What is the Intraarticular Concentration of Tobramycin Using Low-dose Tobramycin Bone Cement in TKA: An In Vivo Analysis?

BACKGROUND: Antibiotic-impregnated bone cement has increased in popularity as an effort to reduce the risk of infection in high-risk TKAs. However, limited data has been reported regarding antibiotic levels achieved when using tobramycin-impregnated bone cement after implanting total knee components. QUESTIONS/PURPOSES: We asked: (1) What is the tobramycin serum and knee intraarticular levels in patients undergoing primary TKA using tobramycin cement? (2) What is the intraarticular tobramycin level for patients receiving only intravenous tobramycin? METHODS: All patients undergoing primary TKA by one of the two study surgeons (GV, JP) during a 6-month period were evaluated for inclusion and invited to participate. The study enrolled 15 patients undergoing primary TKA by one of two surgeons (GV, JP) who met inclusion criteria; treatment allocation was assigned randomly through blinded envelope. The study group consisted of 10 patients whose components were implanted using a commercially prepared low-dose tobramycin bone cement mixture (1 g/40 g). The control group consisted of five patients who received standard weight-based dose intravenous tobramycin. Samples of serum and Hemovac® drain-collected intraarticular hematoma were analyzed at 6, 24, and 48 hours postoperatively. Tobramycin levels were measured using an immunoassay technique with a low-end sensitivity of 0.28 µg/mL. Mann-Whitney U tests were performed to compare the serum and intraarticular tobramycin concentrations at each time in the independent variable of group (Control and Study). RESULTS: The median (interquartile range [IQR]) intraarticular tobramycin concentrations for the study group, with tobramycin-impregnated bone cement, was 31.8 (29.0) µg/mL at 6 hours, 17.1 (13.1) µg/mL at 24 hours, and 6.8 (6.8) µg/mL at 48 hours. The intraarticular tobramycin concentrations of this study group were larger than those for the control group at 6 hours (median = 1.3; IQR = 0.7; p = 0.002), 24 hours (median = 1.3, IQR = 1.0; p = 0.002), and 48 hours (median = 1.4; IQR = 1.0; p = 0.02). The serum concentrations for the tobramycin-impregnated bone cement group were 0.3 µg/mL or less for all samples whereas serum concentrations and median (IQR) for the control group were 1.2 (2.6) µg/mL, 1.6 (4.4) µg/mL, and 2.0 (3.3) µg/mL at 6, 24, and 48 hours respectively. The serum levels for the tobramycin-impregnated cement group were less than those for the control group at 6 hours (p = 0.001), 24 (p = 0.001), and 48 hours (p < 0.001). CONCLUSIONS: Tobramycin-impregnated bone cement provides a way to deliver antibiotics in patients undergoing TKA. This supratherapeutic short-term prophylactic perioperative antibiotic local delivery can be achieved with limited systemic absorption, whereas joint tobramycin levels were less than therapeutic levels when given intravenously alone. In the control group, with only intravenous tobramycin, a subtherapeutic (< 2.0 µg/mL) level of tobramycin was found in all the intraarticular samples at 6, 24, and 48 hours. Based on the evidence obtained in this study, commercially prepared low-dose tobramycin bone cement can be used to obtain short-term supratherapeutic local concentrations in the knee while maintaining serum tobramycin levels at a minimum. LEVEL OF EVIDENCE: Level II, therapeutic study.

Distal femoral fixation: a biomechanical comparison of retrograde nail, retrograde intramedullary nail, and prototype locking retrograde nail.

BACKGROUND: Distal femur fractures continue to be a complex surgical problem for which the incidence is increasing. Presently, there is a need for different constructs to address these complex fractures. This study attempts to define the biomechanical properties of several implants. METHODS: A novel, prototype locking retrograde intramedullary nail and the Russell-Taylor femoral retrograde nail were tested at non-destructive, physiological, axial mode load strength using a young, synthetic bone model for a medial segmental shaft defect in the supracondylar region of the distal femur (medial gap of 10mm, 65mm proximal to the distal joint and parallel to the knee axis). Each specimen was compressively loaded and unloaded to the peak load for 80,000cycles at a 0.5Hz frequency. These were compared to the results from the same lab of the retrograde Trigen intramedullary nail. Motion and peak displacement were measured across the fracture site as a reflection of construct stability. FINDINGS: Previous testing demonstrated that Trigen intramedullary nail had significantly less motion across the gap and increased overall stiffness of the construct (P<0.05) compared to both Russell-Taylor and prototype nails. INTERPRETATION: Locking technology used in a nail biomechanically appears to lead to more micro-motion across the fracture gap and to less stiffness in this construct. Further research needs to be invested into intramedullary, locking technology before introducing it into clinical practice.

Fixation of femoral head fractures using the modified heuter direct anterior approach.

Large displaced fractures of the femoral head require open reduction and internal fixation. If the displaced fragments are small, open reduction may not be possible and excision of the fragment or nonoperative care may be the treatment of choice. Surgical approaches that have been used for open reduction and internal fixation include the Smith-Petersen approach, Watson-Jones approach, Kocher-Langenbeck approach, a posterior approach with a trochanteric flip osteotomy, and surgical dislocation of the hip. Here, we describe the use of the modified Heuter direct anterior approach for open reduction and internal fixation of femoral head fractures in 2 patients.

Distal femoral fixation: a biomechanical comparison of trigen retrograde intramedullary (i.m.) nail, dynamic condylar screw (DCS), and locking compression plate (LCP) condylar plate.

BACKGROUND: The purpose of this study was to establish if there are biomechanical differences between implants in stiffness of construct, microdisplacement, and fatigue failure in a supracondylar femoral fracture model. METHODS: A retrograde intramedullary (i.m.) nail, dynamic condylar screw (DCS), and locked condylar plate (LCP) were tested using 33-cm long synthetic femurs. A standardized supracondylar medial segmental defect was created in the distal femur bone models. A gap away from the distal joint axis and parallel to the knee axis was created for axial testing of the specimens (Arbeitsgemeinschaft fur Osteosynthesefragen [AO] type 33-A) and a T-fracture (33-C) was created for the fatigue testing of the specimens. Peak displacements were measured, and analysis was done to determine construct stiffness and gap micromotion in axial loading. Cyclic loading was performed for fatigue testing. RESULTS: It was observed that there were statistically significant differences in micromotion across the fracture gap and overall stiffness of various implant constructs. The stiffness of the i.m. nail, DCS, and LCP were 1,106, 750, and 625 N/mm, respectively. The average total micromotion across the fracture gap for the i.m. nail, DCS, and LCP were 1.96, 10.55, and 17.74 mm, respectively. In fatigue testing, the i.m. nail distal screws failed at 9,000 cycles, the DCS did not fail (80,000 cycles completed), and the LCP failed at 19,000 and 23,500 cycles. CONCLUSIONS: When considering micromotion and construct stiffness, the i.m. nail had statistically significant higher stiffness and significantly lower micromotion across the fracture gap with axial compression. Hence, the i.m. nail tested had the greatest stability for type 33-A fractures. However, the nail demonstrated the least amount of resistance to fatigue failure with type 33-C fractures, whereas the DCS did not fail with testing in any pattern.

Impact magnitudes applied by surgeons and their importance when applying the femoral head onto the Morse taper for total hip arthroplasty.

INTRODUCTION: This study was designed to test whether the number of impacts, the experience of the surgeon or impact force made significant difference in pull off forces. MATERIALS AND METHODS: The forces applied by 10 orthopaedic surgeons (five residents and five attending staff) to impact the femoral head onto the trunnion of a femoral component were recorded. The resultant forces were then divided into four energy levels and compared to determine if the number of impacts would make a difference in pull off strength. RESULTS: No significant differences existed between the resident versus attending groups in magnitude of force applied. Through ANOVA testing, it was found that at each of the energy levels, multiple blows demonstrated a significant pull off strength difference compared to a single blow. Increased pull off force was also noted when the magnitude of force of the applied blows was increased. CONCLUSION: We recommend at least two firm, axially aligned blows to impact the femoral head onto the trunnion intra-operatively.

Pullout strength variance among self-tapping screws inserted to different depths.

The cortical self-tapping screw (STS) has replaced the non-STS as an aid in fracture fixation. In a recent biomechanical investigation, Berkowitz and colleagues found that STS pullout strength increased with insertion depth up to 1 mm past the far cortex only. In the present study, we wanted to apply a standardized protocol of assessing pullout strength to STSs of different compositions and manufacturers while eliminating the sample-size and block-variance issues that affected the previous investigation. Ninety STSs were randomly divided into 5 groups, each representing a different insertion depth. Peak force was determined with trials ending in screw pullout or failure. A statistically significant difference in pullout strength was identified with insertion depths up to 1 mm past the far cortex. No block variance was detected. These results support the recommendation that STSs be inserted only 1 mm past the far cortex in healthy cortical bone.

Pullout strength and load to failure properties of self-tapping cortical screws in synthetic and cadaveric environments representative of healthy and osteoporotic bone.

BACKGROUND: The parameters of self-tapping screw (STS) performance in normal and osteoporotic bone have been defined in representative environments, but the question remains as to the clinical application of such findings. The goal of this study was to analyze the biomechanical performance of STSs in cadaveric and synthetic environments representative of healthy and osteoporotic bone. METHODS: Ninety-six Synthes STSs were inserted into cadaveric and synthetic models representative of osteoporotic and healthy bone. Screws were inserted to depths of 1 mm short of the far cortex, flush and 1 mm and 2 mm beyond the far cortex. Screws were tested with an Instron 8511 material testing system utilizing axial pullout forces. A SAS procedure was used to conduct analysis of variance for unbalanced datasets. RESULTS: Substantial differences were appreciated with respect to screw performance between osteoporotic and healthy bone specimens. Although a similar pattern of increased pullout strength and loading energy with increasing depth of insertion was demonstrated, absolute values were lower in osteoporotic specimens. Although performance trends were similar in cadaveric and synthetic testing models for both osteoporotic and healthy bone, values obtained during testing were different. Incomplete insertion of STSs resulted in a 21.5% and 37% reduction of biomechanical properties in osteoporotic and normal bone, respectively. CONCLUSIONS: These results indicate that previously published findings on the performance of STSs in synthetic models cannot reasonably be applied to the clinical realm. Although trends may be similar, screw performance in synthetic, as compared with cadaveric, models is markedly different.

The effect of pilot hole size on the insertion torque and pullout strength of self-tapping cortical bone screws in osteoporotic bone.

BACKGROUND: All surgical screws can experience failure if the torsional, tensile, and flexion loads exerted on the screws are excessively high. The use of self-tapping screws (STS) results in higher insertion torques (IT) as these screws cut their own threads in the pilot hole drilled in the bone. In this study, the torque for inserting the STS into an osteoporotic bone block for different pilot hole sizes (PHS) was measured and the pullout strength (PS) for extraction of the screws was determined for different depths of insertion, 0 mm, 1 mm, and 2 mm beyond the far cortex. METHODS: Seventy-two Synthes stainless steel STS (40 mm length and 3.5 mm diameter) were inserted into pilot holes of sizes 2.55 (A: 73% OD), 2.50 (B: 71.5%), 2.45 (C: 70%), and 2.8 mm (D: 80%). Using a digital torque screwdriver, screws were inserted to 0 mm, 1 mm or 2 mm past the far cortex. Pullout tests were conducted with an Instron materials testing system. Analysis of variance and Student-Neuman-Keuls tests were performed to determine the effect of DOI and PHS on the loading energy, PS, and IT. RESULTS: Results demonstrated that IT of the screws inserted into pilot holes A, B, and C were higher than those in D. It was also observed that PS and loading energy for 1 mm and 2 mm penetration past the far cortex were higher than those for 0 mm regardless of PHS. This study also found that an increase in PHS to 2.8 mm will reduce IT but will also reduce the PS relative to a PHS of 2.5 mm, the current standard for 3.5 mm screws. CONCLUSIONS: The results of previously published studies regarding the effect of pilot hole size on PS in healthy cortical bone cannot be applied to the osteoporotic environment. The findings presented in this research support using PHS no larger than 71.5% of the screw outer diameter (i.e., pilot hole size of 2.5 mm for 3.5 mm screws) and inserting screws at least 2 mm beyond the far cortex to maximize PS and minimize iatrogenic damage in osteoporotic bone.

Outcomes of modular proximal femoral replacement in the treatment of complex proximal femoral fractures: a case series.

BACKGROUND: The treatment of complex femur fractures poses a significant challenge. Even with current advancements and the various implements available for the fixation of femoral fractures, results are often disappointing. This study sought to identify problems associated with and examine results of modular proximal femoral replacement. Outcomes were evaluated in two groups of patients: those receiving primary modular proximal femoral replacement for fractures and those treated with salvage arthroplasty for failed internal fixation. METHODS: Twelve patients who had received modular proximal femoral replacement as primary treatment for proximal femoral fractures were evaluated along with nine patients treated with salvage proximal femoral replacement for failed internal fixation. After the surgical procedure, patients were evaluated at regular follow-up intervals and contacted by phone at the conclusion of this study. Patient functional results were evaluated using the Merle D'Aubigne hip rating scale, which measures pain, motion and ambulatory status. Routine radiographs were also obtained at each patient visit. RESULTS: On average, patients who received modular proximal femoral replacement as the primary surgery for their femoral fractures enjoyed a high-level functional result and had few complications. Subjects who received salvage femoral replacement had a less optimal outcome and experienced more complications. Nonetheless, final post-operative MDA score was significantly increased from pre-operative levels. CONCLUSION: Modular proximal femoral replacement is a viable option in the primary fracture or revision setting, and has been shown to have a reasonable outcome, especially when the nature of initial injury is taken into account.

Valgus osteotomy of the proximal femur with sliding hip screw for the treatment of femoral neck nonunions: the technique, a case series, and literature review.

Femoral neck nonunions are a difficult complication in the treatment of femoral neck fractures and have traditionally been managed using an intertrochanteric valgus osteotomy and blade plate. We propose an alternative method, a proximal femoral valgus osteotomy using a sliding hip screw instead of a blade plate. This technique eliminates many of the difficulties experienced with the valgus osteotomy and blade plate by employing a device and instrumentation that is more familiar to orthopedic surgeons. The technique is reproducible and has been used successfully in a series of 4 patients.

Experimental evaluation of the holding power/stiffness of the self-tapping bone screws in normal and osteoporotic bone material.

OBJECTIVE: The goal of this study is to compare the holding power of the self-tapping bone screws in normal and osteoporotic bone materials. BACKGROUND: Self-tapping screws are increasingly being used in orthopaedic surgery due to their advantages over the other bone screws. METHODS: Screws were divided into five groups (six screws per group) based on the depth of insertion in the bone coupons that represented normal and osteoporotic bones. Screws were randomly inserted into the bone coupons with tips of the screws being -1 mm, 0 mm, 1 mm, 2 mm and 3 mm relative to the far cortex. Biomechanical testing was performed using an Instron 8,511 in accordance with the American Society for Testing and Materials standards for bone screws. Two-factor analysis of variance (ANOVA) was used to determine if the holding power of the screws were different with respect to insertion depths and bone materials. FINDINGS: The bone materials had a significant difference (P < 0.05) in the holding power and depths of insertion past the far cortex were significantly different from one another in holding power. The affect of the screw material on the holding power of the self-tapping screws in different bone materials was also examined. The performance of stainless steel screws was superior to that of titanium screws in the osteoporotic material. INTERPRETATION: Based on the results it can be concluded that the depth of insertion of the tip of the screw for adequate fracture fixation in normal bone is 1mm or more past the far cortex and in osteoporotic bone it is at least 2mm past the far cortex.

Pullout strength of self-tapping screws inserted to different depths.

OBJECTIVES: The purpose of this study was to determine whether the depth of insertion through the far cortex of self-tapping screws significantly affects pullout strength. DESIGN: Fifty, Synthes, 3.5-mm, self-tapping screws were inserted into synthetic bone blocks and divided into 5 groups. Group 1 had screws with their tips inserted 1 mm short of the far cortex. Group 2 had screws inserted flush with the far cortex. Groups 3, 4, and 5 had screws inserted 1 mm, 2 mm, and 3 mm past the far cortex respectively. Pullout strength was then tested. SETTING: Institutional research laboratory. MAIN OUTCOME MEASUREMENTS: Pullout strength (peak force) was measured for each group and analyzed using a single factor analysis of variance-balanced incomplete block design. RESULTS: Peak force values presented as mean +/- SD for the 5 groups were as follows: group 1 (1380 +/- 69 N), group 2 (1566 +/- 137 N), group 3 (1956 +/- 137 N), group 4 (2013 +/- 184 N), group 5 (2044 +/- 174 N). With a P < or = 0.05, it was found that groups I and II had statistically different pullout strengths than all other groups. However, there was no significant difference in pullout strength between groups 3, 4, and 5. CONCLUSIONS: Synthes self-tapping screws exhibit their highest pullout strength when inserted 1 mm past the far cortex, and there is no significant increase in pullout strength with deeper insertion depths.

Preinjury warfarin and geriatric orthopedic trauma patients: a case-matched study.

BACKGROUND: This study examined the hypothesis that patients on warfarin before sustaining orthopedic injuries will have increased morbidity and mortality compared with matched control patients not on warfarin. METHODS: Records of consecutive trauma patients on warfarin with orthopedic fractures who presented from January 1997 to June 2002 to a Level I trauma center were retrospectively analyzed. Data were evaluated using the chi and Student's t tests and nonparametric tests when appropriate; values of p < 0.05 were considered significant. RESULTS: A study group of 53 patients was available for review. In comparison with the control group, significant differences were found in time delay from admission to surgery (p = 0.005), hospital length of stay (p = 0.03), total units of blood transfused (p = 0.03), and discharge disposition (p < 0.0003). No difference was found in number of intensive care unit days, complications, or mortality. CONCLUSION: Preinjury warfarin impacts outcomes of geriatric trauma patients sustaining orthopedic injuries.