Articular fractures remain a real challenge for orthopaedic surgeons. Despite well-established repair and postoperative management principles, a successful clinical outcome remains elusive and somewhat unpredictable, suggesting that rigid adherence to these principles may not always be advisable. Until recently, anatomical reduction was regarded as the single most influential factor in predicting clinical outcome. This unchallenged belief may have to be revisited in the light of recent evidence that other factors such as extent and type of articular cartilage injury, local articular thickness, restoration of the limb mechanical axis, associated procedures (such as meniscectomies), joint stability, age, and joint affected may actually play a major role in limiting the progression of debilitating postoperative osteoarthritis (OA).

Articular Cartilage Lesion

While the idea that anatomical reduction closely correlates with clinical outcome is widely accepted, there is growing evidence that articular injuries may have a greater impact than residual step-off on postoperative OA and long-term functional recovery. Three types of articular injuries secondary to mechanical trauma have been described.

Type 1 lesions refer to cellular and cartilaginous extracellular matrix lesions without macroscopic evidence of articular surface disruption. These lesions are insidious, cannot be detected clinically, and may explain the continuous progression of OA despite anatomical reduction. Such lesions result in alteration of the mechanical properties of the articular cartilage, lead to continuous OA and further cartilage damage.

Type 2 lesions are characterized by visible disruption of the articular surface (e.g., fissures, flaps, defects) without exposure or fracture of the subchondral bone. Such defects are usually permanent because of the limited healing ability of the avascular articular cartilage. The effect of type 2 lesions on postoperative prognosis varies with the extent and location of the lesion (load-sharing or not). Iatrogenic surgical traumas to the articular cartilage induce type 2 lesions and emphasize the strict adherence to atraumatic surgery principles.

Type 3 lesions describe lesions with visible exposure and fracture of the subchondral bone. By definition, all articular fractures result in type 3 articular cartilage lesions. The healing process associated with type 3 lesions differs from that associated with type 2 lesions. Exposure of the subchondral bone (SCB) results in local hemorrhage with secondary invasion of the defects by growth factors, mesenchymal stem cells (MSC), and a fibrin clot scaffold. Over a 6- to 8-week period, this more complete healing response leads to bone repair and generation of a hyaline-like cartilage, starting around 2 weeks with MSC differentiation in chondroblasts. Although the repair tissue initially displays mechanical properties closer to articular cartilage than fibrocartilage, over time the repair tissue shows evidence of continuous degradation in most cases.

Treatment Principles

Early Intervention

Because motion of bone fragments within the joint space often leads to irreversible articular cartilage lesions, articular fractures are considered orthopaedic emergencies and should be treated as soon as the animal is stable.

Atraumatic Surgery

This often creates a challenge for the orthopaedic surgeon who must strike a balance between limited surgical approaches that will preserve local blood supply and soft tissue attachments to bony fragments, and adequate visualization and mobilization of the articular fragment without generating iatrogenic lesions to the articular cartilage. In general, osteotomies tend to heal better than tenotomies, desmotomies, or myotomies and may be preferred. As minimally invasive surgical (MIS) techniques mature, intraoperative fluoroscopy or even (dry) arthroscopy combined with indirect reduction techniques may supplant traditional approaches in achieving and evaluating fracture reduction.

Anatomical Reduction

While anatomical reduction should always be attempted, there is some debate regarding what constitutes optimal reduction and what is the amount of acceptable residual step-off. In humans, a step-off smaller than the thickness of the local articular cartilage is considered acceptable (at 1 mm in most cases). Indeed, experimental studies have demonstrated that, in the presence of small incongruences, the articular cartilage shows great remodeling capacity. This adaptive remodeling may lead to a marked decrease in local articular stresses and eventually to near-normal joint function.

Stable Fixation

To avoid postoperative ankylosis and poor functional outcome, it is absolutely necessary to provide 1) stable intra-articular interfragmentary compression (via lag screws and anti-rotational wires) and 2) metaphyseal to diaphyseal rigid fixation. While the former will optimize even load distribution within the joint, the latter will permit early restoration of the joint range of motion. Poor plate contouring may result in loss of articular surface anatomical reduction as the plate is tightened; intimate plate contact with the metaphysis may require extensive soft tissue dissection and jeopardize functional recovery. The newly introduced locking compression plates have the potential to considerably simplify the treatment of articular fractures, because they do not require accurate contouring and allow rigid bridging osteosynthesis without direct contact between plate and bone.

Restoration of the Limb Mechanical Axis

One of the most significant improvements in articular fracture treatment in human orthopaedics is the recognition of the importance of restoring limb alignment. This concept is particularly important when considering rotational and valgus-varus angulations. With the increased popularity of MIS, however, anatomical reduction of the metaphyseal-diaphyseal region is not attempted during surgery, and reliance on intraoperative fluoroscopy to verify limb alignment may be preferred to clinical evaluation alone.

Postoperative Management

Early Mobilization

Early mobilization is necessary to optimize functional recovery. Conversely, restriction of postoperative range of motion with bandages is likely to result in temporary or even permanent ankylosis. Physical rehabilitation should be implemented as soon as tolerated by the animal. Although there is some debate regarding what constitutes an ideal rehabilitation program, continuous active mobilization has been shown to be effective in human medicine. Such a program is difficult to implement in veterinary patients and may be substituted by passive range-of-motion exercises, low impact activities such as leash walks uphill, wading, swimming, and use of an the underwater treadmill.

Weight Control

Because lean and fit animals tend to recover faster and more completely than obese patients, it is important to convince owners to maintain or restore their pet's optimal bodyweight.

NSAIDs

The progression of OA following treatment of articular fractures may require long-term use of NSAIDs if more conservative protocols are insufficient (physical rehabilitation, weight loss, etc.). The use of NSAIDs during the immediate postoperative periods is also recommended to facilitate early mobilization of the limb and optimize functional recovery.