Case 3 cont'd
A. Insufficiency fractures are a type of stress fracture, which are the result of normal stresses on abnormal bone. Looser zones are also a type of insufficiency fracture. They should not be confused with fatigue fractures which are due to abnormal stresses on normal bone, or with pathological fractures, the result of diseased, weakened bone due to focal pathology such as tumors (both malignant and benign). Insufficiency fractures are associated with vitamin D deficiency, long-term bisphosphonate used and osteoporosis.
These fractures are most common in the pelvis, specifically in the pelvis ring in the superior or inferior ramus. The sacrum is the second most common area of breakage. Other common areas are the vertebrae (vertebral crush or wedge fractures), the femoral neck, the sternum, the fibula and the tibia.
B. Osteochondritis dissecans is the end result of aseptic separation of an osteochondral fragment with the gradual fragmentation of the articular surface and results in an osteochondral defect. It is thought to be associated with repeated microtrauma. It is often associated with intraarticular loose bodies, and common associated findings are joint effusions and synovitis. The femoral condyles are the most affected (95%) This condition occurs bilaterally in 25% of cases, and has the following characteristic distribution:
Medial condyle: ~78.5% (range 70-85%)
"classic" lateral surface of the medial condyle: ~70%
(*tip: this can be remembered by the mnemonic "LAME"; Lateral Aspect of the Medial Epicondyle)
Lateral condyle: 15%
inferocentral portion: 13%
anterior surface: 2%
Patella: ~7.5% (range 5-10%)
typically inferomedial
patellofemoral groove (femoral trochlea): <1%
C. Rhabdomyolysis occurs due to skeletal muscle injuries. The calcium buildup causes higher tracer uptake, resulting in higher densities on bone scans. On a scan, typically uptake will be seen in soft tissues and localization corresponds to injured group of muscles.
D. On scintigraphy, subchondral insufficiency fracture of the knee is primarily unilateral and usually affects the medial femoral condyle. This affliction is associated with meniscal tears. Subchondral insufficiency fracture of the knee is not thought to be caused by osteonecrosis (bone death), but instead by osteoporosis, insufficiency fractures, and micro-traumatic forces. On histology, weakened trabeculae can be seen.
Answer: D
Q2. Answer: Right first MTP joint uptake
Discussion:
In this case, key to diagnosis was correlating bone scan findings with clinical presentation. A summary of osteochondral defects and their pathological mechanisms is shown below (see Figure 1). A diagram is also provided to demonstrate typical radiological appearances of each defect. When correlating appearance of scintigraphy and patient presentation, sex and age, the most likely diagnosis is subchondral insufficiency fracture of the knee.
https://pubs.rsna.org/doi/full/10.1148/rg.2018180044
Figure 1 – Comparison between osteochondral defects
https://pubs.rsna.org/doi/full/10.1148/rg.2018180044
Figure 2 – Appearances of different osteochondral defects