Abstract: Planning and control of a TPLO operation

The following comments are largely based on the very good article by Prof. Andrea Meyer-Lindenberg and summarizes the essential points.

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

Introduction Planning and controlling a TPLO operation

Veterinary medicine has changed significantly in the last few decades. In the past, the focus was primarily on diagnosing and treating diseases in farm animals. Since the middle of the 20th century, however, this focus increasingly shifted towards caring for pets, especially dogs and cats. This change can be seen parallel to the development in human medicine, which has also increased the demands of animal owners on veterinary care. As a result, there was an expansion and establishment of advanced diagnostic and therapeutic procedures in veterinary medicine.

The knee joint - anatomical aspects

A dog's knee joint is structured analogously to the human knee joint, consisting of the condyles of the femur and the tibia. In contrast to humans, however, the dog's cranial cruciate ligament plays a more central role in the stability of the knee joint. 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 special feature of the dog's knee joint is muscle coactivity, which supports the stability of the knee joint. Muscles such as the biceps femoris and quadriceps femoris act as agonists and antagonists of the anterior cruciate ligament, respectively. The main load during the dog's stance and loading phase is borne by the tibial plateau, which has concave and convex shapes depending on the viewing plane. The tilt of the tibial plateau results in a forward thrust on the cruciate ligaments with each step, particularly the cranial cruciate ligament.

The anatomical and biomechanical alignment of the tibial plateau plays a critical role in the health and functionality of the knee joint. Measurements of the angle of inclination of the tibial plateau are crucial for the diagnosis and planning of orthopedic procedures. A correctly measured Tibial Plateau Angle (TPA) is crucial for the success of surgical interventions, with the ideal angle for healthy dogs usually being less than 20°. Incorrect X-ray techniques can lead to incorrect measurements, which can affect the success of an operation.

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

The angle of inclination of the tibial plateau, also known as the tibial plateau angle (TPA), is determined by special measurement points on a correctly aligned mediolateral x-ray image. The axis of the tibia is represented as a straight line that runs 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 to the medial articular surface of the proximal tibia, with the boundaries of the tibial plateau determined by anatomical landmarks.

The Tibial Plateau Slope (TPS) results from 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. Incorrect X-ray techniques can affect the visualization of the TPA and lead to measurement errors that can jeopardize the success of surgical procedures. The TPA varies between different dog breeds and the angulation of the knee joints can also be different in different breeds. In healthy dogs, the TPA is usually below 20°​​.

Measurements to detect axial deviation of the tibia in the frontal plane

Correct diagnosis of axial deviations of the tibia in the frontal plane is crucial for orthopedic evaluation and treatment. There are four main aspects to consider: the height of the apex, the plane of the deviation, the size of the deviation and the direction of the apex. The Center of Rotation of Angulation (CORA) is a central point that is defined by the intersection of the proximal and distal axis lines of the femur and tibia.

To detect tibial torsion as well as varus and valgus deformities, special x-rays are required, which are taken in a caudocranial beam path with a knee joint angulation of approximately 132°. It is important that the patella is positioned centrally in the patellar sulcus and that certain anatomical markers, such as the fabellae and the medial edge of the calcaneus, are clearly visible.

For the measurement, specific points are defined 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 about 90° and the mMDTA is about 93°. Significant differences between the different dog breeds regarding these angles were not found​​.

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

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

Cranial cruciate ligament rupture is a common orthopedic condition in dogs that usually results in significant lameness. In contrast to humans, where cruciate ligament tears are usually caused by trauma, in dogs degenerative changes to the ligament are the more common cause. These changes can be triggered by a variety of factors, including inflammation, immunological processes, aging, obesity, instabilities such as patellar luxation, and limb misalignments.

A steep slope of the tibial plateau could also predispose to cruciate ligament rupture. The disease affects both large breeds and smaller breeds, with larger breeds being affected at younger ages and smaller breeds often being affected at older ages. However, a clear racial predisposition is not certain.

Partial or complete ruptures of the cranial cruciate ligament lead to increasing instability of the knee joint, which, if left untreated, leads to secondary changes such as osteoarthritis and capsular shrinkage. Cruciate ligament rupture is often associated with damage to the caudal portion of the internal meniscus, while primary meniscal lesions are rare in dogs.

Diagnosis is based on history, clinical symptoms and palpation findings, with drawer phenomenon and tibial compression test being important diagnostic tools. X-rays in two planes are essential for diagnosis and treatment planning, and magnetic resonance imaging or arthroscopy can be performed if there is uncertainty or for a more detailed examination of meniscus lesions.

In terms of treatment, numerous surgical procedures have been developed. These can basically be divided into those that change the joint statics and those that do not. Surgical treatment is often necessary for medium to large dogs due to the strong forces acting on the joint. The conventional methods that do not change the joint statics are not always successful because the material introduced can tear or new instability can occur. Therefore, surgical methods have been developed specifically for medium to large breeds that change the joint statics in order to neutralize the function of the cranial cruciate ligament and thus enable better stability and healing.

Diagnosis of anterior cruciate ligament rupture

Diagnosis of anterior cruciate ligament rupture in dogs is based on a careful history, clinical signs, and thorough palpation findings. Typically, the dog exhibits mild to severe lameness, accompanied by a relaxed posture and standing on tiptoes. On examination of the knee joint, it may appear thickened and exhibit instability manifested by the drawer phenomenon in which 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 support phase, which typically occurs due to body weight and contraction of the gastrocnemius muscle. This test simulates the forces acting on the knee joint and is designed to demonstrate instability by sliding the tibia forward while the tarsal joint is flexed.

To confirm the diagnosis and plan therapy, x-rays should be taken in two planes. These can help identify secondary changes such as increased joint filling or osteoarthritis. In unclear cases or for a more precise assessment of meniscus lesions, magnetic resonance imaging can also be helpful. This allows a more detailed view of the ruptured cruciate ligament, meniscus and cartilage lesions, as well as changes in the bone or surrounding soft tissue. Arthroscopy can also be used to directly examine meniscus injuries.

Treatment options for anterior cruciate ligament rupture

There are many surgical methods for the treatment of anterior cruciate ligament rupture in dogs, which can basically be divided into two categories: those that change the joint statics and those that do not change it. The latter methods are further divided into extracapsular and intracapsular ligament replacement methods. Traditional methods that do not change the joint statics are often not successful, especially for medium-sized and large dogs that weigh more than 20 kg. Problems can arise from tearing of the material used or loosening of the fixation during the healing process, which can lead to renewed lameness and the further development of osteoarthritis or meniscus damage.

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

A prominent example of such a method is the tibial plateau leveling osteotomy (TPLO), in which the caudally inclined tibial plateau is surgically altered to eliminate the anterior translation of the tibia (Cranial Tibial Translation, CTT). This is accomplished by rotating and caudally elevating the tibial plateau through a semicircular saw cut, altering the biomechanical relationships of the knee joint to obviate the need for a functioning anterior cruciate ligament. After the operation, the caudal cruciate ligament takes on additional stabilizing functions in the knee joint, meaning that the joint remains functionally stable even without the anterior cruciate ligament.

Principles of TPLO

The principles of tibial plateau leveling osteotomy (TPLO) are based on changing the joint statics and biomechanics of the knee joint. Normally, the axial reaction force during hindlimb weight-bearing is aligned along the long axis of the tibia. When this force hits the tibial plateau sloping from cranial to caudal, it is converted into a compression force (perpendicular to the tibial plateau) and a cranially directed force (parallel to the tibial plateau), which triggers the forward movement of the tibia. If the cranial cruciate ligament ruptures, this inevitably leads to an undesirable cranial displacement of the tibia.

The goal of TPLO is to eliminate this unwanted cranial displacement. This is done by raising the caudally inclined tibial plateau using a special corrective osteotomy. This elevation alters the biomechanical inclination of the tibial plateau such that cranial translation of the tibia (CTT) is abolished and instead converted 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 using the x-ray image and determining the required rotation of the tibial plateau

To perform a tibial plateau leveling osteotomy (TPLO), two x-rays are first required: one in the mediolateral and one in the craniocaudal beam path. These images make it possible to determine the degree of rotation of the tibial plateau and any necessary axis corrections. Determining these angles is crucial to achieving correct adjustment of the knee joint and changing the forces acting on the tibial plateau so that they can be absorbed by the caudal cruciate ligament. The goal is to enable muscular compensation during the loading phase and thereby change the biomechanical conditions in the knee joint so that the anterior displacement of the tibia (Cranial Tibial Translation, CTT) is eliminated.

The TPLO aims to rotate and raise the plateau caudally by elevating the caudally sloping tibial plateau using a customized semicircular saw cut in the proximal tibia. This changes the biomechanics of the knee joint so that functional stability occurs during the stance phase. By rotating the tibial plateau to approximately 65°, the forward thrust of the tibia is eliminated, allowing the caudal cruciate ligament to take on an additional stabilizing role.

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

Preparation of the patient and control of the procedure

Special instruments and precautions are required for the preparation and control of the surgical procedure of a tibial plateau leveling osteotomy (TPLO). In addition to the standard instruments and special tools for bone surgery, such as special saw blades and TPLO jigs, specially developed plates are also required to fix the tibial plateau. There are a number of different plate models, with angle-stable plate systems in particular having proven successful.

Before the operation, the patient is surgically prepared and is positioned either on his side or on his back. After preparation, access to the knee joint is established, possibly after prior arthroscopy to evaluate or treat meniscal lesions.

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

After positioning the jig and preparing the tibia, the osteotomy is performed. The exact position and inclination of the saw cut are determined in advance to allow ideal rotation of the tibial plateau. After sawing, the tibial plateau is rotated accordingly and fixed in the correct position with a TPLO plate. It is important to ensure that the plate is correctly adapted to the bone and does not injure any joint structures.

Postoperatively, a careful check is carried out using x-rays in the mediolateral and craniocaudal beam path. These recordings are used to check the saw cut, the rotation of the tibial plateau, the position of the plate and screws and the corrections made. Intraoperatively, the position of the screws can also be checked fluoroscopically to avoid incorrect placement.

Finally, regular radiographic checks 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 control of TPLO

Intra- and postoperative control of a tibial plateau leveling osteotomy (TPLO) is crucial to ensure the success of the procedure and minimize potential complications. During the operation, the correct positioning of the screws can be checked fluoroscopically using a C-arm. This control is particularly important because incorrect positioning of the screws - especially when using non-angle-stable plates - is one of the most common problems with TPLO. Screws that protrude into the joint often need to be repositioned or replaced with shorter ones.

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

After completion of the operation and routine wound closure, further examination is carried out using x-rays in mediolateral and craniocaudal views. These recordings are used to check the fit of the plate and screws, the correct position of the saw cut, the correction of the tibial plateau and the axis of the tibia. In addition, the rotation of the tibial plateau, especially in the caudal area, should be checked again.

In the postoperative period, further radiographic checks 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 controlling a TPLO operation

Summary Planning and controlling a TPLO operation

1. Planning and monitoring TPLO surgery begins with a comprehensive diagnosis and the decision that this treatment is the best option for the patient.
2. Thorough planning and control of TPLO surgery includes selecting the appropriate timing for the procedure to ensure optimal recovery.
3. Before the operation, detailed planning, preparation and control of a TPLO operation necessary to provide all necessary instruments and materials.
4. The planning and control of a TPLO operation also includes informing the animal owner about the process and the subsequent rehabilitation phase.
5. During the planning and control of a TPLO operation, the surgical team is carefully assembled and instructed to ensure maximum efficiency and safety.
6. Effective planning and control of a TPLO operation involves creating a detailed surgical plan based on the individual anatomical characteristics of the animal.
7. Planning and controlling a TPLO procedure requires accurate determination of the rotation angle of the tibial plateau to achieve the best possible results.
8. As part of the planning and control of a TPLO operation, the anesthesia is carefully selected and dosed to minimize risks.
9. Planning and control of TPLO surgery includes careful review of patient positioning to optimize access and visibility during the procedure.
10. Thorough planning and control of a TPLO operation ensures that all necessary postoperative measures are prepared to promote a rapid recovery.
11. Planning and control of TPLO surgery involves providing resources for immediate postoperative monitoring and care.
12. During the planning and control of TPLO surgery, potential complications are taken into account and plans for their management are developed.
13. Planning and control of TPLO surgery involves close monitoring of blood loss and vital signs during the procedure.
14. As part of the planning and control of a TPLO operation, specific aftercare instructions are developed for the pet owner.
15. Planning and monitoring TPLO surgery includes setting up a follow-up plan to monitor the healing and function of the operated leg.
16. Careful planning and control of TPLO surgery includes selection of the optimal plate and screws for fixation.
17. When planning and controlling a TPLO operation, the precise determination of the cutting angle for the osteotomy is crucial.
18. The planning and control of a TPLO operation includes the preoperative determination of the correct rotation of the tibial plateau.
19. As part of the planning and control of a TPLO operation, the need for meniscus treatment is assessed.
20. The planning and control of a TPLO operation requires that all people involved are informed and trained about the specific steps of the procedure.
21. Successful planning and control of TPLO surgery requires a postoperative pain management strategy.
22. Planning and monitoring TPLO surgery includes reviewing and adjusting physical therapy measures based on the dog's recovery.
23. Comprehensive planning and monitoring of a TPLO operation includes regular X-ray checks to confirm the correct position of the implants.
24. Planning and monitoring TPLO surgery requires continuous assessment of limb function during the rehabilitation period.
25. During the planning and control of a TPLO operation, special attention is paid to the prevention of infections.
26. Planning and controlling a TPLO operation involves careful selection of materials and equipment to ensure the best possible surgical results.
27. During the planning and monitoring of a TPLO operation, long-term strategies for the dog's health and mobility are developed.
28. Finally, thoughtful planning and control of a TPLO operation the highest standards in surgical practice and patient care.