Abstract: Planning and control of a TPLO operation

The following explanations are largely based on the Excellent article by Prof. Andrea Meyer-Lindenberg and summarizes the key points.

Precise pre-operative examination and planning are crucial before surgical procedures, especially tibial plateau leveling osteotomy (TPLO) in veterinary medicine, to understand the biomechanical conditions of the knee joint and to determine the correct surgical approach. This includes a comprehensive assessment of the joint anatomy, muscle function, and body weight of the animal to ensure optimal functionality after the procedure. Detailed planning prevents postoperative complications and contributes to the animal's long-term health and mobility.

Introduction Planning and control of a TPLO-Operation

Veterinary medicine has changed considerably in recent decades. Previously, the focus was primarily on the diagnosis and treatment of diseases in farm animals. Since the mid-20th century, however, this focus has increasingly shifted towards the care of companion animals, particularly dogs and cats. This change parallels developments in human medicine, which has also led to increased demands from pet owners regarding veterinary care. Consequently, advanced diagnostic and therapeutic procedures have expanded and become established in veterinary medicine.

The knee joint – anatomical aspects

A dog's knee joint is structured similarly to a human knee joint, consisting of the condyles of the femur and tibia. However, unlike in humans, the cranial cruciate ligament plays a more central role in the stability of the knee joint in dogs. An injury to this ligament can have serious consequences, as it limits the forward movement of the tibia, as well as its internal rotation and hyperextension of the knee joint.

A unique feature of the canine knee joint is the muscle co-activity that supports its stability. Muscles such as the biceps femoris and quadriceps femoris act as agonists and antagonists, respectively, of the anterior cruciate ligament. The primary load during the dog's stance and weight-bearing phases is borne by the tibial plateau, which exhibits concave and convex shapes depending on the viewing plane. The inclination of the tibial plateau results in a forward thrust on the cruciate ligaments with each step, particularly on the cranial cruciate ligament.

The anatomical and biomechanical alignment of the tibial plateau plays a crucial role in the health and function of the knee joint. Measurements of the tibial plateau angle are essential for the diagnosis and planning of orthopedic procedures. A correctly measured tibial plateau angle (TPA) is critical for the success of surgical interventions, with the ideal angle for healthy dogs typically being less than 20°. Faulty radiographic techniques can lead to inaccurate measurements, which can compromise the success of surgery.

Measurements to detect deviations of the tibial plateau angle in the lateral plane

The tibial plateau angle (TPA) is determined using specific measurement points on a correctly aligned mediolateral radiograph. The tibial axis is represented as a straight line running from the center of the os tali to the highest point of the tibia between the intercondylar tuberosities. The tibial plateau itself is represented by a line oriented along the medial articular surface of the proximal tibia, with its boundaries defined by anatomical landmarks.

The tibial plateau slope (TPS) is the angle between the tibial axis and the line of the tibial plateau. To ensure accurate and consistent results, standardized radiographs with correct positioning of the animal are essential. Faulty radiographic techniques can impair the visualization of the TPS and lead to measurement errors that can jeopardize the success of surgical interventions. The TPS varies between different dog breeds, and the angulation of the knee joints can also differ between breeds. In healthy dogs, the TPS is typically less than 20°.

Measurements for detecting tibial axis deviation in the frontal plane

The correct diagnosis of tibial angulation in the frontal plane is crucial for orthopedic assessment and treatment. Four main aspects must be considered: the height of the apex, the plane of the deviation, the magnitude of the deviation, and the direction of the apex. The Center of Rotation of Angulation (CORA) is a key point defined by the intersection of the proximal and distal axes of the femur and tibia.

To detect tibial torsion as well as varus and valgus deformities, special X-ray images are required, taken in a caudocranial projection with the knee joint angled at approximately 132°. It is important that the patella is positioned centrally in the patellar groove and that certain anatomical markers, such as the fabellae and the medial border of the calcaneus, are clearly visible.

Specific points are defined for measurement to determine the mechanical medial proximal tibial angle (mMPTA) and the mechanical medial distal tibial angle (mMDTA) in the frontal plane. The average mMPTA is approximately 90° and the mMDTA is approximately 93°. No significant differences between the various dog breeds with respect to these angles were found.

(C) https://todaysveterinarypractice.com/orthopedics/small-animal-cruciate-disease-tibial-plateau-angle/

Rupture of the cranial cruciate ligament – occurrence, etiology and pathogenesis

Rupture of the cranial cruciate ligament is a common orthopedic condition in dogs, usually resulting in marked lameness. Unlike in humans, where cruciate ligament ruptures are most often caused by trauma, degenerative changes in the ligament are the more frequent cause in dogs. These changes can be triggered by a variety of factors, including inflammation, immunological processes, aging, obesity, instabilities such as patellar luxation, and limb malalignment.

A steep inclination of the tibial plateau may also predispose to cruciate ligament ruptures. The condition affects both large and small breeds, with larger breeds being affected at a younger age and smaller breeds often at an older age. However, a clear racial predisposition has not been established.

Partial or complete ruptures of the cranial cruciate ligament lead to increasing instability of the knee joint, which, if left untreated, can result in secondary changes such as osteoarthritis and capsular contracture. Cruciate ligament ruptures are frequently associated with damage to the caudal portion of the medial meniscus, while primary meniscal lesions are rare in dogs.

The diagnosis is based on medical history, clinical symptoms, and palpation findings, with the drawer sign and tibial compression test being important diagnostic tools. X-rays in two planes are essential for diagnosis and treatment planning, and in cases of uncertainty or for a more detailed examination of meniscal lesions, magnetic resonance imaging or arthroscopy may be performed.

Numerous surgical procedures have been developed for the treatment of cranial cruciate ligament injuries. These can be broadly divided into those that alter the joint's statics and those that do not. In medium to large dogs, surgical intervention is often necessary due to the significant forces acting on the joint. Conventional methods that do not alter the joint's statics are not always successful, as the implanted material can tear or instability can recur. Therefore, surgical techniques have been developed specifically for medium to large breeds that alter the joint's statics to neutralize the cranial cruciate ligament's function, thus promoting better stability and healing.

Diagnosis of anterior cruciate ligament tear

The diagnosis of an anterior cruciate ligament rupture in dogs is based on a careful history, clinical symptoms, and thorough palpation. Typically, the dog exhibits lameness ranging from mild to severe, accompanied by a weight-bearing stance and standing on its toes. Examination of the stifle joint may reveal thickening and instability, manifested by the drawer sign, where the tibia can be displaced anteriorly relative to the femur.

An additional diagnostic method is the tibial compression test, in which the tibia is compressed between the femur and tarsus during the stance phase, typically by body weight and contraction of the gastrocnemius muscle. This test simulates the forces acting on the knee joint and serves to demonstrate instability by causing the tibia to slide forward when the tarsal joint is flexed.

To confirm the diagnosis and plan treatment, X-rays should be taken in two planes. These can help identify secondary changes such as increased joint effusion or osteoarthritis. In unclear cases or for a more precise assessment of meniscal lesions, magnetic resonance imaging (MRI) can also be helpful. This allows for a more detailed examination of the ruptured cruciate ligament, meniscal and cartilage lesions, as well as changes in the bone or surrounding soft tissue. Arthroscopy can also be used for the direct examination of meniscal injuries.

Treatment options for anterior cruciate ligament rupture

For the treatment of anterior cruciate ligament rupture in dogs, there are many surgical methods, which can be broadly divided into two categories: those that alter the joint's statics and those that do not. The latter are further subdivided into extracapsular and intracapsular ligament reconstruction techniques. Particularly in medium and large dogs weighing over 20 kg, traditional methods that do not alter the joint's statics are often unsuccessful. Problems can arise from the graft material tearing or from loosening of the fixation during the healing process, which can lead to recurrent lameness and the progression of osteoarthritis or meniscal damage.

Due to these challenges, procedures have been developed specifically for medium to large dog breeds that modify joint statics. These approaches consider joint anatomy, muscle function, and body weight as an integrated system to replace or neutralize the function of the cranial cruciate ligament, thus making direct cruciate ligament replacement unnecessary.

A prominent example of such a method is tibial plateau leveling osteotomy (TPLO), in which the caudally inclined tibial plateau is surgically altered to eliminate anterior tibial translation (CTT). This is achieved by rotating and caudally elevating the tibial plateau through a semicircular saw cut, thereby altering the biomechanical relationships of the knee joint and circumventing the need for a functioning anterior cruciate ligament (ACL). After the operation, the caudal cruciate ligament assumes additional stabilizing functions in the knee joint, thus maintaining functional stability even without the ACL.

Principles of TPLO

The principles of tibial plateau leveling osteotomy (TPLO) are based on altering the joint statics and biomechanics of the knee joint. Normally, the axial reaction force during weight-bearing of the hind limb is directed along the longitudinal axis of the tibia. When this force encounters the tibial plateau, which slopes from cranial to caudal, it is converted into a compressive force (perpendicular to the tibial plateau) and a cranially directed force (parallel to the tibial plateau), triggering the forward movement of the tibia. In the case of a cranial cruciate ligament rupture, this inevitably leads to an undesirable cranial displacement of the tibia.

The goal of TPLO is to eliminate this unwanted cranial displacement. This is achieved by elevating the caudally inclined tibial plateau using a specific corrective osteotomy. This elevation alters the biomechanical inclination of the tibial plateau, eliminating the cranial translation of the tibia (CTT) and instead converting it into a gravitational thrust. This biomechanical correction leads to stabilization of the knee joint, replacing the original function of the damaged or torn cranial cruciate ligament.

Planning based on X-ray image and determination of the required rotation of the tibial plateau

Two X-rays are initially required to perform a tibial plateau leveling osteotomy (TPLO): one in the mediolateral and one in the craniocaudal projection. These images allow for the determination of the degree of rotation of the tibial plateau and any necessary axial corrections. Determining these angles is crucial for achieving correct realignment of the knee joint and modifying the forces acting on the tibial plateau so that they can be absorbed by the cruciate ligament. The goal is to enable muscular compensation during the weight-bearing phase and thereby alter the biomechanical conditions in the knee joint so that the anterior displacement of the tibia (cranial tibial translation, CTT) is eliminated.

The TPLO procedure aims to rotate and elevate the caudally sloping tibial plateau by means of a custom-designed, semicircular saw cut in the proximal tibia. This alters the biomechanics of the knee joint, resulting in functional stability during the stance phase. Rotating the tibial plateau to approximately 65° eliminates the forward thrust of the tibia, thereby allowing the cruciate ligament to assume an additional stabilizing role.

It is important that the posterior cruciate ligament (PCL) is intact, as it is subjected to increased forces after TPLO surgery. Exceeding the optimal angle can endanger the PCL. Therefore, careful planning and execution of the TPLO are crucial to ensure correct biomechanical adaptation and long-term stability of the knee joint.

Patient preparation and monitoring of the procedure

Preparing for and monitoring the surgical procedure of a tibial plateau leveling osteotomy (TPLO) requires specialized instruments and precautions. In addition to standard surgical instruments and tools, such as special saw blades and TPLO jigs, specially designed plates are needed to fix the tibial plateau. Several different plate models are available, with angle-stable plate systems proving particularly effective.

Before the operation, the patient undergoes surgical preparation, being positioned either on their side or supine. Following preparation, access to the knee joint is established, possibly after prior arthroscopy to assess or treat meniscal tears.

During the operation itself, a special TPLO jig is used, which is attached to the tibial plateau and tibial diaphysis via two Kirschner wires. This allows for precise control and adjustment of the saw cut during the procedure. The jig also serves to prevent or correct malalignments such as varus or valgus deviations or tibial torsion.

After positioning the jig and preparing the tibia, the osteotomy is performed. The precise position and angle of the saw cut are determined beforehand to allow for ideal rotation of the tibial plateau. After sawing, the tibial plateau is rotated accordingly and fixed in the correct position with a TPLO plate. Care must be taken to ensure that the plate is correctly fitted to the bone and does not injure any joint structures.

Postoperatively, a thorough examination is performed using mediolateral and craniocaudal radiographs. These images serve to check the saw cut, the rotation of the tibial plateau, the position of the plate and screws, and the corrections made. Intraoperatively, the screw position can also be checked fluoroscopically to avoid misplacement.

Finally, regular X-ray checkups are important to monitor the healing process and the integration of the osteotomy gap. The TPLO plate usually remains in the body unless complications arise.

Intra- and postoperative monitoring of the TPLO

Intra- and postoperative monitoring of tibial plateau leveling osteotomy (TPLO) is crucial to ensure the success of the procedure and minimize potential complications. Even during the operation, the correct positioning of the screws can be verified fluoroscopically using a C-arm. This monitoring is particularly important because screw misalignment—especially when using non-angle-stable plates—is among the most common problems in TPLO. Frequently, screws that protrude into the joint must be repositioned or replaced with shorter ones.

When using angle-stable plates, such as those offered by companies like Synthes, the screw direction is already predetermined, which reduces the risk of misalignment. Nevertheless, careful checking is necessary, as errors mainly occur due to incorrect plate placement.

After completion of the operation and routine wound closure, a further check is performed using radiographs in mediolateral and craniocaudal views. These radiographs serve to verify the position of the plate and screws, the correct position of the saw cut, the correction of the tibial plateau, and the axis of the tibia. Additionally, the rotation of the tibial plateau, particularly in the caudal region, should be rechecked.

In the postoperative phase, further radiographic examinations of the knee joint are recommended to monitor the healing process and the integration of the osteotomy gap. The plate used usually remains in the body unless specific complications arise.

Overview of planning and control of a TPLO operation

Summary: Planning and Control of a TPLO Operation

1. The Planning and monitoring of a TPLO operation It begins with a comprehensive diagnosis and the decision that this treatment is the best option for the patient.
2. A thorough Planning and monitoring of a TPLO operation This includes selecting the appropriate time for the procedure to ensure optimal recovery.
3. Before the operation, a detailed Planning, preparation and control of a TPLO operation necessary to provide all necessary instruments and materials.
4. The Planning and monitoring of a TPLO operation This also includes informing the pet owner about the procedure and the subsequent rehabilitation phase.
5. During the Planning and monitoring of a TPLO operation The surgical team is carefully assembled and instructed to ensure maximum efficiency and safety.
6. An effective Planning and monitoring of a TPLO operation This includes the creation of a detailed surgical plan based on the individual anatomical characteristics of the animal.
7. The Planning and monitoring of a TPLO operation This requires precise determination of the rotation angle of the tibial plateau in order to achieve the best possible results.
8. As part of the Planning and monitoring of a TPLO operation The anesthesia is carefully selected and dosed to minimize risks.
9. The Planning and monitoring of a TPLO operation includes a careful review of patient positioning to optimize access and visibility during the procedure.
10. A thorough Planning and monitoring of a TPLO operation ensures that all necessary postoperative measures are prepared to promote a rapid recovery.
11. The Planning and monitoring of a TPLO operation This includes providing resources for immediate postoperative monitoring and care.
12. During the Planning and monitoring of a TPLO operation Potential complications are taken into account and plans for their management are developed.
13. The Planning and monitoring of a TPLO operation This includes close monitoring of blood loss and vital signs during the procedure.
14. In the course of the Planning and monitoring of a TPLO operation Specific aftercare instructions will be developed for the pet owner.
15. The Planning and monitoring of a TPLO operation This includes setting up a follow-up plan to monitor the healing and function of the operated leg.
16. A careful Planning and monitoring of a TPLO operation This includes the selection of the optimal plate and screws for fixation.
17. At the Planning and monitoring of a TPLO operation Accurate determination of the cutting angle is crucial for the osteotomy.
18. The Planning and monitoring of a TPLO operation This includes the preoperative determination of the correct rotation of the tibial plateau.
19. As part of the Planning and monitoring of a TPLO operation The need for meniscus treatment will be assessed.
20. The Planning and monitoring of a TPLO operation It stipulates that all persons involved are informed and trained about the specific steps of the procedure.
21. A successful Planning and monitoring of a TPLO operation requires a postoperative pain management strategy.
22. The Planning and monitoring of a TPLO operation includes the review and adjustment of physiotherapy measures based on the dog's recovery.
23. A comprehensive Planning and monitoring of a TPLO operation This includes regular X-ray checks to confirm the correct position of the implants.
24. The Planning and monitoring of a TPLO operation requires continuous assessment of limb function during the rehabilitation phase.
25. During the Planning and monitoring of a TPLO operation Special attention is paid to the prevention of infections.
26. The Planning and monitoring of a TPLO operation This includes the careful selection of materials and equipment to ensure the best possible surgical results.
27. In the course of the Planning and monitoring of a TPLO operation Long-term strategies for the health and mobility of the dog are being developed.
28. Finally, a well-thought-out Planning and monitoring of a TPLO operation the highest standards in surgical practice and patient care.