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Synovium of the Knee

Pigmented villonodular synovitis (PVNS) is a rare, benign locally aggressive disorder of the synovium of joints, bursae and tendon sheaths and has three main subtypes. The World Health Organisation classifies intra-articular diffuse PVNS as ‘diffuse-type giant cell tumour’ (Dt-GCT), differentiating it from the localised intra-articular form of PVNS and from GCTTS (giant cell tumours of tendon sheaths) commonly encountered in fingers and toes. The histological appearances are similar across all three PVNS sub-types (https://www.sciencedirect.com/science/article/pii/S1877132712000991).

The pathoaetiology of PVNS has been linked to inflammatory, vascular and traumatic causes but chromosomal abnormalities, autonomous growth, bone invasion and the rare malignant transformation of PVNS suggest a neoplastic cause (https://online.boneandjoint.org.uk/doi/epub/10.1302/0301-620X.95B3.30192).

Typically patients are between the age of 20 and 50 years, although many examples have been reported involving infants, children and adolescents (https://online.boneandjoint.org.uk/doi/epub/10.1302/0301-620X.95B3.30192). As the diffuse-type insidiously infiltrates the synovial cavity lining leading to eventual osseous erosions and sub- chondral cysts, patients present with insidious swelling and/or pain which has been present for months or years.

The mainstay of treatment for diffuse PVNS remains radical surgical excision. The recurrence rate of diffuse PVNS of knee after attempted arthroscopic resection is very high, therefore open surgery is preferred as the recurrence rate is reported to be less than 30% after two years. (https://europepmc.org/article/PMC/2758986)

Readers will also find it useful to read Jonathan Stevensons complimentary technique Excision of synovial chondromatosis using a posterior approach to the knee

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- See:
- Bursae of the knee:
- Pigmented Villonodular synovitis

- Discussion:
- synovial cavity is deepest layer of joint capsule & it often has several embryological invaginations called plica that persist into adult life;
- these may cuase anterior knee symptoms,
- although synovium membrane is attached all around, above to articular margins of femur and below to articular margins of tibia, it is not
everywhere coextensive w/ capsule or ligament and tendons;
- on lateral & medial sides of joint, it lies on inner surface of capsular ligament except where it is interrupted by attachments of meniscii
and separated from capsule on lateral side by tendon of popliteus muscle;
- it swings anteriorly, covering deep surface of tendons lateral to & above patella, & attaches to articular margins of patella;
- below the patella it covers deep surface of infrapatellar pad of fat that lies on the deep surface of the ligamentum patellae;
- on each side of infrapatellar fat, horizontal alar fold is identified;
- because of folds of synovial membrane, synovial cavity is not simple, short, cylindrical cavity;
- behind and above the patella, it is single cavity that is usually continuous above w/ suprapatellar bursa between the tendon of quads &
femur;
- below patella, synovial cavity is divided into lateral & medial compartments by the infrapatellar synovial fold;
- posteriorly, synovial cavity is divided into two compartments by fold that contains the cruciate ligaments;
- cruciate ligaments, meniscii, & infrapatellar fat pad are outside the synovial cavity;


Villous lipomatous proliferation of the synovial membrane (lipoma arborescens).

Synovectomy of the rheumatoid knee using intra-articular injection of dysprosium-165-ferric hydroxide macroaggregates.

A prospective clinical five year follow up study after open synovectomy of the knee joint in patients with chronic inflammatory joint disease. The prognostic power of clinical, arthroscopic, histologic and immunohistologic variables.