Comparison of Acute Histologic and Biomechanical Effects of Radiofrequency Ablation and Cryoablation on Periarticular Structures in a Swine Model.

PURPOSE: To compare the acute effects of radiofrequency (RF) ablation and cryoablation on the structural integrity of nontarget periarticular tissues that may be placed at risk during percutaneous bone ablation. MATERIALS AND METHODS: RF ablation and cryoablation were separately performed on tendon, articular cartilage, and ligament in an ex vivo porcine model by using standard bone ablation protocols. Gross and histopathologic analysis was performed on cartilage and tendon (n = 6 for each treatment group, n = 5 controls). Tendon lengths were measured before and after ablation. Biomechanical tensile testing was performed on each ligament sample after ablation, with quantification of ultimate load at failure and linear stiffness (n = 7 ligaments in treatment and control groups). RESULTS: RF ablation and cryoablation injured chondrocytes within the ablation zones but caused minimal effects on gross and histologic cartilage architecture. Cryoablation resulted in minimal gross and histologic effects on tendon whereas RF ablation resulted in marked disruption of collagen fibers and significant longitudinal shortening (P = .002). Similarly, cryoablation did not alter ligament strength or stiffness compared with control, whereas RF ablation resulted in a significant decrease in tensile strength and stiffness compared with control and cryoablation samples (P < .001). CONCLUSIONS: Neither RF ablation nor cryoablation resulted in significant acute changes in cartilage architecture. However, RF ablation resulted in marked disruption of tendon architecture, tendon shortening, ligament weakening, and loss of ligament stiffness, whereas cryoablation had no significant effect on any of these parameters. These findings suggest that cryoablation may have fewer negative acute effects than RF ablation, although long-term outcomes are currently unknown.

Biomechanical comparison of prophylactic medial malleolar fixation in total ankle arthroplasty.

The purpose of this study was to compare the biomechanical properties of two common forms of prophylactic fixation of the medial malleolus during total ankle arthroplasty (TAA). Ten matched pairs of cadaveric lower extremities were fixed with a single cannulated cortical screw or a one-third tubular plate after preparation for TAA. Ten unmatched single cadaver lower extremities were used as the control. A transverse load was applied to the medial malleolus. Bone mineral density, peak loads at fracture, and fracture pattern were noted. There was no statistically significant difference in peak load to failure between either fixation cohorts or between the fixation cohort and the control cohort. There was a moderate positive correlation between bone mineral density and peak load for all three experimental groups. The peak load was significantly (p = .035) increased in male cadavers. Fractures occurred almost exclusively at the apex of the tibial and malleolar cuts with a vertical fracture pattern.

A biomechanical analysis of two anterior ankle arthrodesis systems.

BACKGROUND: An increasingly popular ankle fusion method uses plates and screws positioned on the anterior aspect of the tibiotalar joint. This study compared the mechanical properties of 2 contemporary plate systems for ankle arthrodesis, one based on a single anterior plate and the other comprising paired anteromedial and anterolateral plates. METHODS: Ten matched pairs of fresh-frozen cadaver ankle joints underwent arthrodesis with a single anatomically contoured anterior plate or 2 anatomic plates applied anteromedially and anterolaterally. Each arthrodesed specimen was subjected to controlled sagittal and coronal plane bending and internal and external rotation. Tibiotalar joint bending stiffness, bending angulation, torsional stiffness, and joint rotation were documented. RESULTS: Bending stiffness of the 2-plate system was 1.5 to 5 times greater than that of the single-plate system in plantarflexion, dorsiflexion, eversion, and inversion (P = .005-.050). Angulation in each bending direction was several-fold greater than for the single plate (P = .005-.014) at the peak applied moment. Torsional stiffness of the 2-plate system nearly doubled that of the single plate in both rotation directions (P = .014, P = .005). Approximately half as much arthrodesis site rotation occurred with 2-plate fixation at the peak applied torque (P = .005, P = .007). CONCLUSION: The tested 2-plate arthrodesis system has the potential to optimize arthrodesis site stiffness compared with fixation with a contemporary single plate. CLINICAL RELEVANCE: Use of the stiffer 2-plate system could improve the clinical fusion rate, especially in patients with suboptimal bone quality.

Biomechanical Comparison of Nonlocked Minimally Invasive and Locked Open Achilles Tendon Simulated Rupture Repairs.

BACKGROUND: Open repair of Achilles tendon ruptures is associated with a risk of infection and other wound complications. Although percutaneous repairs reduce these complications, they may increase the risk of nerve injury. This study was designed to determine whether a percutaneous nonlocking repair can approach the gapping resistance offered by a standard open repair under conditions approximating typical postoperative physiotherapy. METHODS: Ten pairs of cadavers Achilles tendons were transected in situ 5 cm above the insertion. One tendon from each pair was repaired using an open 4-strand Krackow locking loop, and the contralateral tendon was repaired with the Achillon system using the same suture material. Displacement transducers were attached to the medial, lateral, anterior, and posterior aspects of the tendon, spanning the repair. Each tendon underwent 1000 tensile loading cycles to 86.5 N, simulating passive ankle range-of-motion physiotherapy. Gapping was documented on the 1st, 50th, 100th, 500th, and 1000th cycles. The ultimate tensile strength of each repaired tendon was then measured by distracting until gross failure occurred. RESULTS: Gapping of the percutaneous repairs exceeded that of conventional open repairs on the first, 500th, and 1000th load cycles. All 10 conventionally repaired tendons withstood 1000 load cycles without gross failure, but 4 of 10 percutaneous minimally invasive repairs failed, one on the 9th load cycle and the others between the 100th and 500th cycles. On average, tendons repaired with the open technique withstood 66% greater tensile load in failure testing than those repaired with the percutaneous technique. CONCLUSION: Open Krackow Achilles tendon repairs may better withstand more aggressive postoperative physiotherapy than nonlocked percutaneous repairs. CLINICAL RELEVANCE: The study suggests that surgeons should consider locking suture approaches to avoid loss of repair integrity with early motion.

Compression screw fixation of the syndesmosis.

BACKGROUND: Screw fixation of syndesmotic injuries facilitates ligament healing and restoration of ankle stability, but little information regarding screw performance is available. This study quantified the reduction obtained with three common 2-screw configurations using different methods of reduction and novel methods of subsequently provoking and measuring diastasis. METHODS: Seven fresh-frozen lower extremities were subjected to 100 N medial and lateral tibia loads with the talus restrained. Tibia displacement, indicative of ankle clear space, was recorded. The syndesmosis and distal interosseous ligament were disrupted and measurements repeated. A pressure sensor was inserted into the syndesmosis and three 2-screw fixation methods were evaluated in each specimen: 3.5-mm screws engaging both fibula cortices and the lateral tibial cortex, inserted while using a clamp to achieve syndesmosis reduction; 3.5-mm lag screws engaging both tibia cortices; and 4.5-mm lag screws engaging both tibia cortices. One thousand 100 N medial and lateral loads were applied and clear space and syndesmosis compression were quantified every 100 cycles. RESULTS: Normal ankle clear space averaged 1.98 mm and increased to 3.02 mm after syndesmosis disruption. Fixation decreased the clear space to 1.36 mm, 1.22 mm, and 1.19 mm for the 3.5-mm tricortical, 3.5-mm lag, and 4.5-mm lag screws, respectively, remaining steady throughout cyclic loading. Syndesmosis compression dropped markedly from 61N to 23 N on clamp release after tricortical screw insertion. The 3.5-mm and 4.5-mm lag screws exerted 112 N and 131 N, respectively, after insertion, and maintained compression several-fold greater than the tricortical screws during cyclic loading. No difference was demonstrable between the two lag screw sizes. CONCLUSION: While all screw configurations successfully reduced ankle clear space, syndesmosis reduction was more effectively maintained by lag screws than by tricortical screws inserted with clamp reduction. The transient nature of compression achieved by the reduction clamp suggests that use of lag screws for this application may more reliably maintain syndesmosis reduction in vivo. CLINICAL RELEVANCE: Optimizing reduction of syndesmosis injuries is critical for favorable outcomes. This study offers concrete information on screw performance in this application.

J. Leonard Goldner Award 2010. Ligament balancing for total ankle arthroplasty: an in vitro evaluation of the elongation of the hind- and midfoot ligaments.

BACKGROUND: The changes in length of the hindfoot ligaments in response to alterations in ankle and subtalar joint orientation under physiologic load in eight fresh-frozen cadaver limbs were documented. RESULTS: In eversion, the tibiocalcaneal (11% ± 4%, mean ± SD], calcaneofibular (6% ± 4%), posterior talofibular (7% ± 4%), posterolateral talocalcaneal (21% ± 9%), posteromedial talocalcaneal (33% ± 45%) and calcaneonavicular (bifurcate) (8% ± 7%) ligaments were elongated relative to their lengths in inversion. In inversion, the anterior capsular (talocalcaneal) (5% ± 3%) and the plantar cuboidnavicular (5% ± 6%) ligaments were elongated relative to their everted lengths. In dorsiflexion, the superficial (26% ± 8%) and deep posterior tibiotalar (30% ± 13%), calcaneofibular (8% ± 4%), tibiocalcaneal (4% ± 2%) and lateral talocalcaneal (cervical) (2% ± 1%) ligaments were elongated. In plantarflexion, the tibionavicular (26% ± 5%) and the anterior talofibular (7% ± 4%) ligaments were lengthened. No statistically significant elongation was documented in any ankle position for the anterior tibiotalar, talocalcaneal interosseous, plantar calcaneocuboid, calcaneocuboid (bifurcate), all components of the spring ligament, and the dorsal cuboidnavicular ligaments. CONCLUSION: Components of the deltoid ligament complex elongated largest at the ankle joint with any hindfoot movement but inversion. Therefore, selective release of components of the deltoid ligament complex may provide a means for achieving optimal ligament balancing in total ankle arthroplasty. Specifically, release of the superficial and deep posterior tibiotalar ligament may improve range of motion in total ankle arthroplasties, whereas the release of the tibiocalcaneal ligament may correct a varus talar tilt.

Talonavicular joint fixation using augmenting naviculocalcaneal screw in modified double hindfoot arthrodesis.

BACKGROUND: Triple arthrodesis and combined talonavicular/subtalar arthrodesis are procedures for hindfoot disorders. Achieving talonavicular joint fusion can be problematic. We hypothesized that talonavicular joint fixation bending stiffness could be increased by adding a fully-threaded screw inserted through the lateral navicular into the calcaneus. MATERIALS AND METHODS: We used ten fresh-frozen cadaver hindfeet. The calcaneus and talus were immobilized, and talonavicular joint stripped of cartilage. Two partially-threaded 4.5-mm cannulated screws were placed across the talonavicular joint, one traversing the central third of the navicular and a second through the medial third of the navicular. We quantified talonavicular fixation bending stiffness and angulation in response to 4N-m bending moments applied to the navicular in four directions: plantar-to-dorsal (P-D), medial-to-lateral (M-L), dorsal-to-plantar (D-P), and lateral-to-medial (L-M). An augmenting fully-threaded 4.5 mm cannulated screw was then placed through the lateral third of the navicular into the calcaneus and the specimens retested. RESULTS: The mean bending stiffness in each direction increased significantly after addition of the third screw. The stiffness increase in each direction was: P-D 92%, D-P 39%, L-M 108%, and M-L 56%. Correspondingly, mean talonavicular angulation significantly decreased in each direction: P-D 43%, D-P 28%, L-M 47%, and M-L 34%. CONCLUSION: A third, fully-threaded screw from the lateral navicular into the calcaneus significantly increases talonavicular bending stiffness and decreases angulation. CLINICAL RELEVANCE: The increased resistance to arthrodesis site motion afforded by the addition of a naviculocalcaneal screw may improve the likelihood of achieving successful talonavicular fusion in combined talonavicular/subtalar arthrodesis.

Screw placement in subtalar arthrodesis: a biomechanical study.

BACKGROUND: Clinical outcomes of subtalar arthrodesis using screw fixation have been reported but biomechanical support for selection of screw trajectories and patterns has been lacking. This investigation was designed to assess the compressive and stabilizing abilities of different common screw insertion patterns for subtalar arthrodesis. MATERIALS AND METHODS: Forty-two cadaveric subtalar joints underwent arthrodesis with a single talar neck screw, a single talar dome screw, double parallel screws, or double diverging screws. Single talar dome screw fixation was subdivided by screw tip placement in the anteromedial, posteromedial, anterolateral, or posterolateral dome. Joint compression, construct torsional stiffness, and joint angulation under torsional load were quantified. RESULTS: Higher compressive force, torsional stiffness, and joint rotation resistance were achieved by double screw fixation compared to single screws (p < 0.001). Torsional stiffness with double diverging screws exceeded that of double parallel screws in internal rotation (p < 0.05). There was greater internal rotation with a single talar neck screw (p < 0.001) and greater external rotation with an anterolateral talar dome screw (p < 0.01) compared to the other single-screw orientations. Greater rotation in both directions was noted with the single screw tip located in the posterolateral talar dome (p < 0.01). CONCLUSION: Under the described testing conditions, double diverging screws confer the highest compression, the greatest torsional stiffness, and the least joint rotation. When a single screw is used, placement of the screw tip in the talar neck or lateral talar dome should be avoided. CLINICAL RELEVANCE: The results provide an objective basis for selection of optimal screw placement by the surgeon.

External ring fixation versus screw fixation for ankle arthrodesis: a biomechanical comparison.

BACKGROUND: The use of external ring fixation for ankle arthrodesis offers an alternative to internal screw fixation when bone quality is suboptimal, when complex ankle pathology is present, and as a salvage procedure for complicated cases. Additionally, it permits earlier weightbearing and postoperative adjustment of bone alignment and joint compression. This study was designed to determine whether there are differences in initial ankle joint fixation integrity between these two techniques. MATERIALS AND METHODS: Ten fresh-frozen cadaveric lower extremities underwent ankle arthrodesis with a hybrid ring fixator, and the bending and torsional stiffness of each arthrodesed joint was quantified. Stiffness was calculated from angulation measured at the tibiotalar joint using electronic clinometers attached to those bones. The external fixators were then removed and ankle arthrodesis performed using 6.5-mm cannulated screws: three across the ankle joint, one fixing the fibula to the tibia, and one fixing the fibula to the talus. Stiffness testing was then repeated. RESULTS: No statistically significant difference in bending stiffness, torsional stiffness, or joint rotation under torsional load was demonstrable between the two techniques. CONCLUSION: The similarity in ankle fusion site stability achieved with external ring fixation and an optimized screw fixation technique under the described testing conditions indicates that, in cases in which suboptimal bone quality or complex ankle pathology preclude the use of internal fixation, an external fixator is a viable option. CLINICAL RELEVANCE: Establishing that the primary stability of external ring fixation is comparable to that of screw fixation provides a basis for its use in cases in which screw fixation may be problematic.

Biomechanical comparison of screws and plates for hallux valgus opening-wedge and Ludloff osteotomies.

BACKGROUND: The optimal osteotomy type and fixation method for hallux valgus correction have not been defined. This study examined the mechanical properties of corrective opening-wedge and Ludloff oblique osteotomies under conditions approximating postoperative weight-bearing. METHODS: Twenty-nine pairs of fresh-frozen metatarsals were divided into three groups. In Group 1, headless screws were compared with standard cortical screws for Ludloff osteotomy fixation. In Groups 2 and 3, Ludloff osteotomies fixed with headless screws were compared with opening-wedge osteotomies fixed with non-locking and locking plates, respectively. Constructs underwent dorsally-directed cantilever loading for 1000 cycles. FINDINGS: No significant differences in angulation or stiffness were demonstrable in Group 1. In Group 2, Ludloff/headless screw construct stiffness exceeded non-locking plate construct stiffness. The mean angulation on the 1000th load cycle was greater for plates than for Ludloff/headless screws. In Group 3, locking plate construct stiffness and angulation did not differ from Ludloff/headless screws in early cyclic loading, but fixation failure of the locking plate constructs was common. INTERPRETATION: The results indicate that screw type for Ludloff fixation may be left to surgeon preference and that opening-wedge plates exhibit mechanical properties inferior to that of the Ludloff osteotomy under the tested conditions. Lateral cortex continuity and bone density remain important factors in the performance of opening-wedge osteotomies.

A new option for intramedullary fixation of Jones fractures: the Charlotte Carolina Jones Fracture System.

BACKGROUND: A number of different screws are used for Jones fracture fixation in cases in which hastened healing is desirable or nonoperative treatment has failed. None of them were designed for this application, and consequently there is a lack of continuity in screw configuration and sizing that can force the use of a screw that is not optimally size-matched to the metatarsal. This can be particularly problematic in high-demand patients such as athletes, in whom screw fixation failure is more likely to occur. Application-specific screws available in graduated sizes are now an option. This study was designed to compare the bending fatigue resistance of the new screws with that of clinically-proven contemporary Jones fracture fixation screws. The results may provide a basis for judging the probability of successful screw performance relative to the other established screw options. MATERIALS AND METHODS: Bending fatigue resistance of the smallest-diameter Wright Medical Technologies Charlotte Carolina screw was compared to that of three commonly used contemporary screws. Cyclic three-point bending was applied to the screw shafts for 2,000,000 cycles or until 5 mm of deflection occurred. Four to six samples of each screw were tested. RESULTS: The number of load cycles withstood by the new screws greatly exceeded the number of cycles tolerated by Acutrak 4/5 screws, Synthes 4.5-mm malleolar screws, and Synthes 4.5 mm cannulated screws. CONCLUSION: The fatigue resistance of the smallest-diameter Charlotte Carolina screw exceeds that of other contemporary screws known to possess sufficient strength for Jones fracture fixation. CLINICAL RELEVANCE: It is likely that this system of graduated-size screws may be implemented for treatment of acute Jones fractures without concern for device failure. Patients may benefit from more accurate matching of the screw size to the fractured metatarsal.

Tibiotalocalcaneal arthrodesis: a biomechanical comparision of multiplanar external fixation with intramedullary fixation.

BACKGROUND: Methods of achieving tibiotalocalcaneal arthrodesis include intramedullary nailing, crossed lag screws, blade plates, and external fixation. While reports in the orthopaedic literature have compared the biomechanical properties of some of these fixation techniques, to our knowledge none has evaluated multiplanar external fixation. The purpose of this study was to compare the biomechanical properties of intramedullary nail fixation and external ring fixation for tibiotalocalcaneal arthrodesis. MATERIALS AND METHODS: Tibiotalocalcaneal arthrodesis was performed on ten matched pairs of fresh-frozen human cadaveric legs. A ring fixator stabilized the arthrodesis in one leg from each pair and a 10 mm x 150 mm nail inserted retrograde across the subtalar and ankle joint stabilized the arthrodesis in the contralateral leg. The bending stiffness of the resulting constructs was quantified in plantarflexion, dorsiflexion, inversion, and eversion, and torsional stiffness was measured in internal and external rotation. RESULTS: No difference in bending stiffness between the two constructs was identifiable in any of the four bending directions (p > 0.05). Torsional stiffness was approximately two-fold greater in both internal and external rotation in specimens with the ring fixator arthrodesis than in those with the intramedullary nail (p = 0.002). CONCLUSION: The ring fixator provides a stiffer construct than a 10 mm x 150 mm intramedullary nail in torsion, but no difference in bending stiffness was demonstrable. Both techniques can provide satisfactory fixation; however, the ring fixator may better minimize rotational joint motion. CLINICAL RELEVANCE: This study provides a basis for selecting an arthrodesis method that offers optimized fixation.

Examining the viability of carbon fiber reinforced three-dimensionally printed prosthetic feet created by composite filament fabrication.

BACKGROUND:: A low-cost, yet high-functioning, fabrication method for prosthetic components is needed to provide underserved amputee communities with quality mobility devices. Three-dimensional printing is a potential alternative, yet limitations in material characteristics have previously prevented the technology from emerging as a solution. OBJECTIVE:: To validate the application of a novel three-dimensional printing technique as a fabrication method for creating fiber composite patient end-use prosthetic feet. STUDY DESIGN:: Experimental designs were iterated upon throughout mechanical testing. METHODS:: A testing apparatus capable of loading prosthetic feet in dorsiflexion and plantarflexion was constructed. Load displacement data were gathered, and energy analyses were conducted. The three-dimensionally printed feet were compared to a Freedom Innovations Renegade® MX carbon fiber foot and a solid-ankle cushion heel foot. RESULTS:: The three-dimensionally printed feet achieved energy profiles that were similar, and in some cases preferable, to the energy profiles of the Renegade MX and solid-ankle cushion heel foot. The stiffness profiles of the three-dimensionally printed feet varied widely and depended greatly on the design of the feet, as well as the amount and location of the fiber reinforcement. CONCLUSION:: Composite filament fabrication three-dimensional printing has the potential to serve as a fabrication method for the production of energy returning prosthetic feet. CLINICAL RELEVANCE:: The results of this study indicate that carbon fiber reinforced three-dimensionally printed prosthetic feet have the potential to serve as a low-cost alternative to carbon fiber prosthetic feet and that three-dimensional printing has the capacity to function as a viable fabrication method for patient end-use prosthetic components.

Simultaneous Intraoperative Measurement of Cadaver Ankle and Subtalar Joint Compression During Arthrodesis With Intramedullary Nail, Screws, and Tibiotalocalcaneal Plate.

BACKGROUND: Suboptimal tibiotalocalcaneal arthrodesis (TTCA) fusion rates may result from inadequate compression that increases motion and interferes with bony bridging. The aim of this study was to evaluate compressive forces at the ankle and subtalar joints with 3 contemporary TTCA constructs. METHODS: Thirty fresh-frozen cadaveric lower extremity specimens were divided into 3 groups of 10 each: 3 partially threaded cannulated screws, hindfoot nail, and lateral plate. Specimens were mounted to a testing apparatus, and compression was independently measured at the tibiotalar and talocalcaneal interfaces. Statistical analysis included paired Student t tests, analysis of variance, and Tukey post hoc tests. RESULTS: Mean forces at the ankle joint for the screws, nail, and plate constructs were 331 ± 86, 479 ± 137, and 548 ± 199 N, respectively, with plates providing significantly more compression than screws ( P < .01). Similarly, subtalar compressive forces demonstrated 319 ± 105 N in the screws group, 466 ± 125 N, in the nail group, and 513 ± 181 N in the plate group, with plate compression greater than that achieved with screws ( P < .01). No differences were identified in compression between ankle and subtalar joints within specimens in any group. CONCLUSIONS: Lateral TTCA plates provided increased compressive forces at the ankle and subtalar joint compared with screws-only constructs. Hindfoot nails did not demonstrate significant differences in either of these parameters compared with plates or screws in this study. CLINICAL RELEVANCE: Hindfoot nail and lateral plate options should be strongly considered when aiming to maximize compression in patients undergoing TTCA.

Modifying hernia mesh design to improve device mechanical performance and promote tension-free repair.

PURPOSE: Approximately 348,000 ventral hernia repairs are performed annually in the United States and the incisional hernia recurrence rate is approximately 20% as a result of suture and mesh device failure. Device failure is related to changes at the suture/tissue interface that leads to acute or chronic suture pull-through and surgical failure. To better manage mechanical tension, we propose a modified mesh design with extensions and demonstrate its mechanical superiority. METHODS: Comparative uniaxial static tensile testing was conducted on polypropylene suture and a modified mesh. Subsequently, a standard of care (SOC) mesh and modified mesh were evaluated using a tensometer in an acute hernia bench-top model. RESULTS: Modified mesh breaking strength, extension knot breaking strength, extension disruption, and extension anchoring were superior to suture (p < .05). Modified mesh ultimate tensile strength of anchoring was superior to SOC mesh (p < .05). Various stitch patterns and modifications in device design significantly improved device tension-free performance far beyond clinically relevant benchmarks (p < .05). CONCLUSIONS: Testing demonstrates that the modified mesh outperforms SOC mesh and suture in all tested failure modes. SOC hernia mesh tears through tissue at stress levels below maximum physiologic stress, whereas, the modified hernia mesh is up to 200% stronger than SOC mesh at resisting suture tearing through tissue and maintains anchoring at stresses far beyond clinically relevant benchmarks. Modifying hernia mesh design significantly improves device mechanical performance and enhances tension-free repair.

Augmentation of posterior wall acetabular fracture fixation using calcium-phosphate cement: a biomechanical analysis.

OBJECTIVE: This study investigates if the use of calcium phosphate cement as an adjunct to internal fixation for posterior wall acetabular fracture will result in acute restoration of joint loading parameters to the intact condition. METHODS: Ten fresh-frozen cadaveric pelves were used for this investigation. Simulated abductor mechanism was used to load the hip. Pressure-sensitive film was used to measure contact area and pressure within the anterior, superior, and posterior regions of the acetabulum for all experimental conditions. The hips were loaded under the following 4 conditions: 1) intact; 2) following posterior wall osteotomy; 3) following reduction and standard internal fixation; and 4) following reduction of the posterior wall using calcium phosphate cement, as a grout, in addition to internal fixation. A posterior wall fracture was created along an arc of 40-90 degrees about the acetabular rim. Extensometers were utilized to measure posterior wall fragment micromotion under conditions 3 and 4 above. Statistical analysis was performed using multivariate analysis of variance to assess the significance of the difference among and between conditions simultaneously for each region. Fragment motion data were analyzed using a 2-tailed t test. RESULTS: Fragment micromotion was reduced to 78 microm superiorly and 46 microm inferiorly with the use of calcium phosphate cement (P < 0.05). Creation of a posterior wall defect resulted in increased load in the superior acetabulum (1201N) as compared to the intact condition (902N, P = 0.024). Following reduction and internal fixation, the load distributed to the superior acetabulum (1132N) was not statistically different from the displaced condition. Following the addition of calcium phosphate cement, the load seen at the superior region of the acetabulum (883N) was less than fixation without calcium phosphate cement and was not different from the intact state (P = 0.85). CONCLUSION: The use of calcium-phosphate cement as a fracture grout with internal fixation resulted in a partial restoration of joint loading parameters toward the intact state. Further work will be needed to determine if similar types of augmented articular fixation may result in a clinical benefit.

Torsional stiffness after subtalar arthrodesis using second generation headless compression screws: Biomechanical comparison of 2-screw and 3-screw fixation.

BACKGROUND: Subtalar joint arthrodesis is a common operative treatment for symptomatic subtalar arthrosis. Because excessive relative motion between the talus and calcaneus can delay or prohibit fusion, fixation should be optimized, particularly in patients at risk for subtalar arthrodesis nonunion. Tapered, fully-threaded, variable pitch screws are gaining popularity for this application, but the mechanical properties of joints fixed with these screws have not been characterized completely. We quantified the torsion resistance of 2-screw and 3-screw subtalar joint fixation using this type of screw. METHODS: Ten pairs of cadaveric subtalar joints were prepared for arthrodesis and fixed using Acutrak 2-7.5 screws. One specimen from each pair was fixed with two diverging posterior screws, and the contralateral joint was fixed using two posterior screws and a third screw directed through the anterior calcaneus into the talar neck. Internal and external torsional loads were applied and joint rotation and torsional stiffness were measured at two torque levels. FINDINGS: Internal rotation was significantly less in specimens fixed with three screws. No difference was detectable between 2-screw and 3-screw fixation in external rotation or torsional stiffness in either rotation direction. Both 2-screw and 3-screw fixation exhibited torsion resistance surpassing that reported previously for subtalar joints fixed with two diverging conventional lag screws. INTERPRETATION: Performance of the tapered, fully threaded, variable pitch screws exceeded that of conventional lag screws regardless of whether two or three screws were used. Additional resistance to internal rotation afforded by a third screw placed anteriorly may offer some advantage in patients at risk for nonunion.

Compressive Force With 2-Screw and 3-Screw Subtalar Joint Arthrodesis With Headless Compression Screws.

BACKGROUND: Joint compression is an essential element of successful arthrodesis. Although subtalar joint compression generated by conventional screws has been quantified in the laboratory, compression obtainable with headless screws that rely on variable thread pitch to achieve bony contact has not been assessed. This study measured subtalar joint compression achieved by 2 posteriorly placed contemporary headless, variable-pitch screws, and quantified additional compression gained by placing a third screw anteriorly. METHODS: Ten, unpaired fresh-frozen cadaveric subtalar joints were fixed sequentially using 2 diverging posterior screws (one directed into the talar dome, the other into the talar neck), 2 parallel posterior screws (both ending in the talar dome), and 2 parallel screws with an additional anterior screw inserted from the plantar calcaneus into the talar neck. Joint compression was quantified directly during screw insertion using a novel custom-built measuring device. RESULTS: The mean compression generated by 2 diverging posterior screws was 246 N. Two parallel posterior screws produced 294 N of compression, and augmentation of that construct with a third, anterior screw increased compression to 345 N (P < .05). Compression subsequent to 2-screw fixation was slightly less than that reported previously for subtalar joint fixation with 2 conventional lag screws, but was comparable when a third screw was added. CONCLUSIONS: Under controlled testing conditions, 2 tapered, variable-pitch screws generated somewhat less compression than previously reported for 2-screw fixation with conventional headed screws. A third screw placed anteriorly increased compression significantly. CLINICAL RELEVANCE: Because headless screws are advantageous where prominent screw heads are problematic, such as the load-bearing surface of the foot, their effectiveness compared to other screws should be established to provide an objective basis for screw selection. Augmenting fixation with an anterior screw may be desirable when conditions for fusion are suboptimal.

Biomechanical Comparison of Intramedullary Screw Versus Low-Profile Plate Fixation of a Jones Fracture.

BACKGROUND: Intramedullary screw fixation of fifth metatarsal Jones fractures often produces satisfactory results, however, nonunion and refracture rates are not negligible. The low-profile "hook" plate is an alternative fixation method that has been promoted to offer improved rotational control at the fracture site, but this remains to be proven. The purpose of this study was to document biomechanical performance differences between this type of plate and a contemporary solid, dual-pitch intramedullary screw in a cadaveric Jones fracture model. METHODS: Simulated Jones fractures were created in 8 matched pairs of fresh-frozen cadaveric fifth metatarsals. One bone from each pair was stabilized using an intramedullary TriMed Jones Screw and the other using a TriMed Jones Fracture Plate (TriMed, Inc, Santa Clarita, CA). Controlled bending and torsional loads were applied. Bending stiffness and fracture site angulation, as well as torsional stiffness, peak torque, and fracture site rotation were quantified and compared. RESULTS: Intramedullary screw fixation demonstrated greater bending stiffness and less fracture site angulation than plate fixation during plantar-to-dorsal and lateral-to-medial bending. Torsional stiffness of screw-fixed metatarsals exceeded that of plate-fixed bones at initial loading; however, as rotation progressed, the plate resisted torque better than the screw. No difference in peak torque was demonstrable between fixation methods, but it was reached earlier in specimens fixed with screws and later in those fixed with plates as rotation progressed. CONCLUSION: In this cadaveric Jones fracture model, intramedullary screw fixation demonstrated bending stiffness and resistance to early torsional loading that was superior to that offered by plate fixation. CLINICAL RELEVANCE: Although low-profile "hook" plates offer an alternative for fixation of fifth metatarsal Jones fractures, intramedullary screw fixation may provide better resistance to bending and initiation of fracture site rotation. The influence of these mechanical characteristics on fracture healing is unknown, and further clinical investigation is warranted.

The influence of patient age and bone mineral density on osteotomy fixation stability after hallux valgus surgery: A biomechanical study.

BACKGROUND: Oblique osteotomies of the first metatarsal are common surgical treatments for moderate to severe hallux valgus deformity. Osteotomy fixation integrity is important to minimize interfragment motion and maintain correction during healing, and our clinical observations suggest that patient age and bone quality affect fixation stability and ultimately the clinical outcome. Accordingly, this study correlated these patient factors with key mechanical measures of osteotomy angulation resistance in a cadaver hallux valgus correction model. METHODS: Standard Ludloff osteotomies were created in 31 fresh-frozen first metatarsals and fixed with two cannulated, dual-pitch headless screws. Each specimen underwent 1000 plantar-to-dorsal bending loads while monitoring bending stiffness and distal fragment dorsal angulation. Donor age and bone mineral density were then correlated with each mechanical measure at selected cycling increments. FINDINGS: We found significant positive correlation between bone mineral density and osteotomy fixation stiffness for all evaluated load cycles. Moderate negative correlation between bone density and angulation was identified, significant for load cycle 500. There was a weak, nonsignificant negative correlation between donor age and osteotomy bending stiffness, with r ranging from -0.134 to -0.243 between the first and 1000th loads. Little correlation was demonstrable between age and angulation. INTERPRETATION: Because low bone density correlates with decreased osteotomy site stiffness and increased angulation under load, patient compliance and protected weight bearing in the early postoperative phase are particularly important if bone mineral density is exceptionally low. Correspondingly, patients with especially high bone mineral density may be considered candidates for earlier weight bearing and active physical therapy.