Cranial cruciate ligament rupture is likely an underdiagnosed cause of lameness in cattle.1,2 In cattle, CCL injuries account for about 21% of lamenesses localized to the stifle joint; other causes of stifle joint lameness in cattle include septic arthritis, meniscal injury, and collateral ligament injury.3 Although 80% to 90% of lamenesses in cattle are localized to a digit,4,5 results of a recent study6 suggest that, at least in commercial feedlot cattle, lameness of the proximal portion of a limb (upper limb lameness), including stifle joint injuries, may be more prevalent than previously reported. For cattle with CCL injury that remain untreated, stifle joint instability often leads to debilitating osteoarthritis and economic losses owing to an increase in the amount of time affected animals spend laying down and the resultant decreases in feed intake, weight gain, and milk production as well as poor reproductive performance (eg, reluctance to breed, especially for bulls).2,7
Several intra-articular ligament replacement and prosthetic techniques have been described for CCL rupture repair in cattle.2,8–10 However, prosthesis or ligament failure, surgical site dehiscence, and septic arthritis are commonly associated with those techniques owing to the large biomechanical loads placed on the CCL or prosthesis and the inherent extensive range of motion for the stifle joint of cattle.2,5,8–12 Stifle joint imbrication is an extracapsular stabilization technique that involves placement of mattress sutures in the joint capsule and periarticular fascia to facilitate fibrosis and stabilization of the joint. Currently, imbrication is the only extracapsular technique described for stifle joint stabilization in cattle with CCL injury, and although it avoids some of the complications associated with intra-articular stabilization techniques, it is generally ineffective in large adult cattle.13,14 In dogs with CCL injury, extracapsular stifle joint stabilization techniques involve placement of a prosthesis around the fabella or anchoring of the fabella to the lateral femoral condyle.15–17
The study reported here had 3 objectives. The first objective was to determine the isometric points between the distal aspect of the femur (distal femur) and proximal aspect of the tibia (proximal tibia) that could be used as anchoring points for an extracapsular prosthesis in cadaveric adult bovine stifle joints that would provide stabilization of the stifle joint through its complete range of motion in an ex vivo model. The second objective was to determine the ideal crimping sleeve configuration for securing a loop of nylon leader line used as an extracapsular prosthesis for stabilization of CCL-deficient stifle joints in adult cattle. The third objective was to evaluate the efficacy of a novel extracapsular technique for ex vivo stabilization of adult bovine CCL-deficient stifle joints. We hypothesized that bone tunnels located in the caudodistal aspect of the femur and cranioproximal aspect of the tibia would be the most isometric locations for placement of an extracapsular prosthesis for stabilization of adult bovine stifle joints and cause minimal restriction on the range of motion for the joint. We also hypothesized that 800-lb-test monofilament nylon leader line secured in a loop with three 316 stainless steel crimping sleeves would yield similar elongation patterns and have similar force at failure as clinically normal adult bovine CCLs as determined in previous studies18–20 and that use of 3 crimping sleeves to secure the ends of the nylon line would provide more pullout strength, whereas use of 4 crimping sleeves would provide no benefit in terms of prosthesis strength.
Materials and Methods
Specimens
Thirteen stifle joints were obtained from 13 adult bovine cadavers (ie, 1 stifle joint/animal) that weighed between 450 and 800 kg. All cattle were euthanized for reasons unrelated to the musculoskeletal system and unrelated to the study; therefore, institutional animal care and use committee approval was not required. For each harvested limb, both the femur and tibia were transected at the mid-diaphyseal level. Specimens were stored at −18°C. Prior to testing, specimens were allowed to thaw at ambient room temperature (approx 20°C) for 24 to 48 hours, then all soft tissues other than the ligamentous structures of the stifle joint and the femorotibial joint capsule were removed.
Isometric testing
One cadaveric stifle joint was randomly selected and allowed to thaw for 36 hours prior to testing. On a piece of lightweight cardboard, a grid with 7 femoral (F) and 9 tibial (T) points was created such that there were 2 cm between each point. The grid was then positioned over the selected stifle joint so that point F2 was centered over the lateral femoral epicondyle and point T3 was located 2 cm caudal to the most cranial aspect of the tibial tuberosity crest and used as a template to create depressions in the lateral aspect of the distal femur and proximal tibia. Steel 4.5-mm ball bearings were inserted into the depressions. A type 1a external fixator was applied to the femur and tibia such that it spanned the stifle joint. The external fixator was used to maintain the stifle joint in flexion at angles of 135°, 90°, 65°, and 35° (as determined by a goniometer) while lateromedial radiographs were obtained (Figure 1).
For each radiograph, the location of each femoral point relative to that of each tibial point was assessed, and the distance between each femoral and each tibial point was measured. The measurements for each femoral-tibial point pair were included in subsequent analyses only if the femoral point remained caudal to the tibial point throughout the entire range of motion for the stifle joint (ie, at each of the 4 joint angles for which lateromedial radiographic images were obtained). If a particular femoral point was cranial to a given tibial point on any radiograph, that pairing was omitted from further analyses because placement of a prosthesis between those 2 points would not prevent cranial displacement of the tibia. For each femoral-tibial point pair, the maximum elongation was calculated as the difference between the longest and shortest measurements between the 2 points as determined from the lateromedial radiographs at each of the 4 joint flexion angles.
The femoral-tibial point pair with the smallest maximum elongation was considered the most isometric pairing and was used for all further analyses. Bone tunnels were drilled through the distal femur and proximal tibia at the identified points. Nylon leader line was passed through the tunnels and secured in a loop. The stifle joint was then manually manipulated through its complete range of motion to evaluate the feasibility of the prosthesis (leader line) for joint stabilization in regard to the 3-D anatomy of the stifle joint.
Mechanical testing of nylon loop constructs
Prior to initiation of this part of the study, a sample size calculation was performed with a commercial power calculatora to determine how many replicates would be necessary in each suture loop construct group. Assumptions used for that calculation were derived from a previous study18 in which the tensile forces and elongation of various prosthetic sutures were compared with those of bovine CCLs. In that study,18 bovine CCLs ruptured at a mean force of approximately 4,500 N and 3 parallel strands of 450-lb-test monofilament nylon leader line ruptured at a mean force of approximately 6,200 N. Therefore, we wanted to be able detect a mean ± SD difference at failure of at least 2,000 ± 1,000 N between constructs. Power was set at 0.8 and α was set at 0.05. Results of that calculation indicated that a minimum of 4 replicates would be necessary for each construct.
Measurements were made on the cadaveric limb used for isometric testing to estimate the length of nylon leader line necessary to create a loop through the drilled tunnels in the distal femur and proximal tibia. Nonsterile 800-lb-test monofilament nylon leader lineb was cut into thirty-six 73-cm-long segments. Each segment was made into a loop by securing the nylon to itself with 2 (n = 12), 3 (12), or 4 (12) crimping sleeves. All crimping sleeves were 316 stainless steel oval sleevesb that were 9.5 mm in length with an inner diameter of 3.2 mm and outer diameter of 4.8 mm. Each sleeve was compressed with a commercial 18-inch fence crimperc at 3 locations along its length so that the entire sleeve was compressed to a uniform width. All sleeves were compressed by the same investigator (JWL).
The suture loop constructs were fixed in a hydraulic load frame.d One end of the load frame was equipped with a hydraulic ram. The other end was equipped with a load cell with a maximum force capacity of 100 kN and a force transducere that was used to measure the tensile force applied to the constructs and that had a temperature effect on sensitivity of 0.001% of reading/°F. The constructs were loaded to failure by displacement at a constant rate of 1 mm/s as described in another study.18 Distraction measurements were begun at a preload force of 20 N and were acquired at a rate of 100 measurements/s.18 Failure was defined as acute rupture of the nylon leader line or slippage of the line through the crimping sleeves as observed visually and was objectively indicated as a sudden decrease in the measured force. The compressed width of each sleeve and the mode of failure were recorded for each replicate.
Biomechanical evaluation of an extracapsular prosthesis for stabilization of the bovine stifle joint
After identification of the most isometric points on the femur and tibia for stabilization of the stifle joint and the optimum crimp configuration for the prosthetic suture, the remaining 12 cadaveric limbs were thawed and processed as previously described. The CCL was also transected. For each limb, a 5.5-mm drill bit was used to create bone tunnels in the distal femur at point F7 and the proximal tibia at point T3. Then 800-lb-test monofilament nylon leader lineb was threaded through the bone tunnels, manually pulled tight, and crimped with 3 stainless steel crimping sleeves. All prosthetic sutures were placed and secured by the same investigator (JWL).
A custom-made apparatus was used to fix the femorotibial joint, femur, and tibia to the same hydraulic load frame that was used for mechanical testing of the nylon loop constructs. For each limb, two 6.35-mm bone tunnels were drilled in the diaphyseal-metaphyseal region of the femur and tibia. A 6.35-mm positive-profile, stainless steel threaded pin was placed in each bone tunnel without prior tapping. An adjustable jigf was constructed to maintain the stifle joint at 135° of extension and secure it to the load frame for distraction. The stifle joint specimens were loaded to failure at a constant rate of 1 mm/s. The force generated by the displacement was measured by the load cell at a rate of 100 measurements/s. The compressed width of each sleeve and the mode of failure were recorded for each stifle joint.
Statistical analysis
The data distribution for each continuous variable was assessed for normality with the Shapiro-Wilk test. Normally distributed variables (maximum force at failure and AUC [measure of energy stored in the material just prior to failure]) were compared among the 3 suture loop constructs with a 1-way ANOVA followed by the Sidak test when post hoc pairwise comparisons were necessary. Nonnormally distributed variables (elongation) were compared among the 3 suture loop constructs with a Kruskal-Wallis test followed by the Bonferroni test when post hoc pairwise comparisons were necessary. Descriptive data regarding mode of failure (rupture of the nylon leader line [rupture] or slippage of the line through the crimping sleeves [slippage]) for each construct were generated. The compressed crimping sleeve width data was normally distributed for constructs that failed because of slippage but not for constructs that failed because of rupture. Thus, a Wilcoxon rank sum test was used to compare the compressed crimping sleeve width between constructs that failed because of slippage and those that failed because of rupture. All analyses were performed with statistical software program,g and values of P ≤ 0.05 were considered significant.
Results
Isometric testing
The maximum elongation between all possible pairwise combinations of femoral and tibial points (ie, potential locations of bone tunnels for placement of a prosthesis) was summarized (Table 1). The maximum elongation was shortest between points F7 (the most caudal and distal point assessed on the femur) and T3 (the most proximal and cranial point assessed on the tibia; Figure 1). A bone tunnel was drilled through the distal femur at point F7 and through the proximal tibia at point T3. Nylon leader line (prosthesis) was threaded through the tunnels and secured in a loop; however, a large step (or deviation) in the craniocaudal plane was created in the prothesis owing to the lateral femoral epicondylar flare and proximolateral extensor groove of the tibia. That deviation resulted in an increase in prosthesis elongation throughout the range of motion for the stifle joint. The tibial bone tunnel was subsequently modified to mitigate that elongation. The tunnel was drilled beginning on the lateral aspect of the tibia in the same horizontal plane as T3 but was located directly distal to the femoral tunnel. It was directed cranially and medially and exited the medial side of the tibial tuberosity directly opposite of T3 (Figure 2). In cattle, the medial aspect of both the femur and tibia is fairly flat, which permitted the prosthesis to be placed without the creation of a large deviation in and subsequent elongation of the suture and prevented cranial displacement of the tibia during movement of the stifle joint throughout its range of motion. Because the prosthesis was looped around both the lateral and medial aspects of the stifle joint and secured on the lateral aspect, internal rotation of the tibia was eliminated. If the construct had not been a loop and had been simply secured as a band on the medial aspect, internal rotation of the tibia would have been possible.
Maximum elongation (cm) between each femoral (F) and tibial (T) point combination assessed as potential locations for bone tunnels for placement of a prosthesis to stabilize CCL-deficient joints.
Femoral point | |||||||
---|---|---|---|---|---|---|---|
Tibial | F1 | F2 | F3 | F4 | F5 | F6 | F7 |
T1 | 3.7* | 2.4 | 4.8 | 2.2 | 2.4 | 2.8 | 1.8 |
T2 | 2.1* | 1.2* | 3.4* | 1.4* | 2.8 | 3 | 1.7* |
T3 | 5.5 | 3.9 | 6.4 | 3.2 | 1.7 | 3 | 1.1 |
T4 | 4.8 | 3.1 | 5.8 | 2.6 | 2.7 | 3 | 1.3 |
T5 | 2.8* | 1.5* | 4 | 1.5 | 2.7 | 3 | 1.5 |
T6 | 1.7* | 1.6* | 3.2* | 1.2* | 3 | 2.9* | 1.7* |
T7 | 5.1 | 3.3 | 6.1 | 3 | 1.8 | 3 | 1* |
T8 | 4.2 | 2.6 | 5.2 | 2.3 | 2.1 | 3 | 1.2 |
T9 | 3* | 1.5* | 4 | 1.6 | 2.6 | 2.9 | 1.2 |
The distance between each femoral and tibial point was measured on each of 4 lateromedial radiographic images, which were obtained with the stifle joint maintained at angles of 135°, 90°, 65°, and 35°. The maximum elongation was calculated as the difference between the longest and shortest measurements between the 2 points as determined from the 4 lateromedial radiographs.
Indicates that the femoral point was located cranial relative to the given tibial point on at least 1 of the 4 radiographic images, which prevented that pairing from further consideration for prosthesis placement because placement of a prosthesis at that location would not prevent cranial displacement of the tibia.
Mechanical testing of nylon loop constructs
The mean ± SD prosthesis elongation was 36.4 ± 1.8 mm, 40.8 ± 3.0 mm, and 41.1 ± 8.1 mm for the 2-, 3- and 4-sleeve constructs, respectively. The elongation rank as determined by a Kruskal-Wallis test for the 2-sleeve construct (12.46) was significantly (P = 0.048) lower than that for the 3- (22.17) and 4-sleeve (20.88) constructs.
The mean ± SD force at failure for the 2-sleeve construct (2,472.8 ± 448.9 N) was significantly lower than that for the 3-sleeve (3,636.2 ± 594.2 N; P = 0.002) and 4-sleeve (3,806.9 ± 1,084.7 N; P < 0.001) constructs. The mean force at failure did not differ significantly (P = 0.929) between the 3- and 4-sleeve constructs. Similarly, the mean ± SD AUC for the 2-sleeve construct (38.07 ± 5.31 NM) was significantly lower than that for the 3-sleeve (56.32 ± 10.92 NM; P = 0.026) and 4-sleeve (59.97 ± 23.69 NM; P = 0.006) constructs, and the mean AUC did not differ significantly (P = 0.927) between the 3- and 4-sleeve constructs.
The mode of failure was suture rupture for 9, 8, and 11 replicates of the 2-, 3-, and 4-sleeve constructs, respectively. All the remaining replicates (ie, 3, 4, and 1 replicates in the 2-, 3-, and 4-sleeve construct groups, respectively) failed because of suture slippage. The mean ± SD compressed crimping sleeve width for replicates that failed because of suture slippage (4.4 ± 0.3 mm) was significantly (P = 0.007) greater than that for replicates that failed because of suture rupture (4.0 ± 0.3 mm).
Biomechanical testing of an extracapsular prosthesis in bovine cadaveric CCL-deficient stifle joints
The 3-sleeve construct was selected for ex vivo stabilization of CCL-deficient bovine stifle joints and biomechanical testing. The 3-sleeve construct was preferred over the 2-sleeve construct because its mean force at failure was significantly greater. It was preferred over the 4-sleeve construct because the inclusion of an additional sleeve did not provide any benefit in terms of construct strength (ie, the mean force at failure did not differ between the 3- and 4-sleeve constructs) and added to the amount of foreign material present within the construct. All 12 replicates failed because of suture slippage. Unfortunately, the bolts used to fix the specimens to the testing apparatus flexed extensively during biomechanical loading, which resulted in highly variable and exaggerated data for suture elongation, force at failure, and AUC; therefore, the data were not formally analyzed.
Discussion
Results of the present study indicated that placement of a prosthesis through bone tunnels in the caudodistal aspect of the femur and cranioproximal aspect of the tibia might be a viable alternative for extracapsular stabilization of the stifle joint in adult cattle. However, the bone tunnel in the tibia could not be drilled in a straight lateral-to-medial direction at the identified isometric point (T3) because the anatomy of the femur and tibia caused a step-like deviation in the prosthetic suture, which resulted in suture elongation and inadequate joint stabilization throughout its range of motion. Instead, the tunnel had to be drilled beginning on the lateral aspect of the tibia in the same horizontal plane as point T3 and directly distal to the femoral tunnel. It was directed cranially and medially and exited the medial side of the tibial tuberosity directly opposite T3. Results also supported our hypotheses that 800-lb-test monofilament nylon leader line secured with three 316 stainless steel crimping sleeves would have similar elongation patterns and force at failure as clinically normal bovine CCLs and that the addition of a fourth crimping sleeve for securing the prosthetic construct would provide no benefit in terms of construct strength.
In the present study, isometric points in the distal aspect of the femur (distal femor) and proximal aspect of the tibia (proximal tibia) for prosthesis placement were initially determined by measurements obtained from serial lateromedial radiographic images with the stifle joint flexed at angles of 135°, 90°, 65°, and 35°. Metallic markers were placed on the distal femur and proximal tibia of the evaluated specimen prior to radiographic evaluation in a manner similar to that used in studies involving dogs.21,22 Unfortunately, the true isometry of the stifle joint cannot be determined from lateromedial radiographic images alone. Instead, isometry is often determined by measurement of tension and elongation in sutures implanted in the joint as has been described for human knees.23,24 When nylon suture was threaded through bone tunnels placed at the radiographically determined isometric points in the caudodistal aspect of the femur and cranioproximal aspect of the tibia, lateral motion caused by the lateral epicondylar flare of the femur and extensor groove of the tibia resulted in elongation of the prosthetic suture. This necessitated modification in the placement of the tibial tunnel as previously described so that the prosthesis would not interact with the lateral epicondylar flare of the femur and extensor groove of the tibia.
The use of only 1 cadaveric specimen to determine the most isometric points in the distal femur and proximal tibia was a limitation of the present study. Studies21,22,25–27 of the canine stifle joint have used 6 to 32 specimens for kinematic and radiographic evaluations to more accurately determine the isometric points of the joint. A study involving multiple bovine stifle joint specimens and the use of radiography, in vivo fluoroscopy, kinematic analyses, and in vitro suture tension evaluation through the complete range of motion for the joint is necessary to definitively determine the optimal location for femoral and tibial bone tunnels for placement of a prosthesis for extracapsular stabilization of the stifle joint in adult cattle. In particular, the optimal placement of the femoral tunnel warrants further investigation because the location identified for the 1 specimen evaluated in the present study was dangerously close to the intercondylar fossa. If the bone tunnel passed through the intercondylar fossa, the joint capsule would be penetrated, and the benefits associated with an extracapsular procedure would be obviated. The evaluation of multiple bovine stifle joints will allow for more precise determination of the most isometric location for placement of the femoral bone tunnel without entering the intercondylar fossa. Elucidation of that location will provide surgeons with external landmarks with or without radiographic guidance and enable them to drill femoral and tibial tunnels in patients with CCL-deficient stifle joints.
The mean force at failure did not differ between the 3- and 4-sleeve constructs and was significantly greater for those 2 constructs, compared with that for the 2-sleeve construct. We chose to use the 3-sleeve construct for ex vivo biomechanical testing because, relative to the 4-sleeve construct, we felt its use in clinical patients would result in the implantation of less foreign material, which in turn would decrease the surgical time for prothesis placement and decrease the potential for foreign material reaction or infection.
Commercially available crimping sleeves and crimpers were used for all nylon loop constructs evaluated in the present study, because surgical-grade alternatives of appropriate size to secure the 800-lb-test nylon leader line were not available. Specialized surgical equipment made of implant-grade stainless steel and custom-made surgical crimpers would be ideal for use in clinical patients and would help standardize the crimped width of the suture-securing sleeves regardless of operator. Although 1 investigator applied all the crimping sleeves in the present study, the mean width of the crimped sleeves of replicates that failed because of suture rupture was significantly less than that of the crimped sleeves of replicates that failed because of suture slippage. Consequently, we believe that, for the replicates that failed because of suture rupture, overcompression of the crimping sleeves likely compromised the integrity of the nylon suture, which contributed to its rupture. Further investigation is warranted to determine the optimum width of crimped sleeves relative to the suture size and mode of suture failure as well as to assess whether force at failure, suture elongation, and AUC vary significantly between constructs that fail because of suture rupture and those that fail because of suture slippage. That information is important because it can guide construct development. Additionally, the use of a custom-made tensioning device to tighten and secure the prosthesis should be investigated because manual tightening of the prosthesis is variable and may not provide enough tension to adequately stabilize the stifle joint in adult cattle with CCL-deficient joints.
The elongation, tensile force, and AUC at failure of adult bovine CCLs have been investigated. In 1 study,19 the ultimate tensile strength of the CCL was correlated with body weight (CCL ultimate tensile strength-to-body weight ratio, 1.4). In another study18 conducted by our research group, the CCL of adult cattle had a mean ± SD force at failure of 4,541 ± 1,417 N and an elongation of 20 ± 3 mm. In yet another study,20 the CCL of adult cattle had a mean ± SD ultimate tensile strength of 4,372 ± 1,485 N and load at first physical signs of tearing of 3,315 ± 1,336 N; however, the load at failure and body weight were not significantly correlated.
Several studies have attempted to determine the optimal prosthetic material for adult bovine CCL replacement. The single strand of 800-lb-test monofilament nylon leader line used for the constructs of the present study had a mean ± SD elongation of 40.8 ± 3.0 mm and force at failure of 3,636.2 ± 594.2 N, which was approximately 20 mm longer than the mean elongation and 80% of the mean force at failure for adult bovine CCLs evaluated in another study.18 The mean ± SD force at failure for the 3-sleeve constructs with a single strand of 800-lb-test monofilament nylon leader line evaluated in the present study was substantially lower, whereas the mean ± SD elongation was substantially longer, compared with the mean ± SD force at failure (6,260 ± 239 N) and elongation (33 ± 1 mm) for 3 parallel strands of 450-lb-test nylon leader line (6,260 ± 239 N) evaluated in that study.18 However, the mean force at failure for the 3-sleeve construct of the present study was greater than that for the established and tested over-the-top method (ie, Crawford technique) for bovine stifle joint stabilization.2 Moreover, the ultimate tensile strength of the Crawford technique2 is only 29.7 ± 0.67% that of adult bovine CCLs.18 To our knowledge, the force exerted on the CCL of healthy adult cattle while at a walk has not been investigated. In an in vivo human study,28 the peak tensile force applied to the ACL at a walk was approximately 28.5% of the peak force at failure for the ACL. It is likely that the ratio of peak tensile force at a walk to the peak force at failure for the CCL of quadrupeds will substantially differ from that for the ACL of humans. Nevertheless, the fact that the mean force at failure for the 3-sleeve construct evaluated in the present study was 80% that for clinically normal bovine CCLs indicated that the construct will be adequate for stifle joint stabilization of adult cattle. The AUC of a construct is important because it reflects the amount of energy required to rupture the material of interest, and a higher AUC is indicative of a more durable material. The mean AUC for the 3-sleeve construct evaluated in the present study was 92.0% that for clinically normal bovine CCLs and 59.8% that for 3 parallel 450-lb-test nylon lines evaluated in another study.18
A limitation of the present study was that the nylon loop constructs were tested in a single distraction-to-failure model. Cycling the constructs through a series of physiologic tensions would have been beneficial to determine how many cycles the constructs would withstand before failing and should be performed in a future ex vivo study. That information is important because the nylon suture makes sharp turns when it exits the bone tunnels, and the stress at those points under physiologic loads could impair the integrity and result in the premature rupture of the suture. It may also be beneficial to reevaluate all the nylon loop constructs assessed in the present study in ex vivo models because placement of the nylon suture through bone tunnels followed by biomechanical cycling through physiologic loads might reveal that the 3-sleeve construct was not the optimum construct.
We found the 800-lb-test nylon leader line used in the present study easy to manipulate despite its large size. The line is designed to be looped and crimped for deep sea fishing purposes, and it was not difficult to thread the line through the bone tunnels and crimping sleeves. In fact, the large diameter of the line allowed it to be manually threaded through the bone tunnels much more easily than suture with a smaller diameter and less stiffness. Also, it is easier to thread a single strand of suture through the bone tunnels than multiple strands of suture. The ease of prosthesis placement through bone tunnels in the presence of overlying soft tissues has yet to be determined.
All 12 replicates in the present study failed because of suture slippage during ex vivo biomechanical testing. We attributed the slippage to the presence of both tissue and fat on the cadaveric specimens, which made the constructs slippery, and the difficulty associated with the use of the large crimper against the femur and tibia to effectively crimp the crimping sleeves when the prosthesis was pulled tight. That problem further highlighted the need for a custom-manufactured tensioning device and crimper.
The ex vivo model used in the present study had several limitations. The tension was applied to the prosthesis with the stifle joint in a fairly extended position (135°), which was perhaps not very biologically relevant because in vivo, the stifle joint is generally loaded in flexion with translational movement. Additionally, the jigs created to secure the specimens to the testing apparatus were imperfect. Specifically, the bolts that were passed through the bone flexed during loading, which resulted in exaggerated force measurements. In future ex vivo studies, the femur and tibia should be potted in bone cement or polymethyl methacrylate, and the stifle joint should be stressed translationally in flexion to more accurately investigate prosthesis strength.
Findings of the present study suggested that 800-lb-test monofilament nylon leader line threaded through bone tunnels in the distal femur and proximal tibia and secured in a loop with 3 stainless steel crimping sleeves on the lateral aspect of the stifle joint might be a viable alternative for extracapsular stabilization of CCL-deficient joints in adult cattle. Further research is necessary to confirm the isometric points in the distal femur and proximal tibia, develop tools for more efficient prosthesis placement, and determine the optimal prosthesis construct for clinical patients.
ABBREVIATIONS
ACL | Anterior cruciate ligament |
AUC | Area under the curve |
CCL | Cranial cruciate ligament |
NM | Newton meter |
Footnotes
Power and Sample Size. Available at: powerandsamplesize.com/. Accessed Nov 19, 2018.
Blue Ocean Tackle, Coconut Creek, Fla.
Agri-Supply, Garner, NC.
LANDMARK, MTS Systems Corp, Eden Prairie, Minn.
Model 661.20F-03, MTS Systems Corp, Eden Prairie, Minn.
Unistrut, Atkore International, Harvey, Ill.
SPSS, version 25, IBM Corp, Armonk, NY.
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