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Radiographic Findings of Osteoarthritis versus Arthroscopic Findings of Articular Cartilage Degeneration in the Tibiofemoral Joint¹

¹ From the Departments of Radiology (R.K., D.G.B., P.T.S., J.P.F., A.A.D.S.) and Statistics (J.P.F.), University of Wisconsin Hospital, Clinical Science Center-E3/311, 600 Highland Ave, Madison, WI 53792-3252. Received April 7, 2005; revision requested June 7; revision received July 1; accepted July 21; final version accepted August 5. Address correspondence to R.K. (e-mail: rkijowski{at}mail.radiology.wisc.edu).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 
Purpose: To retrospectively correlate radiographic findings of osteoarthritis of the tibiofemoral joint with arthroscopic findings of articular cartilage degeneration within the tibiofemoral joint in patients with chronic knee pain.

Materials and Methods: The study was performed in compliance with HIPAA regulations. Approval from an institutional review board and a waiver of informed consent were obtained. The study group consisted of 125 patients with osteoarthritis of the tibiofemoral joint (66 men, 59 women; age range, 35–77 years; average age, 52 years) and 25 patients of similar age (14 men, 11 women; age range, 36–69 years; average age, 50 years) with no osteoarthritis of the tibiofemoral joint. All patients underwent standing anteroposterior radiography of the knee prior to arthroscopic knee surgery. Each articular surface of the tibiofemoral joint was graded at arthroscopy. Two radiologists retrospectively reviewed the knee radiographs to determine the presence of marginal osteophytes, joint space narrowing, subchondral sclerosis, and subchondral cysts. The sensitivity and specificity of the radiographic features of osteoarthritis for the detection of articular cartilage degeneration within the medial and lateral compartments of the tibiofemoral joint were determined.

Results: The sensitivity of marginal osteophytes, joint space narrowing, subchondral sclerosis, and subchondral cysts for the detection of articular cartilage degeneration was 67%, 46%, 16%, and 10%, respectively, for the medial compartment and 49%, 7%, 6%, and 3%, respectively, for the lateral compartment. The specificity of marginal osteophytes, joint space narrowing, subchondral sclerosis, and subchondral cysts for the detection of articular cartilage degeneration was 73%, 95%, 100%, and 100%, respectively, for the medial compartment and 81%, 100%, 100%, and 100%, respectively, for the lateral compartment.

Conclusion: Marginal osteophytes were the most sensitive radiographic feature for the detection of osteoarthritis of the tibiofemoral joint. Joint space narrowing, subchondral sclerosis, and subchondral cysts were less sensitive radiographic features of osteoarthritis and rarely occurred in the absence of associated osteophyte formation.

© RSNA, 2006

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 
Osteoarthritis of the tibiofemoral joint is a common cause of pain and disability in older individuals. The prevalence of osteoarthritis of the tibiofemoral joint in the adult population increases with age. As many as 30% of individuals older than 45 years and nearly 75% of individuals older than 65 years show evidence of osteoarthritis of the tibiofemoral joint on knee radiographs (1,2). Furthermore, 40%–80% of individuals with radiographic evidence of osteoarthritis have symptomatic disease (3).

Radiography is usually the initial imaging examination performed in patients with osteoarthritis of the tibiofemoral joint. Radiography is also commonly used in population studies to define the presence of osteoarthritis of the tibiofemoral joint and to document changes in the severity of the disease process over time. Characteristic radiographic features of osteoarthritis include marginal osteophytes, joint space narrowing, subchondral sclerosis, and subchondral cysts and reflect the pathologic changes that occur during the disease process.

Although radiography is commonly used to evaluate patients with osteoarthritis of the tibiofemoral joint, few previous studies have documented the usefulness of various radiographic features of osteoarthritis for the detection of articular cartilage degeneration (4–10). Thus, our study was performed to retrospectively correlate radiographic findings of osteoarthritis of the tibiofemoral joint with arthroscopic findings of articular cartilage degeneration within the tibiofemoral joint in patients with chronic knee pain.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 
Study Group
The study was performed in compliance with Health Insurance Portability and Accountability Act regulations. Approval from our institutional review board and a waiver of informed consent were obtained.

The study group consisted of 125 patients (66 men, 59 women; age range, 35–77 years; average age, 52 years) with osteoarthritis of the tibiofemoral joint and 25 patients of similar age (14 men, 11 women; age range, 36–69 years; average age, 50 years) with no osteoarthritis of the tibiofemoral joint. A diagnosis of osteoarthritis was made when a patient had chronic knee pain that lasted longer than 2 months and articular cartilage degeneration within the tibiofemoral joint at arthroscopic knee surgery. The same diagnostic criteria were used in previous studies that correlated radiographic findings with arthroscopic findings in patients with osteoarthritis of the tibiofemoral joint (4,5,8–10).

The patients in the study group were selected from files in a database of magnetic resonance (MR) imaging examinations of the knee performed at our institution between January 1999 and June 2004. The MR database was used to identify 1554 patients who had osteoarthritis of the tibiofemoral joint. The medical records of these 1554 patients were reviewed by one of the authors (P.T.S.) to identify the 125 patients who subsequently underwent arthroscopic surgery on their symptomatic knee. The presence of articular cartilage degeneration within the tibiofemoral joint in all 125 patients was confirmed at arthroscopic surgery. The same MR database was used to identify 845 patients with normal articular cartilage within the tibiofemoral joint. The medical records of these 845 patients were reviewed by the same author (P.T.S.) to identify the 25 patients who were of similar age as the patients with osteoarthritis of the tibiofemoral joint and who subsequently underwent arthroscopic surgery on their symptomatic knee. The presence of normal articular cartilage within the tibiofemoral joint in all 25 patients was confirmed at arthroscopic surgery. All 125 patients with osteoarthritis of the tibiofemoral joint and all 25 patients without osteoarthritis of the tibiofemoral joint had chronic knee pain that lasted longer than 2 months and no history of recent knee trauma, prior knee surgery, inflammatory arthritis, septic arthritis, or crystalline-induced arthritis.

A Fisher test showed no statistically significant difference in sex between patients with osteoarthritis of the tibiofemoral joint and those without (P < .05). A two-sample Student t test showed no statistically significant difference in the mean age between patients with osteoarthritis of the tibiofemoral joint and those without (P < .05).

Radiographic Examination
An anteroposterior radiograph of the knee was obtained for all 150 patients in the study group. All radiography was performed with the patient in the upright standing position with the knee fully extended. All radiography was performed by using standardized technique with the x-ray cassette placed posterior to the knee, with a tube-film distance of 40 inches (102 cm), and with the x-ray beam projecting parallel to the tibial plateau and aimed at the patella (5,8).

Arthroscopic Knee Surgery (Reference Standard)
Arthroscopic knee surgery was performed on all 150 patients in the study group within 2 months (range, 3–55 days; median time, 17 days) after radiographic examination. All arthroscopic knee surgeries were performed by one of three orthopedic surgeons at our institution who specialized in sports medicine and who had 5–20 years of clinical experience. The indications for surgery were débridement or repair of a meniscal tear in 81 patients, débridement or repair of a meniscal tear and débridement of an articular cartilage defect in 42 patients, débridement of an articular cartilage defect in 22 patients, and removal of intraarticular loose bodies in five patients. The articular cartilage of the medial femoral condyle, lateral femoral condyle, medial tibial plateau, and lateral tibial plateau of each patient was graded at arthroscopic knee surgery by using the Noyes and Stabler classification system (Table 1) (11). The orthopedic surgeons were aware of the radiographic and MR imaging findings of all patients at arthroscopic knee surgery.

Statistical Analysis
The sensitivity and specificity with 95% confidence intervals of marginal osteophytes, joint space narrowing, subchondral sclerosis, and subchondral cysts for the detection of articular cartilage degeneration within the medial and lateral compartments of the tibiofemoral joint were calculated. Sensitivity was defined as the proportion of individuals with articular cartilage degeneration who were classified as having a certain radiographic feature of osteoarthritis. Specificity was defined as the proportion of patients with normal articular cartilage who were classified as not having a certain radiographic feature of osteoarthritis. Arthroscopic findings were used as the reference standard for the calculation of all sensitivity and specificity values. Differences in the sensitivity and specificity of the various radiographic features of osteoarthritis were formally tested with paired McNemar tests. Differences were considered to be statistically significant if the P value was less than .05. All P values were two tailed.

A univariate logistic regression model was used to calculate odds ratios with 95% confidence intervals to describe the usefulness of marginal osteophytes, joint space narrowing, subchondral sclerosis, and subchondral cysts for determining the presence or absence of articular cartilage degeneration within the medial and lateral compartments of the tibiofemoral joint. A multivariate logistic regression model was used to calculate the sensitivity and specificity of using any radiographic feature of osteoarthritis for the detection of articular cartilage degeneration within the medial and lateral compartments of the tibiofemoral joint. Patients were classified at statistical analysis as having articular cartilage degeneration if the probability from the logistic regression model was greater than .5 and as not having articular cartilage degeneration if the probability was less than .5.

The relationship between the presence of various radiographic features of osteoarthritis and the severity of the articular cartilage degeneration within the tibiofemoral joint was determined. The severity of articular cartilage degeneration within the medial and lateral compartments was estimated for each patient. Articular cartilage defects of grades 1A, 1B, 2A, 2B, 3A, and 3B were given numeric values of 1, 2, 3, 4, 5, and 6, respectively. The severity of articular cartilage degeneration within the medial and lateral compartments was estimated by summing the numeric values of the grades of the cartilage defects identified on the femoral condyle and tibial plateau at arthroscopy. For example, a numeric value of 9 was used to represent the severity of articular cartilage degeneration within the medial compartment in a patient with a grade 2B defect (numeric value, 4) and grade 3A defect (numeric value, 5) of the medial tibial plateau. There was a direct correlation between the numeric value and the severity of articular cartilage degeneration within the tibiofemoral joint. The mean numeric values with 95% confidence intervals representing the severity of the articular cartilage degeneration in patients with marginal osteophytes, joint space narrowing, subchondral sclerosis, and subchondral cysts within the medial and lateral compartments of the tibiofemoral joint were calculated. Differences in the severity of articular cartilage degeneration in patients with various radiographic features of osteoarthritis were formally tested by using repeated measures analysis of variance F tests. Differences were considered to be statistically significant if the P value was less than .05.

Statistical software (S-Plus, version 3.4; Mathsoft, Seattle, Wash) was used to perform all statistical analyses in the study.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 
Twenty-three patients had articular cartilage degeneration within the medial compartment, 12 patients had articular cartilage degeneration within the lateral compartment, and 90 patients had articular cartilage degeneration within both the medial and lateral compartments of the tibiofemoral joint. The remaining 25 patients in the study group had chronic knee pain and arthroscopically confirmed normal articular cartilage within the tibiofemoral joint.

Arthroscopic Findings in Medial Compartment
Seventy-six of the 113 patients with articular cartilage degeneration within the medial compartment of the tibiofemoral joint had marginal osteophytes. Twenty-seven of these 76 patients had marginal osteophytes but no joint space narrowing. Ten of the 37 patients with normal articular cartilage within the medial compartment had marginal osteophytes. The average age of these patients was 50 years.

Fifty-two of the 113 patients with articular cartilage degeneration within the medial compartment had joint space narrowing. Only two of these 52 patients had joint space narrowing but no marginal osteophytes. Two of the 37 patients with normal articular cartilage within the medial compartment had joint space narrowing.

Eighteen of 113 patients with articular cartilage degeneration within the medial compartment had subchondral sclerosis within the medial tibial plateau. Eleven of 113 patients with articular cartilage degeneration within the medial compartment had subchondral cysts within the medial tibial plateau. All patients with subchondral sclerosis or subchondral cysts had high-grade partial-thickness or full-thickness defects within the overlying articular cartilage of the medial tibial plateau. Sixteen of the 18 patients with subchondral sclerosis and 10 of the 11 patients with subchondral cysts also had high-grade partial-thickness or full-thickness defects within the articular cartilage of the medial femoral condyle.

Arthroscopic Findings in Lateral Compartment
Fifty of the 102 patients with articular cartilage degeneration within the lateral compartment of the tibiofemoral joint had marginal osteophytes. Forty-three of these 50 patients had marginal osteophytes but no joint space narrowing. Nine of the 48 patients with normal articular cartilage within the lateral compartment had marginal osteophytes. The average age of these patients was 51 years.

Seven of the 102 patients with articular cartilage degeneration within the lateral compartment had joint space narrowing. None of these patients had joint space narrowing but no marginal osteophytes. None of the 48 patients with normal articular cartilage within the lateral compartment had joint space narrowing.

Six of the 102 patients with articular cartilage degeneration within the lateral compartment had subchondral sclerosis within the lateral tibial plateau. Three of the 102 patients with articular cartilage degeneration within the lateral compartment had subchondral cysts within the lateral tibial plateau. All patients with subchondral sclerosis or subchondral cysts had high-grade partial-thickness or full-thickness defects within the overlying articular cartilage of the lateral tibial plateau. Five of the six patients with subchondral sclerosis and two of the three patients with subchondral cysts also had high-grade partial-thickness or full-thickness defects within the articular cartilage of the lateral femoral condyle.

Results of Statistical Analysis
The sensitivity and specificity with 95% confidence intervals of marginal osteophytes, joint space narrowing, subchondral sclerosis, and subchondral cysts for the detection of articular cartilage degeneration within the medial compartment are listed in Table 2, and those for the lateral compartment of the tibiofemoral joint are listed in Table 3. The difference between the sensitivity and specificity of marginal osteophytes and the sensitivity and specificity of joint space narrowing, subchondral sclerosis, and subchondral cysts was statistically significant (P < .05) for both the medial and the lateral compartments. The difference between the sensitivity of joint space narrowing and the sensitivity of subchondral sclerosis and subchondral cysts was also statistically significant (P < .05) for both the medial and the lateral compartments.

The mean numeric values with 95% confidence intervals that represent the severity of articular cartilage degeneration within the medial and lateral compartments of the tibiofemoral joint in patients with marginal osteophytes, joint space narrowing, subchondral sclerosis, and subchondral cysts are listed in Table 5. Patients with marginal osteophytes, on average, had less severe articular cartilage degeneration within both the medial and the lateral compartments than did patients with joint space narrowing, subchondral cysts, or subchondral sclerosis. The differences between the severity of articular cartilage degeneration in patients with marginal osteophytes and in patients with joint space narrowing, subchondral sclerosis, or subchondral cysts were statistically significant (P < .05) for the medial compartment. These differences, however, were not statistically significant (P = .12–.52) for the lateral compartment.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

Our study has shown that marginal osteophytes are an important radiographic feature of osteoarthritis of the tibiofemoral joint. In our study, marginal osteophytes were the most sensitive radiographic finding for the detection of articular cartilage degeneration within the tibiofemoral joint. Furthermore, marginal osteophytes were the most common radiographic finding in patients with early osteoarthritis.

Previous studies have correlated the radiographic finding of marginal osteophytes with findings of articular cartilage degeneration within the tibiofemoral joint. Blackburn and associates (9) found that the Kellgren-Lawrence grading scale, which emphasizes the presence of marginal osteophytes in the diagnosis and grading of osteoarthritis, significantly underestimated the degree of articular cartilage degeneration in 36 patients with arthroscopically confirmed osteoarthritis of the tibiofemoral joint. Other authors, however, found a much stronger association between marginal osteophytes and osteoarthritis of the tibiofemoral joint. Boegard and associates (6) described marginal osteophytes in 27 of 35 patients with osteoarthritis of the tibiofemoral joint depicted at MR imaging. Wada and associates (10) described marginal osteophytes in 170 of 173 patients with arthroscopically confirmed advanced osteoarthritis of the medial compartment of the tibiofemoral joint.

In our study, marginal osteophytes were the least specific radiographic finding of osteoarthritis of the tibiofemoral joint. Marginal osteophytes were present in 10 of 37 patients with normal articular cartilage within the medial compartment of the tibiofemoral joint and in nine of 48 patients with normal articular cartilage within the lateral compartment of the tibiofemoral joint. Similarly, Brandt and associates (8) found marginal osteophytes in nine of 32 patients with arthroscopically confirmed normal articular cartilage within the tibiofemoral joint. Furthermore, Boegard and associates (6) described marginal osteophytes identified at MR imaging in four of 24 patients with normal articular cartilage within the tibiofemoral joint.

Narrowing of the tibiofemoral joint space seen on knee radiographs reflects loss of cartilage on the articular surface of the femoral condyle and tibial plateau and is thought to represent an important radiographic feature of osteoarthritis. Joint space narrowing, however, was a relatively less sensitive radiographic feature of osteoarthritis of the tibiofemoral joint in our study. Joint space narrowing was rarely present in the absence of marginal osteophytes and was most common in patients with advanced articular cartilage degeneration within the tibiofemoral joint.

Previous clinical studies have correlated the radiographic finding of joint space narrowing with findings of articular cartilage degeneration within the tibiofemoral joint. Lysholm and associates (4) found joint space narrowing in 20 of 35 patients with arthroscopically confirmed osteoarthritis of the tibiofemoral joint. Fife and associates (5) described joint space narrowing in 32 of 45 patients with arthroscopically confirmed osteoarthritis of the medial compartment of the tibiofemoral joint and in nine of 33 patients with arthroscopically confirmed osteoarthritis of the lateral compartment. Boegard and associates (7) found joint space narrowing identified at MR imaging in 15 of 35 patients with osteoarthritis of the tibiofemoral joint. Wada and associates (10) described joint space narrowing in 150 of 173 patients with arthroscopically confirmed advanced osteoarthritis of the medial compartment of the tibiofemoral joint.

Joint space narrowing, in our study, was present in only two of 37 patients with normal articular cartilage within the medial compartment and in none of 48 patients with normal articular cartilage within the lateral compartment. In contrast, Fife and associates (5) found joint space narrowing in 44 of 103 patients with arthroscopically confirmed normal articular cartilage within the medial compartment and in 13 of 128 patients with arthroscopically confirmed normal articular cartilage within the lateral compartment. In their study, an experienced musculoskeletal radiologist assessed for the presence of joint space narrowing on knee radiographs without the aid of a standardized atlas. The higher specificity of joint space narrowing for the detection of articular cartilage degeneration in our study likely resulted from our use of a standardized atlas to determine the presence of joint space narrowing.

In our study, joint space narrowing without associated marginal osteophytes was present in only two of 113 patients with articular cartilage degeneration within the medial compartment and in none of 102 patients with articular cartilage degeneration within the lateral compartment. Joint space narrowing without associated marginal osteophyte formation is rarely seen in patients with osteoarthritis of the tibiofemoral joint. Furthermore, even an experienced musculoskeletal radiologist may overcall joint space narrowing on knee radiographs in patients with normal articular cartilage (5). As a result, the radiographic diagnosis of osteoarthritis of the tibiofemoral joint exclusively based on the presence of joint space narrowing should be made with extreme caution.

Subchondral cysts and subchondral sclerosis were rarely seen in our patients with articular cartilage degeneration and were present only in individuals with severe osteoarthritis of the tibiofemoral joint. Despite having extremely low sensitivity for the detection of osteoarthritis, subchondral cysts and subchondral sclerosis may serve as a reliable indicator of the presence of advanced articular cartilage degeneration within the tibiofemoral joint.

In our study, the sensitivity of all radiographic features of osteoarthritis was lower for the detection of articular cartilage degeneration within the lateral compartment of the tibiofemoral joint than for that within the medial compartment of the tibiofemoral joint. This lower sensitivity in our study may be partly explained by the fact that a larger proportion of patients with lateral compartment osteoarthritis than with medial compartment osteoarthritis had early articular cartilage degeneration. Other authors have also described a weaker correlation between radiographic findings of osteoarthritis and arthroscopic findings of articular cartilage degeneration within the lateral compartment than within the medial compartment (4,10).

In our study, the use of all radiographic features of osteoarthritis together did not improve the ability of knee radiographs to depict the presence of articular cartilage degeneration within the tibiofemoral joint. Marginal osteophytes were the most sensitive individual radiographic feature for the detection of articular cartilage degeneration. The sensitivity of using any radiographic feature of osteoarthritis for the detection of articular cartilage degeneration within the medial and lateral compartments was almost identical to the sensitivity of using marginal osteophytes. This was because of the vast majority of patients in our study with joint space narrowing, subchondral sclerosis, or subchondral cysts who also had associated marginal osteophytes.

The major limitation of our study was the presence of selection bias. All patients in our study group were symptomatic and were selected from a database of MR examinations of the knee performed at our institution over the past several years. Furthermore, our patients with osteoarthritis had knee pain that was severe enough to warrant arthroscopic evaluation and intervention and thus were more likely to have advanced articular cartilage degeneration within the tibiofemoral joint. Because of inherent selection bias, our patient population represented only a small subset of individuals in our community with and without osteoarthritis of the tibiofemoral joint. It would be practically impossible, however, to design a study to investigate the usefulness of radiographic features of osteoarthritis that was free of selection bias if arthroscopic findings were chosen as the reference standard to determine the presence and severity of the disease process.

In conclusion, marginal osteophytes were the most sensitive radiographic feature for the detection of osteoarthritis of the tibiofemoral joint. Joint space narrowing, subchondral sclerosis, and subchondral cysts were less sensitive radiographic features of osteoarthritis and rarely occurred in the absence of associated osteophyte formation. Furthermore, these radiographic findings were most commonly seen in patients with advanced articular cartilage degeneration. The results of this study strongly suggest that osteoarthritis of the tibiofemoral joint should be diagnosed on the basis of marginal osteophytes and that the severity of the disease process should be assessed on the basis of joint space narrowing, subchondral sclerosis, and subchondral cysts.

	ADVANCES IN KNOWLEDGE

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 

• Marginal osteophytes are the most sensitive radiographic feature of osteoarthritis of the tibiofemoral joint.
  
• Joint space narrowing, subchondral sclerosis, and subchondral cysts are less sensitive radiographic features of osteoarthritis of the tibiofemoral joint and rarely occur in the absence of associated osteophyte formation.
  

	FOOTNOTES

 
Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, R.K., D.G.B., P.T.S.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of final version of submitted manuscript, all authors; literature research, R.K., D.G.B., P.T.S., A.A.D.S.; clinical studies, R.K., D.G.B., P.T.S., A.A.D.S.; statistical analysis, P.T.S., J.P.F.; and manuscript editing, R.K., D.G.B., P.T.S., A.A.D.S.

	References

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE References

 

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This Article Abstract Full Text (PDF) All Versions of this Article: 2393050584v1 239/3/818    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kijowski, R. Articles by De Smet, A. A. Search for Related Content PubMed PubMed Citation Articles by Kijowski, R. Articles by De Smet, A. A.