David Putzer

Efficacy of antibacterial bioactive glass S53P4 against S. aureus biofilms grown on titanium discs in vitro

We evaluated the effectiveness of different sizes of bioactive glass S53P4 against Staphylococcus aureus biofilms grown on metal discs in vitro. S. aureus biofilms were cultivated on titanium discs. BAG‐S53P4 (0.5–0.8 mm and <45 µm) were placed in contact with the discs containing biofilms. Glass beads (0.5 mm) were used as a control. After each interval, the pH from each sample was measured. Colony forming units were counted for the biofilm recovery verification. In parallel, we tested the activity of bioactive glass against S. aureus planktonic cells. We found that BAG‐S53P4 can suppress S. aureus biofilm formation on titanium discs in vitro. The suppression rate of biofilm cells by BAG‐S53P4 <45 µm was significantly higher than by BAG‐S53P4 0.5–0.8 mm. BAG‐S53P4 has a clear growth‐inhibitory effect on S. aureus biofilms. BAG‐S53P4 <45 µm is more efficient against biofilm growth in vitro comparing with BAG‐S53P4 0.5–0.8 mm. Bioactive glass S53P4 has potential to be used as bone substitute for the resolution of infection complications in joint replacement surgeries and treatment of chronic osteomyelitis.

Impaction bone grafting: A LABORATORY COMPARISON OF TWO METHODS

In revision total hip replacement, bone loss can be managed by impacting porous bone chips. In order to guarantee sufficient mechanical strength, the bone chips have to be compacted. The aim of this study was to determine in an in vitro simulation whether the use of a pneumatic hammer leads to higher primary stability than manual impaction. Bone mass characteristics were measured by force and distance variation of a penetrating punch, which was lowered into a plastic cup filled with bone chips. From these measurements bulk density, contact stiffness, impaction hardness and penetration resistance were calculated for different durations of impaction. We found that the pneumatic method reached higher values of impaction hardness, contact stiffness and bulk density suggesting an increase in stability of the implant. No significant differences were found between the two different methods concerning the penetration resistance. The pneumatic method might reduce the risk of fracture in vivo, as force peaks are smaller and applied for a shorter period. Results from manual impaction showed higher variability and depend much on the experience of the surgeon. The pneumatic hammer is a suitable tool to standardise the impaction process.

Optimizing the grain size distribution of allografts in bone impaction grafting

In bone impaction grafting, allografts in the form of bone chips are used for reconstruction of defects and to induce bone remodeling. Optimizing grain size distribution of this allograft material should help prevent implant subsidence by achieving higher primary stability of the graft. We evaluated the influence of grain size distribution on the mechanical stability of allograft material. Bone tissue was rinsed, and the grain size distribution of the allograft material was determined by performing a sieve analysis. Uniaxial compression tests were carried out before and after a standardized compaction procedure for samples with controlled grain size distribution and a control group. Allografts with controlled grain size distribution showed a yield limit almost twice as high as in the control group after a standardized compaction procedure. A better interlocking between bone particles was observed compared to the control group. Thus, grain size distribution has a major impact on the mechanical stability of bone grafts. By controlling the grain size distribution of allograft material, a tighter packing can be achieved and subsequently implant subsidence of implants could be avoided.

The Mechanical Stability of Allografts After a Cleaning Process: Comparison of Two Preparation Modes

In revision hip arthroplasty, bone loss can be compensated by impacting allograft material. Cleaning processes reduce the risk of bacterial and viral contamination. Cleaned allograft material was compared to native untreated allografts by using a uniaxial compression test. 30 measurements were performed for each group before and after compaction. Grain size distribution and weight loss were determined. A reduction in the amount of large bone fragments and a higher compaction rate were observed in the cleaned bone grafts. The cleaned bone chips presented with a better mechanical resistance to a compression force and a reduced flowability. The benefit of a cleaner and a mechanical stable graft material comes with the drawback that higher initial amounts of graft material are needed.

Force transmission in offset broach handles used for hip replacement: comparison of three different designs.

In minimally invasive hip arthroplasty double offset broach handles are used, to facilitate the preparation of the femoral canal. The aim of this study was to quantify the differences in force and impulse transmission between two double offset broach handles and a single offset broach handle. Two double offset broach handles (A European version, B American version) were compared to a single offset broach handle. A surgical hammer was used to give a variable impact to the head of the broach handle. Thirty measurements for each of five falling heights were recorded for each broach handle. The force measured by a load cell connected to the broaches was used to obtain the maximum force peak and to calculate the impaction impulse. Normal data distribution was assumed and analysis of variances was performed. Results have demonstrated that the highest values of the force peak and force impulse were found in the single offset broach handle. Broach handle A had higher impulse values and lower maximum force values compared to broach handle B. The lateral lever arm has a measurable effect on the force transmission. In double offset broach handles less energy is transmitted to the tip. Surgeons have to be aware of the differences between the broach handles when using them intraoperatively.

Comparison of two- and three-dimensional measurement of the Cobb angle in scoliosis

PurposeThe Cobb angle as an objective measure is used to determine the progression of deformity, and is the basis in the planning of conservative and surgical treatment. However, studies have shown that the Cobb angle has two limitations: an inter- and intraobserver variability of the measurement is approximately 3–5 degrees, and high variability regarding the definition of the end vertebra. Scoliosis is a three-dimensional (3D) pathology, and 3D pathologies cannot be completely assessed by two-dimensional (2D) methods, like 2D radiography. The objective of this study was to determine the intraobserver and interobserver reliability of end vertebra definition and Cobb angle measurement using X-rays and 3D computer tomography (CT) reconstructions in scoliotic spines.MethodsTo assess interoberver variation the Cobb angle and the end vertebra were assessed by five observers in 55 patients using X-rays and 3D CT reconstructions. Definition of end vertebra and measurement of the Cobb angle was repeated two times with a three-week interval. Intraclass correlation coefficients (ICC) were used to determine the interobserver and intraobserver reliabilities. 95% prediction limits were provided for measurement errors.ResultsIntraclass correlation coefficient (ICC) showed excellent reliability for both methods. The measured Cobb angle was on average 9.2 degrees larger in the 3D CT group (72.8°, range 30–144) than on 2D radiography (63.6°, range 24–152).ConclusionsIn scoliosis treatment it is very essential to determine the curve magnitude, which is larger in a 3D measurement compared to 2D radiography.

Occult intra-operative periprosthetic fractures of the acetabulum may affect implant survival

PurposeOccult intra-operative periprosthetic acetabular fracture is a seldom-reported complication of primary total hip arthroplasty (THA). It may potentially be associated with cup instability and implant loosening. The present study aimed to investigate clinical consequences of this complication.MethodsBetween 2003 and 2012, a total of 3390 cementless total hip arthroplasties (THA) were performed at our institution. Their medical histories were retrospectively reviewed to identify all patients who received a thin-layer computer tomography (CT) scan of the pelvis including the acetabulum within the first 30 post-operative days. They were evaluated and classified by two radiologists independently with respect to the presence of recent acetabular fractures. All cases with acetabular and periacetabular fractures were included in this study. Electronic medical records were reviewed to assess implant revision. Cup stability was measured with EBRA (Einzel-Bild-Röntgen-Analyse) from plain X-rays.ResultsPeriprosthetic fractures of the acetabulum were identified in 58 (50.4%) of 115 selected patients. Fractures close to but not including the acetabulum were identified in 45% (n = 26/58) of the patients, at the superolateral wall in 17% (n = 10/58), at the anterior wall of the acetabulum in 16% (n = 9/58) and in 10% (n = 6/58) each at the medial wall, and at the posterior wall respectively. One out of these 58 fractures could not be classified. Three of a total of six occult medial wall fractures had to be revised, and another two showed a high implant migration. The highest cup migration values however were found after fractures of the superolateral wall. Incomplete column fractures did not influence implant survival.ConclusionCentral wall acetabular fractures, although unrecognized intra- and post-operatively may impair implant survival after THA.

The Use of Time-of-Flight Camera for Navigating Robots in Computer-Aided Surgery: Monitoring the Soft Tissue Envelope of Minimally Invasive Hip Approach in a Cadaver Study

Background. Time-of-flight (TOF) cameras can guide surgical robots or provide soft tissue information for augmented reality in the medical field. In this study, a method to automatically track the soft tissue envelope of a minimally invasive hip approach in a cadaver study is described. Methods. An algorithm for the TOF camera was developed and 30 measurements on 8 surgical situs (direct anterior approach) were carried out. The results were compared to a manual measurement of the soft tissue envelope. Results. The TOF camera showed an overall recognition rate of the soft tissue envelope of 75%. On comparing the results from the algorithm with the manual measurements, a significant difference was found (P > .005). Conclusions. In this preliminary study, we have presented a method for automatically recognizing the soft tissue envelope of the surgical field in a real-time application. Further improvements could result in a robotic navigation device for minimally invasive hip surgery.

How deep can straight instruments be inserted into the femoral canal: a simulation study based on cadaveric femora*

Abstract Determining how deep instruments can be inserted into the femoral canal without touching adjacent structures is a fundamental necessity for navigating instruments in primary and revision total hip arthroplasty. The aim of the study was to determine the reachable depth of a straight instrument inserted into the femur canal during primary and revision total hip arthroplasty. Based on the three-dimensional data of twenty-six femurs, obtained from a CT scan, the insertion depth of a virtual, straight instrument was accessed by a simulation. The effect of the diameter of the virtual instrument and the extension of the osteotomy were evaluated. Without extending the osteotomy, 100% of the femoral canal was reachable to a depth of 5.1–6.3 cm for instruments with a diameter of 10 mm. The depth was measured from the lower edge of the osteotomy. A maximum lateral extension of the osteotomy by 1 cm enlarges the access to a depth of 8.8 cm. The results provide a theoretical basis for the limitations of guiding instruments used for the preparation of the femoral canal. Bone preserving methods need the development of angulated instruments to reach deep areas in the femoral canal.

Retracting Soft Tissue in Minimally Invasive Hip Arthroplasty Using a Robotic Arm: A Comparison Between a Semiactive Retractor Holder and Human Assistants in a Cadaver Study

Background. All surgical procedures in orthopedics involve the retraction of soft tissue. In this study, the performance of 3 assistants holding the medial retractor during minimally invasive hip arthroplasty was compared with a semiactive retractor holder in a cadaver setup. Methods. A total of 40 measurements on 3 cadavers were carried out with each subject (3 human, 1 robot) measuring each cadaver 10 times. The retractor was equipped with a sensor array on both sides, to measure variations of the retracting pressures over a 2-minute interval. Results. The semiactive retractor holder showed an almost constant performance compared with the test subjects. There was no significant reduction of the applied pressure and almost no variation during the 2-minute interval and across all measurements. Conclusions. The performance of the semiactive retractor holder was more stable than that of a human assistant, making it suitable for intraoperative usage.