Week 2: The OR - A Memoir from a Biomedical Engineer

The second week of the Immersion Program was all about discovery! In less than five days, I was able to briefly cover the entire spectrum of a hip arthroplasty, a surgical reconstruction or replacement of a joint. It all started on Tuesday by learning about the use of patient-specific triflange designs in cases where patients have a surgical revision after a total hip arthroplasty (THA). Patients may need to have a THA revision due to post-surgical complications such as instability, aseptic loosening, osteolysis and/or wear, and infection (Springer et al., 2009). A patient-specific triflange is often considered as an alternative solution when a severe bone loss prevents the reconstruction of the joint using other well-established surgical techniques. The term triflange is used to describe the three areas where the implant is attached to the hip bone: ilium, ischium, and pubis (Fig. 1). During the presentation hosted by the Biomechanics Lab Meeting, I learned that design engineering is a crucial portion of the development of a custom triflange.

A computer generated three-dimensional reconstruction is obtained from the affected pelvis of each patient (Fig. 2).The imaging findings are used by engineers and surgeons to assess the feasibility of the surgical procedure (Goodman & Engh Jr, 2016). Also, during the entire process, there is a constant communication between the engineers from HSS and the orthopedic company making the implant. On their dialogue, they usually approach the solution as separate entities at first to identify areas of disagreement and mutual consensus in the design and manufacturing of the implant. Multiple 3D-printed reconstructions of the patient's pelvis with the custom-built triflange are also given to surgeons to identify flaws in the design from their pre-operative standpoint of view. Lastly, the patient-specific triflange offers optimal results to patients in need of a THA revision where severe bone loss or pelvic discontinuity prevent the use of other surgical techniques. However, it requires an extensive pre-operative planning and design which can take anywhere from four to six months before being utilized in the patient.

Figure 1: A patient-specific triflange showing the anatomical areas of the hip where the flanges of the implant are attached to the bone by surgical rods.

Figure 2: 3-D reconstructions generated from CT scans of each patient's pelvis are essential for the design of the custom-build triflange and the surgical planning of the procedure (Bone Joint J 2016;98-B(1 Suppl A):68–72).

The second and most memorable experience of the week was entering the operating room (OR) for the first time. The first case was a white male in his mid-thirties with a mild degree of osteonecrosis of the right femoral head. If untreated, osteonecrosis of the femoral head can lead to total destruction of the hip joint, thus the development of arthritis. There was an extensive preoperative process before the actual surgery of the patient. After placing the patient under general anesthesia, the staff from the Radiology department brought a portable X-Ray machine to have real-time imaging of the surgical procedure. The surgery itself was relatively short and minimally invasive. The orthopedics fellow, under the supervision of the attending orthopedic surgeon, made an incision and perforated the iliac crest of the patient just above the injured hip. They extracted about 30cc of bone marrow through a metallic guide wire from the patient. The bone marrow contains a significant number of mesenchymal stromal cells which are believed to be a useful strategy for the treatment of osteonecrosis in the femoral head. 

Next, they did a core decompression of femur of the patient to relieve pressure and create a channel to infuse the bone marrow into the femoral head. The radiographic image of the femur was continually updated upon the surgeon request to see the positioning of the surgical drill and its trajectory. Injecting the bone marrow into the femoral head was a challenging process which made me realize why they often collect a greater amount of bone marrow than the one that they really need in the surgery. Lastly, the Dr. Joseph Lane, the attending surgeon, confirmed that the bone marrow was successfully injected into the patient's femoral head and the surgery was concluded. Due to the simplicity of the procedure, most of the suturing of the incision was done by one of the attending first-year medical students under the supervision of the orthopedic fellow.  

The second surgery of the day was a hemiarthroplasty, a surgical procedure where only half of the hip joint is replaced with a prosthesis. The case was a 65 y/o African-American male with a long-standing history of drug abuse. The patient was diagnosed with lung cancer which eventually metastasized to the lower extremities creating a large tumor on his right femoral head. The rigorousness and level of sterilization for this procedure were much higher. The surgery was performed by the attending orthopedic surgeon, two orthopedic fellows, and an OR specialized nurse. I was fascinated by the preventive measurements taken to prevent the spread of infection within and outside the patient's body. After the surgery had started, I approached one of the nurses in the room and asked her the purpose of what initially seemed like "space suits" to me. She explained to me that those were sterile helmets using a closed air circuit system to prevent germs being spread by the orthopaedic surgeon in the OR. It took a reasonable amount of time before the femur of the patient was completely exposed. The doctors used surgical strings to mark the different soft tissue body parts found in the area. They have to reposition the patient's femur soon after removing the femoral head which was collected for additional pathology studies. 

Then they performed a cautious drill of the medullary cavity of the femur starting from the proximal metaphysis. The doctors used multiple surgical tools to increase the diameter of the hole where the metal stem of the hip implant was introduced. For this surgery, they were two technical advisors of the orthopedic company that made the implants to answer any questions that the surgeon had about the product during the procedure. Dr. Lane tried different size combinations between the femoral stem and the acetabular shell. Once the appropriate size for all the components was confirmed, the technical advisors brought a sealed surgical implant for the patient. On the meantime, the nurse prepared the bone cement to be used in the patient's implant which was also brought by technical (sales representatives) of the company. Just before placing the final femoral stem for the hip implant, a senior orthopedic fellow made an incision in the distal metaphysis of the patient and perforated the femur. Soon after the surgery was completed, Dr. Lane explained to me that the femur had to be perforated to reduce the amount of pressure inside the medullary canal after the bone was filled with the bone cement. Also, it helped to decrease the risk of a fat embolism which is prone to happen after hip replacement surgeries due to the disruption of the intramedullary cavity. Lastly, after both components of the hip implant were inserted into the patient' limb, Dr. Lane did a final check where he moved the leg to multiple locations to have an initial evaluation of how the implant was going to perform under normal forces in the joint and the gait of the patient.

As a concluding statement, during this week I had direct exposure to OR where I was able to witness the miracles of engineering in the life of a person. I was fascinated with the complexity, the synergy, and the degree of professionalism within the operating room. As mentioned in the introductory paragraph, I was able to have both a theoretical and practical introduction to the field of orthopedics in the context of total and partial hip arthroplasty. I am optimistic about the upcoming week and looking forward to being immersed in the OR one more time!