In vitro biomechanical comparison of a plate-rod combination-construct and an interlocking nail-construct for experimentally induced gap fractures in canine tibiae

Ex vivo biomechanical evaluation of 2.4 mm LCP plate rod constructs versus 2.7 mm LCP applied to the feline tibia

OBJECTIVE

To compare the stiffness and strength of three plate and rod fixation constructs applied to a feline tibial gap model.

STUDY DESIGN

Ex vivo study.

SAMPLE POPULATION

Thirty-three unpaired tibiae obtained from skeletally mature cats.

METHODS

The tibiae were randomly divided into three groups. The following implants were then applied to the feline tibiae prior to the creation of a 10 mm diaphyseal gap. Group 1: 2.4 mm locking compression plate (LCP) and 1.0 mm intramedullary pin (IMP). Group 2: 2.4 mm LCP and 1.6 mm IMP. Group 3: 2.7 mm LCP. Subsequently, each specimen was tested for torsion, axial compression, and axial load until construct failure. Student's t-tests were used to compare the torsional and axial stiffness, yield load, and maximum axial force.

RESULTS

Group 2 had higher axial stiffness than group 3 (p = .013). Group 1 showed a lower maximum axial force and yield point than groups 2 and 3 (p < .01; p < .05, respectively). There were no among-group differences in torsional stiffness.

CONCLUSION

Constructs with a 2.4 mm LCP and 1.6 mm IMP provided the strongest and most rigid constructs in a feline tibia gap model.

CLINICAL SIGNIFICANCE

A plate-rod construct combining a 2.4 mm LCP and a 1.6 mm IMP is appropriate for achieving high implant stiffness and resisting maximum axial force in treatment of tibial fractures in cats.

Lateral Approach and Plate Rod Sliding Humeral Osteotomy in Dogs-A Short Case Series

Five dogs of different breeds and ages were diagnosed with medial compartment disease of the elbow (MCDE). To resolve the condition, a modified technique using a lateral approach and plate/rod sliding humeral osteotomy (SHO) was considered. All dogs recovered uneventfully after surgery. There were no major complications, and all dogs were significantly improved compared to pre-operative condition. This novel technique of adding a pin, based on the alteration of the original technique, optimized resistance to fixation failure. An additional benefit was that the lateral approach was surgically familiar and easily allowed bone grafting. All five dogs treated with the novel approach had improved scores for pain and lameness. This study showed that SHO was more stable and less technically demanding with the addition of an intramedullary pin. This is the first report of a lateral approach and plate rod sliding humeral osteotomy to treat MCDE in dogs.

Management of Feline Femoral, Tibial and Humeral Fractures Using a 3.5 mm Titanium Interlocking Nail

OBJECTIVE

 Our objectives were to report complications associated with stabilization of long-bone fractures in cats using a 3.5-mm titanium interlocking nail and to examine the influences of signalment, fracture type and fixation evaluations on the occurrence of complications.

STUDY DESIGN

 Retrospective clinical study.

MATERIAL AND METHODS

 Medical and radiographic records of cats with long-bone fractures treated with an interlocking nail were reviewed. Data included age, sex, weight, cause of the fracture, fractured bone(s) and fracture type. Complications were classified as minor and major complications. Fisher's exact tests and logistic regression analysis were used to test whether certain variables of signalment and interlocking nail configuration had an effect on the occurrence of complications.

RESULTS

 Sixty-seven fractures of 67 cats were examined in this study. Forty-eight femora, sixteen tibiae and three humeri were included. Complications occurred in 11/67 fractures. Major complications occurred in 8/67 fractures and included screw breakage (n = 3), nail breakage (n = 2), nail bending (n = 1), screw loosening (n = 1), non-union (n = 1). Statistical analysis showed a significant difference between fracture types and the occurrence of major complications (p = 0.02).

CONCLUSION

 In conclusion, use of this commercially available standard 3.5-mm titanium interlocking nail for stabilization of comminuted and oblique humeral, femoral and tibial fractures in cats is feasible.

Angle-stable interlocking nailing in a canine critical-sized femoral defect model for bone regeneration studies: In pursuit of the principle of the 3R’s

Introduction: Critical-sized long bone defects represent a major therapeutic challenge and current treatment strategies are not without complication. Tissue engineering holds much promise for these debilitating injuries; however, these strategies often fail to successfully translate from rodent studies to the clinical setting. The dog represents a strong model for translational orthopedic studies, however such studies should be optimized in pursuit of the Principle of the 3R’s of animal research (replace, reduce, refine). The objective of this study was to refine a canine critical-sized femoral defect model using an angle-stable interlocking nail (AS-ILN) and reduce total animal numbers by performing imaging, biomechanics, and histology on the same cohort of dogs.

Methods: Six skeletally mature hounds underwent a 4 cm mid-diaphyseal femoral ostectomy followed by stabilization with an AS-ILN. Dogs were assigned to autograft (n = 3) or negative control (n = 3) treatment groups. At 6, 12, and 18 weeks, healing was quantified by ordinal radiographic scoring and quantified CT. After euthanasia, femurs from the autograft group were mechanically evaluated using an established torsional loading protocol. Femurs were subsequently assessed histologically.

Results: Surgery was performed without complication and the AS-ILN provided appropriate fixation for the duration of the study. Dogs assigned to the autograft group achieved radiographic union by 12 weeks, whereas the negative control group experienced non-union. At 18 weeks, median bone and soft tissue callus volume were 9,001 mm³ (range: 4,939–10,061) for the autograft group and 3,469 mm³ (range: 3,085–3,854) for the negative control group. Median torsional stiffness for the operated, autograft treatment group was 0.19 Nm/° (range: 0.19–1.67) and torque at failure was 12.0 Nm (range: 1.7–14.0). Histologically, callus formation and associated endochondral ossification were identified in the autograft treatment group, whereas fibrovascular tissue occupied the critical-sized defect in negative controls.

Conclusion: In a canine critical-sized defect model, the AS-ILN and described outcome measures allowed refinement and reduction consistent with the Principle of the 3R’s of ethical animal research. This model is well-suited for future canine translational bone tissue engineering studies.

Mechanical evaluation of a novel angle-stable interlocking nail in a gap fracture model

OBJECTIVE

To describe the mechanical characteristics of a novel angle-stable interlocking nail (NAS-ILN) and compare them to those of a locking compression plate (LCP) by using a gap-fracture model.

STUDY DESIGN

Experimental study.

SAMPLE POPULATION

Synthetic bone models.

METHODS

Synthetic bone models simulating a 50 mm diaphyseal comminuted canine tibial fracture were treated with either a novel angle-stable interlocking nail (NAS-ILN) or a locking compression plate (LCP). Maximal axial deformation and load to failure in compression and 4-point bending, as well as maximal angular deformation, slack, and torque to failure in torsion, were statistically compared (P < .05).

RESULTS

In compression, the maximal axial deformation was lower for NAS-ILN (0.11 mm ± 0.03) than for LCP (1.10 mm ± 0.22) (P < .0001). The ultimate load to failure was higher for NAS-ILN (803.58 N ± 29.52) than for LCP (328.40 N ± 11.01) (P < .0001). In torsion, the maximal angular deformation did not differ between NAS-ILN (22.79° ± 1.48) and LCP (24.36° ± 1.45) (P = .09). The ultimate torque to failure was higher for NAS-ILN (22.45 Nm ± 0.24) than for LCP (19.10 Nm ± 1.36) (P = .001). No slack was observed with NAS-ILN. In 4-point bending, the maximal axial deformation was lower for NAS-ILN (3.19 mm ± 0.49) than for LCP (4.17 mm ± 0.34) (P = .003). The ultimate bending moment was higher for NAS-ILN (25.73 Nm, IQR [23.54-26.86] Nm) than for LCP (16.29 Nm, IQR [15.66-16.47] Nm) (P = .002).

CONCLUSION

The NAS-ILN showed greater stiffness in compression and 4-point bending, and a greater resistance to failure in compression, torsion, and 4-point bending, than LCP.

CLINICAL IMPACT

Based on these results, NAS-ILNs could be considered as alternative implants for the stabilization of comminuted fractures.

Feline Femoral Fracture Fixation: What are the options?

Practical relevance:

The femur is the most commonly fractured bone in cats. Femoral fractures usually result from high-velocity trauma such as a road traffic accident or fall from a height and, as such, are associated with a wide variety of concurrent injuries. The initial focus of treatment should always be on assessment and stabilisation of the major body systems. Once any concurrent injuries have been addressed, all femoral fractures need surgical stabilisation, with the notable exception of greenstick fractures in very young cats, which can heal with cage rest alone. A number of different surgical options are available depending on the fracture type, location, equipment, surgeon experience and owner finances.

Clinical challenges:

Femoral fractures can vary hugely in complexity and the small size of feline bones can limit the choice of implants. Furthermore, cats can present unique challenges in the postoperative period due to their active nature and the limited means to control their exercise level.

Audience:

This review is aimed at general and feline-specific practitioners who have some experience of feline orthopaedics, as well as those simply wishing to expand their knowledge.

Aims:

The aim of this review is to help clinicians assess, plan and manage feline femoral fractures. It provides an overview of diagnostic imaging and a discussion of a range of suitable surgical options, including the principles of different types of fixation. It also highlights cat-specific issues, approaches and implants pertinent to the management of these cases.

Evidence base:

A number of original articles and textbook chapters covering many aspects of femoral fractures in cats and dogs have been published. Where possible, this review draws on information from key feline research and, where necessary, extrapolates from relevant canine literature. The authors also offer practical guidance based on their own clinical experience.

Clinical application of the small I-Loc interlocking nail in 30 feline fractures: A prospective study

OBJECTIVE

To describe medium-term functional outcome after nail osteosynthesis in feline traumatology and report clinically relevant recommendations for I-Loc angle-stable interlocking nail use in cats.

STUDY DESIGN

Prospective clinical study.

SAMPLE POPULATION

Client-owned cats (n = 29).

METHODS

Consecutive cases with femoral, tibial, or humeral fractures were included. Outcome measures included fracture and surgical procedure description, limb alignment, nail size vs body weight (BW), percentage of nail medullary canal (MC) fill, time to limb function at clinical union (CU), and complications. Descriptive statistics were reported and compared with historical data.

RESULTS

Bone distribution was 53.3% femora, 30% tibiae, and 16.7% humeri. There were six epimetaphyseal and 24 diaphyseal fractures. Overall, 67% of fractures were comminuted. Open reduction and minimally invasive techniques were used in 73% and 27% of cases, respectively. Seventeen I-Loc 3 (cat mean BW 4.4 ± 2.2 kg) and 13 I-Loc 4 (cat mean BW 5.2 ± 1.2 kg) nails were placed with mean MC fill of ≤50%. Average time to CU was 7.2 weeks. At CU, lameness had resolved or was mild in every cat, and all cats ultimately regained full limb function. No major complications were encountered.

CONCLUSION

Because of improved CU times, excellent functional outcomes, and low complication rate, our results provide evidence that I-Loc nails are safe and effective for feline traumatology.

CLINICAL SIGNIFICANCE

The I-Loc may be advantageous for fixation of epimetaphyseal fractures. Because of feline bone specific dimensional constraints, I-Loc 3 is likely appropriate for all feline humeri and most tibiae, while I-Loc 4 is well sized for feline femora.

Mechanical comparison of two small interlocking nails in torsion using a feline bone surrogate

OBJECTIVE

To compare the torsional behavior of two small angle-stable interlocking nails (I-Loc and Targon) with that of locking compression plates (LCP). To evaluate the effect of implant removal on the torsional strength of feline bone surrogates.

STUDY DESIGN

Experimental.

SAMPLE POPULATION

Fracture gap constructs and intact explanted bone surrogates.

METHODS

Fracture gap constructs were stabilized with one of six implants (I-Loc 3 and 4, Targon 2.5 and 3.0, LCP 2.0 and 2.4) and then cyclically tested in torsion (n = 4/group). To simulate implant removal, intact surrogates with implant-specific pilot holes were then twisted to failure (n = 4/group). Torsional compliance (TC; °/Nm), angular deformation (AD; °), and failure torque (F_T ; Nm) were statistically compared (P < .05).

RESULTS

The I-Loc 4 had the smallest TC and AD of all constructs (P < .05). The largest TC (P < .05) was seen with the LCP 2.0. The Targon 2.5 had the largest AD (P < .05) secondary to locking interface slippage. Targon surrogates F_T were the lowest of all groups (P < .05). Conversely, there was no difference between the F_T of the I-Loc, LCP, and intact surrogates (P > .05).

CONCLUSION

We showed that I-Loc nails provided greater torsional stability than size-matched Targon nails and LCPs. Conversely, Targon 2.5 locking interface slippage may jeopardize that construct's stability. Furthermore, the significantly reduced bone surrogate torsional strength provided evidence that the large Targon bolt holes increased the risk of postexplantation iatrogenic fracture.

CLINICAL SIGNIFICANCE

Our results provide evidence to conclude that the small I-Loc nails may be valid alternatives to other osteosynthesis options for feline fracture repair.

Interlocking Nails and Minimally Invasive Osteosynthesis

Reviews of clinical outcomes led to the foundation of a new approach in fracture management known as biological osteosynthesis. As intramedullary rods featuring cannulations and locking devices at both extremities, interlocking nails are well suited for bridging osteosynthesis. Unique biological and mechanical benefits make them ideal for minimally invasive nail osteosynthesis and an attractive, effective alternative to plating, particularly in revisions of failed plate osteosynthesis. Thanks to a new angle-stable locking design, interlocking nailing indications have been expanded to osteosynthesis of epi-metaphyseal fractures, including those with articular involvement and angular deformities such as distal femoral varus and associated patellar luxations.

Ex vivo torsional properties of a 2.5 mm veterinary interlocking nail system in canine femurs

Objective: To evaluate the torsional properties of the Targon® Vet Nail System (TVS) in small canine femurs and to compare these properties to those of the 2.4 mm LC-DCP® plates.

Methods: Thirty-six cadaveric femurs were allocated to three groups (n = 12). In all bones, points just distal to the lesser trochanter and just proximal to the fabellae were marked and a midshaft transverse osteotomy was performed. Group 1: bones were fixed with the 2.5 mm TVS with the bolts applied at the pre-identified marks. Group 2: A TVS system with 25% shorter inter-bolt distance was used. Group 3: A 7-hole 2.4 mm LCDCP® plates were applied. All constructs were tested non-destructively for 10 cycles, followed by an acute torsion to failure.

Results: Torque at yield was 0.806 ± 0.183 and 0.805 ± 0.093 Nm for groups 1 and 2 and 1.737 ± 0.461 Nm for group 3. Stiffness was 0.05 ± 0.01, 0.05 ± 0.007, and 0.14 ± 0.015 Nm/° for groups 1 to 3 respectively. Maximal angular displacement under cyclic loading was 16.6° ± 2.5°, 15.6° ± 2.1°, and 7.8° ± 1.06° respectively. There was no significant difference for any of the parameters between groups 1 and 2. Both torque at yield and stiffness were significantly greater between group 3 and groups 1 and 2.

Clinical significance: The TVS had approximately half the torsional strength and approximately 1/3 of the stiffness of the 2.4 mm bone plate. Slippage of the locking mechanism was probably the cause of the early failure. The system should be considered as a low-strength and low-stiffness system when compared to bone plates.

The effect of intramedullary pin size and monocortical screw configuration on locking compression plate-rod constructs in an in vitro fracture gap model

Objective: To investigate the effect of intramedullary pin size in combination with various monocortical screw configurations on locking compression plate-rod constructs.

Methods: A synthetic bone model with a 40 mm fracture gap was used. Locking compression plates with monocortical locking screws were tested with no pin (LCP-Mono) and intramedullary pins of 20% (LCPR-20), 30% (LCPR-30) and 40% (LCPR-40) of intramedullary diameter. Locking compression plates with bicortical screws (LCP-Bi) were also tested. Screw configurations with two or three screws per fragment modelled long (8-hole), intermediate (6-hole), and short (4-hole) plate working lengths. Responses to axial compression, biplanar four-point bending and axial load-to-failure were recorded.

Results: LCP-Bi were not significantly different from LCP-Mono control for any of the outcome variables. In bending, LCPR-20 were not significantly different from LCP-Bi and LCP-Mono. The LCPR-30 were stiffer than LCPR-20 and the controls. The LCPR-40 constructs were stiffer than all other constructs. The addition of an intramedullary pin of any size provided a significant increase in axial stiffness and load to failure. This effect was incremental with increasing intramedullary pin diameter. As plate working length decreased there was a significant increase in stiffness across all constructs.

Clinical significance: A pin of any size increases resistance to axial loads whereas a pin of at least 30% intramedullary diameter is required to increase bending stiffness. Short plate working lengths provide maximum stiffness. However, the overwhelming effect of intramedullary pin size obviates the effect of changing working length on construct stiffness.

The effect of intramedullary pin size and plate working length on plate strain in locking compression plate-rod constructs under axial load

Objective: To investigate the effect of intramedullary pin size and plate working length on plate strain in locking compression plate-rod constructs.

Methods: A synthetic bone model with a 40 mm fracture gap was used. Locking compression plates with monocortical locking screws were tested with no pin (LCP-Mono) and intramedullary pins of 20% (LCPR-20), 30% (LCPR-30) and 40% (LCPR-40) of intramedullary diameter. Two screws per fragment modelled a long (8-hole) and short (4-hole) plate working length. Strain responses to axial compression were recorded at six regions of the plate via three-dimensional digital image correlation.

Results: The addition of a pin of any size provided a significant decrease in plate strain. For the long working length, LCPR-30 and LCPR-40 had significantly lower strain than the LCPR-20, and plate strain was significantly higher adjacent to the screw closest to the fracture site. For the short working length, there was no significant difference in strain across any LCPR constructs or at any region of the plate. Plate strain was significantly lower for the short working length compared to the long working length for the LCP-Mono and LCPR-20 constructs, but not for the LCPR-30 and LCPR-40 constructs.

Clinical significance: The increase in plate strain encountered with a long working length can be overcome by the use of a pin of 30–40% intramedullary diameter. Where placement of a large diameter pin is not possible, screws should be placed as close to the fracture gap as possible to minimize plate strain and distribute it more evenly over the plate.

An in vitro biomechanical investigation of an interlocking nail system developed for buffalo tibia

Objectives: The objectives of the study were to determine the mechanical properties of a customized buffalo interlocking nail (BIN), intact buffalo tibia, and ostectomized tibia stabilized with BIN in different configurations, as well as to assess the convenience of interlocking nailing in buffalo tibia.

Methods: The BIN (316L stainless steel, 12 mm diameter, 250 mm long, nine-hole solid nails with 10° proximal bend) alone was loaded in compression and three-point bending (n = 4 each); intact tibiae and ostectomized tibiae (of buffaloes aged 5–8 years, weighing 300–350 kg) stabilized with BIN using 4.9 mm standard or modified locking bolts (4 or 8) in different configurations were subjected to axial compression, cranio-caudal three-point bending and torsion (n = 4 each) using a universal testing machine. Mechanical parameters were determined from load-displacement curves and compared using Kruskal-Wallis test (p <0.05).

Results: Intact tibiae were significantly stronger than BIN and bone-BIN constructs in all testing modes. The strength of fixation constructs with eight locking bolts was significantly more than with four bolts. Overall strength of fixation with modified locking bolts was better than standard bolts. Based on technical ease and biomechanical properties, cranio-caudal insertion of bolts into the bone was found better than medio-lateral insertion.

Clinical significance: The eight bolt BINbone constructs could be useful to treat tibial fractures in large ruminants, especially buffaloes.

Segmented interlocking nail: An in vivo evaluation of a novel humeral osteotomy fixation device in a caprine model

Objectives: To describe a novel humeral fixation device, the insertion technique, healing of humeral osteotomies, and clinical outcomes in a caprine model over a six month period.

Methods: Fourteen mature female Boer/Nubian cross goats with a mean body weight of 50.7 kg were implanted with a proprietary segmented interlocking nail (SILN) in both humeri. Each goat had one humerus randomly selected for mid-diaphyseal osteotomy.

Results: Immediately after surgery all but one goat was able to stand, although none of the goats were weight bearing on the osteotomy limb. During the six month study, clinical lameness was always associated with the osteotomy limb. One month after surgery, lameness for twelve of the goats was grade 2/5 or better. At three months, 11 of the 14 did not exhibit any signs of lameness. On radio-graphic images, notable malalignment of the osteotomy was observed, although all osteotomies went to bone union.

Clinical significance: The results of this study suggest that despite misalignment, the SILN maintained adequate osteotomy fixation to achieve bone union in the research model studied, with reduced morbidity and early return to function with bilateral implantation. The SILN used in this study allowed intramedullary fixation of humeral diaphyseal osteotomies with a limited and safe surgical approach.

Biomechanical Comparison of Locking Compression Plate and Limited Contact Dynamic Compression Plate Combined with an Intramedullary Rod in a Canine Femoral Fracture-Gap Model

OBJECTIVE

To compare the biomechanical properties of locking compression plate (LCP) and a limited contact dynamic compression plate combined with an intramedullary rod (LC-DCP-R) in a cadaveric, canine, femoral fracture-gap model.

STUDY DESIGN

In vitro biomechanical study; nonrandomized, complete block (dog).

SAMPLE POPULATION

Paired cadaveric canine femora (n = 10 dogs).

METHODS

Paired femurs with a mid-diaphyseal 20 mm gap were stabilized with either LCP or LC-DCP-R. Nondestructive testing up to 60% of body weight (BW) was followed by a continuous destructive test. Comparative structural properties, 3-dimensional (3D) interfragmentary motion, and plate linear strain were evaluated. Paired comparisons were made between LCP and LC-DCP-R.

RESULTS

Stiffness after nondestructive testing was significantly lower for LCP with a mean (95% confidence interval [CI]) of 61 N/mm (46-76) versus 89 N/mm (67-110) for LC-DCP-R (P = .0072). Ultimate load to failure was significantly lower for LCP with a median (interquartile range [IQR]) of 270 N (247-286) versus 371.5 (353-385) for LC-DCP-R (P = .002). Axial motion at 60% BW was significantly higher for LCP with a median (IQR) of 1.01 mm (0.71-1.26) versus 0.36 mm (0.20-0.49) for LC-DCP-R (P = .002). Shear motion was significantly higher for LCP with a median (IQR) of 1.18 (0.78-1.58) versus 0.72 mm (0.45-1.00) for LC-DCP-R (P = .018). Strain was significantly higher for mid-LCP surface with a mean (95%CI) at 60% BW of 979 μdef (579-1378) versus 583 μdef (365-801) at mid-LC-DCP-R surface (P = .0153). The elastic limit strain of the plates was not different and was reached at a mean (95%CI) load of 241 N (190-292) for LCP versus 290 N (245-336) for LC-DCP-R (P = .12).

CONCLUSION

The LC-DCP-R showed higher stiffness and resistance to failure, lower interfragmentary motion, and lower plate strain and stress compared to LCP.

Effect of bending direction on the mechanical behaviour of 3.5 mm String-of-Pearls and Limited Contact Dynamic Compression Plate constructs

OBJECTIVE

To compare the bending properties of String-of-Pearls® (SOP) and Limited Contact Dynamic Compression Plate® (LC-DCP) constructs in orthogonal bending directions.

METHODS

3.5 mm SOP and LC-DCP plates were fixed to a bone model simulating a comminuted tibial fracture. Specimens were non-destructively tested in both mediolateral and craniocaudal bending for 10 cycles. Bending stiffness and total angular deformation were compared using parametric analyses (p <0.05).

RESULTS

For both constructs, stiffness was significantly less when bending moments were applied against the thickness of the plates (mediolateral bending) than against the width (craniocaudal bending). When compared to the mediolateral plane, bending constructs in the craniocaudal plane resulted in a 49% (SOP group) and 370% (LC-DCP group) increase in stiffness (p <0.001). Mediolateral bending stiffness was significantly greater in the SOP than the LC-DCP constructs. Conversely, in craniocaudal bending, SOP constructs stiffness was significantly less than that of the LC-DCP constructs. The differences between the two constructs in total angular deformation had an identical pattern of significance.

CLINICAL SIGNIFICANCE

This study found that SOP showed less variability between the orthogonal bending directions than LC-DCP in a comminuted fracture model, and also described the bi-planar bending behaviour of both constructs. Although not exhibiting identical bending properties in both planes, SOP constructs had a more homogenous bending behaviour in orthogonal loading directions. The difference between the SOP with a circular cross sectional shape compared to the rectangular shape of standard plates is probably responsible for this difference.

Angle stable nails provide improved healing for a complex fracture model in the femur

BACKGROUND

Conventional nails are being used for an expanding range of fractures from simple to more complex. Angle stable designs are a relatively new innovation; however, it is unknown if they will improve healing for complex fractures.

QUESTIONS/PURPOSES

When comparing traditional and angle stable nails to treat complex open canine femur fractures, the current study addressed the following questions: do the two constructs differ in (1) radiographic evidence of bone union across the cortices; (2) stability as determined by toggle (torsional motion with little accompanying torque) and angular deformation; (3) biomechanical properties, including stiffness in bending, axial compression, and torsional loading, and construct failure properties in torsion; and (4) degree of bone tissue mineralization?

METHODS

Ten hounds with a 1-cm femoral defect and periosteal stripping were treated with a reamed titanium angle stable or nonangle stable nail after the creation of a long soft tissue wound. Before the study, the animals were randomly assigned to receive one of the nails and to be evaluated with biomechanical testing or histology. After euthanasia at 16 weeks, all operative femora were assessed radiographically. Histological or biomechanical evaluation was conducted of the operative bones with nails left in situ compared with the nonoperative contralateral femora.

RESULTS

Radiographic and gross inspection demonstrated hypertrophic nonunion in all 10 animals treated with the nonangle stable nail, whereas six of 10 animals treated with the angle stable nail bridged at least one cortex (p = 0.023). The angle stable nail construct demonstrated no toggle in nine of 10 animals, whereas all control femora exhibited toggle. The angle stable nail demonstrated less angular deformation and toggle (p ≤ 0.005) and increased compressive stiffness (p = 0.001) compared with the conventional nonangle stable nail. Histology demonstrated more nonmineralized tissue in the limbs treated with the conventional nail (p = 0.005).

CONCLUSIONS

Angle stable nails that eliminate toggle lead to enhanced yet incomplete fracture healing in a complex canine fracture model.

CLINICAL RELEVANCE

Care should be taken in tailoring the nail design features to the characteristics of the fracture and the patient.

A modified intramedullary nail interlocking design yields improved stability for fatigue cycling in a canine femur fracture model

Intramedullary nailing has evolved to become the standard of care for most diaphyseal femoral and tibial fractures, as well as an expanding number of metaphyseal fractures. Owing to the unstable nature of some fractures, the intramedullary device may be subjected to significant stresses owing to a lack of solid cortical contact after nailing. In such cases, excessive interfragmentary motion (due to construct toggle) has been shown to occur. Such motion increases the likelihood of a non- or delayed-union. In the current study, two versions of a modified, angle stable interlocking design were subjected to fatigue testing in a segmental defect fracture model representing a canine femur. As a control, a third group of constructs were stabilized with a traditional nail that allowed a small amount of toggle. All constructs were subjected to 50,000 fatigue cycles representing 12 weeks of cage activity at physiologic levels of combined axial-torsional loading. Torsional testing pre- and post-fatigue revealed 4.6 +/- 1.3 degrees of toggle in the traditional nail and no toggle with the angle stable nail designs. The stable nails were also significantly stiffer in axial compression and torsion before and after cycling. These data indicate that the enhanced stability of the modified interlocking designs can be maintained throughout fatigue cycling in a challenging fracture model.

Development of an interlocked nail for segmental defects in the rabbit tibia

Previous animal models have been developed to study intramedullary nailing for challenging segmental defects in the tibia. In large animals, interlocked nail fixation created a stable environment suitable to study new bone growth technologies placed in the defect. To our knowledge, there are no comparable interlocked tibial defect models for the rabbit in which new technologies could be evaluated. Such a model would be helpful since the rabbit is a popular initial model for orthopedic research studies owing to its wide availability and low cost. While numerous studies have nailed the rabbit tibia, all were non-locked implants that allowed some degree of instability between the fracture fragments. In addition, the non-locked nails were constructed of stainless steel, whereas human nails are increasingly made from titanium alloy. In the current study, an interlocked titanium nail was developed for the rabbit tibia. It was implanted in cadaver tibiae and subjected to fatigue cycling in combined compression and bending at physiologic levels to 21,061 cycles. This duration is estimated to represent 12 weeks of gait by the animal. Before and after fatigue cycling, monotonic testing was performed in compression and bending at physiologic levels. The intact contralateral limbs served as controls. All limbs completed the cycling; the instrumented limbs exhibited interfragmentary cyclic strain amplitudes during fatigue (616 ± 139 microstrain), which was significantly greater than the control limbs (136 ± 35 microstrain). Monotonic strain amplitudes for the test limbs in bending and compression were 4839 ± 1028 and 542 ± 122 microstrain, respectively; corresponding values for the control bones were 407 ± 118 and 95 ± 38 microstrain, respectively. These data are similar to those presented in prior studies in larger bone models. The current study presents one method for interlocked nail fixation for this complex tibial shaft fracture in a small animal.

Intercalary allograft reconstructions using a compressible intramedullary nail: a preliminary report

BACKGROUND

Although intercalary allograft reconstructions are commonly performed using intramedullary devices, they cannot generate compression across host-allograft junctions. Therefore, they sometimes are associated with gap formation and suboptimal healing conditions.

QUESTIONS/PURPOSES

We describe a new technique and present preliminary results for intercalary allograft reconstructions for tumors using a compressible intramedullary nail.

PATIENTS AND METHODS

We retrospectively reviewed 10 patients (19 host-allograft junctions) who underwent intercalary allograft reconstruction using the compression nailing technique. Two patients were excluded as they had additional vascularized fibular autografts, leaving 15 junctions in eight patients for analysis. Three of the intercalary reconstructions had supplemental plate fixation at one junction. All patients received host bone reamings and cancellous allograft and one had bone marrow aspirate and demineralized bone matrix in addition to the cancellous allograft. The minimum followup was 3 months (mean, 18 months; range, 3-39 months).

RESULTS

Thirteen of 15 junctions healed without additional surgery. Two diaphyseal-diaphyseal junctions did not unite after allograft arthrodeses. One patient underwent revision for nonunion 8 months after the initial procedure, with subsequent healing. The second patient had no evidence of union at 6 months, after which he was lost to followup. There were no allograft fractures or infections in any reconstruction. One patient died of metastatic renal cell carcinoma, and one patient had multicentric local soft tissue recurrences of a periosteal osteosarcoma requiring resection.

CONCLUSIONS

Our early observations indicate newer compressible intramedullary nails reliably address junctional gap formation, providing for a high rate of union while retaining the long-term benefits of intramedullary stabilization.

LEVEL OF EVIDENCE

Level IV, case series. See Guidelines for Authors for a complete description of levels of evidence.

In Vitro Mechanical Comparison of Screwed, Bolted, and Novel Interlocking Nail Systems to Buttress Plate Fixation in Torsion and Mediolateral Bending

OBJECTIVE

To compare standard interlocking nails (ILN) with a newly designed ILN featuring an angle-stable locking mechanism (ILNn).

STUDY DESIGN

Six experimental groups.

SAMPLE POPULATION

Bone models (n=48) treated with 6 and 8 mm nails locked with screws or bolts (ILN6s, ILN8s, ILN6b, ILN8b, respectively), ILNn, and a 3.5 mm broad-DCP (br-DCP); n=4/testing mode.

METHODS

Specimens were tested in torsion or 4-point bending. Construct compliance, deformation, and slack were statistically compared (P<.05).

RESULTS

Regardless of testing mode, construct compliance was greater with smaller ILN. Screwed constructs were more compliant than bolted ones, with a significant difference between ILN6s and ILN6b in torsion. Plated constructs were significantly more compliant than the ILNn. Angular deformation was consistently greater with smaller ILN. Screwed ILN constructs sustained approximately 2 x the torsional deformation of the bolted ones (approximately 36 degrees [ILN6s] versus approximately 18 degrees [ILN6b]). Comparatively, ILNn constructs had significantly less torsional (approximately 8 degrees) and bending (approximately 4 degrees) deformation than other constructs. Whereas standard ILN constructs had slack in both modes, ILNn and br-DCP construct deformations consistently occurred without slack.

CONCLUSIONS

Use of bolts rather than screws improved ILN mechanical behavior, but neither locking mechanism completely counteracted torsion and bending forces. Conversely, the ILNn angle-stable locking system eliminated torsional and bending slack, resulting in comparable mechanical performances between ILNn and plated constructs.

CLINICAL RELEVANCE

The angle-stable locking mechanism of the new ILN eliminates all slack in the system; thus, interfragmentary motion will likely be reduced compared with standard ILN, which may improve the local environment for fracture healing.

Mechanical Comparison of an Interlocking Nail Locked with Conventional Bolts to Extended Bolts Connected with a Type-Ia External Skeletal Fixator in a Tibial Fracture Model

OBJECTIVE

To compare the structural properties of interlocking nails (ILNs) locked with bolts (ILNb) to ILN locked with extended bolts connected with a type-IA external skeletal fixator (ILN-ESF) in a fracture gap model.

STUDY DESIGN

Experimental study.

SAMPLE POPULATION

Synthetic tibial bone substitutes.

METHODS

Custom-made synthetic tibial bone substitutes were implanted with standard ILNs locked with either bolts or extended bolts connected to an external skeletal fixation (ESF). Constructs were tested in torsion, bending, and axial compression (n=4/testing mode). Data, consisting of construct compliance and associated deformation, were compared using t-tests.

RESULTS

The ILN-ESF construct compliance and deformation were significantly less than those of the ILNb construct in torsion, bending, and compression (P<.001). Slack was present in the ILNb construct under torsion and bending, but not in the ILN-ESF construct, regardless of testing mode.

CONCLUSIONS

Substitution of locking bolts with extended bolts connected to an ESF significantly reduced the construct compliance and overall deformation in torsion, bending, and compression. Furthermore, the inherent slack of the ILNb was eliminated by the use of an ESF in torsion and bending.

CLINICAL RELEVANCE

The improvement in structural properties of the ILN-ESF constructs could diminish interfragmentary motion at the fracture site and potentially improve bone healing.

In vitro mechanical evaluation of torsional loading in simulated canine tibiae for a novel hourglass-shaped interlocking nail with a self-tapping tapered locking design

OBJECTIVE

To describe a novel interlocking nail (ILN) and locking system and compare the torsional properties of constructs implanted with the novel ILN or a standard 8-mm ILN (ILN8) by use of a gap-fracture model.

SAMPLE POPULATION

8 synthetic specimens modeled from canine tibiae.

PROCEDURES

An hourglass-shaped ILN featuring a tapered locking mechanism was designed. A synthetic bone model was custom-made to represent canine tibiae with a 50-mm comminuted diaphyseal fracture. Specimens were repaired by use of a novel ILN or an ILN8 with screws. Specimens were loaded for torsional measurements. Construct compliance and angular deformation were compared.

RESULTS

Compliance of the ILN8 was significantly smaller than that of the novel ILN. Mean +/- SD maximum angular deformation of the ILN8 construct (23.12 +/- 0.65 degrees) was significantly greater, compared with that of the novel ILN construct (9.45 +/- 0.22 degrees). Mean construct slack for the ILN8 group was 15.15 +/- 0.63 degrees, whereas no slack was detected for the novel ILN construct. Mean angular deformation for the ILN8 construct once slack was overcome was significantly less, compared with that of the novel ILN construct.

CONCLUSIONS AND CLINICAL RELEVANCE

Analysis of results of this study suggests that engineering of the locking mechanism enabled the novel hourglass-shaped ILN system to eliminate torsional instability associated with the use of current ILNs. Considering the potential deleterious effect of torsional deformation on bone healing, the novel ILN may represent a biomechanically more effective fixation method, compared with current ILNs, for the treatment of comminuted diaphyseal fractures.