Complications of thermal energy in knee surgery--Part I

Diseases of Subchondral Bone 2

Osteonecrosis of the knee can be divided into the following 3 categories: primary or Spontaneous osteonecrosis of the knee (SONK), secondary osteonecrosis (ON), and postarthroscopic osteonecrosis. Patient characteristics as well as underlying risk factors can help categorize the type of osteonecrosis and guide treatment. SONK was first described by Ahlback et al in 1968. It is described as a disease of subchondral bone that leads to focal ischemia and bone marrow edema, necrosis, and possible subsequent structural collapse. SONK typically presents in the older women with frequent involvement of the medial femoral condyle. Secondary osteonecrosis is typically present in patients below 55 years of age. Unlike SONK, secondary ON presents multiple foci of bone marrow involvement with extension into the metaphysis and diaphysis. Postarthroscopic ON has been described after arthroscopic meniscectomy, shaver-assisted chondroplasty, anterior cruciate ligament reconstruction, and laser or radiofrequency-assisted debridement.

Magnetization transfer based contrast for imaging denatured collagen

PURPOSE

To study of the sensitivity of various NMR and MRI methods and parameters to the degree of thermal denaturation of collagen.

MATERIALS AND METHODS

Collagen type I powder was washed with methanol:chloroform to remove traces of lipids and then suspended in saline. Denaturation was carried out by heating the suspension for 5-120 minutes at a temperature range of 50-100 degrees C. The NMR methods tested were two T(2) filter methods: Goldman-Shen (GS) and Edzes-Samulski (ES); magnetization transfer contrast (MTC); double quantum filtering (DQF) and high resolution spectroscopy. MRI contrasts based on these methods were compared.

RESULTS

The following parameters were found to be sensitive to denaturation of collagen: 1) the amount of spins that experience high dipolar interactions as assessed by DQF; 2) MTR; 3) k(w)T(1w) (where k(w) is the magnetization transfer rate from water to collagen, and T(1w) is the water protons longitudinal relaxation time); and 4) aliphatic residues content. The contrast between native and denatured collagen was improved by all the tested methods, with ES and DQF producing the highest contrast.

CONCLUSION

Methods depending on T(2) filtering and DQF were found to be sensitive to the degree of thermal denaturation of collagen and improve the contrast between native and denatured collagen.

Thermal Damage Prediction for Collagenous Tissues Part I: A Clinically Relevant Numerical Simulation Incorporating Heating Rate Dependent Denaturation*

Subablative thermotherapy is frequently used for the treatment of joint instability related diseases. In this therapy, mechanically deformed collagenous tissues are thermally shrunk and the stability of the tissue is re-established. In this research, the thermal damage fields generated by three different clinical heating modalities (monopolar and bipolar radio frequency and Ho:YAG laser) are compared numerically using finite element analysis. The heating rate dependent denaturation characteristics of collagenous tissues are incorporated into the model using experimental data from in vitro experimentation with rabbit patellar tendons. It is shown that there are significant differences among the thermal damage profiles created by these modalities, explaining the main reason for the discrepancies reported in the literature in terms of the efficacy and safety of each modality. In the complementary paper, the accuracy of the model presented here is verified by in vitro experimentation with a model collagenous tissue and by quantifying the denaturation-induced birefringence change using Optical Coherence Tomography and Magnetic Resonance Imaging.