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UPDATE_August2013: Orthopaedics - The injured knee
 

UPDATE Jai Chitnavis

 

MA, FRCS, FRCS(Ed)

Eugene McNally

FRCR

Christopher Bulstrode

MA, MCh, FRCS(Orth).


Knee injuries cause more sports-related disability than any other joint in the body, although injuries do occur unrelated to sport. Here the management of acute knee injuries in general practice is described.




The knee is much more than a hinge joint, comprising not one joint surface but two: the tibio-femoral and the patello-femoral joints.


Knee movements include flexion, extension and lateral deviation both away from (valgus) and towards (varus) the midline, as well as some internal and external rotation.


A joint with such a wide range of movements in several planes is inherently unstable and relies for support from muscles and ligaments; these include the quadriceps muscles, the cruciate ligaments (which prevent antero-posterior shift) and the collateral ligaments (which limit sideways shift). The meniscal cartilages also help to stabilise the joint (Figure 1).

Figure 1: Important soft tissues likely to be damaged in acute knee injury.

Knee injuries can involve any of these soft tissue structures in addition to adjacent bony surfaces, either singly or in combination.1


After a knee injury, patients usually present with one of two common problems:

  • a painful swollen knee - the most frequent complaint; or
  • difficulty in moving the joint, especially an inability to straighten it fully.

The painful swollen knee

In the painful swollen knee, the swelling is caused by the accumulation of either blood (a haemarthrosis) or synovial fluid (a traumatic effusion).


A swelling that develops immediately after injury or within the first few hours signals a haemarthrosis. A traumatic effusion takes longer to develop and might not be evident until the next day. Distinguishing between these is important.

A haemarthrosis implies significant intra-articular damage and warrants immediate referral. If the diagnosis remains doubtful after full assessment of the knee, aspiration under aseptic conditions is helpful (Box 1, Figure 2).

Figure 2: Aspirating a haemarthrosis, the most common cause of a swollen, painful knee.

Haemarthrosis

Nearly 80 percent of haemarthrosis follow disruption of the anterior cruciate ligament (ACL).1 The history is typically of hyper-extension or internal rotation of a flexed knee, after which the patient will often have heard a snap. The affected leg gives way and swelling and pain soon follow. Other possible causes of haemarthrosis include:

  • Intra-articular fractures involving the distal femur, proximal tibia or patella, usually after direct trauma to the fractured bone. (Exceptions include: fracture-separation of the distal femoral epiphysis in children, caused when the extended knee is forced into a hyper-extended or valgus position; patella fractures secondary to sudden quadriceps contraction; and supra-condylar fractures in osteoporotic femurs, which may occur after minimal trauma.)
  • Isolated meniscal tears, which typically follow twisting injury to a weight-bearing knee.
  • Lateral patellar dislocation (Figure 3). This usually follows internal rotation of the femur on a fixed tibia. The patient feels pain and notices a mis-shapen knee, and often mistakes the prominence of the medial femoral condyle for the patella.

    Figure 3: Lateral patellar dislocation of the left knee, another cause of haemarthrosis.

Traumatic effusions

Traumatic effusions are usually associated with less trauma than haemarthroses, and any underlying injury is correspondingly less serious.

The knee that cannot fully extend

Inability to extend the knee may be caused by true locking, `pseudo-locking` or disruption of the extensor mechanism.


True locking results form a physical block to knee extension. Usually a fragment of torn meniscal cartilage is responsible and pain is not a dominant feature.


`Pseudo-locking` is caused not by a physical block but by a hamstring spasm secondary to a painful knee effusion.


Extensor mechanism disruption occurs when forcible quadriceps contraction against resistance results in either a quadriceps tear at the patellar insertion or avulsion of the patellar ligament at its tibial insertion.

Selective examination of the injured knee

Can the patient stand on the injured leg? An inability to weight-bear is more suggestive of serious injury than is a limp.

Look at the skin and soft tissues on all sides of the knee for penetrating injuries. Assess swelling, using the uninjured joint for comparison, but beware! The degree of swelling is not directly related to the severity of injury.


Is the knee flexed, suggesting a physical limitation to extension? Is there foot-drop, indicating damage to the common peroneal nerve?


Always examine the distal neurovasculature, because both vascular and neurological trauma can result from knee injuries. Look specifically at the capillary refill time (time taken for blood to return to the skin after it has been lightly pressed, usually less than three seconds) and the pedal pulses. Assess light touch sensation throughout the dorsum and sole of the foot.

Diagnostic signs in swollen knees

It can be very difficult to examine accurately a knee with an effusion but are there signs of patellar dislocation? When gently pushing down on the patella you may feel it tap the femur; this `Tap test` is one way to look for fluid within the knee.3 Fracture is likely when bony surfaces are tender and crepitant and there is a palpable gap in the contour of the patella.


If a patellar dislocation has been reduced, attempted lateral displacement of the patella will make the patient fear recurrent dislocation (`Apprehension test`).3 Tenderness along the joint line, especially on the medial side, is suggestive of meniscal tear.

Active knee movement

Ask the patient to extend the knee. If he or she cannot, consider a quadriceps tear or avulsion of a patellar ligament. Limited active extension is suggestive of a physical block, especially if the action is not painful.

Passive knee movement

Gently assess passive extension and flexion. If there is a `springy` block to extension, this again suggests a physical block. Ask the patient to raise the leg with it extended at the knee and then to flex the knee by about 30 degrees. Now ask for the leg to be straightened. If this cannot be fully achieved, there is an `extensor lag` equal to the remaining angle needed to get the knee straight (`Lag test`, Figure 4). This implies quadriceps weakness, and means that affected patients are unsafe walking unsupported and thus require knee support in the form of a brace and crutches.

Figure 4: Failing the lag test for quadriceps weakness. a) The patient raises the leg while keeping it straight. b) He is then asked to flex it at the knee. c) The patient cannot fully straighten the flexed knee.

Testing the integrity of ligaments

Test for the integrity of the anterior cruciate ligament by pulling the upper tibia anteriorly as the knee is held flexed (`Anterior draw test`, Figure 5).3 If more laxity is felt than in the uninjured knee, a complete tear of the ligament is likely. Assess the integrity of the collateral ligament by putting a valgus or varus strain on the lightly flexed knee.3

Figure 5: The anterior draw test of the integrity of the anterior cruciate ligament. The examiner sits on the patient`s foot to stabilise it as he pulls the tibia forward below the flexed knee.

Special considerations in children and adolescents

It is vital to consider referred pain from the hip in all children who present with suspected knee injuries, especially if there are no signs in the knee. Adolescents with slipped upper femoral epiphyses are the most important examples. If there is any limitation to hip movement on examination, refer the patient to an orthopaedic unit urgently.

Investigation of the injured knee

Difficulty in moving the knee is the main indication for performing an x-ray. Request antero-posterior, lateral and patella skyline views of the knee.


When reviewing the x-rays, look for signs of effusion within the knee and scrutinise the bony margins for fracture. Beware a fracture that separates the distal femoral or tibial epiphyses in children. If the history suggests the patient has a patellar dislocation, a skyline view may reveal an osteochondral `flake` fracture (Figure 6).


Figure 6: Skyline view of lateral patellar dislocation. Note the defect (red arrow) in the medial facer of the patella and the fragment (white arrow; osteochondral `flake`) removed from it by the dislocation.

Look specifically for separation of the tibial spine, this will be present in an avulsion injury of the anterior cruciate ligament (Figure 7a); early diagnosis and treatment significantly improves outcome for the patient (Figure 7b).

Figure 7: Injury to the knee in a 15-year-old boy. a) Avulsion of the tibial spine after traction on the anterior cruciate ligament; b) the avulsed tibial spine put back in place using a screw.

Practical management

Patients who have a painful swollen knee with synovial effusion or `pseudo-locking` of the knee can be managed with analgesics, local ice-packs and a bandage. Emphasise the need for regular quadriceps exercises, such as straight-leg raises 10 times/h. If the quadriceps waste during convalescence, the knee will become unstable and give way when the patient begins to walk. As the pain settles, flexion and extension of the knee should gradually be increased. Patients should be seen to be safe on their feet and educated in the use of crutches if necessary. All patients require review within a week.


Patients should be safe to return to work if they can crouch down and get up without difficulty (`Crouch test`). Sportsmen are ready to go back to sport if they can run backwards in a figure of eight without problems (`Figure-of-eight-test`).

Indications for referral

All patients who have haemarthrosis, true locking of the knee, extensor mechanism disruption or penetrating injuries, and those with an injured knee that is difficult to assess should be referred immediately to the emergency orthopaedic team. Patients with `pseudo-locking` or a traumatic effusion that does not settle in a week should also be referred.

Outline of hospital management of knee injury

In hospital, assessment of the injured knee begins with history and examination and, usually, a set of plain radiographs. The aim is to exclude an injury that warrants urgent action.

Vascular injury

When there is injury to the vasculature, arteriography to display the patency of surrounding vessels will precede surgical exploration unless there has been more than a 4-h delay since the injury; in the latter case, surgery comes first. Combined orthopaedic and vascular intervention usually begins with stabilisation of any long bone fractures followed by vascular repair.

Open injury

When there is an open knee injury, the goal is to debride all soft tissues, wash out the knee thoroughly and close the capsule with sutures.

Haemarthrosis

Aspiration is performed to confirm the diagnosis of haemarthrosis. If fat globules are present, plain radiographs, especially patella skyline views, will be reviewed to identify any fracture (Figure 6).

Fracture management

The management of femoral, tibial or patellar fractures takes priority over that of soft-tissue injuries within the knee.

The goal is to stabilise intra-articular fractures with metalwork, restore alignment and allow early mobilisation. Exceptions include femoral and tibial fractures in children and undisplaced patellar fractures in all age groups. These fractures are managed by manipulation under anaesthesia and application of a cast to maintain reduction.

Patellar dislocation and soft tissue injuries

Patellar dislocations are reduced under analgesia, usually in the accident and emergency department. Early repair of soft-tissue tears caused by the displacement will decrease the risk of recurrent dislocation. Similar considerations apply to quadriceps avulsion from the superior pole of the patella and patellar ligament avulsions.

Examination under anaesthesia

If full knee examination is impossible and no fractures are evident, the knee can be examined under anaesthesia to assess stability. Gross instability will suggest damage to the collateral and cruciate ligaments that requires surgical repair.


Arthroscopy can be used to delineate internal soft-tissue injuries if there is a tense haemarthrosis. However, magnetic resonance imaging (MRI) is an alternative which is making diagnostic arthroscopy of acute injuries less common.


Most injuries to the anterior cruciate ligament are partial or complete tears in the body of the ligament. In general, partial tears can be treated conservatively with careful rehabilitation. Some young and active patients with complete tears are candidates for reconstructive surgery, which is usually performed at a later date. Most patients with complete tears are treated conservatively with physiotherapy and do not undergo (ligament) repair.


Patients who have a `locked` knee can also be investigated using arthroscopy or MRI. A longitudinal tear of the medial meniscus is often responsible and the options are partial menisectomy or meniscal repair.

Recent advances in the management of knee injuries

Improvements are occurring in both the diagnosis of knee injury, with the use of MRI, and in surgical repair of the meniscal cartilage and the anterior cruciate ligament.

Magnetic resonance imaging

MRI is probably the most important advance in the management of knee injuries since development of the arthroscope. In many centres its increasing use has made diagnostic arthroscopy a second-line investigation and knee arthrography largely obsolete.

MRI is noninvasive, uses no ionising radiation and has no known side-effects. It detects 90-96 percent of meniscal tears and 95-97 percent of tears in the anterior cruciate ligament4 (Figures 8 and 9) and is extremely sensitive in the detection of sub-chondral fractures. Scanning is possible in any place - which is useful in the management of intra-articular fractures - and takes about 20 min. These include the posterior meniscal horn, collateral ligaments and the subchondral region. Image quality is not diminished by a haemarthrosis.

Figure 8: A `bucket-handle` tear of the anterior cruciate ligament shown in a saggital magnetic resonance imaging (MRI) scan. The posterior horn (PH) of the cartilage looks different from the anterior horn (AH) because cartilage has been displaced medially by a tear.

In the acutely `locked` knee, clinical examination alone may not easily distinguish between true and `pseudo` locking.


Figure 9: Anterior cruciate ligament (ACL) in saggital view (MRI scan). a) Intact ligament; b) haematoma arising secondary to complete rupture of the ACL.

In a study at Oxford (Dawson et al, Personal communication) patients with a diagnosis of acute `locking` were examined by MRI shortly after presentation; 50 persent had no evidence of a mechanical block. In most of the remaining patients, a bucket-handle tear was identified in the meniscal cartilage; resulting in a high therapeutic arthroscopy rate (96 percent).


MRI has limitations; it is, for example, unable to detect small fragments within the joint, for which plain x-rays remain essential. MRI scans also often underestimate the degree of injury to articular cartilage. Many surgeons still favour arthroscopy, because of its combined therapeutic and diagnostic capacity.

Meniscal repair

Conservative management is important in all patients with acute rest, intensive rehabilitation with physiotherapy and modification of activity. Referral to an orthopaedic surgeon is important if diagnosis is uncertain or there is minimal improvement at clinical review.

Non operative treatments are often successful in patients with certain types of tear - patients who have no loss of joint function, suffer minimal pain or swelling and are willing to reduce their activities.

Surgical treatment is usually reserved for younger patients with a vertical longitudinal tear with the vascularized outer third of the meniscus. This is termed the red-red zone (denoting area of vascularity). Repair of the red-white zone (watershed area between vascular and avascular meniscus) is controversial. Tears in the white-white zone (avascular zone) are rarely repaired - rather the damaged segment is resected (meniscectomy). However meniscectomy causes long term osteoarthritis so is only performed when the patients suffers joint locking or meniscal pain that is refractory to conservative management.

Anterior cruciate ligament reconstruction

Conservative treatment entails rigorous physiotherapy to strengthen the hamstring and quadriceps muscles.

The following factors need to be considered when deciding whether to perform reconstructive surgery:

  • Pre-injury activity level
  • Desire to return to sports
  • Associated injuries
  • Abnormal laxity
  • Patient expectations

Surgical intervention is usually delayed for at least 3 weeks after injury. Three methods of surgical repair exist viz. primary repair (not recommended except for bony avulsions mostly seen in adolescents), extra - articular repair (this technique uses the iliotibial tract on the lateral aspect of the knee to mimic the actions of the ACL), and intra-articular repair (where reconstruction tries to reproduce the anatomic ACL).

Rehabilitation following ACL Reconstruction

Accelerated rehabilitation emphasizing immediate full range of motion, early full weight bearing and strength training allows prompt resumption of activities of daily living and sport.

A return to sedentary tasks is possible within a fortnight. More manual occupations will require at least three months off work.

Usually patients return to activities of daily living within a few weeks and sports by six months post surgery.

Figure 10: Arthroscopic meniscal repair. A tear of the posterior horn is being repaired using sutures and a metal knot pusher. The entire process is performed endoscopically.

Courtesy of Mr Richard Coombs, Hammersmith Hospital, London.


Conclusion

The injured knee is common. Injuries are incurred mainly but not exclusively during sporting activity. Several require urgent orthopaedic review but most can be managed without specialist intervention.


Failure to progress within a week is an indication for hospital assessment. MRI is a safe and accurate investigation for assessing knee injuries and is displacing diagnostic arthroscopy in some centres.

Surgically, there is an increasing tendency to preserve torn meniscal cartilages, where possible, in preference to performing anterior cruciate ligament reconstruction continue to improve.

Practical Points

  • A painful, swollen knee may be caused by a haemarthrosis or synovial fluid. Haemarthrosis implies significant intra-articular damage and warrants immediate referral. If the diagnosis is in doubt, aspirate under aseptic conditions.
  • Most haemarthroses result from anterior cruciate ligament disruption, caused by hyperextension or internal rotation of the flexed knee.
  • True locking of the knee occurs when there is a physical block to knee extension - usually a fragment of torn cartilage.
  • Inability to weight-bear is more suggestive of serious injury than is a limp.
  • When examining the knee always examine the distal neurovasculature. Consider referred pain from the hip in all children who present with suspected knee injuries, especially if signs are absent in the knee.
  • Difficulty in moving the knee is the main indication for an x-ray.
  • A painful, swollen knee where there is synovial effusion can be managed with analgesics, ice-packs and a Tubigrib bandage. Emphasise quadriceps exercises and review in a week.
  • The following should be referred: haemarthrosis, true locking, extensor mechanism disruption, penetrating injuries, injured knees difficult to assess and a traumatic effusion not settling within a week.
  • MRI scanning is replacing diagnostic arthroscopy in some centres.

References

  1. Leffers D. Dislocations and soft tissue injuries of the knee. In: Browner BD, Jupiter JB, Levine AM, Trafton PG. Skeletal trauma. Philadelphia: WB Saunders, 1992; chapter 49, pp. 1717-43.
  2. Gumpel M. Aspiration and injection of joints. In: Procedures in practice. London: British Medical Journal, 1989; chapter 2, pp. 8-18.
  3. Apley AG, Solomon L. The knee. In: Apley`s System of Orthopaedics and Fractures. Oxford: Butterworth Heinemann, 1993; pp. 432-70.
  4. Whitehouse GH. MRI in sports injuries. Curr Orthopaed 1993; 7: 106-16.
  5. Jackson JP. Degenerative changes in the knee after menisectomy. Br Med J 1986; 2: 525-7.
  6. Allen PR, Denham RA, Swan AV. Late degeneratve changes after menisectomy. J Bone Joint Surg 1984; 66-B: 666-71.
  7. DeHaven KE. Decision making factors in the treatment of meniscal lesions. Clin Orthopaed Rel Res 1990; 252: 49-53.

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Posted on Tuesday, September 17 @ 10:59:53 SAST by E-Doc
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