Michael Yancey - Dr. Ting Cong - Week 4

Today, I had the opportunity to shadow a multi-ligamentous knee reconstruction, including the ACL, PCL, MCL, and LCL, performed by Dr. Anil Ranawat. The surgery involved, first, harvesting tendon from the hamstring to be used as a graft for the various ligaments, followed by arthroscopic-led clearing of the surgical ligamentous entheses, and finally femoral tunnel creation and graft attachment. This was my first opportunity to shadow a surgery and there were a number of things I found interesting:

- The dynamics between the scrub tech, primary surgeons, and anesthesia. It was fascinating for example, watching the scrub tech prepare instruments and anticipate Dr. Ranawat's needs. It was also interesting that there was very little interaction between anesthesia and the rest of the team—each mostly-independently managed their own responsibilities.

- The flexibility required of surgeons during a procedure. In this particular operation, the surgical team discovered that the ACL was actually healthy and intact, which was unclear from the prior CT scans. In addition, there were a number of other decisions that needed to be made over the course of this surgery, including the best way to handle the accidental deformation of an instrument head inside the patient.

- The invasiveness of orthopedic procedures. Before this surgery, I did not realize the extend of soft tissue that is ablated/shaved to clear the surgical site. It was fascinating to watch the arthoscopic view of the ablation wand and tissue shavers.

- The number of redundant decontamination procedures performed to minimize the risk of infection. To list a few I saw today: the patient is instructed to wash before the procedure, the surgical area is shaved, a tech sponge cleanses the site, topical antiseptics are used, and an ioban drape is placed over the site. 

Here is one image during the procedure of the harvested hamstring tendon being prepared as a ligament graft:

----------------------------------

For the femoral impaction grafting project, I analyzed the force-displacement results obtained from our previous compression testing of the femoral head defect site. Specifically, I calculated a toe-region stiffness for each of our femoral head specimens after simulated failure and subsequent repair. The purpose of doing so is to determine if the impaction grafted beads change the force-displacement response of the tissue at low strains.

Following simulated failure, the toe-region modulus (defined as the stress-strain slope between 10 and 100N load), was 1.03±0.17 MPa. However, after subsequent repair, the toe-region modulus was 4.05±1.47 MPa. Paired t-tests demonstrate significance (p<0.05) when comparing toe-region moduli before and after repair.

In this defect model, stiffness at low loads (10-100N) is very low due to gaps in the morselized bone. However, following repair using impacted allograft bone, stiffness at low loads (10-100N) is increased by a factor of approximately 4 by filling the previously empty spaces. This reduces the displacement that occurs without the impaction grafting repair by approximately 50%.

As established in previous posts, repair does significantly change the defect area's stiffness at higher loads (800N, approximating bodyweight), so primary mechanism of the impaction graft is increasing stiffness at low loads to reduce displacement.

----------------------------------

For the Khormaee lab mesenchymal stem cell project, we continued maintaining our cell culture flasks and organized prior imaging results. Once the culture flasks are confluent, we will be making more alginate hydrogels of different stiffnesses and viscoelasticities for imaging.

----------------------------------

As a final note, I finally gained access to the HSS network as of Monday.