Thursday, December 31, 2009

Bone Graft Substitute Materials


Bone Graft Substitute Materials

Author: Cato T Laurencin, MD, PhD, Van Dusen Chair Professor of Academic Medicine, Distinguished Professor of Orthopaedic Surgery, and Chemical, Materials, and Biomolecular Engineering, University of Connecticut
Coauthor(s): Yusuf Khan, PhD, Assistant Professor of Research, Departments of Orthopedic Surgery and Biomedical Engineering, University of Virginia School of Medicine
Updated: Dec 3, 2009
Introduction

More than 500,000 bone graft procedures are performed in the US each year and approximately 2.2 million worldwide.1 The estimated cost of these procedures approaches $2.5 billion per year.
Either autograft or allograft tissue is used in 90% of procedures. The current standard is for autograft tissue bone grafts, in which tissue is harvested from the patient, usually from the iliac crest, but possibly from the distal femur or the proximal tibia. The graft is then placed at the injury site. This tissue is ideal as a bone graft because it possesses all of the characteristics necessary for new bone growth—namely, osteoconductivity, osteogenicity, and osteoinductivity.
Osteoconductivity refers to the situation in which the graft supports the attachment of new osteoblasts and osteoprogenitor cells, providing an interconnected structure through which new cells can migrate and new vessels can form. Osteogenicity refers to the situation when the osteoblasts that are at the site of new bone formation are able to produce minerals to calcify the collagen matrix that forms the substrate for new bone. Osteoinductivity refers to the ability of a graft to induce nondifferentiated stem cells or osteoprogenitor cells to differentiate into osteoblasts.
Harvesting the autograft requires an additional surgery at the donor site that can result in its own complications, such as inflammation, infection, and chronic pain that occasionally outlasts the pain of the original surgical procedure. Quantities of bone tissue that can be harvested are also limited, thus creating a supply problem.
Allografts are alternatives to autografts and are taken from donors or cadavers, circumventing some of the shortcomings of autografts by eliminating donor-site morbidity and issues of limited supply. However, allografts present risks as well; although allograft tissue is treated by tissue freezing, freeze-drying, gamma irradiation, electron beam radiation, ethylene oxide, etc, the risk of disease transmission from donor to recipient is not completely removed. Some have estimated that the risk of human immunodeficiency virus (HIV) transmission alone with allograft bone is 1 case in 1.6 million population.2 A case of hepatitis B transmission and 3 cases of hepatitis C transmission have been reported with allograft tissue. More recently, cases of disease transmission have been reported.
Although rigorous donor screenings and tissue treatments have greatly reduced the incidence of HIV and hepatitis transmission, other diseases have been passed on as recently as 2000 and 2001. In April 2000, 2 different patients received bone-tendon-bone allografts for anterior cruciate ligament reconstruction from a common donor. Each patient developed septic arthritis from the donor tissue.5 In November 2001, a patient underwent reconstructive knee surgery, and within 4 days of the surgery, the patient died of infection caused by Clostridium sordellii.6 After these and similar cases were reported, the CDC began an investigation that revealed 25 other cases of allograft-related infection or illness.6 Although many methods can reduce the risk of disease transmission, the treatments used to sterilize the tissue remove proteins and factors, reducing or eliminating the osteoinductivity of the tissue.
Despite the benefits of autografts and allografts, the limitations of each have necessitated the pursuit of alternatives. Using the 2 basic criteria of a successful graft, osteoconduction and osteoinduction, investigators have developed several alternatives, some of which are available for clinical use and others of which are still in the developmental stage. Many of these alternatives use a variety of materials, including natural and synthetic polymers, ceramics, and composites, whereas others have incorporated factor- and cell-based strategies that are used either alone or in combination with other materials. This article reviews what is currently available and what is on the horizon.

Recent studies

Mulconrey et al performed a prospective radiographic analysis of anterior and posterior adult spinal deformity fusions with bone morphogenetic protein (rhBMP-2) to determine the ability of rhBMP-2 to achieve multilevel spinal fusion. The patients were divided into 3 groups: group 1 (10 mg/level) contained 47 patients who underwent anterior spinal fusion (ASF) with BMP on an absorbable collagen sponge (ACS) with a titanium mesh cage; group 2 (20 mg/level) included 43 patients who underwent posterior spinal fusion (PSF) with BMP on an ACS with local bone graft (LBG) and bulking agent [tricalcium phosphate/hydroxyapatite (TCP-HA)]; and group 3 (40 mg/level) contained 8 patients who underwent PSF with rhBMP-2 and TCP-HA with no autologous bone. Overall fusion rate was 95% (group 1, 91%; group 2, 97%; group 3, 100%). In multilevel spinal fusion, rhBMP-2 eliminated the necessity for iliac crest bone graft and yielded an excellent fusion rate.7 

Bansal et al studied the use of porous hydroxyapatite and β-tricalcium phosphate as a scaffold combined with bone marrow aspirate in dorsal and lumbar spinal injuries. In this study, 30 patients were followed who had unstable dorsal and lumbar spinal injuries and needed posterior stabilization and fusion. Posterior stabilization was done using pedicle screw and rod assembly, and fusion was done using hydroxyapatite and β-tricalcium phosphate mixed with bone marrow aspirate as a bone graft substitute on one side of the spine and autologous iliac crest bone graft on the other side. Graft incorporation and fusion occurred in all patients on the bone-graft substitute side and in 29 patients on the autologous bone graft side. One patient showed lucency and breakage of the distal pedicle screw on the autologous side. According to the authors, hydroxyapatite and β-tricalcium phosphate with bone marrow aspirate is a promising alternative to autologous iliac bone graft for posterolateral spinalfusion.8 


Bone Graft Classification System


Several categories of bone graft substitutes exist (see the Table below) and encompass a variety of materials, material sources, and origins (natural vs synthetic). Many are formed from composites of 1 or more types of material; however, the composite is usually built on a base material.9,10
Laurencin et al have suggested a classification scheme of material-based groups11 :
  • Allograft-based bone graft substitutes involve allograft bone, used alone or in combination with other materials (eg, Allogro [AlloSource, Centennial, Colo], Opteform [Exactech, Inc, Gainesville, Fla], Grafton [BioHorizons, Birmingham, Ala], OrthoBlast [IsoTis OrthoBiologics, Irvine, Calif]).
  • Factor-based bone graft substitutes are natural and recombinant growth factors, used alone or in combination with other materials such as transforming growth factor-beta (TGF-beta), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), and bone morphogenetic protein (BMP).
  • Cell-based bone graft substitutes use cells to generate new tissue alone or are seeded onto a support matrix (eg, mesenchymal stem cells).
  • Ceramic-based bone graft substitutes include calcium phosphate, calcium sulfate, and bioglass used alone or in combination (eg, OsteoGraf [DENTSPLY Friadent CeraMed, Lakewood, Colo], Norian SRS [Synthes, Inc, West Chester, Pa], ProOsteon [Interpore Cross International, Irvine, Calif], Osteoset [Wright Medical Technology, Inc, Arlington, Tenn]).
  • Polymer-based bone graft substitutes, degradable and nondegradable polymers, are used alone or in combination with other materials (eg, Cortoss [Orthovita, Inc, Malvern, Pa], open porosity polylactic acid polymer [OPLA], Immix [Osteobiologics, Inc, San Antonio, Tex]).
Table.Bone Graft Substitutes
Class
Description
Examples
Allograft based
Allograft bone, used alone or in combination with other materials
Allogro, OrthoBlast, Opteform, Grafton
Factor based
Natural and recombinant growth factors, used alone or in combination with other materials
TGF-beta, PDGF, FGF, BMP
Cell based
Cells used to generate new tissue alone or seeded onto a support matrix
Mesenchymal stem cells
Ceramic based
Includes calcium phosphate, calcium sulfate, and bioglass, used alone or in combination
Osteograf, Norian SRS, ProOsteon, Osteoset
Polymer based
Both degradable and nondegradable polymers, used alone or in combination with other materials
Cortoss, OPLA, Immix



Allograft-based Bone Graft Substitutes


Allogro (AlloSource) is demineralized bone matrix.
The use of allografts for bone repair often requires the sterilization and deactivation of proteins normally found in healthy bone. Contained in the extracellular matrix of bone tissue are the full cocktail of bone growth factors, proteins, and other bioactive materials necessary for osteoinduction and, ultimately, successful bone healing. To capitalize on this cocktail of proteins, the desired factors and proteins are removed from the mineralized tissue by using a demineralizing agent such as hydrochloric acid. The mineral content of the bone is degraded, and the osteoinductive agents remain in a demineralized bone matrix (DBM).

Allogro (AlloSource) is demineralized bone matrix.


(A) DynaGraft (IsoTis OrthoBiologics) is a mixtur...

(A) DynaGraft (IsoTis OrthoBiologics) is a mixture of demineralized bone matrix (DBM) and a reverse-phase polymer and forms a solid matrix, putty, or injectable paste. (B) OrthoBlast (IsoTis OrthoBiologics) is the same polymer mixed with cancellous bone chips and DBM to create a formable paste.

DBM has been incorporated into several products currently on the market. Allogro is a DBM product (see Image 1). AlloMatrix (Wright Medical Technology, Inc) is Allogro combined with calcium sulfate; this paste can be formed into an onlay or injected directly into a defect site. DynaGraft II (IsoTis OrthoBiologics) is DBM mixed with a temperature-sensitive polymer and forms a solid, putty, or injectable paste, depending on the composition (seeImage 2). OrthoBlast is DBM mixed with the same polymer and cancellous bone chips and is also available as a putty or a paste.


Factor-based Bone Graft Substitutes


The factors and proteins that exist in bone are responsible for regulating cellular activity. Growth factors bind to receptors on cell surfaces, stimulating the intracellular environment to act. Generally, this activity translates to a protein kinase that induces a series of events resulting in the transcription of messenger ribonucleic acid (mRNA) and, ultimately, into the formation of a protein to be used intracellularly or extracellularly.
The combination and simultaneous activity of many factors result in the controlled production and resorption of bone. These factors, residing in the extracellular matrix of bone, include TGF-beta, insulinlike growth factors I and II, PDGF, FGF, and BMPs.12,7 Researchers have been able to isolate and, in some cases, synthesize these factors. Much work continues in the research setting, and some products for clinical use have appeared on the market.


Cell-based Bone Graft Substitutes


With current techniques, in vitro differentiation of mesenchymal stem cells toward the osteoblast lineage is possible. Stem cells are cultured in the presence of various additives such as dexamethasone, ascorbic acid, and β-glycerophosphate to direct the undifferentiated cell toward the osteoblast lineage.
The addition of TGF-beta and BMP-2, BMP-4, and BMP-7 to the culture media can also influence the stem cells toward the osteogenic lineage. In research laboratories, marrow cells containing mesenchymal stem cells have been combined with porous ceramics and implanted into rat and canine critical segmental defects, with bony growth occurring as quickly as 2 months. Mesenchymal stem cells have also been seeded onto bioactive ceramics conditioned to induce differentiation to osteoblasts. These have been proposed for use in bone repair prosthetic coatings.


Ceramic-based Bone Graft Substitutes


Approximately 60% of the bone graft substitutes currently available involve ceramics, either alone or in combination with another material. These include calcium sulfate, bioactive glass, and calcium phosphate. The use of ceramics, especially calcium phosphates, is driven in part by the fact that the primary inorganic component of bone is calcium hydroxyapatite, a subset of the calcium phosphate group. In addition, calcium phosphates are osteoconductive, osteointegrative (the newly formed mineralized tissue forms intimate bonds with the implant material), and, in some cases, osteoinductive. They often require high temperatures for scaffold formation and have brittle properties; therefore, they frequently are combined with other materials to form a composite:

  • Calcium sulfate is also known as plaster of Paris. It is biocompatible, bioactive, and resorbable after 30-60 days. Significant loss of its mechanical properties occurs upon its degradation; therefore, it is a questionable choice for load-bearing applications.
  • Osteoset is a tablet for use for defect packing. It is degraded in approximately 60 days (see Image 3).
  • AlloMatrix is Osteoset combined with DBM. It forms a putty or injectable paste (see Image 3).
Osteoset (left) and Allomatrix (right) are produc...

Osteoset (left) and Allomatrix (right) are produced by Wright Medical Technology, Inc. Osteoset is a calcium sulfate tablet used for bone defect sites, whereas Allomatrix is a combination of calcium sulfate and demineralized bone matrix that forms an injectable paste or a formable putty.

Bioactive glass (bioglass) is a biologically active silicate-based glass.Its high modulus and brittle nature make its applications limited, but it has been used in combination with polymethylmethacrylate to form bioactive bone cement and with metal implants as a coating to form a calcium-deficient carbonated calcium phosphate layer. This layer facilitates the chemical bonding of the implant to surrounding bone. Products include Biogran (developed by Orthovita and licensed to 3i, Implant Innovations, Inc, Palm Beach Gardens, Fla) and PerioGlas (NovaBone Products, LLC, Alachua, Fla).
OsteoGraf (DENTSPLY Friadent CeraMed) uses hydrox...Calcium phosphates account for most of the ceramic-based bone graft substitutes currently available. Several types of calcium phosphates exist, including tricalcium phosphate, synthetic hydroxyapatite, and coralline hydroxyapatite, and are available in pastes, putties, solid matrices, and granules.

ProOsteon (Interpore Cross International, Inc) is...Such calcium phosphate products include Bio-Oss (Geistlich Biomaterials, Inc, Baden Baden, Germany) and OsteoGraf (see Image 4). Both products use hydroxyapatite, either as a particulate (Bio-Oss) or as blocks and particulates (OsteoGraf). Vitoss (Orthovita, Inc) is a tricalcium phosphate available as a solid piece, putties, or pastes. ProOsteon is a unique product based on sea coral, which is converted from calcium carbonate to calcium hydroxyapatite. The advantage of this material is that the structure of the coral, which is similar to that of trabecular bone, is maintained. However, like many of the solid calcium phosphates, ProOsteon is brittle and not suitable for use in load-bearing sites (see Image 5).

OsteoGraf (DENTSPLY Friadent CeraMed) uses hydroxyapatite as bone graft material in either a block or a particulate form.

ProOsteon (Interpore Cross International, Inc) is produced from hydroxyapatite in either a particulate or a block form by chemically treating sea coral. Image courtesy of Interpore Cross International, Inc.



Polymer-based Bone Graft Substitutes


The final group of bone graft substitutes is the polymer-based group. Polymers present some options that the other groups do not. For example, many polymers that are potential candidates for bone graft substitutes represent different physical, mechanical, and chemical properties. The polymers used today can be loosely divided into natural polymers and synthetic polymers. These, in turn, can be divided further into degradable and nondegradable types.
Polymer-based bone graft substitutes include the following:
  • Healos (DePuy Orthopaedics, Inc, Warsaw, Ind) is a natural polymer-based product, a polymer-ceramic composite consisting of collagen fibers coated with hydroxyapatite and indicated for spinal fusions.
  • Cortoss is an injectable resin-based product with applications for load-bearing sites.
  • Rhakoss (Orthovita, Inc) is a resin composite available as a solid product in various forms for spinal applications (see Image 6).
Polymer-based bone graft substitutes include both...

Polymer-based bone graft substitutes include both particulate and solid forms such as Cortoss and Rhakoss, both produced by Orthovita, Inc.

Degradable synthetic polymers, like natural polymers, are resorbed by the body. The benefit of having the implant resorbed by the body is that the body is able to heal itself completely without remaining foreign bodies. To this end, companies have used degradable polymers such as polylactic acid and poly(lactic-co-glycolic acid) as stand-alone devices and as extenders to autografts and allografts.
Degradable polymers allow for complete healing be...BoneTec, Inc (Toronto, Canada) has developed a porous poly(lactic-co-glycolic acid) foam matrix by using a particulate leaching process to induce porosity. Immix Extenders (Osteobiologics, Inc), a particulate poly(lactic-co-glycolic acid) product, is used as a graft extender (see Image 7).

Degradable polymers allow for complete healing because the matrix is completely resorbed by the body. Osteobiologics, Inc, has produced Immix Extenders, a particulate polymer used as a bone graft extender.



Advanced Research Topics


New materials and approaches
Despite the many advances in bone graft substitutes, new materials and approaches to bone healing continue to be investigated. One exciting area is tissue engineering, which can be defined as the application of biologic, chemical, and engineering principles to the repair, restoration, or regeneration of living tissues by using biomaterials, cells, and factors, alone or in combination.
Applying the philosophy of tissue engineering to the healing of bone, Laurencin Laboratories (Charlottesville, Va) has developed biocompatible biodegradable matrices that possess many of the properties essential to successful healing. Using a microsphere-based design, Laurencin et al have created a porous biomimetic matrix that provides an osteoconductive surface for osteoblast attachment and an interconnected pore system to allow cellular proliferation and migration.14
This basic design has also been combined with a ceramic to form a composite matrix. The strategy behind the composite would allow the benefits of both materials to be included in one design. By using both previously synthesized hydroxyapatite and calcium phosphate synthesized within the matrix itself, the polymer-ceramic composite fosters the mineralization of newly forming bone. A similar polymer-ceramic composite has also been shown to be a viable surface for attachment and factor production of murine stromal cells transfected to produce BMP-7.
Future directions
Many products on the market today fill the need for bone grafts. Several of these products capitalize on the necessities of an ideal substitute: osteoconductivity and osteoinductivity. As more materials are adapted and discovered, preexisting products are finding new applications and effectiveness in combination with newly emerging technology. In addition, as investigators continue to find new materials and biologic approaches to bone repair, the future of bone graft substitutes continues to be an expanding topic.

Subtalar Dislocation


Subtalar Dislocation
By Joel Horning, MD; John DiPreta, MD
ORTHOPEDICS 2009; 32:904
Subtalar dislocations are relatively rare, accounting for approximately 1% to 2% of all joint dislocations. This article reviews the diagnosis and management of subtalar dislocations.
Subtalar dislocations represent a relatively rare injury, accounting for approximately 1% to 2% of all joint dislocations.1 First described in 1811 by Judey and Dufaurest, the subtalar dislocation, also referred to as a subastragalar or peritalar dislocation, involves the disruption of the talocalcaneal and talonavicular joints, while the calcaneocuboid joint remains intact.2-5 Because of its rarity, few large series have been published, and a majority of the literature are case reports. This article describes the diagnosis and management of subtalar dislocations.

Anatomy

The subtalar dislocation occurs through the disruption of 2 separate bony articulations, the talonavicular and talocalcaneal joints. These joints act as a hinge that transmits load and movement from the foot to the ankle. There is triplaner movement across the joint: a combination of flexion, supination, and adduction or extension, pronation, and abduction.1 The talocalcaneal, or subtalar, joint is composed of 3 separate articulations. The anterior, middle, and posterior facets provide bony stability to the joint, while ligamentous attachments provide added strength. The majority of the ligamentous stability of the subtalar joint, however, is attributed to the interosseous ligaments found within the sinus tarsi. Medially and laterally, the deep deltoid ligament and the calcaneofibular ligaments, respectively, provide restraint to eversion and inversion forces.
The talonavicular joint’s bony architecture provides the majority of its stability, while relatively weak capsular and ligamentous structures augment its stability. Comparatively, the talonavicular and talocalcaneal ligaments and capsules are weaker than those of the calcaneocuboid joint, explaining the pattern of subtalar dislocation where the calcaneonavicular joint remains intact as the talonavicular and talocalcaneal joints fail.6
The blood supply to the talus is derived from branches of the dorsalis pedis, peroneal artery, and posterior tibial artery. The majority of the dorsal blood supply is contributed by branches of the dorsalis pedis. The lateral and inferior blood supply arises from branches of the dorsalis pedis and peroneal arteries as they course through the sinus tarsi, while the medial talus is supplied by the posterior tibial artery as its branches pass within the tarsal canal.

Classification

In 1852, Broca first classified subtalar dislocations as “inward,” “outward,” or “backward” in a paper presented to the Societe de Chirurgie.4 In 1856, Malgaigne and Beurger expanded Broca’s original classification to include anterior dislocations.1 The classification system today is similar, as it describes anatomically the position of the foot with respect to the talus.
The medial dislocation, sometimes referred to as an “acquired clubfoot,” is the most common of all subtalar dislocations, comprising approximately 80% to 85% of cases.7-9 Described by Grantham10 as the “basketball foot,” the medial dislocation occurs through forceful inversion of the forefoot with the talar neck pivoting on the sustentaculum tali, which acts as a fulcrum to lever the calcaneus from the talus.7,11 Initially, it is believed that the talonavicular joint is the first to dislocate, followed by rotary subluxation through the subtalar joint, with the talar head finally coming to rest between the extensor hallucis longus and the extensor digitorum longus on either the cuboid or navicular (Figure 1).12
Figure 1A: The posteromedial position of the foot relative to the talusFigure 1B: The posteromedial position of the foot relative to the talus
Figure 1C: Radiograph of the patient following closed reductionFigure 1D: Radiograph of the patient following closed reduction
Figure 1: AP (A) and lateral (B) radiographs of a 47-year-old man demonstrating a medial subtalar dislocation after he sustained an inversion-type injury by stepping in a hole in his yard. Of note is the posteromedial position of the foot relative to the talus. AP (C) and lateral (D) radiographs of the patient following closed reduction under local anesthesia (hematoma block) and mild narcotic sedation. The subtalar joint was stable postreduction with no intra-articular fracture as documented on CT. The patient was immobilized in a well-padded posterior splint and discharged nonweight bearing on the affected extremity.
The lateral is the second most common subtalar dislocation, occurring in 15% to 20% of dislocations.8,9 Also known as an “acquired flatfoot,” the lateral dislocation typically results from the forceful eversion of the foot with the anterolateral talus pivoting over the anterior calcaneal process.7 The talar head is often displaced through the talonavicular capsule. Buckingham and LeFlore12 described injury to the deep deltoid and calcaneofibular ligaments in the lateral and medial subtalar dislocations, respectively, with sparing of the spring ligament. The lateral subtalar dislocation is historically associated with higher-energy trauma as compared with medial dislocations such as motor vehicle accidents and falls from a height (Figure 2).
Figure 2A: Open lateral subtalar dislocationFigure 2B: Open lateral subtalar dislocationFigure 2C: The capsule was also closed
Figure 2D: Reduction of the lateral subtalar dislocationFigure 2E: Removal of fragments from the sinus tarsi
Figure 2: AP (A) and lateral (B) radiographs of a 25-year-old woman who presented with open lateral subtalar dislocation. The dislocation was reduced in the emergency department, and the wound was irrigated and debrided in the operating room. The fragments seen in the area of the sinus tarsi were removed during the irrigation and debridment procedure. At the time, the capsule was also closed (C). AP (D) and lateral (E) radiographs showing reduction of the lateral subtalar dislocation and removal of fragments from the sinus tarsi.
First described in 1907 by Luxembourg, the posterior dislocation accounts for <1% of all subtalar dislocations.13The posterior dislocation most commonly occurs as the foot is excessively plantarflexed. The talar head becomes perched on the navicular and the foot does not have much medial or rotational deformity on frontal radiographs.14This has rarely been described in the literature.
The least common of all subtalar dislocations is the anterior dislocation, which results from forces being transmitted through an excessively dorsiflexed foot.13,15 The posterior facet of the talus comes to rest on the calcaneal tuber, and there may be some lateral displacement of the foot on frontal radiographs.

Diagnosis

The patient sustaining subtalar dislocations typically presents with significant pain and deformity to the affected extremity. The dislocation commonly results from motor vehicle accidents, falls from a height, sporting activities, jumping, running, or twisting.16 Men are affected more commonly than women (6:1), and mean patient age is 38.11,16 High-energy mechanisms are often associated with open injury, although this has not been shown to occur more frequently with medial or lateral dislocations.16
There is a higher incidence of associated fracture about the ankle in lateral dislocations, with the talus most commonly affected.3,16 In addition, the ipsilateral extremity and spine must be evaluated carefully, especially with high-energy injury.
All areas of concern should be evaluated radiographically in orthogonal planes. With respect to the subtalar dislocation, both frontal and sagittal views should be obtained to document the position of the foot and associated fractures of the foot and ankle. Following radiographic evaluation, the subtalar dislocation should be promptly reduced using the techniques described below.

Treatment

After confirmation of subtalar dislocation, attention should be turned to prompt reduction of the dislocation. Typically, this can be undertaken in a closed manner. Early cases described operating room reduction under general anesthesia. Prior to 1920, open reduction and talus removal were advocated by some for the treatment of subtalar dislocation.2 Plewes and McKelvey2 described 2 cases of subtalar dislocation reduced in the operating room under general anesthesia with Steinman pin placement through the calcaneus, through which traction was applied over a Böhler frame for over an hour prior to reduction. In addition, Böhler’s maneuver was used where the foot was forcibly reduced over a block.17
Today, the majority of subtalar dislocations can be reduced in a closed manner in the emergency department with the use of local anesthesia and procedural sedation. After appropriate anesthesia and analgesia, the reduction maneuver is completed with the patient’s knee flexed to 90° to release tension from the gastrocnemius. With an assistant providing counter-traction, the foot deformity is recreated, longitudinal traction is applied, and the foot is then directed into its appropriate position with the foot in plantarflexion to open the subtalar joint. This should be completed without excessive force. Manual pressure can be applied on the talar head to aid in reduction. Following confirmation of reduction, the leg should be immobilized and a computed tomography (CT) scan obtained to confirm absence of osteochondral fractures and stability of the subtalar joints. Neurologic and vascular status of the foot should be assessed and documented pre- and postreduction.
No consensus exists in the literature as to which type of immobilization should be used. Treatment has been described with initial nonweight bearing in a short posterior splint, short leg cast, and long leg cast lasting between 4 and 6 weeks.1,3,9,11,18,19 Care must be taken when choosing the method of immobilization with regard to the patient’s swelling. It may be prudent to initially immobilize the patient in a posterior splint and change to cast immobilization once the swelling has begun to subside. Patients can begin partial weight bearing at that time. This course is altered by the presence of associated fractures of the foot and ankle. There has been support in the literature for early range of motion after an initial period of immobilization of 3 weeks to minimize the incidence of fibrosis.20 The ability to engage in this aggressive rehabilitation is due to the inherent stability of the subtalar and midtarsal joints postreduction.
Failed reduction by closed means occurs in 10% to 20% of cases of medial and lateral dislocations.3,21 A number of anatomic explanations exist for failed closed reduction. Historically, irreducible medial dislocations have been attributed “buttonholing” of the talar head through the extensor digitorum brevis, extensor retinaculum, talonavicular ligaments, or joint capsule. Talonavicular impaction and interposition of the extensor digitorum brevis have also been implicated. Heck et al22 found in a cadaveric study that the talar head tended to come to rest dorsal to the extensor digitorum brevis, making buttonholing unlikely. They observed entrapment of the extensor retinaculum and talonavicular impaction and also obstruction by the deep peroneal nerve, which was not previously reported.
The posterior tibial tendon, talar head impaction, and entrapment of the joint capsule have been described as causes of irreducible lateral dislocations. In 1954, Leitner23 initially proposed a mechanism by which the flexor retinaculum is disrupted, allowing the tendon to drape over the talar head and preventing reduction. This was later challenged by Mulroy,17 who presented a case of an irreducible lateral dislocation where the flexor retinaculum was still intact. Subsequent cadaveric studies have supported Leitner’s23 original theory.24

Results

Outcomes following closed reduction of isolated subtalar dislocation have been favorable. Several long-term studies with long-term follow-up have shown minimal disability despite significant loss of subtalar motion.3,7 As much as 80% of subtalar dislocations have restriction in motion after healing, and 50% to 80% have radiographic evidence of post-traumatic subtalar arthritis.25 Associated fractures are common in nearly 50% of cases and are most often intra-articular, osteochondral fractures.3,6
Monson and Ryan7 reported a series of 11 patients with medial subtalar dislocations treated over a 9-year span. They found minimal disability, pain mainly localized to the talonavicular joint, and significant loss of subtalar motion.
DeLee and Curtis3 described 17 subtalar dislocations, 3 open, that were treated with immobilization in a short leg cast for 3 weeks when there was no associated fracture. They also found a significant decrease in subtalar motion in all patients, especially those with associated fractures immobilized >6 weeks. This is despite the early mobilization of the subtalar joint as described by McKeever.20
Zimmer and Johnson9 described 9 patients treated for subtalar dislocations, most commonly resulting from a fall, with a 56-month average follow-up. Patients were treated with cast immobilization for an average of 6 weeks. Five patients reported a sensation of instability, and radiographs showed degenerative changes in 2 patients with no incidence of avascular necrosis. As a result, they proposed lengthier immobilization for younger, more active patients, along with inversion and eversion strengthening.9
Perugia et al1 reported a large series of 45 patients who sustained closed subtalar dislocations with an average follow-up of 7.5 years. All patients were treated with closed reduction and placed in a short leg cast, and CT scans were obtained. Patients were immobilized and nonweight bearing for 4 weeks, after which aggressive rehabilitation was performed. The patients had a mean AOFAS score of 83.8 and reported minimal or no limitation in daily or recreational activity. The patients reported discomfort on stairs, inclines, and uneven ground. Only 1 patient went on to subtalar fusion due to instability and pain.1
Goldner et al19 described long-term follow-up of 15 Gustilo grade III open subtalar dislocations treated with urgent irrigation and debridement followed by reduction and immobilization, nonweight bearing in an above-the-knee cast initially for 4 to 6 weeks. They were then transitioned into a below-the-knee walking cast for an additional 6 weeks. Seven of these patients were unstable following reduction, and a Steinman pin was placed across the subtalar joint. The early course was complicated by wound infections in 2 patients and causalgia in 7 lateral dislocations, where the tibial nerve was observed to be injured. Five patients were observed to have osteonecrosis of the talus that required ankle arthrodesis in 1 patient, and 2 patients sustained large osteochondral fractures at the subtalar joint that required subsequent subtalar fusion as late complications. All patients demonstrated loss of motion at the ankle, subtalar joint, and midfoot in addition to difficulty walking on uneven ground.19
Finally, Bibbo et al16 presented a series of 25 patients with acute subtalar dislocation, the majority of whom sustained their injury through a high-energy mechanism. They found an association between high-energy mechanism and open dislocation, but found no correlation between direction of dislocation and mechanism of injury. A high radiographic incidence of degenerative changes was noted, and a significant decrease in AOFAS score was observed.

Authors’ Preferred Method

When presented with a patient with an acute dislocation of the subtalar joint, especially one that resulted from a high-energy mechanism such as a motor vehicle accident or fall from a height, care must be taken to ensure a proper evaluation as described by ATLS protocol. In addition, a complete secondary survey and judicious evaluation for associated musculoskeletal injuries must be completed. Following the initial assessment, thorough evaluation of the patient’s neurovascular status and skin must performed, including appropriate radiographic imaging. Closed injuries should be promptly reduced under either local anesthesia or procedural sedation, followed by repeat radiographic assessment and CT scans to evaluate for associated osteochondral fractures.
Failed closed reduction attempts are brought to the operating room, where closed reduction should be attempted under general anesthesia. Failure to achieve closed reduction in this setting necessitates open reduction with removal of any impediments to reduction should this attempt fail. The reduction is tested for stability, and additional percutaneous fixation is added as necessary. Open dislocations are urgently brought to the operating room, where irrigation and debridement are performed with copious pulsatile lavage, reduction, and closure of the wound. Standard intravenous antibiotics and tetanus vaccination are administered at presentation and for a course of 48 hours.
Open dislocations and those associated with significant swelling are initially immobilized in a posterior splint to aid in skin evaluation. Subsequently and following those successfully reduced in a closed fashion, the patient is placed nonweight bearing into a below-the-knee cast for 4 weeks, followed by progressive mobilization and rehabilitation.

Conclusion

Subtalar dislocations are rare, accounting for only 1% to 2% of all dislocations. The majority of these cases can be treated in a closed manner with a period of nonweight bearing and immobilization with satisfactory results. Occasionally, especially in cases as a result of high-energy trauma and open dislocations, open reduction is necessary. While radiographic evidence of subtalar degenerative change is often present, rarely is the patient symptomatic. Subtalar arthrodesis is an option for patients with refractory subtalar pain and instability.

References

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Authors

Drs Horning and DiPreta are from the Division of Orthopedic Surgery, Albany Medical Center, Albany, New York.
Drs Horning and DiPreta have no relevant financial relationships to disclose.
Correspondence should be addressed to: John DiPreta, MD, Division of Orthopedic Surgery, 1367 Washington Ave, Albany, NY 12206.
doi: 10.3928/01477447-20091020-17

Wednesday, December 30, 2009

Stable distal radius fracture fixation possible with threaded pinning method


With this method, fractured wrists typically reached over 90% normal motion by 1 year postop.
By Susan M. Rapp
ORTHOPEDICS TODAY 2009; 29:34
A new distal radius fracture fixation technique developed to reduce the malunion rate that often accompanies traditional cast immobilization fixation effectively restored 60% to 80% of wrist arc of motion by 3 months and over 90% of normal motion by 1 year postoperatively, according to the surgeon who developed the technique.
The less-invasive pinning technique achieved stability of distal radius fractures, including comminuted ones, according to developer John S. Taras, MD, of Philadelphia.
The technique typically involves two threaded variable-length cannulated T-Pins (Union Surgical), which act like a screw to gain good purchase of the bone and fix the fragments. The T-Pin is a more stable alternative to the smooth pins hand surgeons usually place in various configurations to treat these fractures, Taras said.
Imaging helpful
John S. Taras, MD
John S. Taras
“This is done through small incisions with visualization of the bone to protect against damage or irritation to the radial sensory nerve or adjacent tendons,” Taras said in describing his surgical technique at a symposium on distal radius fractures at the American Academy of Orthopaedic Surgeons annual meeting.
“Fluoroscopy imaging is really essential to do this technique,” he said, noting the importance of protecting the tissue in the area and avoiding extensor pollicis longus (EPL) ruptures and other complications.
Advantages of the new fixation approach include the ability to perform the technique under local anesthesia, insertion of the pins over guide wires for accuracy, and the fact that the driver portion of the pin easily breaks away manually, precluding the need to use other tools or disturbance of the implant once it is in place, Taras said.

Early range of motion

Among the 71 distal radius fractures Taras treated with the technique, three complications occurred by the 1-year follow-up, including one loss of reduction, an EPL rupture and a case of reflex sympathetic dystrophy.
“The early range of motion restoration was good,” he said.
By 1 year postoperative, the restored arc of motion in most of the wrists Taras treated reached over 90% of preoperative motion.
T-Pins
Typical placement of two T-Pins for fixing a distal radius fracture is shown in this posterior-anterior radiograph.
T-Pins radial styloid
The surgeon has inserted two T-Pins from the radial styloid to stable fracture fixation.
Images: Taras JS

Maintains reduction

In addition, “The reduction achieved in the operating room was preserved within the acceptable parameters,” Taras said.
Fracture reductions performed in the emergency room had 11° to 12° dorsal angulation with -1 mm ulnar variance. After treatment these parameters measured 5° volar of tilt and +0.7 mm of ulnar variance.
The technique utilizing two pins placed through the radial styloid is also indicated for moderately comminuted fractures, but for more severely comminuted fractures or those in osteoporotic patients Taras has successfully implanted two T-Pins using a cross-pin technique.
T-Pin over guidewire
John S. Taras, MD, inserts the T-Pin over the guidewire in a patient’s wrist. He usually inserts two threaded, variable-length cannulated T-Pins to gain good purchase of bone.
T-Pin minimally invasive
In this minimally invasive method for fixing distal radius fractures, the T-Pin acts like a screw, according to Taras. He has treated at least 71 distal radius fractures with the technique.

Effective option

Although level 1 and level 2 clinical studies have not been conducted into the T-Pin fixation method, Taras found it provides an effective option that is associated with less surgical trauma and permits patients to move their wrists earlier.
Therapy is initiated under the guidance of a hand therapist for active and passive digital range of motion, edema control and gentle wrist active range of motion at the first postoperative visit.
“Restoring range of motion, because there is not a lot of surgical trauma, can proceed relatively quickly, but will vary based on patients’ response to the fracture,” he said.
Pins can stay in or come out. Taras said he has left most of them in place without any problems.
For more information:
John S. Taras, MD, can be reached at The Philadelphia and South Jersey Hand Centers, 834 Chestnut St., Suite G114, Philadelphia, PA 19107; 215-521-3004; e-mail:jstaras@handcenters.com. He receives payments for presentations from Integra Life Sciences, research or institutional support from Axogen and was a founder of Union Surgical.
  • Reference:
Taras JS. New fixation options. Symposium L: Distal radius fractures: new concepts in treatment. Presented at the American Academy of Orthopaedic Surgeons 76th Annual Meeting. Feb. 25-28, 2009. Las Vegas.