- Email: [email protected]
Comparison of Arthroscopic and Open Assessment of Size and Grade of Cartilage Defects of the Knee
Comparison of Arthroscopic and Open Assessment of Size and Grade of Cartilage Defects of the Knee Philipp Niemeyer, M.D., Jan M. Pestka, M.D., Christoph Erggelet, M.D., Matthias Steinwachs, M.D., Gian M. Salzmann, M.D., and Norbert P. Südkamp, M.D., Ph.D.
Purpose: The purpose of our study was to compare arthroscopic versus open measurement of cartilage defects and determination of defect grade according to the International Cartilage Repair Society (ICRS) classification. Methods: Arthroscopic determination of defect size and grade according to the ICRS classification of 450 focal cartilage defects in 407 patients who underwent autologous chondrocyte implantation was compared with definite findings at the time of open knee surgery. Results were analyzed based on defect location, defect size, and experience of the treating surgeon. Results: Open evaluation of all cartilage defects showed a mean size of 4.54 ⫾ 2.11 cm2, whereas arthroscopic determination resulted in a significantly larger mean defect size of 5.69 ⫾ 1.81 cm2 (P ⬍ .001, r ⫽ 0.757). This observation was found in all subgroups concerning defect location and experience of the treating surgeon (P ⬍ .001). Overestimation was pronounced among inexperienced surgeons (all P ⬍ .01) and in smaller defects (P ⬍ .01). Concerning grading of the defect according to the ICRS classification, there was a consensus in 80.9% of the cases when arthroscopic grading was compared with open grading. No differences were found based on defect location or experience of the treating surgeon (P ⬎ .05). Conclusions: Although a high correlation was found between arthroscopic and open evaluation of the cartilage defect size, there is a significant overestimation of the cartilage defect size during arthroscopy. This observation is independent of defect location. Smaller defects and inexperienced surgeons are factors that make an overestimation of defect size more likely. Arthroscopic detection and estimation of the full-thickness cartilage defects according to the ICRS classification seem reliable. Level of Evidence: Level IV, therapeutic case series.
A
ccurate determination of defect size and grade is an essential step in any cartilage repair technique such as autologous chondrocyte implantation (ACI),
From the Department of Orthopedic Surgery and Traumatology, Freiburg University Hospital (P.N., J.M.P., G.M.S., N.P.S.), Freiburg, Germany; Center for Biomechanics and Skeletal Biology, University Medical Center Hamburg-Eppendorf (J.M.P.), Hamburg, Germany; Center for Biologic Joint Surgery (C.E.), Zürich, Switzerland; and Department of Orthobiologics & Cartilage Regeneration, Schulthess-Klinik (M.S.), Zürich, Switzerland. Supported by a grant from the Freiburg University. The authors report no conflict of interest. Received September 28, 2009; accepted May 25, 2010. Address correspondence and reprint requests to Philipp Niemeyer, M.D., Department for Orthopedic Surgery and Traumatology, Freiburg University Hospital, Hugstetter Strasse 55, D-79095 Freiburg, Germany. E-mail: [email protected] © 2011 by the Arthroscopy Association of North America 0749-8063/9578/$36.00 doi:10.1016/j.arthro.2010.05.024
46
arthroscopic microfracturing, osteochondral transplantation, and others, because the appropriate indication for all these operative therapies depends on an accurate assessment of the existing defect.1-3 Before any subsequent surgical intervention to treat defective cartilage at the knee, arthroscopy of the joint cavity is normally conducted, during which defect size and grade are assessed to initialize further treatment. Therefore an accurate arthroscopic determination of the exact size and grade of the defect is of utmost importance. Concerning the indication for different cartilage repair techniques, there is consensus that only symptomatic full-thickness cartilage defects (grades III and IV according to International Cartilage Repair Society [ICRS] grading4) should be treated. At our institution, smaller lesions under a critical size of 4 cm2 are usually treated with arthroscopic microfracturing5 whereas defects of 4 cm2 or more are primarily treated
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 27, No 1 (January), 2011: pp 46-51
KNEE CARTILAGE DEFECTS with ACI by use of a cell-seeded collagen membrane for cell application.6 If the patient was treated with any kind of bone-stimulating technique before and it failed, the indication for ACI is given in defects measuring 2 cm2 or more. Osteochondral defects (which were not part of this study) are usually treated either with autologous osteochondral graft or with subchondral cancellous augmentation in combination with a cartilage repair technique such as ACI. This treatment algorithm basically conforms to the recommendations given by the national and international societies.1,2,7 For the German-Speaking Arthroscopic Society, 1,000 arthroscopies are mandatory to apply for the “instructorship.” Therefore a surgeon who has conducted more than 1,000 arthroscopies is considered an expert arthroscopist, whereas a surgeon who has not conducted more than 100 arthroscopies is considered inexperienced. Therefore, for the selection of adequate therapy, accurate determination of size and grade of a cartilage defect is essential. The purpose of this study was to determine whether there are differences in arthroscopic versus open assessment of cartilage defects. We hypothesized that cartilage defects would appear larger during arthroscopy than during open surgery. METHODS Between January 2002 and December 2008, a total of 1,452 patients were treated for cartilage defects at our institution. A majority of these patients were treated with arthroscopic microfracturing. This study includes 407 patients with 450 focal circumscribed cartilage defects of the knee joint who underwent ACI at our institution (defect locations are given in Table 1). In all patients, before arthroscopic treatment, a symptomatic full-thickness cartilage defect was found on magnetic resonance tomography. On the basis of this examination, arthroscopy of the affected knee was conducted. In every patient the indication for subsequent ACI was confirmed during this initial arthros-
TABLE 1.
Distribution of Cartilage Defects
Defect Location
No. of Cases
MFC LFC Patella Trochlea
195 38 158 59
Abbreviations: MFC, medial femoral condyle; LFC, lateral femoral condyle.
47
copy. Cartilage defect size and grade were determined by the treating surgeon. Whereas defect size was estimated by use of a scaled arthroscopic instrument with 5-mm increments, the grading of the defect was performed according to the ICRS classification.8 In brief, according to the ICRS classification, superficial lesions and superficial fissures and cracks are considered grade 1 cartilage defects whereas lesions extending down less than 50% of the cartilage depth are considered grade 2 defects. Grade 3 defects are defined as those extending down more than 50% but not involving the subchondral bone. Defects involving the subchondral bone are classified as grade 4 defects according to the ICRS classification.4 A cartilage biopsy specimen was taken from the intercondylar notch as described elsewhere.9 After in vitro expansion of the autologous chondrocytes, ACI was performed approximately 3 to 4 weeks after the initial arthroscopy through an arthrotomy of the index knee joint. Size and grade of the defective cartilage were again recorded within the open knee joint before and after debridement. Arthroscopic determination of defect grade and size was correlated with findings during the open ACI procedure and was compared by use of standard statistical instruments. In addition, depending on the treating surgeon’s experience, we evaluated who performed the initial arthroscopy. Surgeons were arbitrarily divided into 3 groups based on their arthroscopic experience. Surgeons who had performed fewer than 100 knee arthroscopies were considered inexperienced (6 surgeons), whereas those who had performed between 100 and 1,000 knee arthroscopies were considered experienced (2 surgeons) and those who had performed more than 1,000 knee arthroscopies were considered experts (3 surgeons). To compare the influence of defect size on precision of size determination, according to the defect size evaluated during open assessment, defects were grouped as follows: small defects, 4 cm2 or less; medium defects, greater than 4 cm2 but less than 6 cm2; and large defects, 6 cm2 or greater. Open assessment of the defect size and grade was considered the gold standard, because the defect is more accessible and measurement of the size is easier in an open setting. In this setting a ruler with 1-mm increments was used for accurate determination of the defect size. Statistical Analysis SPSS for Windows, version 17.0 (SPSS, Chicago, IL), was used for the statistical analysis. For statistical evaluation, Pearson correlation was calculated to de-
48
P. NIEMEYER ET AL.
tect correlations between arthroscopic and open findings in the study population and within subgroups depending on defect location and experience of the treating surgeon. To evaluate differences between different defect locations and levels of experience of the treating surgeons, data were checked for normality by use of the Kolmogorov-Smirnov test. After verification of normality, a paired Student t test for different locations was used to evaluate significant differences between arthroscopic and open assessment of cartilage defect size. To evaluate differences between the 3 different groups of surgeons, analysis of variance was performed. For both tests, P ⬍ .05 was considered significant and P ⬍ .001 was considered strongly significant. Power analysis concerning the comparison of size determination based on defect location and experience of the surgeon based on mean values, standard deviation, and sample size was conducted by use of OpenEpi software10 and showed a statistical power of more than 80% for all subgroups. In all boxplots shown in the figures, dots represent statistical outliers, while asterisks, in combination with bars, represent statistical significances in between different groups (P ⬍ .05). RESULTS The mean age of the patients treated in this study was 35.7 ⫾ 9.2 years. A total of 407 patients with 450 cartilage defects of the knee joint were included in the study. Of the patients, 365 presented with a single defect of the knee joint, 41 had 2 cartilage lesions, and 1 had 3 cartilage defects. The mean defect size as assessed during open surgery was 4.54 ⫾ 2.11 cm2, whereas arthroscopic estimation of defect size showed a significantly larger mean defect size of 5.69 ⫾ 1.81 cm2 (P ⬍ .001). Nevertheless, the overall Pearson coefficient for correlation was r ⫽ 0.757 (Fig 1). A significant overestimation of defect size during open assessment compared with arthroscopic size evaluation was found for all defect locations (all P ⬍ .001). Differences between open and arthroscopic assessment based on the defect location are given in Fig 1. Determination of defect location based on experience of the treating surgeon showed that in all groups of surgeons, defect size was overestimated during arthroscopy of the knee joint compared with defect size assessed during open surgery (P ⬍ .001 for all groups of surgeons). Comparison of accuracy between the different groups of surgeons showed inferiority in the accuracy for defect size determination in the subgroup of inexperienced surgeons (⬍100 knee arthroscopies)
FIGURE 1. No differences were found concerning the influence of defect location on arthroscopic (light gray) versus open (dark gray) size determination. (MFC, medial femoral condyle; LFC, lateral femoral condyle.)
(P ⫽ .006 v experienced surgeons and P ⬍ .001 v experts). Expert surgeons showed a non–statistically significant trend (P ⫽ .081) toward greater accuracy compared with experienced surgeons (Fig 2). According to the classification of defect size, a total of 233 defects were assigned to the small group whereas 171 defects were grouped as medium and 46 defects were considered large. When we analyzed the differences between open and arthroscopic determination of defect size, a significantly higher overestima-
FIGURE 2. Differences between arthroscopic (light gray) and open (dark gray) size determination based on experience of treating surgeon. In inexperienced surgeons a significant trend toward overestimating defect size was found compared with experienced surgeons and experts (P ⫽ .006 v experienced surgeons and P ⬍ .001 v experts). *P ⬍ .05.
KNEE CARTILAGE DEFECTS TABLE 2.
49 Arthroscopic Versus Open Grading of Cartilage Defects
Grade by ICRS Classification (Arthroscopic v Open) Location MFC LFC Patella Trochlea
Underestimation Correct Overestimation Overestimation by 1 Grade Grading by 1 Grade by 2 Grades 7 5 16 7
161 28 132 44
26 5 10 8
1 0 0 0
NOTE. Independent of defect location, there was a slight tendency to overestimate the cartilage defect grade during arthroscopy. An overestimation by 2 grades only occurred in 1 of 450 defects. Abbreviations: MFC, medial femoral condyle; LFC, lateral femoral condyle. FIGURE 3. Differences between arthroscopic and open size determination based on size of defect determined during open surgery. For a better comparison of the influence of defect size on accuracy of size determination, defect sizes were categorized as small (ⱕ4 cm2), medium (⬎4 cm2 but ⬍6 cm2), and large (ⱖ6 cm2). Significant differences were found between all groups compared by use of analysis of variance (P ⬍ .01 for all groups).
tion of defect size was found in small defects (mean overestimation, 1.64 cm2; SD, 1.05) compared with medium defects (mean overestimation, 0.91 cm2; SD, 1.15) and large defects (mean overestimation, ⫺0.36 cm2; SD, 2.22) (P ⬍ .01 for all comparisons between different groups of defect sizes). In the group of large defects, a tendency to underestimate defect size was thus found; nevertheless, standard deviation increased with defect size (Fig 3). Open versus arthroscopic grading of the severity of the defect according to the ICRS was evaluated separately. Because, during open surgery using ACI, debridement of the defect is performed, which allows a more detailed inspection, especially of the subchondral bone, this was taken as the “gold standard diagnosis.” Overall, in 80.9% of the cases the correct grade according to the ICRS classification was recognized during arthroscopic assessment of the cartilage defect. The Pearson correlation coefficient was r ⫽ 0.544. In the remaining 19.1% of cases in which there was a misdiagnosis, no trend concerning underestimation or overestimation was found (Table 2). Concerning the accuracy of grading based on defect location, in 82.6% of the lesions located on the medial femoral condyle, grading was correct. Percentages of correct grading in the remaining locations were 73.7% for the lateral femoral condyle, 83.5% for patella lesions, and 74.6% for defects located on the trochlea. No statistically significant differences were found. In those cases
of inaccurate grading, overestimation by 2 grades occurred in only 1 case, whereas in all other cases underestimation and overestimation occurred by 1 grade according to the ICRS classification (Table 2). No statistically significant differences were found in the accuracy of grading between expert, experienced, and inexperienced surgeons (83.0%, 79.1%, and 81.4%, respectively). DISCUSSION Accurate arthroscopic determination of defect size and grade is an important step in any cartilage reparative surgery, because indication and choice of technique applied in each individual patient generally depend on these 2 parameters.1-3 This study evaluates the reliability and accuracy of arthroscopic evaluation of 450 cartilage defects by comparing the arthroscopically estimated defect size and grade according to the ICRS classification with findings evaluated during open knee surgery at the time of ACI. In this study all defects underwent debridement related to the ACI procedure. Therefore the subchondral bone, which is relevant to discriminate between grade III and IV lesions, could be perfectly evaluated during open surgery. This was the reason for deciding to consider open assessment as the standard. This observation is also supported by a recent article by Spahn et al.,11 who describe an uncertainty concerning the appropriate assessment of cartilage defects evaluated by a survey among arthroscopic surgeons, although arthroscopy is considered the gold standard for diagnosis of cartilage defects by some other authors.12 In this study we observed a pattern of cartilage defect locations similar to other studies that reported that a majority of the
50
P. NIEMEYER ET AL.
defects were localized on the medial femoral condyle, followed by the patella.13 Concerning estimated defect size, arthroscopic evaluation led to a significantly larger estimated defect size when compared with open evaluation. On average, arthroscopically estimated sizes exceeded the real defect sizes by more than 1 cm2, which was more than 25% with regard to the mean defect size of 4.5 cm2. This observation supported our initial hypothesis. Similar trends for overestimation have also been described for the evaluation of defect size by use of magnetic resonance imaging.14 An additional question in our study was whether overestimation depends on defect location, which seemed possible because in some locations, such as the trochlea, a scaled instrument can be introduced parallel to the joint surface, which makes it easier to accurately measure the size of the defect. With regard to defect location, similar results were found in all 4 locations investigated (medial and lateral femoral condyle, trochlea, and patella). Interestingly, the trend for overestimation of defect size seems to be dependent on defect size. Whereas the difference between arthroscopic and open determination of the defect size seemed low in defects of 6 cm2 or larger, the difference between arthroscopic and open determination of defect size increased in defects measuring less than 6 cm2 and it even became more prominent in defects measuring less than 4 cm2. Nevertheless, there is a higher standard deviation for the group with large cartilage defects, which can be interpreted as follows: despite the trend showing that the mean size determination for all cartilage defects is satisfactory, the uncertainness of the surgeon increases analogous to defect size (Fig 3). In addition, our data concerning size determination with regard to the experience of the treating surgeon suggest that the experience of the treating surgeon significantly influences the accuracy of size determination in the evaluation of cartilage defects. In the group of inexperienced surgeons with fewer than 100 knee arthroscopies, the difference between arthroscopic and open estimation of defect size was significantly greater compared with more experienced surgeons (P ⫽ .006 v experienced surgeons and P ⬍ .001 v experts) (Fig 4). This observation argues convincingly that cartilage surgery should be performed by more experienced surgeons or at least in the presence of experienced surgeons, who are aware of the problems associated with arthroscopic determination of defect size. In contrast to our findings concerning estimated defect size, the arthroscopic determination of the grade of cartilage damage seems to be reliable and
FIGURE 4. Comparative size assessment based on defect location and size assessment with respect to surgeon experience. The y-axis shows arthroscopy minus open defect size in square centimeters. (MFC, medial femoral condyle; LFC, lateral femoral condyle.)
accurate. Interestingly, a validation study of the arthroscopic estimation of defect grade according to the ICRS classification has not yet been performed, although various studies have validated the ICRS scoring system for the arthroscopic assessment of cartilage repair tissue.15,16 Although this study was not designed to provide a comprehensive validation of arthroscopic evaluation of defect grade according to the ICRS classification, it provides interesting information. In more than 80% of the defects, the initial arthroscopically determined defect grade agreed with the open assessment of defect grade according to the ICRS classification. This observation was mainly independent of defect location and size. Furthermore, no significant influence of the experience of the treating surgeon was found. Nevertheless, this study has a severe limitation. Concerning the evaluation of arthroscopic determination of the defect grade, only those defects that were considered full-thickness defects were included in this study, because ACI was indicated in these patients. Discriminating between grade III and IV lesions is certainly more difficult than discriminating between full- and partial-thickness defects. This probably explains the low rate of correct diagnosis of only 80.9%. Furthermore, all patients underwent debridement of the defect during open knee surgery, because ACI was applied. This enables the surgeon to accurately analyze the involvement of the subchondral bone plate throughout the entire defect. In our opinion this can cause misdiagnosis. Involvement of the subchondral bone is probably more difficult to determine during arthroscopy in which no
KNEE CARTILAGE DEFECTS debridement at all is performed. In addition, with regard to this, the conclusions drawn about reliability and accuracy of grading are limited to those defects. Among those 450 defects considered “full thickness” during arthroscopy, only 1 case of a “partial-thickness” defect was found during open evaluation of the defect. This misdiagnosis has a potential influence regarding clinical treatment in terms of indications for the cartilage repair procedure, but the misdiagnosis would have changed the treatment plan in this study in only 1 of 450 cases. This low percentage of misinterpretation seems satisfactory; however, no conclusions can be drawn about any defects that were evaluated as “partial thickness” during arthroscopy, because these defects were not treated with ACI and therefore were not part of this study.
CONCLUSIONS Although a high correlation was found between arthroscopic and open evaluation of the cartilage defect size, there is a significant overestimation of the cartilage defect size during arthroscopy. This observation is independent of defect location. Smaller defects and inexperienced surgeons are factors that make an overestimation of defect size more likely. Arthroscopic detection and estimation of the full-thickness cartilage defects according to the ICRS classification seem reliable. REFERENCES 1. Behrens P, Bosch U, Bruns J, et al. Indications and implementation of recommendations of the working group “Tissue Regeneration and Tissue Substitutes” for autologous chondrocyte transplantation (ACT). Z Orthop Ihre Grenzgeb 2004;142:529539 (in German).
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2. Niemeyer P, Kreuz PC, Steinwachs M, Sudkamp NP. Operative treatment of cartilage lesions in the knee joint. Sportverletz Sportschaden 2007;21:41-50 (in German). 3. Steadman JR, Rodkey WG, Briggs KK. Microfracture to treat full-thickness chondral defects: Surgical technique, rehabilitation, and outcomes. J Knee Surg 2002;15:170-176. 4. Brittberg M, Peterson L, Sjogren-Jansson E, Tallheden T, Lindahl A. Articular cartilage engineering with autologous chondrocyte transplantation. A review of recent developments. J Bone Joint Surg Am 2003;85:109-115 (Suppl 3). 5. Steadman JR, Rodkey WG, Rodrigo JJ. Microfracture: Surgical technique and rehabilitation to treat chondral defects. Clin Orthop Relat Res 2001:S362-S369. 6. Steinwachs M. New technique for cell-seeded collagen matrixsupported autologous chondrocyte transplantation. Arthroscopy 2009;25:208-211. 7. Cole BJ, Pascual-Garrido C, Grumet RC. Surgical management of articular cartilage defects in the knee. J Bone Joint Surg Am 2009;91:1778-1790. 8. Brittberg M, Winalski CS. Evaluation of cartilage injuries and repair. J Bone Joint Surg Am 2003;85:58-69 (Suppl 2). 9. Niemeyer P, Pestka JM, Kreuz PC, et al. Standardized cartilage biopsies from the intercondylar notch for autologous chondrocyte implantation (ACI). Knee Surg Sports Traumatol Arthrosc 2010;18:1122-1127. 10. OpenEpi software. Available from: http://www.openepi.com/ Menu/OpenEpiMenu.htm. Accessed January 15, 2010. 11. Spahn G, Klinger HM, Hofmann GO. How valid is the arthroscopic diagnosis of cartilage lesions? Results of an opinion survey among highly experienced arthroscopic surgeons. Arch Orthop Trauma Surg 2009;129:1117-1121. 12. Figueroa D, Calvo R, Vaisman A, Carrasco MA, Moraga C, Delgado I. Knee chondral lesions: Incidence and correlation between arthroscopic and magnetic resonance findings. Arthroscopy 2007;23:312-315. 13. Widuchowski W, Widuchowski J, Trzaska T. Articular cartilage defects: Study of 25,124 knee arthroscopies. Knee 2007; 14:177-182. 14. Graichen H, Al-Shamari D, Hinterwimmer S, von EisenhartRothe R, Vogl T, Eckstein F. Accuracy of quantitative magnetic resonance imaging in the detection of ex vivo focal cartilage defects. Ann Rheum Dis 2005;64:1120-1125. 15. van den Borne MP, Raijmakers NJ, Vanlauwe J, et al. International Cartilage Repair Society (ICRS) and Oswestry macroscopic cartilage evaluation scores validated for use in autologous chondrocyte implantation (ACI) and microfracture. Osteoarthritis Cartilage 2007;15:1397-1402. 16. Smith GD, Taylor J, Almqvist KF, et al. Arthroscopic assessment of cartilage repair: A validation study of 2 scoring systems. Arthroscopy 2005;21:1462-1467.
Purpose: The purpose of our study was to compare arthroscopic versus open measurement of cartilage defects and determination of defect grade according to the International Cartilage Repair Society (ICRS) classification. Methods: Arthroscopic determination of defect size and grade according to the ICRS classification of 450 focal cartilage defects in 407 patients who underwent autologous chondrocyte implantation was compared with definite findings at the time of open knee surgery. Results were analyzed based on defect location, defect size, and experience of the treating surgeon. Results: Open evaluation of all cartilage defects showed a mean size of 4.54 ⫾ 2.11 cm2, whereas arthroscopic determination resulted in a significantly larger mean defect size of 5.69 ⫾ 1.81 cm2 (P ⬍ .001, r ⫽ 0.757). This observation was found in all subgroups concerning defect location and experience of the treating surgeon (P ⬍ .001). Overestimation was pronounced among inexperienced surgeons (all P ⬍ .01) and in smaller defects (P ⬍ .01). Concerning grading of the defect according to the ICRS classification, there was a consensus in 80.9% of the cases when arthroscopic grading was compared with open grading. No differences were found based on defect location or experience of the treating surgeon (P ⬎ .05). Conclusions: Although a high correlation was found between arthroscopic and open evaluation of the cartilage defect size, there is a significant overestimation of the cartilage defect size during arthroscopy. This observation is independent of defect location. Smaller defects and inexperienced surgeons are factors that make an overestimation of defect size more likely. Arthroscopic detection and estimation of the full-thickness cartilage defects according to the ICRS classification seem reliable. Level of Evidence: Level IV, therapeutic case series.
A
ccurate determination of defect size and grade is an essential step in any cartilage repair technique such as autologous chondrocyte implantation (ACI),
From the Department of Orthopedic Surgery and Traumatology, Freiburg University Hospital (P.N., J.M.P., G.M.S., N.P.S.), Freiburg, Germany; Center for Biomechanics and Skeletal Biology, University Medical Center Hamburg-Eppendorf (J.M.P.), Hamburg, Germany; Center for Biologic Joint Surgery (C.E.), Zürich, Switzerland; and Department of Orthobiologics & Cartilage Regeneration, Schulthess-Klinik (M.S.), Zürich, Switzerland. Supported by a grant from the Freiburg University. The authors report no conflict of interest. Received September 28, 2009; accepted May 25, 2010. Address correspondence and reprint requests to Philipp Niemeyer, M.D., Department for Orthopedic Surgery and Traumatology, Freiburg University Hospital, Hugstetter Strasse 55, D-79095 Freiburg, Germany. E-mail: [email protected] © 2011 by the Arthroscopy Association of North America 0749-8063/9578/$36.00 doi:10.1016/j.arthro.2010.05.024
46
arthroscopic microfracturing, osteochondral transplantation, and others, because the appropriate indication for all these operative therapies depends on an accurate assessment of the existing defect.1-3 Before any subsequent surgical intervention to treat defective cartilage at the knee, arthroscopy of the joint cavity is normally conducted, during which defect size and grade are assessed to initialize further treatment. Therefore an accurate arthroscopic determination of the exact size and grade of the defect is of utmost importance. Concerning the indication for different cartilage repair techniques, there is consensus that only symptomatic full-thickness cartilage defects (grades III and IV according to International Cartilage Repair Society [ICRS] grading4) should be treated. At our institution, smaller lesions under a critical size of 4 cm2 are usually treated with arthroscopic microfracturing5 whereas defects of 4 cm2 or more are primarily treated
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 27, No 1 (January), 2011: pp 46-51
KNEE CARTILAGE DEFECTS with ACI by use of a cell-seeded collagen membrane for cell application.6 If the patient was treated with any kind of bone-stimulating technique before and it failed, the indication for ACI is given in defects measuring 2 cm2 or more. Osteochondral defects (which were not part of this study) are usually treated either with autologous osteochondral graft or with subchondral cancellous augmentation in combination with a cartilage repair technique such as ACI. This treatment algorithm basically conforms to the recommendations given by the national and international societies.1,2,7 For the German-Speaking Arthroscopic Society, 1,000 arthroscopies are mandatory to apply for the “instructorship.” Therefore a surgeon who has conducted more than 1,000 arthroscopies is considered an expert arthroscopist, whereas a surgeon who has not conducted more than 100 arthroscopies is considered inexperienced. Therefore, for the selection of adequate therapy, accurate determination of size and grade of a cartilage defect is essential. The purpose of this study was to determine whether there are differences in arthroscopic versus open assessment of cartilage defects. We hypothesized that cartilage defects would appear larger during arthroscopy than during open surgery. METHODS Between January 2002 and December 2008, a total of 1,452 patients were treated for cartilage defects at our institution. A majority of these patients were treated with arthroscopic microfracturing. This study includes 407 patients with 450 focal circumscribed cartilage defects of the knee joint who underwent ACI at our institution (defect locations are given in Table 1). In all patients, before arthroscopic treatment, a symptomatic full-thickness cartilage defect was found on magnetic resonance tomography. On the basis of this examination, arthroscopy of the affected knee was conducted. In every patient the indication for subsequent ACI was confirmed during this initial arthros-
TABLE 1.
Distribution of Cartilage Defects
Defect Location
No. of Cases
MFC LFC Patella Trochlea
195 38 158 59
Abbreviations: MFC, medial femoral condyle; LFC, lateral femoral condyle.
47
copy. Cartilage defect size and grade were determined by the treating surgeon. Whereas defect size was estimated by use of a scaled arthroscopic instrument with 5-mm increments, the grading of the defect was performed according to the ICRS classification.8 In brief, according to the ICRS classification, superficial lesions and superficial fissures and cracks are considered grade 1 cartilage defects whereas lesions extending down less than 50% of the cartilage depth are considered grade 2 defects. Grade 3 defects are defined as those extending down more than 50% but not involving the subchondral bone. Defects involving the subchondral bone are classified as grade 4 defects according to the ICRS classification.4 A cartilage biopsy specimen was taken from the intercondylar notch as described elsewhere.9 After in vitro expansion of the autologous chondrocytes, ACI was performed approximately 3 to 4 weeks after the initial arthroscopy through an arthrotomy of the index knee joint. Size and grade of the defective cartilage were again recorded within the open knee joint before and after debridement. Arthroscopic determination of defect grade and size was correlated with findings during the open ACI procedure and was compared by use of standard statistical instruments. In addition, depending on the treating surgeon’s experience, we evaluated who performed the initial arthroscopy. Surgeons were arbitrarily divided into 3 groups based on their arthroscopic experience. Surgeons who had performed fewer than 100 knee arthroscopies were considered inexperienced (6 surgeons), whereas those who had performed between 100 and 1,000 knee arthroscopies were considered experienced (2 surgeons) and those who had performed more than 1,000 knee arthroscopies were considered experts (3 surgeons). To compare the influence of defect size on precision of size determination, according to the defect size evaluated during open assessment, defects were grouped as follows: small defects, 4 cm2 or less; medium defects, greater than 4 cm2 but less than 6 cm2; and large defects, 6 cm2 or greater. Open assessment of the defect size and grade was considered the gold standard, because the defect is more accessible and measurement of the size is easier in an open setting. In this setting a ruler with 1-mm increments was used for accurate determination of the defect size. Statistical Analysis SPSS for Windows, version 17.0 (SPSS, Chicago, IL), was used for the statistical analysis. For statistical evaluation, Pearson correlation was calculated to de-
48
P. NIEMEYER ET AL.
tect correlations between arthroscopic and open findings in the study population and within subgroups depending on defect location and experience of the treating surgeon. To evaluate differences between different defect locations and levels of experience of the treating surgeons, data were checked for normality by use of the Kolmogorov-Smirnov test. After verification of normality, a paired Student t test for different locations was used to evaluate significant differences between arthroscopic and open assessment of cartilage defect size. To evaluate differences between the 3 different groups of surgeons, analysis of variance was performed. For both tests, P ⬍ .05 was considered significant and P ⬍ .001 was considered strongly significant. Power analysis concerning the comparison of size determination based on defect location and experience of the surgeon based on mean values, standard deviation, and sample size was conducted by use of OpenEpi software10 and showed a statistical power of more than 80% for all subgroups. In all boxplots shown in the figures, dots represent statistical outliers, while asterisks, in combination with bars, represent statistical significances in between different groups (P ⬍ .05). RESULTS The mean age of the patients treated in this study was 35.7 ⫾ 9.2 years. A total of 407 patients with 450 cartilage defects of the knee joint were included in the study. Of the patients, 365 presented with a single defect of the knee joint, 41 had 2 cartilage lesions, and 1 had 3 cartilage defects. The mean defect size as assessed during open surgery was 4.54 ⫾ 2.11 cm2, whereas arthroscopic estimation of defect size showed a significantly larger mean defect size of 5.69 ⫾ 1.81 cm2 (P ⬍ .001). Nevertheless, the overall Pearson coefficient for correlation was r ⫽ 0.757 (Fig 1). A significant overestimation of defect size during open assessment compared with arthroscopic size evaluation was found for all defect locations (all P ⬍ .001). Differences between open and arthroscopic assessment based on the defect location are given in Fig 1. Determination of defect location based on experience of the treating surgeon showed that in all groups of surgeons, defect size was overestimated during arthroscopy of the knee joint compared with defect size assessed during open surgery (P ⬍ .001 for all groups of surgeons). Comparison of accuracy between the different groups of surgeons showed inferiority in the accuracy for defect size determination in the subgroup of inexperienced surgeons (⬍100 knee arthroscopies)
FIGURE 1. No differences were found concerning the influence of defect location on arthroscopic (light gray) versus open (dark gray) size determination. (MFC, medial femoral condyle; LFC, lateral femoral condyle.)
(P ⫽ .006 v experienced surgeons and P ⬍ .001 v experts). Expert surgeons showed a non–statistically significant trend (P ⫽ .081) toward greater accuracy compared with experienced surgeons (Fig 2). According to the classification of defect size, a total of 233 defects were assigned to the small group whereas 171 defects were grouped as medium and 46 defects were considered large. When we analyzed the differences between open and arthroscopic determination of defect size, a significantly higher overestima-
FIGURE 2. Differences between arthroscopic (light gray) and open (dark gray) size determination based on experience of treating surgeon. In inexperienced surgeons a significant trend toward overestimating defect size was found compared with experienced surgeons and experts (P ⫽ .006 v experienced surgeons and P ⬍ .001 v experts). *P ⬍ .05.
KNEE CARTILAGE DEFECTS TABLE 2.
49 Arthroscopic Versus Open Grading of Cartilage Defects
Grade by ICRS Classification (Arthroscopic v Open) Location MFC LFC Patella Trochlea
Underestimation Correct Overestimation Overestimation by 1 Grade Grading by 1 Grade by 2 Grades 7 5 16 7
161 28 132 44
26 5 10 8
1 0 0 0
NOTE. Independent of defect location, there was a slight tendency to overestimate the cartilage defect grade during arthroscopy. An overestimation by 2 grades only occurred in 1 of 450 defects. Abbreviations: MFC, medial femoral condyle; LFC, lateral femoral condyle. FIGURE 3. Differences between arthroscopic and open size determination based on size of defect determined during open surgery. For a better comparison of the influence of defect size on accuracy of size determination, defect sizes were categorized as small (ⱕ4 cm2), medium (⬎4 cm2 but ⬍6 cm2), and large (ⱖ6 cm2). Significant differences were found between all groups compared by use of analysis of variance (P ⬍ .01 for all groups).
tion of defect size was found in small defects (mean overestimation, 1.64 cm2; SD, 1.05) compared with medium defects (mean overestimation, 0.91 cm2; SD, 1.15) and large defects (mean overestimation, ⫺0.36 cm2; SD, 2.22) (P ⬍ .01 for all comparisons between different groups of defect sizes). In the group of large defects, a tendency to underestimate defect size was thus found; nevertheless, standard deviation increased with defect size (Fig 3). Open versus arthroscopic grading of the severity of the defect according to the ICRS was evaluated separately. Because, during open surgery using ACI, debridement of the defect is performed, which allows a more detailed inspection, especially of the subchondral bone, this was taken as the “gold standard diagnosis.” Overall, in 80.9% of the cases the correct grade according to the ICRS classification was recognized during arthroscopic assessment of the cartilage defect. The Pearson correlation coefficient was r ⫽ 0.544. In the remaining 19.1% of cases in which there was a misdiagnosis, no trend concerning underestimation or overestimation was found (Table 2). Concerning the accuracy of grading based on defect location, in 82.6% of the lesions located on the medial femoral condyle, grading was correct. Percentages of correct grading in the remaining locations were 73.7% for the lateral femoral condyle, 83.5% for patella lesions, and 74.6% for defects located on the trochlea. No statistically significant differences were found. In those cases
of inaccurate grading, overestimation by 2 grades occurred in only 1 case, whereas in all other cases underestimation and overestimation occurred by 1 grade according to the ICRS classification (Table 2). No statistically significant differences were found in the accuracy of grading between expert, experienced, and inexperienced surgeons (83.0%, 79.1%, and 81.4%, respectively). DISCUSSION Accurate arthroscopic determination of defect size and grade is an important step in any cartilage reparative surgery, because indication and choice of technique applied in each individual patient generally depend on these 2 parameters.1-3 This study evaluates the reliability and accuracy of arthroscopic evaluation of 450 cartilage defects by comparing the arthroscopically estimated defect size and grade according to the ICRS classification with findings evaluated during open knee surgery at the time of ACI. In this study all defects underwent debridement related to the ACI procedure. Therefore the subchondral bone, which is relevant to discriminate between grade III and IV lesions, could be perfectly evaluated during open surgery. This was the reason for deciding to consider open assessment as the standard. This observation is also supported by a recent article by Spahn et al.,11 who describe an uncertainty concerning the appropriate assessment of cartilage defects evaluated by a survey among arthroscopic surgeons, although arthroscopy is considered the gold standard for diagnosis of cartilage defects by some other authors.12 In this study we observed a pattern of cartilage defect locations similar to other studies that reported that a majority of the
50
P. NIEMEYER ET AL.
defects were localized on the medial femoral condyle, followed by the patella.13 Concerning estimated defect size, arthroscopic evaluation led to a significantly larger estimated defect size when compared with open evaluation. On average, arthroscopically estimated sizes exceeded the real defect sizes by more than 1 cm2, which was more than 25% with regard to the mean defect size of 4.5 cm2. This observation supported our initial hypothesis. Similar trends for overestimation have also been described for the evaluation of defect size by use of magnetic resonance imaging.14 An additional question in our study was whether overestimation depends on defect location, which seemed possible because in some locations, such as the trochlea, a scaled instrument can be introduced parallel to the joint surface, which makes it easier to accurately measure the size of the defect. With regard to defect location, similar results were found in all 4 locations investigated (medial and lateral femoral condyle, trochlea, and patella). Interestingly, the trend for overestimation of defect size seems to be dependent on defect size. Whereas the difference between arthroscopic and open determination of the defect size seemed low in defects of 6 cm2 or larger, the difference between arthroscopic and open determination of defect size increased in defects measuring less than 6 cm2 and it even became more prominent in defects measuring less than 4 cm2. Nevertheless, there is a higher standard deviation for the group with large cartilage defects, which can be interpreted as follows: despite the trend showing that the mean size determination for all cartilage defects is satisfactory, the uncertainness of the surgeon increases analogous to defect size (Fig 3). In addition, our data concerning size determination with regard to the experience of the treating surgeon suggest that the experience of the treating surgeon significantly influences the accuracy of size determination in the evaluation of cartilage defects. In the group of inexperienced surgeons with fewer than 100 knee arthroscopies, the difference between arthroscopic and open estimation of defect size was significantly greater compared with more experienced surgeons (P ⫽ .006 v experienced surgeons and P ⬍ .001 v experts) (Fig 4). This observation argues convincingly that cartilage surgery should be performed by more experienced surgeons or at least in the presence of experienced surgeons, who are aware of the problems associated with arthroscopic determination of defect size. In contrast to our findings concerning estimated defect size, the arthroscopic determination of the grade of cartilage damage seems to be reliable and
FIGURE 4. Comparative size assessment based on defect location and size assessment with respect to surgeon experience. The y-axis shows arthroscopy minus open defect size in square centimeters. (MFC, medial femoral condyle; LFC, lateral femoral condyle.)
accurate. Interestingly, a validation study of the arthroscopic estimation of defect grade according to the ICRS classification has not yet been performed, although various studies have validated the ICRS scoring system for the arthroscopic assessment of cartilage repair tissue.15,16 Although this study was not designed to provide a comprehensive validation of arthroscopic evaluation of defect grade according to the ICRS classification, it provides interesting information. In more than 80% of the defects, the initial arthroscopically determined defect grade agreed with the open assessment of defect grade according to the ICRS classification. This observation was mainly independent of defect location and size. Furthermore, no significant influence of the experience of the treating surgeon was found. Nevertheless, this study has a severe limitation. Concerning the evaluation of arthroscopic determination of the defect grade, only those defects that were considered full-thickness defects were included in this study, because ACI was indicated in these patients. Discriminating between grade III and IV lesions is certainly more difficult than discriminating between full- and partial-thickness defects. This probably explains the low rate of correct diagnosis of only 80.9%. Furthermore, all patients underwent debridement of the defect during open knee surgery, because ACI was applied. This enables the surgeon to accurately analyze the involvement of the subchondral bone plate throughout the entire defect. In our opinion this can cause misdiagnosis. Involvement of the subchondral bone is probably more difficult to determine during arthroscopy in which no
KNEE CARTILAGE DEFECTS debridement at all is performed. In addition, with regard to this, the conclusions drawn about reliability and accuracy of grading are limited to those defects. Among those 450 defects considered “full thickness” during arthroscopy, only 1 case of a “partial-thickness” defect was found during open evaluation of the defect. This misdiagnosis has a potential influence regarding clinical treatment in terms of indications for the cartilage repair procedure, but the misdiagnosis would have changed the treatment plan in this study in only 1 of 450 cases. This low percentage of misinterpretation seems satisfactory; however, no conclusions can be drawn about any defects that were evaluated as “partial thickness” during arthroscopy, because these defects were not treated with ACI and therefore were not part of this study.
CONCLUSIONS Although a high correlation was found between arthroscopic and open evaluation of the cartilage defect size, there is a significant overestimation of the cartilage defect size during arthroscopy. This observation is independent of defect location. Smaller defects and inexperienced surgeons are factors that make an overestimation of defect size more likely. Arthroscopic detection and estimation of the full-thickness cartilage defects according to the ICRS classification seem reliable. REFERENCES 1. Behrens P, Bosch U, Bruns J, et al. Indications and implementation of recommendations of the working group “Tissue Regeneration and Tissue Substitutes” for autologous chondrocyte transplantation (ACT). Z Orthop Ihre Grenzgeb 2004;142:529539 (in German).
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2. Niemeyer P, Kreuz PC, Steinwachs M, Sudkamp NP. Operative treatment of cartilage lesions in the knee joint. Sportverletz Sportschaden 2007;21:41-50 (in German). 3. Steadman JR, Rodkey WG, Briggs KK. Microfracture to treat full-thickness chondral defects: Surgical technique, rehabilitation, and outcomes. J Knee Surg 2002;15:170-176. 4. Brittberg M, Peterson L, Sjogren-Jansson E, Tallheden T, Lindahl A. Articular cartilage engineering with autologous chondrocyte transplantation. A review of recent developments. J Bone Joint Surg Am 2003;85:109-115 (Suppl 3). 5. Steadman JR, Rodkey WG, Rodrigo JJ. Microfracture: Surgical technique and rehabilitation to treat chondral defects. Clin Orthop Relat Res 2001:S362-S369. 6. Steinwachs M. New technique for cell-seeded collagen matrixsupported autologous chondrocyte transplantation. Arthroscopy 2009;25:208-211. 7. Cole BJ, Pascual-Garrido C, Grumet RC. Surgical management of articular cartilage defects in the knee. J Bone Joint Surg Am 2009;91:1778-1790. 8. Brittberg M, Winalski CS. Evaluation of cartilage injuries and repair. J Bone Joint Surg Am 2003;85:58-69 (Suppl 2). 9. Niemeyer P, Pestka JM, Kreuz PC, et al. Standardized cartilage biopsies from the intercondylar notch for autologous chondrocyte implantation (ACI). Knee Surg Sports Traumatol Arthrosc 2010;18:1122-1127. 10. OpenEpi software. Available from: http://www.openepi.com/ Menu/OpenEpiMenu.htm. Accessed January 15, 2010. 11. Spahn G, Klinger HM, Hofmann GO. How valid is the arthroscopic diagnosis of cartilage lesions? Results of an opinion survey among highly experienced arthroscopic surgeons. Arch Orthop Trauma Surg 2009;129:1117-1121. 12. Figueroa D, Calvo R, Vaisman A, Carrasco MA, Moraga C, Delgado I. Knee chondral lesions: Incidence and correlation between arthroscopic and magnetic resonance findings. Arthroscopy 2007;23:312-315. 13. Widuchowski W, Widuchowski J, Trzaska T. Articular cartilage defects: Study of 25,124 knee arthroscopies. Knee 2007; 14:177-182. 14. Graichen H, Al-Shamari D, Hinterwimmer S, von EisenhartRothe R, Vogl T, Eckstein F. Accuracy of quantitative magnetic resonance imaging in the detection of ex vivo focal cartilage defects. Ann Rheum Dis 2005;64:1120-1125. 15. van den Borne MP, Raijmakers NJ, Vanlauwe J, et al. International Cartilage Repair Society (ICRS) and Oswestry macroscopic cartilage evaluation scores validated for use in autologous chondrocyte implantation (ACI) and microfracture. Osteoarthritis Cartilage 2007;15:1397-1402. 16. Smith GD, Taylor J, Almqvist KF, et al. Arthroscopic assessment of cartilage repair: A validation study of 2 scoring systems. Arthroscopy 2005;21:1462-1467.