Intramedullary nailing of diaphyseal fractures with self-reinforced polylactide implants

In fracture treatment, several adverse effects of metal, especially its excessive rigidity, often require the removal of the implants after a fracture has healed. Recent research with biodegradable polymers has contributed to the development of totally biodegradable polylactic acid implants with very high initial bending and shear strengths, but a modulus of elasticity comparable to that of bone. These implants were originally intended for use in fractures involving cancellous bone. Encouraging results from treating experimentally produced diaphyseal fractures led the authors to use these implants in a clinical trial on shaft fractures in dogs and cats. In this study, a total of 11 dogs and 14 cats had 28 diaphyseal fractures treated with one or several intramedullary pins of self-reinforced left isomeric polylactic acid. Of the 25 treated cases, 23 healed. Four of these had an unsatisfactory end result attributed to the implants used and one developed an osteomyelitis. Thus, out of 25 fractures, 23 united (92 per cent] and 18 [72 per cent) had a good or excellent outcome.     

Internal fracture fixation

Over the past decade, many improvements to small animal internal fracture fixation have been developed, including improved fixation techniques and a more diverse selection of implants. The understanding that appropriate fixation selection is based on a plethora of biologic, mechanical, and clinical factors has also emerged. Classically, the methods of internal fracture fixation have used pins, wires, screws, and plates to rigidly stabilize fractures that have been anatomically reduced with significant disruption to the biologic fracture environment. Newer methods attempt to minimize trauma to the soft tissues surrounding a fracture and promote biologic osteosynthesis using such implants as interlocking nails and plate-rod fixations. This review provides an overview of both the traditional and current principles of small animal internal fracture fixation.     

Fracture healing after stabilization with intramedullary xenograft cortical bone pins: a study in pigeons

OBJECTIVE: To investigate the effectiveness of intramedullary xenograft cortical bone pins compared with stainless steel Kirschner wire for the repair of a standardized avian humeral fracture. STUDY DESIGN: Prospective randomized study. SAMPLE POPULATION: Thirty mature pigeons (Columba livia). METHODS: Birds were randomly assigned to 3 groups. Transverse mid-diaphyseal humeral fractures were created in 1 humerus in each bird. Fractures were stabilized with intramedullary ostrich or canine xenograft cortical bone pins or Kirschner wire. Radiographic, histological, and biomechanical assessments were used to compare fracture healing 6 weeks after fracture stabilization. The contralateral humerus of each bird was used as a control. RESULTS: All fractures healed regardless of intramedullary pin type. There were no statistically significant biomechanical differences among groups or within groups. Xenograft cortical bone pins induced a mononuclear inflammatory reaction that did not impair bone healing. Bones stabilized with intramedullary cortical bone pins had more periosteal callus and inflammation at the fracture site than bones stabilized with stainless steel Kirschner wires. CONCLUSIONS: Intramedullary xenograft cortical bone pins, derived from mammalian or avian sources, appear to represent an alternative for the repair of avian humeral fractures. CLINICAL RELEVANCE: Intramedullary xenograft cortical bone pins are biodegradable and may reduce the need for additional surgery to remove implants after fracture healing.     

The use of a biodegradable implant in fracture fixation: a review of the literature and a report of two clinical cases

A method of internal fracture fixation using rod-shaped biodegradable implants made of self-reinforced polyglycolic acid (PGA) is described. These biodegradable implants were employed in the fixation of fractures in a metaphysis and diaphysis. The fractures healed clinically and radiolo-gically in six weeks without complicatons. The patients started to use the operated limbs during the first postoperative week and lameness disappeared within six weeks. Biodegradable fixation devices will be a useful tool in the treatment of fractures in veterinary surgery.     

Fixation of Cancellous Bone and Physeal Fractures in Dogs and Cats. A Comparison of the Use of Self-reinforced Biodegradable Devices to the Use of Metallic Devices and External Fixations

The use of self-reinforced biodegradable devices made of polyglycolide in the cancellous bone and physeal fractures of dogs and cats was compared to the use of metallic devices and external fixations on similar fractures. The series consisted of 64 dogs and 22 cats divided into 6 comparable groups. The patients in the 2 groups fixed with biodegradable devices started to use their operated limbs earlier than in the other groups. The same 2 groups also healed clinically (showed no lameness) earlier than the other groups. Radiographically there was no statistical difference between the 6 groups.On the basis of this study it may be concluded that the fixation with self-reinforced biodegradable devices is as suitable for the fixation of cancellous bone and physeal fractures of dogs and cats as the fixation with metallic devices or external fixation. This biodegradable technique has additional benefits allowing the patients to feel less pain in their operated limbs and making secondary operations to remove the devices unnecessary.     

Correlation of histology of healed fractures and tissue surrounding implants with ultrasonographic and radiographic appearance

OBJECTIVES: To determine if there was histological correlation with ultrasonographic images of healed fractures and implant-associated tissue after fracture treatment by plate osteotomy. METHODS: Eight adult dogs were included in this retrospective study. Ultrasonography (B-mode and power Doppler) and radiography were performed before plate removal. Surgical biopsies were taken of the fracture site and the tissue adjacent to the plate. These were stained with haematoxylin and eosin to assess histomorphology and bone content and immunolabelled with CD31 to assess vascularity. RESULTS: Ultrasound and radiographic diagnoses of a healed fracture correlated with histological finding of bone healing. Ultrasonography and histology findings of vascularity were also highly correlated. The tissue surrounding the surgical implants was significantly more vascularised on both ultrasonography and histology than that at the fracture site itself. CLINICAL RELEVANCE: Ultrasonography can be used to diagnose fracture healing in plated fractures. Power Doppler ultrasonography examination of fracture healing should be performed away from surgical implants to avoid false-positive results of vascularisation.     

Assessment of stiffness and strength of 4 different implants available for equine fracture treatment: a study on a 20 degrees oblique long-bone fracture model using a bone substitute

OBJECTIVE: To compare the mechanical properties of 4 stabilization methods for equine long-bone fractures: dynamic compression plate (DCP), limited contact-DCPlate (LC-DCP), locking compression plate (LCP), and the clamp-rod internal fixator (CRIF--formerly VetFix). STUDY DESIGN: In vitro mechanical study. SAMPLE POPULATION: Bone substitute material (24 tubes) was cut at 20 degrees to the long axis of the tube to simulate an oblique mid-shaft fracture. METHODS: Tubes were divided into 4 groups (n=6) and double plated in an orthogonal configuration, with 1 screw of 1 implant being inserted in lag fashion through the "fracture". Thus, the groups were: (1) 2 DCP implants (4.5, broad, 10 holes); (2) 2 LC-DCP implants (5.5, broad, 10 holes); (3) 2 LCP implants (4.5/5.0, broad, 10 holes) and 4 head locking screws/plate; and (4) 2 CRIF (4.5/5.0) and 10 clamps in alternating position left and right of the rod. All constructs were tested in 4-point bending with a quasi-static load until failure. The implant with the interfragmentary screw was always positioned on the tension side of the construct. Force, displacement, and angular displacement at the "fracture" line were determined. Construct stiffness under low and high loads, yield strength, ultimate strength, and maximum angular displacement were determined. RESULTS: None of the implants failed; the strength of the bone substitute was the limiting factor. At low loads, no differences in stiffness were found among groups, but LCP constructs were stiffer than other constructs under high loads (P=.004). Ultimate strength was lowest in the LCP group (P=.01), whereas yield strength was highest for LCP constructs (409 N m, P=.004). CRIF had the lowest yield strength (117 N m, P=.004); no differences in yield strength (250 N m) were found between DCP and LC-DCP constructs. Differences were found for maximum angular displacement at the "fracture" line, between groups: LPC相似文献   

Comparison of porous titanium-surfaced and standard smooth-surfaced bone plates and screws in an unstable fracture model in dogs

Bilateral midshaft femoral osteotomies were fixed with a 3-mm fracture gap in 6 dogs. In each dog, one femur was fixed with a porous titanium-surfaced bone plate and screws, whereas the opposite femur was fixed with a standard smooth-surfaced bone plate and screws. The mean removal torque for porous titanium-surfaced screws (32.3 kg X cm) was significantly (P less than 0.01) greater than the mean removal torque for standard screws (4.4 kg X cm). Osseous tissue ingrowth into the surface of porous titanium-surfaced screws was verified by histologic examination of the bone-screw interface. Radiographic and histologic examinations of the osteotomy gaps showed accelerated primary gap healing in osteotomies fixed with porous titanium-coated implants, compared with slower callus healing seen in osteotomies fixed with standard smooth-surfaced implants.     

Principles of long bone fracture management.

The fixation of fractures in which one of the following primary devices is used: IM pins, bone plates, external skeletal fixators, can benefit from the additional application of any number of secondary devices. The secondary devices include cerclage, hemicerclage, or interfragmentary wires, skewer-pins, screws, and external skeletal fixators. These are indicated to facilitate the repair and eliminate the forces acting on the fracture site. A complete understanding of all the methods of fixation facilitates the selection of the proper implant or combination of implants. This information must be combined with the knowledge of how each device is most appropriately used depending on both the fracture type and fracture location. Taking into consideration all of these factors helps ensure that fracture healing occurs in the shortest possible time with the fewest complications. The ultimate goal of obtaining a full return to function may thereby be achieved.     

Rehabilitation of fractures in small animals: maximize outcomes, minimize complications

Successful fracture management accomplishes 2 major objectives: bony union and return to functional activities. For many years, Physical Therapy has routinely helped human patients recovering from fractures reach their functional goals by helping them regain movement, flexibility, strength, coordination, and balance. Rehabilitation is now commonly provided to small animals recovering from fractures to accomplish similar goals. Knowledge of tissue healing is critical when determining the appropriate stresses to apply throughout the healing timeline. The detrimental effects of immobilization, including the potential for development of fracture disease, must be considered when formulating a Rehabilitation plan of care. Many Rehabilitation interventions are readily amenable to application by both Veterinary professionals and owners of patients. Superficial thermal modalities, passive range of motion and stretching, soft tissue massage, therapeutic ultrasound, electrical stimulation, and therapeutic exercise can ensure a more complete patient recovery. Providing owners with education regarding appropriate patient handling and home modifications allows a safer return to the home environment. Detailed written instructions for rehabilitation at home promotes owner compliance and accurate completion.     

Implantation of canine umbilical cord blood-derived mesenchymal stem cells mixed with beta-tricalcium phosphate enhances osteogenesis in bone defect model dogs

This study was performed to evaluate the osteogenic effect of allogenic canine umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) mixed with beta-tricalcium phosphate (β-TCP) in orthotopic implantation. Seven hundred milligrams of β-TCP mixed with 1 × 10⁶ UCB-MSCs diluted with 0.5 ml of saline (group CM) and mixed with the same volume of saline as control (group C) were implanted into a 1.5 cm diaphyseal defect and wrapped with PLGC membrane in the radius of Beagle dogs. Radiographs of the antebrachium were made after surgery. The implants were harvested 12 weeks after implantation and specimens were stained with H&E, toluidine blue and Villanueva-Goldner stains for histological examination and histomorphometric analysis of new bone formation. Additionally, UCB-MSCs were applied to a dog with non-union fracture. Radiographically, continuity between implant and host bone was evident at only one of six interfaces in group C by 12 weeks, but in three of six interfaces in group CM. Radiolucency was found only near the bone end in group C at 12 weeks after implantation, but in the entire graft in group CM. Histologically, bone formation was observed around β-TCP in longitudinal sections of implant in both groups. Histomorphometric analysis revealed significantly increased new bone formation in group CM at 12 weeks after implantation (p < 0.05). When applied to the non-union fracture, fracture healing was identified by 6 weeks after injection of UCB-MSCs. The present study indicates that a mixture of UCB-MSCs and β-TCP is a promising osteogenic material for repairing bone defects.     

Maxillofacial and mandibular fractures.

Any traumatic event that produces maxillofacial and/or mandibular fractures generally results in gross and usually severe patient disfigurement and often results in the patient's inability to eat and drink. These fractures are exceptionally rewarding cases as simple techniques may be performed resulting in a successful functional outcome (ability to eat and drink) within a very short period of time (24 hours) after fracture stabilization. A markedly improved cosmetic appearance follows shortly thereafter once inflammation and edema resolve. The primary principle of fracture treatment, ie, providing stable fixation to the bone fragments, may be successfully used with wiring techniques only through an appreciation and proper application of biomechanical principles. Knowledge that bending forces (divided into their tensile and compressive components) are the primary forces to be neutralized dictates the use of the wiring techniques outlined as the "standard" to which all other methods of fixation for maxillofacial and mandibular fractures are compared. The location of the tension-band surface of the bone, the alveolar (oral) surface, dictates the most appropriate position for wire placement. Successful treatment is predicted on obtaining a cosmetically acceptable and functional result (Fig 29). Anatomic reduction and rigid fixation of fractures that can be reconstructed piece-by-piece creates optimal conditions for uncomplicated healing. Fractures in which bone loss or severe comminution exists, and which cannot be anatomically reconstructed, must be reduced using dental occlusion as the template for fracture fixation, thereby avoiding malocclusion. Excessive leverage on the bone fragments may occur secondary to malocclusion, resulting in an increased risk of complications (fragment motion, loosening of implants, infection). Some fractures with comminution or bone loss may not be suitable for wire fixation and must be treated by alternate methods (eg, external skeletal fixators, plates).     

Bone grafts.

Bone grafting provides a method of enhancing bone healing in veterinary orthopedic patients. Specifically, autogenous cancellous bone graft provides the cellular components and matrix proteins that can accelerate bone healing, dramatically. Allografts provide immediate mechanical support for fracture repair and patient function, but these grafts do not create the osteogenic environment seen with the use of autogenous cancellous bone graft. Xenograft bone implants may also hold a place for use in fracture management. With the advent of recombinant bone-derived tissue growth factor technology, bone grafting may some day become a practiced technique of the past. For now, however, bone grafting still holds a strong place in orthopedic surgery when dealing with bone defects in animals.     

Miniplate Fixation for Repair of Mandibular and Maxillary Fractures in 15 Dogs and 3 Cats

Maxillofacial miniplates and screws were used for skeletal fixation in 15 dogs and 3 cats that sustained a variety of mandibular and maxillary fractures. These implants were used as neutralization or buttress fixation in 11 caudal (junction of the ramus with the mandibular body) and 2 rostral mandibular fractures, 4 maxillary fractures, and 2 zygomatic arch fractures. All but one of the fractures healed with appropriate occlusion and excellent function. In one case of a rostral mandibular fracture, soft tissue dehiscence occurred accompanied by a loss of the fixation and subsequent distraction of the bone fragments; reasonable function was obtained by performing a rostral mandibulectomy. Plate contouring and application of the miniplates along the appropriate biomechanical lines of stress was easily performed and permitted the biomechanical principles of tension band fixation to be applied in most cases. Miniplate fixation, either used alone or in combination with other fracture fixation techniques, achieved sufficiently rigid skeletal fixation to provide uncomplicated healing and good to excellent functional and cosmetic results in 14 dogs and 3 cats.     

BIODEGRADABLE IMPLANTS IN FRACTURE FIXATION IN SMALL ANIMAL SURGERY

The Finnish group led by Rokkanen and Tormala has developed a biodegradable implant for fracture fixation. Results from experimental and clinical studies of polyglycolic acid (PGA) are encouraging, and further studies are being made in the use the biorod, which has been used successfully to treat an avulsed calcaneal fracture in a puppy. Other biodegradable substances are being investigated to improve biodegradable fracture fixation devices.     

Biomechanical Study of Canine Spinal Fracture Fixation Using Pins or Bone Screws With Polymethylmethacrylate

Five configurations of pins or screws interconnected with polymethylmethacrylate (PMMA) were applied to isolated canine lumbar spines (L2 to L5) in which a complete fracture-luxation had been produced at L3 to L4. Twenty-five repaired spines and five intact control spines were subjected to four-point bending and tested once to failure in ventral flexion. The purpose of this study was to determine the effects of pin number, pin angle, and use of 3.5-mm cortical bone screws instead of smooth 3.2-mm diameter pins on rigidity and ultimate strength of spinal fractures repaired by the implant-PMMA fixation technique. Bending moment versus the angular deformation curves were recorded. Rigidity, bending moment at 10° angular deformation, moment at failure, and deformation at failure of each type of fixation were compared using analysis of variance. Spinal segments stabilized with eight pin-PMMA fixation had significantly greater rigidity and strength at failure than four pin-PMMA fixations ( P < .05). Furthermore, spinal segments stabilized with eight pins angled away from the fracture failed at significantly greater bending moment than those with eight pins angled toward the fracture ( P < .05). However, for four-pin fixation, greater strength was achieved by angling pins in the bone toward the fracture site ( P < .05). Screw-PMMA fixations failed by screw bending and were less rigid and weaker at failure than the corresponding configuration of pin-PMMA fixation ( P < .05).     

Use of intramedullary fully-threaded pins in the fixation of feline and canine humeral, femoral and tibial fractures

Intramedullary fully-threaded pins were manufactured from an alloy of titanium, aluminium and vanadium in a fully-threaded style. Pins were produced in various diameters, ranging from 4 mm to 11 mm. Pin lengths varied from 5 cm to 22 cm. The proximal end of the pins was designed to fit into a hexagonal screwdriver, while the distal end was slightly tapered to allow for ease of entry into cancellous bone. Treatment using the fully-threaded intra- medullary pin was carried out in a total of 175 fractures of the humerus, femur, and tibia in 95 cats (bilateral femur in 1 case) and 77 dogs (bilateral femur in 2 cases). Radiographic follow-up for the cases was performed at monthly intervals. Non-union developed in one dog with a femoral fracture in which cerclage wire had also been used. Delayed healing and lameness were observed in two other dogs. Healing with excessive callus formation was observed in 16 dogs. However, there were not any problems noted in these dogs in regards to limb usage. Clinical and radiological results obtained for the remaining cases were found to be very good. Normal, complete fracture healing occurred between four to 14 weeks in dogs, and between four to 12 weeks in cats. Pins were removed upon observation of satisfactory functional and radiographic recovery. Pins could not be removed from 26 cats and 21 dogs as the owners had declined pin removal, or because the owners were lost to follow-up.     

Complications of fractures repaired with plates and screws

The complications associated with bone plates and screws often are related to undersized or oversized implant selection, improper number of implants, inadequate or improper screw fixation, malpositioned plates or screws, poor plate contouring, and failure to use cancellous bone grafts when a gap is present at the fracture site. A thorough understanding of the principles of plate and screw application helps to avoid most problems. The surgeon must use an implant that will stabilize the fracture adequately during the healing process. The patient's activity levels must not exceed the mechanical limits of the implant. Methods to promote bone healing, such as using cancellous bone grafts when a deficit is present, help to protect the implant from fatiguing before the fracture is healed. Proper positioning and contouring of the implants are important to the successful application of plates and screws. It must be realized that even if all of these things are done, some complications still will occur. When that happens, the complication should be dealt within a manner that will allow the objectives of fracture treatment (a healed bone and normal limb function) to be achieved.     

Compressive Forces Achieved in Simulated Equine Third Metacarpal Bone Lateral Condylar Fractures of Varying Fragment Thickness with Acutrak Plus Screw and 4.5 mm AO Cortical Screws

Objectives— To compare compression pressure (CP) of 6.5 mm Acutrak Plus (AP) and 4.5 mm AO cortical screws (AO) when inserted in simulated lateral condylar fractures of equine 3rd metacarpal (MC3) bones. Study Design— Paired in vitro biomechanical testing. Sample Population— Cadaveric equine MC3 bones (n=12 pair). Methods— Complete lateral condylar osteotomies were created parallel to the midsagittal ridge at 20, 12, and 8 mm axial to the epicondylar fossa on different specimens grouped accordingly. Interfragmentary compression was measured using a pressure sensor placed in the fracture plane before screw placement for fracture fixation. CP was acquired and mean values of CP for each fixation method were compared between the 6.5 mm (AP) and 4.5 mm (AO) for each group using a paired t‐test within each fracture fragment thickness group with statistical significance set at P<.05. Results— AO screw configurations generated significantly greater compressive pressure compared with AP configurations. The ratio of mean CP for AP screws to AO screws at 20, 12, and 8 mm, were 21.6%, 26.2%, and 34.2%, respectively. Conclusion— Mean CP for AP screw fixations are weaker than those for AO screw fixations, most notably with the 20 mm fragments. The 12 and 8 mm groups have comparatively better compression characteristics than the 20 mm group; however, they are still significantly weaker than AO fixations. Clinical Relevance— Given that the primary goals of surgical repair are to achieve rigid fixation, primary bone healing, and good articular alignment, based on these results, it is recommended that caution should be used when choosing the AP screw for repair of lateral condylar fractures, especially complete fractures. Because interfragmentary compression plays a factor in the overall stability of a repair, it is recommended for use only in patients with thin lateral condyle fracture fragments, as the compression tends to decrease with an increase in thickness.     

Osteosarcoma following total hip arthroplasty in a dog

Osteosarcoma involving the distal right femur was diagnosed in a nine-year-old female neutered Rottweiler seven years after total hip arthroplasty had been performed on that limb. The findings were consistent with a primary bone tumour and pathological fracture of the right femoral condyle with loosening of the orthopaedic implant and fracture of the polymethylmethacrylate at the distal aspect of the femoral component. Possible hypotheses to explain the association of osteosarcoma with total hip arthroplasty suggest that the neoplastic process was the result of some derangement of host tissue and the healing process or that the implants or their by-products were carcinogenic. Given the large number of total hip arthroplasties that are routinely performed in dogs, the development of a malignant lesion appears to be an extraordinary complication and may be completely coincidental.