What did the study look at?
Just below the kneecap (patella) lies a pad of fatty tissue known as Hoffa's fat pad (infrapatellar fat pad). Oedema in its upper outer part is thought to be linked to friction between the kneecap and the thigh bone. When the kneecap does not glide properly in the groove of the thigh bone, this is called patellar maltracking.
The aim was to examine whether MRI measurements of the kneecap–thigh bone joint are related to fat pad oedema and to softening of the kneecap cartilage (chondromalacia patella).
How was it done?
- This was a retrospective study of the radiology archive, covering knee MRIs taken between January 2010 and January 2013.
- 50 patients with oedema in the upper outer fat pad (study group) were compared with 50 people with a normal fat pad (control group).
- People with direct knee trauma, meniscal problems, joint effusion, major ligament tears or previous knee surgery or arthroscopy were excluded.
- Five measurements were taken: trochlear (groove) depth, trochlear sulcus angle, sideways shift of the kneecap (patellar translation), lateral patellofemoral angle, and the Insall-Salvati ratio, which reflects kneecap height.
- The same measurements were also compared between people with and without chondromalacia patella on MRI.
What did it find?
- In the oedema group, the Insall-Salvati ratio (1.4 versus 1.1) and sulcus angle (148.2° versus 134.6°) were significantly higher, and trochlear depth (3.2 versus 4.6 mm) and lateral patellofemoral angle were lower. Patellar translation did not differ.
- A high-riding kneecap (Insall-Salvati ratio above 1.3; patella alta) was seen in 58% of the oedema group and 20% of controls.
- In the chondromalacia group (30 patients), the Insall-Salvati ratio and sulcus angle were significantly higher and trochlear depth lower; lateral patellofemoral angle and patellar translation showed no significant difference.
- Patients in the oedema group were older than controls (mean 38.6 versus 26.3 years).
The authors' conclusion
The authors conclude that oedema in the upper outer part of Hoffa's fat pad and chondromalacia patella are associated with patellar maltracking. They note that investigating this relationship may help identify the underlying cause of anterior knee pain, and that radiologists should be aware of it.
Limitations
- The study was retrospective, and the radiologist taking the measurements knew whether oedema was present, which may have introduced bias.
- Chondromalacia was diagnosed on MRI only and could not be correlated with arthroscopy; cartilage that looked normal on MRI might have been early-stage disease.
- Standard MRI sequences were used; cartilage-specific three-dimensional techniques might have revealed mild lesions.
Reference
Gürsoy M, Dirim Mete B, Oyar O, Erdoğan N, Uluç ME, Bulut T, Gürsoy S. The association of patellar maltracking with infrapatellar fat pad edema and chondromalacia patella: A quantitative morphological magnetic resonance imaging analysis. Turkish Journal of Physical Medicine and Rehabilitation. 2018;64(3):246–252. © 2018 Turkish Society of Physical Medicine and Rehabilitation.
Free full text: PubMed Central – PMC6657784
This article summarises a published scientific paper for general information; it does not replace an examination or a personal medical assessment. Please consult your doctor about your symptoms.
