MR appearance of SONK-like subchondral abnormalities in the adult knee: SONK redefined

Treating Extensive Spontaneous Osteonecrosis of the Tibia by the Medial Opening Wedge High Tibial Osteotomy Procedure: A Case Report

Osteonecrosis of the tibia is less common than that of the femoral condyle, with no consensus on surgical indications. In this study, a medial opening wedge high tibial osteotomy (OWHTO) was performed to treat the very extensive osteonecrosis of the tibia. This case demonstrates significant symptomatic relief and functional improvement following OWHTO for spontaneous tibial plateau osteonecrosis. The findings support the hypothesis that changes in mechanical stress contribute to disease progression. The promising results of this case study highlight the need for further studies to confirm its efficacy in a larger patient cohort, sparking interest in the future of this field. This case report is complemented by a literature review, which provides insights into management based on the patient's clinical course.

Does the osteonecrotic volume/other factors predict progression to total knee arthroplasty in spontaneous osteonecrosis of the knee? An MRI study

Background

The aim of this study is to determine whether the volume of the osteonecrotic lesion in spontaneous osteonecrosis of the knee (SONK) or other prognostic factors predict progression to total knee arthroplasty (TKA). The secondary aim is to analyse co-relation of volume of osteonecrotic lesion versus other prognostic factors The authors hypothesize that a greater osteonecrotic volume predicts progression to TKA.

Materials and methods

A retrospective study was conducted at a single tertiary hospital. All patients under the care of a single surgeon with magnetic resonance imaging (MRI)-proven SONK were included from the period of January 2011 to January 2018. Survival analysis was conducted to evaluate for progression to TKA based on volume and location of osteonecrotic lesion. Univariate and multivariate analyses were performed to identify potential risk factors for TKA.

Results

42 patients with MRI-proven SONK were evaluated. 9 patients (21.4 %) required TKA. There was no significant association between progression to TKA with volume of the osteonecrotic lesion. Other factors such as age, gender, body mass index, degree of bony edema and cartilage damage, presence of meniscal tear and subchondral fractures and location of osteonecrotic lesion were also not significant.

Conclusion

The volume of the osteonecrotic lesion and other evaluated prognostic factors were not predictive of the progression to TKA for patients with SONK.

[Bone marrow edema syndromes of the knee]

Bone marrow edema represents a common finding on magnetic resonance imaging (MRI) of the knee and other joints, which can occur as a primary pathology or as a secondary phenomenon of various bone and joint pathologies. This article reviews the terminology, definition, pathology and differential diagnosis of bone marrow edema of the knee taking into consideration current concepts.

Risk of Arthroplasty in Patients with Subchondral Insufficiency Fractures of the Knee: A Matched Study of the Implantable Shock Absorber using a Validated Predictive Model

Subchondral insufficiency fractures of the knee (SIFK) can result in high rates of osteoarthritis and arthroplasty. The implantable shock absorber (ISA) implant is a titanium and polycarbonate urethane device which reduces the load on the medial compartment of the knee by acting as an extra-articular load absorber while preserving the joint itself. The purpose of this study was to evaluate whether partially unloading the knee with the ISA altered the likelihood of progression to arthroplasty utilizing a validated predictive risk model (SIFK score). A retrospective case-control (2:1) study was performed on patients with SIFK without any previous surgery and on those implanted with the ISA with the primary outcome being progression to arthroplasty compared with nonoperative treatment at 2 years. Baseline and final radiographs, as well as magnetic resonance imagings, were reviewed for the evaluation of meniscus or ligament injuries, insufficiency fractures, and subchondral edema. Patients from a prospective study were matched using the exact SIFK Score, a validated predictive score for progression to arthroplasty in patients with SIFK, to those who received the ISA implant. Kaplan-Meier analysis was conducted to assess survival. A total of 57 patients (38 controls:19 ISA) with a mean age of 60.6 years and 54% female were included. The SIFK score was matched exactly between cases and controls for all patients. The 2-year survival rate of 100% for the ISA group was significantly higher than the corresponding rate of 61% for the control group (p < 0.01). In ISA, 0% of the patients converted to arthroplasty at 2 years, and 5% (one patient) had hardware removal at 1 year. When stratified by risk, the ISA group did not have a significantly higher survival compared with low-risk (p = 0.3) or medium-risk (p = 0.2) controls, though it had a significantly higher survival for high-risk groups at 2 years (100 vs. 15%, p < 0.01). SIFK of the medial knee can lead to significant functional limitation and high rates of conversion to arthroplasty. Implants such as the ISA have the potential to alter the progression to arthroplasty in these patients, especially those at high risk.

Bilateral trochlear subchondral insufficieny fracture of the knee in a professional cyclist

This case report presents a rare case of subsequent ipsilateral and contralateral subchondral insufficiency fracture of the knee (SIFK) in the trochlea of the femur within months, manifested in a professional cyclist. SIFKs in the trochlea have not yet been reported in the literature; however, their appearance in a professional cyclist might be explained by the amount of repetitive pressure on the patellofemoral joint when cycling. In both instances, atraumatic anterior knee pain occurred, resolving after conservative treatment for 6-9 weeks. The patient reached their previous activity level. The authors believe SIFK in the younger population may be more common than currently perceived due to its self-limiting behaviour and a lack of performing immediate MRIs in this younger group whenever an overload injury is suspected.

Subchondral insufficiency fractures, subchondral insufficiency fractures with osteonecrosis, and other apparently spontaneous subchondral bone lesions of the knee-pathogenesis and diagnosis at imaging

Subchondral insufficiency fractures (SIFs) and SIFs with osteonecrosis (SIF-ONs) of the knee (previously misnamed spontaneous osteonecrosis of the knee (SONK)) are bone lesions that appear without prior traumatic, tumoral, or inflammatory event.Both conditions are characterized in the early stages by epiphyseal bone marrow edema (BME)-like signal at MRI. However, while SIFs usually heal spontaneously, they can also evolve to osteonecrosis (i.e., SIF-ON), which may progress to an irreversible collapse of the articular surface. Careful analysis of other MRI signs may help differentiate the two conditions in the early phase. In SIFs, the BME edema-like signal extends to the area immediately adjacent to the subchondral plate, while in SIF-ONs, this subchondral area shows low signal intensity on fluid-sensitive MR images due to altered bone marrow. The thickness and length of subchondral areas with low fluid-sensitive signal intensity are important factors that determine the prognosis of SIF-ONs. If they are thicker than 4 mm or longer than 14 mm, the prognosis is poor. The differential diagnosis of SIFs and SIF-ONs include bone lesions associated with the "complex regional pain syndrome" (CRPS), epiphyseal osteonecrosis of systemic origin, and those related to cartilage pathology.Clinical relevance statement Imaging plays an essential role in diagnosing subchondral insufficiency fractures (SIFs) from subchondral insufficiency fractures with osteonecrosis (SIF-ONs) and collapse, as well as in distinguishing them from other spontaneous knee subchondral bone lesions presenting with bone marrow edema-like signal.Key points• Subchondral insufficiency fractures may affect the knee, especially in older adults.• Subchondral insufficiency fractures usually heal spontaneously.• Sometimes, subchondral osteonecrosis and collapse may complicate subchondral insufficiency fractures.• Bone marrow-like edema is an aspecific sign seen in all these lesions.• Degraded marrow in osteonecrosis complicating fractures is hypointense on fluid-sensitive sequences.

Subchondral Insufficiency Fractures of the Knee: A Clinical Narrative Review

» Subchondral insufficiency fractures of the knee (SIFKs) are subchondral plate fractures with a prevalence of 2% to 4% of all knee injuries.» Magnetic resonance imaging is the gold standard for evaluating SIFK, while plain radiographs have limited the use in the diagnosis of SIFK.» Among patients with SIFK, 50% to 100% have meniscal pathology.» Medical therapies and standard treatments traditionally used in the management of knee osteoarthritis differ from recommended management of SIFK patients.» Randomized controlled trials and cohort studies with long-term follow-up are needed to determine the optimal rehabilitation protocol, interventional therapy, and prognosis of SIFK patients.

Atraumatic Bone Marrow Edema Involving the Epiphyses

Bone marrow edema (BME)-like signal intensity involving the epiphyses of tubular bones represents a frequent magnetic resonance imaging finding associated with a wide spectrum of bone and joint disorders. It is important to distinguish this finding from cellular infiltration of bone marrow and to be aware of the differential diagnosis of underlying causes. With a general focus on the adult musculoskeletal system, this article reviews the pathophysiology, clinical presentation, histopathology, and imaging findings of nontraumatic conditions associated with epiphyseal BME-like signal intensity: transient bone marrow edema syndrome, subchondral insufficiency fracture, avascular necrosis, osteoarthritis, arthritis, and bone neoplasms.

Osteonecrosis of the Knee: Not all Bone Edema is the Same

Knee pain is among the most common complaints that an orthopedic surgeon may see in practice. It is often worked up with X-rays and MRI, leading to a myriad of potential diagnoses ranging from minimal edema patterns to various types of osteonecrosis. Similarities in certain causes can pose diagnostic challenges. The purpose of this review was to present the 3 types of osteonecrosis observed in the knee as well as additional causes to consider to help aid in the diagnosis and treatment..

Proximal fibular osteotomy relieves pain in spontaneous osteonecrosis of the knee: A retrospective study

Spontaneous osteonecrosis of the knee (SONK) causes knee pain and joint motion limitation. Ischemia or insufficiency fracture may be the cause, but no consensus has been developed. Proximal fibular osteotomy (PFO) has been reported to relieve pain from osteoarthritis through medial compartment decompression. We reviewed the effect of this procedure on medial compartment SONK patients and explored clinical and radiological results. Since January 2018 to January 2020, the data of 12 knees (8 right and 4 left) from 11 SONK patients (9 women and 2 men) who received PFO were analyzed. The average age was 61.5 years. The diagnosis of SONK was established through weight-bearing anterior-posterior radiographs or magnetic resonance imaging (MRI). Visual analog scale (VAS) scores, Oxford knee score (OKS), Femorotibial angle (FTA), medial joint space, and lateral joint space were documented preoperatively and at follow up visits. Outcome assessment for the clinical and radiographic data was reviewed at 12- and 24-month follow-up visits. The mean follow up period was 33 months. All patients were able to walk with or without cane assistance the day after surgery. Both VAS score and OKS (preoperative: 6.6 ± 0.9 and 24.7 ± 3.8, respectively) improved significantly at the 12-month follow-up, and to 24-month follow-up (3.6 ± 1.3 and 35.6 ± 4.5, respectively, P < .05). Medial joint space ratio increased from 0.36 to 0.50 (P < .05). Changes of FTA were insignificant at any point of follow up. Four patients underwent follow-up MRI, and a decrease in the osteonecrotic area was clearly observed in 2 patients. By achieving medial knee decompression, PFO allowed quick weight-bearing recovery, pain relief, and improvement in knee function in SONK patients.

Subchondral insufficiency fracture of the knee: review of current concepts and radiological differential diagnoses

Subchondral insufficiency fracture of the knee (SIFK) is a common cause of knee joint pain in older adults. SIFK is a type of stress fracture that occurs when repetitive and excessive stress is applied to the subchondral bone. If the fracture does not heal, the lesion develops into osteonecrosis and results in osteochondral collapse, requiring surgical management. Because of these clinical features, SIFK was initially termed "spontaneous osteonecrosis of the knee (SONK)" in the pre-MRI era. SONK is now categorized as an advanced SIFK lesion in the spectrum of this disease, and some authors believe the term "SONK" is a misnomer. MRI plays a significant role in the early diagnosis of SIFK. A subchondral T2 hypointense line of the affected condyle with extended bone marrow edema-like signal intensity are characteristic findings on MRI. The large lesion size and the presence of osteochondral collapse on imaging are associated with an increased risk of osteoarthritis. However, bone marrow edema-like signal intensity and osteochondral collapse alone are not specific to SIFK, and other osteochondral lesions, including avascular necrosis, osteochondral dissecans, and osteoarthritis should be considered. Chondral lesions and meniscal abnormalities, including posterior root tears, are also found in many patients with SIFK, and they are considered to be related to the development of SIFK. We review the clinical and imaging findings, including the anatomy and terminology history of SIFK, as well as its differential diagnoses. Radiologists should be familiar with these imaging features and clinical presentations for appropriate management.

Is bone marrow edema syndrome a precursor of hip or knee osteonecrosis? Results of 49 patients and review of the literature

PURPOSE

Diagnosis of bone marrow edema syndrome (BMES) can be challenging. There is sometimes uncertainty about the correct diagnosis of BMES on morphologic magnetic resonance imaging (MRI), since subchondral findings like lines and spots can be misinterpreted as "beginning" or "possible" avascular osteonecrosis (AVN). The aim of our study was to systematically assess the temporal course of BMES from first diagnosis on MRI until the end of clinical symptoms and the full disappearance of bone marrow edema (BME) to determine whether subchondral lines and spots detected in these patients can develop into osteonecrosis.

METHODS

In a combined retrospective and prospective study, we retrieved serial MRI scans of hips and knees with BME from the hospital database. According to clinical and imaging data, all patients with degenerative, infectious/inflammatory, rheumatic, neoplastic conditions and those showing typical osteonecrosis were excluded. We collected all available MRI examinations from first detection of BME until its disappearance. In case edema had not fully resolved in the last available MRI scan, we performed an MRI with an additional dynamic contrast-enhanced (DCE-MRI) sequence. For each MRI scan, we recorded the severity of edema, the presence of subchondral hypointense lines and the presence of subchondral focal hypointense zones on T1-weighted images by two independent readers. The DCE-MRI scans were used to calculate parameter maps to assess the perfusion characteristics.

RESULTS

The study comprised 49 patients aged 22-71 years. In total, 171 morphologic and 5 DCE-MRI scans were evaluated. In 44 patients (89.8%), the BMES completely healed without remnants. In 18 of 49 patients (36.7%), a subchondral line was present in the first MRI exam. Nine patients (18.4%) developed a subchondral line within 1-5 months after the first MRI. In total, 27 out of 49 patients (55.1%) had subchondral lines (12 knees, 15 hips) during the timeframe of the study. All subchondral lines disappeared in the timeframe of the study. Subchondral focal hypointense zones were present in 14 out of 49 patients (28.6%): in 9 cases, subchondral focal hypointense zones disappeared after a median of 5.5 months (range, 1-85 months), while in 5 cases, subchondral focal lesions persisted until the end of the study (up to more than 85 months) without edema in the surrounding bone. All persisting subchondral focal lesions were hyperperfused. These 5 patients had associated meniscal lesions.

CONCLUSION

Our study shows that subchondral lines and spots found in patients with BMES do not develop into AVN. Subchondral lines, which resemble subchondral insufficiency fractures, are associated with BMES. Subchondral focal T1-hypointense zones do not represent AVN; most probably these areas represent reparative processes within the subchondral bone, where tensile and shear force overload is present due to altered biomechanics.

Lateral femoral condyle insufficiency fractures: imaging findings, demographics, and analysis of outcomes

OBJECTIVE

To describe imaging characteristics and demographics of lateral femoral condyle insufficiency fractures (LFCIFs) and identify characteristics associated with progression to epiphyseal collapse.

MATERIALS AND METHODS

A retrospective review of 105 consecutive patients with LFCIF was performed (mean age 58.1 years) after excluding post-traumatic and pathological fractures. Lesion size and location, presence of bone marrow edema-like signal, soft tissue edema, chondrosis grade, and meniscus pathology were documented. Demographics were recorded from the electronic patient record. Follow-up MRI and/or radiographs were evaluated for healing/stability or progression to epiphyseal collapse. Bone mineral density was assessed from dual-energy x-ray absorptiometry (DEXA) scans and/or radiographs.

RESULTS

Fifty-six female and 49 male subjects were included. Female subjects were older at presentation (60.5 versus 56.3 years, p = .02). A total of 61.7% of the subjects with available DEXA and/or radiographs had osteopenia/osteoporosis. The central weight-bearing (61%) and outer condyle (54.3%) were most involved. High-grade chondrosis was present in ≥ 1 compartment in 70.5% including 42% in the lateral compartment. A total of 67.6% had ≥ 1 meniscus tear with similar frequency of medial and lateral tears (47.6% versus 41%). Bone marrow edema-like signal was present in all cases; soft tissue edema was present in 83.8%. Fifty-three subjects had available follow-up MRI (n = 24) and/or radiographs (n = 29). Increased age, fracture dimensions, presence of medial meniscus tears, and high-grade patellofemoral chondrosis were associated with progression (p ≤ .05).

CONCLUSION

LFCIFs are associated with meniscus tears, high-grade chondrosis, and osteopenia/osteoporosis with more global knee pathology present when compared with medial femoral condyle insufficiency fracture. Increased age, medial meniscus tears, fracture dimensions, and high-grade patellofemoral chondrosis were associated with progression.

Subchondral fracture caused by unevenly stiffened meniscus after radiofrequency-assisted arthroscopic knee meniscectomy: A case report and review of the literature

•

Although the worsening of symptoms following knee arthroscopy in older patients is often labeled as progression of arthritic symptoms, subchondral insufficiency fracture following arthroscopy may be underdiagnosed.

•

There is a possibility that uneven stiffening of the meniscus causes concentration of stress that resulted in postarthroscopic subchondral fracture.

•

Surgeons should consider avoiding subsequent subchondral fracture when to use radiofrequency in the debridement of a torn meniscus.

Introduction

Causality for postarthroscopic osteonecrosis of the knee is unknown, and related mechanisms have been poorly characterized.

Presentation of case

This report describes a case of a 69-year-old man with subchondral fracture occurring after arthroscopic meniscectomy using a radiofrequency assisted shaver. The patient experienced increasingly intense knee pain 10 months after the meniscectomy. MR imaging revealed postarthroscopic osteonecrosis of the knee in the femoral medial condyle, requiring unicompartmental knee arthroplasty. A mid-coronal cut section of the resected medial femoral condyle showed a linear fracture line parallel to the subchondral bone endplate. Histopathological examination showed prominent callus formation on both sides of the fracture, comprised of reactive woven bone and granulation tissue. The middle portion of the resected medial meniscus was of uneven height, with significant stiffening of the higher side. The stiffened region of the medial meniscus corresponded to the subchondral fracture in the medial femoral condyle.

Discussion

The etiology of post-arthroscopic osteonecrosis of the knee is controversial, but it seems possible that altered knee biomechanics after meniscectomy may predispose patients to osteonecrosis. The findings of the current case suggested that uneven stiffening of the meniscus caused concentration of stress that resulted in postarthroscopic subchondral fracture.

Conclusion

Subchondral insufficiency fracture following arthroscopy may be underdiagnosed. Surgeons need to carefully consider the risk of subchondral fracture following uneven stiffening of the meniscus when to use radiofrequency in the debridement of a torn meniscus.

Nomenclature of Subchondral Nonneoplastic Bone Lesions

OBJECTIVE. The purpose of this article is to summarize the nomenclature of nonneoplastic conditions affecting subchondral bone through a review of the medical literature and expert opinion of the Society of Skeletal Radiology Subchondral Bone Nomenclature Committee. CONCLUSION. This consensus statement summarizes current understanding of the pathophysiologic characteristics and imaging findings of subchondral nonneoplastic bone lesions and proposes nomenclature to improve effective communication across clinical specialties and help avoid diagnostic errors that could affect patient care.

Prayer's fracture: rare cases of knee insufficiency fracture in non-weight-bearing femoral condyle

Insufficiency fractures are a relatively common sub-type of stress fractures and occur as a result of decreased bone resistance due to underlying conditions such as osteoporosis. Insufficiency fractures of the knee most commonly occur at the central weight-bearing zone of the medial femoral condyle. We present five unusual cases of insufficiency fractures occurring at the posterior non-weight-bearing zone of condyles. After investigating commonalities between these patients, we discovered that all of these patients performed the daily practice of prayer rituals that include high knee flexion. We have chosen to coin this type of fracture a "Prayer's fracture". Considering the mechanics of high knee flexion, transient changes in the weight-bearing zone of knee explain the unusual location of this fracture. We describe these cases, the characteristic imaging appearance, and the probable biomechanics that we believe predispose patients to this type of injury.

Accelerated Knee Osteoarthritis Is Characterized by Destabilizing Meniscal Tears and Preradiographic Structural Disease Burden

OBJECTIVE

To determine whether accelerated knee osteoarthritis (KOA) is preceded by, and characterized over time by, destabilizing meniscal tears or other pathologic changes.

METHODS

We selected 3 sex-matched groups of subjects from the first 48 months of the Osteoarthritis Initiative, comprising adults who had a knee without KOA (Kellgren/Lawrence [K/L] radiographic grade <2) at baseline. Subjects in the accelerated KOA group developed KOA of K/L grade ≥3, those with typical KOA showed increased K/L radiographic scores, and those with no KOA had the same K/L grade over time. An index visit was the visit when the radiographic criteria for accelerated KOA and typical KOA were met (the no KOA group was matched to the accelerated KOA group). The observation period was up to 2 years before and after an index visit. Radiologists reviewed magnetic resonance (MR) images of the index knee and identified destabilizing meniscal tears (root tears, radial tears, complex tears), miscellaneous pathologic features (acute ligamentous or tendinous injuries, attrition, subchondral insufficiency fractures, other incidental findings), and meniscal damage in >2 of 6 regions (3 regions per meniscus: anterior horn, body, posterior horn). In addition, bone marrow lesions (BMLs) and cartilage damage on MR images were quantified. Linear mixed regression models were performed to analyze the results.

RESULTS

At 1 year before the index visit, >75% of adults with accelerated KOA had meniscal damage in ≥2 regions (odds ratio 3.19 [95% confidence interval 1.70-5.97] versus adults with typical KOA). By the index visit, meniscal damage in ≥2 regions was ubiquitous in adults with accelerated KOA, including 42% of subjects having evidence of a destabilizing meniscal tear (versus 14% of subjects with typical KOA). These changes corresponded to findings of larger BMLs and greater cartilage loss in the accelerated KOA group.

CONCLUSION

Accelerated KOA is characterized by destabilizing meniscal tears in a knee compromised by meniscal damage in >2 regions, and also characterized by the presence of large BMLs and greater cartilage loss.

Does unicompartmental knee arthroplasty have worse outcomes in spontaneous osteonecrosis of the knee than in medial compartment osteoarthritis? A systematic review and meta-analysis

INTRODUCTION

The role of unicompartmental knee arthroplasty (UKA) in spontaneous osteonecrosis of the knee (SONK) remains controversial, even though SONK involves only one compartment of the knee joint. We aimed to compare the survival rate and clinical outcomes of UKA in SONK and medial compartment osteoarthritis (MOA) via a meta-analysis of previous studies.

MATERIALS AND METHODS

MEDLINE, Embase, and Cochrane Library were searched up to January 2018 with keywords related to SONK and knee arthroplasty. Studies were selected with predetermined inclusion criteria: (1) medial UKA as the primary procedure, (2) reporting implant survival or clinical outcomes of osteonecrosis and osteoarthritis, and (3) follow-up period > 1 year. Quality assessment was performed using the risk of bias assessment tool for non-randomized studies. A random-effects model was used to estimate the pooled relative risk (RR) and standardized mean difference.

RESULTS

The incidence of UKA revision for any reason was significantly higher in SONK than in MOA group (pooled RR = 1.83, p = 0.009). However, the risk of revision due to aseptic loosening was not significantly different between the groups. Moreover, when stratified by the study quality, high-quality studies showed similar risk of overall revision in SONK and MOA (p = 0.71). Subgroup analysis revealed no significant difference in failure between SONK and MOA after cemented mobile and fixed bearing UKA. Results of uncemented UKA were reported only in one study, which showed higher failure of SONK compared to MOA. Clinical outcomes after UKA were similar between SONK and MOA (p = 0.66).

CONCLUSIONS

Cemented UKA has similar survival and clinical outcomes in SONK and MOA. Prospective studies designed specifically to compare the UKA outcomes in SONK and MOA are necessary.

The Role of Meniscal Tears in Spontaneous Osteonecrosis of the Knee: A Systematic Review of Suspected Etiology and a Call to Revisit Nomenclature

BACKGROUND

The cause of spontaneous osteonecrosis of the knee (SONK) and postarthroscopic osteonecrosis of the knee is unknown, and the mechanisms involved have been poorly characterized.

HYPOTHESIS/PURPOSE

The purpose of this study was to perform a detailed systematic review of the literature to examine proposed etiological mechanisms for SONK in order to establish an improved understanding of the processes involved. We hypothesized that the etiology of SONK would be multifactorial.

STUDY DESIGN

Systematic review.

METHODS

A systematic review of the literature was performed by searching PubMed, Medline, Cochrane Database of Systematic Reviews, and the Cochrane Central Register of Controlled Trials. Inclusion criteria were all original research articles presented in the English language that reported on the suspected etiology of SONK. Reviews, case reports with fewer than 3 patients, cost-effectiveness studies, technical reports, editorial articles, surveys, special topics, letters to the editor, personal correspondence, and studies that only proposed factors for the progression of SONK were excluded.

RESULTS

After a comprehensive review of 255 articles, 26 articles were included for final analysis. Twenty-one (80.7%) of 26 articles implicated the role of the meniscus in the development of SONK, in an association with either meniscal tears or its development after meniscectomy. The medial meniscus and posterior meniscal root tears were implicated more frequently. All 4 studies incorporating histological findings supported the insufficiency fracture hypothesis as a pathological basis of SONK.

CONCLUSION

Physicians should be cognizant of the high prevalence of medial meniscus root tears in patients with SONK. Meniscectomy and meniscal tears, particularly of the medial meniscus posterior root, increase contact pressures and create an environment from which insufficiency fractures can emanate. We believe the term SONK is a misrepresentation of the etiology and pathogenesis of the condition and should be replaced with subchondral insufficiency fractures of the knee. Further elucidation of the etiology is required.

Osteochondral Lesions of the Knee: Differentiating the Most Common Entities at MRI

Several pathologic conditions may manifest as an osteochondral lesion of the knee that consists of a localized abnormality involving subchondral marrow, subchondral bone, and articular cartilage. Although understanding of these conditions has evolved substantially with the use of high-spatial-resolution MRI and histologic correlation, it is impeded by inconsistent terminology and ambiguous abbreviations. Common entities include acute traumatic osteochondral injuries, subchondral insufficiency fracture, so-called spontaneous osteonecrosis of the knee, avascular necrosis, osteochondritis dissecans, and localized osteochondral abnormalities in osteoarthritis. Patient demographics, the clinical presentation, and the role of trauma are critical for differential diagnosis. A localized osteochondral defect can be created acutely or can develop as an end result of several chronic conditions. MRI features that aid in diagnosis include the location and extent of bone marrow edema, the presence of a fracture line, a hypointense area immediately subjacent to the subchondral bone plate, and deformity of the subchondral bone plate. These findings are essential in diagnosis of acute traumatic injuries, subchondral insufficiency fracture, and its potentially irreversible form, spontaneous osteonecrosis of the knee. If the lesion consists of a subchondral region demarcated from the surrounding bone, the demarcation should be examined for completeness and the presence of a "double-line sign" that is seen in avascular necrosis or findings of instability, which are important for proper evaluation of osteochondritis dissecans. Subchondral bone plate collapse, demonstrated by the presence of a depression or a fluid-filled cleft, can be seen in advanced stages of both avascular necrosis and subchondral insufficiency fracture, indicating irreversibility. Once the diagnosis is established, it is important to report pertinent MRI findings that may guide treatment of each condition. ^©RSNA, 2018 An earlier incorrect version of this article appeared online. This article was corrected on August 23, 2018.

Subchondral Insufficiency Fracture in the Lateral Compartment of the Knee in a 64-Year-Old Marathon Runner

A 64-year-old marathon runner presented to our clinic with a history of worsening pain in her left knee. Following magnetic resonance imaging, the diagnosis of subchondral insufficiency fracture of the knee (SIFK) was made. A course of conservative management via bisphosphonates was initiated. The patient successfully recovered and returned to full athletic function, having recently returned to competitive marathon running. This article aims to present this unusual case of lateral compartment SIFK and summarise the literature on this uncommon condition.

MR appearance of the temporal evolution and resolution of spontaneous osteonecrosis of the knee: a case report

Spontaneous osteonecrosis of the knee (SONK) is a feared condition of unknown cause, in its classic form appearing in the medial femoral condyle in middle-aged or elderly subjects. Diagnosis with radiography is notoriously difficult with a long latency before typical changes appear. Magnetic resonance imaging (MRI) is regarded as a diagnostic tool with the possibility to give an earlier diagnosis with improved chances for treatment. However, also with MRI there may be an initial diagnostic blind spot before typical changes appear. Little is known about the temporal evolution of the MRI changes. In the current case report, a case of SONK is reported where serial imaging with MRI was performed, from initial symptoms to eventual resolution after almost three years.

Subchondral insufficiency fracture of the knee: A recognizable associated soft tissue edema pattern and a similar distribution among men and women

OBJECTIVE

Primary: to describe the presence and pattern of soft tissue edema in subchondral insufficiency fractures of the knee (SIFK). Secondary: to investigate the gender distribution and identify factors associated with disease progression.

METHODS

MR images of 74 SIFKs in 74 patients were retrospectively reviewed for soft tissue edema presence and location, meniscal tears and extrusion and synovitis. The clinical records were reviewed for age, gender, and BMI. Follow up examinations were reviewed to assess for progression. Data were analyzed for gender distribution and for association between each imaging finding as a predictor of SIFK location and progression.

RESULTS

Soft tissue edema was present in 89% (66/74) of SIFK. It was located around the MCL in 78% (58/74), posterior to and abutting on the posterior distal femur in 68% (50/74), around to the tibia in only 18% (13/74), but when present it strongly predicted the presence of a medial tibial plateau SIFK (p=5.6×10^-12). Edema extended to the vastus medialis fascia in 51% (38/74) and vastus lateralis fascia in 24% (18/74). Gender distribution was 1:1 (males=38, females=36), most common in the 6th decade (29/74, 39%). Lesion progression showed a trend towards being more common in females (8/9, 89%) compared to males (9/16, 56%), and in patients with meniscal extrusion (≥3mm) (13/14, 93%) compared to those with no extrusion (2/7, 29%).

CONCLUSION

A recognizable soft tissue edema pattern is seen in SIFK and may have an important role in early diagnosis. Also, SIFK may affect equally males and females in the 6th decade and may progress more in females. Meniscal extrusion may predispose to disease progression.

Bone marrow lesions and subchondral bone pathology of the knee

Bone marrow lesions (BMLs) around the knee are a common magnetic resonance imaging (MRI) finding. However, despite the growing interest on BMLs in multiple pathological conditions, they remain controversial not only for the still unknown role in the etiopathological processes, but also in terms of clinical impact and treatment. The differential diagnosis includes a wide range of conditions: traumatic contusion and fractures, cyst formation and erosions, hematopoietic and infiltrated marrow, developmental chondroses, disuse and overuse, transient bone marrow oedema syndrome and, lastly, subchondral insufficiency fractures and true osteonecrosis. Regardless the heterogeneous spectrum of these pathologies, a key factor for patient management is the distinction between reversible and irreversible conditions. To this regard, MRI plays a major role, leading to the correct diagnosis based on recognizable typical patterns that have to be considered together with coexistent abnormalities, age, and clinical history. Several treatment options have been proposed, from conservative to surgical approaches. In this manuscript the main lesion patterns and their management have been analysed to provide the most updated evidence for the differential diagnosis and the most effective treatment.

Analysis of risk factors for poor prognosis in conservatively managed early-stage spontaneous osteonecrosis of the knee

BACKGROUND

Management guidelines for early-stage spontaneous osteonecrosis of the knee (SONK) have not been established. The purposes of this study were to review the outcome of conservative treatment for patients with early-stage SONK and to examine clinical factors affecting the prognosis.

METHODS

Diagnosis of early-stage SONK was made based on the criteria consisting of specific clinical features including magnetic resonance imaging (MRI) findings. During the study period, all patients with this diagnosis underwent standardized conservative treatment. The study population comprised 38 knees in 36 patients with a mean age at presentation of 66.4years. The mean follow-up period was 34.9months. During the treatment course, progressive joint space narrowing or collapse of bony contours identified in serial follow-up radiographs was regarded as indicating a poor prognosis. The significance of potential prognostic factors such as age, gender, obesity, coronal alignment, lesion size, and MRI findings was analyzed using a multivariate logistic regression analysis.

RESULTS

The prognosis was defined to be poor in eight knees (21.1%). The multivariate logistic regression analysis for potential risk factors revealed that only varus alignment with a femorotibial angle (FTA) of 180° or more on the initial radiograph was significantly associated with the poor prognosis (P=0.01, odds ratio 28.1) while no other factors significantly correlated with the prognosis.

CONCLUSIONS

Approximately 80% of patients with early-stage SONK could be managed successfully with conservative treatment without progression of the disease process. The presence of varus deformity (FTA of 180° or more) was significantly associated with poor prognosis complicated with progressive deformity and prolonged disability.

LEVEL OF EVIDENCE

Level IV, case series.

Subchondral Impaction Fractures of the Medial Femoral Condyle in Weightlifters: A Report of 5 Cases

Although subchondral impaction fractures have already been reported in the non-weight-bearing portion of the lateral femoral condyle, this study reveals the presence of an intra-articular impaction fracture of the postero-superior region of the non-weight-bearing portion of the medial femoral condyle recognized in 5 of a group of 22 representatives of the Polish national Olympic weightlifting team, who underwent 1.5T magnetic resonance imaging examination. Articular cartilage lesions varied with regard to the type of injury and its severity ranging from healed or subchronic injuries to acute trauma. All described individuals had no clinical history of acute knee trauma and only 3 of them had minor pain symptoms. The accumulation of microtraumas occurring during participation in particular activities associated with weightlifting training seems to be responsible for the development of this type of contusion. This is the first description of impaction fracture observed in this location in professional weightlifters.

Femoral condyle insufficiency fractures: associated clinical and morphological findings and impact on outcome

OBJECTIVE

To determine the characteristics of femoral condyle insufficiency fracture (FCIF) lesions and their relative associations with the risk of clinical progression.

MATERIALS AND METHODS

This HIPAA-compliant retrospective study was approved by our Institutional Review Board. Seventy-three patients (age range, 19-95) were included after excluding patients with post-traumatic fractures, bone marrow infarct, osteochondritis dissecans, or underlying tumor. Two board-certified musculoskeletal radiologists classified morphologic findings including lesion diameter, associated bone marrow edema pattern, and associated cartilage/meniscus damage. Electronic medical charts were evaluated for symptoms, risk factors, and longitudinal outcomes, including total knee arthroplasty (TKA). Imaging characteristics were correlated with clinical findings, and comparison of outcome groups was performed using a regression model adjusted for age.

RESULTS

The majority of patients with FCIF were women (64.4%, 47/73), on average 10 years older than men (66.28 ± 15.86 years vs. 56.54 ± 10.39 years, p = 0.005). The most common location for FCIF was the central weight-bearing surface of the medial femoral condyle; overlying full thickness cartilage loss (75.7%, 53/70) and ipsilateral meniscal injury (94.1%, 64/68) were frequently associated. Clinical outcomes were variable, with 23.9% (11/46) requiring TKA. Cartilage WORMS score, adjacent cartilage loss, and contralateral meniscal injury, in addition to decreased knee range of motion at presentation, were significantly associated with progression to TKA (p < 0.05).

CONCLUSIONS

FCIF are frequently associated with overlying cartilage loss and ipsilateral meniscal injury. The extent of cartilage loss and meniscal damage, in addition to loss of knee range of motion at the time of presentation, are significantly associated with clinical progression.

Subchondral insufficiency fractures of the knee: review of imaging findings

Subchondral insufficiency fracture of the knee (SIFK) is a potentially devastating disorder that may progress rapidly to osteoarthritis with articular surface collapse. It should be suspected in the appropriate clinical setting, as in early stages it is usually indistinct on initial plain radiographs and magnetic resonance imaging is required for a definitive diagnosis. Outcome of SIFK depends on several factors, including the initial subchondral fracture size, patient BMI, degree of osteopenia, as well as early diagnosis and initial treatment. The purpose of this paper is to review the clinical presentation, pathophysiology, image findings, complications and outcome of SIFK.

Stress fracture of the pelvis and lower limbs including atypical femoral fractures-a review

Stress fractures, that is fatigue and insufficiency fractures, of the pelvis and lower limb come in many guises. Most doctors are familiar with typical sacral, tibial or metatarsal stress fractures. However, even common and typical presentations can pose diagnostic difficulties especially early after the onset of clinical symptoms. This article reviews the aetiology and pathophysiology of stress fractures and their reflection in the imaging appearances. The role of varying imaging modalities is laid out and typical findings are demonstrated. Emphasis is given to sometimes less well-appreciated fractures, which might be missed and can have devastating consequences for longer term patient outcomes. In particular, atypical femoral shaft fractures and their relationship to bisphosphonates are discussed. Migrating bone marrow oedema syndrome, transient osteoporosis and spontaneous osteonecrosis are reviewed as manifestations of stress fractures. Radiotherapy-related stress fractures are examined in more detail. An overview of typical sites of stress fractures in the pelvis and lower limbs and their particular clinical relevance concludes this review.

Teaching Points

• Stress fractures indicate bone fatigue or insufficiency or a combination of these.

• Radiographic visibility of stress fractures is delayed by 2 to 3 weeks.

• MRI is the most sensitive and specific modality for stress fractures.

• Stress fractures are often multiple; the underlying cause should be evaluated.

• Infratrochanteric lateral femoral fractures suggest an atypical femoral fracture (AFF); endocrinologist referral is advisable.

MRI of subchondral fractures: a review

Several authors have recently emphasized the role of magnetic resonance imaging (MRI) in the diagnosis of subchondral fractures. There is increasing interest about this type of fractures, mostly because they have been implicated in the genesis of some well-known destructive articular conditions whose cause was previously undetermined, such as distal clavicular osteolysis, rapidly progressive osteoarthritis of the hip, spontaneous osteonecrosis of the knee and adult-type Freiberg's infraction. Subchondral fractures may ultimately lead to bone collapse, secondary osteonecrosis and severe articular damage, and there may be rapid progression of joint destruction over a period of weeks to months. It has been suggested that timely diagnosis might potentially improve the outcome and avoid the onset of destructive joint disease, making MRI even more important in this setting. The fracture line usually appears as a band of low signal intensity in the subchondral bone plate, adjacent to the articular surface, most often surrounded by bone marrow edema. In this article the authors review the most relevant imaging features of subchondral fractures in several joints, stressing the importance of early recognition for a better outcome.

Subchondral insufficiency fractures and spontaneous osteonecrosis of the knee may not be related to osteoporosis

The term insufficiency fracture implies inadequate bone and is applied to some subchondral knee magnetic resonance images. We reviewed bone mineral density, body mass index, meniscal extrusion, comorbidities, and demographics in 32 knee insufficiency fracture patients. Only five were osteoporotic. Meniscal extrusion was predominant.

PURPOSE

The literature supports systemic osteoporosis as a risk fracture for spontaneous osteonecrosis of the knee (SONK). SONK is also called a subchondral insufficiency fracture. Recognizing that insufficiency fracture and SONK are related, we designed this retrospective study to determine if knee subchondral insufficiency fractures were associated with osteoporosis based on bone mineral density.

METHODS

Based on magnetic resonance imaging findings, 32 patients were diagnosed as having an insufficiency fracture by an orthopaedic surgeon with magnetic resonance imaging confirmation by a musculoskeletal radiologist. We reviewed body mass index, age, sex, comorbidities, demographics, and bone mineral density using both T-scores and Z-scores.

RESULTS

The average age was 70, and only five patients were osteoporotic. Twenty-six of the 32 patients were female. The average age-related Z-score was 1 standard deviation above normal.

CONCLUSIONS

We conclude that osteoporosis is not the underlying cause of this disorder in the majority of patients.

Conservative treatment of spontaneous osteonecrosis of the knee in the early stage: pulsed electromagnetic fields therapy

BACKGROUND

HYPOTHESIS

pulsed electromagnetic fields treatment might improve symptoms in the early stage of spontaneous osteonecrosis of the knee.

METHODS

Twenty-eight patients (19M/9F, age 49.8±16.4 years) suffering from symptomatic (pain) Koshino stage I spontaneous osteonecrosis of the knee, confirmed by magnetic resonance imaging (MRI) were treated with local pulsed electromagnetic fields therapy (6 h daily for 90 days). Clinical evaluation: baseline, 6- and 24-month follow-up by VAS for pain, knee society score (KSS), Tegner and EQ-5D scales. MRI evaluation: baseline and 6-month follow-up, measuring bone marrow lesion's areas and grading these lesions by WORMS score. Failures: patients undergoing knee arthroplasty.

RESULTS

Pain significantly reduced at 6 months (from 73.2±20.7 to 29.6±21.3, p<0.0001), which remained almost unchanged at final follow-up (27.0±25.1). KSS significantly increased in first 6 months (from 34.0±13.3 to 76.1±15.9, p<0.0001) and was slightly reduced at final follow-up (72.5±13.5, p=0.0044). Tegner median level increased from baseline to 6-month follow-up (1(1-1) and 3(3-4), respectively, p<0.0001) and remained stable. EQ-5D improved significantly throughout the 24 months (0.32±0.33, baseline; 0.74±0.23, 6-month follow-up (p<0.0001); 0.86±0.15, 24-month follow-up (p=0.0071)). MRI evaluation: significant reduction of total WORMS mean score (p<0.0001) and mean femoral bone marrow lesion's area (p<0.05). This area reduction was present in 85% and was correlated to WORMS grading both for femur, tibia and total joint (p<0.05). Four failures (14.3%) at 24-month follow-up.

CONCLUSIONS

Pulsed electromagnetic fields stimulation significantly reduced knee pain and necrosis area in Koshino stage I spontaneous osteonecrosis of the knee already in the first 6 months, preserving 86% of knees from prosthetic surgery at 24-month follow-up. No correlation was found between MRI and clinical scores.

LEVEL OF EVIDENCE

Level IV; case series.

Osteonecrosis of the knee and related conditions

Osteonecrosis (ON) of the knee is a progressive disease that often leads to subchondral collapse and disabling arthritis. Recent studies have identified three distinct pathologic entities, all of which were previously described as knee ON: secondary ON, spontaneous ON of the knee, and postarthroscopic ON. Radiographic and clinical assessment is useful for differentiating these conditions, predicting disease progression, and distinguishing these conditions from other knee pathologies. The etiology, pathology, and pathogenesis of secondary ON of the knee are similar to those found at other sites (eg, hip, shoulder). Spontaneous ON is a disorder of unknown etiology. Postarthroscopic ON has been described as an infrequent but potentially destructive complication. Various treatment modalities (eg, core decompression, bone grafting, high tibial osteotomy, arthroplasty), have been used with varying degrees of success for each type of ON. Secondary ON frequently progresses to end-stage disease, and early surgical intervention is recommended. Initial management of spontaneous ON of the knee and postarthroscopic ON is typically nonsurgical, with observation for clinical or radiographic progression.

[Can MRI determine whether acute or chronic processes predisposing conditions are present in spontaneous osteonecrosis of the knee?]

OBJECTIVE

To analyze possible underlying causes of spontaneous osteonecrosis of the knee in adults in function of the lesion's behavior on magnetic resonance imaging (MRI): acute lesion (insufficiency fractures) or chronic lesion (osteoarthritic degeneration).

MATERIAL AND METHODS

We retrospectively evaluated knee MRI studies in 48 patients who fulfilled criteria for spontaneous osteonecrosis. A total of 51 subchondral lesions were included and classified in two groups: those in which linear images were present (Group A) and those in which linear images were not present (Group B). We recorded the location and size of the lesions, their signal intensity, their relation with bone edema, ipsilateral meniscal tear and abnormalities in the adjacent cartilage, as well as the presence of osteoarthritis.

RESULTS

We studied 28 men and 20 women (mean age, 55.1+/-18.0 years). Linear images were present in 58.5% of lesions (group A) and absent in 41.2% (group B). The most common location in both groups was the internal femoral condyle (56.7% in group A and 52.4% in group B), and 88.2% of lesions were hypointense on T1-weighted and fat suppressed proton density sequences. The mean size of the anteroposterior and transversal diameters was 11.9+/-3.6 x 9.4+/-3.9 mm in group A and 10.9+/-5.1 x 10.5+/-4.5 mm in group B. The predominant bone edema was severe (grade 2-3) in group A and mild (grade 0-1) in group B (p=0.033). Defects in the cartilage ipsilateral to the subchondral lesion were more common in group B than in group A, although this difference was not significant (76.2% and 56.7%, respectively; p=0.33). The frequency of ipsilateral meniscal tear was similar in the two groups (56.7% in group A and 57.1% in group B; p=0.97).

CONCLUSION

Knowing the MRI findings for spontaneous osteonecrosis and evaluating other data (type of lesion, bone edema, meniscal tear, and ipsilateral cartilage defects) can help determine the primary predisposing process. Linear lesions might be related to an acute process (insufficiency fractures) and non-linear lesions might be related to a chronic process (osteoarthritis).

Ressonância magnética da osteonecrose do joelho: estudo de 19 casos

OBJETIVO: Descrever os achados epidemiológicos, clínicos e de ressonância magnética da osteonecrose das porções distal do fêmur e proximal da tíbia. MATERIAIS E MÉTODOS: Avaliação de 19 pacientes (12 mulheres e 7 homens), sem história prévia de fatores causais, com achados à ressonância magnética sugestivos de osteonecrose do platô tibial ou côndilo femoral. RESULTADOS: Verificou-se a presença de anormalidades osteocondrais em 63,1% dos casos e em 73,6% destes houve associação com lesão meniscal ipsilateral. Houve também importante associação com edema na medular óssea em correspondência (grau III em 16 casos). CONCLUSÃO: A ressonância magnética demonstrou ser um método não invasivo com boa sensibilidade no diagnóstico da osteonecrose do joelho, bem como das lesões associadas, sendo mais frequente nas mulheres (63% dos casos).

Epidemiology and imaging of the subchondral bone in articular cartilage repair

Articular cartilage and the subchondral bone act as a functional unit. Following trauma, osteochondritis dissecans, osteonecrosis or osteoarthritis, this intimate connection may become disrupted. Osteochondral defects-the type of defects that extend into the subchondral bone-account for about 5% of all articular cartilage lesions. They are very often caused by trauma, in about one-third of the cases by osteoarthritis and rarely by osteochondritis dissecans. Osteochondral defects are predominantly located on the medial femoral condyle and also on the patella. Frequently, they are associated with lesions of the menisci or the anterior cruciate ligament. Because of the close relationship between the articular cartilage and the subchondral bone, imaging of cartilage defects or cartilage repair should also focus on the subchondral bone. Magnetic resonance imaging is currently considered to be the key modality for the evaluation of cartilage and underlying subchondral bone. However, the choice of imaging technique also depends on the nature of the disease that caused the subchondral bone lesion. For example, radiography is still the golden standard for imaging features of osteoarthritis. Bone scintigraphy is one of the most valuable techniques for early diagnosis of spontaneous osteonecrosis about the knee. A CT scan is a useful technique to rule out a possible depression of the subchondral bone plate, whereas a CT arthrography is highly accurate to evaluate the stability of the osteochondral fragment in osteochondritis dissecans. Particularly for the problem of subchondral bone lesions, image evaluation methods need to be refined for adequate and reproducible analysis. This article highlights recent studies on the epidemiology and imaging of the subchondral bone, with an emphasis on magnetic resonance imaging.

Osteonecrosis of the tibial plateau: magnetic resonance imaging appearances with quantitation of lesion size and evidence of a pathogenesis of meniscal injury

PURPOSE

To determine the magnetic resonance (MR) imaging appearances of osteonecrosis of the tibial plateau and perform quantitative analysis of the extent of the necrotic area.

MATERIALS AND METHODS

Twenty-eight patients (34 knees) with osteonecrosis were retrospectively evaluated using MR imaging and other modalities where available. A computerized image analysis program that allowed quantification of the lesion size was used to obtain measurements of the extent of involvement, which were then incorporated into each stage of the disease.

RESULTS

The MR imaging findings of osteonecrosis of the tibial plateau included subchondral regions of abnormal signal intensity (n = 28), a double-line sign (n = 11), and fractures (n = 9). Meniscal tears and cartilage abnormalities were disclosed in the affected knee compartment with an equal frequency (n = 17). The size of the necrotic lesion varied among different stages of the disease as follows: 6.8% to 15.7% (stage I); 6.5% to 59.3% (stage II); 23.5% to 61.3% (stage III); and 34.3% to 75% (stage IV). The extent of involvement was greater in stage II than that in stage I (P < 0.001) and in stage IV than that in stage III (P < 0.05), whereas the extent of involvement in stage III was not significantly greater than that in stage II (P > 0.05).

CONCLUSIONS

The MR imaging characteristics of osteonecrosis of the tibial plateau are variable. The association of osteonecrosis at this site with meniscal tears and cartilage abnormalities has important implications for pathogenesis of the disease as it relates to physical stress. Quantification of the lesion size provides precise information for optimal staging of the disease.

Transient osteoporosis of the hip and spontaneous osteonecrosis of the knee: a common aetiology?

INTRODUCTION

The aetiologies of transient osteoporosis of the hip (TOH) and spontaneous osteonecrosis of the knee (SONK) are still unknown. Both entities present with pain and extensive bone marrow oedema is seen on magnetic resonance imaging.

METHODS AND MATERIALS

We describe a patient who presented with TOH and later also developed SONK. Initial magnetic resonance imaging findings of both the hip and the knee showed extensive bone marrow oedema and a subchondral fracture line suggesting that subchondral fractures might be of importance to the aetiology of both conditions.

CONCLUSION

To our knowledge, this is the first case report that describes the occurrence of TOH and SONK in the same patient and introduces the possibility of a common aetiology.

Meniscal root injury and spontaneous osteonecrosis of the knee: an observation

We describe injuries to the posterior root of the medial meniscus in patients with spontaneous osteonecrosis of the medial compartment of the knee. We identified 30 consecutive patients with spontaneous osteonecrosis of the medial femoral condyle. The radiographs and MR imaging were reviewed. We found tears of the posterior root of the medial meniscus in 24 patients (80%). Of these, 15 were complete and nine were partial. Complete tears were associated with > 3 mm of meniscal extrusion. Neither the presence of a root tear nor the volume of the osteonecrotic lesion were associated with age, body mass index (BMI), gender, side affected, or knee alignment. The grade of osteoarthritis was associated with BMI. Although tears of the posterior root of the medial meniscus were frequently present in patients with spontaneous osteonecrosis of the knee, this does not prove cause and effect. Further study is warranted.

Risk of osteonecrosis of the femoral condyle after arthroscopic chondroplasty using radiofrequency: a prospective clinical series

Radiofrequency (RF) energy can be used for treatment of intraarticular pathologies in knee joint. RF energy was found to be superior to mechanical techniques in smoothening the articular surface (chondroplasty), shortening the operation time and reducing the blood loss. As RF produces thermal energy it has been reported to be responsible for the postoperative osteonecrosis however, there is no clinical evidence in the literature supporting that RF causes osteonecrosis. The current study searches for an answer whether surgical arthroscopic modalities using RF energy causes osteonecrosis. We hypothesize in the presented study that chondroplasty with RF has no effect on increasing the incidence of osteonecrosis in knee joint. In a prospective clinical trial, arthroscopic chondroplasty was performed in 50 patients with degenerative changes of the articular cartilage, stage II and III according to Outerbridge. To be included in the study, the patients had to meet the following criteria: (1) Preoperative MRI and plain film radiographs showing no evidence of osteonecrosis. (2) Patients had to be symptomatic for at least 6 weeks before the preoperative MRI. (3) Arthroscopically confirmed stage II or III. Preoperative MRI was taken in all patients. For chondral lesions bipolar RF energy system (VAPR-DePuy Mitek, Norwood, USA) was used. The patients were examined at the end of the sixth month and we performed MRI. Fifty patients with an average of age 45.54 (between 18 and 64) (SD, 10.63). During arthroscopy, together with chondropathy 22 patients pure medial meniscus tears, 7 patients medial and lateral meniscus tears, 7 patients pure lateral meniscus tears, 2 patients medial plica, and 3 patients synovial hypertrophy were detected. Among all 50 patients, osteonecrosis were detected at only 2 (4%) in the postoperative period. Until now it was not clear that RF energy causes osteonecrosis; however, according to this study if proper method is used, bipolar RF energy used for arthroscopic chondroplasty does not causes subchondral osteonecrosis.

MRI-demonstrated outcome of subchondral stress fractures of the knee after treatment with iloprost or tramadol: observations in 14 patients

OBJECTIVE

To investigate the outcome of subchondral stress fractures (SSF) of the knee after treatment with the prostacyclin analogue Iloprost or the opioid analgesic Tramadol.

DESIGN

Case series/retrospective review.

SETTING

Tertiary care center.

PATIENTS

Fourteen patients with at least a single subchondral stress fracture of the knee, surrounded by bone marrow edema, visible on T1-weighted and short tau inversion recovery magnetic resonance images.

INTERVENTIONS

Nine patients had been treated with oral Iloprost (group 1; 11 SSF) and 5 patients with Tramadol (group 2; 5 SSF) for 4 weeks in the course of a double-blind, randomized clinical trial. MR images were obtained at baseline (1 day before the start of treatment), after 3 months, and after 1 year.

MAIN OUTCOME VARIABLES

SSF volumes and their rates of change between baseline and follow-up examinations, as determined on T1-weighted images by computer-assisted quantification.

RESULTS

After three months, the SSF volumes had decreased by a median of 42.2% in group 1 and increased by a median of 2.2% in group 2 (P = 0.008). After 1 year, the median decrease in SSF volumes was 100.0% in group 1 and 65.7% in group 2 (P = 0.017).

CONCLUSION

This small case series suggests that healing of SSF is more pronounced after Iloprost treatment.

Spontaneous osteonecrosis of the knee

Spontaneous osteonecrosis of the knee presents with acute onset of severe, pain in elderly patients, usually female and usually without a history of trauma. Originally described as idiopathic osteonecrosis, the exact etiology is still debated. Evidence suggests that an acute fracture occurs as a result of chronic stress or minor trauma to a weakened subchondral bone plate. The imaging characteristics on MR reflect the age of the lesion and the symptoms. More appropriate terminology may be " subchondral insufficiency fracture of the knee" or "focal subchondral osteonecrosis".

Acute non-traumatic marrow edema syndrome in the knee: MRI findings at presentation, correlation with spinal DEXA and outcome

PURPOSE

The aim of the study was to present the MRI findings of non-traumatic edema-like lesions presented acutely in the adult knee and to correlate them with the 3-year outcome and the bone mineral density (BMD) in the spine.

MATERIALS AND METHODS

Ninety-eight patients (40 men, 58 women, mean age 60.1+/-11 years, age range 27-82 years), were followed up clinically as well as with MR imaging, when indicated, for at least 3 years. Patients were classified according to presentation in 3 groups (A: bone marrow edema (BME), B: BME and subchondral fracture, C: BME and articular collapse) and according to outcome in 2 groups (A: reversible BME, B: articular collapse). BMD measurements of the spine were carried out in males over 70 and females over 60 years old using DEXA.

RESULTS

The isolated BME pattern was observed in 64.3% (Group A), subchondral fractures without articular collapse in 11.2% (Group B) and articular collapse in 24.5% (Group C). Significant differences were found among the 3 groups at presentation, regarding the age, sex, BMD, affected area and duration of symptoms prior to imaging (p<0.05). Localization of the lesions in the weight-bearing areas of the knee was shown in 100% of C, in 90.9% of B and in 50.8% of A. The duration of symptoms prior to imaging was longer in C (7.6+/-2.8m) than in A (2.5+/-1.7m) and B (4.0+/-3.2m) (p<0.05). Group B progressed to articular collapse in 45.5%, the rest demonstrating a favourable outcome. Group C showed clinical improvement in 75% and persistent symptoms that required knee arthroplasty in 25% of cases. Articular collapse was the final outcome in 29.6% and transient BME in 70.4% of patients. These two groups showed significant differences regarding the age (p approximately 0), sex (p=0.002), low BMD (p=0.004), affected area (p approximately 0), presence of subchondral sparing (p approximately 0), duration of symptoms prior to imaging (p approximately 0), time from onset of symptoms to the final outcome (p approximately 0) and need for arthroplasty (p=0.001). None of the patients with transient BME syndrome eventually progressed to articular collapse.

CONCLUSION

In the context of acute non-traumatic knee BME, the age and sex of the patient, the duration of symptoms before imaging, the pattern of BME, and the BMD appear to correlate with the final outcome.

Magnetic resonance imaging of subarticular bone marrow lesions in dogs with stifle lameness

A bone bruise is a magnetic resonance (MR) imaging sign thought to signify acute traumatic microfracture of trabecular bone with hemorrhage and edema in the marrow that may occur without grossly visible disruption of the adjacent cortices or overlying cartilage. In approximately 75% of people with acute anterior-cruciate ligament tears, bone bruises are detected in characteristic locations within the femur and tibia and are best seen as high-signal lesions using fat-suppression sequences. We questioned whether this is a component of naturally acquired stifle lameness in dogs and obtained short-tau inversion recovery (STIR) images of six dogs with stifle lameness. High-signal STIR lesions were detected in five of six (83%) dogs and eight of 12 (67%) limbs. We observed these lesions deep to the intercondylar fossa of the femur and intercondylar eminence of the tibia, which are atypical locations in people. High-signal STIR lesions were detected in dogs with only synovitis, partial tear of the cranial cruciate ligament (CCL) and complete tear of the CCL. One of these lesions was seen in the lateral tibial condyle, a typical location in humans with acute anterior cruciate ligament tear. As the MR imaging appearance of stress fractures and bone bruises are similar, and the high-signal STIR lesions are at attachment sites of the CCL, this finding may be due to stress disease or other unknown causes, rather than bone bruising. High-signal STIR lesions may be a common sign in naturally acquired canine stifle disease, but the pathogenesis, prognostic and diagnostic values need further investigation.

Stress fractures in athletes

A stress fracture is a partial or complete bone fracture that results from repeated application of stress lower than the stress required to fracture the bone in a single loading. Otherwise healthy athletes, especially runners, sustain stress injuries or fractures. Prevention or early intervention is the preferable treatment. However, it is difficult to predict injury because runners vary with regard to biomechanical predisposition, training methods, and other factors such as diet, muscle strength, and flexibility. Stress fractures account for 0.7% to 20% of all sports medicine clinic injuries. Track-and-field athletes have the highest incidence of stress fractures compared with other athletes. Stress fractures of the tibia, metatarsals, and fibula are the most frequently reported sites. The sites of stress fractures vary from sport to sport (eg, among track athletes, stress fractures of the navicular, tibia, and metatarsal are common; in distance runners, it is the tibia and fibula; in dancers, the metatarsals). In the military, the calcaneus and metatarsals were the most commonly cited injuries, especially in new recruits, owing to the sudden increase in running and marching without adequate preparation. However, newer studies from the military show the incidence and distribution of stress fractures to be similar to those found in sports clinics. Fractures of the upper extremities are relatively rare, although most studies have focused only on lower-extremity injuries. The ulna is the upper-extremity bone injured most frequently. Imaging plays a key role in the diagnosis and management of stress injuries. Plain radiography is useful when positive, but generally has low sensitivity. Radionuclide bone scanning is highly sensitive, but lacks specificity and the ability to directly visualize fracture lines. In this article, we focus on magnetic resonance imaging, which provides highly sensitive and specific evaluation for bone marrow edema, periosteal reaction as well as detection of subtle fracture lines.