Anatomy of the knee
For guidance on examination of the knee, see also separate Knee Assessment article.
- Magnetic resonance imaging (MRI) is the technique of choice for evaluating internal derangement of the knee since even serious internal derangements of the knee may not be demonstrated on X-rays.
- The Ottawa Knee Rules can be used to decide whether an X-ray is indicated. An X-ray should be performed if any of the following are present:
- Age over 55 years (because of the risk of osteoporosis).
- Tenderness over the fibular head.
- Discomfort confined to the patella upon palpation.
- Inability to flex the knee to 90°.
- Inability to bear weight, immediately and in the emergency department, for at least four steps.
- Incidental meniscal findings on MRI scan of the knee are common in the general population and increase with increasing age: in one study of almost 1,000 people, 61% had meniscal tears on MRI but had no knee symptoms in the previous month.
- Delayed, gadolinium-enhanced MRI of cartilage (dGEMRIC) is useful for assessing cartilage health.
The two menisci in each knee are crescent-shaped pads of cartilage tissue. The main functions of the menisci are tibiofemoral load transmission, shock absorption, lubrication of the knee joint and to improve the stability of the knee joint.
- The mean annual incidence of meniscal tears is about 60-70 per 100,000.
- Male-to-female ratio is from 2.5:1 to 4:1.
- Meniscal tears in younger people are usually due to acute trauma, most commonly affecting men aged 21-30 years and girls and young women aged 11-20 years.
- Degenerative changes are the more likely the cause at an older age, most commonly in men aged 40-60 years.
Mechanism of injury
The mechanism of injury is typically twisting or pivoting. Acute meniscal tears occur in young, active people. No or minimal force can be sufficient to cause a degenerative meniscal tear in middle-aged and older people.
- There may be acute pain, especially following obvious trauma or if a fragment of meniscus becomes trapped.
- Often patients cannot remember the exact nature of an injury but complain of popping, catching, locking (usually in flexion) or buckling, along with joint line pain.
- There may be slow onset of swelling (over 2-36 hours) due to an effusion. Effusions can be recurrent.
- If swelling is rapid in onset (0-2 hours) this may be due to a haemarthrosis or a large tense effusion when the tear is associated with a significant ligament injury.
- Advise PRICER:
- Protect from further injury.
- Rest (crutches for the initial 24-48 hours).
- Ice (application of ice on the injured region for 20 minutes of each waking hour during the initial 48 hours after injury).
- Compression (with a knee brace or splint, if necessary).
- Elevation (above the level of the heart).
- An urgent referral to an orthopaedic surgeon is advised if the person has locking of the knee and a meniscal injury is suspected.
- Refer to physiotherapy if there are mild-to-moderate symptoms. A physiotherapy regime will involve daily progressive exercises at home plus attendance at a physiotherapist.
- Refer routinely to an orthopaedic surgeon if a meniscal injury is suspected, and symptoms interfere with the ability to work or persist, despite 6-8 weeks of rehabilitation by a physiotherapist.
- Surgical options include repair (there are various techniques) or partial meniscectomy. Repair operations have better long-term outcomes, better activity levels and lower failure rates than meniscectomy (partial or total).
- Total meniscectomy - this is no longer a common procedure, as long-term results are unfavourable.
- Meniscal transplantation is an option for selected symptomatic patients with previous complete or near-complete meniscectomy.
- A novel treatment is the partial replacement of the meniscus using a biodegradable scaffold but it is uncertain whether this offers any long-term advantages over other options.
Several recent studies have questioned the efficacy of surgery, particularly when the meniscal tear is degenerate:
- Patients with a meniscal tear and evidence of mild-to-moderate osteoarthritis were randomly assigned to either arthroscopic partial meniscectomy with postoperative physical therapy or a standardised physical-therapy regimen alone. There was no significant difference in functional status and pain at six months. However, 30% of patients assigned to the physical-therapy group crossed over to surgery in the first six months.
- A double-blind sham-controlled trial involving patients aged 35-65 years with symptoms of a degenerative medial meniscus tear (but without knee osteoarthritis) demonstrated no better outcomes after arthroscopic partial meniscectomy than after a sham surgical procedure. The authors suggest that a degenerative meniscal tear may be an early sign of osteoarthritis of the knee rather than a separate clinical entity and noted that osteoarthritis may progress more quickly in people undergoing arthroscopy.
- A systematic review and meta-analysis concluded that there is moderate evidence to suggest that there is no additional benefit of arthroscopic meniscal debridement for degenerative meniscal tears compared to exercise, and no benefit in comparison with sham surgery or injection therapy[12, 13].
- A further systematic review and meta-analysis showed that the small inconsequential benefits were absent by one and two years.
- Despite this emerging evidence, rates of arthroscopic meniscectomy are stable or continue to increase.
- Knee arthroscopy is associated with deep vein thrombosis, pulmonary embolism, infection and death.
- Following partial or total meniscectomy, functional activities may be commenced on day 7-8 and running commenced from days 10-14, depending on the the underlying knee condition and health of the patient.
- Rehabilitation protocols following meniscal repair vary.
Articular chondral and osteochondral injuries
The articular surfaces of the femur and tibia are covered with hyaline cartilage. Damage to this hyaline cartilage is known as a chondral injury or, if the underlying bone is also fractured, an osteochondral injury.
Articular chondral and osteochondral injuries of the knee are much less common than meniscal injuries. They generally occur in people aged under 35 years, usually in combination with other ligamentous or meniscal injuries to the knee.
Mechanism of injury
- Trauma is the most common mechanism; however, the repetitive stress associated with osteochondritis dissecans and with chondromalacia patellae is also the cause of symptomatic lesions.
- Rotational force in direct trauma is the most common cause of injury to the articular cartilage. In most cases injury is in weight-bearing regions of articular cartilage and is usually in the medial compartment (four times more common that lateral injuries).
- Osteochondral lesions are most common in adolescents.
Articular cartilage has little capacity to repair itself or regenerate. Therefore, cartilage defects repair by forming scar tissue from the subchondral bone. This scar tissue is deficient in type II collagen and has lower load-bearing capacity. This later surface deterioration may progress to give chronic pain and poor function and may, in some cases, lead to early-onset osteoarthritis.
- Articular cartilage is avascular and aneural, so pain would not be expected; however, some patients do present with pain. It may be present at rest and is exacerbated by weight-bearing exercises.
- The knee may give way if a long-standing injury results in substantial muscle wasting or there is associated ligamentous instability.
- Locking is reported if a loose fragment impedes articular movement.
- There may be an effusion.
- Tenderness is found on palpation of the joint line, with pain induced both by passive and active movements.
- Wasting of the quadriceps will be seen later on.
- Crepitus is palpable on passive joint movement in a usually stable knee.
Lesions may not be diagnosed or may present late because patients will often give a history of an apparently insignificant trauma. Doctors may fail to understand the importance of an effusion in the knee joint, which always indicates joint disease.
Injuries that are new are given time to settle to see if the chondral lesion will become symptomatic or not. If pain fails to resolve after the initial acute phase, surgical treatment gives better outcomes if done sooner rather than later.
Advise 'PRICER', as detailed under 'meniscal injuries', above.
After pain and inflammation subside, aim to increase strength and pain-free range of motion (ROM). Continuous passive motion enhances the healing potential of articular cartilage:
- It enables the movement of synovial fluid, allowing better diffusion of nutrients into the damaged cartilage and diffusion out of other materials (such as blood and metabolic waste products).
- It reduces the formation of fibrous scar tissue in the joint; this tends to decrease ROM for a joint, which enhances the healing potential of articular cartilage.
Treatment of larger and symptomatic lesions is surgical and techniques include arthroscopic debridement, marrow-stimulating techniques, such as microfracture, autologous chondrocyte transfers and implantation, and allografts. Microfracture is the most commonly used procedure and it is suggested that enhanced microfracture techniques may offer the best long-term outcomes; however, evidence is lacking.
Return to the pre-injury level of sports has been found to be fastest after osteoarticular transplantation (OATS) and slowest after autologous chondrocyte implantation (ACI).
- If symptomatic lesions are untreated they may lead to chronic pain and disability and possible early osteoarthritis.
- Significant soft tissue injuries of the knee and lower leg put the lower leg at risk for compartment syndrome.
Several factors have been associated with improved postoperative recovery:
- Defect size of less than 2 cm.
- Pre-operative duration of symptoms of less than 18 months.
- No previous surgical treatment.
- Younger patient age.
- Higher pre-injury level of sports.
However, no consensus exists on the most effective treatment and there are no long-term studies comparing the results of treatment with the natural history of the condition.
Further reading and references
Knee pain - assessment; NICE CKS, March 2011 (UK access only)
Sprains and strains; NICE CKS, March 2016 (UK access only)
Teh J, Kambouroglou G, Newton J; Investigation of acute knee injury. BMJ 2012344:e3167
Stiell IG, Greenberg GH, Wells GA, et al; Derivation of a decision rule for the use of radiography in acute knee injuries. Ann Emerg Med. 1995 Oct26(4):405-13.
Englund M, Guermazi A, Gale D, et al; Incidental meniscal findings on knee MRI in middle-aged and elderly persons. N Engl J Med. 2008 Sep 11359(11):1108-15.
Chang G, Sherman O, Madelin G, et al; MR imaging assessment of articular cartilage repair procedures. Magn Reson Imaging Clin N Am. 2011 May19(2):323-37. doi: 10.1016/j.mric.2011.02.002.
Maffulli N, Longo UG, Campi S, et al; Meniscal tears. Open Access J Sports Med. 2010 Apr 261:45-54. eCollection 2010.
Knee pain - assessment; NICE CKS, March 2011 (UK access only)
Meniscii; Wheeless' Textbook of Orthopaedics
Xu C, Zhao J; A meta-analysis comparing meniscal repair with meniscectomy in the treatment of meniscal tears: the more meniscus, the better outcome? Knee Surg Sports Traumatol Arthrosc. 2015 Jan23(1):164-70. doi: 10.1007/s00167-013-2528-6. Epub 2013 May 14.
Partial replacement of the meniscus of the knee using a biodegradable scaffold; NICE Interventional Procedure Guidance, July 2012
Katz JN, Brophy RH, Chaisson CE, et al; Surgery versus physical therapy for a meniscal tear and osteoarthritis. N Engl J Med. 2013 May 2368(18):1675-84. doi: 10.1056/NEJMoa1301408. Epub 2013 Mar 18.
Sihvonen R, Paavola M, Malmivaara A, et al; Arthroscopic partial meniscectomy versus sham surgery for a degenerative meniscal tear. N Engl J Med. 2013 Dec 26369(26):2515-24. doi: 10.1056/NEJMoa1305189.
Khan M, Evaniew N, Bedi A, et al; Arthroscopic surgery for degenerative tears of the meniscus: a systematic review and meta-analysis. CMAJ. 2014 Oct 7186(14):1057-64. doi: 10.1503/cmaj.140433. Epub 2014 Aug 25.
Roos EM, Thorlund JB, Juhl CB, et al; A more correct interpretation. CMAJ. 2015 Mar 17187(5):358. doi: 10.1503/cmaj.1150018.
Thorlund JB, Juhl CB, Roos EM, et al; Arthroscopic surgery for degenerative knee: systematic review and meta-analysis of benefits and harms. Br J Sports Med. 2015 Oct49(19):1229-35. doi: 10.1136/bjsports-2015-h2747rep.
The diagnosis and management of soft tissue knee injuries - internal derangements; New Zealand Guidelines Group
Chondral and Osteochondral Injuries of the Knee; Wheeless' Textbook of Orthopaedics
Macmull S, Skinner JA, Bentley G, et al; Treating articular cartilage injuries of the knee in young people. BMJ. 2010 Mar 5340:c998. doi: 10.1136/bmj.c998.
Bark S, Piontek T, Behrens P, et al; Enhanced microfracture techniques in cartilage knee surgery: Fact or fiction? World J Orthop. 2014 Sep 185(4):444-9. doi: 10.5312/wjo.v5.i4.444. eCollection 2014 Sep 18.
Harris JD, Brophy RH, Siston RA, et al; Treatment of chondral defects in the athlete's knee. Arthroscopy. 2010 Jun26(6):841-52.
Vaquero J, Forriol F; Knee chondral injuries: clinical treatment strategies and experimental models. Injury. 2012 Jun43(6):694-705. doi: 10.1016/j.injury.2011.06.033. Epub 2011 Jul 5.