Management of meniscal injuries of the knee

                       Management of meniscal injuries of the knee

                                              Dr KS Dhillon FRCS

Introduction

The role played by the menisci in function of the knee has been well established. It is important to preserve the meniscus whenever possible. Degenerative tears of the meniscus are common and can be present in asymptomatic individual. Arthroscopic partial meniscectomy is and has been one of the most common orthopaedic surgical procedure in most countries around the world. However, there is now good evidence available to show that arthroscopic partial meniscectomy does not benefit most patients with meniscal tears. This article reviews the recent literature and attempts to settles some of the controversies associated with the management of meniscal injuries of the knee.

Anatomy of the meniscus

The are two menisci in the knee, namely the medial and lateral meniscus. The medial meniscus is C-shaped with a triangular cross section. The average width is about 9 to 10 mm and the average thickness is about 3 to 5 mm. The lateral meniscus is almost circular in shape and it covers a large portion of the articular cartilage. Its average width is 10 to 12 mm and its average thickness is about 4 to 5 mm.
The menisci are composed of fibroelastic cartilage. The fibroelastic cartilage is made of an interlacing network of collagen, proteoglycan, glycoproteins, cellular elements and 65-75% water. Ninety percent of the collagen is type I collagen. There are two types of fibres, the longitudinal
(circumferential) and the radial fibres, which allow the meniscus to expand under compressive load, expand the contact area and reduce stresses across the the joint.
The medial inferior genicular artery supplies the peripheral 20-30% of medial meniscus and the lateral inferior genicular artery supplies peripheral 10-25% of lateral meniscus. The central 75% of both menisci receive nutrition through diffusion.

Classification of meniscus tears

A.Descriptive classification of meniscal tear by location

Meniscal tears can occur in the red zone (outer third, vascularized), in the
red-white zone (middle third) or in the white zone (inner third, avascular).

 B.Descriptive classification of meniscal tear by pattern of tear

Meniscal tears can be classified into three types based on the pattern of tear [1]:

1.Basic tears
   A.Longitudinally oriented tears
       i.Horizontal tears (cleavage tears)--These tears are parallel to the    tibial plateau involving one of the articular surfaces or free edge and they divide the meniscus into superior and inferior parts.
        ii. longitudinal tear (vertical tear)--The tear is perpendicular to the tibial plateau and parallel to the long axis of the meniscus. It divides the
divides the meniscus into medial and lateral parts. A Wrisberg rip is a specific subtype, longitudinal tear in the posterior horn of the lateral meniscus that extends laterally from the Wrisberg ligament attachment.
  B.Radial tears -- These tears are perpendicular to both the tibial plateau and the long axis of the meniscus.
  C.Root tears: These tears are typically radial-type tear located at the root of the meniscus.

2.Complex tears
These tears are a combination of all or some of the horizontal, longitudinal and radial-type tears.

3.Displaced tears
Displaced tears are those in which the torn portion of the meniscus is displaced and it can still be attached to the  parent meniscus or detached. There are 3 subtype of displaced tears.
Flap tear: displaced horizontal or longitudinal tears
Bucket-handle tear: displaced longitudinal tear
Parrot beak tear: displaced radial tear

Radiological diagnosis

An MRI has a sensitivity of about 95% and a specificity of 81% for medial meniscal tears and a sensitivity of about 85% and a specificity of 93% for lateral meniscal tears [2]. An MRI of the knee is the modality of choice for investigating a suspected tear of the meniscus and sagittal images are  most useful [3]. A MRI of the knee has an overall 88% sensitivity and 94% specificity for detecting meniscal lesions [4].
There are three MRI criteria for diagnosis of meniscal tears [3]:
A high intrameniscal signal extending to at least one articular surface
The high intrameniscal signal should be seen in at least two slices  (two slice touch rule).
Distortion of the normal meniscal morphology if there has been no prior surgery.
In the T1 sequence a hyperintense line in the meniscus can be due to a tear or due to degeneration. When there is a bucket handle tear an empty groove may be seen.
In the T2 sequence the hyperintense line in the meniscus which indicates synovial fluid in the meniscus may be due to degeneration and not a tear in an adult and due to high vascularity in children [5].
MRI grading system for meniscal signal intensity [6].
The MRI abnormal high meniscal signal intensity can be graded into three:
Grade 1: There is a small focal area of hyperintensity with no extension to the articular surface
Grade 2: There is a linear area of hyperintensity with no extension to the articular surface
2a: There is a linear abnormal hyperintensity with no extension to the articular surface
2b: There is an abnormal hyperintensity which reaches the articular surface on only one single image
2c: There is a globular wedge-shaped abnormal hyperintensity with no extension to the articular surface
Half of the patients with grade 2c abnormal meniscal signals have been found to have meniscal tears on arthroscopy [7]
Grade 3: There is abnormal hyperintensity which extends to at least one articular surface (superior or inferior) which is indicative of a definite tear of the meniscus

A grade 3 MRI signal is indicative of a tear of the meniscus and a "double anterior horn" sign and a "double PCL"  sign are both indicative of a bucket handle tear of the meniscus.

Prevalence of meniscal abnormalities on MRI of the knee

Zanetti et al (8] studied 100 patients with suspected meniscal tears, who had one symptomatic knee and the other asymptomatic knee, with an MRI of the knee to evaluate the prevalence of meniscal abnormalities in the knee. The mean age of these 100 patients was 42.7 years with a range between 18 to 73 years.
They found meniscal tears in 57 symptomatic knees (57%) and in 36 contralateral asymptomatic knees (36%). In the 57 patients who had a tear of the meniscus on the symptomatic side, 63% of these patients had a tear in the contralateral asymptomatic side. In other words, if there is a tear of the meniscus on the symptomatic side, there is a 63% chance that there will be a tear on the opposite asymptomatic side.
Radial, vertical, complex, or displaced meniscal tears and abnormalities of the collateral ligaments, pericapsular soft tissues, and bone marrow abnormalities were mostly seen in symptomatic knees and these findings appear to be clinical significant. Horizontal or oblique meniscal tears on the other hand were frequently seen in both asymptomatic and symptomatic knees and these findings may not often be related to symptoms [8].
Englund et al [9] studied the prevalence of meniscal damage in the general population and the association of meniscal tears with knee symptoms and with radiographic evidence of osteoarthritis. They found that the prevalence of a meniscal tear or of meniscal damage in the right knee as seen on a MRI ranged from 19% (range 15 to 24), among women 50 to 59 years of age, to 56% (range 46 to 66) among men 70 to 90 years of age. Among individuals with radiographic evidence of osteoarthritis (Kellgren–Lawrence grade 2 or higher) the prevalence of a meniscal tear was 63% among those with knee symptoms on most days and 60% among those without symptoms. The corresponding prevalence of meniscal tears among persons without radiographic osteoarthritis were 32% and 23%. Sixty-one percent of the individuals who had meniscal tears in their knees had no symptoms during the previous month.
The authors concluded that incidental findings of meniscal abnormalities on MRI of the knee are common in the general population and increases with age, irrespective of knee symptoms, and often accompanies knee osteoarthritis. Hence clinicians who order MRI of the knee should keep in mind the high prevalence of incidental tears when interpreting the MRI and  planning therapy.
Other authors have reported a high prevalence of meniscal damage ranging from 67 to 91% in patients with symptomatic osteoarthritis of the knee [10,11,12,13].
In the study by Bhattacharyya et al [13], which involved U.S. veterans,  most of whom were men, meniscal tears were noted in 75.5% control subjects who had no knee pain (mean age, 67 years) and had sought medical care for other conditions. They also found that knees with meniscal tear were not more painful than those without a tear and that meniscal tears do not affect functional status in patients with knee OA.
Other studies have also showed that a meniscal tear of the knee is common in individuals who had no symptoms of the knee [14,15,16,17,18].

Treatment of meniscal tears

There are three treatment options for patients with symptomatic tears of the meniscus. These include non-operative treatment, meniscectomy and meniscal repair. Selecting appropriate treatment can often be difficult and will depend on the patient characteristics such as age, co-morbidities and tear characteristics such as the type, location and size of tear.
Non-operative treatment of meniscal tears
There is level I irrefutable evidence that patients with osteoarthritis of the knee with meniscal tears do not benefit from arthroscopic debridement of the joint. Hence the treatment of choice for degenerative meniscus tears is non-surgical.
Moseley et al (19) did a randomised, placebo-controlled trial to assess the efficacy of arthroscopic knee surgery to relieve knee pain and improve function in patients with OA of the knee. They had three groups of patients who either had, joint lavage, joint debridement or sham incisions at the arthroscopic portals. Their study showed strong evidence that arthroscopic lavage with or without debridement is no better than placebo in relieving pain and improving self-reported knee function.
Kirkley et al (20) in 2008 published the outcome of a single-center, randomized, controlled trial of arthroscopic surgery in patients with moderate-to-severe osteoarthritis of the knee. They randomly assigned patients to arthroscopic joint debridement with surgical lavage and  physical plus  medical therapy or to treatment with physical and medical therapy alone. At 2 years follow up they found that arthroscopic surgery for osteoarthritis of the knee provided  no additional benefit as compared to optimized physical and medical therapy.
Sihvonen et al (21) did a multicenter, randomized, double-blind, sham-controlled trial to assess the efficacy of arthroscopic partial meniscectomy in patients who had a degenerative tear of the medial meniscus without knee osteoarthritis. Patients with obvious traumatic onset of symptoms and those with OA were excluded. The study showed that arthroscopic partial meniscectomy was not superior to sham surgery, with regard to pain and functional knee scores assessed during a 12-month follow-up period. The authors concluded that partial meniscectomy for degenerative tears provides no benefit to the patients and that there is no scientific basis for continuing the current practice of doing partial meniscectomy for degenerative tears of the meniscus.
Thorlund et al [22] did a comparative prospective cohort study, to compare patient reported outcomes, of arthroscopic partial meniscectomy in patients with traumatic meniscal tears as compared to that in patients with degenerative meniscal tears, at 52 weeks follow up.
They studied four of five subscales of the knee injury and osteoarthritis outcome score (KOOS) which covered pain, symptoms, sport and recreational function, and quality of life (KOOS4). Their study showed
better self-reported outcomes in patients with degenerative tears as compared to patients with traumatic tears but the difference between the two groups ‘was at no time point considered clinically meaningful’ [22].
The authors questioned the ‘current tenet that patients with traumatic meniscal tears experience greater improvements in patient reported outcomes after arthroscopic partial meniscectomy than patients with degenerative tears’ [22].
So far there have been no randomised controlled trials comparing the outcome of arthroscopic partial meniscectomy with sham surgery or non-surgical treatment for traumatic meniscal tears [23].
Sihvonen et al’s  study (21) provides level I evidence that arthroscopic partial meniscectomy in patients with degenerative tear of the meniscus provides no benefit to the patient when compared with a sham operation. Thorlund et al’s [22] comparative prospective cohort study shows that the outcome of arthroscopic partial meniscectomy in patients with traumatic meniscal tears is no better than that of partial meniscectomy in patients with degenerative tear of the meniscus. This would mean that arthroscopic partial meniscectomy has no role to play in the treatment of partial tears of the meniscus.
Non-operative treatments such as exercise and quadricep strengthening improves knee function and reduces knee pain [24,25,26]. Pain and swelling associated with meniscal tears can be treated non-steroidal medications.
There is definitely no role for surgery in the treatment of degenerative tears of the meniscus. The outcome of partial meniscectomy for traumatic tears of the meniscus is not better than that of partial meniscectomy for degenerative tears as has been believed in the past.

Surgical treatment of traumatic tears of the meniscus

The role played by the menisci in function of the knee has been well established. The main function includes load bearing, shock absorption, stabilisation, joint lubrication, nutrition of the articular cartilage and proprioception [27]. Hence in the management of patients with traumatic meniscal tears all attempts to preserve the meniscus are made.
Pain and mechanical symptoms such as clicking, catching, locking, pinching, or a sensation of giving way associated with unstable meniscal fragment may need surgical intervention.
Unstable meniscal fragments not amenable to repair have to be excised by arthroscopic partial meniscectomy. Tears in the red-red zone, where there is blood supply, can be repaired because there is potential for healing. Some in the red-white zone can heal when repaired. Tears in the rest of the meniscus which is avascular, cannot be repaired, are subjected to a meniscectomy.
Studies comparing the outcome of meniscal repair with meniscectomy are limited. It is difficult to postoperatively define a healed meniscus because postoperative MRIs are not very accurate in defining a successful repair. High signal seen on an MRI may represent oedema, degeneration of the meniscus, an actual tear or postoperative healing and scar [28]. The most accurate way to access a successful repair would be a second look arthroscopy but there can be ethical concerns when second-look arthroscopies are performed to evaluate the success of a meniscal repair. Randomising patients to receive a repair or a meniscectomy can also lead to ethical concern[29].
Seo et al [30] did a second look arthroscopy in 11 patients (who were available for review) out of 21 consecutive patients who underwent arthroscopic pullout suture repair for a posterior root tear of the medial meniscus, at an average of 13.4 months (range 10 to 22 months) follow up. In this case series (level 4 evidence), they found that in none of the patients a complete healing had occurred.
In 5 knees there was lax healing, 2 of which were symptomatic and three asymptomatic. In 4 knees there was scar tissue healing and all 4 were asymptomatic. In  2 knees there was no healing and of the 2, one was symptomatic and one asymptomatic. There was progression of the chondral lesion in one case. The mean Lysholm scores improved from 56.1 preoperatively to 83.0 at follow-up and the mean Hospital for Special Surgery score also significantly increased, from 64.1 to 87.4.
Despite the lack of complete healing in all patients,why there was significant clinical improvement remains unexplained.
Cho et al [31] retrospectively reviewed 13 of 20 consecutive patients who underwent arthroscopic modified pull-out suture repair for a posterior root tear of the medial meniscus. The 13 were available for a second-look arthroscopic evaluation. In 4 cases there was complete healing , in 4 lax healing, in 4 scar tissue healing and in 1 there was no healing. Seven of the 13 patients were asymptomatic. The mean Lysholm scores increased from 34.7 points before the repair to 75.6 points at the second-look arthroscopy and the HSS scores increased from 33.5 to 82. Functional outcome was good in these patients despite incomplete healing of the repair.
Pujol et al [32] evaluated healing of the meniscus after a repair using arthro-CT scans. At 6 months post repair of the meniscus an arthro-CT scan showed complete healing in 58% of the patients, partial healing in 24% and failed healing in 18% of the patients. They also found that the healing in posterior segment tears was lower than that in middle portion tears. Despite the the lack of complete healing in almost half of the patients, the clinical outcome was good in most of the patients.
Paxton et al [33] did a systematic literature review to compare reoperation rates and clinical outcomes after meniscal repair and partial meniscectomy in patients with traumatic meniscal tears. At short and long term follow up partial meniscectomy had lower reoperation rates. The short and long term reoperation rates for partial meniscectomy were 1.4% and 3.9% respectively whereas for meniscal repair were 16.5% and 20.7% respectively. There were a limited number of studies with long term clinical outcome and these small number of studies reported that a meniscal repair was associated with higher Lysholm scores and less radiologic degeneration than partial meniscectomy.
Noyes and Barber-Westin [34] did a systematic review of the literature in 2012 to find out the incidence of meniscectomy, meniscus repair, and tears left in situ during ACL reconstruction in the previous 10 years. In the 159 studies analysed, there were 11,711 meniscal tears. Sixty-five percent of the tears were treated by meniscectomy, 26% of the tears were repaired and 9% were left in situ without any treatment. The incidence of meniscal repair was 26% in patients undergoing ACL reconstruction.
Mutsaerts et al [35] in 2016 did a literature review of all randomized controlled clinical trials which compared various surgical techniques for the treatment of meniscal injuries including; total and partial meniscectomy; meniscectomy and meniscal repair; meniscectomy and meniscal transplantation; open and arthroscopic meniscectomy and various different repair techniques.
This Level I meta-analysis showed that there is a lack of level I evidence to guide the surgical management of meniscal tears.
Degenerative tears of the meniscus do not need any surgery and most traumatic tears of the meniscus also do not need surgery. Patients with traumatic tears who have mechanical symptoms may need surgery. Tears in the avascular region would need a partial meniscectomy. Whether to do a meniscal repair or not remains unclear since there is a lack of level I evidence to guide treatment options. There have been case reports where spontaneous healing of bucket handle tears of the meniscus have occurred, when patients have opted for non-operative treatment or surgery has been delayed for some reason [35,36,37]. Furthermore, definitely there are patients who sustain meniscal injuries and never seek treatment, where spontaneous healing occurs.

Complications of arthroscopic surgery

The overall complications for knee arthroscopy are about 8.2% [38]. Sherman et al [38] retrospectively reviewed 2640 arthroscopic procedures and found an 8.2% incidence of complications,of which 4.8% were major and 3.6% minor complications.The major complications included infections, hemarthrosis, adhesions, effusions, cardiovascular, neurological, reflex sympathetic dystrophy, and instrument breakage, and the minor complications included problems with wound-healing and ecchymosis. Diagnostic arthroscopy had the lowest complication rate and partial medial meniscectomy was associated with a higher complication rate and highest hemarthrosis rate, while partial lateral meniscectomy was associated with the highest rate of instrument breakages. Age more than 50 years and a tourniquet time of more than 60 minutes were risk factors for complications. Surgeon experience had no influence on the complication rates [38].
Salzler et al [39] found a 2.8% complication rate for meniscectomy and a 7.6% complication rate for meniscal repair. They found that the complication rates were higher with sports fellowship-trained surgeons as compared to those who had no sports fellowship training.
Austin and Sherman [40] in a study involving 101 consecutive arthroscopic meniscal repairs found an overall complication rate of 18%. In patient with anterior cruciate tears the meniscus repair was associated with a 20% risk of complication and in those without anterior cruciate injury the complication rate was 14%. The incidence of arthrofibrosis was 10% when there was an ACL tear and 6% when there was no ACL tear in patients undergoing meniscal repair. The overall risk of complications was 19% with medial meniscus repair and 13% with lateral meniscus repairs. The reoperation or rehospitalization rate (excluding repair failures) was 8%.

Infection
Septic knee arthritis following simple arthroscopy procedures is uncommon but it is dreaded complication. The incidence of septic arthritis following simple arthroscopic procedures ranges from 0.009% to 1.1% [41].
In this study the most common pathogen causing infection was Staphylococcus , both coagulase positive and negative. Other bacterias implicated included Enterobacter cloacae, Streptococcus spp. and Serratia marcescens [41].
Risk factors for septic arthritis include age more than 50 years, tourniquet time more than 60 min, longer duration of surgery, male sex, diabetes, morbid obesity, tobacco use, use of intra-articular steroids and complex procedures [41].

Thromboembolic complications
Venographic incidence of deep-vein thrombosis (DVT) after arthroscopy can be up to 17.9% [42]. Most of these are distal and of not much clinical significance.
The incidence of symptomatic and proximal thromboembolic disease,
which can progress to pulmonary embolism (PE), is less than 1% in patients undergoing knee arthroscopy [43-47]. Routine thromboprophylaxis is not recommended for patients undergoing arthroscopy unless certain risk factors such as older age, history of cancer, complexity of surgery, female sex, longer duration of surgery, history of previous DVT, obesity, immobility, varicose veins and use of oral contraceptives, are present [48,49]. A postoperative high index of suspicion is essential in patients where these risk factors are present.

Vascular complications
The Committee on Complications of the Arthroscopy Association of North
America, reported 12 vascular injuries (0.0032 %) in 375,069 knee arthroscopies carried out in North America. Out of these 12 cases of vascular injury reported, 4 required an amputation [50]. DeLee [51], in the
AANA review of complication of arthroscopy in the US, reported six cases of penetrating injury to the popliteal artery (0.005%) in 118,590 arthroscopic procedures. In 4 of these 6 patients an amputation was required.
Although the incidence of vascular injury is low in patients undergoing arthroscopy, a high index of suspicion is necessary and a prompt diagnosis, and early surgical intervention is essential to prevent a risk of loss of limb or life.

Neurological injury
Rodeo et al [52] reported that there are 4 mechanisms by which nerve injury can occur during arthroscopy.These include, direct trauma, pressure
secondary to a compartment syndrome occurring as a result of extravasation of fluid, damage related to the use of a tourniquet and due to reflex sympathetic dystrophy. The reported incidence of neurological injury following knee arthroscopy ranges between 0.01 to 0.6 percent [51]. The nerves that can be injured include the saphenous, tibial and peroneal nerves. The most commonly injured nerve is the saphenous nerve followed by the peroneal nerve. Neurological complications are more often seen with meniscus repairs.

Conclusions

A clinical diagnosis of meniscus tear should be made when a patients complains of knee pain following trauma to the knee. A history of mechanical symptoms of catching, click and giving way would suggest the presence of an unstable meniscus tear which would require treatment. All other tears of the meniscus do not need treatment and hence there is no need for radiological investigations. When clinical diagnosis of an unstable tear of the meniscus which requires surgery is made, an MRI of the knee would be a useful investigation. There is no role of arthroscopic meniscectomy in the treatment of degenerative and traumatic tears when the tear is stable.
There is, however, a lack of Level I evidence to guide the surgical management of traumatic meniscal tears. Studies comparing the outcome of meniscal repair with meniscectomy are limited and of not good quality. Arthroscopy and meniscal surgery can be associated serious complication although the incidence of serious complications is low.




References

1. Nguyen JC, De Smet AA, Graf BK et-al. MR imaging-based diagnosis and classification of meniscal tears. Radiographics. 2014;34 (4): 981-99. doi:10.1148/rg.344125202.
2. Crawford R, Walley G, Bridgman S et-al. Magnetic resonance imaging versus arthroscopy in the diagnosis of knee pathology, concentrating on meniscal lesions and ACL tears: a systematic review. Br. Med. Bull. 2007;84 (1): 5-23.
3. De Smet AA. How I diagnose meniscal tears on knee MRI. AJR Am J Roentgenol. 2012;199 (3): 481-99. doi:10.2214/AJR.12.8663 .
4. Mackenzie R, Palmer CR, Lomas DJ, Dixon AK. Magnetic resonance imaging of the knee: diagnostic performance studies. Clin Radiol 1996;51:251–257.
5. Helms CA. The meniscus: recent advances in MR imaging of the knee. AJR Am J Roentgenol. 2002;179 (5): 1115-22.
6. Lotysch M, Mink J, Crues JV, Schwartz SA. Magnetic resonance imaging in the detection of meniscal injuries (abstract). Magn Reson Imaging 1986;4:185.
7. Dillon EH, Pope CF, Jokl P et-al. The clinical significance of stage 2 meniscal abnormalities on magnetic resonance knee images. Magn Reson Imaging. 1990;8 (4): 411-5.
8. Zanetti M, Pfirrmann CW, Schmid MR, Romero J, Seifert B, Hodler J. Patients with suspected meniscal tears: prevalence of abnormalities seen on MRI of 100 symptomatic and 100 contralateral asymptomatic knees. AJR Am J Roentgenol 2003;181:635-41.
9. Englund, M., Guermazi, A., Gale, D., Hunter, D. J., Aliabadi, P., Clancy, M., & Felson, D. T. Incidental Meniscal Findings on Knee MRI in Middle-Aged and Elderly Persons. The New England Journal of Medicine. 2008; 359(11), 1108–1115.
10.  Englund M, Niu J, Guermazi A, et al. Effect of meniscal damage on the development of frequent knee pain, aching, or stiffness. Arthritis Rheum 2007;56:4048-4054.
11. Kornaat PR, Bloem JL, Ceulemans RY, et al. Osteoarthritis of the knee: association between clinical features and MR imaging findings. Radiology 2006;239:811-817.
12. Link TM, Steinbach LS, Ghosh S, et al. Osteoarthritis: MR imaging findings in different stages of disease and correlation with clinical findings. Radiology 2003;226:373-381.
13. Bhattacharyya T, Gale D, Dewire P, et al. The clinical importance of meniscal tears demonstrated by magnetic resonance imaging in osteoarthritis of the knee. J Bone Joint Surg Am 2003;85:4-9.
14. Boks SS, Vroegindeweij D, Koes BW, Hunink MM, Bierma-Zeinstra SM. Magnetic resonance imaging abnormalities in symptomatic and contralateral knees: prevalence and associations with traumatic history in general practice. Am J Sports Med 2006;34:1984-1991.
15. Ding C, Martel-Pelletier J, Pelletier JP, et al. Meniscal tear as an osteoarthritis risk factor in a largely non-osteoarthritic cohort: a cross-sectional study. J Rheumatol 2007;34:776-784.
16.  Zanetti M, Pfirrmann CW, Schmid MR, Romero J, Seifert B, Hodler J. Patients with suspected meniscal tears: prevalence of abnormalities seen on MRI of 100 symptomatic and 100 contralateral asymptomatic knees. AJR Am J Roentgenol 2003;181:635-641.
17. Hayes CW, Jamadar DA, Welch GW, et al. Osteoarthritis of the knee: comparison of MR imaging findings with radiographic severity measurements and pain in middle-aged women. Radiology 2005;237:998-1007.
18. Beattie KA, Boulos P, Pui M, et al. Abnormalities identified in the knees of asymptomatic volunteers using peripheral magnetic resonance imaging. Osteoarthritis Cartilage 2005;13:181-186.
19. Moseley JB, O'Malley K, Petersen NJ, et al. A controlled trial of arthroscopic surgery for osteoarthritis of the knee. N Engl J Med 2002;347:81-88.
20. Kirkley A, Birmingham TB, Litchfield RB, Giffin JR, Willits KR, Wong CJ, Feagan BG, Donner A, Griffin SH, D'Ascanio LM, Pope JE, Fowler PJ. A randomized trial of arthroscopic surgery for osteoarthritis of the knee. N Engl J Med. 2008;359((11)):1097–107.
21. Sihvonen R, Paavola M, Malmivaara A, Itälä A, Joukainen A, Nurmi H, Kalske J, Järvinen TL, Finnish Degenerative Meniscal Lesion Study (FIDELITY) Group. Arthroscopic partial meniscectomy versus sham surgery for a degenerative meniscal tear. N Engl J Med. 2013 Dec 26; 369(26):2515-24.
22. Thorlund JB, Englund M., Christensen R, Nissen N, Pihl K, Jørgensen U.et al. Patient reported outcomes in patients undergoing arthroscopic partial meniscectomy for traumatic or degenerative meniscal tears: comparative prospective cohort study. The BMJ 2017; 356, j356. http://doi.org/10.1136/bmj.j356.
23. Thorlund JB, Juhl CB, Roos EM, Lohmander LS. Arthroscopic surgery for degenerative knee: systematic review and meta-analysis of benefits and harms. BMJ 2015;350:h2747. 
24. Börjesson M, Robertson E, Weidenhielm L, Mattsson E, Olsson E. Physiotherapy in knee osteoarthrosis: effect on pain and walking. Physiother Res Int. 1996;1:89–97.
25. Matthews P, St-Pierre DM. Recovery of muscle strength following arthroscopic meniscectomy. J Orthop Sports Phys Ther. 1996;23:18–26. 
26. Mangione KK, McCully K, Gloviak A, Lefebvre I, Hofmann M, Craik R. The effects of high-intensity and low-intensity cycle ergometry in older adults with knee osteoarthritis. J Gerontol A Biol Sci Med Sci. 1999;54:M184–M190.
27. Krause WR, Pope MH, Johnson RJ, Wilder DG. Mechanical changes in the knee after meniscectomy. J Bone Joint Surg Am. 1976;58:599–604.
28. Getgood A, Robertson A. Meniscal tears, repairs and replacement – a current concepts review. Orthop Trauma. 2010;24:121–128.
29. Mordecai, S. C., Al-Hadithy, N., Ware, H. E., & Gupte, C. M. (2014). Treatment of meniscal tears: An evidence based approach. World Journal of Orthopedics, 5(3), 233–241. http://doi.org/10.5312/wjo.v5.i3.233. 
30. Seo HS, Lee SC, Jung KA. Second-look arthroscopic findings after repairs of posterior root tears of the medial meniscus. Am J Sports Med. 2011;39:99–107.
31. Cho JH and Song JG. Second-Look Arthroscopic Assessment and Clinical Results of Modified Pull-Out Suture for Posterior Root Tear of the Medial Meniscus. Knee Surgery & Related Research 2014; 26(2): 106–113.
32. Pujol N, Panarella L, Selmi TA, Neyret P, Fithian D, Beaufils P. Meniscal healing after meniscal repair: a CT arthrography assessment. Am J Sports Med. 2008;36:1489–1495.
33. Paxton ES, Stock MV, Brophy RH. Meniscal repair versus partial meniscectomy: a systematic review comparing reoperation rates and clinical outcomes. Arthroscopy. 2011 Sep;27(9):1275-88.
34. Noyes FR AND S. D. Barber-Westin SD. Systematic Review. Treatment of Meniscus Tears During Anterior Cruciate Ligament Reconstruction. Arthroscopy: The Journal of Arthroscopic and Related Surgery. 2012: 28 (1);123-130.
35. Han JH, Song JG, Kwon JH, Kang KW, Shah D, Nha K-W. Spontaneous Healing of a Displaced Bucket-Handle Tear of the Lateral Meniscus in a Child. Knee Surgery & Related Research. 2015;27(1):65-67. doi:10.5792/ksrr.2015.27.1.65.
36. McAllister DR, Motamedi AR. Spontaneous healing of a bucket-handle lateral meniscal tear in an anterior cruciate ligament-deficient knee. A case report. Am J Sports Med. 2001 Sep-Oct;29(5):660-2.
37. Rabelo NN, Rabelo NN, Cunha AAG & Correia F. Spontaneous healing of bucket handle tear of the medial meniscus associated with ACL tear. Revista Brasileira de Ortopedia. 2013; 48(1): 100-103. https://dx.doi.org/10.1016/j.rboe.2012.05.004.
38. Sherman OH, Fox JM, Snyder SJ, Del Pizzo W, Friedman MJ, Ferkel RD, Lawley MJ. Arthroscopy--"no-problem surgery". An analysis of complications in two thousand six hundred and forty cases. J Bone Joint Surg Am. 1986 Feb;68(2):256-65.
39. Salzler MJ, Lin A, Miller CD, Herold S, Irrgang JJ, Harner CD. Complications after arthroscopic knee surgery. Am J Sports Med. 2014 Feb;42(2):292-6.
40. Austin KS, Sherman OH. Complications of arthroscopic meniscal repair. Am J Sports Med. 1993 Nov-Dec;21(6):864-8. 
41. Balato, G., Di Donato, S. L., Ascione, T., D’Addona, A., Smeraglia, F., Di Vico, G., & Rosa, D. (2017). Knee Septic Arthritis after Arthroscopy: Incidence, Risk Factors, Functional Outcome, and Infection Eradication Rate. Joints. 2017; 5(2), 107–113. http://doi.org/10.1055/s-0037-1603901.
42. Demers C, Marcoux S, Ginsberg JS, et al. Incidence of venographically proved deep vein thrombosis after knee arthroscopy. Arch Intern Med 1998;158:47-50.
43. Dahl OE, Gudmundsen TE, Haukeland L. Late occurring clinical deep vein thrombosis in joint-operated patients. Acta Orthop Scand 2000;71:47-50.
44. Geerts WH, Bergqvist D, Pineo GF, et al; American College of Chest Physicians. Prevention of venous thromboembolism: American College of Chest Physicians evidence-based clinical practice guidelines (8th Edition). Chest 2008;133(Suppl):381-453.
45. Jaureguito JW, Greenwald AE, Wilcox JF, Paulos LE, Rosenberg TD. The incidence of deep venous thrombosis after arthroscopic knee surgery. Am J Sports Med 1999;27:707-10.
46. Ramos J, Perrotta C, Badariotti G, Berenstein G. Interventions for preventing venous thromboembolism in adults undergoing knee arthroscopy. Cochrane Database Syst Rev 2008;4:CD005259.
47. Sherman OH, Fox JM, Snyder SJ, et al. Arthroscopy: “no problem surgery”: an analysis of complications in two thousand six hundred and forty cases. J Bone Joint Surg [Am] 1986;68-A:256-65.
48. Hetsroni I. Lyman S, Do H, Mann G and Marx RG. Symptomatic pulmonary embolism after outpatient arthroscopic procedures of the Knee: The incidence and risk factors in 418,322 arthroscopies. J Bone Joint Surg [Br] 2011;93-B:47-51.
49. Anderson FA and Spencer FA. Risk Factors for Venous Thromboembolism. Circulation. 2003;107:I-9–I-16.
50. Small NC. Complications in arthroscopy: the knee and other joints, Committee on Complications of the Arthroscopy Association of North America. Arthroscopy 1986;2:253-8.
51. DeLee JC. Chairman, Committee on Complications of Arthroscopy Association of North America. Complications of arthroscopy and arthroscopic surgery: results of a national survey. J Arthroscopic Rel Surg 1985;1:214-20.
52. Rodeo SA, Sobel M, Weiland AJ. Deep peroneal-nerve injury as a result of arthroscopic meniscectomy: a case report and review of the literature. J Bone Joint Surg [Am] 1993;75-A:1221-4.