy-based method described by Ness22 were fairly low (20/38 [53%]). The true cutoff value for underreduction of the PTA is unknown. A PTA reduction close to the ideal 90° may be sufficient to adequately neutralize femorotibial shear forces in most cases, but the angle may be more critical in some dogs than in others.38 A substantial margin of error without a meaningful clinical impact has been suggested to exist for TTA in regard to the final PTA,19–21,40–42 as observed with tibial plateau leveling osteotomy. However, we are convinced that an accurate and reproducible preoperative planning method is essential.19,41,42 Indeed, at least in some cases, an underreduction of the PTA could lead to the persistence of instability, which could explain the high rate of late meniscal tears (19/501 [4%] to 5/18 [28%]) observed for dogs that underwent the original TTA.20,39–42 We believe that the osteotomy axis and cage position method described in the present study will be a useful means to achieve the desired postoperative PTA in dogs.
Several factors can influence measurements for advancement procedure planning, including the stifle joint extension angle,21,27,43,44 the stifle joint extension angle measurement method,23 the degree of femorotibial joint subluxation,45 the PTA measurement method,35,36 and the advancement measurement method.24,35,36 To the best of our knowledge, the impact of these factors on the required advancement when an MMT is performed has not been evaluated; however, all of these factors, with the exception of the advancement measurement method, would be expected to have similar influences in both procedures.
In the present study, the stifle extension angle was fixed and maintained with an external skeletal fixator during all of the manipulations because stifle joint flexion is a major contributor to the PTA (there is a linear decrease of the PTA with increasing stifle joint flexion).27 A recent study45 found that cranial tibial subluxation causes underestimation of the PTA; thus, the cranial cruciate ligament was kept intact in the stifle joints of this study. A spring and a turnbuckle were used to simulate the quadriceps mechanism.6,26 The adjustable turnbuckle was turned as necessary to straighten the patellar tendon, which facilitated the identification of the patellar tendon axis (cranial aspect of the patellar tendon). Because the cranial and caudal cruciate ligaments were kept intact, the patellar tendon was indeed straightened subjectively without overtensioning, so that the tension applied was not similar between dogs but depended on the stifle joint conformation. Standardizing the tension applied could have predisposed some of the stifle joints to be overextended or could have prevented the cranial translation of the tibial crest. Only images in the true lateral position were used to ensure both the accurate identification of the different anatomic and PTA landmarks.26,28
All described advancement measurement methods required the identification of the tibial plateau landmarks and PTA measurement, which can be determined with the tibial plateau method8,10 or the with common tangent method.23 Because the identification of tibial plateau landmarks can introduce variability,28,35 identical tibial plateau slopes were obtained for pretreatment and posttreatment radiographs through digital image superimposition. This methodology permitted comparison of the desired advancement measurements with the true advancement measurements. Moreover, intraobserver and interobserver agreement for PTA measurement methods28,35 and the impact of PTA measurements on advancement measurements35 have already been studied. Therefore, we also chose to use the same tibial plateau slope between observers and reading sessions to allow evaluation of the intraobserver and interobserver agreements for advancement measurement methods only. The intraobserver and interobserver agreements of the a5 measurements were excellent; however, we are aware that the true intraobserver and interobserver agreements for the whole method would be lesser, as identification of the tibial plateau landmarks can introduce some variability. All described advancement measurement methods require the identification of the tibial plateau landmarks and PTA measurement, so we anticipate that the amount of variability between methods resulting from variability in identification of the tibial plateau landmarks would be the same, but further research is needed to address this appropriately.
Because the purpose of this study was to focus on the evaluation of the impact of the new advancement measurement method, the assessment of the tibial plateau slope was performed with only 1 method. Results of a recent study29 showed that the common tangent and the tibial plateau methods underestimate and overestimate the PTA measurements, respectively, and the authors recommended use of the method that overestimates the PTA. Moreover, this method was reported to be easier, faster, and more reliable than the common tangent method.29,35 Thus, the tibial plateau method was used for the present study. As a consequence of using superimposition of radiographic images, we were able to use the same tibial plateau landmarks for the determination of the desired radiographic advancements and the true advancement required for PTA reduction to 90°. Therefore, we believe that the method used for PTA measurement had no impact on the study results and that the degree of disparity between the desired and true advancements would be the same had the alternate method been applied.
The difference between the planned and true osteotomy positions was < 5% in all of the limbs studied, indicating that the planned osteotomy is easy to report on the tibia. However, it will be interesting to evaluate the agreement between the planned and true osteotomy position in clinical situations. A discrepancy between the planned and true osteotomy might lead to inadequate reduction of the PTA. Studies of tibial plateau leveling osteotomy in dogs have evaluated differences between planned and true osteotomy positions.46,47 We believe that the difference between the planned and the true osteotomy position would be low in dogs undergoing the procedure evaluated in the present study, because it is easy to perform a straight osteotomy in comparison to a circular osteotomy. Further studies are needed to investigate this point.
As in any cadaveric study, the lack of normal forces exerted by muscles and anatomic variations was also a limitation of this study. Other variables must also be considered to properly assess the efficacy of the MMT, including the proximodistal displacement of the patella, the translation of the femur relative to the tibia, and the tibia-ground angle.24 However, results of the present study suggested that the osteotomy axis and cage position method with adjustment for a distal patellar translation distance of 5 mm has the potential to improve the success rates for achieving the desired postoperative PTA of 90° in dogs treated for cranial cruciate ligament rupture with the MMT, and further research is warranted.
Acknowledgments
No support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
The authors thank Dr. Sylvain Larrat for assistance with statistical analyses.
ABBREVIATIONS
| CCC | Concordance correlation coefficient |
| CI | Confidence interval |
| CPF | Cage position factor |
| IQR | Interquartile range (25th to 75th percentile) |
| MMT | Modified Maquet technique |
| PTA | Patellar tendon-tibial plateau angle |
| TTA | Tibial tuberosity advancement |
Footnotes
Fujifilm FCR XG-1 Computed Radiography, Fujifilm, Düsseldorf, Germany.
Osirix, 64 bit, Pixmeo, Geneva, Switzerland.
PMF 10.8 V 2B oscillating saw, Bosch, Gerligen, Germany.
R, version 3.2.0, R Foundation for Statistical Computing, Vienna, Austria. Available at: www.R-project.org. Accessed Apr 17, 2015.
Epi.ccc, epiR, version 0.9–79, R Foundation for Statistical Computing, Vienna, Austria. Available at: www.R-project.org. Accessed Jul 16, 2016.
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