PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
Anatomy of the knee
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For guidance on examination of the knee, see separate article Knee Assessment.
- Magnetic resonance imaging 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.
- Plain X-rays are of limited value and require skilled interpretation.
- The Ottawa Knee Rules can be used to decide whether an X-ray is recommended. 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.
- Delayed, gadolinium-enhanced MRI of cartilage (dGEMRIC) is useful for assessing cartilage health.
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 common in people aged under 35 years, but a second peak occurs in patients older than 60 years.
Mechanism of injury
- Trauma is the most common mechanism, but the repetitive stress associated with osteochondritis dissecans and 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 usually in the medial compartment (four times more common that lateral injuries).
- Isolated articular cartilage injuries secondary to trauma are rare; more often, articular cartilage injuries are seen with other traumatic injuries to the knee, such as ligamentous or meniscal damage.
- 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 by both 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.
- 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).
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, autologous chondrocyte transfers and implantation, and allografts.
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.
Development of recurrent locking, popping, or effusions after an adequate trial of conservative therapy may suggest the need for surgical intervention.
The two meniscii 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.
Mechanism of injury
The mechanism of injury is typically twisting or pivoting. Typically, meniscal tears occur in young, active people, with a second peak in middle age. 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 an effusion - which can be recurrent.
- There may be a haemarthrosis if the tear is associated with a significant ligament injury.
- PRICE method, as detailed under 'Articular chondral and osteochondral injuries', above.
- Early referral to an orthopaedic surgeon if an associated ACL injury is suspected.
- Otherwise, referral to physiotherapy if there are mild-to-moderate symptoms.
- Referral 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.
- Total meniscectomy - this is no longer a common procedure, as long-term results are unfavourable.
- Options include repair (there are various techniques) or partial meniscectomy.
- A recent study found that symptomatic patients with a meniscal tear and evidence of mild-to-moderate osteoarthritis, who were randomly assigned to arthroscopic partial meniscectomy with postoperative physical therapy, had improvements in functional status and pain at six months that did not differ significantly from the improvements in patients randomly assigned to a standardised physical-therapy regimen alone. However, 30% of patients assigned to the physical-therapy group crossed over to surgery in the first six months.
- Furthermore, in another recent trial involving patients aged 35-65 without knee osteoarthritis but with symptoms of a degenerative medial meniscus tear, the outcomes after arthroscopic partial meniscectomy were no better than those after a sham surgical procedure.
- More recently, meniscal transplantation has become acceptable 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.
- Following partial or total meniscectomy, functional activities may be commenced on day 7-8 and running from days 10-14, depending on the the underlying knee condition and health of the patient.
- Rehabilitation protocols following meniscal repair vary.
- It is important to remember the functions of the menisci - meniscectomy may lead to further destruction of cartilage and to osteoarthritis of the knee joint.
Further reading & references
- Knee Joint - Anatomy & Function; arthroscopy.com
- Knee pain - assessment; NICE CKS, March 2011 (UK access only)
- Teh J, Kambouroglou G, Newton J; Investigation of acute knee injury. BMJ 2012;344:e3167
- McNally EG; Magnetic resonance imaging of the knee. BMJ. 2002 Jul 20;325(7356):115-6.
- 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 Oct;26(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 11;359(11):1108-15.
- 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 5;340:c998. doi: 10.1136/bmj.c998.
- Harris JD, Brophy RH, Siston RA, et al; Treatment of chondral defects in the athlete's knee. Arthroscopy. 2010 Jun;26(6):841-52.
- Maffulli N, Longo UG, Campi S, et al; Meniscal tears. Open Access J Sports Med. 2010 Apr 26;1:45-54. eCollection 2010.
- Knee pain - assessment; NICE CKS, March 2011 (UK access only)
- Meniscii; Wheeless' Textbook of Orthopaedics
- Holzer LA, Leithner A, Holzer G; Surgery versus physical therapy for meniscal tear and osteoarthritis. N Engl J Med. 2013 Aug 15;369(7):677. doi: 10.1056/NEJMc1307177#SA1.
- 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 26;369(26):2515-24. doi: 10.1056/NEJMoa1305189.
- Partial replacement of the meniscus of the knee using a biodegradable scaffold; NICE Interventional Procedure Guideline (July 2012)
- The diagnosis and management of soft tissue knee injuries - internal derangements; New Zealand Guidelines Group
- Frizziero A, Ferrari R, Giannotti E, et al; The meniscus tear. State of the art of rehabilitation protocols related to surgical procedures. Muscles Ligaments Tendons J. 2013 Jan 21;2(4):295-301. Print 2012 Oct.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Hayley Willacy
Dr Nick Imm
Dr John Cox