Short-term Clinical Importance of Osseous Injuries Diagnosed at MR Imaging in Patients with Anterior Cruciate Ligament Tear 1

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1 Note: This copy is for your personal non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at Richard Kijowski, MD Mamadou L. Sanogo, MD Kenneth S. Lee, MD Alejandro Muñoz del Río, PhD Tim A. McGuine, PhD Geoffrey S. Baer, MD Ben K. Graf, MD Arthur A. De Smet, MD Short-term Clinical Importance of Osseous Injuries Diagnosed at MR Imaging in Patients with Anterior Cruciate Ligament Tear 1 Purpose: Materials and Methods: To determine the association between osseous injuries and short-term clinical outcome in patients with anterior cruciate ligament (ACL) tear. The retrospective study was performed with institutional review board approval, and the requirement to obtain informed consent was waived. The study group consisted of 114 patients (57 male and 57 female patients with a mean age of 26.1 and 25.1 years, respectively) with ACL tear who underwent magnetic resonance (MR) imaging and ACL reconstruction surgery and who filled out International Knee Documentation Committee (IKDC) knee evaluation questionnaires before and 1 year after surgery. All MR images were independently reviewed by two radiologists to determine the presence of a cortical depression fracture on each surface of the knee joint. Bone marrow edema volume was quantified by using segmentation software. Correlation coefficients were used to determine the association between bone marrow edema volume and IKDC score. A multivariate analysis model was used to compare IKDC scores in patients without fracture, patients with a single fracture, and patients with multiple fractures. Original Research n Musculoskeletal Imaging Results: Conclusion: There was no significant association between total bone marrow edema volume and preoperative or postoperative IKDC score (P =.32 and P =.91, respectively). The mean preoperative and postoperative IKDC scores were and , respectively, for patients without fracture, and for patients with a single fracture, and and for patients with multiple fractures. Patients with single and multiple fractures had similar (P =.91) preoperative IKDC scores but significantly lower (P,.001) postoperative IKDC scores compared to patients without fracture. Cortical depression fractures in patients with ACL tear are associated with decreased clinical outcome scores 1 year after ACL reconstruction surgery. 1 From the Departments of Radiology (R.K., M.L.S., K.S.L., A.M.d.R., A.A.D.S.) and Orthopedic Surgery (T.A.M., G.S.B., B.K.G.), University of Wisconsin School of Medicine and Public Health, 600 Highland Ave, Clinical Science Center- E3/311, Madison, WI Received October 11, 2011; revision requested November 12; revision received January 18, 2012; accepted February 8; final version accepted March 6. Address correspondence to R.K. ( r.kijowski@hosp.wisc.edu). q RSNA, 2012 Supplemental material: /suppl/doi: /radiol /-/dc1 q RSNA, 2012 Radiology: Volume 264: Number 2 August 2012 n radiology.rsna.org 531

2 Anterior cruciate ligament (ACL) tears are a common sports-related injury (1). Osseous injuries frequently occur in patients with ACL tear and are typically due to the pivot shift mechanism when a valgus load is applied to the knee joint with the tibia in external rotation or the femur in internal rotation (2 7). Disruption of the ACL leads to anterior subluxation of the tibia with impaction of the anterior lateral femoral condyle against the posterior lateral tibial plateau (2 7). Osseous injuries to the posterior medial tibial plateau may also occur due to contrecoup forces on the medial compartment during resolution of the valgus load (8). The articular cartilage overlying areas of osseous injury in patients with ACL tear typically appears normal at magnetic resonance (MR) imaging and arthroscopy (3,5,9,10). However, biochemical changes of acute cartilage injury have been detected at histologic analysis (11) and with use of advanced MR imaging techniques such as delayed gadolinium-enhanced imaging (12) and T1r imaging (13,14). The clinical significance of osseous injuries in patients with ACL tear remains unknown. Bone marrow edema eventually resolves with a median interval of 4 8 months (5,15 20). However, persistent morphologic (5,16,19) and biochemical (21,22) changes in Advances in Knowledge nn Fractures are common in patients with anterior cruciate ligament (ACL) tear and are significantly associated (P,.001) with larger volumes of underlying bone marrow edema. nn Cortical depression fractures in patients with ACL tear are significantly associated (P,.001) with worse clinical outcome scores 1 year after ACL reconstruction surgery. nn Cortical depression fractures in patients with ACL tear are significantly associated (P,.05) with meniscal tears in the same knee compartment. the overlying articular cartilage have been reported in patients months to years following ACL injury. Few previous studies have investigated the relationship between osseous injuries and clinical symptoms in patients with ACL tear (9,23,24). For this reason, it is unknown whether these injuries are benign and self-limiting or whether they represent a potential source of persistent pain and disability. Thus, this study was performed to determine the association between osseous injuries and short-term clinical outcome in patients with ACL tear. Materials and Methods Study Group Our retrospective study was in compliance with Health Insurance Portability and Accountability Act regulations and was approved by our institutional review board. The requirement to obtain informed consent was waived. The study group was selected from a sports medicine research database that included all patients undergoing knee surgery at our institution between May 1, 2008, and May 1, The database contained records from 240 consecutive patients (121 male patients aged years [mean age, 26.5 years] and 119 female patients aged years [mean age, 25.7 years]) who underwent ACL reconstruction surgery during this period. All 240 patients filled out an International Knee Documentation Committee (IKDC) knee evaluation questionnaire (25) before undergoing ACL reconstruction surgery. One hundred seventy-three patients also filled out an IKDC knee evaluation questionnaire 1 year after ACL reconstruction surgery. All IKDC questionnaires were administered by a sports medicine research coordinator (T.A.M.) who was Implication for Patient Care nn Detection of cortical depression fractures in patients with ACL tear on preoperative MR images may help identify patients at increased risk of having a suboptimal clinical outcome 1 year after ACL reconstruction surgery. blinded to the MR imaging and surgical findings of all patients. The medical records of the 173 patients who prospectively filled out IKDC knee evaluation questionnaires before and 1 year after ACL reconstruction surgery were reviewed by a radiology research assistant (M.L.S.) who was blinded to the MR imaging and surgical findings, to determine whether patients met the following inclusion criteria for the study: (a) documented history of acute knee injury; (b) no history of previous knee trauma or surgery; (c) body mass index of less than 30; (d) MR examination performed at our institution within 3 weeks of knee injury; (e) ACL reconstruction surgery performed at our institution within 3 months of knee injury; (f) no additional ligament injury necessitating surgical treatment diagnosed by using a combination of MR imaging, examination under anesthesia, and arthroscopy; (g) no complications following surgery; and (h) no history of repeat knee injury following surgery. One hundred fourteen patients (57 male patients aged years [mean age, 26.1 years] and 57 female patients aged years [mean age, 25.1 years]) met these inclusion criteria and were included in the study group. MR Examination All 114 patients in the study group underwent MR examination of the knee Published online before print /radiol Content code: Radiology 2012; 264: Abbreviations: ACL = anterior cruciate ligament IKDC = International Knee Documentation Committee Author contributions: Guarantors of integrity of entire study, R.K., G.S.B.; study concepts/study design or data acquisition or data analysis/ interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, R.K., M.L.S., K.S.L.; clinical studies, R.K., M.L.S., K.S.L., G.S.B., B.K.G., A.A.D.S.; statistical analysis, A.M.d.R., T.A.M., A.A.D.S.; and manuscript editing, R.K., K.S.L., A.M.d.R., G.S.B., B.K.G., A.A.D.S. Potential conflicts of interest are listed at the end of this article. 532 radiology.rsna.org n Radiology: Volume 264: Number 2 August 2012

3 within 3 weeks of their knee injury (range, 1 20 days; mean 6 standard deviation, 12.2 days 6 5.6). All MR examinations were performed with the same 1.5- or 3.0-T MR unit (Signa HDx; GE Healthcare, Waukesha, Wis) by using an eight-channel phased-array extremity coil (Precision Eight TX/TR High Resolution Knee Array; Invivo, Orlando, Fla). Seventy patients were imaged at 1.5 T and 44 were imaged at 3.0 T. MR examinations consisted of an axial frequency-selective fatsuppressed T2-weighted fast spin-echo sequence, a coronal intermediateweighted fast spin-echo sequence, a coronal frequency-selective fatsuppressed intermediate-weighted fast spin-echo sequence, a sagittal intermediate-weighted fast spin-echo sequence, and a sagittal frequency-selective fat-suppressed T2-weighted fast spin-echo sequence. Imaging parameters are summarized in Table 1. Arthroscopic Knee Surgery All 114 patients in the study group underwent ACL reconstruction surgery at our institution within 3 months of their knee injury (range, days; mean, 39.3 days ). All surgical procedures were performed by one of three orthopedic surgeons (G.S.B. [surgeon 1], B.K.G. [surgeon 2], and a nonauthor [surgeon 3], with 5, 26, and 30 years of clinical experience, respectively) who specialized in sports medicine and who were aware of the MR imaging findings for all patients at the time of surgery. During ACL reconstruction surgery, the surgeons documented the presence or absence of medial and lateral meniscal tears and graded each articular surface of the knee joint with use of the Noyes classification system (26). The surgeons also assessed the ligaments of the knee joint by using a combination of MR imaging, examination under anesthesia, and arthroscopy. ACL reconstruction surgery was performed by using a bone patellar tendon bone graft in 58 patients and a hamstring tendon graft in 56. All patients underwent similar rehabilitation regimens following ACL reconstruction surgery, and these regimens are described in Appendix E1 (online). Review of Medical Records The medical records of all 240 patients in the sports medicine research database who underwent ACL reconstruction surgery at our institution were reviewed by the radiology research assistant, who was blinded to the MR imaging and surgical findings. The following information was recorded for each patient: (a) age, (b) sex, (c) body mass index, (d) injured knee, (e) surgeon who performed the procedure, (f) type of ACL graft, (g) preoperative IKDC score, (h) postoperative IKDC score, (i) presence of medial and lateral meniscus tear at surgery, and Table 1 MR Imaging Parameters Parameter Axial Fat-suppressed T2-weighted Fast Spin-Echo Sequence Coronal Intermediateweighted Fast Spin-Echo Sequence Coronal Fat-suppressed Intermediate-weighted Fast Spin-Echo Sequence Sagittal Intermediateweighted Fast Spin-Echo Sequence Sagittal Fat-suppressed T2-weighted Fast Spin-Echo Sequence Repetition time (msec) 1.5 T T Echo time (msec) 1.5 T T Matrix size 1.5 T T Field of view (cm) 1.5 T T Section thickness (mm) 1.5 T T Bandwidth (khz) 1.5 T T Echo train length 1.5 T T No. of signals acquired 1.5 T T Radiology: Volume 264: Number 2 August 2012 n radiology.rsna.org 533

4 (j) Noyes cartilage grade on each articular surface of the knee joint at surgery. A cartilage score was used to determine the overall severity of cartilage degeneration within the knee joint for each patient. Cartilage lesions of Noyes grades 1A, 1B, 2A, 2B, 3A, and 3B were given numerical values of 1, 2, 3, 4, 5, and 6, respectively. The cartilage score was calculated by summing the numerical values of the grades of the cartilage lesions seen on each articular surface of the knee joint. Review of MR Images The MR images from all 114 patients in the study group were independently reviewed by two fellowship-trained musculoskeletal radiologists who were blinded to the clinical and surgical findings (R.K. and K.S.L., with 10 and 7 years of clinical experience, respectively). The radiologists determined the presence or absence of a fracture on each surface of the knee joint. When a fracture was present, the radiologists classified it as a trabecular fracture or a cortical depression fracture. A trabecular fracture was defined as a line of low T1 and T2 signal intensity extending from the cortex into the trabecular bone with surrounding bone marrow edema (27). A cortical depression fracture was defined as compressed cortical bone with or without cortical discontinuity (27). When a cortical depression fracture was present, the radiologists further classified the fracture as articular or nonarticular depending on whether the compressed cortical bone involved the articular surface. When the two radiologists disagreed about the presence or absence of a fracture or the type of fracture, a third fellowship-trained musculoskeletal radiologist (A.A.D.S., with 30 years of clinical experience), who was blinded to the clinical and surgical findings of all patients, reviewed the MR images to help make the final interpretation. Quantitative Assessment of Bone Marrow Edema Volume The volume of bone marrow edema on each surface of the knee joint on the MR images of all 114 patients in the study group was measured by using segmentation software (GE Healthcare). Regions of interest were placed around areas of bone marrow edema on the sagittal fat-suppressed T2-weighted fast spin-echo images. Signal intensity thresholds were used to remove areas of residual fat signal from the regions of interest to provide more accurate measurements of reticular patterns of bone marrow edema. The total volume of bone marrow edema on each surface was calculated by summing the volumes of the regions of interest on all images through the surface. Bone marrow edema volume measurements were performed by the radiology research assistant under the supervision of a fellowship-trained musculoskeletal radiologist (R.K., with 10 years of clinical experience); both investigators were blinded to the clinical and surgical findings of all patients. At a separate sitting, repeat bone marrow edema volume measurements were performed independently by the research assistant and musculoskeletal radiologist in 10 randomly chosen patients. Statistical Analysis All statistical analyses were performed by using the R programming environment (version 2.3.1, R Foundation of Statistical Imaging, Vienna, Austria; For all statistical tests, differences were considered statistically significant if the P value was less than.05. Exploratory and residual plots were obtained to assess possible violations in test assumptions. Statistical analysis was used to determine whether there was bias between the 114 patients in the study group and the 126 patients identified in the sports medicine research database who underwent ACL reconstruction at our institution but were not included in the study group. The Student t test was used to compare both groups of patients with regard to the age of the male and female patients, body mass index, preoperative IKDC score, postoperative IKDC score, and cartilage score. The Fisher exact test was used to compare both groups of patients with regard to sex, affected knee (right or left), orthopedic surgeon who performed the reconstruction, type of graft (bone patellar tendon bone vs hamstring tendon), and presence of medial and lateral mensical tears. The k statistic was used to assess interobserver agreement between radiologists for determining the presence or absence of a fracture and for classifying the type of fracture on each surface of the knee joint for the 114 patients in the study group. Bland-Altman analysis was used to measure interobserver agreement between the radiology research assistant and radiologist in the measurement of bone marrow edema volume and the intraobserver agreement of the radiology research assistant in the measurement of bone marrow edema volume twice at separate sittings for the 10 randomly chosen patients in the study group. Pearson product moment correlation coefficients were used to determine the association between the preoperative and postoperative IKDC scores and the volume of bone marrow edema on each surface and on all surfaces of the knee joint. Analysis of covariance tests were used to create a multivariate model to compare preoperative and postoperative IKDC scores in patients without fracture, those with a single fracture, and those with multiple fractures. The multivariate model included other demographic and surgical factors that may influence IKDC score, including the age and sex of the patient, type of ACL graft, orthopedic surgeon who performed the procedure, presence of a single meniscal tear or multiple meniscal tears, and cartilage score. If a statistically significant difference between groups was identified, pairwise comparisons were then used to compare the IKDC scores for patients without fracture and those with a single fracture, patients without fracture and those with multiple fractures, and patients with a single fracture and those with multiple fractures. Analysis of covariance was used to determine if there was an association between each variable included in the multivariate model and the preoperative and postoperative IKDC score. The multivariate model was performed only in patients with 534 radiology.rsna.org n Radiology: Volume 264: Number 2 August 2012

5 Figure 1 Figure 1: Bland-Altman plots show (a) inter- and (b) intraobserver agreement for the measurement of bone marrow edema volume on 20 surfaces in 10 randomly chosen patients with ACL tear. Only surfaces of knee joint with bone marrow edema were assessed. Dotted line = bias, dashed lines = 95% limits of agreement. cortical depression fractures because of the small number of patients in the study group with trabecular fractures and the potentially different influences of trabecular and cortical depression fractures on IKDC scores. One-way analysis of variance tests were used to determine the association between the presence of a trabecular or cortical depression fracture and the volume of bone marrow edema on each surface of the knee joint. Oneway analysis of variance tests were also used to determine the association between the presence of a meniscal tear and the volume of bone marrow edema within each compartment of the knee joint. Fisher exact tests were used to determine the association between the presence of a meniscal tear and the presence of a cortical depression fracture within each compartment of the knee joint. Statistical analysis was not used to determine the association between the presence of a meniscal tear and the presence of a trabecular fracture because of the small number of patients in the study group with trabecular fractures. Results There was no statistically significant difference between patients in the study group and patients identified in the sports medicine research database who were not included in the study group with regard to the age of male patients (study group: age range = years, mean age = 26.1 years; nonstudy group: age range = years, mean age = 26.4 years; P =.86) or female patients (study group: age range = years, mean age = 25.1 years; nonstudy group: age range = years, mean age = 25.9 years; P =.72), body mass index (mean body mass index of 23.1 for the study group and 23.5 for the nonstudy group; P =.73), preoperative IKDC score (mean score of 51.5 for the study group and 53.8 for the nonstudy group; P =.40), postoperative IKDC score (mean score of 83.4 for the study group and 85.6 for the nonstudy group; P =.31), and cartilage score (mean score of 1.2 for the study group and 1.3 for the nonstudy group; P =.76). There was also no significant difference between the two groups with regard to the number of male and female patients (57 male and 57 female patients in the study group and 64 male and 62 female patients in the nonstudy group; P =.50), the knee involved with ACL tear (60 right and 54 left knee injuries for the study group and 73 right and 53 left knee injuries for the nonstudy group; P =.43), the orthopedic surgeon who performed the ACL reconstruction surgery (24, 63, and 27 patients in the study group were treated by surgeons 1, 2, and 3, respectively, and 26, 75, and 25 patients in the nonstudy group were treated by for surgeons 1, 2, and 3; P =.49), type of graft (58 and 56 patients in the study group had bone patellar tendon bone and hamstring tendon grafts, respectively, and 65 and 61 patients in the nonstudy group had bone patellar tendon bone and hamstring tendon grafts; P =.51), patients with medial meniscal tears (34 patients in the study group and 41 in the nonstudy group; P =.68), and patients with lateral meniscal tears (51 patients in the study group and 55 in the nonstudy group; P =.89). At arthroscopic surgery, 34 patients in the study group were found to have medial meniscal tears, 51 were found to have lateral meniscal tears, 16 were found to have both medial and lateral meniscal tears, and 48 were found to have at least one cartilage lesion within the knee joint. Twenty-two patients were found to have partial-thickness medial collateral ligament tears, all of which were treated conservatively. No patient was found to have a posterior cruciate ligament tear or lateral collateral ligament tear. There was high interobserver agreement between radiologists for determining the presence or absence of a fracture (k = 0.82, standard error = 0.11) and for classifying the type of fracture (k = 0.75, standard error = 0.10). There was high inter- and intraobserver Radiology: Volume 264: Number 2 August 2012 n radiology.rsna.org 535

6 Table 2 Figure 3 Distribution of Fractures in Patients with ACL Tear Articular Surface Trabecular Fracture Articular Cortical Depression Nonarticular Cortical Depression Patella Femoral trochlea Medial femoral condyle Lateral femoral condyle Medial tibial plateau Lateral tibial plateau Note. Data are numbers of patients. Figure 2 Figure 3: Sagittal fat-suppressed T2-weighted fast spin-echo MR image of knee in 17-year-old girl with ACL tear. Preoperative IKDC score was 55.4, and postoperative IKDC score was There is articular cortical depression fracture on anterior lateral femoral condyle (small arrow) and nonarticular cortical depression fracture on posterior lateral tibial plateau (large arrow) with surrounding bone marrow edema (arrowheads). Figure 2: MR images of knee in 34-year-old man with ACL tear. Preoperative IKDC score was 67.1, and postoperative IKDC score was (a) Sagittal intermediate-weighted fast spin-echo image shows articular cortical depression fracture on posterior medial tibial plateau (arrow). (b) Corresponding sagittal fat-suppressed T2-weighted fast spin-echo image shows articular cortical depression fracture on posterior medial tibial plateau (small arrow) with surrounding bone marrow edema (arrowhead). Also note increased signal intensity within overlying articular cartilage of medial tibial plateau (large arrow), which is suggestive of acute injury. agreement for measuring bone marrow edema volume (Fig 1). One hundred nine of the 114 patients in the study group (96%) had bone marrow edema on at least one surface of the knee joint. Thirty patients had bone marrow edema on the medial femoral condyle, 88 had bone marrow edema on the lateral femoral condyle, 57 had bone marrow edema on the medial tibial plateau, and 106 had bone marrow edema on the lateral tibial plateau. No patients had bone marrow edema on the patella or femoral trochlea. Eighty-one of the 114 patients in the study group (71%) had at least one fracture within the knee joint. Forty-seven patients had one fracture, 27 had two fractures, and seven had three fractures. Forty-one patients had fractures on the anterior lateral femoral condyle, 18 had fractures on the posterior medial tibial plateau, and 63 had fractures on the posterior lateral tibial plateau. Eight-one patients had cortical depression fractures. Only six patients had trabecular fractures, and all of these individuals had cortical depression fractures on other surfaces of the knee joint (Table 2). There was no significant association between the preoperative and postoperative IKDC scores and the total volume of bone marrow edema within the knee joint (r = 0.11, P =.32 for preoperative IKDC score; r = 20.01, P =.91 for postoperative IKDC score). The mean preoperative and postoperative IKDC scores were 53.4 (range, ; standard deviation, 18.6) and 93.0 (range, ; standard deviation, 5.0), respectively, for patients without fracture, 54.8 (range, ; standard deviation, 13.6) and 87.3 (range, ; standard deviation, 10.8) for patients with a single cortical depression fracture, and 53.1 (range, ; standard deviation, 17.2) and 83.4 (range, ; standard deviation, 12.7) for patients with multiple cortical depression fractures (Figs 2 5 ). The mean preoperative and postoperative IKDC score for the six patients with multiple fractures who had a combination of trabecular and cortical depression fractures was 53.6 (range, ; standard deviation, 21.2) and 83.2 (range, ; standard deviation, 14.2), respectively. 536 radiology.rsna.org n Radiology: Volume 264: Number 2 August 2012

7 Figure 4 Figure 4: MR images of knee in 19-year-old woman with ACL tear. Preoperative IKDC score was 65.6, and postoperative IKDC score was (a) Sagittal intermediate-weighted fast spin-echo image shows articular cortical depression fracture on posterior lateral tibial plateau consisting of a fractured piece of articular cartilage (small arrow) with mild depression of underlying cortical bone (large arrow). (b) Corresponding sagittal fat-suppressed T2-weighted fast spin-echo image shows an articular cortical depression fracture on posterior lateral tibial plateau consisting of a fractured piece of articular cartilage (small arrow) with mild depression of the underlying cortical bone (large arrow). Also note bone marrow edema (arrowheads) within posterior lateral tibial plateau and anterior lateral femoral condyle. (c) Sagittal fat-suppressed T2-weighted fast spin-echo image shows articular cortical depression fracture on anterior lateral femoral condyle (arrow) with bone marrow edema (arrowheads) within anterior lateral femoral condyle and posterior lateral tibial plateau. There was no significant difference in preoperative IKDC scores (P =.91) but a significant difference in postoperative IKDC scores (P,.001) between patients without fracture, patients with a single cortical depression fracture, and patients with multiple cortical depression fractures. Pairwise analysis also showed a significant difference in the postoperative IKDC scores between patients without fracture and those with a single cortical depression fracture (P =.02) and between patients without fracture and those with multiple cortical depression fractures (P,.001). However, there was no significant difference in the postoperative IKDC scores between patients with a single cortical depression fracture and those with multiple cortical depression fractures (P =.44). Analysis of covariance showed a significant association between the postoperative IKDC score and the presence of cortical depression fracture (P,.001) and the surgeon who performed the procedure (P =.03). There was no significant association between the other variables included in the Figure 5 Figure 5: MR images of knee in 25-year-old man with ACL tear. Preoperative IKDC score was 88.7, and postoperative IKDC score was (a) Sagittal fat-suppressed T2-weighted fast spin-echo image of knee shows articular cortical depression fracture on anterior lateral femoral condyle (small thin arrow) and nonarticular cortical depression fracture on posterior lateral tibial plateau (large thin arrow) with surrounding bone marrow edema (arrowheads). Also note increased signal intensity within overlying articular cartilage of lateral tibial plateau (large thick arrow), which is suggestive of acute injury. (b) Sagittal fat-suppressed T2-weighted fast spin-echo image shows articular cortical depression fracture of posterior medial tibial plateau (arrow) with surrounding bone marrow edema (arrowhead). multivariate model and the preoperative and postoperative IKDC scores (Table 3) (P =.18.96). There was a significant association (P,.001) between the presence of a fracture and a larger volume of bone Radiology: Volume 264: Number 2 August 2012 n radiology.rsna.org 537

8 Table 3 Association between Preoperative and Postoperative IKDC Score and Each Variable Included in the Multivariate Analysis Model for the 108 Patients in the Study Group with ACL Tear Who Had No Fracture, a Single Cortical Depression Fracture, and Multiple Cortical Depression Fractures Variable Preoperative IKDC Score Postoperative IKDC Score Cortical depression fracture*.91,.001 Age Sex Graft type Surgeon Meniscal tear # Cartilage score** Note. Data are P values. * Thirty-three patients had no fracture, 47 had a single fracture, and 28 had multiple fractures. Patients ranged in age from 16 to 50 years (mean, 25.6 years ). There were 55 male and 53 female patients. Fifty-four patients received a bone patellar tendon bone graft and 54 received a hamstring tendon graft. Twenty-three patients were treated by surgeon 1, 60 by surgeon 2, and 25 by surgeon 3. # Forty-four patients had no tear, 46 had one tear, and 18 had two tears. ** Cartilage score ranged from 0 to 9 (mean score, ). marrow edema on each surface of the knee joint, which was consistent for both trabecular and cortical depression fractures. There was no significant association between the presence of a medial meniscus tear and the volume of bone marrow edema within the medial compartment of the knee joint (P =.12) or between the presence of a lateral meniscal tear and the volume of bone marrow edema volume within the lateral compartment of the knee joint (P =.23). Medial meniscal tears were present in one of the five patients with a trabecular fracture, eight of the 13 patients with a cortical depression fracture, and 25 of the 96 patients without fracture on the medial tibial plateau. Lateral meniscal tears were not present in the patient with a trabecular fracture but were seen in 24 of 40 patients with a cortical depression fracture and 27 of 73 patients without fracture on the lateral femoral condyle. Lateral meniscal tears were present in 33 of 63 patients with a cortical depression fracture and 18 of 51 patients without fracture on the lateral tibial plateau. There was a significant association between the presence of a medial meniscal tear and a cortical depression fracture on the medial tibial plateau (P =.01) and between the presence of a lateral meniscal tear and a cortical depression fracture on the lateral femoral condyle (P =.03). There was only a marginally significant association (P =.09) between the presence of a lateral meniscal tear and a cortical depression fracture on the lateral tibial plateau. Discussion Osseous injuries in patients with ACL tear represent a spectrum of abnormalities identified on MR images. The most common finding is bone marrow edema, which was seen in 96% of patients in our study and in 68% 98% of patients in previous studies (2 4,9,27). Areas of bone marrow edema or bone bruises are believed to represent trabecular microfractures (6) and correspond to areas of significantly elevated water and unsaturated lipid content and significantly decreased saturated lipid content at MR spectroscopy (13). Fractures are also common in patients with ACL tear and were seen in 72% of the patients in our study and 60% of the patients in the study by Frobell et al (27). Trabecular fractures were rare in our patient population and most likely represent a severe form of bone bruise where a discrete fracture line can be identified through the injured trabecular bone. Cortical depression fractures were by far the most common fracture type identified in our study and most frequently involved the nonarticular cortex of the posterior lateral tibial plateau. Cortical depression fractures in this location may occur when the pivot shift mechanism takes place with the knee flexed, which results in impaction between the lateral femoral condyle and lateral tibial plateau in a more posterior location than with the knee extended (28). The more posterior directed force may result in buckling of the posterior cortex of the lateral tibial plateau in addition to impaction of the posterior articular surface. In our study, postoperative IKDC scores were significantly lower in patients with cortical depression fractures than in those without fractures. Both our study and the study by Frobell et al (27) found a significant association between the presence of fractures and larger volumes of underlying bone marrow edema, indicating stronger compressive forces to the articular surface at the time of ACL tear. Articular surface impaction injury may disturb the normal homeostasis between the synovium and articular cartilage and cause the release of proinflammatory cytokines such as tumor necrosis factor, interleukin, nitric oxide, and metalloproteinases (29,30). These catabolic agents may stimulate chondrocyte damage and matrix degradation, which may lead to a deterioration of clinical symptoms and the eventual development of osteoarthritis (29,30). In our study, we used a multivariate analysis model to investigate the relationship between cortical depression fractures and postoperative IKDC scores in patients with ACL tear taking into account other demographic and surgical factors that may potentially influence clinical outcome. Multiple previous studies have shown that factors such as older age (31), female sex (32,33), preexisting cartilage degeneration (34 36), 538 radiology.rsna.org n Radiology: Volume 264: Number 2 August 2012

9 and meniscal tears (34 36) are associated with decreased clinical outcome following ACL reconstruction surgery. Furthermore, a meta-analysis by Goldblatt et al (37) highlights the advantages and disadvantages of using bone patellar tendon bone grafts and hamstring tendon grafts during ACL reconstruction surgery. Interestingly, the only factor other than the presence of cortical depression fractures that was significantly associated with postoperative IKDC scores in our study was the surgeon who performed the procedure. Although all orthopedic surgeons at our institution are experienced sports medicine specialists, one surgeon in particular performs only knee surgeries and specializes in the treatment of patients with ACL tear. Our study showed no significant association between the postoperative IKDC score and bone marrow edema volume in patients with ACL tear. Boks et al (23) and Vincken et al (24) also investigated the relationship between bone marrow edema and short-term clinical outcome in patients with posttraumatic knee pain, many of whom had ACL tear. Both groups of authors found no significant difference in subjective pain intensity scores between patients with and patients without bone marrow edema at 6 months to 1 year of follow-up (23,24). In addition, Hanypsiak et al (9) found that the IKDC scores of patients with ACL tear and bone marrow edema were similar to those of patients without bone marrow edema at 12-year follow-up. The results of our study suggest that the presence of cortical depression fractures in patients with ACL tear should be considered a more important risk factor for a suboptimal clinical outcome than the presence or degree of bone marrow edema. Our study found no significant association between preoperative IKDC score and any variable, including the presence of cortical depression fractures and meniscal tears, the degree of cartilage degeneration, and the volume of bone marrow edema within the knee joint. Dunn et al (38) also found that the preoperative IKDC scores of patients with ACL tear and bone marrow edema were similar to those of patients without bone marrow edema. In addition, Boks et al (23) found no significant difference between baseline subjective pain intensity scores in patients with and patients without bone marrow edema who sustained acute knee trauma. The preoperative IKDC score may reflect an individual s psychologic response to acute injury to a greater extent than the degree of damage to the knee joint. Our study found a significant association between the presence of cortical depression fractures and meniscal tears within the same compartment of the knee joint. Frobell et al (27) found no such association but used MR imaging and not arthroscopy to determine the presence or absence of meniscal tears. The presence of cortical depression fractures in patients with ACL tear may indicate stronger compressive forces between the femoral condyle and tibial plateau, which may lead to an impaction injury to the meniscus lying between the two osseous structures. The results of our study suggest that if a cortical depression fracture is identified on MR images in patients with ACL tear, careful search for an associated meniscal tear within the same compartment should be performed. Our study had several limitations. One limitation was the retrospective study design. However, we used well-defined inclusion criteria, and all patients prospectively filled out IKDC knee evaluation questionnaires before and 1 year after ACL reconstruction surgery. A second limitation was that the segmentation software used in our study was not validated at outside institutions for the measurement of bone marrow edema volume. Another limitation of our study was potential selection bias. However, statistical analysis showed no significant difference between patients in our study group and those who underwent ACL reconstruction surgery at our institution but were not included in our study group with regard to various factors including age, sex, body mass index, injured knee, surgeon who performed the procedure, type of ACL graft, preoperative and postoperative IKDC scores, presence of medial and lateral meniscus tears, and cartilage score. Furthermore, some patients with ACL injury had partial-thickness tears of the medial collateral ligament, which may have influenced the postoperative IKCD score. However, previous studies have documented excellent clinical outcomes in patients with ACL reconstruction who had conservatively treated partial-thickness medial collateral ligament tears (39 41). In addition, our study included only a small number of patients with trabecular fractures and thus did not have the statistical power to investigate the influence of this fracture type on clinical outcome following ACL reconstruction surgery. A final limitation of our study was the absence of physiologic cartilage imaging sequences in the MR protocol. For this reason, we were unable to determine whether the presence of fractures in patients with ACL tear was associated with greater injury to the overlying articular cartilage. In conclusion, our study showed that cortical depression fractures are common in patients with ACL tear and are associated with larger volumes of underlying bone marrow edema and decreased clinical outcome scores 1 year after ACL reconstruction surgery. Previous studies investigating the relationship between osseous injuries and clinical symptoms in patients with ACL tear have focused on bone marrow edema (9,23,24). However, the results of our study suggest that the presence of cortical depression fractures should be considered a more important risk factor for a suboptimal clinical outcome following ACL reconstruction surgery than the presence or degree of bone marrow edema. Future research in patients with ACL tear should be directed at investigating the influence of cortical depression fractures and not merely bone marrow edema on long-term clinical outcome and the development of osteoarthritis. Disclosures of Potential Conflicts of Interest: R.K. Financial activities related to the present article: none to disclose. Financial activities not related to the present article: has stock/stock options in Flex Biomedical. Other relationships: Radiology: Volume 264: Number 2 August 2012 n radiology.rsna.org 539

10 none to disclose. M.L.S. No potential conflicts of interest to disclose. K.S.L. Financial activities related to the present article: none to disclose. Financial activities not related to the present article: receives payment for lectures including service on speakers bureaus from MTMI. Other relationships: none to disclose. A.M.d.R. Financial activities related to the present article: none to disclose. Financial activities not related to the present article: is a paid consultant for Lippincott, Williams, and Wilkins. Other relationships: none to disclose. T.A.M. Financial activities related to the present article: none to disclose. Financial activities not related to the present article: receives payment for lectures including service on speakers bureaus from Mueller Sports Medicine. Other relationships: none to disclose. G.S.B. No potential conflicts of interest to disclose. B.K.G. Financial activities related to the present article: none to disclose. 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