1) A 🧵 looking at Subchondral Insufficiency Fractures of the Knee (SIFK).

2) Previously referred to as SONK, recent histopathological studies have found this term to be inaccurate and instead SIFK is used due to an insufficiency # of the subchondral bone secondary to underlying causes (Hussain et al., 2019).

3) Pathophysiology: Insufficiency # is thought to increase subchondral oedema which impedes blood flow and may result in ischaemia (Hussain et al., 2019). They are graded from 1-4 (low to high severity).

4) These can develop due to secondary causes (sickle cell, ++ glucocorticoid use, heavy smoking or alcoholism), post-arthroscopy (such as meniscectomy) or due to intrinsic factors within the knee joint itself

5) More specifically, mid meniscus extrusions >5mm are associated with high grade SIFK and these can usually develop following posterior root or radial tears that are undiagnosed (Okazaki et al., 2022).

Grade of Subchondral Insufficiency Fracture of the Knee and the Presence of a Posterior Shiny-Corner Lesion are Correlated with Duration of Medial Meniscus Posterior Root Tear in Women - PubMed

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Bone marrow edema (BME) after meniscus injury and risk factors for subchondral insufficiency fracture of the knee (SI...

https://pubmed.ncbi.nlm.nih.gov/35503439/

6) Meniscal pathology can impact the hoop mechanism = cannot convert axial loads radially as efficiently and this increases contact pressure through the tibiofemoral joint which may predispose to excessive load on chondral surfaces Pic from Sayyid et al (2019)

7) Features: Often an acute onset of severe knee pain which occurs in the absence of trauma. Can be associated with prolonged weight bearing. Greater prevalence in females aged 50-60yrs

8) The medial femoral condyle is more susceptible due to watershed areas and ? Increased prevalence of medial meniscal pathology. Pt’s will often be exquisitely tender along this landmark and the joint line. Mechanical features and instability are less common

9) Imaging: MRI is gold standard. Often hypointense signal or line on T1 & T2 grade. You will also be able to see bone marrow oedema which will not be evident on plain radiographs. (Pic from radiopaedia)

10) Prognostic Factors; Pareek & colleagues (2020) summarised this nicely with a predictive model that had an AUC of 82.5%. Those with >4pt’s were 39x more likely to undergo an arthroplasty!

11) Individuals with low grade lesions or w/o cystic formation, osteonecrosis or articular collapse had favourable outcomes of reversibility and could commence on TTWB protocol to facilitate recovery of the # site (Sayyid et al., 2019).

12) Recovery is slow with these types of injuries and can take up to 3yrs (Gourlay et al., 2015). Period of protected weight bearing accompanied with potentially Vit D, Calcium, statins or biphosphonates is often recommended

13) For further reading;

Subchondral insufficiency fracture of the knee: review of current concepts and radiological differential diagnoses - Japanese Journal of Radiology

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Subchondral insufficiency fracture of the knee (SIFK) is a common cause of knee joint pain in older adults. SIFK is a...

https://link.springer.com/article/10.1...