Effect of loading and fracture motions on diaphyseal tibial fractures

Evaluation of a New Patellar Tendon Bearing Brace With Offloading Monitoring and Adjustability: A Pilot Study

Background and Aims

The patellar tendon-bearing (PTB) brace is a crucial device designed to lessen axial forces on the tibia. The newly designed PTB brace allows clinicians to measure offloading amount in the realtime. This study aimed to explore the relationship between a rise in displacement between the foot plate and calf shells of this new PTB brace and changes in the amount of offloading on the tibia.

Methods

This pilot study used a sample of five individuals with midshaft tibia fractures to investigate the effectiveness of the PTB brace under different conditions. The PTB brace was tested in six different conditions, with the displacement between the foot plate and calf shells varying in increments of 0.5 cm, from 1 cm to 3.5 cm.

Results

The new PTB brace provided varying levels of offloading, ranging from 22% to 38%. As the vertical distance between the calf shells and foot plate increased, the offloading levels also increased significantly. The study observed significant differences in weight reduction (p = 0.02) and offloading percentages (p = 0.048) when comparing 1 cm and 1.5 cm displacement.

Conclusion

The findings suggest that maintaining a distance of 1.5 cm or more between the calf shells and foot plate is effective in reducing weight and offloading on the tibia. These results have important implications for clinicians using PTB braces to treat tibia fractures, highlighting the importance of adjusting the displacement of the PTB brace to optimize patient outcomes.

Significance of mechanical loading in bone fracture healing, bone regeneration, and vascularization

In 1892, J.L. Wolff proposed that bone could respond to mechanical and biophysical stimuli as a dynamic organ. This theory presents a unique opportunity for investigations on bone and its potential to aid in tissue repair. Routine activities such as exercise or machinery application can exert mechanical loads on bone. Previous research has demonstrated that mechanical loading can affect the differentiation and development of mesenchymal tissue. However, the extent to which mechanical stimulation can help repair or generate bone tissue and the related mechanisms remain unclear. Four key cell types in bone tissue, including osteoblasts, osteoclasts, bone lining cells, and osteocytes, play critical roles in responding to mechanical stimuli, while other cell lineages such as myocytes, platelets, fibroblasts, endothelial cells, and chondrocytes also exhibit mechanosensitivity. Mechanical loading can regulate the biological functions of bone tissue through the mechanosensor of bone cells intraosseously, making it a potential target for fracture healing and bone regeneration. This review aims to clarify these issues and explain bone remodeling, structure dynamics, and mechano-transduction processes in response to mechanical loading. Loading of different magnitudes, frequencies, and types, such as dynamic versus static loads, are analyzed to determine the effects of mechanical stimulation on bone tissue structure and cellular function. Finally, the importance of vascularization in nutrient supply for bone healing and regeneration was further discussed.

Effective Treatment of Femur Diaphyseal Fracture with Compression Plate - A Finite Element and In Vivo Study Comparing the Healing Outcomes of Nailing and Plating

BACKGROUND

The rigidity in osteosynthesis causes primary healing, and it takes longer to heal. The flexibility provided to the fixation allows micromotion between fragments which accelerates secondary healing.

METHODS

In this study, the healing outcomes of nailing and plating in different fixation stabilities were investigated and compared by using a finite element tool. The clinical observational study was also performed to verify the results of the finite element analysis. The nonlinear contact analysis was performed on 5 different fixation configurations capturing nail and plate in immediate post-surgery.

RESULTS

The finite element analysis results showed that flexibility instead of rigidity in interlock nail implantation increases the axial and shear micromotion near the fracture site by 47.4% (P < 0.05) and 12.4% (P < 0.05), respectively. For LCDCP implantation, the flexible fixation increases the axial and shear micromotion near fracture site by 75.7% (P < 0.05) and 25.3% (P < 0.05), respectively.

CONCLUSION

Our findings suggest that flexible fixations of interlock nail and LCDCP provide a preferred mechanical environment for healing, and hence, the LCDCP in flexible mode can be an effective alternative to interlock nail for the femur diaphyseal fracture.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s43465-022-00795-1.

Concepts and clinical aspects of active implants for the treatment of bone fractures

Nonunion is a complication of long bone fractures that leads to disability, morbidity and high costs. Early detection is difficult and treatment through external stimulation and revision surgery is often a lengthy process. Therefore, alternative diagnostic and therapeutic options are currently being explored, including the use of external and internal sensors. Apart from monitoring fracture stiffness and displacement directly at the fracture site, it would be desirable if an implant could also vary its stiffness and apply an intervention to promote healing, if needed. This could be achieved either by a predetermined protocol, by remote control, or even by processing data and triggering the intervention itself (self-regulated 'intelligent' or 'smart' implant). So-called active or smart materials like shape memory alloys (SMA) have opened up opportunities to build active implants. For example, implants could stimulate fracture healing by active shortening and lengthening via SMA actuator wires; by emitting pulses, waves, or electromagnetic fields. However, it remains undefined which modes of application, forces, frequencies, force directions, time durations and periods, or other stimuli such implants should ideally deliver for the best result. The present paper reviews the literature on active implants and interventions for nonunion, discusses possible mechanisms of active implants and points out where further research and development are needed to build an active implant that applies the most ideal intervention. STATEMENT OF SIGNIFICANCE: Early detection of delays during fracture healing and timely intervention are difficult due to limitations of the current diagnostic strategies. New diagnostic options are under evaluation, including the use of external and internal sensors. In addition, it would be desirable if an implant could actively facilitate healing ('Intelligent' or 'smart' implant). Implants could stimulate fracture healing via active shortening and lengthening; by emitting pulses, waves, or electromagnetic fields. No such implants exist to date, but new composite materials and alloys have opened up opportunities to build such active implants, and several groups across the globe are currently working on their development. The present paper is the first review on this topic to date.

Utility of cement injection to stabilize split-depression tibial plateau fracture by minimally invasive methods: A finite element analysis

BACKGROUND

Treatment for fractures of the tibial plateau is in most cases carried out by stable fixation in order to allow early mobilization. Minimally invasive technologies such as tibioplasty or stabilization by locking plate, bone augmentation and cement filling (CF) have recently been used to treat this type of fracture. The aim of this paper was to determine the mechanical behavior of the tibial plateau by numerically modeling and by quantifying the mechanical effects on the tibia mechanical properties from injury healing.

METHODS

A personalized Finite Element (FE) model of the tibial plateau from a clinical case has been developed to analyze stress distribution in the tibial plateau stabilized by balloon osteoplasty and to determine the influence of the cement injected. Stress analysis was performed for different stages after surgery.

FINDINGS

Just after surgery, the maximum von Mises stresses obtained for the fractured tibia treated with and without CF were 134.9 MPa and 289.9 MPa respectively on the plate. Stress distribution showed an increase of values in the trabecular bone in the treated model with locking plate and CF and stress reduction in the cortical bone in the model treated with locking plate only.

INTERPRETATION

The computed results of stresses or displacements of the fractured models show that the cement filling of the tibial depression fracture may increase implant stability, and decrease the loss of depression reduction, while the presence of the cement in the healed model renders the load distribution uniform.

Carbon-Fibre-Reinforced PEEK radiolucent intramedullary nail for humeral shaft fracture fixation: technical features and a pilot clinical study

PURPOSE

This prospective pilot study investigated the safety and efficacy of a novel radiolucent intramedullary nail (IMN) made of Carbon-Fibre-Reinforced Polyaryl-Ether-Ether-Ketone (CFR-PEEK) for humeral shaft fracture fixation.

STUDY DESIGN

A prospective, single-arm, four-centre study.

PATIENTS AND METHODS

A total of 46 patients with 46 humeral fractures classified as 12 A-B were treated with a novel CFR-PEEK IMN and followed for 12 months.

RESULTS

Most of the patients (65%) were female; the mean age was 65 ± 17 years. The average operating time was 66.75 ± 19.84 minutes and X-ray exposure was 104.11 ± 98.01 seconds. All patients postoperatively reported selflimiting shoulder pain and three patients developed iatrogenic transient radial palsy. Two patients required repositioning of the implant. No implant-related complications were observed. Radiological consolidation was achieved in all 43 patients who completed the 12-month follow-up.

CONCLUSIONS

The CFR-PEEK IMN is user-friendly and safe. Its bone-matching elastic modulus seems to contribute to its clinical efficacy. This, together with compatibility with modern imaging techniques, can be considered a further evolution of IMN designed to stabilise humeral shaft fractures.

Comparison of 4 Methods for Dynamization of Locking Plates: Differences in the Amount and Type of Fracture Motion

BACKGROUND

Decreasing the stiffness of locked plating constructs can promote natural fracture healing by controlled dynamization of the fracture. This biomechanical study compared the effect of 4 different stiffness reduction methods on interfragmentary motion by measuring axial motion and shear motion at the fracture site.

METHODS

Distal femur locking plates were applied to bridge a metadiaphyseal fracture in femur surrogates. A locked construct with a short-bridge span served as the nondynamized control group (LOCKED). Four different methods for stiffness reduction were evaluated: replacing diaphyseal locking screws with nonlocked screws (NONLOCKED); bridge dynamization (BRIDGE) with 2 empty screw holes proximal to the fracture; screw dynamization with far cortical locking (FCL) screws; and plate dynamization with active locking plates (ACTIVE). Construct stiffness, axial motion, and shear motion at the fracture site were measured to characterize each dynamization methods.

RESULTS

Compared with LOCKED control constructs, NONLOCKED constructs had a similar stiffness (P = 0.08), axial motion (P = 0.07), and shear motion (P = 0.97). BRIDGE constructs reduced stiffness by 45% compared with LOCKED constructs (P < 0.001), but interfragmentary motion was dominated by shear. Compared with LOCKED constructs, FCL and ACTIVE constructs reduced stiffness by 62% (P < 0.001) and 75% (P < 0.001), respectively, and significantly increased axial motion, but not shear motion.

CONCLUSIONS

In a surrogate model of a distal femur fracture, replacing locked with nonlocked diaphyseal screws does not significantly decrease construct stiffness and does not enhance interfragmentary motion. A longer bridge span primarily increases shear motion, not axial motion. The use of FCL screws or active plating delivers axial dynamization without introducing shear motion.

Monitoring Healing Progression and Characterizing the Mechanical Environment in Preclinical Models for Bone Tissue Engineering

The treatment of large segmental bone defects remains a significant clinical challenge. Due to limitations surrounding the use of bone grafts, tissue-engineered constructs for the repair of large bone defects could offer an alternative. Before translation of any newly developed tissue engineering (TE) approach to the clinic, efficacy of the treatment must be shown in a validated preclinical large animal model. Currently, biomechanical testing, histology, and microcomputed tomography are performed to assess the quality and quantity of the regenerated bone. However, in vivo monitoring of the progression of healing is seldom performed, which could reveal important information regarding time to restoration of mechanical function and acceleration of regeneration. Furthermore, since the mechanical environment is known to influence bone regeneration, and limb loading of the animals can poorly be controlled, characterizing activity and load history could provide the ability to explain variability in the acquired data sets and potentially outliers based on abnormal loading. Many approaches have been devised to monitor the progression of healing and characterize the mechanical environment in fracture healing studies. In this article, we review previous methods and share results of recent work of our group toward developing and implementing a comprehensive biomechanical monitoring system to study bone regeneration in preclinical TE studies.

Biomechanical assessment of composite versus metallic intramedullary nailing system in femoral shaft fractures: A finite element study

BACKGROUND

Intramedullary nails are the primary choice for treating long bone fractures. However, complications following nail surgery including non-union, delayed union, and fracture of the bone or the implant still exist. Reducing nail stiffness while still maintaining sufficient stability seems to be the ideal solution to overcome the abovementioned complications.

METHODS

In this study, a new hybrid concept for nails made of carbon fibers/flax/epoxy was developed in order to reduce stress shielding. The mechanical performance of this new implant in terms of fracture stability and load sharing was assessed using a comprehensive non-linear FE model. This model considers several mechanical factors in nine fracture configurations at immediately post-operative, and in the healed bone stages.

RESULTS

Post-operative results showed that the hybrid composite nail increases the average normal force at the fracture site by 319.23N (P<0.05), and the mean stress in the vicinity of fracture by 2.11MPa (P<0.05) at 45% gait cycle, while only 0.33mm and 0.39mm (P<0.05) increases in the fracture opening and the fragments' shear movement were observed. The healed bone results revealed that implantation of the titanium nail caused 20.2% reduction in bone stiffness, while the composite nail lowered the stiffness by 11.8% as compared to an intact femur.

INTERPRETATION

Our results suggest that the composite nail can provide a preferred mechanical environment for healing, particularly in transverse shaft fractures. This may help bioengineers better understand the biomechanics of fracture healing, and aid in the design of effective implants.

Pediatric physeal slide-traction plate fixation for comminuted distal femur fractures in children

BACKGROUND

Operative stabilization without inhibiting epiphyseal growth of pediatric comminuted distal femur fractures presents specific challenges. The purpose of this study was to evaluate the clinical efficacy of pediatric physeal slide-traction plate (PPSP) fixation for comminuted distal femur fractures in children.

METHODS

We prospectively followed 16 children who were managed PPSP for the treatment of comminuted distal femur fractures between 2005 and 2009. There were 9 boys with a mean age of 10.4 years (range, 8 to 14 y) and 7 girls with a mean age of 9.9 years (range, 6 to 12 y). The mean follow-up was 36.4 months (range, 18 to 54 mo).

RESULTS

There were no intraoperative complications related to this technology. All patients were healed, and the mean time was 10.1 weeks (range, 8 to 13 wk). X-ray analysis of the injured limb revealed that the PPSP could be extended as the femur grew, with a mean sliding length of 5.6 mm (range, 3 to 15 mm). All patients had excellent final outcomes, and had the plates removed with no noted complications except 1 patient who had valgus malalignment of 10 degrees at 6 months after the plate removal, which was of no clinical concern and required no intervention.

CONCLUSIONS

These findings suggest that PPSP is a safe and effective treatment for children with comminuted distal femur fractures that can be extended as the epiphyseal plate grows with reliable internal fixation.

LEVEL OF EVIDENCE

Therapeutic level IV.

Rap system of stress stimulation can promote bone union after lower tibial bone fracture: a clinical research

BACKGROUND

Lower tibial bone fracture may easily cause bone delayed union or nonunion because of lacking of dynamic mechanical load.

OBJECTIVE

Research Group would design a new instrument as Rap System of Stress Stimulation (RSSS) to provide dynamic mechanical load which would promote lower tibial bone union postoperatively.

METHODS

This clinical research was conducted from January 2008 to December 2010, 92 patients(male 61/female 31, age 16-70 years, mean 36.3 years) who suffered lower tibial bone closed fracture were given intramedullary nail fixation and randomly averagely separated into experimental group and control group(according to the successively order when patients went for the admission procedure). Then researchers analysed the clinical healing time, full weight bearing time, VAS (Visual Analogue Scales) score and callus growth score of Lane-Sandhu in 3,6,12 months postoperatively. The delayed union and nonunion rates were compared at 6 and 12 months separately.

RESULTS

All the 92 patients had been followed up (mean 14 months). Clinical bone healing time in experimental group was 88.78±8.80 days but control group was 107.91±9.03 days. Full weight bearing time in experimental group was 94.07±9.81 days but control group was 113.24±13.37 days respectively (P<0.05). The delayed union rate in 6 months was 4.3% in experimental group but 10.9% in control group(P<0.05). The nonunion rate in 12 months was 6.5% in experimental group but 19.6% in control group(P<0.05). In 3, 6, 12 months postoperatively, VAS score and Lane-Sandhu score in experimental group had more significantly difference than them in control group.

CONCLUSIONS

RSSS can intermittently provide dynamic mechanical load and stimulate callus formation, promote lower tibial bone union, reduce bone delayed union or nonunion rate. It is an adjuvant therapy for promoting bone union after lower tibial bone fracture.

Effects of a pediatric physeal slide-traction plate on fracture healing: an experimental study in a goat model

BACKGROUND

It has been an intractable issue for the orthopaedic surgeons to treat pediatric epiphyseal injury and surrounding bone fracture using Kirschner wires and screws, etc. Earlier research has indicated that pediatric physeal slide-traction plate (PPSP) can fix bone fracture without restricting growth. However, it is not clear whether this material can be clinically used to treat pediatric epiphyseal injury and surrounding bone fracture.

METHODS

The PPSP and standard plate (SP) were designed to configure to the femoral condyle. Twelve premature female goats were enrolled in this study. Fracture models were successfully established on goats, on which the right femurs were fixed with SP, and the left femurs were fixed with PPSP. Radiographic analysis and biomechanical tests were done at 4 and 8 weeks after surgery.

RESULTS

The callus gray density increased with time going on in each group, at the same postoperational time point, the PPSP group was higher than that of the SP group. The difference between PPSP group and SP group was statistically significant at the same stage (P<0.01). The biomechanical tests showed that the PPSP group was stronger than the SP group in anticompression, antibending, and antitorsion at the same stage (P<0.05). In addition, it was shown through the radiographic analysis that PPSP extended accordingly as the epiphyseal plate grows, and the epiphyseal morphology was considered normal all the time. However, epiphyseal premature closure and angular deformity were observed in the samples of the SP group.

CONCLUSIONS

PPSP contributed greatly to healing of bone fracture with increased callus density and callus strength in the early stage, and did not restrict the growth of the epiphyseal plate. It may be clinically applied in the treatment of pediatric epiphyseal injury and surrounding bone fracture in the future.

LEVEL OF EVIDENCE

Therapeutic level II.

Toe-touch weight bearing: myth or reality?

Toe-touch weight bearing and partial weight bearing are commonly prescribed orders. The purpose of this study is to evaluate the validity of toe-touch weight bearing and partial weight bearing regimens. Twenty-five orthopedic surgeons participated in the study. They were asked to answer a questionnaire regarding toe-touch weight bearing and partial weight bearing definitions, and were asked to bear weight partially according to the accepted definitions of each order. Weight bearing on the affected limb was measured by the SmartStep System (Andante Medical Devices, Ltd, Omer, Israel). There was a 40% success rate for toe-touch weight bearing as measured by kilograms and 58% as measured by percentage of body weight. There was a 22% success rate for partial weight bearing as measured by kilograms and 50% success rate as measured by percentage of body weight. For toe-touch weight bearing as measured by kilograms, 52% exerted a mean 15.9 kg more than the maximum. For partial weight bearing as measured by kilograms, 64% exerted too much weight with an average of 14.2 kg more than the maximum. There was a significantly higher success rate for the percentage of body weight order than the kilogram order. The partial weight bearing order with the percent body weight order had a lower mean deviation from desired performance. This study and others demonstrate the need for standardization of weight bearing orders.

A prospective study comparing attempted weight bearing in fiberglass below-knee casts and prefabricated pneumatic braces

Partial weight bearing is commonly advised after fracture of the lower extremity. Research has determined this to be inaccurate both in its instruction and its reproducibility. Many trauma departments are commonly using alternatives to plaster in the splintage of fractures, such as fiberglass and the prefabricated pneumatic braces. This study's null hypothesis is that there is no difference between partial weight bearing through a fiberglass cast as compared with a pneumatic walker. A prospective study was conducted in our department including all patients who had metatarsal or ankle fractures and could partially weight bear. Patients were excluded if they were not allowed to bear weight, had received operative fixation of their fracture, or were younger than age 16 years. The patients' total weight was measured first, and then they were trained to place 50% of their weight through the splinted limb. Three measurements were taken of their attempted weight bearing at 50%, and they were blinded to the results. Over a 16-month period, 117 patients were enrolled for this study: 72 in the pneumatic walker group and 45 in the fiberglass group. There was no significant difference in sex, age, or fracture type. There was a significant difference in percentage of weight placed through the splinted limb, with the pneumatic brace group placing much greater force than the fiberglass group. This may have been caused by altered proprioception from the walker. It is important to realize this when prescribing partial weight bearing in a particular splint as this may result in avoidable complications.

A biodegradable scaffold for the treatment of a diaphyseal bone defect of the tibia

The aim of this study was to compare angiogenesis and osteogenesis occurring within 8.0 mm diaphyseal defects created in canine tibiae treated using autograft or a biodegradable bone scaffold. All tibiae were reamed to 7.0 mm and fixed with a 6.5-mm statically locked intramedullary nail. Each of the 18 canines as allotted to one of three treatment groups: (1) left empty (N = 5), (2) treated with iliac crest autograft (N = 6), or (3) treated with a PLGA/calcium phosphate biodegradable scaffold (N = 7). Fluorescent markers were given at successive time periods: calcein green at 6 weeks, xylenol orange at 9 weeks, and tetracycline at 11 and 14 weeks. Animals were sacrificed at 15 weeks and their legs were perfused with a radio opaque compound. Samples were analyzed using Micro CT, bright-field microscopy and fluorescent microscopy. Scaffold samples were found to have significantly greater bone formation (p = 0.015) and blood vessel formation (p < 0.001) at their osteotomy sites than autograft samples. Bone formation rate in the periosteum was significantly greater in the autograft samples than the scaffold samples for all time periods. Bone formation at the osteotomy site was found to be significantly greater when associated with greater blood vessel formation (p = 0.026). The PLGA/calcium phosphate biodegradable scaffold we have employed supports angiogenesis within a segmental tibial defect that has adequate soft tissue coverage.

Comparison of percutaneous dorsal versus volar fixation of scaphoid waist fractures using a computer model in cadavers

PURPOSE

Percutaneous screw fixation (PSF) is widely used to treat acute nondisplaced scaphoid waist fractures. PSF can be performed through a volar or dorsal approach. The aim of our study was to compare a dorsal versus volar surgical approach for PSF according to the sagittal orientation of the waist fracture (B1 or B2 in Herbert and Fisher's classification scheme, in which B1 and B2 designate, respectively, oblique and transverse nondisplaced scaphoid waist fractures) on computer modeling of cadaver wrists.

METHODS

We used 12 upper limbs, and for each wrist we performed 3 computed tomography scans in maximal flexion, neutral position, and maximal extension. For each position, a parasagittal slice corresponding to the plane of ideal screw placement was obtained by numerical reconstruction. On each slice, we modeled B1- and B2-type fractures and the placement of the corresponding screws (S1 and S2) inserted through a volar or dorsal approach. Optimal screw orientation was perpendicular to the fracture. For each configuration, we measured the angle between the S1 screw and B1 fracture, which we designated V1 when modeling volar PSF and D1 when modeling dorsal PSF. Similarly, we measured angles V2 and D2.

RESULTS

For B2 fractures, virtual screw placement perpendicular to the fracture was achieved equally well with the 2 approaches. For B1 fractures, the virtual screw could not be placed perpendicular to the fracture with either approach, but the dorsal approach with maximal wrist flexion allowed the best screw placement.

CONCLUSIONS

For B2 fractures, the dorsal and volar approaches allow optimal virtual screw placement, and the choice of the approach depends on the surgeon's preference. For B1 fractures, we recommend the dorsal approach.

Quantification of fracture healing from radiographs using the maximum callus index

Callus formation and growth are an essential part of secondary fracture healing. Callus growth can be observed radiographically and measured using the "Callus Index," which is defined as the maximum diameter of the callus divided by the diameter of the bone. We compared three groups of patients with tibial fractures treated by external fixation, intramedullary nailing, and casting to assess the validity of using serial measurements of callus index as a measure of fracture healing. When callus index was plotted against time for each patient, the point at which the fracture began to remodel, indicated by the highest point of the curve, was observed as a consistent feature regardless of fixation method. This occurred on average at 2(1/2) weeks after plaster cast removal (14 weeks post injury), 5 weeks after external fixator removal (22 weeks post injury), and 27 weeks post injury for the intramedullary nailed fractures. Because remodeling only occurs once the fracture is stable, a peak in callus index is a reliable sign that the fracture has united. Serial measurements of callus index would therefore appear to offer a simple method of quantifying secondary fracture healing regardless of the treatment method used.

LEVEL OF EVIDENCE

Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Monitoring the mechanical properties of healing bone

Fracture healing is normally assessed through an interpretation of radiographs, clinical evaluation, including pain on weight bearing, and a manual assessment of the mobility of the fracture. These assessments are subjective and their accuracy in determining when a fracture has healed has been questioned. Viewed in mechanical terms, fracture healing represents a steady increase in strength and stiffness of a broken bone and it is only when these values are sufficiently high to support unrestricted weight bearing that a fracture can be said to be healed. Information on the rate of increase of the mechanical properties of a healing bone is therefore valuable in determining both the rate at which a fracture will heal and in helping to define an objective and measurable endpoint of healing. A number of techniques have been developed to quantify bone healing in mechanical terms and these are described and discussed in detail. Clinical studies, in which measurements of fracture stiffness have been used to identify a quantifiable end point of healing, compare different treatment methods, predictably determine whether a fracture will heal, and identify factors which most influence healing, are reviewed and discussed.

Angle stable interlocking screws improve construct stability of intramedullary nailing of distal tibia fractures: a biomechanical study

INTRODUCTION

Intramedullary nailing is the treatment of choice for most displaced tibial shaft fractures. The ability to maintain a mechanically stable fixation becomes more difficult the further the fracture extends distally or proximally or when unreamed tibial nails are used. We assumed that a new angular stable locking option would provide improved stability and reduced interfragmentary movements in a distal tibia in vitro fracture model.

MATERIALS AND METHODS

Left and right bones of 8 pairs of human cadaveric tibiae were randomly assigned to either a group with conventional locked or a group with angular stable locked intramedullary nails. Nails of 10-mm-diameter were used after reaming up to 11 mm. A transverse distal osteotomy was performed and the specimens were tested mechanically under eccentric axial load. A video optical measurement system was used to determine the angular displacement of the osteotomy gap during loading.

RESULTS

Construct stiffness, maximum load of the bone-nail construct and gap angle at 0.5 kN load were measured. The group with the angular stable locking option showed significantly higher stiffness values and reduced fracture gap motion compared to the group with conventional locked nails.

DISCUSSION

A new angular stable locking option of intramedullary nails provides higher stability in terms of construct stiffness and reduced interfragmentary movements in a distal tibia in vitro fracture model.

Fractures of the middle third of the tibia treated with a functional brace

It generally is accepted that fractures of the tibia located in the proximal and distal thirds tend to angulate more than midshaft fractures when treated with intramedullary nails. We therefore compared the angular deformities and final shortening of 434 closed fractures located in the middle third of the tibia treated with a functional brace with those in fractures in the proximal and distal thirds treated in the same manner. Ninety-seven percent in the middle third healed with 8 degrees or less angulation in the mediolateral plane, which was a higher percentage than we had experienced in distal and proximal third fractures treated with this method. Nonunions occurred in four (0.9%) fractures. We found correlations between initial shortening, final shortening, initial displacement, final displacement, and time to brace with initial angulation and final angulation in the mediolateral and anteroposterior planes. The overall mean final shortening of the fractures located in the middle third was 4.3 mm. These experiences suggest satisfactory results can be obtained in most instances using a functional brace for management of closed fractures of the middle third of the tibia.

LEVEL OF EVIDENCE

Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Joint loading modality: its application to bone formation and fracture healing

Sports-related injuries such as impact and stress fractures often require a rehabilitation programme to stimulate bone formation and accelerate fracture healing. This review introduces a recently developed joint loading modality and evaluates its potential applications to bone formation and fracture healing in post-injury rehabilitation. Bone is a dynamic tissue whose structure is constantly altered in response to its mechanical environments. Indeed, many loading modalities can influence the bone remodelling process. The joint loading modality is, however, able to enhance anabolic responses and accelerate wound healing without inducing significant in situ strain at the site of bone formation or fracture healing. This review highlights the unique features of this loading modality and discusses its potential underlying mechanisms as well as possible clinical applications.

Combination of anorganic bovine-derived hydroxyapatite with binding peptide does not enhance bone healing in a critical-size defect in a rabbit model

Anorganic bovine-derived hydroxyapatite (ABM) in combination with binding peptid (P-15) has demonstrated the capacity to improve the healing of periodontal defects. This study evaluated the benefit of ABM/P-15 to promote healing of cortical long bone defects in a rabbit model. A 5-mm segmental bone defect was created in the femur and fixed with a plate. There were two treatment groups: no implant (n = 12) and ABM/P-15 (n = 12). At 4, 8, and 12 weeks, healing of the defect was evaluated with radiographs and histomorphometric examination of the treated femora. After 4 weeks, radiographs showed bone formation without signs of complete consolidation in three of four animals in the control group and two of four ABM/P-15 treated animals. At the later course of the treatment, no radiologic difference was evident between the treatment groups. Histomorphometric evaluation revealed an area of 1.29 +/- 0.11 mm(2) and 0.97 +/- 0.21 mm(2) of newly produced bone in animals of the control group and ABM/P-15 group after 4 weeks. After 8 and 12 weeks, animals in the control group had an area of 2.44 +/- 0.62 mm(2) and 2.5 +/- 0.2 mm(2) of newly produced bone within the osteotomy gap compared to 1.6 +/- 0.65 mm(2) and 1.56 +/- 0.27 mm(2) in the ABM/P-15 group (p = 0.0004). An enhanced or accelerated ingrowth of bone, as reported in previous studies, was not observed. Our results imply that the ABM/P-15 is not a suitable graft for the treatment of critical-sized segmental defects in long bones.

Knee loading accelerates bone healing in mice

Knee loading is an anabolic loading modality that applies lateral loads to the knee. This study shows that loads applied to the proximal tibial epiphysis stimulate healing of surgically generated wounds in the tibial diaphysis.

INTRODUCTION

Wound healing is sensitive to mechanical stimulation such as various forms of stress and different magnitudes of strain. Knee loading has been shown to induce anabolic responses to murine tibias and femora when a strain of 10-20 mustrain is applied at the site of new bone formation. The object of this study was to address a question: does knee loading accelerate closure of open wounds in the tibia?

MATERIAL AND METHODS

Fifty-three C57/BL/6 female mice were used. A surgical wound (0.5 mm in diameter) was generated in the left tibia (loaded) and the right tibia (sham-loaded control). From the fourth postoperative day, knee loading was performed to the left knee with a custom-made piezoelectric loader for 3 min/d for 3 consecutive days. The peak-to-peak force was 0.5 N. Animals were killed 1, 2, or 3 wk after surgery, and the healing process was evaluated with muCT, pQCT, and bone histomorphometry with calcein labeling.

RESULTS

The measured strain was <20 mustrain with 0.5-N force regardless of the presence or absence of surgical wounds. Compared with sham-loaded controls, the results showed load-driven acceleration of wound healing. First, muCT data revealed that knee loading reduced the size of surgical wounds by 13% (p < 0.01; 1 wk), 25% (p < 0.001; 2 wk), and 15% (p < 0.01; 3 wk). Second, pQCT data indicated that total BMD and BMC and cortical BMD and BMC were significantly increased in the third postoperative week. Last, bone histomorphometry revealed that bone formation was stimulated from the site proximal (close to the knee) to the wound.

CONCLUSIONS

The reparative and remodeling phases of wound healing were enhanced by loads applied to the knee without inducing significant in situ strain at the site of wounds. Noninvasive knee loading might therefore be useful clinically to stimulate bone healing in the entire tibia along its length (including cast immobilized wounds).

Conversion from temporary external fixation to definitive fixation: shaft fractures

Temporary external fixation is the most common method of initial stabilization of diaphyseal fractures in forward surgical hospitals. Once the patient arrives at a stable environment, usually the United States, the fracture is managed with intramedullary nailing, small-pin external fixation, or a modified external fixator. Future research should be directed toward improving methods of care. It is not precisely known when is the best time to convert to definitive fixation without increasing the risk of infection. The risk factors leading to infection and nonunion are not well-established, making that determination even more difficult. Clinical studies of a suitable size should provide insight into these problems. Although temporary external fixation is commonly used, an optimal construct has not been determined. Data from studies of in vivo fracture-site motion after application of the temporary external fixator should be compared with biomechanical testing of similar constructs. These data could be used to recommend optimal temporary external fixation constructs of tibia, femur, and humerus fractures using currently available devices as well as to provide groundwork for the next generation of fixators.

Shear does not necessarily inhibit bone healing

Interfragmentary shear has been perceived as inhibitory to bone healing. We think this is because of inadequate balance between stimulatory and disruptive interfragmentary displacement magnitudes in the shear direction. We hypothesized that pure shear is not necessarily detrimental to bone healing. This was investigated by comparing bone healing under interfragmentary torsional shear, axial compression, and no applied motion. Applied motion was controlled carefully with similar interfragmentary principal strain magnitudes found to stimulate healing under axial compression. The observation period was 8 weeks. Torsional rotation stimulated intercortical mineralized callus formation with greater area than the group without applied motion, and led to a stiffness and rate of bony bridging similar to that of the no motion group. Axial compression stimulated less intercortical mineralized callus of a lower density than the no motion group, and there also was little bridging. These results support the hypothesis that interfragmentary shear does not necessarily inhibit bone healing.

Gait evaluation: a tool to monitor bone healing?

BACKGROUND

Current clinical methods for monitoring fracture healing are often invasive and inaccurate. This paper evaluates the use of a pressure sensitive platform to improve monitoring.

METHODS

Standardised 3 mm diaphyseal bone defects were created in the right tibia of 64 female sheep and stabilised with either a rigid monolateral external fixator or a more flexible variant. Over a nine week healing period gait parameters were measured using a pressure sensitive platform and interfragmentary movements at the fracture site were monitored. Frequency spectra were calculated for the ground reaction forces. The tibiae were tested biomechanically after sacrifice and callus sections were analysed histomorphometrically.

FINDINGS

All animals unloaded the operated and overloaded the contralateral hindlimb. Callus mineralisation and stiffness, as well as limb loading increased during healing whilst interfragmentary movements were reduced. Larger interfragmentary movements resulted in a slower fracture healing rate as documented histologically and biomechanically. Frequency analysis showed upto 14 dB loss of power at frequencies associated with bone mechanotransduction at four weeks postoperatively, reducing to a 3 dB loss at nine weeks.

INTERPRETATION

Gait analysis is a valuable tool for monitoring the course of fracture healing. Different fixation stiffnesses caused different initial interfragmentary movements leading to different healing rates. Ground reaction forces were strongly related to the course of callus mineralisation and thus directly reflected the recovery of stiffness at the fracture site. Reduced levels of loading frequencies that may affect bone healing persist to nine weeks postoperatively.

The course of bone healing is influenced by the initial shear fixation stability

Fracture healing is influenced by fixation stability and experimental evidence suggests that the initial mechanical conditions may determine the healing outcome. We hypothesised that mechanical conditions influence not only the healing outcome, but also the early phase of fracture healing. Additionally, it was hypothesised that decreased fixation stability characterised by an increased shear interfragmentary movement results in a delay in healing. Sixty-four sheep underwent a mid-shaft tibial osteotomy which was treated with either a rigid or a semi-rigid external fixator. Animals were sacrificed at 2, 3, 6 and 9 weeks postoperatively and the fracture callus was analysed using radiological, biomechanical and histological techniques. The tibia treated with semi-rigid fixation showed inferior callus stiffness and quality after 6 weeks. At 9 weeks, the calluses were no longer distinguishable in their mechanical competence. The calluses at 9 weeks produced under rigid fixation were smaller and consisted of a reduced fibrous tissue component. These results demonstrate that the callus formation over the course of healing differed both morphologically and in the rate of development. In this study, we provide evidence that the course of healing is influenced by the initial fixation stability. The semi-rigid fixator did not result in delayed healing, but a less optimal healing path was taken. An upper limit of stability required for successful healing remains unknown, however a limit by which healing is less optimal has been determined.

Initial vascularization and tissue differentiation are influenced by fixation stability

Fracture healing requires a certain degree of mechanical stability and an adequate blood supply. The hypothesis of the present study was that increased interfragmentary shear leads to a reduced initial vascularization and prolonged healing. The aim of the study was to quantitatively analyze the histological appearance of vascularization and tissue differentiation with regard to fracture stability during the course of healing. A mid-shaft osteotomy of the tibia was performed in two groups of sheep and stabilized with either a rigid or semirigid external fixator, differing in bending stiffness. Interfragmentary movements and ground reaction forces were evaluated in vivo during a 9-week period. The sheep were sacrificed at 2, 3, 6, and 9 weeks postoperatively. The tibiae were tested biomechanically and histological sections from the callus were prepared for analysis of tissue differentiation and vascularization. Larger interfragmentary shear movements in the semirigid fixator group were associated with a reduced initial blood supply. At 6 weeks the semirigid fixator group showed a significantly lower percentage of mineralized bone and a higher amount of fibrous tissue leading to a significantly lower stiffness of the callus than the rigid fixator group. This initial delay in healing was compensated for in the later stages with the production of greater volumes of callus tissue so that both groups showed the same callus stiffness at 9 weeks. However, the rigid fixator group showed signs of the beginning of callus remodeling at the latest time points suggesting a faster bone healing. The results indicate the important role of the initial mechanical stability specifically in the vascularization of an osteosynthesis. Further studies should illustrate the precise role of mechanical conditions on the regulation of angiogenesis during early bone healing.

Mechanics and mechano-biology of fracture healing in normal and osteoporotic bone

Fracture repair, which aims at regaining the functional competence of a bone, is a complex and multifactorial process. For the success of fracture repair biology and mechanics are of immense importance. The biological and mechanical environments must be compatible with the processes of cell and tissue proliferation and differentiation. The biological environment is characterized by the vascular supply and by many biochemical components, the biochemical milieu. A good vascular supply is a prerequisite for the initiation of the fracture repair process. The biochemical milieu involves complex interactions among local and systemic regulatory factors such as growth factors or cytokines. The mechanical environment is determined by the local stress and strain within the fracture. However, the local stress and strain is not accessible, and the mechanical environment, therefore, is described by global mechanical factors, e.g., gap size or interfragmentary movement. The relationship between local stress and strain and the global mechanical factors can be obtained by numerical models (Finite Element Model). Moreover, there is considerable interaction between biological factors and mechanical factors, creating a biomechanical environment for the fracture healing process. The biomechanical environment is characterized by osteoblasts and osteocytes that sense the mechanical signal and express biological markers, which effect the repair process. This review will focus on the effects of biomechanical factors on fracture repair as well as the effects of age and osteoporosis.

450 closed fractures of the distal third of the tibia treated with a functional brace

Four hundred fifty closed fractures of the distal third of the tibial diaphysis, treated with a functional brace, are the subject of this study. Four (0.9%) of the fractures resulted in nonunion. The average healing time was 16.6 +/- 5.6 weeks, with a range from 10-40 weeks. The average final shortening was 5.1 +/- 4.8 mm with a range from 0-25 mm. Four hundred twenty four (94.2%) fractures healed with < 12 mm shortening. Initial shortening at the time of injury essentially was unchanged, from 4.4 +/- 4.5 mm to 4.4 +/- 3.9 mm final shortening. Axially unstable closed tibial fractures do not shorten beyond the initial shortening. Four-hundred five fractures (90.0%) healed with less than 8 degrees angular deformity in either the frontal or sagittal planes, and 302 (67.1%) healed with less than 5 degrees deformity in any plane. Overall, 391 fractures (87%) healed with shortening less than 12 mm and angulation in any plane less than 8 degrees . These degrees of angular deformity and shortening seem to compare favorably with those reported by other investigators using intramedullary nails. It seems that functional bracing is an effective method of treatment of a selected group of tibial fractures.

Comparison of unreamed nailing and external fixation of tibial diastases--mechanical conditions during healing and biological outcome

Locked intramedullary nailing and external fixation are alternatives for the stabilization of tibial shaft fractures. The goal of this study was to determine to what extent the mechanical conditions at the fracture site influence the healing process after unreamed tibial nailing compared to external fixation. A standardized tibial diastasis was stabilized with either a locked unreamed tibial nail or a monolateral fixator in a sheep model. Interfragmentary movements and ground reaction parameters were monitored in vivo throughout the healing period. After sacrifice, the tibiae were examined mechanically and histologically. Bending angles and axial torsion at the fracture site were larger in the nail group within the first five weeks post-operatively. Unlike the fixator group, the operated limb in the nail group did not return to full weight bearing during the treatment period. Mechanical and histomorphometrical observations showed significantly inferior bone healing in the nail group compared to the fixator group. In this study, unreamed nailing of a tibial diastasis did not provide rotational stability of the osteosynthesis and resulted in a significant delay in bone healing.

The influence of cyclic compression and distraction on the healing of experimental tibial fractures

Interfragmentary displacement has a main effect on callus formation in fracture healing. To test whether compressive or distractive displacements have a more pronounced effect on new bone formation, a sheep osteotomy model was created whereby the gap tissue was subjected to constant bending displacement. A diaphyseal osteotomy with a gap of 2 mm was created in 18 sheep tibiae and stabilized with a special unilateral actuator-driven external fixator. Two experimental groups with six sheep each received either 10 or 1000 cycles evenly distributed over 24 h. The third group of six sheep served as a control group without actively induced displacement. The amount and direction of cyclic displacement was kept constant throughout the observation period, resulting in 50% compressive and 50% distractive displacement within the osteotomy gap. At sacrifice, six weeks after surgery, bending stiffness was measured and new bone formation was assessed radiologically and microradiographically. In all cycled groups, the amount of periosteal callus formation was up to 25 times greater on the compression compared to the distraction side (p < 0.001). The application of the higher number of daily cycles resulted in an up to 10-fold greater amount of periosteal new bone formation on the compression side (p < 0.012), while the difference on the distraction side was not significant. Ten cycles applied a day were sufficient to create an abundant periosteal callus on the compression side. In the 1000 cycle group, bending stiffness revealed slightly lower values but the difference was not significant. Solid periosteal bridging of the gap was observed in two sheep in the control group, whereas bridging in the cycled groups was observed exclusively at the medullary side. In conclusion, cyclic compressive displacements were found to be superior over distractive displacements. A higher number of enforced and maintained compressive displacements enhanced periosteal callus formation but did not allow bony bridging of the gap.

How accurate is partial weightbearing?

The accuracy of partial weightbearing was assessed in six healthy volunteers and 23 patients who had sustained either a fracture of a lower limb or surgery. They were trained to weightbear partially using the conventional bathroom scale method and were assessed in a gait laboratory using force platforms. The amount of weight exerted on the involved limb during three-point crutch walking was determined. Four of six volunteers exerted a mean of 27% of body weight more than required. The remaining two volunteers exerted a mean of 8.5% of body weight less than required. Of the 23 patients, 21 exerted a mean of 35.3% of body weight more than that prescribed and two patients exerted a mean of 11.97% of body weight less than that prescribed. In both groups there was little relationship between the weightbearing prescribed and actual weightbearing. None of the patients or volunteers was able to reproduce the extent of partial weightbearing for which they were trained using the bathroom scale method, confirming that this technique of instructing patients in partial weightbearing is inaccurate.

Neuromuscular electrical stimulation enhances fracture healing: results of an animal model

Neuromuscular electrical stimulation (NMES) could simulate physiological muscle functions known to be associated with the normal bone healing process. The object of the present study was to evaluate the effect of NMES on fracture healing, using an animal model. Thirty rabbits received unilateral, transverse, mid-tibial, 3-mm gapped osteotomies that were stabilized with double-bar external fixators. The femoral vein was ligated to induce venous stasis. From the fourth post-operative day, the study group was treated with 1 h daily of NMES for four weeks, while the control group was treated without NMES. For NMES, two surface electrodes were used: one above the patellar tendon and another around the lateral thigh. Callus area and mineral content at the osteotomy gap were measured, biweekly, using computerized tomographic examinations. Biomechanical properties of healing were evaluated with a torsion test, eight weeks after the index operation. Osteotomies treated with NMES exhibited 31% (p=0.01) higher mineral content and 27% (p=0.009) larger callus area than control osteotomies at eight weeks. The maximum torque, torsional stiffness, angular displacement at maximum torque, and energy required to failure of specimens in the study group were 62% (p=0.006), 29% (p=0.03), 34.6% (p=0.008), and 124% (p<0.0001) higher, respectively, than those in the control group at eight weeks. The results of the present study demonstrated that the use of NMES can enhance callus development and mineralization, with the consequent improvement in biomechanical properties of the healing bone.

Experimental Study on the Effect of Mechanical Stimulation on the Early Stage of Fracture Healing

In an attempt to ascertain the effects of mechanical stimulation on callus in the early stage of bone fracture healing, a tibial fracture was induced in rats and mechanical stimulation applied to the fractures. The callus was then measured quantitatively, while the fractures were analyzed both radiographically and histologically. Following the induction of a closed transverse fracture in the tibia, external anchors were applied and the rats raised by suspending the fractured leg. The rats were divided into two main groups: a Stimulation Group (S Group) and a Control Group (C Group) without the application of any mechanical stimulation. The S Group was further divided into the following three subgroups: an axial compression group (Sc Group) receiving stimulation in the positive direction; an axial distraction group (Sd Group) receiving stimulation in the negative direction; and an axial dynamization group (Sdy Group) receiving stimulation in both directions alternately. For mechanical stimulation, 1.4-N sine waves were applied continuously for 30 minutes a day, three times a week, starting 2 days after fracture-inducing surgery. At 3, 7, and 14 days after surgery, transverse sections of each fractured bone sample were prepared. At 14 days after surgery, each transverse section was divided into two peripheral and central regions to permit calculation of the area ratio of callus. Radiographically, no marked differences were observed among the groups; histologically, differences were seen 7 days after surgery, suggesting that mechanical stimulation facilitated bone healing soon after surgery. At 14 days after surgery, the amount of callus for the C Group was less than that for all three stimulation groups. In the C Group, the amount of callus in the peripheral region was greater than in the central region, and in the Sc Group, the results were the same: callus in the peripheral region was greater than in the central region. In the Sd Group, callus was greater in the central region than in peripheral regions. In the Sdy Group, favorable callus was observed in both the central and peripheral regions. These findings suggest that axial compression facilitates callus primarily in the peripheral region, while axial distraction facilitates callus primarily in the central region. When axial compression and distraction were alternated (dynamization), callus was significantly facilitated in both the central and peripheral regions. Of the three axial stimulation techniques, dynamization was the most effective in facilitating callus in the early stage of bone fracture healing.

Shear movement at the fracture site delays healing in a diaphyseal fracture model

This study tested the hypothesis that interfragmentary axial movement of transverse diaphyseal osteotomies would result in improved fracture healing compared to interfragmentary shear movement. Ten skeletally mature merino sheep underwent a middiaphyseal osteotomy of the right tibia, stabilized by external fixation with an interfragmentary gap of 3 mm. A custom made external fixator allowed either pure axial (n=5) or pure shear movement (n=5) of 1.5 mm amplitude during locomotion by the animals. The movement of the osteotomy gap was monitored weekly in two sheep by an extensometer temporarily attached to the fixator. After 8 weeks the sheep were killed, and healing of the osteotomies was evaluated by radiography, biomechanical testing, and undecalcified histology. Shear movement considerably delayed the healing of diaphyseal osteotomies. Bridging of the osteotomy fragments occurred in all osteotomies in the axial group (100%), while in the shear group only three osteotomies (60%) were partially bridged. Peripheral callus formation in the shear group was reduced by 36% compared to the axial group (p<0.05). In the axial group bone formation was considerably larger at the peripheral callus and in between the osteotomy gaps but not in the intramedullary area. The larger peripheral callus and excess in bone tissue at the level of the gap resulted in a more than three times larger mechanical rigidity for the axial than for the shear group (p<0.05). In summary, fixation that allows excessive shear movement significantly delayed the healing of diaphyseal osteotomies compared to healing under axial movement of the same magnitude.

The initial phase of fracture healing is specifically sensitive to mechanical conditions

Interfragmentary movements affect the quality and quantity of callus formation. The mounting plane of monolateral external fixators may give direction to those movements. Therefore, the aim of this study was to determine the influence of the fixator mounting plane on the process of fracture healing. Identically configured fixators were mounted either medially or anteromedially on the tibiae of sheep. Interfragmentary movements and ground reaction forces were evaluated in vivo during a nine week period. Histomorphological and biomechanical parameters described the bone healing processes. Changing only the mounting plane led to a modification of interfragmentary movements in the initial healing phase. The difference in interfragmentary movements between the groups was only significant during the first post-operative period. However, these initial differences in mechanical conditions influenced callus tissue formation significantly. The group with the anteromedially mounted fixator, initially showing significantly more interfragmentary movements, ended up with a significantly smaller callus diameter and a significantly higher callus stiffness as a result of advanced fracture healing. This demonstrates that the initial phase of healing is sensitive to mechanical conditions and influences the course of healing. Therefore, initial mechanical stability of an osteosynthesis should be considered an important factor in clinical fracture treatment.

Gertzbein and load sharing classifications for unstable thoracolumbar fractures

From 1996 to 1998, 30 consecutive patients with Level 1 thoracolumbar spinal injury were classified and treated according to the Gertzbein classification and the load sharing classification. A posterior short segment pedicle screw implant was used in 21 patients; anterior decompression with strut grafting and application of the Kaneda device was used in three patients; and six patients were treated with short posterior instrumentation and an anterior strut graft. The average followup was 32 months (range, 24-50 months). The clinical outcome was satisfactory in 22 of 30 patients. Five of nine patients had neurologic improvement. Radiographic imaging findings showed a slight loss of reduction, but the clinical outcome of the patients was not affected. No pseudarthrosis and no implant failures were recorded. The Gertzbein classification correlates the type of fracture with the degree of mechanical instability and neurologic lesion. The load sharing classification correlates fracture comminution and displacement with mechanical stability and implant failure. Patient selection is a fundamental component for a successful outcome. The best candidates for surgery are cooperative patients who require spinal mobility, patients who are able to tolerate a two-stage reconstruction, and patients in good general health.

Successful short-segment instrumentation and fusion for thoracolumbar spine fractures: a consecutive 41/2-year series

STUDY DESIGN

A retrospective review of all the surgically managed spinal fractures at the University of Missouri Medical Center during the 41/2-year period from January 1989 to July 1993 was performed. Of the 51 surgically managed patients, 46 were instrumented by short-segment technique (attachment of one level above the fracture to one level below the fracture). The other 5 patients in this consecutive series had multiple trauma. These patients were included in the review because this was a consecutive series. However, they were grouped separately because they were instrumented by long-segment technique because of their multiple organ system injuries.

OBJECTIVES

The choice of the anterior or posterior approach for short-segment instrumentation was based on the Load-Sharing Classification published in a 1994 issue of Spine. The purpose of this review was to demonstrate that grading comminution by use of the Load-Sharing Classification for approach selection and the choice of patients with isolated fractures who are cooperative with spinal bracing for 4 months provide the keys to successful short-segment treatment of isolated spinal fractures.

SUMMARY OF BACKGROUND DATA

The current literature implies that the use of pedicle screws for short-segment instrumentation of spinal fracture is dangerous and inappropriate because of the high screw fracture rate.

METHODS

Charts, operative notes, preoperative and postoperative radiographs, computed tomography scans, and follow-up records of all patients were reviewed carefully from the time of surgery until final follow-up assessment. The Load-Sharing Classification had been used prospectively for all patients before their surgery to determine the approach for short-segment instrumentation. Denis' Pain Scale and Work Scales were obtained during follow-up evaluation for all patients.

RESULTS

All patients were observed over 40 months except for 1 patient who died of unrelated causes after 35 months. The mean follow-up period was 66 months (51/2 years). No patient was lost to follow-up evaluation. Prospective application of the Load-Sharing Classification to the patients' injury and restriction of the short-segment approach to cooperative patients with isolated spinal fractures (excluding multisystem trauma patients) allowed 45 of 46 patients instrumented by the short-segment technique to proceed to successful healing in virtual anatomic alignment.

CONCLUSIONS

The Load-Sharing Classification is a straightforward way to describe the amount of bony comminution in a spinal fracture. When applied to patients with isolated spine fractures who are cooperative with 3 to 4 months of spinal bracing, it can help the surgeon select short-segment pedicle-screw-based fixation using the posterior approach for less comminuted injuries and the anterior approach for those more comminuted. The choice of which fracture-dislocations should be strut grafted anteriorly and which need only posterior short-segment pedicle-screw-based instrumentation also can be made using the Load-Sharing Classification.

On the behavior of closed tibial fractures: clinical/radiological correlations

OBJECTIVE

To review the treatment of closed diaphyseal tibial fractures with functional braces and to identify patient and fracture characteristics, as well as possible correlations, that could be used to determine final outcomes.

DESIGN

A comprehensive review of data obtained from 1,000 diaphyseal tibial fractures.

SETTING

Major university teaching hospital.

INTERVENTION

Identification of patient and fracture characteristics, including type and level of fracture, initial shortening and angulation, and severity of injury, to be correlated with final shortening and angulation and speed of healing.

MAIN OUTCOME MEASUREMENTS

Degree of shortening and angulation; speed of healing.

RESULTS

Neither the level nor the type of tibial fracture significantly influenced healing time, although there was a considerably higher probability of delayed union in fractures produced from vehicular accidents, as well as in comminuted and segmental fractures. Any delay in application of the functional brace resulted in slower healing. Maximum shortening of the fractures occurred at the time of the initial injury, with no additional shortening experienced after the introduction of graduated weight-bearing ambulation. Compared with a mean initial shortening of 4.25 millimeters, the overall final shortening of fractures was 4.28 millimeters.

CONCLUSIONS

Correlations exist between patient and fracture characteristics that influence the final outcome for closed diaphyseal fractures treated with functional braces.

Periosteum responds to dynamic fluid pressure by proliferating in vitro

Periosteum provides a source of undifferentiated chondrocyte precursor cells for fracture healing that can also be used for cartilage repair. The quantity of cartilage that can be produced, which is a determining factor in fracture healing and cartilage repair, is related to the number of available stem cells in the cambium layer. Cartilage formation during both of these processes is enhanced by motion of the fracture or joint in which periosteum has been transplanted. The effect of dynamic fluid pressure on cell proliferation in periosteal tissue cultures was determined in 452 explants from 60 immature (2-month-old) New Zealand White rabbits. The explants were cultured in agarose suspension for 1-14 days. One group was subjected to cyclic hydrostatic pressure, which is referred to as dynamic fluid pressure, at 13 kPa and a frequency of 0.3 Hz. Control explants were cultured in similar chambers without application of pressure. DNA synthesis ([3H]thymidine uptake) and total DNA were measured. The temporal pattern and distribution of cell proliferation in periosteum were evaluated with autoradiography and immunostaining with proliferating cell nuclear antigen. Dynamic fluid pressure increased proliferation of periosteal cells significantly, as indicated by a significant increase in [3H]thymidine uptake at all time points and a higher amount of total DNA compared with control values. On day 3, when DNA synthesis reached a peak in periosteal explants, [3H]thymidine uptake was 97,000+/-5,700 dpm/microg DNA in the group exposed to dynamic fluid pressure and 46,000+/-6,000 dpm/microg in the controls (p < 0.001). Aphidicolin, which blocks DNA polymerase alpha, inhibited [3H]thymidine uptake in a dose-dependent manner in the group subjected to dynamic fluid pressure as well as in the positive control (treated with 10 ng/ml of transforming growth factor-beta1) and negative control (no added growth factors) groups, confirming that [3H]thymidine measurements represent proliferation and dynamic fluid pressure stimulates DNA synthesis. Total DNA was also significantly higher in the group exposed to dynamic fluid pressure (5,700+/-720 ng/mg wet weight) than in the controls (3,700+/-630) on day 3 (p < 0.01). Autoradiographs with [3H]thymidine revealed that one or two cell cycles of proliferation took place in the fibrous layer prior to proliferation in the cambium layer (where chondrocyte precursors reside). Proliferating cell nuclear antigen immunophotomicrographs confirmed the increased proliferative activity due to dynamic fluid pressure. These findings suggest either a paracrine signaling mechanism between the cells in these two layers of the periosteum or recruitment/migration of proliferating cells from the fibrous to the cambium layer. On the basis of the data presented in this study, we postulate that cells in the fibrous layer respond initially to mechanical stimulation by releasing growth factors that induce undifferentiated cells in the cambium layer to divide and differentiate into chondrocytes. These data indicate that cell proliferation in the early stages of chondrogenesis is stimulated by mechanical factors. These findings are important because they provide a possible explanation for the increase in cartilage repair tissue seen in joints subjected to continuous passive motion. The model of in vitro periosteal chondrogenesis under dynamic fluid pressure is valuable for studying the mechanisms by which mechanical factors might be involved in the formation of cartilage in the early fracture callus and during cartilage repair.

Reduced gap strains induce changes in bone regeneration during distraction

A bilateral New Zealand white rabbit model of distraction osteogenesis (DO) was used to investigate the relationship between strain environment and bone regeneration during limb lengthening. In seven (n = 7) rabbits, a stiffener was applied to the fixator on one side to reduce strains within the gap tissue after lengthening was completed. Animals were euthanized six days later and their distraction zones were harvested and analyzed for changes in new bone volume and architecture. Nonlinear finite element analyses (FEA) were performed to predict changes in the gap strain environment. FEA results predicted a nearly uniform sevenfold decrease in average strain measures within the distraction zone. No change in total average new bone volume and significant decreases in both bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) were observed in tibiae in which gap strains were reduced experimentally, compared to contralateral controls. These results suggest that fixator stiffening influenced the architecture but not the amount of newly formed bone. This animal model of distraction might be used to study the mechanisms by which strain fields affect events in bone repair and regeneration, such as cell proliferation, precursor tissue differentiation, and altered growth factor and nutrient delivery to tissues.

Functional fracture bracing

Functional bracing is an effective therapeutic modality in the management of selected fractures of the tibia, humerus, and ulna, particularly low-energy injuries. In the case of tibial fractures, it is applicable only to reduced transverse fractures and to axially unstable fractures with an acceptable degree of shortening. The rate of union of tibial fractures after functional bracing is approximately 97%. The initial shortening noted with closed tibial fractures rarely increases with weight bearing. Shortening has been reported to be as little as 12 mm in 95% of patients, with angulation of 8 degrees in 90%. Such minimal shortening and angulation do not affect functional results. In closed and type I open diaphyseal humeral fractures treated with functional braces, the nonunion rate is approximately 3%. Most of the reported residual angular deformities have been functionally and cosmetically acceptable. For isolated ulnar fractures, the nonunion rate is approximately 2%. Functional fracture bracing is predicated on the premise that motion at the fracture site encourages osteogenesis. The method is applicable only to selected fractures, and it is necessary to have a clear understanding of its rationale, indications, and technique.

A portable monitoring system for measuring weight-bearing during tibial fracture healing

An ambulatory monitoring system has been developed to measure the weight-bearing achieved by a patient on their fractured leg. The system is lightweight, portable, and can monitor weight-bearing continuously over an extended period of time. In addition to mean weight-bearing, the system can also determine temporal parameters associated with the patients' gait. This system was used to measure the weight-bearing achieved during the course of fracture healing in a small number of patients being treated by a variety of fixation methods for a tibial fracture. In general, weight-bearing was observed to increase with time post fracture, and the fixation method employed appeared to influence the rate of increase of loading of the fractured limb, more rigid methods of fixation enabling full-weight-bearing to be achieved sooner.