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The changes in human synovial fluid osmolality associated with traumatic or mechanical abnormalities of the knee
Arthroscopy: The Journal of Arthroscopic and Related Surgery 4(3):179-181 Published by Raven Press, Ltd. © 1988 Arthroscopy Association of North America
The Changes in Human Synovial Fluid Osmolality Associated with Traumatic or Mechanical Abnormalities of the Knee P. J a m e s
N e w m a n , M . D . and William A. G r a n a , M . D .
Summary: Synovial fluid osmolatity was determined in 22 knees at the time of arthroscopic evaluation. The arthroscopy was for traumatic or mechanical abnormality of the knee. The results indicate no significant difference in osmolality among the conditions studied, but there was a significant decrease in synovial fluid osmotality compared to the values for the normal knee. The information presented provides baseline data for various pathologic conditions and a basis for future work. Key Words: Synovial fluid--Osmolality--Knee.
which showed a decrease compared to those values at rest (1). On the other hand, serum osmolality was unchanged with exercise. These findings support the study of Ropes (2) on pooled bovine synovial fluid, in which a difference was noted between serum and synovial fluid osmolality using freezing point depression techniques. In other studies it appears that the osmolality of synovial fluid changes in pathologic conditions. Lipson (3,4) reported that the osmotic pressure of synovial fluid in the rheumatoid joint was equal to or less than that of the serum, and that the osmotic pressure increased as the inflammation in the joint subsided. Jensen and Zachariae (5) noted a difference in osmotic pressure between a knee with a meniscal tear and one with severe osteoarthritis. It is the purpose of this paper to present the results of a study of the osmolality of human knee synovial fluid with different pathologic conditions and to compare them to the normal as determined by Baumgarten (1).
Baumgarten noted there is little research that investigates the osmolality of normal human synovial fluid, let alone the synovial fluid osmolality in pathologic conditions (1). With improved technology, more accurate determination with smaller size samples of synovial fluid are possible and therefore there is a greater opportunity for such investigation on human joints, such as the knee. A recent study by Baumgarten of normal human synovial fluid from the knee supplies baseline values for osmolality at rest that serve as controls against determined values during different activities or in pathologic conditions. Osmolality is the concentration of osmotically active particles of solute in a solvent. In a solution containing more than one solute, such as synovial fluid, osmolality is the sum of the partial pressure of solutes and is the effective osmotic pressure of the solution or its tonicity. In pathologic or stressful conditions there may be changes in the normal osmolality of a joint fluid. Baumgarten reported exercise-induced changes in the osmolality of otherwise normal human knee synovial fluid,
MATERIALS AND METHODS From the Oklahoma Center for Athletes, Oklahoma City, Oklahoma, U.S.A. Address correspondence and reprint requests to Dr. William A. Grana at Oklahoma Center For Athletes, Presbyterian Professional Office Building, 711 Stanton L. Young Boulevard, Suite 310, Oklahoma City, OK 73104, U.S.A.
Thirty "symptomatic" knees from 23 men and seven women, who ranged in age from 16-57 years, were aspirated just prior to arthroscopy. The patients had varying degrees of disability from the 179
180
P. J. N E W M A N A N D W. A. G R A N A
knee disorder (some were chronic and some were acute) but all were judged severe enough to require a r t h r o s c o p i c t r e a t m e n t by the senior author (WAG). The pathologic conditions suspected after performance of a clinical examination included chondromalacia patella, osteoarthritis, anterior cruciate ligament (ACL) instability, and meniscal pathology. Many of the patients were on a nonsteroidal anti-inflammatory medication at the time of arthroscopy, but were otherwise healthy. The aspiration of the knee was performed with the patient under epidural or general anesthesia with the knee flexed approximately 10°, prepped, and draped just prior to making the arthroscopic portals. A 5 cc syringe with an 18 gauge needle was used through a lateral parapatellar approach to the suprapatellar pouch. Within 10 s, 2 cc of the aspirate was transferred from the 5 cc syringe to a 3 cc syringe with its plunger removed. A 20-~L sample was then taken from the 3 cc syringe using the Advanced 20-Microliter Sampler. The sample was then inserted into the precalibrated advanced MicroOsmometer Model 3MO that was specially designed for freezing-point depression osmometry, and the reading recorded. Sufficient synovial fluid remained in the 3 cc syringe to permit two more osmolality determinations for each knee. The three samples were run in succession and completed well within 5 min of the aspiration. After each knee determina-
tion, the osmometer was cleaned and retested with a known standard. No attempt was made to perform any other synovial fluid analysis other than osmolality or to quantitate the volume of effusions if >2 cc. Eight of the thirty knees aspirated just prior to arthroscopy yielded <2 cc of synovial fluid ("dry taps"). These eight knees were excluded from this study due to an inability to perform the three successive osmolality determinations with such a small volume of synovial fluid. Of the twenty-two knees that provided >2 cc of synovial fluid, three successive osmolality determinations were performed for each knee within 5 min of the joint aspiration (Table I). The importance of rapid determination of the osmolality was clearly demonstrated by Baumgarten. He noted a statistically significant decrease in the osmolality of the synovial fluid when it was kept in a closed system after aspiration for 20 min prior to the performance of the osmolality determination. RESULTS Of some concern is the greater than expected range noted between the three successive osmolality determinations for some patients (i.e., patient 22 A.G.--310, 302, 306). The large range was not due to intrinsic error in the osmometer (---2 mmoles/kg) and was not present when three successive determinations were performed with the standard fluid.
T A B L E 1. Osmolality determinations performed within 5 min o f joint aspiration Patient 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
G.M. D.A. S.H. T.L. T.R. S.M. M.T. K.J. T.P. K.U. M.V. D.J. R.C. T.J. J.H. B.J. S.P. J.M. G.T. M.H. M.F. A.G.
Sex
Dx
Osmolality (Mmoles/kg)
M M M M M M M M F F M M M M M M F M M M M M
ACL out only ACL out-only ACL out-only ACL out-only ACL out-only ACL out-only ACL out-only ACL out-only Chondromalacia Chondromalacia Chondromalacia Chondromalacia (+ meniscal tear) Chondromalacia Tricompartment DJD Tricompartment DJD Tricompartment DJD Meniscal tear (+chronic ACL out) Meniscal tear Meniscal tear Meniscal tear (+chronic ACL out) Meniscal tear Meniscal tear
301 304, 299 295 295, 292 ~ 295. 296, 297 a 295. 291, 299 304. 303, 302a 301. 300, 304 301. 294, 298 307. 304, 302 296. 302, 298 298. 290, 294 299. 297, 296 a 309 300, 302 298 299, 302a 301,295, 300 304, 302, 303 ~ 304, 297, 296 309, 301,303 299, 294, 296 ~ 305,299, 296 302,304, 298 295, 297, 300~ 310, 302, 306
Dx, diagnosis. a Some gross blood is aspirate.
Arthroscopy, Vol. 4, No. 3, 1988
=Ave. osmolality 294 296 295 299 303 3O2 298 3O4 299 } 294 297 299 304 300 299 } 303 300 299
t
296 304 t 294 301 297 306
300
C H A N G E S I N S Y N O V I A L FLUID O S M O L A L I T Y
Moreover, the apparent discrepancy in these successive osmolality determinations was not explained by a delay in the determination because the subsequent determinations were not always less than the initial determination. Qualitatively, it appeared that the variation was smaller when the synovial fluid sampled was less viscous, such as that seen in knees with a mild hemarthrosis (Table I). After determining the average synovial fluid osmolality for each knee from the three successive determinations, the patients were categorized as having following pathologic conditions that were consistent with both the clinical presentation and the findings of arthroscopy: ACL deficiency (eight patients), chondromalacia (five patients), tricomp a r t m e n t a l d e g e n e r a t i v e j o i n t disease (three patients), and meniscal tears (six patients). The average synovial fluid osmolality was then determined for each condition (Table I). There was no statistically significant difference among the four pathologic conditions, but there was a large difference between these findings in the abnormal synovial fluid and the normal synovial osmolality for the human knee (404 mm/kg) as determined by Baumgarten (1). DISCUSSION Osmolality can be determined by measuring either boiling-point elevation, a change in osmotic pressure, vapor-pressure depression, or freezingpoint depression. All four methods of osmolality determination are used by investigators. Lipson (3, 4) and Jensen and Zachariae (5) used changes in osmotic pressure while Ropes (2) used freezingpoint depression. More recently Baumgarten (1) used vapor-pressure depression for determination of osmolality. We chose freezing-point depression for osmolality determination because it reportedly is slightly more accurate than methods utilizing vapor-pressure depression. However, that increase in accuracy appears to be negligible based on the pilot study performed by Baumgarten (1), in which there was no statistically significant difference between the synovial fluid osmolality values obtained via vapor-pressure depression and the osmolality values determined utilizing freezing-point depression. That same study by Baumgarten (1) determined the controls we used in our study, thus precluding our need to obtain both serum and "normal" knee synovial fluid. We observed a marked decrease in synovial fluid osmolality in all pathologic conditions (300) corn-
181
pared to the mean synovial fluid osmolality of a normal knee at rest (404) (1). This finding is consistent with the observation of Lipson (4), who indicated that the osmolality of diseased human knee joints increases as the inflammation subsides and approaches that of a normal knee joint. Interestingly, although all our patients had obvious knee pathology, some had much more inflammation than others yet the osmolality determinations remained in a relatively narrow range (292-310), with none approaching the normal. Unfortunately, we observed no statistically significant difference between the average synovial fluid osmolality for the several pathologic conditions observed, which contradicts the observations of Jensen and Zachariae (5) who noted a difference in osmotic pressure between a knee with a meniscal tear and one with severe osteoarthritis. Baumgarten (1) noted a significant decrease in the synovial fluid osmolality of a normal knee with exercise. This decrease of 103 mM/kg is approximately the same decrease noted in our pathologic conditions. H o w this relates to the effect of exercise and whether this is a comparable physiologic phenomenon is unknown. Although we are currently unable to make a diagnosis by joint aspiration in most pathologic conditions involving the knee, it appears we can assess whether the knee at rest is "diseased" or normal based on synovial fluid osmolality determination. This ability to assess the relative health of a knee may have important clinical applications. It may provide an objective means by which to monitor recovery from a knee injury and help ascertain when that knee is "normal". Obviously, there are many unanswered questions regarding the changes seen in synovial fluid osmolality with exercise and various pathologic conditions. Further study is needed in this area of research. REFERENCES 1. Baumgarten M, Bloebaum RD, Ross SDK, Campbell P, Sarmiento A. Normal human synovial fluid: osmolality and exercise-induced changes. J Bone Joint Surg 1985;67A(9): 1336-9. 2. Ropes MW, Bennet GA, Baur W. The origin and nature of normal synovial fluid. J Clin Invest 1939;18:351-72. 3. Lipson RL. Osmotic pressure measurements of paired specimens of plasma and joint fluid. Fed Proc 1966;25:1120-1. 4. Lipson RL, Baldes E J, Anderson JA, Polley HF. Osmotic pressure gradients and joint effusions. Arthritis Rheum 1965;8:29-37. 5. Jensen CE, Zachariae L. The contributions from hyaluronic acid and from protein to the colloid osmotic pressure of human synovial fluid. Acta Rheumatol Scand 1959;5:18--28. Arthroscopy, Vol. 4, No. 3, 1988
The Changes in Human Synovial Fluid Osmolality Associated with Traumatic or Mechanical Abnormalities of the Knee P. J a m e s
N e w m a n , M . D . and William A. G r a n a , M . D .
Summary: Synovial fluid osmolatity was determined in 22 knees at the time of arthroscopic evaluation. The arthroscopy was for traumatic or mechanical abnormality of the knee. The results indicate no significant difference in osmolality among the conditions studied, but there was a significant decrease in synovial fluid osmotality compared to the values for the normal knee. The information presented provides baseline data for various pathologic conditions and a basis for future work. Key Words: Synovial fluid--Osmolality--Knee.
which showed a decrease compared to those values at rest (1). On the other hand, serum osmolality was unchanged with exercise. These findings support the study of Ropes (2) on pooled bovine synovial fluid, in which a difference was noted between serum and synovial fluid osmolality using freezing point depression techniques. In other studies it appears that the osmolality of synovial fluid changes in pathologic conditions. Lipson (3,4) reported that the osmotic pressure of synovial fluid in the rheumatoid joint was equal to or less than that of the serum, and that the osmotic pressure increased as the inflammation in the joint subsided. Jensen and Zachariae (5) noted a difference in osmotic pressure between a knee with a meniscal tear and one with severe osteoarthritis. It is the purpose of this paper to present the results of a study of the osmolality of human knee synovial fluid with different pathologic conditions and to compare them to the normal as determined by Baumgarten (1).
Baumgarten noted there is little research that investigates the osmolality of normal human synovial fluid, let alone the synovial fluid osmolality in pathologic conditions (1). With improved technology, more accurate determination with smaller size samples of synovial fluid are possible and therefore there is a greater opportunity for such investigation on human joints, such as the knee. A recent study by Baumgarten of normal human synovial fluid from the knee supplies baseline values for osmolality at rest that serve as controls against determined values during different activities or in pathologic conditions. Osmolality is the concentration of osmotically active particles of solute in a solvent. In a solution containing more than one solute, such as synovial fluid, osmolality is the sum of the partial pressure of solutes and is the effective osmotic pressure of the solution or its tonicity. In pathologic or stressful conditions there may be changes in the normal osmolality of a joint fluid. Baumgarten reported exercise-induced changes in the osmolality of otherwise normal human knee synovial fluid,
MATERIALS AND METHODS From the Oklahoma Center for Athletes, Oklahoma City, Oklahoma, U.S.A. Address correspondence and reprint requests to Dr. William A. Grana at Oklahoma Center For Athletes, Presbyterian Professional Office Building, 711 Stanton L. Young Boulevard, Suite 310, Oklahoma City, OK 73104, U.S.A.
Thirty "symptomatic" knees from 23 men and seven women, who ranged in age from 16-57 years, were aspirated just prior to arthroscopy. The patients had varying degrees of disability from the 179
180
P. J. N E W M A N A N D W. A. G R A N A
knee disorder (some were chronic and some were acute) but all were judged severe enough to require a r t h r o s c o p i c t r e a t m e n t by the senior author (WAG). The pathologic conditions suspected after performance of a clinical examination included chondromalacia patella, osteoarthritis, anterior cruciate ligament (ACL) instability, and meniscal pathology. Many of the patients were on a nonsteroidal anti-inflammatory medication at the time of arthroscopy, but were otherwise healthy. The aspiration of the knee was performed with the patient under epidural or general anesthesia with the knee flexed approximately 10°, prepped, and draped just prior to making the arthroscopic portals. A 5 cc syringe with an 18 gauge needle was used through a lateral parapatellar approach to the suprapatellar pouch. Within 10 s, 2 cc of the aspirate was transferred from the 5 cc syringe to a 3 cc syringe with its plunger removed. A 20-~L sample was then taken from the 3 cc syringe using the Advanced 20-Microliter Sampler. The sample was then inserted into the precalibrated advanced MicroOsmometer Model 3MO that was specially designed for freezing-point depression osmometry, and the reading recorded. Sufficient synovial fluid remained in the 3 cc syringe to permit two more osmolality determinations for each knee. The three samples were run in succession and completed well within 5 min of the aspiration. After each knee determina-
tion, the osmometer was cleaned and retested with a known standard. No attempt was made to perform any other synovial fluid analysis other than osmolality or to quantitate the volume of effusions if >2 cc. Eight of the thirty knees aspirated just prior to arthroscopy yielded <2 cc of synovial fluid ("dry taps"). These eight knees were excluded from this study due to an inability to perform the three successive osmolality determinations with such a small volume of synovial fluid. Of the twenty-two knees that provided >2 cc of synovial fluid, three successive osmolality determinations were performed for each knee within 5 min of the joint aspiration (Table I). The importance of rapid determination of the osmolality was clearly demonstrated by Baumgarten. He noted a statistically significant decrease in the osmolality of the synovial fluid when it was kept in a closed system after aspiration for 20 min prior to the performance of the osmolality determination. RESULTS Of some concern is the greater than expected range noted between the three successive osmolality determinations for some patients (i.e., patient 22 A.G.--310, 302, 306). The large range was not due to intrinsic error in the osmometer (---2 mmoles/kg) and was not present when three successive determinations were performed with the standard fluid.
T A B L E 1. Osmolality determinations performed within 5 min o f joint aspiration Patient 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
G.M. D.A. S.H. T.L. T.R. S.M. M.T. K.J. T.P. K.U. M.V. D.J. R.C. T.J. J.H. B.J. S.P. J.M. G.T. M.H. M.F. A.G.
Sex
Dx
Osmolality (Mmoles/kg)
M M M M M M M M F F M M M M M M F M M M M M
ACL out only ACL out-only ACL out-only ACL out-only ACL out-only ACL out-only ACL out-only ACL out-only Chondromalacia Chondromalacia Chondromalacia Chondromalacia (+ meniscal tear) Chondromalacia Tricompartment DJD Tricompartment DJD Tricompartment DJD Meniscal tear (+chronic ACL out) Meniscal tear Meniscal tear Meniscal tear (+chronic ACL out) Meniscal tear Meniscal tear
301 304, 299 295 295, 292 ~ 295. 296, 297 a 295. 291, 299 304. 303, 302a 301. 300, 304 301. 294, 298 307. 304, 302 296. 302, 298 298. 290, 294 299. 297, 296 a 309 300, 302 298 299, 302a 301,295, 300 304, 302, 303 ~ 304, 297, 296 309, 301,303 299, 294, 296 ~ 305,299, 296 302,304, 298 295, 297, 300~ 310, 302, 306
Dx, diagnosis. a Some gross blood is aspirate.
Arthroscopy, Vol. 4, No. 3, 1988
=Ave. osmolality 294 296 295 299 303 3O2 298 3O4 299 } 294 297 299 304 300 299 } 303 300 299
t
296 304 t 294 301 297 306
300
C H A N G E S I N S Y N O V I A L FLUID O S M O L A L I T Y
Moreover, the apparent discrepancy in these successive osmolality determinations was not explained by a delay in the determination because the subsequent determinations were not always less than the initial determination. Qualitatively, it appeared that the variation was smaller when the synovial fluid sampled was less viscous, such as that seen in knees with a mild hemarthrosis (Table I). After determining the average synovial fluid osmolality for each knee from the three successive determinations, the patients were categorized as having following pathologic conditions that were consistent with both the clinical presentation and the findings of arthroscopy: ACL deficiency (eight patients), chondromalacia (five patients), tricomp a r t m e n t a l d e g e n e r a t i v e j o i n t disease (three patients), and meniscal tears (six patients). The average synovial fluid osmolality was then determined for each condition (Table I). There was no statistically significant difference among the four pathologic conditions, but there was a large difference between these findings in the abnormal synovial fluid and the normal synovial osmolality for the human knee (404 mm/kg) as determined by Baumgarten (1). DISCUSSION Osmolality can be determined by measuring either boiling-point elevation, a change in osmotic pressure, vapor-pressure depression, or freezingpoint depression. All four methods of osmolality determination are used by investigators. Lipson (3, 4) and Jensen and Zachariae (5) used changes in osmotic pressure while Ropes (2) used freezingpoint depression. More recently Baumgarten (1) used vapor-pressure depression for determination of osmolality. We chose freezing-point depression for osmolality determination because it reportedly is slightly more accurate than methods utilizing vapor-pressure depression. However, that increase in accuracy appears to be negligible based on the pilot study performed by Baumgarten (1), in which there was no statistically significant difference between the synovial fluid osmolality values obtained via vapor-pressure depression and the osmolality values determined utilizing freezing-point depression. That same study by Baumgarten (1) determined the controls we used in our study, thus precluding our need to obtain both serum and "normal" knee synovial fluid. We observed a marked decrease in synovial fluid osmolality in all pathologic conditions (300) corn-
181
pared to the mean synovial fluid osmolality of a normal knee at rest (404) (1). This finding is consistent with the observation of Lipson (4), who indicated that the osmolality of diseased human knee joints increases as the inflammation subsides and approaches that of a normal knee joint. Interestingly, although all our patients had obvious knee pathology, some had much more inflammation than others yet the osmolality determinations remained in a relatively narrow range (292-310), with none approaching the normal. Unfortunately, we observed no statistically significant difference between the average synovial fluid osmolality for the several pathologic conditions observed, which contradicts the observations of Jensen and Zachariae (5) who noted a difference in osmotic pressure between a knee with a meniscal tear and one with severe osteoarthritis. Baumgarten (1) noted a significant decrease in the synovial fluid osmolality of a normal knee with exercise. This decrease of 103 mM/kg is approximately the same decrease noted in our pathologic conditions. H o w this relates to the effect of exercise and whether this is a comparable physiologic phenomenon is unknown. Although we are currently unable to make a diagnosis by joint aspiration in most pathologic conditions involving the knee, it appears we can assess whether the knee at rest is "diseased" or normal based on synovial fluid osmolality determination. This ability to assess the relative health of a knee may have important clinical applications. It may provide an objective means by which to monitor recovery from a knee injury and help ascertain when that knee is "normal". Obviously, there are many unanswered questions regarding the changes seen in synovial fluid osmolality with exercise and various pathologic conditions. Further study is needed in this area of research. REFERENCES 1. Baumgarten M, Bloebaum RD, Ross SDK, Campbell P, Sarmiento A. Normal human synovial fluid: osmolality and exercise-induced changes. J Bone Joint Surg 1985;67A(9): 1336-9. 2. Ropes MW, Bennet GA, Baur W. The origin and nature of normal synovial fluid. J Clin Invest 1939;18:351-72. 3. Lipson RL. Osmotic pressure measurements of paired specimens of plasma and joint fluid. Fed Proc 1966;25:1120-1. 4. Lipson RL, Baldes E J, Anderson JA, Polley HF. Osmotic pressure gradients and joint effusions. Arthritis Rheum 1965;8:29-37. 5. Jensen CE, Zachariae L. The contributions from hyaluronic acid and from protein to the colloid osmotic pressure of human synovial fluid. Acta Rheumatol Scand 1959;5:18--28. Arthroscopy, Vol. 4, No. 3, 1988