The Acutely Swollen Knee Part 1: Management of Atraumatic Pathology Surg Lt Cdr P M Guyver, Surg Lt Cdr C H C Arthur, Surg Cdr C J Hand

26 Clinical

Clinical The acutely swollen knee Part 1: Management of atraumatic pathology Surg Lt Cdr P M Guyver, Surg Lt Cdr C H C Arthur, Surg Cdr C J Hand

Abstract

The acutely swollen knee is a common presentation of knee pathology in the Emergency Department and the primary care setting whether on board ship, a Regimental Aid Post or Medical Centre. The swollen knee has both traumatic and atraumatic (systemic) causes, all of which can be accurately diagnosed with an understanding of the underlying injury patterns and patho-anatomy. In Part One, we will be examining the management of non-traumatic causes, followed by Part Two, looking at traumatic causes, in the next issue of the Journal. A detailed clinical history combined with thorough clinical examination will establish the diagnosis, or at least the narrow differential diagnosis in the majority of cases. The uses of specialist examination techniques, diagnostic imaging and arthrocentesis can further assist the clinician in confirming the correct diagnosis and thus prescribing the appropriate treatment. This review will endeavour to give a consensus of opinion and structured guidelines in the diagnosis and initial management of patients presenting with acute or recent-onset swelling of the knee related to atraumatic pathology.

Introduction Definition A swollen knee or knee effusion is a common problem A recent collaboration between a committee comprising caused by the accumulation of fluid in or around the knee orthopaedic surgeons and rheumatologists from the joint. Knee effusions may due to traumatic or atraumatic European Federation of National Associations of causes. The most common traumatic causes are fracture Orthopaedics and Traumatology (EFORT) and The or ligamentous and meniscal injuries, and will be discussed European League Against Rheumatism (EULAR) published in Part Two of this article in the next issue. Atraumatic a combined consensus definition of the acutely swollen knee causes include arthritis, infection, crystal deposition, which will be used in this paper (1). They concluded that haematogenous and those resulting from tumours. the definition should be: all patients newly presenting to Effusions can have different rates of onset due to different a doctor with a history or examination finding suggesting causes. Rapid swelling after injury usually indicates onset of swelling (defined as an increase in volume) within bleeding into the joint or haemarthrosis caused by a a recent time (up to four to six weeks) in any anatomical damaged and bleeding intrarticular structure, whereas rapid structure of the knee, intra-articularly and peri-articularly. swelling without injury could indicate infection or crystal The term “acute” in isolation for this review was felt to arthropathy. Delayed swelling with trauma could indicate suggest an emergency and that the patient would need to meniscal injury or ligamentous sprain; an absence of trauma be reviewed without delay. It was also deemed appropriate could indicate arthritis. A detailed history combined with to include the term “recent onset swelling” in order to be thorough clinical examination will establish the diagnosis more encompassing of all types of knee effusion i.e. up or at least a narrow differential diagnosis in the majority to four to six weeks. An example of the appearance of an of cases. The use of specialist examination techniques, acutely swollen knee is shown in Figure 1. diagnostic imaging and arthrocentesis can further assist the clinician in confirming the correct diagnosis and thus prescribing the correct treatment that the patient requires. The aim of this paper is to perform a literature review so as to gain a consensus of opinion and structured guidelines in the diagnosis and initial management of patients presenting with acute or recent onset swelling of the knee relating to atraumatic pathology. J Royal Naval Medical Service 2014, Vol 100.1 27

Figure 1. Clinical photograph - right knee effusion any laboratory or radiological investigation (6). It concluded that if septic arthritis is suspected, “then advice from a musculoskeletal specialist should be sought at the earliest opportunity”. This is an important guiding principle that must be considered by all health professionals likely to encounter patients presenting with an acutely swollen knee.

Presentation 60% of all cases reported involve the hip and knee (7,8), but in up to 22% of cases more than one joint is affected, indicating that a poly-articular presentation does not exclude the diagnosis of septic arthritis (9). In addition, many studies have demonstrated that fever is not a reliable indicator of a septic joint (5,9). Furthermore, if there is a pre-existing inflammatory joint disease present, then pain out of proportion to the patient’s usual pain, or the pain Epidemiology usually felt in other joints, should increase concern about Robust and well-structured epidemiological studies have the diagnosis of an infected joint. not been conducted into the incidence and prevalence of the symptom of acute or recent onset of swelling of the knee. Investigations However, the lifetime prevalence of swelling of the knee has Numerous studies have shown that the presence of a normal been reported as 27% in a British study (2) and 10% in a WCC, ESR or CRP levels does not exclude the diagnosis European study (3). Lifetime prevalence of knee symptoms of sepsis (5). However, the use of these three tests may be is 54% in the same British study and 17% in a Scandinavian useful in monitoring the response to treatment. study (4). Synovial fluid culture has been shown to be more sensitive MANAGEMENT OF SPECIFIC ATRAUMATIC CAUSES than microscopy alone, as synovial fluid Gram staining i. INTRODUCTION is only positive in 50% of cases (10). Hindle et al (11) Delayed or inadequate treatment of septic or infectious demonstrated that detection of an organism on initial arthritis can lead to irreversible joint damage and disability microscopy or on subsequent culture of their aspirate is with a significant mortality rate of 11% (5). It is, therefore, less reliable if the patient had received antibiotics. The imperative that rapid assessment and subsequent diagnosis sensitivity of microscopy and culture dropped from 46% occurs to enable prompt treatment. to 0% and from 69% to 21% respectively, indicating the importance of educating all clinicians to withhold antibiotics Classic teaching states that patients usually have an until microbiology samples have been taken e.g. by joint acute onset of arthralgia and swelling over less than two fluid aspiration. This concern is obviously overridden when weeks. Physical examination can reveal fever, localised the patient is clinically unstable and systemically septic erythema and a reduced range of movement, combined or in a case of prolonged transport time to an orthopaedic with reluctance to weight-bear and a hot, swollen joint. specialist. In this situation gaining physiological stability There are well-recognised risk factors: a previous abnormal is of greater importance than microbiology specimens. In joint, immune-compromised status, intravenous drug addition, the importance of blood cultures should never be use, rheumatoid arthritis (RA) or osteoarthritis (OA), underestimated as they may identify the causative organism diabetes, previous intra-articular corticosteroid injections when synovial fluid culture fails (10). It has been shown that and cutaneous ulcers. The most important investigation is synovial fluid WCC counts are not sufficiently reliable to drawing synovial fluid from the joint (arthrocentesis) and exclude or confirm a diagnosis of septic arthritis (12). examination of the fluid. Organisms present on Gram stain and positive cultures can confirm the diagnosis. An elevated Microbiology peripheral white blood cell count (WCC), C-reactive protein The Staphylococci and Streptococci account for 91% of (CRP) and erythrocyte sedimentation rate (ESR) are also cases of septic arthritis (5, 9,10). Older and immune- indicative of a potential infectious process. Blood cultures compromised patients usually suffer from gram-negative can also aid diagnosis and organism identification. sepsis, whereas anaerobes are more commonly seen in penetrating trauma. A recent systematic review has demonstrated that the overall impression of a clinician experienced in assessing Imaging joint disease is the only gold standard for diagnosing septic Radiographs are usually taken to rule out other pathology, arthritis. The review stated that this had proven superior to including osteomyelitis. Magnetic resonance imaging 28 Clinical

(MRI) is the only imaging modality that can apparently ii. CRYSTAL ARTHROPATHY reliably demonstrate the presence of infection, but in these A. GOUT studies no controls were used and this finding needs to be Gout arises from the deposition of urate crystals in confirmed with further research (10). joints, with an associated inflammatory response. Crystal deposition occurs when serum becomes saturated with Treatment urate, the end product of the purine metabolism. The We found no studies that could statistically prove a prevalence of gout is at least 1% in the UK. Gout is much difference between an arthroscopic or open washout and more common in men than in women (20:1) and in the debridement of a septic joint. The overriding conclusion older population (>55) (13). though is that this should be performed in a timely manner to prevent the sequelae of joint destruction and mortality Presentation previously reported. The management of septic arthritis is The most common presentation of gout is an acute mono- summarized in Box 1. arthritis of the great toe (podagra). The onset of symptoms is usually rapid. Gout can affect any joint, but the foot, Box 1. Management of septic arthritis ankle, knee, wrist, finger, and elbow are the usual sites if the great toe is not involved. Crystal deposits (tophi) may also develop around these joints but most commonly the hands, Pre-shore / pre-hospital management feet, elbows, and ears. An acute attack usually lasts for just History over a week. Some patients only have one or two attacks Acute onset knee swelling with no history of trauma over a lifetime with no sequelae, whilst others may have (<2weeks). Any associated risk factors: previous abnormal joint, immune-compromised status, frequent attacks and be left with permanent joint damage. intravenous drug use, diabetes, previous intra- Subcortical cysts without erosions, peri-articular swellings articular corticosteroid injections or cutaneous ulcers. and chondrocalcinosis are the characteristic signs seen on Polyarticular presentation does not rule out the radiographic examination. diagnosis of septic arthritis. Diagnosis Examination The gold standard diagnostic confirmation of gout is by Pyrexia, localized erythema, joint warmth, a reduced synovial fluid microscopy using polarised light, with which range of movement combined with reluctance to weight method urate crystals can be identified as strongly negatively bear but with stable ligaments. birefringent, needle-shaped intracellular crystals. However, Radiographs the utility of this investigation can be limited, as reports state (if available) Essentially normal. that this is only demonstrated in 11% of cases. This could be due to a number of reasons. Firstly, obtaining fluid can Treatment be difficult, especially from the first metatarsophalangeal If a septic joint is suspected then it is imperative to joint, or if the clinician is inexperienced in arthrocentesis. seek advice from a musculoskeletal specialist clinician Secondly, discarding the needle used for aspiration or a delay at the earliest opportunity. This clinician should be in microscopic examination can lead to failure despite a skilled in the technique of arthrocentesis and have a potentially diagnostic aspirate. Finally, access to a laboratory laboratory available to give immediate microscopy and blood test results. Only in the very rare event that either that provides this test and accurate identification of these patient transfer is limited by military constraints, or crystals has varied greatly across the country in the past that the patient is in extreme systemic sepsis, should (14). Consequently, the American College of Rheumatology antibiotics be given before arthrocentesis and review by requires six or more of the criteria listed below to be a musculoskeletal specialist. present in order to make a clinical diagnosis (Box 2). The Hospital management management of gout is summarized in Box 3. History, Examination and Radiographs as above Investigations Blood FBC, CRP, ESR, Urea and electrolytes, cultures. Arthrocentesis: Urgent microscopy and then culture. Organisms seen on gram stain, WBC > 50 000/mm3 or positive cultures are all suggestive of septic arthritis. Treatment If a septic joint is suspected then it is imperative to seek advice from a musculoskeletal specialist clinician at the earliest opportunity. Open or arthroscopic debridement of the joint should occur in a timely manner to prevent the sequelae of joint destruction. J Royal Naval Medical Service 2014, Vol 100.1 29

Box 2. American College of Rheumatology criteria for Box 3. Management of gout clinical diagnosis of gout

• More than one attack of acute arthritis Pre-shore / pre-hospital management • Maximum inflammation developed within one day History Acute onset knee swelling with no history of trauma (in • Attack of mono-arthritis last two weeks). Any associated risk factors: previous • Redness over joints gout attack, diuretic use, known high SUA and high purine diet. Poly-articular presentation does not rule out • Painful or swollen first metatarsophalangeal joint the diagnosis of gout. • Unilateral attack on first metatarsophalangeal joint • Unilateral attack on tarsal joint Examination Pyrexia, localized erythema, joint warmth, a reduced • Tophus (proved or suspected) range of movement combined with reluctance to weight • Hyperuricaemia bear but with stable ligaments.

• Asymmetric swelling within a joint on radiograph Radiographs • Subcortical cysts without erosions on radiograph (if available) Subcortical cysts without erosions, peri-ar- • Joint fluid culture negative for organisms during attack ticular swellings and chondrocalcinosis. Treatment Initial exclusion of a septic joint is essential via the Investigation guidelines above. Arthrocentesis and examination of Arthrocentesis: To identify urate crystals and exclude the synovial fluid using polarized light microscopy is the infection. gold standard to confirm diagnosis of gout. Alternatively, American College of Rheumatology criteria can be used Bloods: FBC, Urea and electrolytes and CRP to help rule out to make a clinical diagnosis. Acute and chronic treat- septic arthritis. Serum Uric Acid (SUA) levels are usually ment with modification of diet and lifestyle should occur within normal limits during an acute attack but a base line as described above. level should be recorded. Hospital management Radiograph: Subcortical cysts without erosions, peri- History, Examination and Radiographs as above articular swellings and chondrocalcinosis are the Investigations: Blood characteristic signs. FBC, CRP, ESR, Urea and electrolytes, cultures to exclude septic arthritis. Treatment The British Society for Rheumatology recently produced Arthrocentesis guidelines for the treatment of gout (Box 4). This focused Urgent microscopy and then culture. Strongly negatively on three main areas of treatment: management of acute birefringent needle shaped intracellular crystals should gout, recommendations for diet and lifestyle modifications, be seen using polarized light microscopy. and management of recurrent and chronic gout (15). Treatment Open or arthroscopic debridement of the joint is some- times required if there is any concern that septic arthritis is coexistent. This should occur in a timely manner if suspected and can aid in both symptom control with additional microbiology sampling. However it is imperative that the advice from a musculoskeletal specialist clinician should be sought at the earliest opportunity to make this decision. Acute and chronic treatment by modification of diet and lifestyle should follow. 30 Clinical

Box 4. British Society for Rheumatology Guidelines For the Management of Gout

Exclude Septic Arthritis & suppress pain and inflammation

NSAID +/- PPI Review at 4-6 weeks or Colchicine Assess lifestyle factors, blood pressure & perfrom se- or rum urate, renal function & glucose in all patients. Cortocosteroid (i.a,oral,i.m,i.v.)

Resolution

Further attacks (or risk factors+++) Treat acute attack: when resolved add

Allopurinol + prophylactic cover with low dose NSAID +\- PPI or Colchicine All Patients • Optimise weight Titrate allopurinol dose: depending on SUA may require • Increase exercise doses up to 900mg/day • Modify diet • Reduce alcohol intake DO NOT STOP ALLOPURINOL DURING ACUTE • Maintain fluid intake ATTACKS • Treat underlying cardiovascular risk factors

Continuing acute attacks = Treat acute attacks and when resolved go to

No Renal Impairment Renal Impairment Change to Sulphinpryazone or Benzbromarone or Change to Benzbromarone Consider combination Probenecid therapy with low dose allpurinol i. Acute Gout described above. Affected joints should be rested, with non-steroidal ii. Recommendations for diet and lifestyle anti-inflammatory drugs (NSAIDs) being commenced modifications immediately (if no contraindications) and continued for one Overweight patients should have dietary advice in order to to two weeks. In patients with an increased risk of peptic achieve an ideal body weight. This should be attempted in a ulcers, bleeds or perforation, co-prescription of ulcer- controlled fashion with the intake of protein and high purine preventing agents is advised. Oral corticosteroids are an content foods being restricted (red meat, liver, kidneys, effective alternative in patients unable to tolerate NSAIDs. shellfish etc). Alcohol consumption should be restricted to A recent randomised controlled trial (RCT) described less than the weekly-recommended amount. Men should equally effective resolution of symptoms when using either drink no more than 21 units of alcohol per week, no more naproxen or oral prednisolone (16). Colchicine is another than four units in any one day, and have at least two alcohol- alternative therapy, but leads to common side effects of free days a week. Women should drink no more than 14 units diarrhoea and nausea that are not well tolerated by patients. of alcohol per week, no more than three units in any one day, If diuretic drugs are being used to treat hypertension, an and have at least two alcohol-free days a week. alternative antihypertensive agent should be considered. iii. Management of recurrent and chronic gout Allopurinol should not be prescribed during an acute attack, The SUA should be maintained below 300 umol/l by but if allopurinol is already being taken then it should using uric-acid-lowering drug therapy. This should be be continued and the acute attack should be treated as started if a second attack occurs within a year. Uric-acid- J Royal Naval Medical Service 2014, Vol 100.1 31

lowering treatment should also be offered to patients with associations mentioned above. renal insufficiency and to those who need to continue Radiograph: Chondrocalcinosis is the characteristic sign treatment with diuretics. This should be delayed until seen on radiographic examination of the knee. one to two weeks after the acute symptoms have resolved. Colchicine 0.5mg b.d. should be co-prescribed on initiation Treatment of treatment with allopurinol and continued for up to six Affected joints should be rested with NSAIDS being months (side-effect dependent). NSAIDs can be used commenced immediately (if no contraindications) and as an alternative, if not contraindicated, but this should continued until symptoms settle. In patients with increased be limited to six weeks only. This adjunctive therapy has risk of peptic ulcers, bleeds or perforation, co-prescription been proven to prevent early re-occurrence. In patients of ulcer preventing agents is advised. Oral corticosteroids who fail to respond to allopurinol, alternative or adjunctive and colchicine are an effective alternative in patients unable drugs can be used; sulphinpyrazone (200-800 mg/day) or to tolerate NSAIDs. Methotrexate has been shown to benzbromarone (50-200 mg/day) in patients with mild/ decrease the frequency and intensity of recurrent attacks of moderate renal insufficiency. Cardiovascular events have an pseudogout (19). increased prevalence in gout sufferers and so the primary care provider should implement routine monitoring. iii. OSTEOARTHRITIS Regular blood pressure, cholesterol and diabetes tests are Osteoarthritis (OA) is a common chronic and progressive recommended. musculoskeletal disorder that involves all tissue components of the joint: bone, cartilage, synovium, muscle and ligaments. B. PSEUDOGOUT It is characterised by progressive loss of articular cartilage Pseudogout can be defined as acute attacks of synovitis (softening, fibrillation and then ulceration), leading to induced by calcium pyrophosphate dihydrate (CPPD) sclerosis and eburnation of subchondral bone. Subchondral crystals, which clinically resemble gouty arthritis due to cyst and osteophyte formation are later features (20). monosodium urate (MSU) crystal deposition. It mainly affects older people, with over 50% of all octogenarians Presentation displaying some evidence of articular chondrocalcinosis OA is the most common form of arthritis in the UK, with (17). There are no published reports of prevalence in more than 6 million people having painful osteoarthritis in younger people and there is no major gender predominance. one or both knees. Prevalence increases with age with one in However, acute attacks occur more commonly in men (18). five adults aged 50-59, and almost half of all adults aged over 80 having painful osteoarthritis in one or both knees (21). Presentation Common symptoms of patients with OA include gradual Pseudogout attacks may take longer to reach peak intensity onset of swelling with loss of function. The pain is usually and subsequent recovery compared to gout, despite adequate worse with function and better with rest. The joint is not treatment. The knee is the most commonly involved joint, usually extremely warm and the majority of patients are of followed by the wrist, ankle, elbow, toe, shoulder and an age greater than 50 years (21). hip. Localised erythema, joint warmth, reduced range of movement, combined with reluctance to weight-bear, are Diagnosis the common presenting symptoms. Patients are usually The presentation and radiographic findings are usually asymptomatic between attacks. Haemochromatosis and sufficient to be able to make the diagnosis of OA. However, chronic hypomagnesaemia due to Gitelman’s and Bartter’s MRI and ultrasound are also validated non-invasive methods syndromes are known to be strongly associated with of assessing OA (22). Radiographic findings include joint pseudogout. space narrowing and sub-chondral sclerosis followed by sub-chondral cyst and osteophyte formation. In the knee Diagnosis this should be assessed by weight bearing radiographs in The gold standard diagnostic confirmation of psuedogout two planes. Septic arthritis, as well as other differentials, is by synovial fluid microscopy using polarized light. CPPD should always be excluded before treatment is commenced crystals can be identified as rhomboid-shaped, rod-like using the guidelines above. crystals that exhibit weakly positive or no birefringence by this method. Treatment Non-Operative Investigation Non-operative treatments should always be exhausted Arthrocentesis: Exclude sepsis. Confirm CPPD crystals as before any surgical options are considered. described above. i. Muscle-strengthening physiotherapy regimes have been Bloods: FBC, Urea and electrolytes and CRP to help rule shown to be beneficial if there is a high degree of patient out septic arthritis. Ferritin, iron saturation, transferrin, compliance (23,24). calcium and magnesium should be assessed due to the ii. Weight loss has obvious general health benefits, but 32 Clinical

evidence indicating that this halts the progression of OA is iv. RHEUMATOID ARTHRITIS variable (25). Rheumatoid Arthritis (RA) is a chronic, progressive iii. Bracing has been shown to be successful in managing autoimmune disease causing soft tissue swelling and the symptoms of OA but is poorly tolerated by patients inflammation of the lining of the joints. Bone erosions and mainly due to skin complications (26). osteopenia result in painful deformity and immobility. iv. NSAIDs and Paracetamol have been shown to be very effective in pain management (27). However, the long-term Presentation side effects of NSAIDS pose limitations in this regard. RA is the second most common form of arthritis in the UK v. Recent Cochrane reviews demonstrated that intra- and the most common inflammatory joint disorder. The articular steroids are beneficial in the management of OA, prevalence in the UK has been reported as 2% of all adult but have only a short-term effect (28). women and less than 0.5% of men (around 400,000 adults in vi. Further Cochrane reviews indicate that Hyaluronan 2006) (30). The small joints of the hand or feet are usually (HA) viscosupplementations of the knee were not cost the first to be affected. Symptoms vary depending on the effective compared to other OA treatments. However, severity of the disease process. they were found to be beneficial, and comparable to other systemic treatments (29). Box 6. Management of rheumatoid arthritis

Operative Pre-hospital and hospital management Surgical treatment of OA is beyond the scope of this review, History but can range from osteotomy to partial or total knee Gradual onset pain and swelling with progressive replacement. deformity and loss of function. Swelling often presents with acute exacerbations. Poly-articular presentation is The management of OA is summarized in Box 5. common especially of the small joints of the hands and feet. Box 5. Management of osteoarthritis Examination Pre-shore / pre-hospital management Swelling, warmth, synovial thickening, tenderness, History reduced range of movement combined with an antalgic Gradual onset pain and swelling with loss of function. gait. Crepitus, severe deformity and systemic manifesta- Pain is usually worse with function and better with rest. tions can be seen in more advanced disease. Poly-articular presentation common. Investigations Examination FBC, urea and electrolytes and CRP to help rule out Apyrexial, no systemic symptoms, reduced range of septic arthritis. Rheumatoid factor (RhF) and ESR can movement combined with an antalgic gait. Crepitus and also aid diagnosis. However RhF can be found in people deformity are seen in more advanced disease. without RA or with other autoimmune disorders. In general, though, if rheumatoid factor is not present in Radiographs someone with RA, then the course of the disease is (if available) Joint space narrowing and subchondral less severe. Arthrocentesis can reveal elevated syno- sclerosis with subchondral cyst and osteophyte vial fluid protein levels, decreased glucose levels and formation in more advanced disease. synovial fluid WBC count ranging from 2,000 to 50,000 per mm3 (2 to 50 × 109 per L). This is suggestive of any Treatment inflammatory process, not only RA. Non-operative measures as listed above, or orthopaedic specialist referral to decide on surgical management, Radiographs which may range from arthroscopic microfracture and Joint space narrowing, peri-articular osteopenia, margin- biologic treatments to osteotomy and/or partial or total al erosions, and peri-articular soft tissue swellings. knee replacement. Treatment Hospital management Referral to a rheumatology specialist. Pharmacological History, Examination and Radiographs as above treatments range from simple analgesia to disease-mod- Investigations: Bloods to rule out other pathologies. ifying anti-rheumatic drugs (DMARDs) such as methotrexate and TNF-alpha inhibitors e.g. etanercept. If Treatment non-operative measures fail to control symptoms then Orthopaedic specialist referral to decide on surgical orthopaedic interventions (ranging from arthroscopic/ management, which may range from osteotomy to open synovectomy to arthroplasty) can be used. partial or total knee replacement. J Royal Naval Medical Service 2014, Vol 100.1 33

Box 7. American college of Rheumatology Rheumatoid Arthritis Classification 1987

1. Morning stiffness Morning stiffness in and around the joints, lasting at least 1 hour before maximal improvement 2. Arthritis of three or more joint areas At least three joint areas simultaneously have had soft tissue swelling or fluid (not bony overgrowth alone) observed by a physician. The 14 possible areas are right or left PIP, MCP, wrist, elbow, knee, ankle, and MTP joints 3. Arthritis of hand joints At least one area swollen (as defined above) in a wrist, MCP, or PIP joint 4. Symmetric arthritis Simultaneous involvement of the same joint areas (as defined in 2) on both sides of the body (bilateral involvement of PIPs, MCPs, or MTPs is acceptable without absolute symmetry) 5. Rheumatoid nodules Subcutaneous nodules, over bony prominences, or extensor surfaces, or in juxta-articular regions, observed by a physician 6. Serum rheumatoid factor Demonstration of abnormal amounts of serum rheumatoid factor by any method for which the result has been positive in <5% of normal control subjects 7. Radiographic changes Radiographic changes typical of rheumatoid arthritis on postero-anterior hand and wrist radiographs, which must include erosions or unequivocal bony decalcification localized in or most marked adjacent to the involved joints (osteoarthritis changes alone do not qualify) For classification purposes, a patient shall be said to have rheumatoid arthritis if he/she has satisfied at least four of these seven criteria. Criteria 1 through 4 must have been present for at least six weeks.

Patients with two clinical diagnoses are not excluded. Designation as classic, definite, or probable rheumatoid arthritis is not to be made.

Diagnosis of introducing infection. Haemophiliacs and patients with The management of RA is summarised in Box 6. The other bleeding disorders should be assessed and treated in diagnosis of RA is complex, should be made by a specialist a specialist unit, which is beyond the scope of this review. rheumatologist and is beyond the scope of this article. However, as a point of reference, the American College vi. TUMOUR of Rheumatologists published diagnostic clinical criteria Primary bone tumours most commonly present around the guidelines in 1987 to aid in this process (31), as described knee, but only represent 0.2% of all tumours (32). Both in Box 7. benign and malignant tumours can present with a knee effusion. Symptoms such as fever, night sweats, unintentional v. HAEMARTHROSIS weight loss and night pain should alert the clinician to the Bleeding into a joint is referred to as haemarthrosis and is an possibility of a neoplastic process. Plain radiographs can important cause of mono-articular joint pain and swelling. usually rule out a bone lesion. This diagnosis should always Rapid, large swelling (within a few hours) in association be ruled out of the differential diagnosis before embarking with trauma is indicative of a haemarthrosis due to fracture on arthrocentesis or other invasive investigations. These or significant intra-articular injury. A haemarthrosis without patients should be reviewed by an orthopaedic specialist associated trauma may well be the result of haemophilia who will subsequently refer on to a Specialist Bone Tumour (or other bleeding disorder), neoplasm, OA, pigmented Unit, of which there are only a few in the UK. villonodular synovitis or oral anticoagulant therapy. Arthrocentesis can be performed to aid in diagnosis and to Baker’s cyst alleviate pain. However this is contraindicated if a diagnosis A Baker’s cyst is a benign swelling found in the popliteal of neoplasm or bleeding disorders is suspected. The use of fossa. The cyst arises from the synovial sac of the knee joint, arthrocentesis in patients on anticoagulant therapy is not and is usually associated with a form of knee arthritis (OA advised due to the high rates of recurrence and the risk or RA), or occasionally with a meniscal tear. Baker’s cysts 34 Clinical

usually require no treatment and initial treatment should be from a musculoskeletal specialist should be sought at the directed at the underlying cause. earliest opportunity, as previously stated.

BAKER’S CYST AND BURSITIS Conclusion There are numerous bursae around the knee, any of which The acutely swollen knee is a common presentation in can get inflamed or infected. The two main bursae usually primary and secondary care in both the civilian and military affected are the pre-patellar bursa, overlying the patella, and environment. However, with a generally younger and the infra-patellar bursa, located over the tibial tuberosity. more active military population the incidence is probably The pre-patellar bursa tends to become inflamed after much higher. This article has endeavoured to review the prolonged ‘forward’ kneeling. Pre-patellar bursitis, also differential diagnoses and initial management of patients known as ‘housemaid’s knee’ is common in trades such as presenting with acute or recent onset swelling of the knee roofers and carpet fitters. Infra-patellar bursitis, also known in the absence of trauma. The overarching aim is to raise as ‘clergyman’s knee’ is common with more erect kneeling. awareness of these conditions and ultimately lead to earlier evaluation and treatment. We hope it will act as a guide or The pre-patellar bursa may also become infected, which can aide memoire to the medical professionals of the Royal lead to its being confused with septic arthritis. An infected Naval Medical Service, wherever they may be providing care. pre-patellar bursa tends to have a more localised swelling and erythema, and the knee joint movements tend to be well To be continued. Please see Part Two in the next issue of preserved. Should there be any diagnostic concerns, advice the JRNMS.

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Authors Surgeon Lieutenant Commander P M Guyver MBBS FRCS (Tr&Orth) ST 8 Specialist Registrar in Trauma and Orthopaedics RN

Surgeon Lieutenant Commander C H C Arthur MBChB FRCS (Tr&Orth) ST 8 Specialist Registrar in Trauma and Orthopaedics RN

Surgeon Commander C J Hand MB ChB, FRCS (Tr&Orth) Consultant in Trauma and Orthopaedics RN Nuffield Orthopaedic Centre, Windmill Road, Headington, Oxford.