Problems in Family Practice

Knee Effusions

John P. McGahan, MD Hiromu Shoji, MD Davis, California

There are many questions concerning knee effusions and the basic was from 0 to 30 degrees. McMurray’s diagnostic approach to them. The case of a young female with test could not be performed because gonococcal arthritis presenting to the Emergency Room with an of pain. The knee was stable, both to isolated knee effusion is discussed. From the errors in diagnosis of medial and lateral stress, as well as to anterior and posterior stress. this case, a basic outline in the approach and work-up of a knee Laboratory data revealed a serum effusion is detailed, including history and physical examination, and white blood cell count of 10,900/ the use of synovial fluid analysis as a further diagnostic aid. cu mm with 11 percent non-segmented Procedural instructions and contraindications for knee arthrocentesis cells, 58 percent segmented cells, 23 are given, as well as data related to interpretation of pertinent percent lymphocytes, and 7 mono­ cytes. X-ray of the knee showed a laboratory findings of synovial fluid in disease states. moderate effusion without evidence of any other disease process. A knee tap was performed and 100 cc of cloudy green fluid was obtained. Fluid anal­ Knee effusions are often of a defi­ flex her knee. She was initially seen in ysis from the knee showed a white nite and obvious etiology, such as another Emergency Room where the blood cell count of 58,800/cu mm, those associated with trauma. How­ physician examined her and wrapped with 92 percent polymorphonuclear ever, the clinician must have a logical her knee in an Ace wrap. He told her cells and 8 percent monocytes. There approach in dealing with knee effu­ to seek medical attention, as needed, were 657 red blood cells per cu mm in sions and, thus, not overlook less for her “sprained knee” when she the fluid. Synovial fluid protein was obvious causes of the swollen knee, arrived home. Subsequently, the pa­ 5.8 gm percent, while serum protein such as illustrated below. tient came to our Emergency Room was 7.6 gm percent. Synovial fluid complaining of persistence of pain, glucose was 50 mg percent and simul­ swelling, and limited range of motion taneous serum glucose was 110 mg of the right knee. She gave no history percent. Sedimentation rate was 101 Case Report of fever, chills, or arthralgia. She gave mm/hr. A VDRL was non-reactive and A 16-year-old white female pre­ no history of previous infection within ANA from the serum was negative. sented to the Emergency Room with a the past month and no history of any Tuberculosis cultures were taken and complaint of a swollen right knee of sexual contact. She had had no similar later shown to be negative. Cultures five days’ duration. The patient was on episodes previously. Her review of obtained from the knee did, however, a camping trip and reported that she systems was generally unremarkable. grow out 3+ Neisseria gonorrhoea. bent down to pick up an object and Physical examination revealed a After obtaining the green synovial heard a pop in her right knee. When well-developed white female in moder­ fluid, a further physical examination she stood up she reported inability to ate distress from right knee pain. revealed a normal female except for Temperature was 100.2 F. Examina­ pelvic examination. This revealed a tion of the right knee showed that she white discharge from the cervical os. From the Department of Orthopaedic Surgery, University of California, School of had a moderate effusion. The knee was In addition, bimanual examination re­ Medicine, Davis, California. Requests for not warm and was without erythema. vealed bilateral adenexal tenderness MPrints be addressed to Dr. John P. McGahan, Department of Orthopaedic There was diffuse medial tenderness with the right being greater than the Surgery, University of California Sacra­ left. There was exquisite pain with mento Medical Center, 2315 S to c k to n which did not increase with stress of Boulevard, Sacramento, Calif 95817. the knee. Range of motion of the knee motion of the cervix. Gram stain of

the JOURNAL OF F A M IL Y PRACTICE, VOL. 4, NO. 1, 1977 141 Table 1. Synovial Joint Fluid Findings

Normal Non-Inf lammatory Inflammatory Septic

Color Clear Y ellow Yellow to Green Yellow to Green

Clarity Transparent Transparent Transparent to Opaque Opaque

Viscosity High High Low Variable

WBC/mm3 < 2 0 0 2 0 0 -2 ,0 0 0 2,000-150,000 15,000-200,000

Polymorphonuclear Cells <25% <25% >50% >75%

Mucin Clot Good Good Good to Poor Poor

Culture Negative Negative Negative Usually Poor

gm% Protein < 3.5 < 3 .5 > 3 .5 > 3 .5

Example Disease Osteoarthritis, Systemic Rheumatic fever. Bacterial Infection, Lupus Erythematosus, Rheumatoid arthritis. Acute Tuberculosis, Osteochondritis Juvenile Rheumatoid Cocci Dissecans, Early or Arthritis, Gout, Reiter's Subsiding Inflammation Syndrome, Ankylosing Spondylitis, Pseudogout

the cervix revealed gram-negative intra­ motion of her knee at that time was the confusion and questions are: cellular diplococci, although cervical recorded as 0 to 100 degrees of “What are the pertinent physical find­ cultures were negative. flexion. There were no x-ray changes ings to look for in a patient with a After a complete physical examina­ of her knee at that time. knee effusion?” “ Should an arthro- tion, the patient was again questioned centesis of the knee be performed?” concerning any history of sexual inter­ and finally, “What should be done course. She reported that she had had with the synovial fluid once intercourse with several different part­ obtained?” ners in the previous six months, as well as a therapeutic abortion nine months Discussion previously. In the hospital she was treated with This case is presented to demon­ high dosage of intravenous penicillin. strate the value of a knee arthro- As with most medical problems, Aqueous penicillin was continued for a centesis, whether used for diagnostic evaluation first includes a history. total of five days and then the patient purposes or for relief of pain. It is History as to associated mechanism of was switched to oral penicillin before found that in a case of definite trauma injuries sustained, the time sequence, discharge. The patient was completely to the knee, the patient will often and the rate of formation of effusion afebrile after four days. Pain of the appreciate a therapeutic tap to obtain is important. Questions concerning knee was markedly improved by the relief. As seen in this case, a gono­ mechanical blocks of the knee with fifth day after admission. Sedimenta­ coccal infected knee was originally motion, such as locking and clicking, tion rate had decreased from treated with an Ace wrap and crutches should always be asked. These symp­ 101 mm/hr on admission to 72 mm/hr because the diagnosis was missed. This toms may be indicative of internal by the sixth day of hospitalization. would not have happened if an arthro- derangements of the knee. The history Clinic follow-up, six weeks after centesis had been performed. The case should include a probe into possible discharge, revealed that the patient presented is an isolated incident, but infection or other systemic manifesta­ had no pain and was ambulating points to the confusion that exists tions of multisystem disease. These without problems. The range of concerning knee effusions. Some of may include questions concerning

142 THE JOURNAL OF FAMILY PRACTICE, VOL. 4, NO. 1, 1971 fever and chills, involvement of other McMurray’s test is performed with the joints, possible recent sexual contact, knee brought from 90 degrees of Table 2. Laboratory Data That associated back pain, and a quick flexion to full extension with the tibia May Be Obtained on Synovial Fluid review of systems, as indicated. How­ first externally rotated, then internally ever as seen in this case, with initial rotated.4 This test is positive if a click unreliable information from the pa­ is felt or heard on the joint line if Tube 1 (Sterile) tient, even the most compulsive associated with pain. This is usually questioner may have to rely on other indicative of meniscal tear. Culture and Gram Stain (Fungus and Tuberculosis Culture, modalities for diagnosis. The patella is next examined for if indicated) possible pathology. Usually accumula­ tion of fluid in the knee is obvious on inspection. However, in cases where only a small amount of fluid is Tube 2 (Heparinized) Next, a physical examination of the present, by milking the suprapatellar knee is performed. The physician first pouch with one hand and compressing Cell Count and Differential inspects the knee, noting any deformi­ the patella against the femur with the ties or scars. The knee is gently other hand, balloting of the patella may become more obvious. This is palpated for any areas of point tender­ Tube 3 (Clotted) ness (the joint line may be tender with usually indicative of a knee effusion. meniscal tears). The physician feels for Crepitance of the patella may be Glucose, Protein associated warmth in the extremity indicative of fracture of the patella, (ANA, C3, C4, if indicated) (with joint sepsis, the knee is usually chondromalacia of the patella, or warm, but occasionally in early sepsis osteochondromal fragments.4 An this may not be so, as illustrated by apprehension test of the patella may the case presented).1 The range of be used to test for possible patella motion of the knee is recorded. A subluxation or dislocation.5 It is done check for pain on stress of the knee in with lateral stress of the patella with both varus and valgus positions is the knee stable and in extension. It is done. Pain medially with valgus stress positive if pain is produced and/or is indicative of medial collateral patella subluxation occurs. Finally, a involvement, while pain laterally with neurovascular check of the extremity minutes. The site of the tap is 2 cm varus stress is indicative of lateral should always be made. medial to the anterior aspect of the collateral involvement. However, it has patella. The skin is then infiltrated also been shown that not only do the with one percent lidocaine (Xylocaine) collateral ligaments play a role in varus using a 25-gauge needle with an 18 or and valgus stability of the knee, but After physical examination, x-rays 19-gauge needle used for the joint tap. also the joint capsule and cruciate are always obtained of the knee. These If this is done carefully, the patient ligaments contribute to this stability.2 should include routine standing will experience very little discomfort. Examination of the knee in terms of anteroposterior (AP) and lateral views The fluid obtained should always anterior and posterior stability is of the affected knee, as well as intra- be analyzed. Even if there is an obvi­ performed in the form of a drawer condylar and sunrise views. It is neces­ ous history and physical examination sign. This is done with the knee flexed sary to obtain a full complement of compatible with a traumatic effusion to 90 degrees with the examiner’s x-rays to rule out vertical patella frac­ and a frankly bloody tap is obtained, hands in the popliteal fossa behind the tures, osteochondromal fragments, and it is wise not to discard the fluid. It tibia. The tibia is then moved in an other injuries or deformities of the must be remembered that bloody taps anterior and posterior direction with patella, femoral, and tibial joint may be obtained not only with a the femur and the foot stabilized. surfaces.6 traumatic effusion, but also with Laxity of the knee in terms of anterior As clinically indicated, an arthro- hemophilia, synovioma, neuropathic and posterior movement, in compari­ centesis of the joint may be per­ joints, pigmented villonodular syno­ son with the opposite knee, may be formed. As pointed out in the litera­ vitis, and occasionally, in patients on 7 indicative of cruciate injury. Slocum ture, the incidence of introducing an oral anticoagulants. As much fluid has modified this basic drawer sign to infection with arthrocentesis is less should be obtained as possible without test also for rotatory instability of the than one in 20,000 procedures if causing discomfort to the patient. knee.3 Laxity with the anterior drawer performed correctly.1 Precautions With bloody taps from traumatic knee, sign performed with the tibia in 30 must be taken when tapping the knee 10 to 15 cc of one percent lidocaine is degrees of internal rotation, is indica­ since some authors have indicated that injected into the knee joint through tive of posterior or lateral capsule cellulitis, bacteriemia, or bleeding ten­ the arthrocentesis needle. This has disease. The second part of Slocum’s dencies are strict contraindications for been found to be extremely helpful test is also a modified drawer performing arthrocentesis.7 When per­ when re-examining the knee. Before maneuver, but with the tibia in 15 forming a knee tap, the procedure is as the tap, the traumatic knee may be degrees of external rotation. Laxity is follows: the knee is prepped with too painful to examine. However, after indicative of injury to the posterior povidone-iodine (Betadine) alone, or the tap and the injection of the medial capsule of the knee. A with Betadine then alcohol, for ten lidocaine, the pain in the knee is

THE JOURNAL OF FA M IL Y PRACTICE, VOL. 4, NO. 1, 1977 143 Table 3. Etiologies of Knee Effusions decreased, and, therefore, the exami­ vated complement activity has not Trauma nation of the knee is much improved. only been found in bacterial infection but also in gout, pseudogout, psoriatic Meniscus injury Usually gross tears of the ligaments of arthritis, and ankylosing spondylitis.1 Ligament tear (partial or complete) the joint can be recognized upon However, some reports from the litera­ Capsule or synovium injury re-examination of the knee at this time, and can be confirmed by stress ture show occasionally low levels of Fracture with intra-articular complement have been found in bac­ involvement films. If the tap of the joint is clear or terial arthritis and gout.9,10 Theories Polyarthritis of Unknown Etiology cloudy, then routine tests are ob­ accounting for this low complement Rheumatoid arthritis tained. These tests include: (1) gram most often propose an early disease Juvenile rheumatoid arthritis stain and culture, which are sent to the state with intense phagocytosis or acti­ Ankylosing spondylitis laboratory in a sterile tube; (2) a cell vation of the complement sys­ Psoriatic arthritis count and differential, which are tem.7,9’10 In some rheumatological Others placed in a heparinized tube; and (3) a diseases such as rheumatoid arthritis or clot tube for glucose and protein. The systemic lupus erythematosus, Connective Tissue Disorders synovial fluid may also be examined immune complexes are thought to fix Systemic lupus erythematosus for crystals with a polarized light. If complement within the joint.9'12 Dermatomyositis gonococcal infection or gonococcal Therefore, in these diseases, comple­ Scleroderma arthritis is suspected, due to the sensi­ ment level is low. Table 3 gives a Reiter's syndrome tivity and difficulty of growing the detailed but not fully complete list of Others organism, then immediate plating possible etiologies of knee effusions. should be done. The appropriate In summary, careful attention must Degenerative Joint Disease medium for this is either chocolate agar, be given to both the history and Primary Thayer-Martin, or transgrow medium. physical examination, and at times the Secondary In terms of analysis of synovial laboratory findings, in all patients with fluid, the fluid can be divided into a knee effusion. An outline of the Infections four basic groups. These groups approach to a work-up of a patient Bacterial include normal fluid, non-inflamma- with a knee effusion has been Staph, strep, pneumococcus tory fluid, inflammatory fluid, and presented. Gonococcus septic fluid. Normal fluid is usually Mycobacterium tuberculosis clear and transparent with a very high Others viscosity and a good mucin clot. It V iral usually has less than 200 white blood Fungal cells per cu mm and, of these, usually less than 25 percent are polymorpho­ Metabolic or Biochemical nuclear cells. Table 1 gives a s^ort G out synopsis of the synovial fluid findings References Hem ophilia in various disease states. 1. Hollander JL, McCarthy DJ: Arthri­ Chondrocalcinosis Two other points should be made. tis and Allied Conditions. Philadelphia, Lea Hemoglobinopathies First, if a recurrent effusion of the & Febiger, 1972 2. Brantigan OC, Voshell AF: Liga Scurvy knee occurs with associated increased ments of the knee joint. J Bone Joint Surg 28:66-67, 1946 Others white cell count, then the fluid should 3. Slocum DB, Larsen RL: Rotatory be cultured for fungus and tubercu­ instability of the knee. J Bone Joint Surg Tumors 50-A:211-225, 1968 losis. Secondly, if a rheumatological 4. Smillie IS: Injuries of the Knee Pigmented villonodular synovitis work-up is indicated by the history Joint. Baltim ore, W illiam s and W ilkins, 1970 5. Fairbank Sir HAT: Internal derange Primary juxta-articular bone tumors and physical findings, additional labor­ ment of the knee in children and adoles Metastatic atory work consisting of C3 and C4, cents. Proc R Soc Med 30:427-432, 1937 6. Merrill V: Roentgenographic Posi Leukemia (complement) is obtained in a clotted tio n s a n d S ta n d a rd R a d io lo g ic Procedures. tube. Simultaneous C3 and C4, as well St. Louis, CV Mosby, 1975 Multiple myeloma 7. C o h e n A S : L a b o r a to r y Diagnostic Others as protein, is obtained from the serum. Procedures in the Rheumatic Diseases Also, ANA and rheumatoid factor are Boston, Little, Brown, 1975 8. Shapiro R, Castles JJ, W olf AW, e: Allergy and Drug Reactions helpful diagnostic tests which are al: Synovial fluid analysis in the diagnosiso’ arthritis. Presented at the annual meeting of Arthritis due to specific allergens obtained from the serum (Table 2). the American Academy of Orthopedics (ie, serum sickness) Briefly, synovial fluid complement in New Orleans, February 1976 9. Townes AS, Jowa JM: Complemen! Arthritis due to drugs normal synovial fluid is approximately in s y n o v ia l f lu id . J o h n s H o p k in s Med • ten percent of serum complement.8 127:23-37, 1970 10. Bunch TW : Synovial fluid comply Miscellaneous However, with bacterial inflammation ment determination as a diagnostic aid ir inflammatory joint disease. Mayo Clinic Rheumatic fever the complement activity usually in­ Proc 49:715-720, 1974 Sarcoidosis creases as compared to the serum 1 1 . T o w n e s A S : C o m p le m e n t levels!" disease. Johns Hopkins Med J 120:337-343 Neuroarthropathy activity.7 This is thought to be second­ 1 9 6 7 Osteochondritis dissecans ary to the enhanced joint permeability 12. Hedberg H: Studies on the df pressed hem olytic complement activity o Others obtained with an inflammatory s y n o v ia l f lu i d in a d u lt r h e u m a to id arthritis response within the joint. This ele­ Acta Rheum Scand 9:165-193, 1963

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