Ventral femoral head and neck ostectomy: Standard versus novel K-wire guided technique using a premeasured ostectomy angle in canine cadavers.

OBJECTIVE: To assess the accuracy and efficiency of performing ventral FHO (vFHO) after measuring the ideal femoral head and neck ostectomy angle (iFHOA), with and without guidance of a K-wire. To compare the iFHOA to the previously accepted 45° angle to guide vFHOs. STUDY DESIGN: Randomized, controlled, ex vivo study. ANIMALS: Ten mixed-breed canine cadavers. METHODS: A routine un-guided and guided vFHO was performed on each cadaver. A single unmodified ostectomy was performed on all hips. The pre- and postoperative iFHOA and postoperative residual femoral neck were radiographically assessed. Subjective intraoperative palpation and postoperative radiographic ostectomy completeness (OC) scores were assigned. RESULTS: Subjective OC scores (p > .63) did not differ between techniques, and guided vFHOs were as good or better for 7/10 dogs assessed via intraoperative palpation, and 9/10 dogs assessed radiographically. Residual femoral neck measurements were similar in both groups (p > .75). The average iFHOA in this study was 38.5°, with no significant difference between limbs of the same cadaver (p = .34). Guided vFHO took longer (294.5 s, p = .002) than unguided vFHO (166.7 s). CONCLUSION: The mean iFHOA of 38.5° was less than the previously published 45° angulation for vFHOs. Subjectively, use of a K-wire guide improved soft tissue retraction, neck visualization, and confidence in cut angulation. CLINICAL SIGNIFICANCE: Preoperative iFHOA measurement may minimize the risk of inappropriate vFHO angles.

Gait and electromyographic alterations due to early onset of injury and eventual rupture of the cranial cruciate ligament in dogs: A pilot study.

OBJECTIVE: Identify relevant electromyography (EMG), kinematic, and kinetic changes resulting from monopolar radiofrequency energy (MRFE)-induced cranial cruciate ligament (CCL) injury and eventual rupture in dogs. STUDY DESIGN: Experimental, repeated measures. ANIMALS: Five purpose-bred female dogs free of orthopedic and neurologic disease. METHODS: Surface EMG, joint kinematics, and ground reaction forces were assessed at a trot in the pelvic limbs at baseline, at 2 and 4 weeks after unilateral MRFE-induced CCL injury, and at 4, 8, and 16 weeks after CCL rupture (CCLR). RESULTS: After MRFE-induced injury, average hip joint range of motion (ROM) during stance decreased within the untreated pelvic limb. After CCLR, stifle flexion angles decreased within the treated limb at 8 weeks and within the untreated pelvic limb at all time points, whereas average tarsal joint ROM decreased in the treated limb and increased in the untreated limb. Peak vertical ground reaction force and impulse decreased within the treated limb. Qualitative alterations of many EMG values were noted after MRFE-induced injury and CCLR, although significant differences between limbs or from baseline values were not detected. CONCLUSION: Monopolar radiofrequency energy-induced injury altered contralateral hip kinematics, suggesting early regional compensatory gait alterations. After CCLR, additional compensatory gait patterns occurred in both pelvic limbs. CLINICAL IMPACT: The qualitative analysis of trial-averaged EMG data in this small population supports a relationship between neuromuscular function and induced CCL injury leading to rupture.

The effect of polydioxanone hemicerclage suture on the occurrence of fracture during tibial tuberosity advancement with an elongated bi-directional hinged osteotomy.

OBJECTIVE: To investigate the effect of hemicerclage suture on the occurrence of fractures during advancement of an elongated bi-directional hinged osteotomy (EBHO) for tibial tuberosity advancement (TTA) in dogs. STUDY DESIGN: Experimental ex vivo study. ANIMALS: Canine cadavers (n = 14) METHODS: A uniform EBHO was performed in 28 cadaveric hind limbs (n = 28) from 14 skeletally mature, medium-sized, mixed breed dogs. Paired limbs were randomly assigned with or without hemicerclage suture. The osteotomy was slowly spread (TTA) at a rate 1.5 mm every 15 seconds to a maximum distance of 24 mm or until a fracture was detected as an audible crack, visible propagation of the distal osteotomy or transverse fracture of the cortical bridge. The occurrence of fractures was compared between limbs with hemicerclage and without hemicerclage (control) suture using a chi-square analysis. The advancement distance at the time of fracture was compared using a paired t test. A P value <.05 was considered significant. RESULTS: The cumulative occurrence of intraoperative fracture was significantly greater without hemicerclage than with hemicerclage at advancements of 12, 15, 18, and 24 mm. The mean (SD) spreading distance at the time of fracture was significantly less without hemicerclage at 16.85 (4.10) mm with a range of 12-24 mm, than with hemicerclage at 20.62 (2.39) mm with a range of 18-24 mm (P = .029). CONCLUSION: The occurrence of immediate intraoperative fracture during advancement of an EBHO of the tibial tuberosity is less when a hemicerclage suture is placed.

An in vivo ovine model of bone tissue alterations in simulated microgravity conditions.

Microgravity and its inherent reduction in body-weight associated mechanical loading encountered during spaceflight have been shown to produce deleterious effects on important human physiological processes. Rodent hindlimb unloading is the most widely-used ground-based microgravity model. Unfortunately, results from these studies are difficult to translate to the human condition due to major anatomic and physiologic differences between the two species such as bone microarchitecture and healing rates. The use of translatable ovine models to investigate orthopedic-related conditions has become increasingly popular due to similarities in size and skeletal architecture of the two species. Thus, a new translational model of simulated microgravity was developed using common external fixation techniques to shield the metatarsal bone of the ovine hindlimb during normal daily activity over an 8 week period. Bone mineral density, quantified via dual-energy X-ray absorptiometry, decreased 29.0% (p < 0.001) in the treated metatarsi. Post-sacrifice biomechanical evaluation revealed reduced bending modulus (-25.8%, p < 0.05) and failure load (-27.8%, p < 0.001) following the microgravity treatment. Microcomputed tomography and histology revealed reduced bone volume (-35.9%, p < 0.01), trabecular thickness (-30.9%, p < 0.01), trabecular number (-22.5%, p < 0.05), bone formation rate (-57.7%, p < 0.01), and osteoblast number (-52.5%, p < 0.001), as well as increased osteoclast number (269.1%, p < 0.001) in the treated metatarsi of the microgravity group. No significant alterations occurred for any outcome parameter in the Sham Surgery Group. These data indicate that the external fixation technique utilized in this model was able to effectively unload the metatarsus and induce significant radiographic, biomechanical, and histomorphometric alterations that are known to be induced by spaceflight. Further, these findings demonstrate that the physiologic mechanisms driving bone remodeling in sheep and humans during prolonged periods of unloading (specifically increased osteoclast activity) are more similar than previously utilized models, allowing more comprehensive investigations of microgravity-related bone remodeling as it relates to human spaceflight.

The effect of preoperative planning method on recommended tibial tuberosity advancement cage size.

OBJECTIVE: To determine if use of various commonly practiced tibial tuberosity advancement (TTA) preoperative planning methods leads to variable TTA cage size recommendations. STUDY DESIGN: Radiographic study. ANIMALS: Dogs (n = 14) with naturally occurring cranial cruciate ligament disease. METHODS: TTA was planned by a single observer on mediolateral stifle radiographs of each dog using 2 sets of tibial plateau landmarks (anatomic [A] vs. femorotibial common tangent [T]) and 2 advancement measurement techniques (transparent overlay [O] vs. simulated TTA using imaging software [S]) for 4 different planning methods (AO, AS, TO, TS). Cage size recommendations for each stifle were tabulated for each of the 4 planning methods. Mean advancement (mm) required to obtain patellar tendon angle (PTA) = 90° for each of the 4 planning methods were statistically compared. RESULTS: In the 14 stifles studied, the 4 planning methods evaluated led to 4 different cage size recommendations in 1 stifle, 3 different recommendations in 8 stifles, 2 different recommendations in 3 stifles, and 1 recommendation in only 2 stifles. There was a significant difference in the mean advancement measurement between the 4 planning methods (P < .0001); the AS technique was the largest whereas TO resulted in the smallest measurement. Overall, larger advancement was associated with use of anatomic landmarks (vs. common tangent) and imaging software to simulate TTA (vs. overlays). CONCLUSION: Currently practiced methods for TTA pre-planning led to variable cage size recommendations in 86% of the stifles evaluated and may be a source of inconsistent functional outcomes.

Arthroscopic biceps ulnar release procedure (BURP): technique description and in vitro assessment of the association of visual control and surgeon experience to regional damage and tenotomy completeness.

OBJECTIVES: (1) Describe arthroscopic BURP surgical technique, (2) assess association of visual control and surgeon experience to tenotomy completeness and regional iatrogenic tissue damage. STUDY DESIGN: Cadaveric study. SAMPLE POPULATION: Canine cadavers weighing >20 kg (n = 16; 32 elbows). METHODS: Phase 1 = dissection/anatomic description/procedural refinement (n = 6). Phase 2 = technique description (n = 6). Phase 3 = association of surgeon experience and procedural visual control to tenotomy completion and regional iatrogenic damage (n = 20). Elbows were randomly assigned via coin toss to an experienced- or inexperienced-arthroscopist. Using conventional medial portals, surgeons sought to identify the medial collateral ligament (MCL) and ulnar insertion of the biceps tendon (uBT) before attempting complete tenotomy. Upon procedural completion, surgeons assigned a standardized "visual control score" (VCS) describing viewing that governed procedure and predicted % uBT release, MCL, and median nerve damage. Post-procedural dissection determined actual tenotomy completion and iatrogenic tissue damage. RESULTS: Complete BURP was achieved in 16 of 19 elbows. VCS was associated with tenotomy completeness (P < .01). "Blind" BURP was incomplete in both elbows in which it was attempted. Perception of complete BURP was associated with complete release (P < .01). MCL damage occurred in 10% of elbows. Surgeon experience did not influence VCS, regional damage, or BURP completeness. CONCLUSION: In canine cadavers, arthroscopic BURP can be consistently performed using conventional arthroscopic instruments and portals by both experienced and inexperienced arthroscopists when visual control guides the tenotomy into the distal aspect of the tendon.

In vitro incidence of fibular penetration with and without the use of a jig during tibial plateau leveling osteotomy.

OBJECTIVE: To determine the incidence of fibular penetration during placement of the Synthes® locking TPLO plate with and without the use of a jig. STUDY DESIGN: Cadaveric, experimental study. SAMPLE POPULATION: Cadaveric paired pelvic limbs (n = 8) from skeletally mature dogs. METHODS: Limbs were assigned to 1 of 2 groups (jig-less-TPLO = no jig used; jig-TPLO = jig used). Synthes® locking TPLO plates were applied using proximal screws of excessive length to facilitate identification of fibular penetration. Screw tip locations were identified by dissection and frequency of fibular penetration was compared between groups. RESULTS: None of the jig-TPLO limbs and 6 (75%) of jig-less-TPLO limbs had fibular penetration, a difference that was statistically significant. Fibular penetration was most frequently associated with the most proximal screw. CONCLUSIONS: A significantly higher incidence of fibular penetration occurs when Synthes® locking TPLO is performed without use of a jig.

Prevalence of dysphoria after fentanyl in dogs undergoing stifle surgery.

OBJECTIVE: To describe the prevalence of dysphoria after intraoperative administration of fentanyl by infusion and identify other risk factors influencing this in dogs undergoing stifle surgery. STUDY DESIGN: Prospective, randomized clinical study. ANIMALS: Dogs (n = 92) that had tibial plateau leveling osteotomy (TPLO) or tibial tuberosity advancement (TTA). METHODS: Dogs were anesthetized using a standardized anesthetic protocol, and randomly assigned to receive a loading dose followed by 1 of 3 infusions of fentanyl perioperatively: 2 µg/kg/h, 10 µg/kg/h, or 20 µg/kg/h. Dog characteristics and all additional medications were recorded and included as part of the statistical analysis. Dog behavior was scored before anesthesia and during recovery using a scale of 1-4 (Appendices A and B). If no improvement in behavior was seen in 3-5 minutes postextubation, dogs with a score of 3 or 4 during recovery were administered fentanyl (2 µg/kg intravenously [IV]) in the event that the behaviors associated with the higher scores were related to pain. If they did not respond favorably to the administration of additional fentanyl and wound palpation did not elicit a response, but the untoward behaviors continued, dogs were administered either a tranquilizer, sedative, or opioid antagonist, and were considered dysphoric. RESULTS: Of 92 dogs, 22 (23.9%) were considered dysphoric using aforementioned criteria. CONCLUSIONS: About one-fourth of dogs enrolled in this study were dysphoric based on study criteria.

The role of muscle activation in cruciate disease.

Traditional investigations into the etiopathogenesis of canine cranial cruciate ligament (CCL) disease have focused primarily on the biological and mechanical insults to the CCL as a passive stabilizing structure of the stifle. However, with recent collaboration between veterinarians and physical therapists, an increased focus on the role of muscle activity and aberrant motor control mechanisms associated with anterior cruciate ligament (ACL) injuries and rehabilitation in people has been transferred and applied to dogs with CCL disease. Motor control mechanisms in both intact and cruciate-deficient human knees may have direct translation to canine patients, because the sensory and motor components are similar, despite moderate anatomic and biomechanical differences. Components of motor control, such as muscle recruitment and the coordination and amplitudes of activation are strongly influenced by afferent proprioceptive signaling from peri- and intra-articular structures, including the cruciate ligaments. In people, alterations in the timing or amplitude of muscle contractions contribute to uncoordinated movement, which can play a critical role in ACL injury, joint instability and the progression of osteoarthritis (OA). A better understanding of motor control mechanisms as they relate to canine CCL disease is vitally important in identifying modifiable risk factors and applying preventative measures, for development of improved surgical and rehabilitative treatment strategies. The purpose of this review article is to analyze the influence of altered motor control, specifically pelvic limb muscle activation, in dogs with CCL disease as evidenced by mechanisms of ACL injury and rehabilitation in people.

Biomechanical evaluation of interlocking nail and locking compression plating for stabilization of ovine critical-sized segmental tibia defects.

Background: Segmental large volume bone loss resulting from fracture or osseous neoplasia is a major challenge to orthopedic surgeons and there is an ongoing quest to identify treatments that optimize healing. To advance treatment, large animal translational models-such as the ovine critical-sized tibia defect model-are instrumental for testing of novel scaffolds for bone regeneration. However, little standardization in the implants utilized for defect stabilization has been determined and current commercially available implants may be inadequate to replicate the strength of the native tibia. We hypothesize that a 10-mm interlocking nail (ILN) would be stiffer in axial, bending, and torsional loading than its 8-mm counterpart and would be stiffer in axial and torsional loading compared to a 4.5-mm broad locking compression plate (LCP). Methods: Tibias were harvested from 24 ovine hind limbs from skeletally mature ewes euthanized for reasons unrelated to this study and were randomized to treatment group. An ex vivo comparison of a novel 10-mm angle-stable non-tapered ILN was compared to a commercially available 8-mm angle-stable tapered ILN and a broad LCP in an ovine critical-sized (5-cm) tibia defect model. Axial stiffness, torsional stiffness, and bending stiffness were determined in control intact tibia and tibial constructs in the three treatment groups. Following implantation, radiography was performed in all limbs and tibia length and cortical and medullary cavity diameter were measured. Comparisons between groups were assessed with a one-way analysis of variance. Significance was set at P<0.05. Results: The 10-mm ILN in tibia containing a 5-cm ostectomy gap most closely replicated the structural properties of intact tibia compared with other constructs. The 10-mm ILN had significantly stronger torsional (P<0.001) and bending (P=0.002) stiffness than the 8-mm ILN, and was significantly stronger than the LCP in axial (P=0.04) and torsional (P=0.01) stiffness. Conclusions: A 10-mm ILN used to stabilize an ovine critically-sized tibia defect most closely mimicked the structural properties of the intact tibia when compared to a 8-mm ILN or broad LCP. Further in vivo testing will aid in determining which stabilization method is best suited for testing of novel tissue engineering and bone healing studies.

Enhanced bone formation in locally-optimised, low-stiffness additive manufactured titanium implants: An in silico and in vivo tibial advancement study.

A tibial tuberosity advancement (TTA), used to treat lameness in the canine stifle, provides a framework to investigate implant performance within an uneven loading environment due to the dominating patellar tendon. The purpose of this study was to reassess how we design orthopaedic implants in a load-bearing model to investigate potential for improved osseointegration capacity of fully-scaffolded mechanically-matched additive manufactured (AM) implants. While the mechanobiological nature of bone is well known, we have identified a lower limit in the literature where investigation into exceedingly soft scaffolds relative to trabecular bone ceases due to the trade-off in mechanical strength. We developed a finite element model of the sheep stifle to assess the stresses and strains of homogeneous and locally-optimised TTA implant designs. Using additive manufacturing, we printed three different low-stiffness Ti-6Al-4 V TTA implants: 0.8 GPa (Ti1), 0.6 GPa (Ti2) and an optimised design with a 0.3 GPa cortex and 0.1 GPa centre (Ti3), for implantation in a 12-week in vivo ovine pilot study. Static histomorphometry demonstrated uniform bone ingrowth in optimised low-modulus Ti3 samples compared to homogeneous designs (Ti1 and Ti2), and greater bone-implant contact. Mineralising surfaces were apparent in all implants, though mineral apposition rate was only consistent throughout Ti3. The greatest bone formation scores were seen in Ti3, followed by Ti2 and Ti1. Results from our study suggest lower stiffnesses and higher strain ranges improve early bone formation, and that by accounting for loading environments through rational design, implants can be optimised to improve uniform osseointegration. STATEMENT OF SIGNIFICANCE: The effect of different strain ranges on bone healing has been traditionally investigated and characterised through computational models, with much of the literature suggesting higher strain ranges being favourable. However, little has been done to incorporate strain-optimisation into porous orthopaedic implants due to the trade-off in mechanical strength required to induce these microenvironments. In this study, we used finite element analysis to optimise the design of additive manufactured (AM) titanium orthopaedic implants for different strain ranges, using a clinically-relevant surgical model. Our research suggests that there is potential for locally-optimised AM scaffolds in the use of orthopaedic devices to induce higher strains, which in turn encourages de novo bone formation and uniform osseointegration.

Femoral angular correction and lengthening in a large-breed puppy using a dynamic unilateral external fixator.

OBJECTIVE: To report treatment of a large-breed puppy with combined distal femoral valgus and length deficit caused by partial distal physeal closure. STUDY DESIGN: Clinical report. ANIMALS: Bernese Mountain Dog (4.5-month-old male). METHODS: The puppy was admitted for evaluation of a progressive severe left pelvic limb lameness (grade 3/4) of 6-week duration. Distal femoral valgus and severe length deficit deformity were treated by acute angular correction using a closing wedge ostectomy and progressive rapid-rate callus distraction using a dynamic, telescoping unilateral External Skeletal Fixator (ESF) designed for people. After acute angular correction and a 3-day latency period, a mean linear distraction rate of 3 mm/day was maintained for 3 weeks. The dynamic ESF (dESF) was removed at 4 weeks, after a 1-week consolidation phase. RESULTS: The dESF was stable and functional during distraction and bone healing. Distal femoral valgus conformation improved 50° (from 41° to 91°) and femoral length increased 42 mm at dESF removal (from 158 mm to 200 mm; 27%). After cessation of bone growth, no valgus and minimal (6%) length deficit were detected. At 4, 5, 6, 12, and 24 months after surgery, the dog was walking, trotting, and galloping normally. CONCLUSION: Acute angular correction and progressive rapid-rate callus distraction using a unilateral dESF allowed satisfactory treatment of combined distal femoral valgus and length deficit in a large-breed puppy.

Comparison of the mechanical behaviors of locked and nonlocked plate/screw fixation applied to experimentally induced rotational osteotomies in canine ilia.

OBJECTIVE: To compare the mechanical behaviors of 2 locked (parallel and diverging screws) and 1 nonlocked (NL) version of triple pelvic osteotomy (TPO) plate/screw fixation. STUDY DESIGN: In vitro biomechanical evaluation. ANIMALS: Cadaveric canine hemipelves. METHODS: Comparison 1-NL screws 20° TPO (NL-20) construct versus locked parallel (LP) screws 20° TPO (LP-20) construct (n = 7). Comparison 2-LP-20 construct versus locked diverging (LD) screws 20° TPO (LD-20) construct (n = 6). Condition 1-Nondestructive loading to determine stiffness. Condition 2-Cyclic loading to determine stiffness, screw loosening, and osteotomy gap displacement. Condition 3-Load to failure (yield load, yield displacement, maximum load, load to failure, failure mode). RESULTS: Stiffness was not significantly different for NL-20 versus LP-20 constructs (P = .48) or for LP-20 versus LD-20 constructs (P = .83). Screw loosening was significantly more frequent for NL-20 versus LP-20 (P = .01) and for LD-20 versus LP-20 constructs (P = .02). The relative risk for screw loosening with NL-20 constructs versus LP-20 constructs was 1.4 (95% CI: 1.1-1.8). The relative risk for screw loosening with LD-20 versus LP-20 was 1.6 (95% CI: 1.1-2.2). Yield load was significantly greater for LP-20 versus NL-20 and LD-20 constructs (P = .04, P = .03), respectively. CONCLUSIONS: No TPO constructs tested maintained complete integrity after cyclic loading; however, screw loosening was significantly reduced and yield loads were significantly larger for LP-20 plate/screw constructs.

Comparison of femoral angulation measurement between radiographs and anatomic specimens across a broad range of varus conformations.

OBJECTIVE: To determine if measurement of anatomic lateral distal femoral angle (aLDFA) from radiographs is valid across a broad range of femoral varus conformations. STUDY DESIGN: Radiographic and anatomic study. SAMPLE POPULATION: Large breed canine cadavers (n = 5) and femora (n = 10). METHODS: Cadavers were held in dorsal recumbency and 8 craniocaudal radiographic projections made of each femur: 1 image pre- and postosteotomy and at each of 6 progressive levels of induced distal varus deformity. Femurs were collected. Three blinded examiners independently measured varus on each radiograph (R-aLDFA) and femoral specimen (S-aLDFA) on 3 separate occasions. Intra- and interobserver variance in R-aLDFA and S-aLDFA measurements were determined. The strength of relationship between R-aLDFA and S-aLDFA and positive and negative predictive values for R-aLDFA were calculated. CONCLUSION: Intra- and interobserver variance in R-aLDFA (mean, 0.54% and 0.40%, respectively) and S-aLDFA (mean, 0.43% and 0.41%, respectively) were acceptable. The strength of relationship between R-aLDFA and S-aLDFA (adjusted R2 = 78.2%) was marginally below the acceptance criterion of 80%. Using aLDFA ≥ 102° as an indication for corrective femoral osteotomy, radiography was successful in correctly identifying corrective femoral osteotomy candidates (positive predictive value) and noncandidates (negative predictive value) 72% and 96% of the time, respectively.

Mechanical comparison of two suture constructs for extra-capsular stifle stabilization.

OBJECTIVE: Mechanical evaluation of 2 suture constructs for extracapsular stifle stabilization. STUDY DESIGN: In vitro study. SAMPLE POPULATION: Crimped interlocking loop constructs (ILC) of 45 kg nylon leader line (NLL) and Orthofiber® (OF). METHODS: ILC were tightened to 100 N, then crimp secured. Ramp to failure (n=10/group)-Data were derived from force/displacement plots. Stress-relaxation testing (n=10/group)-ILC's were nondestructively loaded and held at resultant displacement as force data were recorded. Incremental, cyclic loading (n=10/group)-ILC's were loaded (5 cycles/set) starting at 100 N and incrementally increased by 50 N (1 and 3 Hz protocols). Loop tension and elongation were recorded after each set. RESULTS: Ramp to failure-initial loop tension was similar (NLL 75.5 ± 9.5 N; OF 68.7 ± 10.4 N, P=.140). Tested OF constructs were stiffer (NLL 125.7 ± 4.0; OF 234.6 ± 25.0 N/mm, P≤.001), had lower yield load (NLL 193.6 ± 13.8; OF 137.3 ± 94.3 N, P≤.001), lower peak load (NLL 873.7 ± 68.6; OF 653.6 ± 80.2 N, P≤.001), and lower elongation at failure (NLL 19.1 ± 1.4; OF 5.2 ± 1.0 mm, P≤.001) and at yield (NLL 1.52 ± 0.2; OF 0.3 ± 0.6 mm, P=.003) than NLL constructs. Yield in NLL ILC's was variable knot tightening/crimp slippage, but only crimp-suture slippage in OF. Stress-relaxation testing-OF demonstrated greater relaxation. Incremental, cyclic loading-induced ILC elongation and tension loss in both groups, independent of loading frequency. NLL lost tension at lower rate, but elongated more than OF. CONCLUSIONS: NLL construct is mechanically superior to OF construct.

The Effect of Anterior Cruciate Ligament Reconstruction with an Electropsun Scaffold on Tibiofemoral Contact Mechanics.

Surgical reconstruction of the torn ACL is performed to restore native contact mechanics. Drawbacks to traditional ACL repair techniques motivate the development of a tissue engineered ACL scaffold. Our group has developed a hierarchical electrospun polycaprolactone (PCL) scaffold that consists of rolled nanofiber bundles attached at each end with solvent-case blocks of PCL. The goal of this study was to compare ovine cadaver tibiofemoral contact mechanics after ACL reconstruction with the electrospun scaffold to a clinically applicable ACL reconstruction with a soft tissue graft and the ACL transected condition (ACLX). In the ACLX group and after ACL reconstruction with either the electrospun scaffold or soft tissue graft, pressure sensors were inserted under the menisci. Loads up to 890 N were applied at various flexion angles. The scaffold performed the best at restoring contact mechanics in the medial hemijoint to that of the native ACL. The scaffold was good at maintaining a medial-lateral balance of pressures as in the native joint whereas the ACLX shifted pressure off the lateral and on to the medial hemijoint. While the ACL scaffold didn't restore mechanics to that of the native condition, it improved contact mechanics compared to the standard graft replacement and ACLX condition.

Investigation of a Prevascularized Bone Graft for Large Defects in the Ovine Tibia.

In vivo bioreactors are a promising approach for engineering vascularized autologous bone grafts to repair large bone defects. In this pilot parametric study, we first developed a three-dimensional (3D) printed scaffold uniquely designed to accommodate inclusion of a vascular bundle and facilitate growth factor delivery for accelerated vascular invasion and ectopic bone formation. Second, we established a new sheep deep circumflex iliac artery (DCIA) model as an in vivo bioreactor for engineering a vascularized bone graft and evaluated the effect of implantation duration on ectopic bone formation. Third, after 8 weeks of implantation around the DCIA, we transplanted the prevascularized bone graft to a 5 cm segmental bone defect in the sheep tibia, using the custom 3D printed bone morphogenic protein 2 (BMP-2) loaded scaffold without prior in vivo bioreactor maturation as a control. Analysis by micro-computed tomography and histomorphometry found ectopic bone formation in BMP-2 loaded scaffolds implanted for 8 and 12 weeks in the iliac pouch, with greater bone formation occurring after 12 weeks. Grafts transplanted to the tibial defect supported bone growth, mainly on the periphery of the graft, but greater bone growth and less soft tissue invasion was observed in the avascular BMP-2 loaded scaffold implanted directly into the tibia without prior in vivo maturation. Histopathological evaluation noted considerably greater vascularity in the bone grafts that underwent in vivo maturation with an inserted vascular bundle compared with the avascular BMP-2 loaded graft. Our findings indicate that the use of an initial DCIA in vivo bioreactor maturation step is a promising approach to developing vascularized autologous bone grafts, although scaffolds with greater osteoinductivity should be further studied. Impact statement This translational pilot study aims at combining a tissue engineering scaffold strategy, in vivo prevascularization, and a modified transplantation technique to accelerate large segmental bone defect repair. First, we three-dimensional (3D) printed a 5 cm scaffold with a unique design to facilitate vascular bundle inclusion and osteoinductive growth factor delivery. Second, we established a new sheep deep circumflex iliac artery model as an in vivo bioreactor for prevascularizing the novel 3D printed osteoinductive scaffold. Subsequently, we transplanted the prevascularized bone graft to a clinically relevant 5 cm segmental bone defect in the sheep tibia for bone regeneration.

Osteoinductive 3D printed scaffold healed 5 cm segmental bone defects in the ovine metatarsus.

Autologous bone grafts are considered the gold standard grafting material for the treatment of nonunion, but in very large bone defects, traditional autograft alone is insufficient to induce repair. Recombinant human bone morphogenetic protein 2 (rhBMP-2) can stimulate bone regeneration and enhance the healing efficacy of bone grafts. The delivery of rhBMP-2 may even enable engineered synthetic scaffolds to be used in place of autologous bone grafts for the treatment of critical size defects, eliminating risks associated with autologous tissue harvest. We here demonstrate that an osteoinductive scaffold, fabricated by combining a 3D printed rigid polymer/ceramic composite scaffold with an rhBMP-2-eluting collagen sponge can treat extremely large-scale segmental defects in a pilot feasibility study using a new sheep metatarsus fracture model stabilized with an intramedullary nail. Bone regeneration after 24 weeks was evaluated by micro-computed tomography, mechanical testing, and histological characterization. Load-bearing cortical bridging was achieved in all animals, with increased bone volume observed in sheep that received osteoinductive scaffolds compared to sheep that received an rhBMP-2-eluting collagen sponge alone.

Comparison of the mechanical behaviors of semicontoured, locking plate-rod fixation and anatomically contoured, conventional plate-rod fixation applied to experimentally induced gap fractures in canine femora.

OBJECTIVE: To compare the mechanical behaviors of a semicontoured, locking compression plate-rod (LCP-rod) construct and an anatomically contoured, limited-contact dynamic compression plate-rod (LC-DCP-rod) construct applied to experimentally induced gap fractures in canine femora. SAMPLE POPULATION: 16 femora from 8 cadaveric dogs. PROCEDURES: 8 limbs from 8 dogs were assigned to the LCP-rod construct group or the LC-DCP-rod construct group. In each femur, a 39-mm mid-diaphyseal ostectomy was performed at the same plate location and the assigned construct was applied. Construct stiffness and ostectomy gap subsidence were determined before and after cyclic axial loading (6,000 cycles at 20%, 40%, and 60% of live body weight [total, 18,000 cycles]). Three constructs from each group further underwent 45,000 cycles at 60% of body weight (total, 63,000 cycles). Following cyclic loading, mode of failure during loading to failure at 5 mm/min was recorded for all constructs. RESULTS: After 18,000 or 63,000 cycles, construct stiffness did not differ significantly between construct groups. No implant failure occurred in any construct that underwent 63,000 cycles. In both construct groups, ostectomy gap subsidence similarly increased as axial load increased but did not change after 18,000 cycles. Mean +/- SEM loads at failure in the LCP-rod (1,493.83 +/- 200.12 N) and LC-DCP-rod (1,276.05 +/- 156.11 N) construct groups were not significantly different. The primary failure event in all constructs occurred at the screw hole immediately distal to the ostectomy. CONCLUSIONS AND CLINICAL RELEVANCE: Biomechanically, the semicontoured LCP-rod construct is similar to the anatomically contoured LC-DCP-rod system.

An assessment of mechanical properties and screw push-out for two 3.5-mm pearl-type locking plate systems.

OBJECTIVE: To compare mechanical properties (stiffness, yield load, failure load, and deformation at failure) of 2 pearl-type locking plate system (PLS) constructs (PLS 1 and PLS 2) in a simulated fracture gap model and to compare screw push-out forces of the 2 PLSs with and without plate contouring. SAMPLE: 40 PLS constructs. PROCEDURES: Mechanical properties of uncontoured PLS 1 (n = 8) and PLS 2 (8) constructs were evaluated in synthetic bone-plate models under axial compression. Screw push-out forces were evaluated in 6 uncontoured and 6 contoured PLSs of each type. Variables of interest were compared between PLS groups and between contoured and uncontoured plates by statistical methods. RESULTS: Yield and failure loads were higher in the PLS 1 group than in the PLS 2 group, but stiffness did not differ significantly between groups. All constructs failed by plate bending, with greater deformation in the PLS 2 group. Push-out force to screw-plate uncoupling was higher in the PLS 2 group than in the PLS 1 group for uncontoured and contoured plates. Locking mechanism failure of PLS 1 specimens was through screw-thread stripping. The PLS 2 specimens failed by node deformation followed by screwhead stripping. CONCLUSIONS AND CLINICAL RELEVANCE: Distinct mechanical differences were identified between the 2 PLSs. The clinical relevance of these differences is unknown. Further research including cyclic fatigue testing is needed to reveal more clinically pertinent information.