Chapter 67: The painful knee

The knee, which is a gliding hinge joint, is the largest synovial joint in the body. Its small area of contact of the bone ends at any one time makes it dependent on ligaments for its stability. Although this allows a much increased range of movement it does increase the susceptibility to injury, particularly from sporting activities. Finding the cause of a knee problem is one of the really difficult and challenging features of practice. It is useful to remember that peripheral pain receptors respond to a variety of stimuli. These include inflammation due either to inflammatory disorders or chemical irritation such as crystal synovitis, traction pain (e.g. trapped meniscus stretching the capsule), tension on the synovium capsule (e.g. effusion or haemarthrosis), and impact loading of the subchondral bone.

Pain from the knee joint

Disorders of the knee joint give rise to pain felt accurately at the knee, often at some particular part of the joint, and invariably in the anterior aspect, very seldom in the posterior part of the knee. An impacted loose body complicating osteoarthritis and a radial tear of the lateral meniscus⁴ are the exceptional disorders liable to refer pain proximally and distally in the limb, but the problems obviously originate from the knee.

Pain referred to the knee

Referred pain to the knee or the surrounding region is a time-honoured trap in medicine. The two classic problems are disorders of the hip joint and lumbosacral spine.

• The hip joint is mainly innervated by L3, hence pain is referred from the groin down the front and medial aspects of the thigh to the knee (see FIG. 67.1). Sometimes the pain can be experienced on the anteromedial aspect of the knee only. It is not uncommon for children with a slipped upper femoral epiphysis to present with a limp and knee pain.

• Knee pain can be referred from the lumbosacral spine. Patients with disc lesions may notice that sitting, coughing or straining hurts the knee, whereas walking does not.

L3 nerve root pressure from an L2–3 disc prolapse (uncommon) and L4 nerve root pain will cause anteromedial knee pain; L5 reference from an L4–5 disc prolapse can cause anterolateral knee pain, while S1 reference from an L5–S1 prolapse can cause pain at the back of the knee (see FIG. 67.1).

A summary of the diagnostic strategy model is presented in TABLE 67.1.

Probability diagnosis

A UK study¹ highlighted the fact that the commonest causes of knee pain are simple ligamentous strains and bruises due to overstress of the knee or other minor trauma. Traumatic synovitis may accompany some of these injuries. Some of these so-called strains may include a variety of recently described syndromes, such as the synovial plica syndrome, patellar tendonopathy and infrapatellar compressive fat-pad inflammation (see FIG. 67.2).

Low-grade trauma of repeated overuse, such as frequent kneeling, may cause prepatellar bursitis known variously as ‘housemaid’s knee’ or ‘carpet layer’s knee’. Infrapatellar bursitis is referred to as ‘clergyman’s knee’.

Osteoarthritis of the knee, especially in the elderly, is a very common problem. It may arise spontaneously or be secondary to previous trauma with associated internal derangement and instability.

The most common overuse problem of the knee is the patellofemoral joint pain syndrome (often previously referred to as chondromalacia patellae).

Serious disorders not to be missed

Neoplasia in the bones around the knee is relatively uncommon but still needs consideration. The commonest neoplasias are secondaries from the breast, lung, kidney, thyroid and prostate. Uncommon examples include osteoid osteoma, osteosarcoma and Ewing tumour (more likely in younger people). Septic arthritis and infected bursitis are prone to occur in the knee joint, especially following contaminated lacerations and abrasions. Septic arthritis from blood-borne infection can be of the primary type in children, where the infection is either staphylococcal or due to Haemophilus influenzae, or gonococcal arthritis in adults. Rheumatic fever should be kept in mind with a fleeting polyarthritis that involves the knees and then affects other joints.

Inflammatory disorders such as spondyloarthropathies, sarcoidosis, chondrocalcinosis (a crystal arthropathy due to calcium pyrophosphate dihydrate in the elderly), gout and juvenile chronic arthritis have to be considered in the differential diagnosis.

Pitfalls

There are myriad pitfalls in knee joint disorders, often arising from ignorance, because there are myriad problems that are difficult to diagnose. Fortunately, many of these problems can be diagnosed by X-ray. A particular trap is a foreign body, such as a broken needle acquired by kneeling on carpet.

The presence of a spontaneous effusion demands careful attention because it could represent a rheumatic disorder or conditions such as osteochondritis dissecans (more common in the young) or osteonecrosis of the femoral condyle (a necrotic problem in the elderly) and perhaps a subsequent loose body in the joint.

A ruptured Baker cyst will cause severe pain behind the knee and can be confused with deep venous thrombosis. It is important to bear in mind complications of varicose veins, which can cause pain or discomfort around the knee joint.

General pitfalls

• Overlooking referred pain from the hip or low back as a cause of knee pain

• Failing to realise that meniscal tears can develop due to degeneration of the menisci with only minimal trauma

• Failing to X-ray the knee joint and order special views to detect specific problems, such as a fractured patella or osteochondritis dissecans

• Patient aged 55 years or more

• Isolated tenderness of the patella

• Tenderness at the head of the fibula

• Inability to flex to 90°

• Immediate inability to weight-bear and in the emergency room (four steps: unable to transfer weight twice onto each lower limb regardless of limping).

Furthermore, a knee X-ray may be indicated following blunt trauma or a fall-type injury if the patient is:

• <12 years or >50 years

• unable to take four weight-bearing steps in front of the clinician⁵

Seven masquerades checklist

Of these, spinal dysfunction is the prime association. Diabetes may cause pain through a complicating neuropathy and drugs such as diuretics may cause gout in the elderly.

Psychogenic considerations

Patients, young and old, may complain of knee pain, imaginary or exaggerated, to gain attention, especially if compensation for an injury is involved. This requires discreet clinical acumen to help patients work through the problem.

History

The history is the key to diagnosis. If any injury is involved careful description of the nature of the injury is necessary. This includes past history. A special problem relates to the elderly who can sustain knee injuries after a ‘drop attack’, but attention can easily be diverted away from the knee with preoccupation with the cerebral pattern.

It is relevant to define whether the pain is acute or chronic, dull or sharp, and continuous or recurring. Determine its severity and position and keep in mind age-related causes.

Key questions

Related to an injury

• Can you explain in detail how the injury happened?

• Did you land awkwardly after a leap in the air?

• Did you get a direct blow? From what direction?

• Did your leg twist during the injury?

• Did you feel a ‘pop’ or hear a ‘snap’?

• Did your knee feel wobbly or unsteady?

• Did the knee feel as if the bones separated momentarily?

• How soon after the injury did the pain develop?

• How soon after the injury did you notice swelling?

• Have you had previous injury or surgery to the knee?

• Were you able to walk after the injury or did you have to be carried off the ground or court?

• Does this involve work care compensation?

No history of injury

• Does the pain come on after walking, jogging or other activity?

• How much kneeling do you do? Scrubbing floors, cleaning carpets?

• Could there be needles or pins in the carpet?

• Does your knee lock or catch?

• Does swelling develop in the knee?

• Does it ‘grate’ when it moves?

• Does the pain come on at rest and is there morning stiffness?

• Do you feel pain when you walk on steps or stairs?

Significance of symptoms

Swelling after injury

The sudden onset of painful swelling (usually within 60 minutes) is typical of haemarthrosis (see FIGS 67.3 and 67.4). Bleeding occurs from vascular structures such as torn ligaments, torn synovium or fractured bones, while injuries localised to avascular structures such as menisci do not usually bleed. About 75% of cases are due to ACL tears.⁶ If a minor injury causes acute haemarthrosis suspect a bleeding diathesis or anticoagulant usage. The causes of haemarthrosis are listed in TABLE 67.2.

Swelling of an intermediate rate of onset, stiffness and pain in the order of hours (e.g. 6–24 hours) is typical of an effusion of synovial fluid. Causes include meniscal tears and milder ligamentous injuries. Swelling gradually developing over days and confined to the anterior knee is typical of bursitis such as ‘housemaid’s knee’.

Recurrent or chronic swelling

This indicates intra-articular pathology and includes:

• patellofemoral pain syndrome

• osteochondritis dissecans

• degenerative joint disease including degenerative meniscus tears

• arthritides

Locking

Locking usually means a sudden inability to extend the knee fully (occurs at 10–45°, average 30°) but ability to flex fully.⁷

True locking:

• torn meniscus (bucket handle)

• loose body (e.g. bony fragment from osteochondritis dissecans)

• torn ACL (remnant)

• flap of articular cartilage

• avulsed anterior tibial spine

• dislocated patella

• synovial osteochondromatosis

Pseudo-locking:

• patellofemoral disorders

• first or second degree medial ligament tear

• strain of ACL

• gross effusion

• pain and spasm of hamstrings

Catching

‘Catching’ of the knee implies that the patient feels that something is ‘getting in the way of joint movement’ but not locking. Causes include any of the conditions that cause locking, but a subluxing patella and loose bodies in particular must be considered.

• Osteochondritis dissecans (usually lateral side of medial femoral condyle)

• Retropatellar fragment (e.g. from dislocation of patella)

• Dislodged osteophyte

• Osteochondral fracture—post injury

• Synovial chondromatosis

Clicking

Clicking may be due to an abnormality such as patellofemoral maltracking or subluxation, a loose intra-articular body or a torn meniscus, but can occur in normal joints when people climb stairs or squat.

Anterior knee pain⁸

Common causes include:

• fat pad disorder (inflammation)

• patellofemoral syndrome

• osteoarthritis of the knee

• patellar tendonopathy

• osteonecrosis

Lateral knee pain

Consider:

• osteoarthritis of lateral compartment of knee

• lesions of the lateral meniscus

• patellofemoral syndrome

Medial knee pain

Consider:

• osteoarthritis of medial compartment of knee

• lesions of the medial meniscus

• patellofemoral syndrome

Examination

The provisional diagnosis may be evident from a combination of the history and simple inspection of the joint but the process of testing palpation, movements (active and passive) and specific structures of the knee joint helps to pinpoint the disorder.

Inspection

Inspect the knee with the patient walking, standing erect and lying supine. Get the patient to squat to help localise the precise point of pain. Get the patient to sit on the couch with legs hanging over the side and note any abnormality of the patella. Note any deformities, swelling or muscle wasting.

The common knee deformities are genu valgum ‘knock knees’ (see FIG. 67.5a), genu recurvatum ‘back knee’ (see FIG. 67.5b) and genu varum ‘bowed legs’ (see FIG. 67.5c).

A useful way of remembering the terminology is to recall that the ‘l’ in valgus stands for ‘l’ in lateral.⁸ In the normal knee the tibia has a slight valgus angulation in reference to the femur, the angulation being more pronounced in women.

Palpation

Palpate the knee generally, concentrating on the patella, patella tendon, joint lines, tibial tubercle, bursae and popliteal fossa.

Palpate for presence of any fluid, warmth, swelling, synovial thickening, crepitus, clicking and tenderness. Feel for a popliteal (Baker) cyst in the popliteal fossa. Draw the fingers upwards over the suprapatellar pouch: synovial thickening, a hallmark of chronic arthritis, is most marked just above the patella—it feels warm, boggy, rubbery and has no fluid thrill.

Flex the knees to 45° and check for a pseudocyst, especially of the lateral meniscus (see FIG. 67.6).

Fluid effusion

The bulge sign: compress the medial side of the joint and evacuate any fluid. The test is positive when the lateral side of the joint is then stroked and the fluid is displaced across the joint, creating a visible bulge or filling of the medial depression (see FIG. 67.7).

The test will be negative if the effusion is gross and tense, in which case the patellar tap test (see FIG. 67.8) is used by sharply tapping the lower pole of the patella against the femur with the index finger. A positive tap is when the patella can be felt to tap against the femur and then float free.

Movements

Extension: normal is 0–5°. The loss of extension is best measured by lifting the heel off the couch with the knee held down. In the normal knee the heel will lift 2.5–4 cm off the couch, that is, into hyperextension.

Flexion (supine or prone): normal to 135°. The normal knee flexes heel to the buttock but in locking due to medial meniscus tears there may be a gap of 5 or more centimetres between the heel and buttock.

Rotation: normal 5–10°. Test at 90° with patient sitting over the edge of the couch; rotate the feet with the hand steadying the knee.

Note: Normally, no abduction, adduction or rotation of the tibia on the femur is possible with the leg fully extended.

Ligament stability tests

Collateral ligaments. Adduction (varus) and abduction (valgus) stresses of the tibia on the femur are applied in full extension and then at 30° flexion with the leg over the side of the couch. With ligament strains there is localised pain when stressed. With a complete (third degree) tear the joint will open out. This end-point feel should be carefully noted: firmness indicates stability, ‘mushiness’ indicates damage (see FIG. 67.9).

Cruciate ligaments. Stability of the ACL can be tested with the anterior drawer test. This is done with the patient supine and the knee flexed to 90°. The tibia is pulled forwards off the femur and in the presence of a cruciate ligament injury there will be increased gliding of the tibia on the femur. An aberrant positive sign can occur in the presence of posterior cruciate ligament (PCL) insufficiency, in which case the knee is actually brought back to its normal site from a dropped-back position. This gives the appearance of a positive anterior drawer sign. In that situation, a Lachman test will be negative. In the presence of medial ligament injury, the increased external rotation of the tibia against the femur may add to the positive drawer sign.

Specific provocation tests

The simplest menisci function tests are those outlined in TABLE 67.4, later in this chapter.

• McMurray test. The patient lies on the couch and the flexed knee is rotated (internally and externally) in varying degrees of abduction as it is straightened into extension. A hand over the affected knee feels for ‘clunking’ or tenderness.

• Thessaly test. The patient stands on the affected leg, flat-footed, with the knee flexed to 20°, with outstretched arms supported by the examiner’s hands. The patient pivots with firm twists of the body and knee three times medially and laterally on the knee. A positive test is when the patient experiences joint line discomfort, or locking or catching. This is the most sensitive and specific clinical test for meniscal injury.⁷

• Apley grind/distraction test. The patient lies prone and the knee is flexed to 90° and then rotated under a compression force. Reproduction of painful symptoms may indicate meniscal tear. Then repeat the rotation under distraction—tests ligament damage.

• Patella apprehension test. At 15–20° flexion, attempt to push the patella laterally and note the patient’s reaction.

• Patellar tendonopathy. Palpate patellar tendon (refer to FIG. 67.19, later in this chapter).

• Patellofemoral pain test. Refer to FIGURE 67.18, later in this chapter.

Examine the lumbosacral spine and the hip joint of the affected side.

Measurements

Quadriceps. For suspected quadriceps wasting, measure the circumference of the thighs at equal points above the tibial tuberosity. It is helpful to assess quadriceps function by feeling the tone.

Static Q angle (see FIG. 67.10).

If the Q angle is >15° in men and >19° in women there is a predisposition to patellofemoral pain and instability.⁹

Investigations

Investigation for the diagnosis of knee pain can be selected from:

• blood tests:

  • – RA factor tests; ANA; HLA–B₂₇

  • – ESR

  • – blood culture (suspected septic arthritis)

• radiology⁹:

  • – plain X-ray

  • – special views: intercondylar (osteochondritis dissecans, loose bodies); tangential (or skyline view for suspected patella pathology); oblique (to define condyles and patella); weight-bearing views looking for degenerative arthritis

  • – bone scan: for suspected tumour, stress fracture, osteonecrosis, osteochondritis dissecans

  • – MRI: excellent for diagnosing cartilage and menisci disorders and ligament damage; the investigation of choice for internal ‘derangement’

  • – arthrography (generally superseded by arthroscopy) or MRI

  • – ultrasound: good for assessment of patellar tendon, soft tissue mass, fluid collection, Baker cyst and bursae

• CT: useful for complex fractures of tibial plateau and patellofemoral joint special dysfunction

• special:

  • – examination under anaesthesia

  • – arthroscopy

  • – knee aspiration: culture or crystal examination

Fractures that may be missed on plain films¹⁰

• Patellar fracture

• Tibial plateau fracture

• Tibial spine fracture

• Epiphyseal injuries in children

• Osteochondral fracture:

  • – patella

  • – femoral condyle

• Stress fracture upper tibia

• Avulsion fracture (e.g. Segond fracture of upper lateral tibia, with ACL tear)

Children may present with unique conditions that are usually related to growth, including epiphyseal problems. Their tendency towards muscle tightness, especially in the growth spurt, predisposes them to overuse injuries such as patellar tendonopathy and patellofemoral pain syndrome.

First decade

A painful knee during the first decade of life (0–10 years) in non-athletes is an uncommon presenting symptom, but suppurative infection and juvenile chronic arthritis have to be considered.

Genu valgum or varum is a common presentation but usually not a source of discomfort for the child. However, genu valgum, which is often seen around 4–6 years, may predispose to abnormal biomechanical stresses, which contribute to overuse-type injuries if the child is involved in sport.

Second decade

Pain in the knee presents most frequently in this decade and is most often due to the patellofemoral syndrome,¹¹ which is related to the retropatellar and peripatellar regions and usually anterior to the knee. It occurs in the late teenage years of both sexes.

An important problem is subluxation of the patella, typically found in teenage girls. It is caused by maltracking of the patellofemoral mechanism without complete dislocation of the patella (see FIG. 67.11).

On examination, the patella is usually in a high and lateral position. Surgery may be required if symptoms persist.

OSD is common in pre-pubertal adolescent boys but can occur in those aged 10–16 years.

Other conditions found typically in this age group include:

• slipped upper femoral epiphysis—usually in middle teenage years after a growth spurt

• anserinus (‘goose foot’) bursitis

• osteochondritis dissecans

Age-related causes of the painful knee are presented in TABLE 67.3.¹¹

The little athlete

Children competing in sporting activities, especially running and jumping, are prone to overuse injuries such as the patellofemoral pain syndrome, traumatic synovitis of the knee joint and OSD. Haemarthrosis can occur with injuries, sometimes due to a synovial tear without major joint disruption. If knee pain persists, especially in the presence of an effusion, X-rays should be performed to exclude osteochondritis of the femoral condyle.¹²

The Ottawa knee rules

A knee X-ray series is only required for children with any of the findings in the Ottawa knee rules (see earlier in this chapter).

Osgood–Schlatter disorder

Osgood–Schlatter disorder (OSD) is a traction apophysitis resulting from repetitive traction stresses at the insertion of the patellar tendon into the tibial tubercle, which is vulnerable to repeated traction in early adolescence.

Clinical features

• Commonest in ages 10–14 years

• Boys:girls = 3:1

• Bilateral in about one-third of cases

• Common in sports involving running, kicking and jumping

• Localised pain in region of tibial tubercle during and after activity

• Aggravated by kneeling down and going up and downstairs

• Development of lump in area

• Localised swelling and tenderness at affected tubercle

• Pain reproduced by attempts to straighten flexed knee against resistance

X-ray to confirm diagnosis (widening of the apophysis and possible fragmentation of bone) and exclude tumour or fracture (see FIG. 67.12).

Management

Treatment is conservative as it is a self-limiting condition (6–18 months: average 12 months).

• If acute, use ice packs and analgesics.

• The main approach is to abstain from or modify active sports.

• Localised treatments such as electrotherapy are unnecessary.

• Corticosteroid injections should be avoided.¹³

• Plaster cast immobilisation should also be avoided.

• Surgery may be used (rarely) if an irritating ossicle persists¹³ after ossification.

• Gentle quadriceps stretching.

• Graded return to full activity.

Prevention

• Promote awareness and early recognition of OSD.

• Program of stretching exercises for quadriceps mechanism in children in sport.

Osteochondritis dissecans: juvenile form⁷

This commonly occurs in adolescent boys aged 5–16 years whereby a segment of articular cartilage of the femoral condyle (85%) undergoes necrosis and may eventually separate to form an intra-articular loose body (see FIG. 67.13).

It usually presents as pain and effusion and locking.

If the fragment has separated, surgery to reattach it can be contemplated.

Rheumatic disorders are very common and responsible for considerable pain or discomfort, disability and loss of independence in the elderly.

Osteoarthritis is the most common cause and excellent results are now being obtained using total knee replacement in those severely affected.

The elderly are particularly prone to crystal-associated joint diseases, including monosodium urate (gout), CPPD (pseudogout) and hydroxyapatite (acute calcific periarthritis).

Chondrocalcinosis of knee (pseudogout)

The main target of CPPD is the knee, where it causes chondrocalcinosis. Unlike gout, chondrocalcinosis of the knee is typically a disorder of the elderly with about 50% of the population having evidence of involvement of the knee by the ninth decade.¹⁴ Most cases remain asymptomatic but patients (usually aged 60 or older) can present with an acutely hot, red, swollen joint resembling septic arthritis.

Investigations include aspiration of the knee to search for CPPD crystals, and X-ray. If positive, consider an associated metabolic disorder such as haemochromatosis, hyperparathyroidism or diabetes mellitus. The treatment is similar to acute gout although colchicine is less effective. Acute episodes respond well to NSAIDs or intra-articular corticosteroid injection.

Osteonecrosis¹⁵

Spontaneous osteonecrosis of the knee (SPONK) is more common after the age of 60, especially in females; it can occur in either the femoral (more commonly) or tibial condyles. The aetiology is unknown. The sudden onset of pain in the knee, with a normal joint X-ray, is diagnostic of osteonecrosis. However, the X-ray (especially later) will demonstrate an area of osteonecrosis. The pain is usually persistent, with swelling and stiffness, and worse at night. It can take three months for the necrotic area to show radiologically although a bone scan or MRI may be positive at an early stage (see FIG. 67.14). The condition may resolve in time with reduction of weight-bearing. Surgery in the form of subchondral drilling may be required for persistent pain in the early stages.

Osteochondritis dissecans: adult form

The adult form occurs more often in males and may be the result of cysts of osteoarthritis fracturing into the joint. Up to 30% are bilateral. Symptoms depend on whether the osteochondral fragment becomes separated. A loose fragment may produce locking or collapse of the knee.

Loose bodies

The large knee joint is a ‘haven’ for intra-articular loose bodies, which may be formed from bone, cartilage or osteochondral fragments following injury (‘chip’ fragment), osteochondritis dissecans, osteoarthritis, synovial chondromatosis or other conditions. They may be asymptomatic but usually cause clicking or locking with swelling. Diagnosis is by X-ray and surgical removal is necessary for recurrent problems.

The knee ‘mouse’

This common complaint is usually a result of a pedunculated fibrous lump in the prepatellar bursa, often secondary to trauma, such as falls onto the knee.

Acute injuries

Meniscal tears

Medial and lateral meniscal tears are usually caused by abduction and adduction forces causing the meniscus to be compressed between the tibial and femoral condyles and then subjected to a twisting force or a rotatory movement on a semi-flexed weight-bearing knee.

The medial meniscus is three times more likely to be torn than the lateral. These injuries are common in contact sports and are often associated with ligamentous injuries. Suspect these injuries when there is a history of injury with a twisting movement with the foot firmly fixed on the ground.

However, pain in the knee can present in the patient aged 30–50 years (and beyond 50) as the menisci degenerate, with resultant cleavage tears from the posterior horn of the medial meniscus and ‘parrot-beak’ tears of the mid-section of the lateral meniscus. These problems cause pain because these particular deformities create tension on the joint capsule and stretch the nerve ends. Refer to the provocation tests—Thessaly, McMurray and Apley grind tests. X-rays are not specifically useful, but an MRI scan should confirm diagnosis.

Clinical features

• General symptoms:⁹

  • – joint-line pain (49%)

  • – locking (17%)

  • – swelling (14%)

  • – loss of movement: restricted flexion, loss of last 5–10° extension

• Parrot-beak tear of lateral meniscus:

  • – pain in the lateral joint line

  • – pain radiating up and down the thigh

  • – pain worse with activity

  • – a palpable and visible lump when the knee is examined at 45°

Arthroscopic partial meniscectomy offers relief. The peripheral meniscus is vascular and can be repaired within 6–12 weeks of injury.¹⁶

• Cleavage tear of medial meniscus:

  • – pain in medial joint line

  • – pain aggravated by slight twisting of the joint

  • – pain provoked by patient lying on the side and pulling the knees together

  • – pain worse with activity

Arthroscopic meniscectomy is appropriate treatment, but some do settle with a trial of physiotherapy.

TABLE 67.4 is a useful aid in the diagnosis of these injuries. There is a similarity in the clinical signs between the opposite menisci, but the localisation of pain in the medial or lateral joint lines helps to differentiate between the medial and lateral menisci.

Note: The diagnosis of a meniscal injury is made if three or more of the five examination findings (‘signs’ in TABLE 67.4) are present.

Ligament injuries

Tears of varying degrees may occur in the:

• anterior cruciate ligament

• posterior cruciate ligament

• medial collateral ligament

• lateral collateral ligament

Anterior cruciate ligament rupture

This is a very serious and disabling injury that may result in chronic instability. Chronic instability can result in degenerative joint changes if not dealt with adequately. Early diagnosis is essential, but there is a high misdiagnosis rate. Sites of ACL rupture are shown in FIGURE 67.15.

Mechanisms

• Sudden change in direction with leg in momentum

• Internal tibial rotation on a flexed knee (commonest) (e.g. during pivoting)

• Marked valgus force (e.g. a rugby tackle)

• May be associated with collateral ligament tears and meniscus injuries. The so-called ‘unhappy triad’ is a ruptured ACL, medial meniscus tear and medial collateral ligament tear.

Clinical features

• Onset of severe pain after a sporting injury, such as landing from a jump, or a forced valgus rotational strain of the knee when another player falls across the abducted leg

• Immediate effusion of blood, usually within 30 minutes

• Common sports: contact sports—rugby, football and soccer, basketball, volleyball, skiing

• Differential diagnosis is a subluxed or dislocated patella

• Subsequent history of pain and ‘giving way’ of the knee

Examination

• Gross effusion

• Diffuse joint-line tenderness

• Joint may be locked due to effusion, anterior cruciate tag or associated meniscal (usually medial) tear

• Ligament tests:

  • – anterior drawer: negative or positive

  • – pivot shift test: positive (only if instability)

  • – Lachman test: lacking an end point

Note: It may be necessary to examine the knee under anaesthesia, with or without arthroscopy, to assess the extent of injury.

This test is emphasised because it is a sensitive and reliable test for the integrity of the ACL. It is an anterior draw test with the knee at 15–20° of flexion. At 90° of flexion, the draw may be negative but the anterior cruciate torn.

Functional instability due to anterior cruciate deficiency is best elicited with the pivot shift test. This is more difficult to perform than the Lachman test.

This is an important test for anterolateral rotatory instability. It is positive when anterior cruciate injuries are sufficient to produce a functional instability.

Management¹⁷

Management depends on the finding by the surgeon. Surgical repair is reserved for complete ligament tears. This usually involves reconstruction of the ligament using patellar or preferably hamstring tendons. Early reconstruction is appropriate in younger patients who participate in high levels of sporting activity for whom it can be predicted that functional instability will be a problem. In less active people, a conservative approach is appropriate. The ACL may be trimmed. Cruciate reconstruction can then be undertaken if the knee becomes clinically unstable. The presence of an ACL injury with a significant medial ligament injury will necessitate reconstructive surgery, but this is probably best delayed for some weeks as the subsequent incidence of knee stiffness is high.

Posterior cruciate ligament rupture

Mechanisms

• Direct blow to the anterior tibia in flexed knee

• Severe hyperextension injury

• Ligament fatigue plus extra stress on knee

Clinical features

• Posterior (popliteal) pain, radiating to calf

• Usually no or minimal swelling

• Minimal disability apart from limitation of running or jumping

• Pain running downhill

• Recurvatum

• Posterior sag or draw

Management

• Usually managed conservatively with immobilisation and protection for 6 weeks

• Graduated weight-bearing and exercises

Medial collateral ligament rupture

Mechanisms

• Direct valgus force to knee—lateral side knee (e.g. rugby tackle from side)

• External tibial rotation (e.g. two soccer players kicking ball simultaneously)

Clinical features

These depend on the degree of tear (1st, 2nd or 3rd degree):

• pain on medial knee

• aggravated by twisting or valgus stress

• localised swelling over medial aspect

• pseudo-locking—hamstring strain

• ± effusion

• no end point on valgus stress testing (3rd degree) (see FIG. 67.9a)

Note: Check lateral meniscus if MCL tear. Pellegrini–Stieda syndrome—calcification in haematoma at upper (femoral) origin of MCL—may follow.

Management

If an isolated event, this common injury responds to conservative treatment with early limited motion bracing to prevent opening of the medial joint line. Six weeks of limited motion brace at 20–70° followed by knee rehabilitation usually returns the athlete to full sporting activity within 12 weeks.

Note: The same principles of diagnosis and management apply to the less common rupture of the lateral collateral ligament, which is caused by a direct varus force to the medial side of the knee. However, lateral ligament injuries tend to involve the cruciate ligament and reconstruction of both ligaments is usually necessary.¹⁶

Complex regional pain syndrome I

A localised complex regional pain syndrome I (also known as reflex sympathetic dystrophy) can follow a direct fall onto the knee. (See CHAPTER 12.)

Symptoms

• Hypersensitivity

• Full extension, loss of flexion

• Possible increased sweating

• Tenderness of the joint

Overuse syndromes

The knee is very prone to overuse disorders. The pain develops gradually without swelling, is aggravated by activity and relieved with rest. It can usually be traced back to a change in the sportsperson’s training schedule, footwear or technique, or to related factors. It may also be related to biomechanical abnormalities ranging from hip disorders to feet disorders.

Overuse injuries include:

• patellofemoral pain syndrome (‘jogger’s knee’, ‘runner’s knee’)

• patellar tendonopathy (‘jumper’s knee’)

• anserinus tendonopathy/bursitis

• semimembranous tendonopathy/bursitis

• biceps femoris tendonopathy

• quadriceps tendonopathy/rupture

• popliteus tendonopathy

• iliotibial band friction syndrome (‘runner’s knee’)

• the hamstrung knee

• synovial plica syndrome

• infrapatellar fat-pad inflammation

It is amazing how often palpation identifies localised areas of inflammation (tendonopathy or bursitis) around the knee, especially from overuse in athletes and in the obese elderly (see FIG. 67.17).

Patellofemoral pain syndrome

This syndrome, also known as chondromalacia patellae or anterior knee pain syndrome and referred to as ‘jogger’s knee’, ‘runner’s knee’ or ‘cyclist’s knee’, is the most common overuse injury of the knee. There is usually no specific history of trauma. It may be related to biomechanical abnormalities and abnormal position and tracking of the patella (e.g. patella alta). It usually presents in females aged 13–15 years with faulty knee mechanisms or in people aged 50–70 years with osteoarthritis of the patellofemoral joint.¹⁸

Clinical features

• Pain behind or adjacent to the patella or deep in the knee

• Pain aggravated during activities that require flexion of the knee under loading:

  • – climbing stairs

  • – walking down slopes or stairs

  • – squatting

  • – prolonged sitting

• The ‘movie theatre’ sign: using aisle seat to stretch knee

• Crepitus around patella may be present

Signs (chondromalacia patellae)

Patellofemoral crepitation during knee flexion and extension is often palpable, and pain may be reproduced by compression of the patella onto the femur as it is pushed from side to side with the knee straight or flexed (Perkins test).

See FIGURE 67.18.

• Have the patient supine with the knee extended.

• Grasp the superior pole of the patella and displace it inferiorly.

• Maintain this position and apply patellofemoral compression.

• Ask the patient to contract the quadriceps (it is a good idea to get the patient to practise quadriceps contraction before applying the test).

• A positive sign is reproduction of the pain under the patella and hesitancy in contracting the muscle.

Treatment

• Give reassurance and supportive therapy.

• Reduce any aggravating activity.

• Refer to a physiotherapist.

• Correct any underlying biomechanical abnormalities such as pes planus (flat feet) by use of orthotics and correct footwear.

• Employ quadriceps (especially) and hamstring exercises.

• Consider course (trial) of NSAIDs.

Patellar tendonopathy (‘jumper’s knee’)

‘Jumper’s knee’, or patellar tendonopathy (see FIG. 67.2, earlier in this chapter), is a common disorder of athletes involved in repetitive jumping sports, such as high jumping, basketball, netball, volleyball and soccer. It probably starts as an inflammatory response around a small tear.

Clinical features

• Gradual onset of anterior pain

• Pain localised to below knee (in patellar tendon)

• Pain eased by rest, returns with activity

• Pain with jumping

The diagnosis is often missed because of the difficulty of localising signs. The condition is best diagnosed by eliciting localised tenderness at the inferior pole of the patella with the patella tilted. There may be localised swelling.

• Lay the patient supine in a relaxed manner with the head on a pillow, arms by the side and quadriceps relaxed (a must).

• The knee should be fully extended.

• Tilt the patella by exerting pressure over its superior pole. This lifts the inferior pole.

• Now palpate the surface under the inferior pole. This allows palpation of the deeper fibres of the patellar tendon (see FIG. 67.19).

• Compare with the normal side.

• Very sharp pain is usually produced in the patient with patellar tendonopathy.

Management

Early conservative treatment, including rest from the offending stresses, is effective. Referral to a physiotherapist for exercise-based rehabilitation is appropriate. This includes adequate warm-up and warm-down. Training modification includes calf, hamstring and quadriceps muscle stretching. Modified footwear and a patellar tendon strap may be helpful in some cases. The use of NSAIDs and corticosteroid injections is disappointing. Chronic cases may require surgery.

Anserinus tendonopathy/bursitis

Localised tenderness is found over the medial tibial condyle where the tendons of the sartorius, gracilis and semitendinosus insert into the bone. It is distal to the joint line. It is a common cause of knee pain in the middle-aged or elderly, especially the overweight woman. Pain is aggravated by resisted knee flexion.

Semimembranous tendonopathy/bursitis

This inflamed area is sited either at the tendon insertion or in the bursa between the tendon and the medial head of the gastrocnemius. It is an uncommon problem. The bursa occurs on the medial side of the popliteal fossa between the medial head of the gastrocnemius and the semimembranous tendon. It often communicates with the knee joint and, if so, treat knee joint pathology. If not, one can give an injection of depot triamcinolone or betamethasone.

Biceps femoris tendonopathy/bursitis

The tendon and/or the bursa that lies between the tendon insertion and the fibular collateral ligament at the head of the fibula may become inflamed due to overuse. It is usually encountered in sprinters.

Popliteus tendonopathy

Tenosynovitis of the popliteus tendon may cause localised pain in the posterior or the posterolateral aspect of the knee. Tenderness to palpation is elicited with the knee flexed to 90°.

Iliotibial band syndrome

Inflammation develops over the lateral aspect of the knee where the iliotibial band passes over the lateral femoral condyle. An inflamed bursa can occur deep to the band. The problem, which is caused by friction of the iliotibial band on the bone, is common in long-distance runners, especially when running up and down hills, and in cyclists. It presents with well-localised lateral knee pain of gradual onset. Palpation reveals tenderness over the lateral condyle 1–2 cm above the joint line.

Treatment of tendonopathy and bursitis (small area)

Generally (apart from patellar tendonopathy), the treatment is an injection of local anaesthetic and long-acting corticosteroids into and deep to the localised area of tenderness. In addition, it is important to restrict the offending activity and refer for physiotherapy for stretching exercises. Attention to biomechanical factors and footwear is important.

If conservative methods fail for iliotibial tract tendonopathy, surgical excision of the affected fibres may cure the problem.

Prepatellar bursitis

Repetitive low-grade direct trauma, such as frequent kneeling, can cause inflammation with swelling of the bursa, which lies between the anterior surface of the patella and the skin. ‘Housemaid’s knee’, or ‘carpet layer’s knee’, can be difficult to treat if rest from the trauma does not allow it to subside. If persistent, drain the fluid with a 23 gauge needle and then introduce 0.5–1 mL of long-acting corticosteroid. The presence of a bursa ‘mouse’ and persistent bursitis usually mean that surgical intervention is required.

Acute bursitis may also be caused by acute infection, or one of the inflammatory arthropathies (e.g. gout, seronegative spondyloarthropathies).

Infrapatellar bursitis

‘Clergyman’s knee’ is produced by the same mechanisms as prepatellar bursitis and can be involved with inflammatory disorders or infection. Treatment is also the same.

The hamstrung knee

Cross describes this condition in young active sportspeople (second decade)⁹ as one that causes bilateral knee pain and possibly a limp. It is caused by a failure to warm up properly and stretch the hamstring muscles, which become tender and tight during the growth spurt. A 6-week program of straight leg raising and hamstring stretching will alleviate the pain completely.

Synovial plica syndrome

This syndrome results from a synovial fold (an embryological remnant) being caught between the patella and the femur during walking or running. It causes an acute ‘catching’ knee pain of the medial patellofemoral joint (see FIG. 67.2, earlier in this chapter) and sometimes a small effusion. It generally settles without treatment.

Infrapatellar fat-pad inflammation

Hoffa fat pad syndrome follows acute compression of the fat-pad, which extends across the lower patella deep to the patellar tendon and into the knee joint (see FIG. 67.2, earlier in this chapter), during a jump or other similar trauma, producing local pain and tenderness similar to the sensation of kneeling on a drawing pin.¹⁸

The pain usually settles without therapy over a period of days or weeks. There is localised tenderness and it can be confused with patellar tendonopathy.

Arthritic conditions

Osteoarthritis

Osteoarthritis is a very common problem of the knee joint. Symptoms usually appear in middle life or later. It is more common in women, obese people, and in those with knee deformities (e.g. genu varum) or previous trauma, especially meniscal tears. The degenerative changes may involve either the lateral or the medial tibiofemoral compartment, the patellofemoral joint or any combination of these sites.

Clinical features

• Slowly increasing joint pain and stiffness

• Aggravated by activities such as twisting, bending, prolonged walking, standing or squatting

• Descending stairs is usually more painful than ascending stairs (suggestive of patellofemoral osteoarthritis)

• Pain may occur after rest, especially prolonged flexion

• Minimal effusion and variable crepitus

• Restricted flexion but usually full extension

• Often quadriceps wasting and tender over medial joint line

• Diagnosis confirmed by X-ray (weight-bearing view)

Management options

• Relative rest

• Weight loss

• Analgesics and/or judicious use of NSAIDs

• Glucosamine: a Cochrane review showed that it is both safe and modestly effective (see CHAPTER 35)

• Walking aids and other supports

• Physiotherapy (e.g. hydrotherapy, quadriceps exercises, mobilisation and stretching techniques)

• Viscosupplementation: intra-articular injection of hylans

• Intra-articular injections of corticosteroids are generally not recommended, but a single injection for severe pain can be very effective

• Surgery is indicated for severe pain and stiffness and includes arthroscopic debridement and wash out, osteotomy, arthrodesis and total joint replacement (see FIG. 67.20) or hemiarthroplasty, especially for the medial compartment with focal arthritis and varus deformity

Rheumatoid arthritis

The knee is frequently affected by rheumatoid arthritis (RA), although it rarely presents as monoarticular knee pain. RA shows the typical features of inflammation—pain and stiffness that is worse after resting. Morning stiffness is a feature.

Note: The spondyloarthropathies have a similar clinical pattern to RA.

Synovectomy is a useful option with persistent boggy thickening of synovial membrane but without destruction of the articular cartilage.²

Baker cyst

A popliteal cyst (Baker cyst) is a herniation of a chronic knee effusion between the heads of the gastrocnemius muscle and is usually associated with osteoarthritis (most common), rheumatoid arthritis or internal derangement of the knee. It presents as a mass behind the knee and may or may not be tender or painful.

It tends to fluctuate in size.

A Baker cyst indicates intra-articular pathology and indicates a full assessment of the knee joint.

Rupture may result in pain and swelling in the calf, mimicking DVT.

Treat underlying knee inflammation (synovitis).

Surgical removal of the cyst is advisable for persistent problems.

Septic arthritis

This tends to be more common in the knee than in other joints. Septic (pyogenic) arthritis should be suspected when the patient complains of intense joint pain, malaise and fever. In the presence of acute pyogenic infection, the joint is held rigidly. The differential diagnosis includes gout and pseudogout (chondrocalcinosis).

Most painful knee conditions are not serious and, providing a firm diagnosis is made and internal knee disruption or other serious illness discounted, a simple management plan as outlined leads to steady relief. For more serious injuries the primary goal is to minimise the adverse consequences of forced inactivity.

• First aid: RICE (avoid heat in first 48 hours).

• Lose weight if overweight.

• Adequate support for ligament sprains—supportive elastic tubular (Tubigrip) bandage or a firm elastic bandage over Velband.

• Simple analgesics—paracetamol (acetaminophen).

• Judicious use of NSAIDs and corticosteroid injections.

• Physiotherapy to achieve strength and stability.

• Attend to biomechanical abnormalities, inappropriate footwear and athletic techniques.

• Orthotics and braces to suit the individual patient.

• Specialised exercise techniques (e.g. the McConnell technique).²

• Quadriceps exercises: these simple exercises are amazingly effective.

Quadriceps exercises (examples)

• Instruct the patient to tighten the muscles in front of the thighs (as though about to lift the leg at the hip and bend the foot back but keeping the leg straight). The patient should hold the hand over the lower quadriceps to ensure it is felt to tighten. This tightening and relaxing exercise should be performed at least 6 times every 2 hours or so until it becomes a habit. It can be done sitting, standing or lying (see FIG. 67.21).

• Sitting on a chair the patient places a weight of 2–5 kg around the ankle (e.g. a plastic bag with sand or coins in a sock) and lifts the leg to the horizontal and then gently lowers it (avoid in patellofemoral problems).

• Early referral is required for knees ‘at risk’ following acute injuries where one or more of the following are present:

  • – locked knee

  • – haemarthrosis

  • – instability

• Clinical evidence of a torn cruciate ligament, third degree tear of the collateral ligaments or torn meniscus

• Undiagnosed acute or chronic knee pain

• Recurrent subluxation or dislocation of the patella

• Suspected septic arthritis

• Presence of troublesome intra-articular loose body

• Evidence of severe osteoarthritis

Hand-out sheets from Murtagh’s Patient Education 7th edition:

• Baker’s cyst

• Exercises for your knee

• Knee: anterior knee pain

• Osgood–Schlatter disorder