The putative mechanism of BC formation in knee OA is the onset of synovial effusion
causing an increase in intra-articular pressure, which in turn causes synovial fluid to
be forced through a weakened posteromedial joint capsule towards the GS bursa.
Anatomically and clinically it can be classified as a primary or, more often, secondary
cyst. If there is a connection between the bursa and the knee joint, the cyst is called
secondary. Almost all popliteal cysts in adults are secondary. In 30-50% of cases, there
is a connection between the knee joint cavity and the gastrocnemio-semimembranosus bursa.
The communication canal is a 15-20 mm transverse slit-like capsular opening adjacent to
the proximal postero-lateral margin of the medial femoral condyle. There is a "valve"
effect between the bursa and the joint due to the movement of the semitendinosus and
gastrocnemius muscles. During flexion, the "valve" opens and synovial fluid under
pressure moves towards the bursa; during extension, due to the tension of these muscles,
the "valve" closes and fluid is trapped in the bursa. Normally the amount of fluid is
small and can be easily reabsorbed, but in OA (mainly active knee osteoarthritis) the
amount of fluid increases, leading to fullness and the formation of popliteal cysts. The
diagnosis of BC can be supported by a number of imaging modalities, including standard
radiographs, arthrography, ultrasonography (US), computed tomography, magnetic resonance
and magnetic resonance arthrography. US is an excellent method to evaluate the popliteal
fossa, showing high sensitivity and specificity in the diagnosis of BC due to its
superficial location and the absence of overlying bony structures.
The treatment approach for Baker's cysts ranges from conservative treatments to
interventional procedures and surgery. It should be kept in mind that the majority of
cysts are secondary in the treatment approach. For this reason, treatment of the primary
pathologies causing Baker's cysts occupies an important place in the treatment approach.
Conservative treatment includes lifestyle changes, weight loss, rest, ice compression,
bandaging, elevation and ROM exercises. In interventional procedures, the most preferred
methods are aspiration of the cyst and corticosteroid injection into the cyst. Surgical
interventions can be planned as the last treatment option in recurrent baker's cysts with
persistent complaints despite conservative and interventional procedures.
Platelet rich plasma (PRP) injections are one of the most commonly used therapies in the
treatment of OA. The mechanism of action of PRP is through growth factors. The main
growth factors and growth factor families in PRP used in OA treatment include tissue
growth factor-β (TGF-β), insulin growth factor 1 (IGF-1), bone morphogenetic proteins
(BMP), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF),
epidermal growth factor (EGF), fibroblast growth factor (FGF) and hepatocyte growth
factor (HGF). TGF-β has been identified as one of the most important factors in cartilage
regeneration due to its role in the proliferation and differentiation of chondrocytes.
TGF-β induces chondrogenic differentiation of MSCs and also antagonizes the suppressive
effects of IL-1, a pro-inflammatory cytokine responsible for stimulating catabolic
factors and predisposing intracapsular structures to further degradation. IGF-1 is a key
component in cartilage development, promoting chondrocyte mitosis and extracellular
matrix synthesis. BMP helps chondrocyte migration and FGF has an important role in
cartilage repair. PDGF helps regenerate articular cartilage by increasing chondrocyte
proliferation and is involved in all cells of mesenchymal origin. VEGF has been shown to
influence vascular structure formation and regeneration and is important in restoring
nutrient flow. PRP contains a high concentration of platelets obtained by centrifugation
of autologous blood. After degranulation of platelets, various growth factors and
cytokines are released and accelerate cartilage matrix synthesis, restrain synovial
membrane inflammation and promote cartilage healing. Due to its regenerative effect and
anti-inflammatory potential properties, PRP is widely used in musculoskeletal diseases
such as rotator cuff tear, lateral epicondylitis, patellar tendinopathy, osteoarthritis.
PRP is also preferred in the treatment of androgenic alopecia lichen planoplaris acne
scatrices in dermatology, in dentistry, in the treatment of corneal ulcers in
ophthalmology and in the clinical applications of various branches and its frequency and
range of use is increasing day by day. The effectiveness of PRP in knee osteoarthritis
has been demonstrated in various studies. Research on the efficacy of PRP has focused on
comparing the effects of intra-articular PRP injections with other injection therapies.
In many studies, PRP injections improved functional outcomes compared with HA and placebo
controls and appear to be more effective in reducing symptoms and improving quality of
life. The effects of PRP are apparently longer lasting and superior compared to
intramuscular injection therapies. Comparisons between intra-articular PRP injection
versus placebo and HA treatment in mild to moderate knee OA have generally shown higher
clinical outcome scores with the use of PRP. In moderate knee OA, functional status and
pain improved with at least two injections. In late-stage knee OA, only a single
intra-articular PRP injection may be sufficient to provide effective pain relief, thus
improving activities of daily living and quality of life.