What causes the scarring and contracture in infrapatellar contracture syndrome?
This condition is likely to have followed a traumatic or surgical incident to the knee, where the joint was for some time full of blood or joint fluid, or both.
With healing, the body gradually absorbs the fluids, but if there is inadequate mobilisation of the knee the residual fluid may become thicker and stickier and forming 'adhesions'. These can stretch from one side of the space to the other, limiting movement which becomes painful.
When these adhesions are still soft, the strands can be broken with physiotherapy procedures such as patellar mobilisations and massage around the patellar tendon. But if this is not done, the body will allow repair cells to migrate into the space and to turn the adhesions into proper scar tissue, which then contracts and pulls the walls of the space tightly together. At this stage it is too late for physiotherapy, and surgery becomes indicated to remove the scar tissue, probably using an arthroscopic radiofrequency wand, which disrupts the structure of the scar tissue..
Peer-reviewed paperQuote from peer-reviewed paper:
"[Infrapatellar contracture syndrome] involves a complex interaction between quadriceps dysfunction, immobilization, and inflammation leading to infrapatellar scarring and adhesions....associated with fractures about the knee and ....surgical procedures such as anterior cruciate ligament (ACL) reconstruction,....high tibial osteotomies (HTOs), tibial tubercle osteotomies (TTOs), and total knee arthroplasties (TKAs)...."
Citation: Barth KA, Strickland SM. Surgical Treatment of Iatrogenic Patella Baja. Curr Rev Musculoskelet Med. 2022 Dec;15(6):673-679. doi: 10.1007/s12178-022-09806-y. Epub 2022 Nov 29. PMID: 36445621; PMCID: PMC9789255.
How does infrapatellar contracture syndrome lead to patella infera/baja?
Gradually, the contracting scar tissue may pull the patella itself into an abnormally low position, which is called 'patella infera' or 'patella baja'.
This may lead to chronic pain from increased pressure on the upper surface of the patella.
The fat pad can also become involved in the scarring process.
Peer-reviewed paperQuote from peer-reviewed paper:
"....Patella baja is an uncommon but devastating complication after knee surgery and may cause loss of knee extension. It can happen after prolonged immobilization, surgery around the tibial tubercle, and patella tendon surgery. ...."
Citation: Vaish A, Vaishya R, Bhasin VB. Etiopathology and Management of Stiff Knees: A Current Concept Review. Indian J Orthop. 2020 Oct 20;55(2):276-284. doi: 10.1007/s43465-020-00287-0. PMID: 33927806; PMCID: PMC8046887.