Brian Gilmer, MD
Hypermobile lateral meniscus (HLM) is a frequently overlooked diagnosis in patients presenting with knee-related symptoms. This condition is characterized by an unusually mobile meniscus in the knee joint, which can lead to a broad spectrum of mechanical symptoms.
HLM is a condition that can have a multitude of presentations, from seemingly innocuous to severe. The symptoms can range from no noticeable discomfort to significant pain and instability. A common complaint associated with HLM is the mechanical locking of the knee, often accompanied by a painful popping sensation. Despite these clear indications, the diagnosis of HLM is frequently missed, leading to prolonged discomfort and potential further injury for the patient.
The pathophysiology of HLM primarily involves the tearing of the meniscotibial and popliteomeniscal ligament fibers. These ligaments play a critical role in maintaining the stability of the meniscus, and any damage to them can result in abnormal movement and subsequent symptoms. It's important to note that while HLM is frequently associated with anterior cruciate ligament (ACL) tears and posterolateral corner tears, it can also occur in isolation.
Diagnosing HLM can be a complex process. Traditional imaging methods like MRI often yield normal results, making it difficult to identify the condition. The definitive diagnosis of HLM is typically made through arthroscopy. In this procedure, the surgeon can directly observe and probe the meniscus. If the meniscus can be mobilized more than 50% forward in the lateral compartment, a diagnosis of HLM can be made. The diagnosis process is further complicated by the fact that HLM often coexists with other knee injuries. This can make it challenging to isolate the symptoms of HLM from those of other conditions. It is common for patients with HLM to have a history of knee injuries or surgeries, and these can contribute to the development of the condition.
Once a diagnosis of HLM has been made, there are several treatment options available. The most common treatment is all-inside repair, a surgical procedure where the torn meniscus is sutured back into its original position. This can be done either to the capsule or the popliteus, depending on the specific location and extent of the tear. This procedure aims to restore the normal function of the meniscus and relieve the symptoms associated with HLM.
In addition to surgical repair, there are other treatment options available for HLM. These include physical therapy, medication, and in some cases, lifestyle modifications. Physical therapy can help to strengthen the muscles around the knee and improve stability, while medication can help to manage pain and inflammation. Lifestyle modifications, such as avoiding activities that put excessive strain on the knee, can also be beneficial. Ultimately, because this is a mechanical problem, the solution is typically surgical.
In conclusion, HLM is a unique and frequently overlooked diagnosis that requires a high index of suspicion and a thorough understanding of knee anatomy and pathology. Despite the challenges associated with its diagnosis, with appropriate treatment, patients with HLM can expect a significant reduction in symptoms and improved knee function. It is important for patients to understand that while HLM can be a challenging condition to live with, it is manageable with the right treatment and care. For surgeons, the treatment is not complex, but having the experience and familiarity with the diagnosis is paramount.
Dr. Gilmer’s Take-
This can be a tough diagnosis to make as the MRI is often normal and complaints are often vague. I have certainly encountered this diagnosis before I knew what it was. As the saying goes in medicine: “You may not have seen it, but it has seen you.”
Since I have become more aware of this I have been more aggressive about the repair specifically when I can displace the meniscus more than 50% into the joint. It’s important to look anterior as radial tears at the mid body will have this same effect and the posterior horn itself does not need repair in those cases if the radial tear is successfully repaired.
In cases where the posterior horn alone is unstable I will probe both at the popliteus and more posterior along the posterior horn and will place all-inside repair sutures at the location where it seems the most instability is occurring.
