Subchondral osteopenia and accelerated bone remodelling post-ovariectomy - a possible mechanism for subchondral microfractures in the aetiology of spontaneous osteonecrosis of the knee?

Correlation Analysis between Fat Fraction and Bone Mineral Density Using the DIXON Method for Fat Dominant Tissue in Knee Joint MRI: A Preliminary Study

Purpose

This study aimed to investigate the correlation between the fat signal fraction (FF) of the fat-dominant bone tissue of the knee joint, measured using the MRI Dixon method (DIXON) technique, and bone mineral density (BMD).

Materials and Methods

Among the patients who underwent knee DIXON imaging at our institute, we retrospectively analyzed 93 patients who also underwent dual energy X-ray absorptiometry within 1 year. The FFs of the distal femur metaphyseal (Fm) and proximal tibia metaphyseal (Tm) were calculated from the DIXON images, and the correlation between FF and BMD was analyzed. Patients were grouped based on BMD of lumbar spine (L), femoral neck (FN), and common femur (FT) respectively, and the Kruskal-Wallis H test was performed for FF.

Results

We identified a significant negative correlation between TmFF and FN-BMD in the entire patient group (r = -0.26, p < 0.05). In female patients, TmFF showed a negative correlation with FN-BMD, FT-BMD, and L-BMD (r = -0.38, 0.28 and -0.27, p < 0.05). In male patients, FmFF was negatively correlated with only FN-BMD and FT-BMD (r = -0.58 and -0.42, p < 0.05). There was a significant difference in the TmFF between female patients grouped by BMD (p < 0.05). In male patients, there was a significant difference in FmFF (p < 0.05).

Conclusion

Overall, we found that FF and BMD around the knee joints showed a negative correlation. This suggests the potential of FF measurement using DIXON for BMD screening.

Characteristics, management, and outcomes of spontaneous osteonecrosis of the knee in Indian population

PURPOSE

Spontaneous osteonecrosis of the knee affects the medial femoral condyle in patients above 55 years of age. Many reports and studies are available from western countries. But there is a gross paucity of literature on spontaneous osteonecrosis of the knee (SPONK) in the Indian subcontinent, either it is under-reported or detected at a later stage. The aim of our study was to detect SPONK in Indian population and describe its characteristics, treatment, and outcome.

MATERIAL AND METHOD

A prospective study was conducted over a period of three years. All patients above 18 years with knee pain at rest and medial condyle tenderness without joint laxity were evaluated with plain radiographs and MRI. Further tests were done if radiological signs of osteonecrosis were present. Various parameters were recoded like Visual Analog Scale (VAS), Knee Society Score (KSS), and MRI Osteoarthritis Knee Score. Conservative treatment consisted of a combination of NSAIDs and bisphosphonates. Decompression with bone grafting was done if there was no improvement or deterioration at three month follow-up.

RESULTS

Ten patients were diagnosed with SPONK. The mean age was 50 years with male predominance (60%) with the involvement of medial femoral condyle (80%) or left knee (70%). Most cases were in Koshino stage 1. Mean VAS was 6.5 and mean KSS was 59. All clinical parameters showed improvement at one year.

DISCUSSION

A study with a bigger sample size and longer follow-up is needed to fill the lacunae of literature on this topic from the Indian subcontinent. In spite of the limitations, we did observe that in our population, males were more commonly affected than females, which is contrary to most studies on the subject. Also, the disease had an early age of onset (50 years) in Indian population as compared to Western and East Asian populations.

CONCLUSION

Combined therapy of NSAIDs and bisphosphonates shows excellent results over a period of one year. Joint-preserving surgeries are effective even in Koshino stage 3 SPONK.

Predictive factors for the progression of spontaneous osteonecrosis of the knee

PURPOSE

To assess potentially predictive factors that were evaluated 1 year after the onset of symptoms in patients with spontaneous osteonecrosis of the knee (SONK) and to determine receiver operating characteristic (ROC) curve cut-off values.

METHODS

Within 1 year of symptom onset, patients with SONK-selected treatment options, mainly based on severity of pain, chose either conservative treatment (n = 27 knees) or operative treatment (n = 27 knees). Knee and whole-leg radiographs, knee MRIs and bone mineral density scans of the lumbar spine, femoral neck and femoral condyles were obtained. The parameters measured were: (1) anatomical angle on whole-leg radiograph and (2) lesion size and medial meniscus extrusion on MRI.

RESULTS

The anatomical angle and lesion size in the sagittal section (depth) on MRI were markedly larger in the operative treatment group than those in the conservative treatment group. The anatomical angle and depth on MRI of SONK at Stages 1-3 were significantly different between groups, with odds ratios (95 % confidence intervals) of 1.16 (1.18-2.34) and 1.11 (1.01-1.23). One year after symptom onset, ROC curve cut-off value for anatomical angle was 180° and depth on MRI was 20 mm.

CONCLUSION

An anatomical angle >180° and depth >20 mm on MRI were predictive factors for a poorer prognosis 1 year after symptom onset in patients with SONK. Our results on radiographs and MRI provided a predictive prognosis for patients with SONK at the initial visit to their orthopaedic surgeons.

LEVEL OF EVIDENCE

III.

The roles of architecture and estrogen depletion in microdamage risk in trabecular bone

Bone quantity, or density, has insufficient power to discriminate fracture risk in individuals. Additional measures of bone quality, such as microarchitectural characteristics and bone tissue properties, including the presence of damage, may improve the diagnosis of fracture risk. Microdamage and microarchitecture are two aspects of trabecular bone quality that are interdependent, with several microarchitectural changes strongly correlated to damage risk after compensating for bone density. This study aimed to delineate the effects of microarchitecture and estrogen depletion on microdamage susceptibility in trabecular bone using an ovariectomized sheep model to mimic post-menopausal osteoporosis. The propensity for microdamage formation in trabecular bone of the distal femur was studied using a sequence of compressive and torsional overloads. Ovariectomy had only minor effects on the microarchitecture at this anatomic site. Microdamage was correlated to bone volume fraction and structure model index (SMI), and ovariectomy increased the sensitivity to these parameters. The latter may be due to either increased resorption cavities acting as stress concentrations or to altered bone tissue properties. Pre-existing damage was also correlated to new damage formation. However, sequential loading primarily generated new cracks as opposed to propagating existing cracks, suggesting that pre-existing microdamage contributes to further damage of bone by shifting load bearing to previously undamaged trabeculae, which are subsequently damaged. The transition from plate-like to rod-like trabeculae, indicated by SMI, dictates this shift, and may be a hallmark of bone that is already predisposed to accruing greater levels of damage through compromised microarchitecture.

Review of various treatment options and potential therapies for osteonecrosis of the femoral head

Size and location of the lesion, subchondral collapse occurrence, and articular cartilage involvement are general disease progression criteria for direct osteonecrosis of the femoral head (ONFH) classifications. Treatment options for ONFH are usually based on individual factors and lesion characteristics. Although spontaneous repair of ONFH occurs in some cases, untreated ONFH is unlikely to escape the fate of subchondral collapse and usually ends up with total hip arthroplasty. Operations to preserve the femoral head, e.g., core decompression and bone grafting, are usually recommended in younger patients. They are helpful to relieve pain and improve function in the affected femoral head without subchondral collapse, however, poor prognosis after surgical procedures remains the major problem for ONFH. Pharmacological and physical therapies only work in the early stage of ONFH and have also been recommended as a supplement or prevention treatment for osteonecrosis. Following advances in basic science, many new insights focus on bone tissue engineering to optimize therapies and facilitate prognosis of ONFH. In this review, disease classifications, current treatment options, potential therapies, and the relevant translational barriers are reviewed in the context of clinical application and preclinical exploration, which would provide guidance for preferable treatment options and translation into novel therapies.

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.

Examination of osteoarthritis and subchondral bone alterations within the stifle joint of an ovariectomised ovine model

The exact relationship between osteoporosis and osteoarthritis is still a matter for debate for many. The ovariectomised ewe is frequently used as a model for osteoporosis, resulting in significant alterations in bone morphometry and turnover in both trabecular and subchondral bone after 1 year. This study examines whether ovariectomy has any impact on development of osteoarthritis within the ovine stifle joint at the same time point. In addition, we investigate whether there are any significant correlations present between articular cartilage degeneration and alterations in microstructural parameters or turnover rates in the underlying bone. Twenty-two sheep were examined in this study; 10 of the sheep underwent ovariectomy and 12 were kept as controls. Five distinctive fluorochrome dyes were administered intravenously at 12-week intervals to both groups, to label sites of bone turnover. All animals were then sacrificed 12 months postoperatively. Although most specimens showed some evidence of osteoarthritis, no measurable difference between the two study groups was detected. Osteoarthritis was associated with a thinning of the subchondral plate, specifically the subchondral cortical bone; however, whereas previous studies have suggested a link between trabecular thinning and osteoarthritis, this was not confirmed. No correlation was found between osteoarthritis and bone turnover rates of either the subchondral trabecular bone or bone plate. In conclusion, despite the fact that ovariectomy results in marked morphological and structural changes in the ovine stifle joint at 1-year postoperatively, no evidence was found to suggest that it plays a direct role in the aetiology of osteoarthritis.