Comparison of Extracapsular Stabilization Techniques Using an Ultrasonically Implanted Absorbable Bone Anchor (Weldix) after Cranial Cruciate Ligament Rupture in Cats-An In Vitro Study

Abstract

Background: This study evaluated joint stability after surgical repair of cranial cruciate ligament (CrCL)-deficient stifle joints in cats using a novel absorbable polylactide bone anchor in an ex vivo model.

Methods: Thirty-six hindlimbs from cats with intact (G_i group) and transected CrCLs were treated with fabellotibial suture alone (G_FW group), suture combined with an absorbable polylactide bone anchor (G_WD group), or suture combined with a nonabsorbable bone anchor (G_FT group), positioned in a limb press with predefined joint angles (stifle joint: 120 ± 5°; hock joint: 120 ± 5°) and loaded with 10%, 20%, and 30% of body mass (BM). Predefined points were measured on lateral radiographs and with a coordinate measurement machine. Distances on radiographs (mm) were measured and angles (°) were calculated to represent the craniocaudal movement and the internal rotation of the tibia.

Results: There were no differences for craniocaudal movement between G_i and G_FW or G_FT, but for G_WD regarding angle measurement at 30% BM. For internal rotation, there was no significant difference between G_i and G_FW or G_WD, but for G_FT.

Conclusion: The used absorbable polylactide bone-anchor was able to stabilize the stifle joint regarding internal rotation and craniocaudal movement as calculated from distance measurements.

Keywords: absorbable bone anchor; cat; cranial cruciate ligament rupture; fabellotibial suture.

Figure 1

Limb press. A = top plate; B = pedestal; C = copper tube holding the femoral shaft; D = spring mechanism to avoid slack; E = force gauge; and F = radiographic magnification marker (Biomedtrix, Whippany, NJ, USA). Arrowhead = screws to fixate the top plate. Arrow = Achilles tendon mechanism.

Figure 2

Illustration of the polylactide absorbable bone anchor (Weldix; VetWelding AG, Stansstad, Switzerland), its position in the femoral condyle and the bone tunnel through the tibia. The smaller images show the process of implantation from top to bottom.

Figure 3

Radiograph showing measurement of stifle and tarsal joint angles (green lines) on the left hindlimb with a transected cranial cruciate ligament and loaded with 20% body mass. Dark blue circles (r = 6 mm) are superimposed over the caudal aspect of the femoral condyles. Distances were measured from its center to the most cranial point of the tibial plateau (pink line).

Figure 4

Illustration of the changes within the angle representing craniocaudal movement (α), showing that the angle becomes smaller after CrCL transection as the tibial crest (T1) is cranially displaced. α = measured angle; orange point T1 = point 1 cm distal to the tibial crest; orange point F2 = lateral aspect of lateral fabella in an intact CrCL; green line G_i = vector between measured points with an intact CrCL; red line G_T = vector between measured points with a transected CrCL; violet arrow = illustration of movement when the CrCL is transected. Scale bar indicates 10 mm.

Figure 5

Illustration of the changes within the angle representing internal rotation of the tibia (β), showing that the angle becomes larger after CrCL transection as with internal rotation of the tibia when the fibular head (T2) moves laterally. β = measured angle; orange point T2 = fibular head in an intact CrCL; orange point F1 = proximal aspect of the trochlea groove in an intact CrCL; green line G_i = vector between measured points with an intact CrCL; red line G_T = vector between measured points with a transected CrCL; violet arrow = illustration of movement when the CrCL is transected. Scale bar indicates 10 mm.