The Meniscus—Why or How to Evaluate
Canine meniscal injury is typically associated with complete cranial cruciate ligament (CrCL) injury, with incidence reported from 50–90% of CrCL cases. Isolated meniscal injury in dogs (unlike humans) is rare, with most damage occurring from repetitive injury to the caudal pole of the medial meniscus with cranial tibial subluxation of the CrCL deficient stifle.
The most common configurations of meniscal injury are vertical longitudinal tears. The classic is referred to as a ‘bucket handle’ tear, with the damaged portion sometimes displaced cranially. Other less common configurations include multiple longitudinal or ‘church pew’ tears, short or incomplete vertical tears, oblique or flap tears, radial tears, or horizontal cleavage tears. Concurrent meniscal injury significantly contributes to morbidity and progressive osteoarthritis in the stifle joint. Hence, thorough evaluation of the meniscus and treatment of any pathology is considered standard of care, as part of any CrCL surgery.
When performing an orthopedic exam, there are some additional findings that may be suggestive of concurrent meniscal injury. These include peracute onset of more severe lameness localized to the stifle joint, increased discomfort associated with stifle range of motion, palpable/audible ‘click’ crepitation in the joint through range of motion, and significant medial buttress. Radiographs can help support the diagnosis of CrCL rupture +/- meniscal injury with the findings of characteristic joint effusion and osteoarthritis. Other imaging modalities such as ultrasound, CT or MRI +/- contrast arthrography have also been reported in the pre-operative setting to support a diagnosis of meniscal injury but are not commonly utilized in the clinical setting.
Surgical Meniscal Evaluation
One of the main goals of stifle arthrotomy or arthroscopy during CrCL surgery is to evaluate the meniscus. When performing an arthrotomy, this author prefers a medial parapatellar approach vs. lateral approach, as this facilitates improved visualization and manipulation of the caudal pole of the medial meniscus. Arthroscopic evaluation of the menisci can provide a minimally invasive, and detailed evaluation of the meniscus.
Regardless of the approach for evaluation, use of a Hohmann retractor or another stifle distractor device to bring the tibial into cranial subluxation, greatly improves the surgeon’s ability to see and manipulate the meniscus. Probing the meniscus (both the femoral and tibial aspects) during this evaluation has also been proven to significantly increase the diagnostic accuracy of detecting a meniscal tear versus visualization alone.
There is little debate that failure to treat meniscal injuries in dogs results in persistent lameness, and more rapid progression of osteoarthritis in the stifle.
A partial meniscectomy involves the removal of only the damaged section of the meniscus for those tears that do not extend to the peripheral rim. The cranial and caudal meniscotibial ligaments and peripheral rim are preserved. This is thought to maintain some of the load distribution and stabilizing functions of the meniscus. Maintaining tension on the torn portion of the meniscus during sharp transection at the junction between normal and abnormal tissue can facilitate a clean partial meniscectomy.
Many injuries of the medial meniscus involve the entire caudal pole, so removal of the entire caudal pole in the form of a hemi-meniscectomy may be required. The procedure is similar to a partial meniscectomy, only sharp transections are performed at the mid-body (level of medial collateral ligament) and meniscotibial ligament.
This is removal of the entire medial meniscus, and is not commonly performed, as it is rare for a meniscus to be so extensively damaged to warrant this more radical procedure.
Meniscal Release Controversies
This technique was described as a way to decrease late meniscal injury after TPLO or other CrCL stabilization procedures. It involves transecting the medial menisco-tibial ligament or a mid-body transection of the medial meniscus just caudal to the medial collateral ligament. Although this has been shown to decrease the incidence of delayed meniscal injury, it does not totally eliminate this risk. Incomplete release, healing of the release site, or an inappropriate release may result in subsequent morbidity due to progressive meniscal and joint pathology. Experimental studies have also shown that performing a meniscal release on a normal joint causes altered joint load distribution and results in progressive osteoarthritis in the stifle. So even though meniscal release remains a commonly performed procedure, and was described as part of the original TPLO technique, this author’s preference is not to perform a meniscal release if the meniscus is normal at the time of CrCL surgery.