Meniscal Tears And ‘Mechanical Symptoms’ – An Unsolved Puzzle

Mechanical symptoms in combination with a meniscal tear on MRI is currently a strong indication for arthroscopic meniscal surgery. We recently conducted several studies that challenge our current understanding of what may cause mechanical knee symptoms. We also explored if patients with mechanical knee symptoms have a particular favorable outcome after meniscal surgery.

The use of arthroscopic surgery to treat degenerative meniscal tears, a very common surgical procedure, has been much debated during the last decade. Despite a series of randomized trials showing no better effect of arthroscopic partial meniscectomy (APM) compared with placebo surgery or exercise therapy to treat patient-reported pain and function,^1,2 there is a strong belief among clinicians that subgroups of patients exist that have a particular favorable effect of surgery.^3,4 One such subgroup is patients with meniscal tears and mechanical symptoms.

Definition of ‘mechanical symptoms’

Symptoms of ‘catching’ and/or ‘locking’ of the knee are typically considered to be of mechanical origin, caused by something being trapped or stuck inside the knee that can be removed with surgery. If mechanical symptoms are present in combination with a meniscal tear confirmed on MRI the symptoms are generally considered to originate from the tear, providing a strong rationale for meniscal surgery.

Similar to other types of symptoms, mechanical symptoms are often fluctuating, and a chronically locked knee is a rare finding. In the clinic the presence/absence of such symptoms are typically determined from the patients’ medical history supplemented with objective tests. The definition and understanding of symptoms of ‘catching’ and ‘locking’ are associated with variation both among patients and clinicians. In the research literature mechanical symptoms are typically patient-reported and determined by asking patients about presence and/or frequency of ‘catching’ and/or ‘locking’ in their symptomatic knee.

Symptoms and outcome after meniscal surgery

Surgery is considered to be particularly beneficial for relieving mechanical knee symptoms.⁴ However, a secondary analysis of the FIDELITY trial comparing APM with placebo surgery in the subgroup of patients with preoperative mechanical symptoms reported no better effect of APM compared with placebo surgery in relieving mechanical symptoms in patients with degenerative meniscal tear.⁵

In addition, observational data from a large Finnish cohort reported no difference after APM in improvement in patient-reported pain and function between patients with degenerative meniscal tears, with and without preoperative mechanical symptoms.⁶ A finding we have recently confirmed.⁷ However, it appears that younger patients (under 40 years of age) with mechanical symptoms improve more in patient-reported pain and function than patients without these symptoms after meniscal surgery.⁷ The reason for this is unclear. It may speculate that this is caused by a larger proportion of patients in the younger population having tear types such as longitudinal-vertical (i.e., bucket-handle) tears that theoretically are more likely to cause mechanical symptoms.⁸

Relationship between ‘mechanical symptoms’ and meniscal tears

We recently conducted a study to investigate if certain meniscal tear types such as ‘unstable’ tears (i.e. vertical or longitudinal-vertical tears)⁸ are more likely to cause ‘mechanical symptoms’ or if other concurrent knee pathologies could explain these symptoms. In the study we included a wide range of meniscal tear characteristics (i.e. tear pattern, location of tear, size of tear, etc.) but also other knee pathologies (i.e. cartilage damage, ACL status, etc.) identified at arthroscopy, that could potentially cause mechanical symptoms. We found no important relationship between any of the included factors and patient-reported ‘catching and/or locking’ of the knee or ‘inability to straighten knee’ (i.e. extension deficit).⁹ These results question the intuitive logic that mechanical symptoms are caused by specific joint pathologies. To further elucidate if mechanical symptoms indeed are a specific symptom of meniscal tears we conducted a second study, comparing the frequency of mechanical symptoms between patients with and without a meniscal tear at knee arthroscopy. We found that about half of all patients reported catching and/or locking and inability to straighten their knee fully. Surprisingly, these mechanical symptoms were equally common among patients with and without a meniscal tear.¹⁰

What does all this mean?

Taken together, these findings suggest that patient-reported mechanical symptoms are not a specific symptom of meniscal tears, but common in patients with knee problems in general. Furthermore, the results do not support a simple cause—effect link between structural knee joint pathologies, including meniscal tears, and patient-reported mechanical symptoms, often suggested to exist. Thus, when encountering a patient reporting mechanical symptoms in the clinic in combination with a confirmed meniscal tear on MRI, one should be very cautious to consider these symptoms to be attributable to the meniscal tear.

The absent relationship between meniscal tears and mechanical symptoms may explain why surgery does not relieve these symptoms better than placebo surgery or result in larger improvements in pain and function compared to patients without mechanical symptoms and degenerative meniscal tears. Importantly, data from two recent randomized trials on patients with degenerative meniscal tears highlight that the subgroup of patients with preoperative mechanical symptoms have the same benefit from exercise therapy as APM. One study found that mechanical symptoms were relieved to the same extent in the exercise as in the APM group.¹¹ In the other study, no differences in pain were observed at 3 years follow-up time between the exercise group and the surgery group.¹²

Arguably patients with meniscal tears exist that present in the clinic with a chronically locked knee or a knee that will catch or lock during objective testing, where surgery may be indicated to relieve these symptoms. These patients likely represent the subgroup for which meniscal surgery were intended in the first place, but may now represent a minority due to subsequent ‘indication drift’? For younger patients (i.e. 40 years or younger) with meniscal tears evidence from randomized trials on best treatment is still lacking. Despite the absence of relationship between mechanical symptoms and meniscal tears our observational data indicate that younger patients with mechanical symptoms experience greater improvements after surgery than those without these symptoms. Future randomized trials will need to confirm this finding and investigate if exercise therapy can also address mechanical symptoms in the younger population with meniscal tears.