To compare the number of airborne bacteria and particles under laminar airflow (LAF) versus turbulent airflow (TAF) with 100% and 50% reduced fresh air exchange during simulated total hip arthroplasty (THA)

Two equally dimensioned operating rooms (OR) build in 2009 with modern ventilation systems of LAF and TAF respectively were used during 32 simulated THA-operations under four different ventilation conditions: LAF or TAF with either full (n=8+8) or 50% reduced (n=8+8) fresh air exchange volume.

We followed a protocol controlling the complete perioperative setup including interior cleaning, sterile materials, OR-personnel procedures, surgical clothing, instruments and 50-minute surgical procedure on a full-sized dummy at 37°C.

Microbial contamination was determined intra-operatively by ISO-validated Microbiological Active Sampler (MAS-100, Merck, 100 L/min) at two 10-minute intervals in 30 cm distance of the operating field. Blood-agar plates from each operation were incubated for 2 days at 35°C and the microbial concentration was determined by viable counting of colony-forming units (CFU) per m3 air.

Furthermore airborne particulate (0,5–10 µm) was sampled with ISO-validated light scattering particle analyzer (MET-one, Beckman Coulter, 28,3 L/min) during the 50-minute surgical procedure (1,42 m3/operation). Large particle sizes (>5 µm) are correlated with microbial contamination (Stocks, 2010). According to standards large-sized particle number must not exceed a 2.900/m3-threshold for cleanroom operations.

Microbial air concentration (mean CFU/m3 ±standard deviation) under LAF conditions with full and 50% reduced fresh air exchange were 0,4±0,8 and 0,4±0,4 respectively, whereas air contamination under TAF conditions were significantly higher with 7,6±2,0 and 10,3±8,1 (p<0,05).

Large (>5 µm) airborne particulate (mean no./m3 ±standard deviation) under LAF conditions with full and 50% reduced fresh air exchange were 1.581±2.841 and 1.018±1.084 respectively, whereas particulate under TAF conditions were 7.923±5.151 and 6.157±2.439 respectively.

Microbial air contamination was significantly lower under LAF ventilation compared to TAF during simulated THA under both full and 50% reduced fresh air exchange in modern operating theatres used in daily clinic. The number of particles measured under TAF conditions exceeded the threshold for cleanroom operations in 12/16 simulated operations. These findings indicate that LAF reduces the airborne microbial risk factor of surgical site infection in comparison to TAF.

A new hinge knee system (LEGION HINGE, Smith & Nephew, Memphis, TN) was designed to treat gross knee instability resulting from loss of collateral ligament function, femoral and/or tibial bone loss, or from comminuted fractures of the proximal tibia or distal femur. The knee system is offered with an insert that guides the motion of the implant for kinematic improvement. The purpose of this study was to evaluate kinematic and wear performance of this novel hinge knee replacement system.

The kinematics and kinetics of the Guided Motion (GM) hinge knee were assessed for a deep knee bend using a numerical lower leg simulator. Measurements of A/P translation and I/E rotation were compared to 3D MRI data of healthy weight bearing knees and measurements of M/L patella shear forces were compared to a standard primary knee implant. Three GM knee systems were tested for wear performance. All metal components were fabricated from cobalt chrome except for the Ti-6Al-4V insert locking screw. All plastic components were fabricated from UHMWPE. Wear testing was conducted on an AMTI 6-station force controlled knee simulator for approximately 5 million cycles under ISO 14243-1 load/motion profiles and soft tissue constraints. Simulation results showed that up to 130° of flexion the anterior/posteror (A/P) translation and internal/external (I/E) rotation followed a similar path over the flexion range compared to the MRI data. The magnitude of A/P translation at 130° was 9.5 mm for the GM design compared to 15.7 mm for the MRI data. The magnitude of I/E rotation at 130° was 18° for the GM design compared to 20.8° for the MRI data. The GM design showed a maximum M/L patella shear force of 456.8 N compared to 1152.4 N for a standard primary knee design over the flexion range. All constructs successfully completed wear testing and were fully functional with no issues for binding of the mating parts. All polyethylene components showed only burnishing on the articulating surfaces. The volumetric wear rate of polyethylene components was 17.54±1.24 mm3/Mcycle. The volumetric wear rate of the metal components (excluding femoral and tibial tray) was 0.045±0.01 mm3/Mcycle.

Testing showed the GM design has A/P and I/E kinematics that are similar to those seen in a normal healthy knee and good patella tracking as evidenced by the low M/L patella shear forces. The wear rate of the polyethylene parts was within the range of wear rates published in the literature for primary knee designs (up to 35.8 mm3/Mcycle). The low metal wear rate indicates that fretting and corrosion of the components was minimal.

We conclude the GM design more closely replicates the kinematics of the natural knee without compromising the wear characteristics. This could lead to better outcomes for the patient population that requires a hinge knee implant.