Cranial cruciate ligament rupture is one of the most common causes of hind limb lameness in dogs and costs owners > $1 billion on an annual basis.1,2 Repair options are often grouped into extra-articular suture repair methods, such as the lateral fabella suture3 and prosthetic ligament4; tibial osteotomies, such as the TPLO,5 triple tibial osteotomy,6 center of rotation of angulation–based leveling osteotomy,7 and tibial tuberosity advancement8; and intra-articular repair methods, such as the over-the-top procedure9 and allograft placement.10 The TPLO was first described in the early 1990s and has become one of the most common cranial cruciate ligament repair methods performed in large-breed dogs.11,12 The TPLO results in equal, if not better, outcomes, compared with extra-articular suture repair methods.13,14 Similarly, TPLO outcomes and complication rates are comparable to those of other tibial osteotomy repair methods.15–18
Reported overall complication rates associated with TPLO range from 9% to 18.5%, with major complication rates ranging from 1.5% to 6.6%.15,16,19 Major complications associated with TPLO include meniscal injury, infection, tibial crest fracture, tibial shaft fracture, patellar ligament injury, and implant failure. Mechanical weakness can lead to partial loss of proximal segment rotation and development of delayed unions, malunions, or nonunions. The mechanical strength of a repair often relies on proper reduction, proper implant selection, proper implant placement, and maintenance of other natural supportive structures, such as the fibula.20
Although a number of TPLO plates are available, mechanical comparisons have not been performed for all available products,21,22 and selection of TPLO implants is often surgeon and cost dependent. Depending on the size of the patient, implant size is often chosen to optimize the number of screws placed in the proximal segment of the osteotomy. Although subjective, patients that are large, overweight, and overactive often raise concerns about implant failure. Precautions, such as the selection of a broad plate, addition of a second linear plate, use of locking screws (if the plate accepts locking screws), and leaving the ARP in place, can be used.19 Mechanical testing indicates that broad plates and locking plates can withstand higher loads than standard TPLO plates.22
Data are lacking regarding the mechanical benefits of the incorporation of the ARP with the plate fixation of a TPLO. If incorporation of the ARP with the plate fixation increases the strength of the repair, it may be more economical to leave the ARP in place rather than adding locking screws or using a larger implant. Conversely, if the benefits of leaving the ARP in place do not outweigh potential complications, such as pin loosening or breakage, then removal of the ARP should be recommended.
Although fibular fractures are rarely repaired in dogs, the contribution of such fractures to crus mechanics is unknown. In humans, the fibula contributes to the torsional strength of the lower portion of the leg,23 but little is known about its role in veterinary species. Fibular fracture has not been associated with an increase in complications following TPLO in dogs. However, an increase in TPA (ie, loss of leveling, or “rockback”) during healing has been described following TPLO for dogs with concurrent fibular fracture of the ipsilateral limb,20 and the contribution of the fibula to the mechanical properties of TPLO-repaired limbs is unknown. Elucidation of the mechanical importance of the fibula to TPLO-repaired limbs will help clinicians take appropriate actions when that bone is damaged before, during, or after surgery.
The objectives of the study reported here were, first, to assess whether the ARP adds to the compressive strength of a TPLO construct (bone and implants) and whether use of a second ARP further contributes to the compressive strength of the repair and, second, to quantify the contribution of an intact fibula to the TPLO construct in a cadaveric model. We hypothesized that the addition of 1 or 2 ARPs would not significantly add to the ex vivo mechanical axial strength of a TPLO repair and that fracture of the fibula would significantly decrease the compressive strength of a TPLO repair.
Supported by the Companion Animal Fund at the University of Tennessee College of Veterinary Medicine.
Tibial plateau angle
Tibial plateau leveling osteotomy
Unity cruciate plate, New Generation Devices, Glen Rock, NJ.
Crescentic osteotomy saw blade, New Generation Devices, Glen Rock, NJ.
Smooth-Cast 300Q, Smooth-On Inc, Macungie, Pa.
ElectroPuls E1000, Instron Norwood, Mass.
SAS, version 9.4, SAS Institute Inc, Cary, NC.
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