6: Pain in the Knee

Adrian Dunbar¹ and Mark Wilkinson^2,3

¹ Skipton, North Yorkshire, UK

² University of Sheffield, Sheffield, UK

³ Sheffield Teaching Hospitals NHS Foundation Trust, President British Orthopaedic Research Society, UK

The knee is the largest joint in the body. It is a complex hinge that is made up of two separate articulations: the tibiofemoral joint and the patellofemoral joint. Knee motion occurs in a complex manner involving three planes, although the vast majority of its motion occurs in the sagittal plane (from full extension through to 140° of flexion).

Pain in the knee joint is one of the most common musculoskeletal complaints that presents to primary care physicians, and may arise from a broad range of pathologies. In the younger patient, pain most commonly arises from sporting or overuse injuries, which may affect the intra‐articular or extra‐articular structures of the knee. The knee is also a common site for inflammatory and infective pathologies. In the older patient, the most common cause is degenerative disease. Knee pain arising from osteoarthritis is a major cause of disability in the older patient, the prevalence and healthcare costs of which continue to rise as the population ages.

The evaluation of knee pain centres on a thorough history and physical examination supplemented, where necessary, with appropriate imaging and laboratory tests (Figure 6.1).

A seated female patient (left) presenting her right knee to a male doctor (right). — **Figure 6.1** A detailed history and examination are required to make an accurate clinical diagnosis in the patient presenting with knee pain

Traumatic causes of knee pain

Injuries are a common cause of knee pain. Most knee injuries in sport occur as a result of indirect trauma, such as a twisting moment to the knee. The structures most commonly injured by this mechanism are the menisci, the collateral ligaments and the cruciate ligaments. These structures may be damaged in isolation, or damage may occur in combination (for example, the anterior cruciate ligament, medial collateral ligament and medial meniscus may be injured in O’Donoghue’s triad). Direct trauma to the knee (such as during contact sport, an industrial accident or a motor vehicle collision) most commonly causes bone contusions, fracture or dislocation that may affect the patellofemoral or tibiofemoral joint. Dislocation of the tibiofemoral joint indicates high‐energy trauma, and is often associated with neurovascular damage.

Meniscus injury

Meniscus injury in young people can present as an acute injury or as a chronic condition with an insidious onset. The majority of meniscus tears in young people occur after mild to moderate energy twisting injuries and are typically isolated injuries or associated with a collateral ligament strain. The medial meniscus is damaged three times more commonly than the lateral meniscus (Figure 6.2). Higher energy twisting injuries are commonly associated with an anterior cruciate ligament injury, an acute haemarthrosis and inability to bear weight. Patients with meniscus tears have focal tenderness over the joint line and may experience mechanical catching and locking symptoms in the knee in addition to joint effusion and pain.

Ege’s test and the Thessaly test, performed with the patient in standing, have much higher sensitivity and specificity for meniscal tears than McMurray’s test and are easy to perform (Figures 6.3, 6.4). Magnetic resonance imaging (MRI) can aid in establishing the diagnosis and in identifying associated conditions, such as degenerate disease affecting the articular cartilage. Acute tears that occur in the well‐vascularized peripheral portion of the meniscus are amenable to arthroscopic repair, which preserves meniscal function. Where an anterior cruciate ligament injury is also present, this is commonly reconstructed concurrently. Chronic meniscal tears are typically avascular with degenerative characteristics and will not heal if repaired.

Image described by caption. — **Figure 6.2** MRI of meniscus injury (sagittal view). The anterior part of the medial meniscus can be seen as a black triangle on the left side of the joint line; the black triangle of the posterior part of the meniscus has a white line running through it, representing an oblique tear

The patient’s maximally internally rotated feet and flexed the knees (left) and maximally externally and flexed the knees (right). — **Figure 6.3** Ege’s test. (a) The patient is asked to maximally internally rotate the feet and flex the knees. A meniscal tear is indicated if the patient’s knee pain is reproduced. (b) The patient is asked to maximally externally rotate the feet and flex the knees. A meniscal tear is indicated if the patient’s knee pain is reproduced

A patient standing on one leg and flexing the knee to approximately 20°. — **Figure 6.4** Thessaly test. The patient is asked to stand on one leg, flex the knee to approximately 20°, then rotate on the knee, medially then laterally. A meniscal tear is present if the patient’s knee pain is reproduced by rotation on the flexed knee

Arthroscopic resection is confined to the torn and degenerate portions of meniscus, as early‐onset osteoarthritis of the knee commonly follows complete meniscal resection.

Articular cartilage injury

Articular cartilage injury is often the result of a traumatic episode that involves an impact injury to the cartilage surface. Articular cartilage injuries can result in focal pain, joint effusion and mechanical catching symptoms. Treatment comprises graduated physiotherapy for undisplaced injuries and arthroscopic repair or removal for displaced osteochondral fragments. Occult episodes of trauma to the knee may result in separation of cartilage from the subchondral bone, termed osteochondritis dissecans. Patients complain of poorly localized pain. The diagnosis is made from plain radiographs or MRI scans, and treatment commonly involves arthroscopic resection of loose cartilage.

Differentiation of cause

A detailed history of the mechanism of injury and physical examination provide valuable information to differentiate between the various traumatic causes of knee pain. Knee pain from injury has a sudden onset at the time of the injury episode and is often accompanied by local soft tissue swelling and an effusion. Certain fractures and dislocations may exhibit gross deformity but the majority of knee and patellar dislocations spontaneously reduce before presentation. A haemarthrosis develops quickly (over a period of minutes to a few hours) and indicates significant intra‐articular injury, such as an anterior cruciate ligament tear, intra‐articular fracture or osteochondral injury, or patellar dislocation. Effusions develop more slowly (over several hours) and tend to be associated with meniscal injuries (Table 6.1).

Table 6.1 Post‐traumatic knee swelling and the most common associated diagnoses

Immediate haemarthrosis	Delayed effusion	Minimal effusion
Anterior cruciate ligament tear	Meniscus tear	Collateral ligament tear
Osteochondral fracture	Posterior cruciate ligament tear
Patellar dislocation

Radiographs should be obtained when evaluating any knee injury to exclude a fracture, dislocation or other significant abnormality. After obtaining radiographs, additional diagnostic tests may be indicated, including a computed tomography scan in the case of intra‐articular fractures or MRI when a soft tissue or osteochondral injury is suspected. In the absence of neurovascular compromise or gross deformity, initial treatment of traumatic knee pain should consist of restricted weight bearing, ice and elevation. Severe injuries require immediate referral for orthopaedic surgical evaluation.

Knee pain in younger people and athletes

Knee pain in younger people and athletes can be caused by overuse syndromes, meniscus injury or articular cartilage abnormality. Common overuse syndromes include patellar tendonopathy, anterior knee pain syndrome, pes anserine bursitis and iliotibial band friction syndrome (Table 6.2).

Table 6.2 Symptoms associated with overuse injuries

Symptom	Likely diagnosis
Pain adjacent to patella Pain ascending/descending stairs Pain when sitting for prolonged periods (‘movie theatre sign’)	Anterior knee pain syndrome
Pain in patellar tendon Pain with jumping	Patellar tendonopathy
Lateral knee pain with repetitive activity	Iliotibial band friction syndrome
Medial knee pain distal to joint line	Pes anserine bursitis

Patellar tendonopathy

Patellar tendonopathy is caused by repetitive activity, particularly ‘explosive’ athletics such as jumping. Patients complain of pain and soft tissue swelling about the patellar tendon, usually at its proximal attachment to the patella. Treatment consists of ice, pain‐relieving medication, activity modification, to reduce inappropriate stress on the tissue as healing takes place, and strengthening exercises, focusing on eccentric loading of the tendon.

Anterior knee pain syndrome

Anterior knee pain syndrome occurs in patients who engage in repetitive athletic activity, in those with abnormalities in extensor mechanism alignment and in those who are overweight. Patients with anterior knee pain syndrome complain of pain in the front of the knee, which is accentuated by ascending and descending stairs, squatting, kneeling and sitting for long periods of time. The pain may be located directly behind the patella or in the medial or lateral retinaculum. Treatment should include activity modification, weight control if necessary, physiotherapy to strengthen the quadriceps muscles (particularly vastus medialis) and core musculature, and appropriate pain‐relieving medication.

Pes anserine bursitis

Pes anserine bursitis is an inflammation of the bursa overlying the insertion site of the semitendinosus, gracilis and sartorius tendons in the anteromedial aspect of the proximal tibia. Patients complain of medial knee pain distal to the medial joint line. Treatment can include activity modification, strengthening exercises and anti‐inflammatory medication. Chronic symptoms may respond to local corticosteroid injection.

Iliotibial band friction syndrome

Iliotibial band friction syndrome is an inflammation of the iliotibial band, the distal portion of the tensor fascia lata muscle that inserts into the anterolateral aspect of the proximal tibia. Patients are usually runners or cyclists who complain of activity‐related lateral knee pain. This condition responds well to activity modification, stretching and strengthening exercises, ice and anti‐inflammatory medication.

Knee pain in older people

Twenty five percent of people over the age of 50 years report chronic knee pain, and degenerative arthritis of the knee is common in this age group (Box 6.1). However, clinical symptoms and radiological severity of arthritis are poorly correlated. Many older people with knee pain have minor radiological evidence of arthritic change. Conversely, many people with advanced radiological changes have little pain. Arthritis of the knee is often associated with periarticular soft tissue problems, and indeed, these can often be a major source of knee pain. Pes anserine bursitis is a common example. Plain radiographic imaging is not always helpful in the assessment of patients with knee pain, and the diagnosis of osteoarthritis is often a clinical one.