Page 603 - ONLINE PROCEEDING BOOK WSAVA 2017
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WSVA7-0579
ORTHOPAEDIC SURGERY
KNOTLESS ANCHORS FOR JOINT INSTABILITY: ADVANTAGES AND APPLICATIONS
A. Pozzi1
1Clinic for Small Animal Surgery, Department of Small Animals, Vetsuisse-Faculty, University of Zurich
Injuries causing joint instability are very common in dogs and cats. These injuries can be treated conservatively in some cases, but often require surgical stabilization. For example, treatment of tarsal medial collateral ligaments sprain depends on the severity of the injury. Some cases can be treated with coaptation only, but the more severe cases require surgical stabilization, which can
be performed using a prosthetic reconstruction of the ligaments using anchors, screws or bone tunnels. Other examples of applications of bone anchors for prosthetic stabilization are sti e and elbow luxation, carpal ligament reconstructions and in selected cases medial patellar luxation and cruciate ligament rupture.
Bone anchors are a typical implant for reattachment of soft tissues to bone or anchoring of prosthetic material to bone. Soft tissue  xation to bone is a basic technique of orthopedic surgery for which many procedures
and devices have been developed. Early techniques used bone tunnels, screws and washers and bone staples. These techniques are relatively simple, but
can have disadvantages including increased surgical exposure, damage to suture material, interference with joint structures and non-isometric placement. Since the suture anchors were developed in the late 1980s, several modi cations and improvements have been made. Suture anchors can be used effectively for reattaching avulsed soft tissues to bone, thus reestablishing integrity to tendons and ligaments. Suture anchors are usually made of stainless steel, titanium, Peek or an absorbable polymer. Design features that vary with suture anchors include size, method of anchoring (toggle, thread, tine), thread design, whether they are preloaded with suture, suture type, position of the anchor after insertion and method of insertion. Suture anchors have the advantage of a lower pro le than screws and washers, which help avoid interference and abrasion of articular surfaces
and adjacent soft tissues during joint movement. They also can be more precisely placed to allow improved reattachment of ligamentous structures to their isometric origin or insertion.
In the knotted bone anchors the suture material is loaded through an eyelid. Examples include the Corkscrew®
and Fastak® anchors (Arthrex Vet Systems, Naples, FL), IMEX, Securos, DePuy Synthes anchors. This method
of suture  xation differ from the knotless anchors
such as the SwiveLock® anchor (Arthrex Vet Systems, Naples, FL), where the suture is secured to the bone
as an interference screw. This anchor can be used for reconstruction of a variety of ligament tears, including cranial cruciate and collateral ligament tears. This anchor sits  ush to the bone and functions as an interference screw. One of the bene ts of the knotless anchors is the ability to apply tension on the suture as desired without the need for a knot. Additionally, the suture and anchors are  ush to the bone, leaving a very low pro le repair.
One of the advantages of knotless anchors is the versatility. Because of their low pro le and the various available sizes, they can be applied to multiple joints. In our experience, one of the most common locations is the tarsus. It is important to understand the anatomy of the tarsus before considering reconstruction. The tarsus is a complex joint and consists of four joint levels, the talocrural, the proximal intertarsal, the distal intertarsal, and the tarsometatarsal joint. The ligamentous support of the tarsus consists of the small dorsal ligaments, the plantar ligaments, which are reinforced by a  brocartilage plate, and the collateral ligaments. In the dog three distinct parts form the medial collateral ligamentous support. The long part runs from the medial malleolus
to the  rst tarsal bone, but also attaches to the central tarsal bone. During extension this long part becomes taut and during  exion it becomes loose. The short part of the ligament lies deeper and consists of two distinct parts. Both attach to the medial malleolus, but the  rst one runs to the talus (tibiotalar portion) and the second one to the central tarsal bone (tibiocentral portion). The medial collateral ligaments prevent varus and the lateral collateral ligaments prevent excessive valgus motion. The lateral collateral ligaments in the dog consist of three components: long lateral ligament, calcaneo bular short ligament and the talo bular short ligament. All of these part are attached to the lateral malleolus of the  bula. During extension of the tarsal joint, the long lateral and the calcaneo bular short ligament are taut, while the talo bular short component is tensioned when the tarsus is in a  exed position.
In contrast to dogs cats are missing the long collateral ligaments, although a tendon running on the lateral
as well as on the medial aspect of the tarsus act as ligaments. This is the tendon of the tibialis caudalis muscle on the medial side and the tendon of the
 bularis brevis muscle on the lateral side. All of the medial collateral joint stabilizers originate at the medial malleolus of the tibia. The tibiocentral ligament as well
as the tibialis caudalis tendon attach then to the central tarsal bone. The tibiotalar ligament consists of two parts: The craniodistal part attaches dorsodistomedial at the talus and the caudoproximal part plataroproximomedial
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