The Fate of Bone Marrow Lesions After Open Wedge High Tibial Osteotomy: A Comparison Between Knees With Primary Osteoarthritis and Subchondral Insufficiency Fractures

Subchondral insufficiency fracture of the knee

Subchondral insufficiency fractures of the knee (SIFK) are a relatively common cause of knee pain, particularly in middle-aged and older adults. The SIFK is a type of stress fracture that occurs when excessive and repetitive or supraphysiologic loads are applied to subchondral bone [1]. Historically, this type of fracture was termed spontaneous osteonecrosis of the knee (SONK) until advances in MRI identified underlying fractures as well as meniscal deficiency as likely attributable etiologies. Consequently, SIFK has replaced SONK as the more appropriate term to refer to this category of conditions, with SONK now viewed as an advanced SIFK lesion. With greater availability of MRI, SIFK has been more frequently recognized and not as commonly mistaken for knee osteoarthritis as it had been in the past, with important implications for treatment and management of this condition.

Bone marrow lesions in osteoarthritis: Characterising genetic and histological changes to understand disease pathophysiology

Osteoarthritis (OA) is a chronic debilitating condition that affects the whole joint. There are several sources of pain in OA that include the synovium, bone, including osteophytes and more recently bone marrow lesions (BML) that correlate with pain. Recent studies have shown that the bone compartment contributes to pain in OA through the development of OA-BMLs which are richly innervated and demonstrate angiogenesis. The synovium is also innervated in OA tissue and is another distinct source of pain, with imaging and genetic studies supporting the observation that synovitis is an important component of pain in OA. Previous studies using magnetic resonance imaging (MRI) have shown that bone marrow lesions (BMLs), observed as high intensity signal on T2 fat-suppressed imaging sequences, are commonly found in OA and are associated with progression of pain symptoms. Recent studies have described the genetic signature of BMLs and the characteristic histological changes of BML tissue. In this narrative review we describe the recent developments in the discovery of the gene expression profiles identified from BMLs. We also review the recently characterised histological changes from BMLs in large weight-bearing joints including the knee and hip. Finally, we discuss the implications of new genetic and histological findings in BML in the context of new developments for pharmacological therapies in OA.

Unicompartmental Knee Arthroplasty Versus Opening-Wedge High Tibial Osteotomy for Spontaneous Osteonecrosis of the Knee: A Retrospective Cohort Study

Background

Unicompartmental knee arthroplasty (UKA) and high tibial osteotomy (HTO) are treatment options for patients with medial spontaneous osteonecrosis of the knee (SONK).

Purpose

To compare the clinical outcomes after UKA and HTO in patients with SONK.

Study Design

Cohort study; Level of evidence, 3.

Methods

This retrospective study included 42 patients who had undergone Oxford UKA and 40 patients who had undergone opening-wedge HTO between 2014 and 2020. All patients were diagnosed with isolated medial SONK without subchondral collapse of the femoral condyle and tibial plateau. The patients were preoperatively and postoperatively evaluated using the Lysholm knee scoring system, the Western Ontario and McMaster Universities Osteoarthritis Index, and a numeric rating scale assessing patient satisfaction.

Results

Patients in the UKA group were significantly older than those in the HTO group (median age, 71.5 years [IQR, 68.0-76.5 years] vs 65.0 years [IQR, 60.0-70.0 years], respectively; P < .001). The median follow-up time was 3.78 years (IQR, 2.45-4.53 years) for the UKA group and 3.87 years (IQR, 2.90-5.60 years) for the HTO group. Significant improvements in functional scores were observed in both the UKA and HTO groups (P < .001 for all), with no significant between-group differences in scores at the final follow-up (≥2 years after surgery). The satisfaction rate was similar (80.95% for UKA and 75.0% for HTO).

Conclusion

According to the study results, significant improvements in clinical outcomes were seen after opening-wedge HTO with microfracture for a younger group of patients with SONK without subchondral collapse, while Oxford UKA had a comparable effect on an older group of patients. Both UKA and HTO were found to be viable surgical approaches for SONK at short- to midterm follow-up.

Postoperative Decrease in Bone Marrow Lesion Associated With Better Clinical Outcomes Following Medial Open-Wedge High Tibial Osteotomy

PURPOSE

To assess serial changes of preoperative bone marrow lesion (BML) following medial open-wedge high tibial osteotomy (MOWHTO) up to 2 years and evaluate whether postoperative change of BML affected patient-reported outcome measures (PROMs) at 2 years' follow-up. Factors related to the postoperative changes in BML also were evaluated.

METHODS

The current study retrospectively assessed prospectively collected data of consecutive patients between December 2016 and March 2018 who underwent MOWHTO for symptomatic knee osteoarthritis with varus malalignment (≥5°) and a minimum 2-year follow-up. Serial magnetic resonance imaging scans at preoperative and postoperative 3, 6, 18, and 24 months were performed, and the extent of BML was evaluated consecutively using 2 validated methods. Clinically, preoperative and postoperative PROMs and their achievement of minimal clinically important difference values were evaluated. The associations of the extent of BMLs with PROMs at each follow-up period over time were analyzed using a linear mixed model. Furthermore, factors related to the postoperative changes of BML were assessed.

RESULTS

Of 26 patients, 21 (80.8%) had preoperative BML at medial femoral and tibial condyles. The postoperative decrease in BML was noted in 17 (81.0%) and 18 (85.7%) at medial femoral and tibial condyles. The BML decreased at postoperative 3 months and, thereafter, the extent of BML gradually reduced until postoperative 24 months. The proportion of patients achieved minimal clinically important difference was 84.6% for total Western Ontario and McMaster Universities Osteoarthritis Index scores and 80.8%, 76.9%, and 84.6% for KOOS symptom, pain, and activity of daily living subscales. Postoperative decrease in BML was significantly associated with better PROMs over postoperative 24 months. Furthermore, normo-correction (2°-5° valgus) was a significant factor for decreased BML following MOWHTO.

CONCLUSIONS

Preoperative BML gradually decreased with time following MOWHTO, and the postoperative decrease in BML related with better PROMs over postoperative 24 months. Moreover, postoperative valgus alignment was a significant factor relating the postoperative decrease of BML.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

Progression of Bone Marrow Lesions and the Development of Knee Osteoarthritis: Osteoarthritis Initiative Data

Background Bone marrow lesions (BMLs) are a known risk factor for incident knee osteoarthritis (OA), and deep learning (DL) methods can assist in automated segmentation and risk prediction. Purpose To develop and validate a DL model for quantifying tibiofemoral BML volume on MRI scans in knees without radiographic OA and to assess the association between longitudinal BML changes and incident knee OA. Materials and Methods This retrospective study included knee MRI scans from the Osteoarthritis Initiative prospective cohort (February 2004-October 2015). The DL model, developed between August and October 2023, segmented the tibiofemoral joint into 10 subregions and measured BML volume in each subregion. Baseline and 4-year follow-up MRI scans were analyzed. Knees without OA at baseline were categorized into three groups based on 4-year BML volume changes: BML-free, BML regression, and BML progression. The risk of developing radiographic and symptomatic OA over 9 years was compared among these groups. Results Included were 3869 non-OA knees in 2430 participants (mean age, 59.5 years ± 9.0 [SD]; female-to-male ratio, 1.3:1). At 4-year follow-up, 2216 knees remained BML-free, 1106 showed an increase in BML volume, and 547 showed a decrease in BML volume. BML progression was associated with a higher risk of developing radiographic knee OA compared with remaining BML-free (hazard ratio [HR] = 3.0; P < .001) or BML regression (HR = 2.0; P < .001). Knees with BML progression also had a higher risk of developing symptomatic OA compared with BML-free knees (HR = 1.3; P < .001). Larger volume changes in BML progression were associated with a higher risk of developing both radiographic OA (HR = 2.0; P < .001) and symptomatic OA (HR = 1.7; P < .001). In almost all subchondral plates, especially the medial femur and tibia, BML progression was associated with a higher risk of developing both radiographic and symptomatic OA compared with remaining BML-free. Conclusion Knees with BML progression, according to subregion and extent of volume changes, were associated with an increased risk of OA compared with BML-free knees and knees with BML regression, highlighting the potential utility of monitoring BML volume changes in evaluating interventions to prevent OA development. ClinicalTrials.gov Identifier: NCT00080171 © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Said and Sakly in this issue.

Increased nerve growth factor expression and osteoclast density are associated with subchondral bone marrow lesions in osteoarthritic knees

Objectives

Subchondral bone marrow lesions (BMLs) detected on magnetic resonance imaging in knee osteoarthritis (OA) are associated with knee pain, though the mechanisms remain unknown. Increased nerve growth factor (NGF) expression and osteoclast density in subchondral bone appear to be the key features associated with bone pain in knee OA. Therefore, we aimed to identify associations among NGF, osteoclasts, and BMLs in knee OA.

Methods

Twenty tibial plateaus were obtained from patients undergoing total knee arthroplasty for medial knee OA with BMLs at the medial tibial plateau (MTP). Osteochondral tissue samples from the weight-bearing part of the MTP, with and without BML, and from the weight-bearing part of the lateral tibial plateau (LTP), without BML, were collected. NGF expression and density of osteoclasts were compared among the three osteochondral tissue types.

Results

MTP bone with BMLs exhibited significantly higher NGF expression in bone marrow space and osteochondral channel, and higher osteoclast density than MTP bone without BML and LTP bone. The mean differences in NGF-positive area in the bone marrow space and the percentage of NGF-positive channels between MTP bones with and without BML were 9.0% (95% confidence interval [CI]: 5.9-12.1%) and 23.1% (95% CI: 11.3-35.0%), respectively. The difference in osteoclast density between MTP bones with and without BML was 0.6 osteoclasts per mm (95% CI: 0.3-0.9 osteoclasts per mm).

Conclusions

Increased NGF expression and osteoclast density are associated with subchondral BMLs in knee OA, contribute to understanding the mechanisms underlying BML-related bone pain in knee OA.

Osteoporosis, Osteoarthritis, and Subchondral Insufficiency Fracture: Recent Insights

The increased incidence of osteoarthritis (OA), particularly knee and hip OA, and osteoporosis (OP), owing to population aging, have escalated the medical expense burden. Osteoarthritis is more prevalent in older women, and the involvement of subchondral bone fragility spotlights its association with OP. Notably, subchondral insufficiency fracture (SIF) may represent a more pronounced condition of OA pathophysiology. This review summarizes the relationship between OA and OP, incorporating recent insights into SIF. Progressive SIF leads to joint collapse and secondary OA and is associated with OP. Furthermore, the thinning and fragility of subchondral bone in early-stage OA suggest that SIF may be a subtype of OA (osteoporosis-related OA, OPOA) characterized by significant subchondral bone damage. The high bone mineral density observed in OA may be overestimated due to osteophytes and sclerosis and can potentially contribute to OPOA. The incidence of OPOA is expected to increase along with population aging. Therefore, prioritizing OP screening, early interventions for patients with early-stage OA, and fracture prevention measures such as rehabilitation, fracture liaison services, nutritional management, and medication guidance are essential.

Short-Term Effects of Genicular Artery Embolization on Symptoms and Bone Marrow Abnormalities in Patients with Refractory Knee Osteoarthritis

PURPOSE

To evaluate the short-term outcomes of genicular artery embolization (GAE) for knee osteoarthritis (OA) with and without bone marrow lesion (BML) and/or subchondral insufficiency fracture of the knee (SIFK).

MATERIALS AND METHODS

This single-institution prospective observational pilot study analyzed 24 knees in 22 patients with mild to moderate knee OA, including 8 knees without BML, 13 knees with BML, and 3 knees with both BML and SIFK. The area and volume of BMLs on magnetic resonance images were measured before and after GAE. Baseline and postoperative pain and physical function were assessed using the visual analog scale (VAS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).

RESULTS

GAE significantly reduced the BML area and volume 3 months after embolization in the knees with BML (both P < .0005). GAE significantly decreased the VAS scores at 3 and 6 months after embolization in patients without BML (both P = .04) and those with BML (both P = .01). GAE also lowered the WOMAC scores 3 months after embolization in patients without and with BML (P = .02 and P = .0002, respectively). However, GAE did not significantly alter the BML area and volume (both P = .25), VAS scores (P = 1.00), and WOMAC scores (P = .08) in patients with BML and SIFK at 3 months after GAE.

CONCLUSIONS

This observational pilot study suggested that GAE effectively reduces the BML area and volume and improves pain and physical function in patients with knee OA accompanied by BML but is inefficacious in those with both BML and SIFK.

Mosaicplasty With High Tibial Osteotomy for Knee Subchondral Insufficiency Fracture Had Better Magnetic Resonance Observation of Cartilage Repair Tissue Scores With Less Bone Marrow Edema and Better Plug Union and Less Plug Necrosis Compared With Mosaicplasty Alone

PURPOSE

To determine the magnetic resonance imaging (MRI) findings after mosaicplasty (MOS) for knee subchondral insufficiency fracture (SIFK), and to analyze the relationship between MRI findings and clinical outcomes.

METHODS

We retrospectively reviewed the cases of consecutive patients who underwent MOS for SIFK with/without high tibial osteotomy (HTO) between January 1998 and December 2015. The MRI findings at 12 months after the surgery were assessed by the modified magnetic resonance observation of cartilage repair tissue (MOCART) score to determine the degree of bone marrow edema (BME), plug union, and plug necrosis. The clinical outcomes were assessed by Lysholm score to clarify the minimal clinically important difference (MCID) and patient acceptable symptom state analysis.

RESULTS

In total, 58 patients (17 men and 41 women) were enrolled in this study. Among them, 30 knees were treated by MOS alone and 28 knees were treated by MOS with HTO. The MOCART scores of patients who received MOS alone were significantly lower in BME score (P = .0060), plug union score (P = .0216), and in plug necrosis score (P = .0326) than patients who received MOS with HTO. BME lesion was less likely to persist among elderly (odds ratio 1.20, P = .0248) and female (OR 41.8, P = .0118) patients. The MCID of Lysholm score was 6.6 in MOS alone and 8.4 in MOS with HTO cases, but there were no significant association between MRI findings and the postoperative Lysholm score.

CONCLUSIONS

The MOS with HTO cases had better MOCART scores with less BME, better plug union, and less plug necrosis compared with MOS alone cases. Female and older patients had better resolution of BME, but there was no significant correlation between MRI findings and the postoperative Lysholm score. All cases in both groups showed improvement of Lysholm score exceeding MCID; thus, MOS may be effective as a joint preserving surgery for SIFK.

LEVEL OF EVIDENCE

Level IV, clinical case series.

Osteoarthritis Bone Marrow Lesions

Assessment and treatment of Bone Marrow Lesions (BMLs) could ultimately make step changes to the lives of people with osteoarthritis (OA). We here review the imaging and pathological characteristics of OA-BMLs, their differential diagnosis and measurement, and cross-sectional and longitudinal associations with pain and OA structural progression. We discuss how biomechanical and cellular factors may contribute to BML pathogenesis, and how pharmacological and non-pharmacological interventions that target BMLs might reduce pain and OA structural progression. We critically appraise semiquantitative and quantitative methods for assessing BMLs, and their potential utilities for identifying people at risk of symptomatic and structural OA progression, and evaluating treatment responses. New interventions that target OA-BMLs should both confirm their importance, and reduce the unacceptable burden of OA.

Bone marrow lesions in the knee are associated with meniscal lesions and cartilage pathologies according to the six-letter system

PURPOSE

This study aims to find a correlation between bone marrow lesions (BMLs) in knee MRI and pathologies of joint structures. In addition, according to the six-letter system classification, the authors analyzed a potential association between the area affected by BMLs and the specific type of joint lesion.

METHODS

The authors screened all the knee MRIs performed in the investigation center between 2017 and 2018 to identify the presence of BMLs. The lesions were then categorized following the "six-letter system". The authors searched the presence of associated meniscal, chondral or ligamentous lesions. Finally, the authors researched a correlation between the lesion type described by the six-letter system classification and the associated lesions.

RESULTS

MRI exams of 4000 patients were studied, identifying 666 BMLs. The associated lesions were collected for all patients, resulting in an overall prevalence of related lesions in almost 90% of patients. The authors found a statistical significance for type TLD (Tibia-Lateral-Articular) and ACL rupture. The study suggests a strong positive correlation between type E (Edge) and meniscal fracture or extrusion.

CONCLUSION

BMLs in the knee are associated in 90% of cases with a radiological sign of related injury to the joint structures. The six-letter system of BMLs type TLD can be considered a sign of ACL rupture and type E as a high suspicious sign for meniscal extrusion. Those very typical BML patterns can help the clinician in the diagnosis of ACL tears and meniscal extrusion. Furthermore, the presence of a BML must be, for the clinician, a high suspicious sign of joint-related injuries.

LEVEL OF EVIDENCE

Level 1.

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.