Novel press-fit technique of patellar bone plug in anterior cruciate ligament reconstruction is comparable to interference screw fixation.

PURPOSE: Conventional press-fit technique for anterior cruciate ligament reconstruction (ACLR) is performed with extraction drilling of the femoral bone tunnel and manual shaping of the patellar bone plug. However, the disadvantages of this technique include variation in bone plug size and, thus, the strength of the press-fit fixation, bone loss with debris distribution within the knee joint, potential heat necrosis, and metal wear debris due to abrasion of the guide wire. To overcome these disadvantages, a novel technique involving punching of the femoral bone tunnel and standardized compression of the bone plug was introduced. In this study, the fixation strength and apparent stiffness were tested and compared to that of the gold-standard interference screw fixation technique in three flexion angle configurations (0°/45°/90°) in a porcine model. We hypothesized that the newly developed standardized press fit fixation would not be inferior to the gold standard method. METHODS: Sixty skeletally mature porcine knees (30 pairs) were used. Full-thickness central third patellar tendon strips were harvested, including a patellar bone cylinder of 9.5 mm in diameter. The specimens were randomly assigned to 10 pairs per loading angle (0°, 45°, 90°). One side of each pair was prepared with the press-fit technique, and the contra-lateral side was prepared with interference screw fixation. Equivalent numbers of left- and right-sided samples were used for both fixation systems. A three-way multifactor ANOVA was carried out to check for the influence of (a) fixation type, (b) flexion angle, and (c) side of the bone pair. RESULTS: The primary fixation strength of femoral press-fit graft fixation with punched tunnels and standardized bone plug compression did not differ significantly from that of interference screw fixation (p = 0.51), which had mean loads to failure of 422.4 ± 134.6 N and 445.4 ± 135.8 N, respectively. The flexion angle had a significant influence on the maximal load to failure (p = 0.01). Load values were highest in 45° flexion for both fixations. The anatomical side R/L was not a statistically significant factor (p = 0.79). CONCLUSION: The primary fixation strength of femoral press-fit graft fixation with punched femoral tunnels and standardized bone plug compression is equivalent to that of interference screw fixation in a porcine model. Therefore, the procedure represents an effective method for ACL reconstruction with patellar or quadriceps tendon autografts including a patellar bone plug.

The Effect of Reducing the Bone to Cast Distance in an Equine Transfixation Pin Cast: An Ex Vivo Biomechanical Study.

OBJECTIVE: The aim of this study was to evaluate the effect of reducing the bone to cast distance on the resistance of the pin to cyclic loading in equine transfixation pin casts. STUDY DESIGN: Eleven pairs of cadaveric equine third metacarpal bones were prepared and one 6.3/8.0 mm transfixation pin was placed in standard fashion 10 mm proximal to the distal physeal scar into each bone. One metacarpus of each pair was tested with a distance of 10 mm (10 mm group) and the contralateral metacarpus with a distance of 20 mm (20 mm group) between the outer cortex of the bone and the fixation of the pin. Eight pairs were tested using a simplified test set-up in which the pins were fastened at both ends to polyoxymethylene-copolymer sleeves. The pins of the remaining three pairs of bones were incorporated into a fibreglass cast. All specimens were tested under cyclic loading until failure of the pin in axial compression. RESULTS: All pins failed uni- or bilaterally at clinically relevant load levels. Pins of the 10 mm group endured significantly (p < 0.05) higher load levels and total number of cycles until failure compared with the pins of the 20 mm group. CONCLUSION: The distance between the bone surface and the cast at the location of pin insertion has a significant effect on resistance of the pins to cyclic loading. Therefore, the amount of padding applied underneath an equine transfixation pin cast can have an influence on the overall stability and durability of the construct.

Spectroscopic characterization of tissue and liquids during arthroscopic radio-frequency ablation.

PURPOSE: Radio-frequency ablation devices generating a local plasma are widely used as a safe and precise tool for tissue removal in arthroscopic surgeries. During this process, specific light emissions are generated. The aim of this study was to investigate the diagnostic potential of optical emission spectrum analysis for liquid and tissue characterization. METHODS: The emissions in different saline solutions and during porcine tendon, muscle, and bone tissue ablation were recorded and analyzed in the range of 200-1000 nm. RESULTS: Specific atomic lines (Na, K, Ca, H, O, W) and molecular bands (OH, CN, C2) were identified, originating from compounds in the liquids and tissues in contact with the probe. A linear correlation between the concentration of both Na and K in solution with the intensities of their spectral lines was observed (Na: R2  = 0.986, P < 0.001; K: R2  = 0.963, P < 0.001). According to the Wilcoxon rank-sum test, the Ca- and K-peak intensities between all three tissue samples and the CN-peak intensities between muscle and bone and tendon and bone differed significantly (P < 0.05). CONCLUSIONS: These findings prove the general feasibility of spectroscopic analysis as a tool for characterization of liquids and tissues ablated during radio-frequency ablation. This method can potentially be further developed into an intraoperative, real-time diagnostic feature aiding the surgical team in further optimizing the procedure.

Problem of Pin Breakage in Equine Transfixation Pin Casting: Biomechanical Ex Vivo Testing of Four Different Pins.

OBJECTIVE: The aim of this study was to evaluate cyclic fatigue behaviour of a new pin with a thread run-out design in comparison with three other types of pins commonly used for equine transfixation pin casting. MATERIALS AND METHODS: Twenty-four pairs of equine cadaveric third metacarpal bones (MC3) equipped with one transfixation pin placed horizontally in the distal metaphysis were tested using a simplified model, mimicking the biomechanical situation of equine transfixation pin casting. A 6.3/8.0-mm Imex Duraface pin with thread run-out design (ITROP) was compared with a 6.1-mm smooth Steinmann pin (SSP), a Securos 6.2-mm, positive-profile pin (SPPP) and an Imex 6.3-mm, positive-profile pin (IPPP) under cyclic loading until failure in axial compression of MC3. RESULTS: All pins broke at clinically relevant load levels and cycle numbers. The SSP endured significantly (p = 0.0025) more cycles before failure (mean: 48685) than the ITROP (mean 25889). No significant differences in cycles to failure were observed comparing the SPPP versus ITROP, and the IPPP versus ITROP, respectively. CLINICAL SIGNIFICANCE: A thread run-out design does not necessarily lead to higher resistance against pin breakage under cyclic loading conditions. The SSP was most resistant against cyclic failure in these testing conditions, even though it was associated with more lateromedial displacement and cortical wear-out. This could outweigh reported disadvantages of the SSP such as reduced resistance to axial extraction and pin loosening.

Mechanical Effects of Heat Exposure From a Bipolar Radiofrequency Probe on Suture Under Simulated Arthroscopic Conditions.

PURPOSE: To determine conditions for the safe use of radiofrequency (RF) tissue ablation probes that avoid damaging suture material. METHODS: Four sutures made of 3 different materials commonly used in arthroscopic procedures were analyzed in a saline bath related to effects of RF-produced heat by proximity, duration, and intensity settings measuring burn-through time and ultimate load to failure. The parameters tested were electrode-to-suture distance, power setting, and the presence of tendon tissue or metallic anchor eyelets. Outcome variables were the burn-through time and the ultimate failure load of differently treated suture samples. RESULTS: Mean burn-through time for suture in direct contact with the RF probe ranged from 57.2 to 14.7 seconds for ultra-high-molecular-weight polyethylene (UHMWPE) sutures, 1.1 seconds for polydioxanone suture, and 0.8 seconds for polyethylene terephthalate suture. One of the UHMWPE sutures was capable of withstanding 3 seconds of direct contact with the RF probe without any compromise in tensile strength. No suture material tested had any mechanical change as long as the RF probe was kept 1 mm from the suture. CONCLUSIONS: Heat from RF tissue ablation probes can cause undetected damage. High-strength UHMWPE sutures were less sensitive to an RF treatment than polyester sutures. The use of different test substrates did not significantly influence the burn through time. CLINICAL RELEVANCE: Heat from RF probes can damage some suture material if direct contact is made even briefly. The use of RF devices may be safe for the suture when a distance between probe and suture of >1 mm is maintained. Suture made from UHMWPE may tolerate up to 3 seconds of RF probe contact and not sustain significant damage. Surgeons must use great care when using RF devices in the vicinity of suture placement.

Are asymmetric metal markings on the cone surface of ceramic femoral heads an indication of entrapped debris?

BACKGROUND: The probability of in vivo failure of ceramic hip joint implants is very low (0.004-0.05%). In addition to material flaws and overloading, improper handling during implantation can induce fractures of the ceramic ball head in the long term. Identifying the causes of an in vivo fracture contributes to improved understanding and potentially to further reduction of the fracture probability for patients. Asymmetric metal markings on the cone surface of in vivo ball head fractures have been reported. The question, therefore, is whether asymmetric loading is the sole cause or whether additional factors, specifically contamination entrapped in the taper fit, also contribute or are even the main cause. METHODS: The influence of the asymmetric physiological load configuration on resulting metal markings in the cone surface of an alumina femoral ball head with and without biological contaminants was investigated. Static and cyclic tests on ball heads were carried out in a load configuration of 0° (axisymmetric) and 40° in a physiological environment. The analysis of the metal marking was carried out to gain a better understanding of the processes that contribute to the generation of metal marking. Fractography was carried out to determine the fracture initiation of failed ball heads. RESULTS: Different types and sizes of residuals entrapped in the conical surface are shown to yield strongly asymmetric metal marking patterns. All heads tested without contaminants exhibited an almost homogenous distribution of residual metal markings around the circumference of the ceramic cone surface at the proximal end of the bore hole. The failure of ball heads that contained entrapped contaminants revealed a common fracture pattern. The site of fracture initiation on two of the failed heads was in the entrance region of the bore hole on the superior half of the head. CONCLUSION: Asymmetric metal markings observed on the ball heads tested in this investigation are most probably caused by the presence of contaminants entrapped in the taper fit. Homogenous metal mark distributions around the circumference indicate proper assembly of the ball head without entrapped contaminants. It should, however, be noted that different taper designs may possibly result in different marking patterns.