Intact, functional menisci are critical to stifle joint health as they provide shock absorption, congruency, stability, lubrication and articular cartilage protection. When meniscal function and structure are lost, pain, inflammation and osteoarthritis follow. Therefore, it is imperative to understand, and to accurately and efficiently diagnose and treat meniscal pathology in order to afford clients with optimal treatment options and prognoses. Meniscal pathology is a prevalent finding associated with joint instability following disruption of the cranial cruciate ligament (CCL) in dogs. The incidence of meniscal tears concurrent with, or subsequent to, cranial cruciate disruption reportedly ranges from 20–77%. When CCL deficiency is present in large-breed dogs, the medial meniscus is more predisposed to tearing than the lateral meniscus.

Diagnosing disorders of canine menisci using physical examination findings, exploratory arthrotomy, arthroscopy, radiography, computed tomography (CT) and magnetic resonance imaging (MRI) have been described in the literature. We consider arthroscopy to be the 'gold standard' for definitive diagnosis of meniscal pathology because it allows for complete visualisation with magnification and manipulation of the menisci, and is minimally invasive with low morbidity. Arthroscopy with probing of menisci provides the highest likelihood for correctly identifying meniscal tears. We have reported the use of ultrasonography for accurately diagnosing meniscal tears in dogs. While meniscal ultrasonography requires specialised equipment and expertise, it can eliminate the need for anaesthesia and surgery for accurate diagnosis and decision making. Currently, we use ultrasonography for all clinical cases in which the presence or absence of meniscal pathology influences surgical treatment options and prognosis.

While repair of meniscal pathology is possible in selected cases, the majority of meniscal surgeries involve resection of a portion of one or both knee menisci, leaving the joint deficient in meniscal function. The need for partial meniscectomy in most cases in dogs is based on both biological and technical factors. The primary biological factor is that the majority of tears occur in the 'white-white' zone of the meniscus which has no inherent blood supply and low cell density. The technical factors primarily rest in our inability to restore normal joint kinematics to the CCL-deficient (CCLD) stifle, difficulties in protecting the menisci during healing and the relatively small size of the menisci and the joint. Partial meniscectomy is indicated for longitudinal, bucket handle, radial, horizontal and complex tears for which an intact 'rim' (peripheral circumferential collagen fibre integrity) can be preserved after resection. Segmental meniscectomy is indicated for all types of tears in the caudal aspect of the meniscus when an intact 'rim' cannot be preserved in conjunction with complete resection of pathological tissue. Total meniscectomy is indicated for tears extending beyond the caudal aspect of the meniscus and for which an intact 'rim' cannot be maintained.

There are several key factors to consider for optimising meniscal resection procedures. First, exposure and access must be achieved such that adjacent structures (articular cartilage, ligaments etc.) are not damaged during resection. Instrumentation specifically designed for meniscal surgery is recommended for minimising iatrogenic damage to the articular cartilage during assessment and treatment. Then, two important goals must be balanced in performing the resection:

 Remove all grossly damaged, displaced, and pathological meniscal tissue.

 Preserve as much functional meniscal tissue as possible.

Damaged, displaced, unstable and pathological meniscal tissue can cause mechanical dysfunction in the joint, direct articular cartilage damage, inflammation, degradation and resultant pain, lameness and progression of osteoarthritis. However, loss or removal of meniscal tissue, especially the peripheral 'rim', severely diminishes load bearing, shock absorption, congruency, stability, lubrication, tissue nutrition and chondroprotection functions of meniscus for the joint. Clearly, the two goals for treatment of meniscal injuries can be at odds to one another and so careful evaluation and decision making with judicious resection are critical to striking the optimal balance for the patient. The evaluation is based on preoperative imaging in conjunction with careful inspection of the entirety of the meniscus, probing and palpation of meniscal tissue and its attachments and assessment of the articular cartilage of the femoral condyle and tibial plateau. Healthy, functional meniscal tissue should appear smooth, white and glistening and not be readily displaced, folded, separated or penetrated with a blunt meniscal probe. Abnormal meniscal tissue is typically soft, fibrillated, discoloured and abnormal in location, architecture and/or integrity, and is often associated with local articular cartilage damage. Taken together, these variables help distinguish pathological from functional meniscal tissue and guide the surgeon in determining what to resect and what to preserve.

Meniscal release, or radial transection, is the other procedure commonly performed in dogs for treatment or attempted prevention of meniscal injuries in dogs. This procedure was initially developed and advocated in conjunction with tibial plateau levelling osteotomy (TPLO) based on the high incidence of subsequent medial meniscal injuries diagnosed after initial clinical introduction of TPLO in dogs. The rationale provided for meniscal release was that because of the inability of TPLO to sufficiently protect the medial meniscus from injury postoperatively, the meniscus should be 'released' allowing it to displace, or subluxate, and avoid the damage and clinical problems that were reported to occur after TPLO. In this way, the need for additional surgeries after TPLO could be minimised. It is important to note that it has been suggested that many meniscal injuries diagnosed after the initial surgery for CCLD may instead be tears that were present, but undetected, at the index surgery. This further highlights the importance of good visualisation, inspection and probing of the menisci during the first surgical procedure. The radial transection for medial meniscal release can be performed at the caudal meniscal horn-caudal meniscotibial ligament junction (caudal release) or at the mid-body of the meniscus (central release) via arthroscopy or arthrotomy using scalpel blades (no. 11, no. 15 or Beaver blades) or meniscal knives. While meniscal release can be associated with significantly lower risk for clinically apparent subsequent meniscal tears, radial transection of the meniscus, regardless of location, completely disrupts the circumferential collagen fibre integrity ('rim') and destroys critical meniscal functions. Released menisci will not functionally heal and will remain biomechanically deficient. In clinical patients with CCLD, however, statistically or clinically significant differences in outcome between groups receiving or not receiving meniscal release have not been noted based on subjective assessments. As such, the authors suggest that meniscal release can be justified when the meniscus cannot be full assessed for pathology, cannot be sufficiently resected safely or the subsequent meniscal tear rate is unacceptably high to the surgeon and/or clientele.

Because of the significance of meniscal resection and meniscal release and the poor healing capabilities of the tissue, preservation of functional meniscal tissue is a surgical priority. However, proper treatment of pathological menisci often requires resection of large amounts of meniscal tissue. Therefore, when meniscal pathology dictates the surgical removal of significant portions of the meniscus, replacement of the tissue removed with tissue of similar size, shape, geometry and composition would appear to be the optimal objective when attempting to preserve the long-term function of the knee joint. Currently, there are multiple strategies for achieving this objective. These strategies include the use of meniscal allografts, tissue-engineered replacement tissue and/or biological stimulation of meniscal tissue regeneration. Many of these could potentially be applied to veterinary medicine in the future.