Learning Objectives/Outcomes:After participating in this CME/CNE activity, the provider should be better able to:
1. Describe 3 of the most common causes of knee pain in adult patients.
2. Explain the various physical examination maneuvers that can be performed to detect mechanical knee injuries.
3. Compare treatment approaches for the common causes of knee pain, including active and passive therapies.
Knee pain is one of the top 10 most common reasons for outpatient visits.1 Data from the National Health and Nutrition Examination Survey and Framingham Osteoarthritis Study found that knee pain and symptomatic knee osteoarthritis have risen 10% to 25% over the past several decades, after adjustments for age and body mass index.2 Athletes with previous knee injuries are at significantly higher risk of suffering from chronic knee pain than the general population.3 Overall, people with knee pain report worse physical functioning and quality of life, compared with those without knee pain, which emphasizes the need for effective management of pain in affected individuals.4 Because knee pain can be caused by a wide range of bone or soft tissue injuries, infections, or chronic diseases (gout, osteoarthritis), identifying the most efficient process for diagnosis and treatment is a priority for clinicians across different settings.
Initial Assessment of Knee Pain
With presentation of acute knee pain, initial assessment should focus on history-taking with determination of mechanism of injury, precise location and characteristics of symptoms, and function.5
The clinician should elicit the patient's description of the pain and its characteristics, such as timing (acute or insidious), location, duration, intensity, quality, radiation, and alleviating or aggravating factors. The clinician should also ask about other symptoms that may not seem to be related, and which either precede or accompany the presence of knee pain. These symptoms might include fever, chills, pharyngitis or sore throat, or skin rash. Examination of the knee includes observation and palpation for joint tenderness, range of motion, weight-bearing ability, and specific tests to identify joint instability (Table 1).6 During the physical examination, compare findings to the contralateral uninjured knee and assess adjacent joints for referral pain, including the hip and ankle.7
Differential Diagnosis
The differential diagnosis list for knee pain is quite extensive but can be narrowed down based on the presence of localized versus systemic signs and symptoms, the presence or absence of inflammation, and anterior or posterior knee pain.
An acute onset of monoarticular pain and swelling is most commonly associated with trauma, infection, or crystalline disease.5,6 In contrast, chronic pain and swelling are associated with autoimmune disorders, such as rheumatoid arthritis, seronegative spondyloarthropathies, sarcoidosis, chronic infection or foreign-body synovitis, avascular necrosis, sickle cell disease, hemophilia, Charcot joint, and joint tumors.6 Arthrocentesis is indicated when infection or crystalline disease, foreign-body synovitis, or neoplasm is suspected.
Knee bursitis (also called housemaid's knee) is associated with localized inflammation and swelling and caused by repeated kneeling, trauma, or conditions such as gout or rheumatoid arthritis. A high index of suspicion for gout should be made for patients with a history of tophi and articular symptoms, particularly the first metatarsophalangeal articulation (MTP).5 Pseudogout is more common in advanced age, particularly in the setting of metabolic stress, such as in patients with pneumonia or recent surgery, and chondrocalcinosis may be seen on radiography.
Systemic disease may be evident from bilateral knee involvement, disorders of the skin and/or involvement of other organ systems. A reddish-purple raised rash may indicate lupus pernio, a cutaneous manifestation of sarcoidosis. Psoriasis may indicate psoriatic arthropathy. Bruising may indicate bleeding diathesis, and a pustular rash may indicate an infectious process such as disseminated gonorrhea.5
Other rare conditions, such as adult-onset Still's disease, can be misdiagnosed as septic arthritis.8 There have been 3 types of disease progression for this condition:
1. Monocyclic type characterized by systemic symptoms of fever, rash, organomegaly, and serositis;
2. Polycystic type characterized by multiple recurrences that may or may not affect the joints; and
3. Chronic articular type that primarily targets the joints with severe joint destruction being an end result in untreated cases.
Criteria of adult onset Still's disease are developed by Yamaguchi et al9 and include major, minor, and exclusion criteria, of which 5 or more major/minor criteria must be present, including 2 or more major criteria. In 2002, Fautrel10 proposed a new set of classification criteria with 4 or more major criteria or 3 major criteria and 2 minor criteria (Table 2) displaying a sensitivity of 80.6%, a specificity of 98.5%, and positive and negative predictive values of 96.7% and 90.1%, respectively. First-line treatment of adult-onset Still's disease is corticosteroids with methotrexate as a second-line treatment.11 Refractory cases have been treated with agents blocking interleukin-1 or interleukin-6.11
Particularly in children, infections such as Group A streptococci (GAS), also known as Streptococcus pyogenes, can cause bacterial pharyngitis and superficial skin infections, and sudden and severe onset of extremity pain.12 Although GAS complicated by streptococcal toxic shock syndrome in children can mimic symptoms of septic knee arthritis, it is more commonly associated with invasive soft tissue infections in adults or children with chickenpox.13,14
If acute traumatic injury is evident on history, a thorough evaluation of the structural integrity of the joint should be assessed (Table 3).15 When performing physical examination maneuvers, keep the patient as comfortable as possible, and test the contralateral noninjured knee first to provide a comparison and show the patient how it is performed. Describe the test before you perform it and stop the maneuver if pain is induced.
Anterior cruciate ligament (ACL) injury is most often accompanied by a positive Lachman test and pivot shift and these 2 tests are preferred tests over the anterior drawer for detecting ACL injury. Medial collateral ligament (MCL) or lateral collateral ligament (LCL) injury should be suspected with a positive varus or valgus stress test. A meniscal injury is supported by a combination of joint-line tenderness, and positive Apley, McMurray, Thessaly, and Ege tests.15,16
As opposed to inflammatory conditions, infections, or acute mechanical injuries, the most common knee conditions, osteoarthritis of the knee and patellofemoral pain syndrome (runner's knee) often present with a more insidious onset. Both conditions increase with age and are more prevalent in women. These 2 conditions are also more prevalent in people with occupations that require frequent repetitive movements of the knee or who participate in sports that predispose to joint injury.5 Pain is reported to be most severe when the knee is bearing weight or moving. Crepitus may be present, especially when going up- and downstairs.17 Osteoarthritis, in particular, is associated with early morning stiffness of the knee that lasts for a short period, and hard bony enlargement of the knees.
Diagnostic Testing
Septic arthritis or an acute inflammatory arthropathy should be considered when patients present with nontraumatic effusion or significant pain with slight range of motion. Evaluation for septic arthritis should start with initial laboratory studies including a complete blood cell count, sedimentation rate, and C-reactive protein.5 In endemic regions, a Lyme disease titer should also be tested. Arthrocentesis may be indicated to rule out septic arthritis or other conditions, such as crystalline disease or neoplasm.
Use the Ottawa Knee Rule or Pittsburgh Knee Rule (Table 4) to determine the need for x-rays (anteroposterior, lateral views +/- skyline view)18-20 in acute injury. However, radiographs should be highly considered in the presence of any of the following to evaluate potentially significant injuries: significant tenderness, loss of range of motion with crepitus, joint effusion within 24 hours of injury, severe muscle tears or tendon rupture, suspected knee dislocation or osteonecrosis, or neurovascular compromise.5 The practitioner should exercise clinical judgment to determine the need for radiographs in all cases, but the decision-guiding knee rules can help reduce unnecessary imaging.19,21
CT is used to evaluate for occult fracture or define the severity of the fracture. Ultrasound may be used to detect patella or quadriceps tendon rupture.22 For clinical suspicion of internal derangement or joint effusion on radiograph, an MRI of the knee can be performed at follow-up. An MRI is also appropriate for primary traumatic patella dislocation to assess chondral and patellofemoral soft-tissue damage.21 In cases of degenerative joint disease, inflammatory arthritis, stress fracture, or osteonecrosis found on radiographs, further imaging with MRI is not indicated, as it will not alter management.5
Treatment Considerations
For the most common causes of knee pain in adults, including osteoarthritis, patellofemoral pain syndrome, and meniscal, tendon, and ligament injuries, nonsurgical approaches are most often the first-line treatment.23-25
Active rehabilitation for osteoarthritis is a cornerstone of therapy and should include components of stretching and a combination of aerobic and strength training.23 Pain relief can be enhanced with patellar taping, therapeutic ultrasonography, ice massage, and weight loss for those with a body mass index of more than 25 kg/m2.25
Extended-release acetaminophen or selective/nonselective nonsteroidal anti-inflammatory drugs (NSAIDs) may also be used for pain relief. However, glucosamine/chondroitin supplements are not recommended by the American Academy of Orthopaedic Surgeons due to low level of effectiveness.25
Corticosteroid injections can be used for short-term improvement but have been associated with complications, including septic arthritis.26
A recent study evaluating intra-articular injection of hyaluronic acid (HA), platelet-rich plasma (PRP), or combination of HA and PRP was evaluated in 360 patients.27 After an 8-week baseline period, participants with knee osteoarthritis were randomized into groups undergoing once-weekly double-blind treatment with HA (0.1-0.3 mg), PRP (2-14 mL), combination therapy of PRP and HA, or placebo (normal saline).
In this study, overall duration of PRP and HA treatment was 8 weeks, and 277 (75%) completed the maintenance period of the study up to 52 weeks, whereas the other 25% stopped the study due to side effects.
The combination treatment significantly improved pain, physical function, stiffness, and total Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score compared with PRP or HA alone (P < 0.05) and PRP treatment was significantly more effective than HA and placebo using the WOMAC pain score (P < 0.05).
Although additional studies need to be completed, the combination therapy seems promising.
As with all patients starting active rehabilitation, adequate supervision should be provided in the early program to ensure that correct techniques are used for the exercises.25 To enhance independence and compliance with the home program, the number of exercises should be minimized to 3 or 4 in the early phase. Assist the patient in independent exercise rehabilitation by using mirrors or videos to monitor quality of the exercises and facilitate good technique.17
Treatment for patellofemoral pain syndrome involves education, active rehabilitation, passive interventions for pain reduction, and optimization of biomechanics.17 Education is focused on understanding potential contributing factors and treatment options and appropriate activity modifications and their role in active rehabilitation.
Consideration of open kinetic chain exercises (nonweight bearing; ie, leg extension and leg curl) may be used in the early stages of rehabilitation to target deficits in strength and movement. However, preference is given to closed kinetic chain exercises to replicate function (ie, squats and lunges).28
Tailored patellar taping can help reduce pain or a patellofemoral brace may be used for people with skin irritation. In addition, foot orthoses may help relieve pain as might massage and/or acupuncture.17,28
Initial management of ACL/posterior cruciate ligament (PCL)/MCL/LCL and meniscal injuries includes analgesia with NSAIDs and acetaminophen, rest, ice, compression, and elevation during the acute phase of recovery.5,29
Immobilization with a functional brace can be used for ACL injuries or acute severe PCL and MCL injuries.5
Gentle mobilization, while avoiding aggravating positions, should be used to restore full range of motion. Practitioners should consider referral to orthopedics for MRI and, if indicated, operative management of the injury, with expedient follow-up for patients with ACL tear or locked knee to avoid development of a stiff joint.30 Referral to physiotherapy should also be made for exercises and rehabilitation.
For patella dislocation, immobilization is performed by placing a cast, splint, or locked orthosis in extension for comfort (2-3 weeks) and referral to orthopedics for consideration of advanced imaging and operative management.5 Education regarding the injury, plan of care, and risks for future instability should be provided to the patient and family, emphasizing the need for follow-up with orthopedics and physiotherapy to progress range of motion and weight-bearing status.
Conclusion
Knee pain is prevalent in the US adult population and disproportionately affects women and athletes. The presentation of knee pain, associated signs and symptoms, and characteristics of the patient can help guide the differential diagnosis and appropriate diagnostic testing. For the most common causes of knee pain, including osteoarthritis, patellofemoral pain syndrome, and meniscal injuries, active and passive rehabilitation and pharmacologic management can help provide the best route for pain management, and for functional recovery.
References