Computational analysis of Lisfranc surgical repairs.

Ligamentous Lisfranc injuries cause debilitating pain and loss of function. Even small diastasis of this normally rigid joint after injury requires surgical treatment, but outcomes remain poor. Existing literature has compared the different surgical procedures using cadaveric models, but no approach has been recommended over others. This study uses a computational biomechanical approach consistent with a cadaveric study to evaluate the different procedures' ability to stabilize the Lisfranc joint without inducing secondary consequences. A validated rigid body model for the cadaver foot with a Lisfranc injury was extended to compare the stability of four different surgical repairs-three open reduction and internal fixation procedures with different hardware (cannulated screws, endobuttons, and screws with a dorsal plate) and primary arthrodesis with screws. Forces calculated from the rigid body model for 50% partial weight bearing provided boundary conditions for a finite element model of the surgical repairs. Comparing the different surgical procedures, the open reduction and internal fixation with screws and primary arthrodesis with screws showed the most stable postoperative Lisfranc joint. However, the use of cannulated screws for fixation showed regions of high stress that may be susceptible to breakage and also resulted in higher contact forces in joints adjacent to the surgery site. Endobuttons and dorsal plates did not restore sufficient stability. Since all procedures showed different points of concern that could impact outcomes, additional surgical approaches could be needed in the future. This study offers a standard protocol for benchmarking the new procedures against those currently used.

Automatic Characterization of Pelvic and Sacral Measures from 200 Subjects.

BACKGROUND: An understanding of pelvic and acetabular morphology and orientation is required for accurate surgical reconstruction of the hip and spine, as well for component placement in a total hip arthroplasty. Our objectives were to develop an automated system for measuring pelvic and sacral orientations utilizing computed tomographic (CT) scans and to characterize these measures across 200 asymptomatic subjects. METHODS: An automated feature recognition algorithm was created to identify acetabular and pelvic orientation across 200 scans generated for non-musculoskeletal conditions. Three-dimensional models were generated from CT data to serve as inputs to the algorithm. Acetabular orientation was defined by comparing a plane fit to the acetabular rim with the anterior pelvic plane. Pelvic inclination, pelvic tilt, and sacral slope were defined as the angles between landmarks identified across the pelvis: pubic tubercles, acetabular center, left and right anterior superior iliac spines, and sacral plate. RESULTS: The mean sacral slope was 36.49°, the mean pelvic tilt was 15.60°, and the mean pelvic incidence was 52.05°. The mean sacropubic angle was 32.48° and the mean pelvic-Lewinnek angle was 8.93°. Significant differences between male and female subjects were observed in the sacral slope (mean difference, 4.72°; p < 0.05), pelvic tilt α (mean difference, 4.17°; p < 0.05), pelvic tilt γ (mean difference, 3.06°; p < 0.05), and the pelvic-Lewinnek angle (mean difference, 1.76°; p < 0.05). The comparison of acetabular orientation measures with those in a prior study of the same cohort yielded intraclass correlation coefficients (ICCs) all above 0.97. The validation of sacral orientation via manual measurement also yielded ICC values all at or above 0.97. CONCLUSIONS: Our algorithm showed a high degree of consistency in acetabular orientation measures with respect to a prior study of the same cohort. The measures of pelvic orientation were found to be accurate and reliable when compared with manual measurements of the same data set. All measurements of pelvic orientation were consistent with the means reported in the literature. CLINICAL RELEVANCE: An accurate and reproducible, automated technique for determining pelvic and acetabular orientation provides a way to characterize these measures as an aid in clinical diagnosis and preoperative planning.

Ibandronate Treatment Before and After Implant Insertion Impairs Osseointegration in Aged Rats with Ovariectomy Induced Osteoporosis.

Excessive decreases in bone volume (BV) and bone mineral density (BMD) can lead to osteoporosis, potentially hindering implant osseointegration. Bisphosphonates are commonly used to combat osteoporosis by slowing osteoclast-mediated resorption; however, functional osteoclasts are integral to bone remodeling and, thus, implant osseointegration, potentially contraindicating bisphosphonate use during implantation. To optimize the use of implant technologies in patients with compromised bone structure and metabolism, we need a more complete understanding of the biological response to surface design. The goal of this study was to assess the effects of osteoporosis and bisphosphonates on osseointegration of titanium (Ti) implants with microstructured surfaces, which have been shown to support osteoblast differentiation in vitro and rapid osseointegration in vivo. Forty, 8-month-old, virgin, female CD Sprague Dawley rats underwent ovariectomy (OVX) or sham (SHOVX) surgery. After 5 weeks, animals were injected subcutaneously with either the bisphosphonate (BIS), Ibandronate (25 µg/kg), or phosphate-buffered saline (PBS) every 25 days. 1 week after the initial injection, Ø2.5mm × 3.5mm microrough (SLA; grit-blasted/acid etched) implants were placed transcortically in the distal metaphysis of each femur resulting in four groups: 1) SHOVX+PBS; 2) SHOVX+BIS; 3) OVX+PBS; and 4) OVX+BIS. After 28d, qualitative properties of the bone and implant osseointegration were assessed using micro-computed tomography (microCT), calcified histomorphometry (Van Gieson's stain), and removal torque testing. microCT revealed decreased bone volume in OVX rats, which was slowed by bisphosphonate treatment. Reduced bone-to-implant contact (BIC) was evident in OVX+PBS compared to SHOVX+PBS. Although BV/TV was increased in OVX+BIS compared to OVX+PBS, bisphosphonate treatment had no effect on BIC. Removal torque testing revealed a higher maximum torque, torsional stiffness, and torsional energy in SHOVX compared to OVX with no effects due to bisphosphonate treatment. Our results show that osseointegration is decreased in osteoporotic animals. Ibandronate halts the progression of osteoporosis but does not enhance osseointegration. © 2019 The Authors. JBMR Plus Published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Biomechanical evaluation of the risk of secondary fracture around short versus long cephalomedullary nails.

INTRODUCTION: For proximal femur fractures, long cephalomedullary nails (CMNs) are often selected to avoid a diaphyseal stress riser at the tip of a shorter nail. Secondary peri-implant fracture rates for long and short CMN have not been shown to differ clinically. This study biomechanically compares both CMN in a cadaveric model. METHODS: Ten matched pairs of cadaveric femora with short or long CMN were axially loaded and internally rotated to failure. RESULTS: Resulting fractures involved distal interlocking screws of the short and long CMN. Energy and rotation to failure were significantly greater for short CMN. Torque at failure trended higher for short CMN but not significantly. No statistical difference was detected in stiffness of the short and long CMN. DISCUSSION: A greater risk of secondary fracture is not indicated for short versus long CMN under torsional stress. Short CMN may be suitable in the younger patient.

High Risk of Surgical Glove Perforation From Surgical Rotatory Instruments.

BACKGROUND: Surgical gloves can be damaged during the course of a procedure, which can place the surgeon and patient at risk. Glove perforation may not always be readily apparent, and determining the risk factors for glove perforation can aid the surgeon in deciding when a glove change is advisable. Time of wear and needle sticks have been well studied; however, other mechanisms including mechanical stress from surgical equipment have had limited evaluation to date. QUESTIONS/PURPOSES: We evaluated the risk of glove perforation in gloves that were caught in a surgical rotatory device (such as drills and reamers). The aims of our study were (1) to determine the percentage of undetected microperforations after entanglement on a rotatory tool during orthopaedic procedures, (2) to determine which kinds of rotatory devices most commonly cause such microperforations, and (3) to assess whether time of wear had an effect on the risk of perforation. METHODS: From July 2014 to September 2015, 33 gloves were obtained from all orthopaedic subspecialties at our Level I trauma center if they were caught in a rotatory device greater than one revolution. Time of glove wear and location of the glove that was caught in a rotatory device were recorded. After an evaluation for macroperforations (≥ 5 mm), the gloves were evaluated for microperforations (< 5 mm) via the American Society for Testing and Materials (ASTM) one-liter load test. Time of wear was compared among gloves with macroperforations, microperforations, and no perforations. RESULTS: The 33 gloves obtained came from 33 procedures. Seventeen of 33 (52 %) gloves had perforations. Seven of the 17 perforated gloves had macroperforations while 10 had microperforations. Eleven of 33 entanglements were caught by drills, nine by reamers, eight by K-wires, and the remaining five gloves were caught by various other instruments. Eight of 17 perforations were caused by drills, three by reamers, three by K-wires, and three by various other instruments. The average time of wear was 58 minutes which did not differ with pattern of glove damage. CONCLUSION: Surgical gloves caught in a rotatory power instrument are likely to have been perforated, regardless of the amount of time that they had been worn. Visual inspection appears to be an inadequate test of glove integrity. When a glove becomes entangled in a rotary instrument such as a drill, pin, or reamer, a surgeon should change the gloves regardless of whether he or she believes a perforation is present. LEVEL OF EVIDENCE: Level IV, therapeutic study.

Bone-Prosthesis Junction for Active Tendon Implants: A Biomechanical Comparison of 2 Fixation Techniques.

PURPOSE: To study the biomechanical characteristics (percent stretch, stiffness, and ultimate load) of 2 distal fixation techniques for an active tendon implant used in the reconstruction of flexor tendons. METHODS: We evaluated percent stretch after cyclical loading and at failure, stiffness during load-to-failure, and peak load of 28 bone-prosthesis junctions using cadaveric canine middle phalanges to study 2 fixation techniques: metal cleat and screw versus polyester cords secured with a knot. RESULTS: The knot constructs displayed greater percent stretch during and following cyclical loading between 2 N and 50 N and at peak load. The screw construct showed greater stiffness from 50 N to 150 N during load-to-failure. Both fixation techniques failed at a mean peak load greater than 340 N. CONCLUSIONS: Both fixation techniques for active tendon implants withstood loads seen with passive and active motion in the immediate postoperative period. Knot constructs displayed significant stretch during cyclical and load-to-failure testing, which would need to be compensated for during surgery. The screw constructs showed greater stiffness than the constructs secured with the surgeon's knot, but failure created an intra-articular fracture. CLINICAL RELEVANCE: The results may aid the surgeon in choosing which fixation technique to use, during tensioning of cords, and in permitting active motion following surgery.

Biomechanical Performance of Lateral Versus Dual Locking Plates for Calcaneal Fractures.

Given the high rates of wound complications with a standard lateral extensile incision, small dual incision techniques might result in less soft tissue destruction. The goal of the present study was to compare the biomechanical performance between a single locking plate and a dual locking plating system for an intra-articular calcaneal fracture model. A Sanders IIB type joint depression calcaneal fracture was created in 10 paired, fresh-frozen, cadaveric calcanei (age 47 ± 12, range 35 to 78 years). The calcanei of each pair were randomly assigned for fixation using either a lateral locking reconstruction plate or lateral and medial locking reconstruction plates. The specimens were axially loaded in cyclic fashion for 1000 cycles, followed by load to failure. The relative fragment movement was monitored optically in both the sagittal and the coronal planes. The amount of overall construct displacement increased with cycling, although no difference was found between the plating techniques. For fragment movement during cycling, the lateral joint fragment migrated anteroinferiorly along the fracture line relative to the tuberosity fragment for dual plated specimens by a small, but statistically significant, amount. This same translation was smaller for lateral plated specimens but was not found to be significant. During load to failure testing, no statistically significant differences were found for construct stiffness. A tendency was seen toward more interfragmentary motion in the sagittal plane (lateral joint fragment movement relative to the fracture line), with less movement overall in the coronal plane (anterior fragment translation and twist) for dual plating, although the difference from the lateral plate was not statistically significant. The present study demonstrated that for this calcaneal fracture model, the dual plating technique experienced a small amount of fragment translation during cycling that was significantly different statistically from that with lateral plating but was not clinically relevant. During the load to failure, the dual plating technique was comparable to the lateral plate. Thus, dual plating could be a viable biomechanical option for fracture reduction if avoidance of a large extensile lateral approach associated with lateral plating is warranted.

Hip contact stress and femoral neck retroversion: a biomechanical study to evaluate implication of femoroacetabular impingement.

The current literature on femoroacetabular impingement (FAI) is focused on acetabular orientation and femoral head asphericity, with little emphasis on the effect of version of the femoral neck. A biomechanical model was developed to determine the causative effect, if any, of femoral retroversion on hip contact stress and, if present, delineate the type of FAI with femoral neck retroversion. Five pairs of cadaveric hips (n = 10) were tested by loading the hip in 90° of flexion and measured the peak joint pressure and the location of the peak joint pressure. The experiment was repeated after performing a subtrochanteric osteotomy and retroverting the proximal femur by 10°. Ten hips were successfully tested, with one hip excluded due to an outlier value for peak joint pressure. Retroversion of the proximal femur significantly increased the magnitude of mean peak joint pressure. With retroversion, the location of the peak joint pressure was shifted posteroinferiorly in all cases. In conclusion, femoral neck retroversion increases peak joint pressure in the flexed position and may act as a cause of femoroacetabular impingement. The location of peak joint pressure suggests a pincer-type impingement with retroversion. The version of femoral neck should be assessed as a possible causative factor in patients with FAI, especially those with pincer-type impingement.

Proximal tendon-prosthesis junction for active tendon implants of the hand: a biomechanical comparison of 2 techniques.

PURPOSE: To study the biomechanical characteristics (percent stretch, stiffness, and ultimate load) of 2 tendon-prosthesis techniques used to connect the proximal tendon stump to silicone active tendon implants used in reconstruction of flexor tendons. METHODS: We evaluated percent stretch following cyclic loading and at failure, stiffness during load to failure, and ultimate load of 16 tendon-prosthesis junctions using cadaveric canine flexor digitorum profundus tendons to re-create 2 junction techniques: the tendon loop (TL) and the polyester weave (PW). RESULTS: The TL junction showed greater percent stretch at a static load of 2 N, following 500 cycles of loading between 2 N and 50 N, and at peak load. The PW junction displayed greater stiffness from 50 to 150 N during load to failure. Both junctions failed at a mean ultimate load greater than 220 N. CONCLUSIONS: The described proximal junction techniques for active tendon implants were strong enough to resist early active motion in the immediate postoperative period without significant elongation. The PW technique displayed greater stiffness and ultimate load compared with the TL. CLINICAL RELEVANCE: Data on tendon-prosthesis characteristics of these 2 methods may aid the surgeon in choosing which junction technique to use, during surgical tensioning decisions, and in considering activity protocols after surgery. These data may also serve as a baseline for further investigations regarding active tendon implants.

A novel approach for determining three-dimensional acetabular orientation: results from two hundred subjects.

BACKGROUND: The inherently complex three-dimensional morphology of both the pelvis and acetabulum create difficulties in accurately determining acetabular orientation. Our objectives were to develop a reliable and accurate methodology for determining three-dimensional acetabular orientation and to utilize it to describe relevant characteristics of a large population of subjects without apparent hip pathology. METHODS: High-resolution computed tomography studies of 200 patients previously receiving pelvic scans for indications not related to orthopaedic conditions were selected from our institution's database. Three-dimensional models of each osseous pelvis were generated to extract specific anatomical data sets. A novel computational method was developed to determine standard measures of three-dimensional acetabular orientation within an automatically identified anterior pelvic plane reference frame. Automatically selected points on the osseous ridge of the acetabulum were used to generate a best-fit plane for describing acetabular orientation. RESULTS: Our method showed excellent interobserver and intraobserver agreement (an intraclass correlation coefficient [ICC] of >0.999) and achieved high levels of accuracy. A significant difference between males and females in both anteversion (average, 3.5°; 95% confidence interval [CI], 1.9° to 5.1° across all angular definitions; p < 0.0001) and inclination (1.4°; 95% CI, 0.6° to 2.3° for anatomic angular definition; p < 0.002) was observed. Intrapatient asymmetry in anatomic measures showed bilateral differences in anteversion (maximum, 12.1°) and in inclination (maximum, 10.9°). CONCLUSIONS: Significant differences in acetabular orientation between the sexes can be detected only with accurate measurements that account for the entire acetabulum. While a wide range of interpatient acetabular orientations was observed, the majority of subjects had acetabula that were relatively symmetrical in both inclination and anteversion. CLINICAL RELEVANCE: A highly accurate and reproducible method for determining the orientation of the acetabulum's aperture will benefit both surgeons and patients, by further refining the distinctions between normal and abnormal hip characteristics. Enhanced understanding of the acetabulum could be useful in the diagnostic, planning, and execution stages for surgical procedures of the hip or in advancing the design of new implant systems.

Reattachment of flexor digitorum profundus avulsion: biomechanical performance of 3 techniques.

PURPOSE: To investigate whether inclusion of the volar plate in repair of flexor digitorum profundus avulsions increases the strength of the repair and resists gapping. METHODS: Cadaveric fingers (n = 18) were divided into 3 equal groups. The first technique involved 2 micro-suture anchors only (A). The second used only volar plate repair (VP). The third group was a hybrid, combining a micro-suture anchor with volar plate augmentation (AVP). Specimens were loaded cyclically to simulate passive motion rehabilitation before being loaded to failure. Clinical failure was defined as 3 mm of gapping, and physical failure as the highest load associated with hardware failure, suture breakage, anchor pullout, or volar plate avulsion. RESULTS: Gapping throughout cycling was significantly greater for the A group than VP and AVP with no difference detected between VP and AVP groups. Gapping exceeded 3 mm during cycling of 3 A specimens, but in none of the VP or AVP specimens. Load at clinical and physical failure for A was significantly lower than for VP and AVP, whereas no difference was detected between VP and AVP. CONCLUSIONS: In this cadaveric model, incorporating the volar plate conferred a significant advantage in strength, increasing the mean load to physical failure by approximately 100 N. CLINICAL RELEVANCE: According to previous biomechanical studies, current reconstructive strategies for flexor digitorum profundus zone I avulsions are not strong enough to withstand active motion rehabilitation. We demonstrated the potential use of volar plate augmentation and the prospective advantageous increase in strength in this cadaveric model. In vivo performance and effects on digital motion are not known.

Plantar measurements to determine success of surgical correction of Stage IIb adult acquired flatfoot deformity.

Adult acquired flatfoot deformity is a degenerative disease causing medial arch dysfunction. Surgical correction has typically involved tendon reconstruction with calcaneal osteotomy; however, the postoperative changes have not been fully characterized. The present study assessed the success of surgical correction of Stage IIb adult acquired flatfoot deformity through changes in plantar pressures and patient-generated outcome scores. With Institutional Review Board approval, 6 participants were evaluated before and after surgery using pedobarography, the Foot and Ankle Outcome Score, and the Medical Outcomes Study 36-item short-form questionnaire. The plantar pressures were recorded using a TekScan HRMat(®) during walking and in a 1- and 2-foot stance. The resulting contour maps were segmented into 9 regions, with the peak pressure, normalized force, and arch index calculated. Surgical effects were analyzed using paired t tests. Postoperatively, the Foot and Ankle Outcome Score and Medical Outcomes Study 36-item short-form questionnaire scores increased significantly from 180 ± 78 to 360 ± 136 (p < .03) and 47 ± 18 to 71 ± 19 (p = .06), respectively. During the 2-foot stance, the normalized force had increased significantly in the lateral midfoot (p < .03), although no significant differences were found in peak pressures. No significant differences were observed in the 1-foot stance. During walking, the normalized force increased significantly in the lateral mid- and forefoot (p < .05). The peak pressure increased significantly in the lateral forefoot (p < .01). The arch index values demonstrated no significant changes. The increased questionnaire scores indicated that surgical correction improved the self-perceived health of the participants. Lateral shifts in the peak pressure and normalized force suggest that forefoot and midfoot loading is altered postoperatively, consistent with the goal of offloading the dysfunctional arch. Thus, the present study has demonstrated that surgical treatment of adult acquired flatfoot deformity can be accurately assessed using patient-reported outcome measures and plantar pressures.

Unicortical PEEK inset locking fixation for metacarpal fractures: a biomechanical study.

PURPOSE: There are numerous constructs employed in the treatment of metacarpal fractures with varying degrees of success. While plate fixation commonly involves dorsal application of a bicortical non-locking plate, there has been recent exploration of other fixation options including unicortical locked plating. The purpose of this study was to evaluate the biomechanical integrity of a polyetheretherketone (PEEK) inset locking plate and, in doing so, compare it to standard plate fixation (utilizing a clinically proven bicortical non-locking titanium plate) in a simulated porcine metacarpal fracture model. METHODS: Reproducible mid-shaft fractures were created in porcine second metacarpals. The fractured specimens were reduced and plated with either a bicortical non-locking plate or a unicortical locking plate with a PEEK locking design. Constructs were then loaded to failure in the same fashion as performed to create the fracture. Peak load was measured as the apex on the load-to-failure deflection curve. Stiffness was calculated as the linear slope on the load-to-failure deflection curve. Data were analyzed via Student's t test. RESULTS: Unicortical locking constructs failed at 344 ± 119 N, while bicortical non-locking constructs were found to fail at 277 ± 101 N (p = 0.19). The unicortical locking constructs demonstrated a stiffness of 80 ± 36 N/mm compared with the bicortical non-locking constructs (69 ± 36 N/mm) although again the difference was not found to be statistically different (p = 0.49). CONCLUSION: Based on this study, a locked plating construct using a polymer mechanism provides an interesting new locking fixation method for small bone fractures and with our limited number of specimens tested, provided at least a similar strength and rigidity profile in comparison with bicortical fixation in the treatment of metacarpal fractures.

Proximal humeral fracture fixation: a biomechanical comparison of two constructs.

BACKGROUND: Different options exist for stabilizing proximal humeral fractures. This study compared the mechanical stability of 2 common proximal humeral fixation plates in bending and torsion. METHODS: Tests were conducted on 40 synthetic and 10 matched pairs of cadaveric humeri (evenly fixed with DePuy S3 proximal humeral plating system [DePuy Orthopaedics, Warsaw, IN, USA] and Synthes proximal humerus locking compression plate [Synthes, Paoli, PA, USA]). Half of the humeri were tested by cantilevered bending in flexion, extension, varus, and valgus for 100 cycles of ±5 mm of displacement at 1 mm/s before loading to failure in varus. The other half were tested in torsion for 100 cycles of ±8° of rotational displacement at 1°/s before loading to failure in external rotation. RESULTS: Peak cyclic loads for synthetic constructs were higher for DePuy plates than Synthes plates in varus and valgus (P < .0001), but a difference was not detected in extension (P > .40) or flexion (P = .0675). Peak cyclic loads for cadaveric constructs showed a significant difference in extension and flexion (Synthes > DePuy, P < .0001) and in varus (DePuy > Synthes, P < .05) but not in valgus (P > .10). Bending stiffness during varus failure testing was higher for DePuy plates than Synthes plates (P < .0001) for synthetic constructs. Regarding torsion of synthetic and cadaveric constructs, DePuy plates experienced higher peak cyclic torques over all cycles in both directions (P < .0001). For synthetic constructs, DePuy plates showed higher torsional stiffness in external failure than Synthes plates (P < .0001). CONCLUSIONS: The DePuy plate was stiffer than the Synthes plate with varus and valgus bending, as well as in torsion. The Synthes plate tended to be stiffer in flexion and extension.

Effect of pressure applied during casting on temperatures beneath casts.

BACKGROUND: Burns and pressure sores are common injuries during cast application. Various factors such as water temperature, padding, and cast material layers may play a role in these injuries; however, the effect of cast molding on temperatures and pressures has not been investigated. This raises the following questions, does the application of molding during cast application: (1) alter skin level temperatures in a variety of cast materials? and (2) risk inducing either thermal injury or pressure necrosis? METHODS: An upper extremity model was created to measure pressure and temperature underneath casting materials. Cast padding, water bath temperature, and cast thickness were standardized. A 3-point mold was simulated using 3 casting materials-Fiberglass only, Plaster Only splint, and Plaster splint overwrapped with Fiberglass-while pressure and temperature were recorded. RESULTS: : Pressure application led to a statistically significant (P<0.0001) increase in temperature at the sites where the mold was applied although absolute temperature did not reach the theoretical burn threshold of 49 to 50°C for the casting materials studied. With pressure applied, the Plaster/Fiberglass combination reached an average peak temperature of 47.9°C, which was maintained for up to 6 minutes. Neither Fiberglass nor Plaster Only reached peak temperatures of this magnitude (average of 42.7 and 43.6°C, respectively). Peak (369 mm Hg) and highest residual (21 mm Hg) pressures were below harmful levels. CONCLUSIONS: Pressure application during casting is a risk factor for burn injuries. Care should be taken when molding a plaster splint overwrapped in fiberglass by waiting until the plaster has fully cooled. CLINICAL RELEVANCE: Combined with other known risk factors, the pressure from molding a cast could increase the likelihood of causing cutaneous burns.

Biomechanical evaluation of a locking and nonlocking reconstruction plate in an osteoporotic calcaneal fracture model.

BACKGROUND: This study evaluated the effects of locking vs nonlocking configuration on the biomechanical performance of a calcaneal reconstruction plate in an osteoporotic cadaveric model. MATERIALS AND METHODS: A Saunders II B type calcaneal fracture was created in ten matched pair of cadaveric calcanei. Each pair was fixed with the Ascension calcaneal reconstruction plate using either locking or nonlocking screws in the same hole pattern. Specimens were axially loaded for 1000 cycles through the talus followed by load to failure. Statistical comparisons were made between the locking and nonlocking constructs on the displacements during cyclic loading as well as construct stiffness and load achieved at selected fragment displacements. RESULTS: No significant difference was detected between the locking and nonlocking constructs in displacement during cyclic loading (p > 0.2) for the numbers available. Similarly no significant difference was found in stiffness of the constructs between the groups: 445.7 ± 148.8 (N/mm ± SD) for the locking plate and 395.2 ± 127.7 for the nonlocking plate (p > 0.14). The load achieved at 2 mm displacement of the posterior fragment for the two groups were not different: locking plate at 744.6 ± 237.2 N and nonlocking plate at 739.3 ± 269.7 N (p > 0.99). CONCLUSION: This study did not reveal a mechanical advantage to locking technology for calcaneal fractures with the selected plate and fracture model. CLINICAL RELEVANCE: While locking plate technology has shown mechanical advantages for fracture management in other osteoporotic models, in our fracture model and plating construct, this was not found. It is still unclear which fixation technique is most beneficial in these calcaneal fractures.

Range of motion effects of distal pole scaphoid excision and triquetral excision after radioscapholunate fusion: a cadaver study.

PURPOSE: Radioscapholunate (RSL) fusion is an effective surgical procedure for the treatment of isolated radiocarpal arthritis. Although functional wrist motion is typically preserved through the midcarpal joint, many patients are still frustrated by postoperative limitations. The purpose of this study was to evaluate motion of cadaver wrists after simulated RSL fusion with excision of the distal pole of the scaphoid and the triquetrum. METHODS: Ten fresh-frozen cadaver upper extremities were mounted on a custom testing apparatus after isolation of the flexor carpi radialis, flexor carpi ulnaris, extensor carpi radialis longus, and extensor carpi ulnaris tendons. Sequential loading of these tendons resulted in flexion, extension, radial, and ulnar deviation. We subsequently measured range of motion with the use of digital photography. All specimens were tested in 4 states: intact (normal), RSL fusion (simulated), RSL fusion with distal scaphoid pole excision, and RSL fusion with distal scaphoid pole and triquetrum excision. The results were statistically analyzed using a repeated measures analysis of variance. RESULTS: Range of motion decreased to 39% to 46% of normal for flexion and extension and 65% to 71% of normal for radial and ulnar deviation after simulated RSL fusion. The addition of distal pole of scaphoid excision resulted in flexion and extension returning to 72% to 79% of normal, and radial and ulnar deviation returning to 84% to 89% of normal. Excision of the triquetrum further increased flexion and extension to 87% to 97% of normal, and radial and ulnar deviation to 119% to 137% of normal. CONCLUSIONS: The combination of triquetral and distal scaphoid pole excision after RSL fusion improves wrist motion to levels close to normal in the cadaver model.

Bioreactor for biaxial mechanical stimulation to tissue engineered constructs.

The complex structure and properties of biological tissues as well as their in situ environment often make it difficult to self-heal. A suitable replacement tissue may be created in vitro through tissue engineering approaches and mechanical stimulation of tissue constructs. A new biaxial bioreactor was designed, constructed, and evaluated for the purposes of developing constructs with specific functional characteristics. Once constructed and assembled, the bioreactor was tested for position accuracy and application of strain. Additionally, a tissue construct was tested in the chamber and compared with a nonstimulated construct. Results showed high position accuracy, but some loss between applied strain via grip movement and strain experienced by the scaffold. The tested construct exhibited an increase in cells and matrix deposition in comparison to the nonstimulated construct. This biaxial bioreactor will be useful for mechanically stimulating tissue constructs in two perpendicular directions to create implants for tissues requiring preferred compressive and tensile resistances.

Complex varus elbow instability: a terrible triad model.

HYPOTHESIS: The terrible triad is a debilitating injury that involves elbow dislocation with injury to the lateral collateral ligament (LCL) complex, the radial head, and the coronoid process. This study investigated the role of these components in varus stability of the elbow. MATERIALS AND METHODS: We investigated the role of these components in varus stability of the elbow using 10 cadaveric fresh frozen upper extremities. The testing order allowed each of four states to be tested (intact, LCL complex deficient or repaired, radial head resected or replaced) at two flexion angles and multiple coronoid resection levels. Values for restraining load (newtons [N]) at 1.5 cm of varus displacement were obtained on a materials testing machine. RESULTS: Beyond a 50% loss of the coronoid process, neither repair of the LCL nor replacing the radial head alone resulted in a statistically significant increase in varus stability. For a loss of the coronoid process between 67-75%, repair of the LCL and replacement of the radial head showed improved stability over repair alone, or radial head replacement alone. For loss of the coronoid beyond 75%, even repair of the LCL and replacement of the radial head did not improve varus stability of the elbow. CONCLUSION: These findings provide a biomechanical basis for aggressive treatment of coronoid fractures as a component of the terrible triad injury. LEVELS OF EVIDENCE: Basic science study.

Biomechanical comparison of the holding strength of a peek-optima circular plate versus a stainless steel oblique T-plate for radioscapholunate arthrodesis.

PURPOSE: Radioscapholunate arthrodesis is an accepted treatment for posttraumatic radiocarpal arthritis that preserves some wrist motion. Good results are dependent on secure fixation while avoiding hardware-related side effects. A small radiolucent countersunk circular plate placed over the radiocarpal joint may offer a low-profile technique for achieving secure fixation of the radioscapholunate joint. The purpose of this study was to compare the biomechanical performance of this circular plate, when applied in this manner, to that of a more conventional fixation technique such as a 3.5-mm T-plate. METHODS: Ten pairs of fresh-frozen cadaveric wrists were amputated 7 cm proximal to the radiocarpal joint. One wrist from each pair was fixed with a T-plate (DePuy, Inc., Warsaw, IN), and the contralateral wrist was fixed with a circular plate (Xpode plate; TriMed, Inc., Valencia, CA). The radius and scaphoid-lunate complex were each rigidly held and mounted into a materials testing machine. Translational forces to mimic extension and flexion movements were applied cyclically for 40 cycles, followed by failure testing in extension. RESULTS: Cyclic tests revealed no statistically significant differences between the 2 fixation plates although resistance to flexion motion was higher than resistance to extension motion. The average load at failure was no different between the T-plate and circular plate. However, a ratio of the failure loads (T-plate to circular plate) demonstrated a 58% higher load for the circular plate. CONCLUSIONS: A countersunk circular plate provides similar biomechanical performance to the T-plate for radioscapholunate arthrodesis.