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.

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.

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.

Effectiveness of Allograft Reconstruction vs Tenodesis for Irreparable Peroneus Brevis Tears: A Cadaveric Model.

BACKGROUND: Irreparable peroneus brevis tendon tears are uncommon, and there is scant evidence on which to base operative treatment. Options include tendon transfer, segmental resection with tenodesis to the peroneus longus tendon, and allograft reconstruction. However, the relative effectiveness of the latter 2 procedures in restoring peroneus brevis function has not been established. METHODS: Custom-made strain gage-based tension transducers were implanted into the peroneus longus and brevis tendons near their distal insertions in 10 fresh-frozen cadaver feet. Axial load was applied to the foot, and the peroneal tendons and antagonistic tibialis anterior and posterior tendons were tensioned to 50% and 100% of physiologic load. Distal tendon tension was recorded in this normal condition and after sequential peroneus brevis-to-longus tenodesis and peroneus brevis allograft reconstruction. Measurements were made in 5 foot inversion/eversion and plantarflexion/dorsiflexion positions. RESULTS: Distal peroneus brevis tendon tension after allograft reconstruction significantly exceeded that measured after tenodesis in all tested loading conditions (P ≤ 0.022). With 50% of physiologic load applied, peroneus brevis tension was 1% to 28% of normal (depending on foot position) after tenodesis and 73% to 101% of normal after allograft reconstruction. Under the 100% loading condition, peroneus brevis tension was 6% to 43% of normal after tenodesis and 88% to 99% of normal after reconstruction with allograft. Distal peroneus longus tension remained within 20% of normal under all operative and loading conditions. CONCLUSION: Allograft reconstruction of a peroneus brevis tendon tear in this model substantially restored distal tension when the peroneal tendons and their antagonists were loaded to 50% and 100% of physiologic load. Tenodesis to the peroneus longus tendon did not effectively restore peroneus brevis tension under the tested conditions. CLINICAL RELEVANCE: Because tenodesis was demonstrated to be ineffective for restoration of peroneus brevis function, this procedure may result in an imbalanced foot clinically.

Systematic Quantification of Stabilizing Effects of Subtalar Joint Soft-Tissue Constraints in a Novel Cadaveric Model.

BACKGROUND: Distinguishing between ankle instability and subtalar joint instability is challenging because the contributions of the subtalar joint's soft-tissue constraints are poorly understood. This study quantified the effects on joint stability of systematic sectioning of these constraints followed by application of torsional and drawer loads simulating a manual clinical examination. METHODS: Subtalar joint motion in response to carefully controlled inversion, eversion, internal rotation, and external rotation moments and multidirectional drawer forces was quantified in fresh-frozen cadaver limbs. Sequential measurements were obtained under axial load approximating a non-weight-bearing clinical setting with the foot in neutral, 10° of dorsiflexion, and 10° and 20° of plantar flexion. The contributions of the components of the inferior extensor retinaculum were documented after incremental sectioning. The calcaneofibular, cervical, and interosseous talocalcaneal ligaments were then sectioned sequentially, in two different orders, to produce five different ligament-insufficiency scenarios. RESULTS: Incremental detachment of the components of the inferior extensor retinaculum had no effect on subtalar motion independent of foot position. Regardless of the subsequent ligament-sectioning order, significant motion increases relative to the intact condition occurred only after transection of the calcaneofibular ligament. Sectioning of this ligament produced increased inversion and external rotation, which was most evident with the foot dorsiflexed. CONCLUSIONS: Calcaneofibular ligament disruption results in increases in subtalar inversion and external rotation that might be detectable during a manual examination. Insufficiency of other subtalar joint constraints may result in motion increases that are too subtle to be perceptible. CLINICAL RELEVANCE: If calcaneofibular ligament insufficiency is established, its reconstruction or repair should receive priority over that of other ankle or subtalar periarticular soft-tissue structures.

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.

Biomechanical Comparison of External Fixation and Compression Screws for Transverse Tarsal Joint Arthrodesis.

BACKGROUND: Transverse tarsal joint arthrodesis is commonly performed in the operative treatment of hindfoot arthritis and acquired flatfoot deformity. While fixation is typically achieved using screws, failure to obtain and maintain joint compression sometimes occurs, potentially leading to nonunion. External fixation is an alternate method of achieving arthrodesis site compression and has the advantage of allowing postoperative compression adjustment when necessary. However, its performance relative to standard screw fixation has not been quantified in this application. We hypothesized that external fixation could provide transverse tarsal joint compression exceeding that possible with screw fixation. METHODS: Transverse tarsal joint fixation was performed sequentially, first with a circular external fixator and then with compression screws, on 9 fresh-frozen cadaveric legs. The external fixator was attached in abutting rings fixed to the tibia and the hindfoot and a third anterior ring parallel to the hindfoot ring using transverse wires and half-pins in the tibial diaphysis, calcaneus, and metatarsals. Screw fixation comprised two 4.3 mm headless compression screws traversing the talonavicular joint and 1 across the calcaneocuboid joint. Compressive forces generated during incremental fixator foot ring displacement to 20 mm and incremental screw tightening were measured using a custom-fabricated instrumented miniature external fixator spanning the transverse tarsal joint. RESULTS: The maximum compressive force generated by the external fixator averaged 186% of that produced by the screws (range, 104%-391%). Fixator compression surpassed that obtainable with screws at 12 mm of ring displacement and decreased when the tibial ring was detached. No correlation was found between bone density and the compressive force achievable by either fusion method. CONCLUSION: The compression across the transverse tarsal joint that can be obtained with a circular external fixator including a tibial ring exceeds that which can be obtained with 3 headless compression screws. Screw and external fixator performance did not correlate with bone mineral density. This study supports the use of external fixation as an alternative method of generating compression to help stimulate fusion across the transverse tarsal joints. CLINICAL RELEVANCE: The findings provide biomechanical evidence to support the use of external fixation as a viable option in transverse tarsal joint fusion cases in which screw fixation has failed or is anticipated to be inadequate due to suboptimal bone quality.

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.

Calcaneal "Z" osteotomy effect on hindfoot varus after triple arthrodesis in a cadaver model.

BACKGROUND: Triple arthrodesis involves subtalar, talonavicular, and calcaneocuboid joint fusion and is performed to relieve pain and correct deformity. Complications include malunion resulting in equinovarus and lateral column overload, which can lead to painful callosities and stress fractures. This study quantified the effectiveness of a closing-wedge calcaneal "Z" osteotomy for correction of the varus condition and reduction of abnormal loading of the lateral border of the foot. METHODS: Ten fresh-frozen feet were used. Angle meters were attached to the calcaneus and second cuneiform to measure hindfoot and midfoot varus, and pressure sensors were placed under the first and fifth metatarsal heads to document loading of the borders of the foot. Tensile loads were applied to ten extrinsic tendons and the Achilles tendon while an 1187 N axial foot load was applied. Calcaneus and second cuneiform coronal plane angles and medial and lateral plantar pressures were measured initially, after triple fusion-induced varus, and after "Z" osteotomy. RESULTS: The calcaneal "Z" osteotomy had no significant corrective effect, with hindfoot alignment virtually identical before and after the procedure under the described foot loading conditions. Similarly, second cuneiform inclination, representative of midfoot alignment, showed no change from the osteotomy. Medial and lateral peak plantar pressures after calcaneal "Z" osteotomy did not differ from those measured after varus triple fusion. CONCLUSION: In this cadaver model of varus malunited triple arthrodesis, the closing-wedge calcaneal "Z" osteotomy was ineffective for correction of bone alignment and lateral forefoot overloading under the tested conditions. CLINICAL RELEVANCE: The results provide additional information on which to base treatment after triple arthrodesis with varus malunion.

Biomechanical assessment of flexible flatfoot correction: comparison of techniques in a cadaver model.

BACKGROUND: Options for surgical correction of acquired flexible flatfoot deformity involve bone and soft-tissue reconstruction. We used an advanced cadaver model to evaluate the ability of key surgical procedures to correct the deformity and to resist subsequent loss of correction. METHODS: Stage-IIB flatfoot deformity was created in ten cadaver feet through ligament sectioning and repetitive loading. Six corrective procedures were evaluated: (1) lateral column lengthening, (2) medial displacement calcaneal osteotomy with flexor digitorum longus transfer, (3) Treatment 2 plus lateral column lengthening, (4) Treatment 3 plus "pants-over-vest" spring ligament repair, (5) Treatment 3 plus spring ligament repair with use of the distal posterior tibialis stump, and (6) Treatment 3 plus spring ligament repair with suture and anchor. Correction of metatarsal dorsiflexion and of navicular eversion were quantified initially and periodically during postoperative cyclic loading. RESULTS: Metatarsal dorsiflexion induced by arch flattening was initially corrected by 5.5° to 10.6°, depending on the procedure. Navicular eversion was initially reduced by 2.1° to 7.7°. The correction afforded by Treatments 1, 3, 4, 5, and 6 exceeded that of Treatment 2 initially and throughout postoperative loading. Inclusion of spring ligament repair did not significantly enhance correction. CONCLUSIONS: Under the tested conditions, medial displacement calcaneal osteotomy with flexor digitorum longus tendon transfer was inferior to the other evaluated treatments for stage-IIB deformity. Procedures incorporating lateral column lengthening provided the most sagittal and coronal midfoot deformity correction. Addition of spring ligament repair to a combination of these three procedures did not substantially improve correction. CLINICAL RELEVANCE: An understanding of treatment effectiveness is essential for optimizing operative management of symptomatic flatfoot deformity. This study provides empirical evidence of the advantage of lateral column lengthening and novel information on resistance to postoperative loss of correction.

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.

Biomechanical comparison of 4 different lateral plate constructs for distal fibula fractures.

BACKGROUND: Displaced lateral malleolar fractures are often treated with reduction and surgical stabilization. However, there has not been a comprehensive laboratory comparison to determine the most appropriate device for treating these patients. This study subjected a range of contemporary lateral fibular plates to a series of mechanical tests designed to reveal performance differences. METHODS: Forty fresh frozen lower extremities were divided into 4 groups. A Weber B distal fibula fracture was simulated with an osteotomy and stabilized using 1 of 4 plate systems: a standard Synthes one-third tubular plate with interfragmentary lag screw, a Synthes LCP locking plate with lag screw, an Orthohelix MaxLock Extreme low-profile locking plate with lag screw, or a TriMed Sidewinder nonlocking plate. Controlled monotonic bending and cyclic torsional loading were applied and bending stiffness, torsional stiffness, and fracture site motion were quantified. Resistance to cyclic torsional loading was determined by quantifying the number of loads withstood before excessive rotation occurred. Correlation between bone mineral density and each of the mechanical measures was determined. RESULTS: There was no difference in angulation or bending stiffness between plates. All plates except the LCP showed greater lateral deflection than in the other bending directions. Bending stiffness was lowest in lateral distal fragment deflection for all 4 plates. There was a positive correlation between bone mineral density and bending stiffness for all plate types. There was no difference in fracture site rotation between plate types in internal or external torsion, but internal rotation of the distal fragment consistently exceeded external rotation. Torsional stiffness in external rotation exceeded stiffness in internal rotation in nearly all specimens. LCP plates performed relatively poorly under cyclic torsion. CONCLUSIONS: Significant differences in plate performance were not demonstrated. The effects of bone quality variability and differences in interfragmentary screw purchase resulted in data dispersion that confounded absolute ranking of plate performance. CLINICAL RELEVANCE: Identification of an optimal lateral fibular plating system has the potential to improve the clinical outcome of malleolar fracture fixation, particularly when patient conditions are unfavorable.

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.

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.

Shortcuts in arthroscopic knot tying: do they affect knot and loop security?

BACKGROUND: Shortcuts for throwing 3 alternating reversed half-hitches on alternating posts (RHAPs), in which the post is switched by alternating strand tension to "flip" the knot, have been advocated but never validated in a biomechanical study. HYPOTHESIS: Shortcut tying techniques will affect knot security or loop security. STUDY DESIGN: Controlled laboratory study. METHODS: A single surgeon tied 90 knots using No. 2 FiberWire through an arthroscopic cannula. Half had a static "surgeon's base," and half had a Tennessee slider base. Three techniques were used to create 3 RHAPs: (1) rethreading, (2) knot "flipping" where half-hitches were tensioned by past-pointing, and (3) knot "flipping" where half-hitches were tensioned by alternating past-pointing and over-pointing. Each knot was subjected to a preload of 5 N, followed by 1000 cycles of 5 N to 45 N at 1 Hz, and a single load to failure. RESULTS: When compared with Tennessee knots, surgeon's knots had a lower incidence of knot slippage and catastrophic failure as well as higher loads to clinical and ultimate failure. Shortcut techniques did not affect the properties of surgeon's knots. However, when used to secure Tennessee knots, past-pointing decreased load to clinical failure and ultimate load to failure. Over-pointing increased the incidence of knot slippage and catastrophic failure and decreased load to clinical failure and ultimate load to failure. Loop security was marginally increased by both past-pointing and over-pointing. CONCLUSION: When all tying techniques are considered, surgeon's knots outperform Tennessee sliding knots. Shortcut techniques do not alter the properties of surgeon's knots. However, when used to secure Tennessee sliding knots, shortcuts lead to unacceptably high rates of knot slippage and catastrophic failure as well as decreased knot security. CLINICAL RELEVANCE: The outcomes of arthroscopic rotator cuff or labral repairs can be compromised when using shortcut tying methods to secure sliding Tennessee knots.

Jones fracture fixation: a biomechanical comparison of partially threaded screws versus tapered variable pitch screws.

BACKGROUND: Stabilization of fifth metatarsal Jones fractures with intramedullary screw fixation is the most common method for surgical fixation when operative treatment is indicated. Conventional partially threaded screws of various diameters are routinely used for Jones fracture fixation. Recently, the use of tapered variable pitch screws has become popular, but information regarding their performance in Jones fracture fixation is limited. No previous studies have compared conventional and tapered variable pitch screws in Jones fracture fixation under physiologic cyclic loading conditions. PURPOSE: To determine whether biomechanical differences exist between appropriately sized conventional partially threaded screws and tapered variable pitch screws under physiologic cyclic loading conditions with regard to Jones fracture fixation. STUDY DESIGN: Controlled laboratory study. METHODS: Simulated Jones fractures were created in 23 matched pairs of fresh-frozen fifth metatarsals. One bone from each pair was stabilized with a conventional partially threaded screw and the contralateral bone with a tapered variable pitch screw. Initial compression, as well as fracture site compression, angulation, and bending stiffness, was compared between groups throughout 1000 physiologic cyclic loads. RESULTS: Conventional partially threaded screws obtained significantly greater initial compression compared with tapered variable pitch screws. Significantly greater compression was maintained throughout cyclic loading with conventional screw fixation compared with tapered variable pitch screws. Fracture site angulation was significantly greater using tapered variable pitch screws from the tenth load cycle through completion of cyclic loading. Despite a trend toward increased fracture site bending stiffness when using conventional screws, no difference in fixation stiffness was demonstrable between the 2 screw types. CONCLUSION: In this cadaveric Jones fracture fixation model, conventional partially threaded screws provided improved fracture site compression and decreased fracture site angulation but offered no advantage in improving fracture site stiffness compared with tapered variable pitch screws. These results provide empirical evidence to guide implant selection decision making for operative fixation of Jones fractures. CLINICAL RELEVANCE: While the use of tapered variable pitch screws is a potential alternative for fixation of fifth metatarsal Jones fractures, conventional partially threaded screws may provide better biomechanical stability, the effect of which on fracture healing is unknown.