Spontaneous osteonecrosis of the knee: tibial plateaus

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 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.

Open-wedge high tibial osteotomy for spontaneous osteonecrosis of the medial tibial plateau shows excellent clinical outcomes

PurposeThere have been few reports on medial tibial plateau osteonecrosis, and treatment options remain controversial. This study aimed to evaluate the clinical outcomes of open-wedge high tibial osteotomy (OWHTO) for osteonecrosis of the medal tibial plateau.MethodsPatients who underwent OWHTO for spontaneous osteonecrosis of the medial tibial plateau from November 2013 to September 2017 at our institution and followed up for at least 2 years after surgery were included in this study. Patients with history of alcohol abuse and corticosteroid therapy were excluded. Clinical evaluations, including the Japanese Orthopedic Association (JOA) score and the Oxford Knee Score (OKS), were measured preoperatively and at the final followup. Radiological evaluations included the weight-bearing line ratio (WBLR) and the lesion stage of the osteonecrosis according to Carpintero, Lotke, and the modified Ficat and Arlet classification. The area and size of the necrosis and the type of meniscus tear were also evaluated using preoperative magnetic resonance imaging (MRI). Additionally, cartilage regeneration was evaluated at plate removal.ResultsTwelve cases that underwent OWHTO for spontaneous osteonecrosis of the medial tibial plateau were enrolled. Eleven cases had isolated medial tibial osteonecrosis, and one case had both femoral and tibial osteonecrosis. The mean age was 59.6 ± 9.0 years, and the mean follow-up period was 41.8 ± 17.6 months.The WBLR significantly changed after OWHTO (24.0% ± 10.7% to 66.3% ± 6.7%, P < 0.001), and all clinical scores significantly improved after surgery: JOA score 63.3 ±12.3 to 95.0 ± 4.8, OKS 27.4 ± 7.8 to 42.6 ± 4.1, both 0.001. There were no adverse complications requiring additional surgery. The MRI findings revealed that all cases had meniscal lesions in addition to a necrotic lesion. Second-look arthroscopy was performed at plate removal in 11 cases, and cartilage regeneration was observed in 9/11 cases (81.8%).ConclusionsThis study's results demonstrated that OWHTO is an effective procedure for spontaneous osteonecrosis of the medial tibial plateau with respect to subjective and objective clinical outcomes.

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.

Magnetic resonance imaging of subchondral insufficiency fractures of the lower limb

Subchondral insufficiency fracture (SIF) is a non-traumatic condition that has historically been associated with elderly, osteoporotic women and patients with systemic conditions. There has been much work done to determine the pathogenesis of SIF, which has previously been regarded as idiopathic, rapid-progressive osteoarthritis or osteonecrosis of the hip, spontaneous osteonecrosis of the knee (SONK), osteochondral defect (OCD) of the talus and adult-onset Freiberg infraction of the metatarsal head. Early diagnosis and management are crucial to prevent subchondral collapse, secondary osteonecrosis and early-onset osteoarthritis. Magnetic resonance imaging (MRI) plays an important role in the diagnosis of SIF, which is often inconspicuous on initial radiographs. In this article, the authors provide an update on the role of MRI in identifying key imaging features of SIF in various joints of the lower limb to aid in its correct diagnosis.

Clinical Characteristics and Treatment of Spontaneous Osteonecrosis of Medial Tibial Plateau: A Retrospective Case Study

Background:

In a small proportion of cases, spontaneous osteonecrosis of the knee (SONK) involves the medial tibial plateau (MT). Here, we introduced the clinical characteristics of spontaneous osteonecrosis of the MT and unicompartmental knee arthroplasty (UKA) as the favorable treatment for this situation based on a retrospective case study.

Methods:

Patients with spontaneous osteonecrosis of the MT, confirmed by magnetic resonance imaging (MRI) at Guangdong Provincial Hospital of Chinese Medicine (China) from March 2015 to June 2016, were included as a case serial and analyzed retrospectively. All patients underwent Oxford Medial UKA. The characteristics of their lesions, corresponding treatment, and results of follow-up were presented. The lesion scores and grade were determined according to the criteria of Ficat and Arlet.

Results:

In total, 22 patients (5 men, 17 women; mean age, 64.1 years) with spontaneous osteonecrosis of the MT were analyzed. The lesion stages assessment showed that 3 (14%) were Stage II, 10 (45%) were Stage III, 7 (32%) were Stage IV, and 2 (9%) were Stage V. In the sagittal plane, 7 (32%) were in the anterior region (MTa) and 15 (68%) were central (MTc). The lesion volume averaged 2.24 ± 0.79 cm³ (range: 1.57–3.08 cm³). Seventeen patients (77%) had Level III posterior medial meniscus root tears (MMRTs). All the patients underwent UKA. Average follow-up was 30.0 ± 6.4 months with a range of 23.0–38.0 months. The visual analog scale score was 7.78 ± 0.67 before surgery while decreased to 2.22 ± 1.09 at the final follow-up (P < 0.001). The Hospital for Special Surgery scores of pre-/post-surgery were 65.67 ± 5.45 and 84.10 ± 4.20, respectively (P < 0.001).

Conclusions:

SONK often occurs in the anterior and central tibial plateau due to abnormal stresses. Most of the patients had Level III posterior medial meniscus root tears. MRI is recommended for suspected cases to identify SONK at an early stage. The use of the Oxford Medial UKA for SONK of the MT is reliable both immediately and at follow-up.

Metaphyseal burst sign: A secondary sign on MRI of subchondral insufficiency fracture of the knee

INTRODUCTION

To describe a novel secondary sign of subchondral insufficiency fracture of the knee, metaphyseal burst sign (soft tissue oedema in the meta-epiphyseal region of the affected condyle).

METHODS

An electronic database research of 7926 knee MRI examinations was performed. Forty-eight scans were included in the study. The diagnosis of subchondral insufficiency fracture (SIF) was confirmed in a consensus review by one fellowship trained musculoskeletal (MSK) radiologist and one radiology fellow. The presence of metaphyseal burst sign was evaluated in the cohort.

RESULTS

Forty-one patients were included in the study (21 males, 20 females). The mean age was 61.5 years (range 41-80 years). The anatomical location was medial femoral condyle (n = 28), the lateral femoral condyle (n = 5) and medial tibial condyle (n = 8). The metaphyseal burst sign was present in 45 of the 48 scans reviewed. The average craniocaudal length of the soft tissue oedema defined as metaphyseal burst sign was 7 cm (range 10.5 to 4.5).

CONCLUSION

The metaphyseal burst sign is an early, indirect sign of SIF.

Unicompartmental knee arthroplasty for spontaneous osteonecrosis of the medial tibial plateau

BACKGROUND

There have been very few reports on isolated medial tibial plateau osteonecrosis, and the condition has not been clearly described. Unicompartmental knee arthroplasty (UKA) may be an appropriate treatment method for this condition. The aims of this study were to report our experience of using mobile-bearing knee implants for osteonecrosis of the medial tibial plateau and to discuss the etiology and treatment of this type of osteonecrosis.

METHODS

This study included six consecutive patients with isolated medial tibial plateau osteonecrosis treated with an Oxford mobile-bearing knee implant. The average age was 71.0 years. We preoperatively graded the tibial necrosis lesion using radiographic findings. We also assessed the area and size of necrosis, extent of the surrounding high-density area, and the presence of any meniscal lesions by preoperative magnetic resonance imaging (MRI), and pre- and postoperative Oxford Knee Scores (OKS) were evaluated.

RESULTS

MRI findings revealed that all patients had meniscal lesions in addition to a necrotic lesion. All patients significantly improved in their OKS. No knees required revision for either infection or loosening.

CONCLUSIONS

The etiology of these cases of necrosis is still unclear, but the current study suggested an association with medial meniscal lesions. The results of the study were promising, showing a good short-term clinical outcome of Oxford mobile-bearing UKA for this type of osteonecrosis.

The Use of Tomosynthesis in the Global Study of Knee Subchondral Insufficiency Fractures

RATIONALE AND OBJECTIVES

Subchondral insufficiency fractures (SIF), previously termed spontaneous osteonecrosis of the knee, are marked by a sudden onset of severe pain. Other than the size of the lesion, prediction for progression to joint replacement is difficult. The objective was to determine if quantitative analysis of bone texture using digital tomosynthesis imaging would be useful in predicting more rapid progression to joint replacement.

MATERIALS AND METHODS

Tomosynthesis studies of 30 knees with documented SIF were quantified by fractal, mean intercept length (MIL), and line fraction deviation analyses. Fractal dimension, lacunarity, MIL, and line fraction deviation variables measured from these analyses were then correlated to short interval progression to joint replacement surgery.

RESULTS

Higher odds for joint replacement were related to higher values of the standard deviation of slope lacunarity and to morphometric measures (eg, MIL).

CONCLUSIONS

Using digital tomosynthesis images for bone texture assessment may help distinguish condylar bone response in SIF, potentially acting as a clinically relevant predictive tool. In the future, contrasting SIF to the more gradual long-term process of osteoarthritis, there may be a better understanding of the different mechanisms for the two conditions.

Post-arthroscopic osteonecrosis of the medial tibial plateau: a case series

Background

Avascular necrosis after arthroscopic surgery of the knee has already been published. The purpose of this article is to report on the frequently misdiagnosed entity of osteonecrosis of the medial tibial plateau.

Case presentation

Charts and radiographs of a consecutive series with isolated medial tibial plateau osteonecrosis were analyzed. The criterion for inclusion was the absence of trauma. Six caucasian female patients with an average age of 76.5 years complied with this criterion. Three of these cases had had arthroscopic intervention for medial meniscal lesion within the previous year.

Conclusions

The etiology of these necroses remains unclear. Osteonecrosis must be taken into account as a possible cause of persistent knee pain after surgery. Correlation between arthroscopic treatment and necrotic processes in the tibial plateau must still be regarded with skepticism.

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.

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.

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.

Postarthroscopic osteonecrosis of the knee

Little is known about the etiology of postarthroscopic osteonecrosis of the knee. Its prevalence is probably very low. The most important differential diagnosis is pre-existing and undiagnosed early-stage spontaneous osteonecrosis of the knee. From the medicolegal point of view, orthopaedic surgeons need to be aware of the diagnostic pitfalls in differentiating between postarthroscopic osteonecrosis of the knee and spontaneous osteonecrosis of the knee, and they must understand that both may be unpreventable conditions. The purpose of this report is to review the presumable pathophysiology and the clinical and radiographic features as well as the pitfalls in diagnosing postarthroscopic osteonecrosis of the knee.

Early MRI diagnosis and non-surgical management of spontaneous osteonecrosis of the knee

Spontaneous osteonecrosis of the knee (SONK) is generally associated with a poor prognosis but the outcome depends on the clinical and radiological stage at which the patients present. The earliest stage of this condition does not necessarily progress in every patient, but discriminatory radiological information is lacking in order to differentiate these patients so that unnecessary surgical intervention can be avoided. We describe 20 sequential cases of early SONK diagnosed by magnetic resonance imaging (MRI) in which non-operative management led to the spontaneous resolution of symptoms and MRI changes. Our data was compared to published series in order to derive more accurate prognostic criteria that may then be used to determine appropriate management. Average age of patients was 52 years (42-64). All patients' symptoms resolved with conservative treatment at an average of 4.8 (3-8) months after symptoms began. All MRIs returned to normal. MRI prognostic criteria that appear to indicate a benign course are the absence of focal epiphyseal contour depression and the absence of lines of low signal intensity deep in the condyles. The presence of high signal T2 rim and a length >14 mm and depth >4 mm of the low signal T2 lesion did not necessarily indicate a bad prognosis. Early SONK in this group of patients resolves without surgical intervention. The group is typically middle aged, present with acute focal pain in the knee, have no secondary cause of osteonecrosis, have minimal or no changes on plain radiographs, and have focal changes on MRI. Recognition of this group using MRI identifies the earliest changes in SONK and gives prognostic information that avoids inappropriate surgical intervention.

MR imaging of epiphyseal lesions of the knee: current concepts, challenges, and controversies

This article focuses on spontaneous painful conditions involving the subchondral bone and marrow of mature knee epiphyses. MR imaging is the technique of choice for the work-up of these lesions and enables distinction of two main categories of lesions on the basis of T1-weighted images: avascular necrosis, and lesions presenting the bone marrow edema pattern. This latter category encompasses spontaneous osteonecrosis of the knee, and a variety of self-resolving conditions that may be differentiated by the study of the subchondral bone marrow area on T2-weighted images. Behind definite appellation of lesions, the challenge for the radiologist is to provide a prognosis: the distinction between self-resolving lesions from those that may evolve to epiphyseal collapse and joint impairment should be possible in most cases.