Meniscal Knee Injuries

The conventional belief has been that patients presenting with clicking, catching, or locking symptoms are more likely to have a meniscal tear and that arthroscopic partial meniscectomy (APM) would yield favorable outcomes. However, current evidence does not support this traditional view. Concerns have been raised about the drift from evidence-based indications, moving from treating permanently locked knees to those with less severe mechanical symptoms.
== Anatomy and Pathophysiology ==
The menisci are crescent-shaped, fibrocartilaginous structures found in the knee joint, with each knee containing two menisci: the medial and the lateral meniscus. These structures play a crucial role in the distribution of load across the articular surfaces, as well as in shock absorption, joint stabilization, and lubrication. Both the medial and the lateral menisci are comprised of an outer fibrous rim that blends with the joint capsule and the coronary ligaments, and an inner portion that is free from attachment. Their composition consists predominantly of type I collagen, along with proteoglycans, glycoproteins, and elastin fibers, which contribute to their biomechanical properties. With respect to blood supply, the menisci are largely avascular, with the exception of the peripheral 10-30%, which is vascularized by the genicular arteries.
Meniscal tears can occur as a result of both traumatic and degenerative processes. Traumatic tears are often associated with sports injuries and are more prevalent in younger populations. These tears typically occur when a sudden twisting force is applied to the knee while the foot is planted and the knee is flexed. In contrast, degenerative tears are more common in older individuals and arise from the gradual wear and tear of the meniscus over time and are associated with underlying knee osteoarthritis. The location and type of tear are important factors in determining the potential for healing and the appropriate treatment approach. Tears located in the vascularised peripheral region, known as the "red zone," have a better chance of healing due to the availability of blood supply, while those in the avascular "white zone" have a limited capacity for repair. Meniscal tear patterns include longitudinal, radial, horizontal, oblique, and complex, with each type having its own implications for treatment and prognosis.
Biomechanical properties of the menisci are crucial in determining their susceptibility to tears. The menisci are made up of a complex network of collagen fibers, primarily type I collagen, which provides the structure with tensile strength and resistance to shear forces. Proteoglycans, such as aggrecan, are interspersed within the collagen network, creating a hydrophilic environment that aids in load distribution and shock absorption. However, these proteoglycans undergo age-related changes, leading to decreased water content, which in turn impairs their ability to effectively distribute load and absorb shock. This predisposes the menisci to degenerative tears, as the diminished biomechanical properties render them more vulnerable to mechanical stress over time.
Inflammation also plays a role in the pathophysiology of meniscal tears. The release of inflammatory mediators, such as cytokines, and recruitment of inflammatory cells in response to injury can contribute to pain, swelling, and joint effusion. Additionally, these inflammatory mediators can promote catabolic processes within the meniscus, leading to further tissue breakdown and potentially exacerbating the injury.
== Clinical Features ==
Mechanical symptoms have been proven to not be associated with the presence of meniscal tear. One systematic review found sensitivity of 0.32 - 0.69 and specificity of 0.45 - 0.74.for meniscal tear, i.e. both crossing 0.5 which is a likelihood ratio of 1.0. 
There may be other explanations for mechanical symptoms. These can include patellofemoral joint giving way, which is transient and related to fatigue or overload of the quadriceps, locking or malalignment of the patella due to Q angle stiffness, loose bodies or chondral lesions causing mechanical symptoms, and ultimately, mechanical symptoms may be multifactorial in their causes.
Degenerative tears are generally not unstable and they usually don't sublux into the joint. This means they shouldn't cause "mechanical symptoms"
==Treatment==
There has been continuous misuse and misapplication of trial data
* Non-inferiority does not justify arthroscopy. We should expect operations to provide clinically important benefits and not merely be "non-inferior" to non-surgical treatments
* Misuse of study conclusions
* Ignoring long term follow up data
* Using cross-over percentages from non-surgical group to APM to justify surgery
* Ignoring the results of negative trials
* Ignoring the evidence that surgeons cannot predict who will benefit from APM
* Ignoring the evidence that APM may be worse than nothing with physical (increased OA) and financial harm
Conceptually the idea of going for a potentially harmful treatment that has been proven not to work because a non-operative treatment didn't work does not make logical sense.
===Non-Operative Management===
This is the "masterly neglect" with the aim of meniscal repair and/or knee adaptation. The greatest healing potential are those that are short (<1cm), longitudinal, stable, and asymptomatic. Stability can be evaluated arthroscopically with probing. In high level athletes there is high risk of tear progression, becoming symptomatic, and eventually requiring APM.
===Operative Mx===
Three broad types of surgery
#Preservation: Long recovery but reduce risk of OA
#Removal of damaged tissue: Speedy recovery but risk future OA
#Replacement of damaged tissue
====Meniscus Zones====
Three zones in the meniscus, with reducing blood supply the more centrally located the tissue
#Red-red zone
#Red-white zone
#White-white zone
====Meniscal Repair====
*Tear selection for repair
**Ideal = Unstable, vertical-longitudinal tear in periphery
**Meniscus zones: Only peripheral 10-25% of the meniscus is vascularised
**However acceptable healing rates can occur in the other zones
**Also beneficial: tear <12 weeks, younger patients, combined ACL repair
*Bucket handle = vertical longitudinal peripheral tear. The classical teaching is that completely locked knees should be repaired urgently to prevent long term motion loss
*Techniques
**Inside-out (gold standard) or outside-in
**Newer fixation devices (all inside)
**All forms of repair require many months of prolonged rehabilitation
*Postoperative rehab 
**typically includes restrictions in knee flexion RO and weight bearing for 6 weeks. 
**Low impact exercise but no running for 2-3 months
**Return to competition in 6-8 months
====Partial Meniscectomy Classic Criteria====
The traditional indication is where masterly neglect or repair have a low chance of success. The following are some typical criteria used in guidelines. However they are not evidence based:
*	complex tear patterns
*	chronic displaced tears with plastic deformation
*	tears in white-white region (rim width > 8mm)
*	Failed repair
*	Degenerative tears (despite being a disproven treatment)
Contrary to received wisdom, mechanical symptoms do not confer better outcomes from APM and there is more long term OA
In middle aged and older patients having APM there is higher risk of accelerated osteoarthritic changes and the risk of TKJR is higher.
====Meniscus Replacement====
*Allografts
*Synthetic scaffolds
*Does not allow return to competitive sport
===Degenerative Tears===
Meniscal surgery is not indicated in the context of degenerative tears. This was evaluated in an RCT by Sihvonen et al 
*146 patients with degenerative meniscal tears without OA. Included those with locking symptoms.
*Partial meniscectomy vs sham surgery
*No difference from 12 months to 5 years follow up. 
*Considered one of the highest quality RCTs that exist in all of the surgical literature, and one of the only placebo controlled trials in the entire orthopaedic surgery literature.
Even experienced orthopaedic surgeons cannot predict who will benefit from surgery for degenerative meniscal tears. If conservative management fails, the default isn’t to do something (surgery) that has been disproven to work (and can even make it worse with OA)
There is increased joint space narrowing after arthroscopic partial meniscectomy compared to patients managed non-surgically.
==References==
Category:Knee and Leg Conditions