Microfracture

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Microfracture is a commonly performed cartilage repair or marrow stimulation method, which induces fibrocartilage growth by creating small microcracks into the subchondral bone.

History

First reports on mesenchymal stem cell stimulation date back to 1946 . The microfracture technique, how it is commonly performed today for marrow stimulation was described by Rodrigo in 1994 .

Indications

The microfracture technique is typically performed in younger patients with more recent full-thickness chondral defects (Outerbridge grade 3 or 4) with a smaller size of e.g. ≤2-3cm and occasionally for treating slightly larger lesions in older low demand patients .

Contraindications

Relative contraindications of the microfracture include :

inflammatory arthritis
partial-thickness chondral defects (Outerbridge grade 1-2)
lower limb malalignment
underlying osteonecrosis
reluctance to participate in rehabilitation

Procedure

The microfracture technique comprises the following :

thorough debridement of cartilage margins
removal of the calcified cartilage (otherwise inhibits the attachment of repair tissue)
creation of multiple systematically dispersed 3-5 mm deep holes within the subchondral bone of the cartilage defect using an arthroscopic awl

Complications

Complications of the microfracture technique comprise the following :

incomplete defect filling
subchondral fractures
delamination of the fibrocartilage subchondral bone junction
bony overgrowth
potentially compromised result following subsequent autologous chondrocyte implantation

Some of the subchondral bone alterations can be counteracted by application of bone marrow aspirate .

Radiographic features

MR imaging can be used for postoperative control and cartilage healing and includes the assessment of defect filling, the peripheral integration and morphologic characteristics of cartilage and subchondral. MRI sequences most commonly used for the evaluation of cartilage are proton density weighted, intermediate weighted images and T2 weighted images with and without fat saturation and 3D images .

MRI

Radiographic features change over time and the repair tissue within the chondral defect will be initially thin in the postoperative period and will usually fill the defect by 1-2 years after surgery .

Sometimes this will be associated by bony overgrowth, which however does not seem to have any negative effect on clinical outcomes .

Signal characteristics

In general signal intensity hyperintense on T2 weighted and intermediate weighted images in the postoperative period. Signal intensity is expected to decrease over time with the maturation of the reparative tissue .

Similarly, subchondral bone marrow edema like signal will fade over time.

Persistent bone marrow edema like signal and incomplete filling of the defect indicates incomplete integration .

Radiological report

The radiological report should include the description of the following features :

degree of the filling defect
signal characteristics of reparative tissue
the articular surface of the reparative tissue and transition zone to the native cartilage
presence of chondral delaminations
adjacent subchondral bone marrow edema

Outcomes

Apparently there are good short-term functional improvements but participation in sports seem to decline over time . The outcome for femoral condyle lesions is better than with patellofemoral lesions .

Fibrocartilage has a different structure, mechanical and biochemical properties and lacks its stability and durability of normal articular cartilage. Therefore clinical results tend to fade over time which leads to less successful outcomes in longer follow-up intervals and athletic, high demand patients .