MR imaging-based diagnosis and classification of meniscal tears.

Magnetic resonance (MR) imaging is currently the modality of choice for detecting meniscal injuries and planning subsequent treatment. A thorough understanding of the imaging protocols, normal meniscal anatomy, surrounding anatomic structures, and anatomic variants and pitfalls is critical to ensure diagnostic accuracy and prevent unnecessary surgery. High-spatial-resolution imaging of the meniscus can be performed using fast spin-echo and three-dimensional MR imaging sequences. Normal anatomic structures that can mimic a tear include the meniscal ligament, meniscofemoral ligaments, popliteomeniscal fascicles, and meniscomeniscal ligament. Anatomic variants and pitfalls that can mimic a tear include discoid meniscus, meniscal flounce, a meniscal ossicle, and chondrocalcinosis. When a meniscal tear is identified, accurate description and classification of the tear pattern can guide the referring clinician in patient education and surgical planning. For example, longitudinal tears are often amenable to repair, whereas horizontal and radial tears may require partial meniscectomy. Tear patterns include horizontal, longitudinal, radial, root, complex, displaced, and bucket-handle tears. Occasionally, meniscal tears can be difficult to detect at imaging; however, secondary indirect signs, such as a parameniscal cyst, meniscal extrusion, or linear subchondral bone marrow edema, should increase the radiologist's suspicion for an underlying tear. Awareness of common diagnostic errors can ensure accurate diagnosis of meniscal tears. Online supplemental material is available for this article.

Observation and inpatient status: clinical impact of the 2-midnight rule.

BACKGROUND: In response to growing concern over frequency and duration of observation encounters, the Centers for Medicare and Medicaid Services enacted a rules change on October 1, 2013, classifying most hospital encounters of <2 midnights as observation, and those ≥2 midnights as inpatient. However, limited data exist to predict the impact of the new rule. OBJECTIVE: To answer the following: (1) Will the rule reduce observation encounter frequency? (2) Are short-stay (<2 midnights) inpatient encounters often misclassified observation encounters? (3) Do 2 midnights separate distinct clinical populations, making this rule logical? (4) Do nonclinical factors such as time of day of admission impact classification under the rule? DESIGN, SETTING AND PATIENTS: Retrospective descriptive study of all observation and inpatient encounters initiated between January 1, 2012 and February 28, 2013 at a Midwestern academic medical center. MEASUREMENTS: Demographics, insurance type, and characteristics of hospitalization were abstracted for each encounter. RESULTS: Of 36,193 encounters, 4,769 (13.2%) were observation. Applying the new rules predicted a net loss of 14.9% inpatient stays; for Medicare only, a loss of 7.4%. Less than 2-midnight inpatient and observation stays were different, sharing only 1 of 5 top International Classification of Diseases, 9th Revision (ICD-9) codes, but for encounters classified as observation, 4 of 5 top ICD-9 codes were the same across the length of stay. Observation encounters starting before 8:00 am less commonly spanned 2 midnights (13.6%) than later encounters (31.2%). CONCLUSIONS: The 2-midnight rule adds new challenges to observation and inpatient policy. These findings suggest a need for rules modification.

MRI characteristics of healed and unhealed peripheral vertical meniscal tears.

OBJECTIVE: The objective of our study was to retrospectively compare the MRI characteristics of surgically confirmed healed and unhealed peripheral vertical meniscal tears. MATERIALS AND METHODS: The study group consisted of 64 patients with 86 peripheral vertical meniscal tears diagnosed on MRI who subsequently underwent knee surgery. The MRI examinations were retrospectively reviewed to assess the following tear characteristics: tear location relative to the meniscocapsular junction, tear width, tear length, tear extension through one or both surfaces, sequences on which tear was visualized, signal intensity of tear on T2-weighted imaging, and presence of low-signal-intensity strands bridging the tear on T2-weighted imaging. Multivariate logistic regression models were used to determine whether MRI characteristics could be used to distinguish between healed and unhealed tears at surgery. RESULTS: Tear location was the most significant characteristic (p<0.001) for distinguishing between healed and unhealed tears: 17 of 18 (94.4%) tears located at the meniscocapsular junction of the medial meniscus were healed and 15 of 68 (22.1%) tears not located at the meniscocapsular junction were healed. For tears not located at the meniscocapsular junction, MRI characteristics significantly associated with healed tears included a tear width of less than 2 mm (p=0.01), tear visualized only on intermediate-weighted imaging (p=0.01), tear showing intermediate or bright signal intensity on T2-weighted imaging (p=0.06), and low-signal-intensity strands bridging the tear on T2-weighted imaging (p<0.001). CONCLUSION: Most peripheral vertical tears at the meniscocapsular junction of the medial meniscus spontaneously heal. The MRI characteristics of tears not located at the meniscocapsular junction can help distinguish between healed and unhealed tears.

Magnetic resonance imaging and arthroscopic appearance of the menisci of the knee.

The menisci are critical for normal function of the knee, providing shock absorption and load transmission that reduce stress on the articular cartilage. When torn, a meniscus may require surgery to restore function, reduce pain, and eliminate mechanical symptoms. Patterns of meniscal tears include longitudinal and bucket-handle, which are often reparable; and horizontal, radial, vertical flap, horizontal flap, and complex. Root tears are usually radial and occur in the posterior roots. When reviewing magnetic resonance images, one must be aware of normal variants and imaging pitfalls that may simulate pathology.

Evaluation of the articular cartilage of the knee joint: value of adding a T2 mapping sequence to a routine MR imaging protocol.

PURPOSE: To determine whether the addition of a T2 mapping sequence to a routine magnetic resonance (MR) imaging protocol could improve diagnostic performance in the detection of surgically confirmed cartilage lesions within the knee joint at 3.0 T. MATERIALS AND METHODS: This prospective study was approved by the institutional review board, and the requirement to obtain informed consent was waived. The study group consisted of 150 patients (76 male and 74 female patients with an average age of 41.2 and 41.5 years, respectively) who underwent MR imaging and arthroscopy of the knee joint. MR imaging was performed at 3.0 T by using a routine protocol with the addition of a sagittal T2 mapping sequence. Images from all MR examinations were reviewed in consensus by two radiologists before surgery to determine the presence or absence of cartilage lesions on each articular surface, first by using the routine MR protocol alone and then by using the routine MR protocol with T2 maps. Each articular surface was then evaluated at arthroscopy. Generalized estimating equation models were used to compare the sensitivity and specificity of the routine MR imaging protocol with and without T2 maps in the detection of surgically confirmed cartilage lesions. RESULTS: The sensitivity and specificity in the detection of 351 cartilage lesions were 74.6% and 97.8%, respectively, for the routine MR protocol alone and 88.9% and 93.1% for the routine MR protocol with T2 maps. Differences in sensitivity and specificity were statistically significant (P < .001). The addition of T2 maps to the routine MR imaging protocol significantly improved the sensitivity in the detection of 24 areas of cartilage softening (from 4.2% to 62%, P < .001), 41 areas of cartilage fibrillation (from 20% to 66%, P < .001), and 96 superficial partial-thickness cartilage defects (from 71% to 88%, P = .004). CONCLUSION: The addition of a T2 mapping sequence to a routine MR protocol at 3.0 T improved sensitivity in the detection of cartilage lesions within the knee joint from 74.6% to 88.9%, with only a small reduction in specificity. The greatest improvement in sensitivity with use of the T2 maps was in the identification of early cartilage degeneration.

Coating with a modular bone morphogenetic peptide promotes healing of a bone-implant gap in an ovine model.

Despite the potential for growth factor delivery strategies to promote orthopedic implant healing, there is a need for growth factor delivery methods that are controllable and amenable to clinical translation. We have developed a modular bone growth factor, herein termed "modular bone morphogenetic peptide (mBMP)", which was designed to efficiently bind to the surface of orthopedic implants and also stimulate new bone formation. The purpose of this study was to coat a hydroxyapatite-titanium implant with mBMP and evaluate bone healing across a bone-implant gap in the sheep femoral condyle. The mBMP molecules efficiently bound to a hydroxyapatite-titanium implant and 64% of the initially bound mBMP molecules were released in a sustained manner over 28 days. The results demonstrated that the mBMP-coated implant group had significantly more mineralized bone filling in the implant-bone gap than the control group in C-arm computed tomography (DynaCT) scanning (25% more), histological (35% more) and microradiographic images (50% more). Push-out stiffness of the mBMP group was nearly 40% greater than that of control group whereas peak force did not show a significant difference. The results of this study demonstrated that mBMP coated on a hydroxyapatite-titanium implant stimulates new bone formation and may be useful to improve implant fixation in total joint arthroplasty applications.

Short-term clinical importance of osseous injuries diagnosed at MR imaging in patients with anterior cruciate ligament tear.

PURPOSE: To determine the association between osseous injuries and short-term clinical outcome in patients with anterior cruciate ligament (ACL) tear. MATERIALS AND METHODS: 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. RESULTS: 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 53.4 ± 18.6 and 93.0 ± 5.0, respectively, for patients without fracture, 54.8 ± 13.6 and 87.3 ± 10.8 for patients with a single fracture, and 53.1 ± 17.2 and 83.4 ± 12.7 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. CONCLUSION: Cortical depression fractures in patients with ACL tear are associated with decreased clinical outcome scores 1 year after ACL reconstruction surgery.

Arthroscopic partial meniscectomy: MR imaging for prediction of outcome in middle-aged and elderly patients.

PURPOSE: To determine whether preoperative magnetic resonance (MR) imaging could help identify factors associated with poor clinical outcome after arthroscopic partial meniscectomy (APM) in middle-aged and elderly patients with meniscal tears. MATERIALS AND METHODS: The prospective, institutional review board-approved, HIPAA-compliant study was performed with informed consent in 53 men and 47 women (average ages, 54.5 and 56.6 years, respectively). Patients underwent knee MR imaging before APM; clinical symptoms were evaluated preoperatively and 1 year postoperatively with International Knee Documentation Committee (IKDC) questionnaire. Overall severity of knee joint degeneration and severity of each feature of joint degeneration were assessed with Boston Leads Osteoarthritis Knee (BLOK) scoring system. Tear length was measured, and type of meniscal tear was classified. Spearman correlation coefficients and relative risks showed the relationship between clinical outcome after APM (difference between preoperative and postoperative IKDC scores) and severity of joint degeneration. RESULTS: Seventy-four patients with isolated medial APM had a significant (P < .05) inverse correlation between clinical outcome and severity of cartilage loss and bone marrow edema in the medial femoral condyle and medial tibial plateau. Fifteen patients with isolated lateral APM had a significant (P < .05) inverse correlation between clinical outcome and severity of cartilage loss in the lateral femoral condyle and lateral tibial plateau and bone marrow edema in the lateral femoral condyle. One hundred patients with APM had a significant (P < .05) inverse correlation between clinical outcome and severity of meniscal extrusion, total BLOK score, and meniscal tear length. A significantly (P < .05) increased relative risk that a patient would not definitely improve after APM was observed if a meniscal root tear was present. CONCLUSION: Poorer clinical outcome after APM was associated with greater severity of cartilage loss and bone marrow edema in the same compartment as the meniscal tear, greater severity of meniscal extrusion, greater overall severity of joint degeneration, a meniscal root tear, and a longer meniscal tear at preoperative MR imaging.

Association of parameniscal cysts with underlying meniscal tears as identified on MRI and arthroscopy.

OBJECTIVE: Although patients with parameniscal cysts usually have underlying meniscal tears, we noted that this association was less common with anterior lateral cysts. We wished to determine whether the frequency of a meniscal tear underlying a parameniscal cyst varied with cyst location. MATERIALS AND METHODS: We reviewed a database of 7,771 knee MR examinations and identified 134 patients with an MR diagnosis of 138 parameniscal cysts and correlative arthroscopy in 78 patients. We reviewed their medical records and MR studies to determine the location of the cysts and presence of an underlying meniscal tear as determined by MRI or arthroscopy. RESULTS: There were 50 lateral and 88 medial parameniscal cysts. Medial meniscal tears were found underlying a cyst in 96% of arthroscopy patients and 86% of patients who had only MR examinations without a location difference in tears (p = 0.68). Meniscal tears were found on MRI or arthroscopy in all 28 patients with a lateral cyst overlying the body or posterior horn of the lateral meniscus, whereas a tear was found on MRI or arthroscopy in only 14 (64%) of 22 patients with cysts adjacent to or extending to the lateral meniscus anterior horn (p = 0.006). Anterior lateral cysts extended medially either into the root or into Hoffa fat-pad, but the type of extension did not correlate with the presence of an underlying meniscal tear. CONCLUSION: In contrast to medial parameniscal cysts or cysts at other locations adjacent to the lateral meniscus, anteriorly located lateral parameniscal cysts are less likely to have underlying meniscal tears.

Influence of hydroxyapatite-coated and growth factor-releasing interference screws on tendon-bone healing in an ovine model.

PURPOSE: Our purpose was to determine whether a bioresorbable interference screw coated with a hydroxyapatite-based mineral layer designed to release an engineered peptide growth factor (linkBMP-2 [where "BMP-2" indicates bone morphogenetic protein 2]) improved tendon-bone healing compared with a screw without coating. METHODS: Tagged linkBMP-2 peptides were used to quantify binding efficiency and release kinetics on 9 mineral-coated BIORCI screws (Smith & Nephew, Andover, MA). Fourteen mature female sheep were used in this study. In each of the 14 sheep, each stifle was randomized to either receive a linkBMP-2-coated or uncoated interference screw (n = 14 per treatment). The sheep were euthanized at 6 weeks after surgery. Eight sheep were subjected to biomechanical testing for peak load at failure and stiffness, and six sheep were used for histologic analysis according to a semiquantitative scoring scale. RESULTS: The linkBMP-2 molecule bound efficiently to the surface of mineral-coated interference screws. Over 80% of the initially bound linkBMP-2 was released during a 6-week time frame in vitro. Peak load at failure in the linkBMP-2-coated interference screw group (mean +/- SD, 449.3 +/- 84.7 N) was not significantly different from that in the uncoated group (421.0 +/- 61.8 N) (P = .22). Stiffness in the linkBMP-2-coated interference screw group (157.3 +/- 39.6 N/mm) was not significantly different from that in the uncoated group (140.6 +/- 20.3 N/mm) (P = .12). Histologic analysis showed that the tendons in the linkBMP-2-coated interference screw group had higher scores (better) than the uncoated group. In the linkBMP-2-coated interference screw group, mesenchymal cells were present at the interface between screw and tendon, whereas these cells were not present in the uncoated group. CONCLUSIONS: We found that linkBMP-2 can be bound onto a mineral-coated BIORCI interference screw surface and subsequently released from the screw surface in a sustained manner. The histologic result of this study showed that the linkBMP-2-coated interference screw significantly improved the histologic scores of early tendon-bone healing in this sheep model. CLINICAL RELEVANCE: This linkBMP-2 coating material may improve early tendon/ligament fixation.

MR diagnosis of posterior root tears of the lateral meniscus using arthroscopy as the reference standard.

OBJECTIVE: The purpose of our study was to determine whether tears of the posterior root of the lateral meniscus can be diagnosed using standard MR criteria of a meniscal tear in the presence or absence of an anterior cruciate ligament (ACL) tear. MATERIALS AND METHODS: From a series of 559 knee MR examinations with arthroscopic correlation, we selected all 16 proven tears isolated to the posterior root of the lateral meniscus for retrospective blinded review, along with 45 cases of arthroscopically intact lateral meniscal posterior roots. The reviewers categorized whether there was a torn, possibly torn, or intact root based on three specific coronal and three specific sagittal image locations. RESULTS: When all possibly torn roots were considered as torn, the sensitivity and specificity for diagnosis of a root tear were 93% and 89%, respectively. The observers' overall diagnosis of a tear based on all images gave a higher combined sensitivity and specificity than if the diagnosis of a tear had been based on one or any combination of the three coronal and three sagittal locations. Root tears were significantly more common in the presence of an ACL tear (p < 0.0001), but the presence or absence of an ACL tear did not change MR diagnostic accuracy. CONCLUSION: The standard MR criteria of meniscal distortion and signal to the surface can be used to diagnose lateral meniscal root tears. The presence or absence of an ACL tear did not change diagnostic accuracy.

Juvenile versus adult osteochondritis dissecans of the knee: appropriate MR imaging criteria for instability.

PURPOSE: To retrospectively compare the sensitivity and specificity of previously described magnetic resonance (MR) imaging criteria for the detection of instability in patients with juvenile or adult osteochondritis dissecans (OCD) of the knee, with arthroscopic findings as the reference standard. MATERIALS AND METHODS: Informed consent was waived by the Institutional Review Board for this HIPAA-compliant study. The study group consisted of 32 skeletally immature patients (25 boys, seven girls; mean age, 14.4 years) with 36 juvenile OCD lesions of the knee and 33 skeletally mature patients (25 men, eight women; mean age, 26.2 years) with 34 adult OCD lesions of the knee. All patients had been evaluated with MR imaging and arthroscopy. MR studies were retrospectively reviewed by two radiologists in consensus to determine the presence of previously described MR imaging criteria for OCD instability (ie, high T2 signal intensity rim, surrounding cysts, high T2 signal intensity cartilage fracture line, and fluid-filled osteochondral defect). Sensitivity and specificity of the criteria were calculated separately for juvenile and adult OCD lesions. RESULTS: Separately, previously described MR imaging criteria for detection of OCD instability were 0%-88% sensitive and 21%-100% specific for juvenile OCD lesions and 27%-54% sensitive and 100% specific for adult OCD lesions. When used together, the criteria were 100% sensitive and 11% specific for instability in juvenile OCD lesions and 100% sensitive and 100% specific for instability in adult OCD lesions. CONCLUSION: Previously described MR imaging criteria for OCD instability have high specificity for adult but not juvenile lesions of the knee.

Clinical and MRI findings associated with false-positive knee MR diagnoses of medial meniscal tears.

OBJECTIVE: The objective of our study was to determine if false-positive MR diagnoses of a medial meniscal tear are more common with specific clinical variables, tear type or location, or MRI findings of a longitudinal tear. MATERIALS AND METHODS: We reviewed the records of 559 patients who underwent knee MR examinations and arthroscopy. We compared the positive predictive values (PPVs) of an MR diagnosis of a medial meniscal tear for differences in tear location or type, delay between knee injury and MRI, delay between MRI and arthroscopy, and the presence of an anterior cruciate ligament (ACL) tear. We also retrospectively reviewed the MR examinations of 50 longitudinal tears to compare the PPVs of various MRI findings of a longitudinal tear. RESULTS: There was no association between either the delay between injury and MRI or the delay between MRI and arthroscopy and false-positive diagnoses. The PPV of 64% (32/50) for longitudinal tears was lower than the values of 83% (15/18) to 100% (116/116) for other types of medial meniscal tears. False-positive diagnoses of medial meniscal tears were more common in patients who had a prior episode of acute trauma (p = 0.004) or an ACL tear (p < 0.0001). Review of longitudinal tears revealed a decreased PPV when MRI showed signal contacting only the superior surface (p = 0.016) or when MRI showed signal contacting the surface at the meniscocapsular junction (p = 0.004). Four of the 18 menisci with a false-positive diagnosis of a longitudinal tear had a healed ACL tear noted at arthroscopy. CONCLUSION: False-positive MR diagnoses of medial meniscal tears are more common for longitudinal tears than other tear types and are also more common with MR abnormalities at either the superior surface or the meniscocapsular junction. Spontaneous healing of longitudinal tears accounts for some false-positive MR diagnoses.