Long-term effects of plate osteosynthesis: comparison of four different plates

Finite element model with realistic bone geometries for the optimal design of internal fixation during the fibula healing process

A finite element model with realistic bone geometries is developed to design optimal internal fixation during the fibula healing process in this study. The effect of bone plate parameters on fibula fracture healing is studied. The relationship between differences in plate length, thickness and working length, and bone healing performance is focused. The optimal combination form of the bone plate parameters was selected by the orthogonal experimental design and fracture block strain to achieve bone healing maximize the performance. The model results show that the maximum equivalent force of the bone plate was below the material yield limit; the higher mean contact stresses in the bone fragments indicate that the bone plate is prone to higher contact stresses when they are long. The working length of the bone plate has a greater effect on callus healing than the thickness and length of the bone plate. The optimal internal fixation option for distal fibula fractures is achieved when it provides the stability required for internal fixation during bone healing. It ensures lower contact stresses in the fibula as well as maximum Young's modulus during callus healing process.

Changes in tibial cortical dimensions and density associated with long-term locking plate fixation in goats

PURPOSE

Cortical porosis, secondary to either vascular injury or stress-shielding, is a comorbidity of fracture fixation using compression bone plating. Locking plate constructs have unique mechanics of load transmission and lack of reliance on contact pressures for fixation stability, so secondary cortical porosis adjacent to the plate has not been widely investigated. Therefore, this study aimed to assess the effects of long-term locking plate fixation on cortical dimensions and density in a caprine tibial segmental ostectomy model.

METHODS

Data was acquired from a population of goats enrolled in ongoing orthopedic research which utilized locking plate fixation of 2 cm tibial diaphyseal segmental defects to evaluate bone healing over periods of 3, 6, 9, and 12 months. Quantitative data included tibial cortical width measurements and three-dimensionally reconstructed slab density measurements, both assessed using computed tomographic examinations performed at the time of plate removal. Additional surgical and demographic variables were analyzed for effect on cortical widths and density, and all cis-cortex measurements were compared to both the trans-cortex and to the contralateral limbs.

RESULTS

The tibial cis-cortex was significantly wider and more irregular than the trans-cortex at the same level. This width asymmetry differed in both magnitude and direction from the contralateral limb. The bone underlying the plate was significantly less dense than the trans-cortex, and this cortical density difference was significantly greater than that of the contralateral limb. These cortical changes were independent of both duration of fixation and degree of ostectomy bone healing.

CONCLUSIONS

This study provides evidence that cortical bone loss consistent with cortical porosity is a comorbidity of locking plate fixation in a caprine tibial ostectomy model. Further research is necessary to identify risk factors for locking-plate-associated bone loss and to inform clinical decisions in cases necessitating long-term locking plate fixation.

Long-term Evaluation Using Finite Element Analysis of Bone Atrophy Changes after Locking Plate Fixation of Forearm Diaphyseal Fracture

Purpose

To determine the optimal timing of plate removal in patients with forearm diaphyseal fractures fixed with a locking plate via the analysis of bone atrophy over time.

Methods

The study subject was a 56-year-old man. Computed tomography was performed at 0.5, 1, 1.5, 2, 3, 4, and 5 years after plate fixation. Finite element analysis was performed to measure the fracture load of the radius and ulna. The fracture loads of the affected and healthy sides were compared, and their ratio was calculated by dividing the value of the affected side by that of the healthy side at each time point.

Results

The strength of the radius and ulna was 40.9% and 29.3%, respectively, on the healthy side at 1 year after surgery. The fracture load increased from the second to the third postoperative year; the strength of the radius and ulna was 62.2% and 37.3%, respectively, on the healthy side after the third year. However, after the third year, the fracture load declined and reached 38.8% and 18.9% for the radius and ulna, respectively, on the healthy side by the fifth postoperative year.

Conclusions

The long-term fixation of forearm diaphyseal fractures using a locking plate leads to progressive bone atrophy. Future bone atrophy during long-term locking plate fixation without removal should be monitored.

Type of study/level of evidence

Therapeutic IV.

Modeling age-related changes in the mechanical behavior of the fracture-fixated human tibia bone during healing

The evolutionary healing phenomenon of fractured tibia bone was investigated by comparing the bio-mechanical response of the human tibia following fracture fixation for two ranges of patient ages, when a body weight pressure (BWP) is applied. Three-dimensional finite element models have been developed by adopting the biomechanical characteristics of cortical and trabecular tibia bones, and considering the time-varying callus properties during the healing process for the two patients. The stress and strain levels generated within the fractured tibia bone by the screw tight fit during the assembly process revealed its dependence on the bone stiffness that degrades with age. They have an impact on primary stability of the implants prior to the osseointegration. The gap capacity to resist and allow a gradual BWP load transfer, through the callus for the tibia bone models, was analyzed. In fact, from 10 weeks after surgery, the callus allowed the BWP transfer for young patients, which guarantees sufficient structure stabilization of the fractured tibia. However, an insufficient load was transferred to the fracture gap for the old patient, even beyond 16 weeks, which delayed the bone consolidation.

Locking Screws With a Threaded Degradable Polymer Collar Reduce Construct Stiffness Over Time

OBJECTIVES

The stiffness of locking plates provide increased stability for early fracture healing but may limit late interfragmentary motion (IFM) necessary for secondary bone healing. An ideal plating construct would provide early rigidity and late flexibility to optimize bone healing. A novel screw plate construct utilizing locking screws with a degradable polymer locking mechanism is a dynamic option.

METHODS

Conventional locked plating constructs (group A) were compared with locking screws with a threaded degradable polymer collar before (group B) and after polymer dissolution (group C). Monotonic axial compression, monotonic torsion, cyclic axial load to failure, and IFM at the near and far cortices were tested on synthetic bone models.

RESULTS

One-way analysis of variance and post hoc Tukey-Kramer testing demonstrated similar axial stiffness in group A (873 ± 146 N/mm) and B (694 ± 314 N/mm) but significantly less stiffness in group C (379 ± 59 N/mm; F(2,15) = 9.12, P = 0.003). Groups A and B also had similar IFM, but group C had significantly increased IFM at both the near (F(2, 15) = 48.66, P = 2.76E-07) and far (F(2, 15) = 11.78, P = 0.0008) cortices. In cyclic axial load to failure, group A (1593 ± 233 N) and B (1277 ± 141 N) were again similar, but group C was significantly less (912 ± 256 N; F(2, 15) = 15.00, P = 0.0003). All failures were above the 500-N threshold seen in typical weight-bearing restrictions for fracture care. Torsional stiffness demonstrated significant differences between all groups (F(2, 15) = 106.64, P = 1.4E-09).

CONCLUSIONS

Use of locking plates with a degradable polymer collar show potential for in vitro construct dynamization. Future in vivo studies are warranted to assess performance under combined loading and the effects of decreasing construct stiffness during the course of bony healing.

Comparison of biomechanical characteristics in treatment of distal humerus fracture using different fixation plates: A finite element study

With the development of digital technology of orthopedics, personalized plate has been applied to treat different kinds of fractures. However, no studies of personalized implants in the treatment of distal humeral fractures have been reported. Therefore, we design a personalized anatomical locking plate (DPALP) to treat distal humerus fracture of adult. The model of humerus and personalized plate and traditional Y-shaped compression plate (YCP) was built and analyzed by finite element method. We found that peak value of stress of humerus fixed by YCP is higher than that of DPALP, and the peak value of stress of screws used in DPALP group is higher than that of YCP. Meanwhile, peak of displacement of YCP is higher than that of DPALP, and the peak value of displacement of humerus bone is higher than that of YCP. The patient with DPALP had a good clinical outcome (83) evaluated with Broberg and Morrey Score. Our results show that DPALP and YCP could get similar mechanical and clinical results for distal humorous intra-articular fractures, and stress distribution of DPALP group is more balanced, and it takes less time in the operation. Furthermore, DPALP can perfectly fit the humeri and achieve the anatomical reduction. In general, DPALP is more suitable for patients with intra-articular complicated fractures. Our findings will benefit clinicians treating distal humeral fractures and provide an alternative option.

Experiences using the Fixin locking plate system for the stabilization of appendicular fractures in dogs

Objectives: To retrospectively evaluate the stabilization of appendicular fractures in dogs using the Fixin locking plate system.

Materials and methods: Medical records and radiographs of dogs with fractures stabilized with the Fixin system in the period from May 2005 to September 2010 were reviewed. For each patient, data pertaining to signalment, the nature of the fracture, implants used, and evidence of fracture healing were recorded. The outcome and complications were determined from clinical and radiographic follow-up examinations. Limb function was evaluated between 40 days and 90 days postoperatively. Owners of pets with complications were contacted by phone for long-term follow-up.

Results: Eighty-two fractures in seventy-five dogs met the inclusion criteria for the study. Radiographic re-examinations were carried out between eight days to two years (median 60 days) following surgery. Seventy-three out of 82 fractures (89%) reached union without complications. Major complications were seen in six dogs (7%). Limb function was graded as ‘normal’ in 73/75 (97%) dogs and ‘mild lameness’ in 2/75 (3%) cases.

Clinical significance: Despite a modest complication rate, the Fixin locking bone plating system appears to be an acceptable choice of implant for the stabilization of appendicular fractures in dogs.

Non-osteotomy and osteotomy large animal fracture models in orthopedic trauma research

Large animal fracture models are important in the field of orthopedic trauma research. New implants are tested in animals before being implanted into humans. Large animals like sheep or swine often are more properly to simulate conditions in humans, e.g. biomechanical demands, compared to rodents. Cited articles mainly analyze shock or fracture healing. Both osteotomy and non-osteotomy fracture models have been used in the past. However, comparative studies are rare and clear recommendation when to use which model are missing. This review will summarize large animal fracture models putting special emphasis on non-osteotomy fracture models.

Dual plating of humeral shaft fractures: orthogonal plates biomechanically outperform side-by-side plates

BACKGROUND

Single large-fragment plate constructs currently are the norm for internal fixation of middiaphyseal humerus fractures. In cases where humeral size is limited, however, dual small-fragment locking plate constructs may serve as an alternative. The mechanical effects of different possible plate configurations around the humeral diaphysis may be important, but to our knowledge, have yet to be investigated.

QUESTIONS/PURPOSES

We used finite element analysis to compare the simulated mechanical performance of five different dual small-fragment locking plate construct configurations for humeral middiaphyseal fracture fixation in terms of (1) stiffness, (2) stress shielding of bone, (3) hardware stresses, and (4) interfragmentary strain.

METHODS

Middiaphyseal humeral fracture fixation was simulated using the finite element method. Three 90° and two side-by-side seven-hole and nine-hole small-fragment dual locking plate configurations were tested in compression, torsion, and combined loading. The configurations chosen are based on implantation using either a posterior or anterolateral approach.

RESULTS

All three of the 90° configurations were more effective in restoring the intact compressive and torsional stiffness as compared with the side-by-side configurations, resulted in less stress shielding and stressed hardware, and showed interfragmentary strains between 5% to 10% in torsion and combined loading.

CONCLUSIONS

The nine-hole plate anterior and seven-hole plate lateral (90° apart) configuration provided the best fixation. Our findings show the mechanical importance of plate placement with relation to loading in dual-plate fracture-fixation constructs.

CLINICAL RELEVANCE

The results presented provide novel biomechanical information for the orthopaedic surgeon considering different treatment options for middiaphyseal humeral fractures.

Rapid prototyping to design a customized locking plate for pancarpal arthrodesis in a giant breed dog

This report describes the treatment of traumatic carpal hyperextension in a giant breed dog by pancarpal arthrodesis using a custom-made Fixin locking plate, created with the aid of a three-dimensional plastic model of the bones of the antebrachium produced by rapid prototyping technology. A three-year-old 104 kg male Mastiff dog was admitted for treatment of carpal hyperextension injury. After diagnosis of carpal instability, surgery was recommended. Computed tomography images were used to create a life-size three-dimensional plastic model of the forelimb. The model was used as the basis for constructing a customized 12-hole Fixin locking plate. The plate was used to attain successful pancarpal arthrodesis in the animal. Radiographic examination after 74 and 140 days revealed signs of osseous union of the arthrodesis. Further clinical and radiographic follow-up examination three years later did not reveal any changes in implant position or complications.

Effects of the bone-plate material and the presence of a gap between the fractured bone and plate on the predicted stresses at the fractured bone

In the present study, 3D finite element models for fractured bones with function-graded (FG) bone-plates and traditional bone-plates made of stainless steel (SS) or titanium (Ti) alloy are generated using the ABAOUS code. The predicted Von Mises stresses at the fracture site and underlying bone-plate are examined at different healing stages. The effects on the predicted Von Mises stresses at the fracture site of the presence of a gap between the plate and fractured bone are also studied. Based on the analytical results, it is found that the stress shielding at the fracture site at the fully healed stages decreases when using FG bone-plates compared to Ti alloy or SS bone-plates. In the initial healing stages, the Von Mises stresses at the fracture site increase (stress shielding decreases) by 17% and 11% when using FG bone-plates as compared to SS bone-plates for contacted and non-contacted bone-plate system, respectively. The significant effects of using an FG bone-plate with a gap on the resultant Von Mises stresses on the bone underneath the plate and on the bone stress shielding should be taken into consideration during fractured bone fixation.

Assessment of function-graded materials as fracture fixation bone-plates under combined loading conditions using finite element modelling

In previous work by Fouad (Medical Engineering and Physics 2010 [23]), 3D finite element (FE) models for fractured bones with function-graded (FG) bone-plates and traditional bone-plates made of stainless steel (SS) and titanium (Ti) alloy were examined under compressive loading conditions using the ABAQUS Code. In this study, the effects of the presence of the torsional load in addition to the compressive load on the predicted stresses of the fracture fixation bone-plate system are examined at different healing stages. The effects on the stress on the fracture site when using contacted and non-contacted bone-plate systems are also studied. The FE modelling results indicate that the torsional load has significant effects on the resultant stress on the fracture fixation bone-plate system, which should be taken into consideration during the design and the analysis. The results also show that the stress shielding at the fracture site decreases significantly when using FG bone-plates compared to Ti alloy or SS bone-plates. The presence of a gap between the bone and the plate results in a remarkable reduction in bone stress shielding at the fracture site. Therefore, the significant effects of using an FG bone-plate with a gap and the presence of torsional load on the resultant stress on the fracture fixation bone-plate system should be taken into consideration.

[Conventional plate osteosynthesis]

Consolidation of bone is an essential clinical problem when treating fractures, fixing osteotomies and fusing joints. In most cases, the means of fixation are plates and screws. The goal is functional postoperative therapy by moving the adjacent joints and thus avoiding the deleterious disadvantages of long-lasting articular immobilization. Pre-operative planning, surgical approach, a good understanding of the precise mechanics of the structure and the biological answer for the various tissues are prerequisites of successful osteosynthesis. The choice of implants and the application of their versatility, as well as their adaptation to individual cases are the key to good results.

Bonding ability evaluation of bone cement on the cortical surface of rabbit's tibia

A composite bone cement designated G2B1 that contains beta tricalcium phosphate particles was developed as a bone substitute for percutaneous transpedicular vertebroplasty. In this study, both G2B1 and commercial PMMA bone cement (CMW1) were implanted into proximal tibiae of rabbits, and their bone-bonding strengths were evaluated at 4, 8, 12 and 16 weeks after implantation. Some of the specimens were evaluated histologically using Giemsa surface staining, contact microradiography (CMR) and scanning electron microscopy (SEM). Histological findings showed that G2B1 contacted bone directly without intervening soft tissue in the specimens at each time point, while there was always a soft tissue layer between CMW1 and bone. The bone-bonding strength of G2B1 was significantly higher than that of CMW1 at each time point, and significantly increased from 4 weeks to 8 and 12 weeks, while it decreased significantly from 12 weeks to 16 weeks. Bone remodeling of the cortex under the cement was observed especially for G2B1 and presumably influenced the bone bonding strength of the cement. The results indicate that G2B1 has bioactivity, and bone bonding strength of bioactive bone cements can be estimated fairly with this experimental model in the short term.

Bone regeneration in long-bone defects: tissue compartmentalisation? In vivo study on bone defects in sheep

Regeneration of living tissue varies with species, age and type of tissue, and undoubtedly with the biological and mechanical environment of the precise tissue. Autologous cancellous bone grafting is a well-known technique that provides bony regeneration. We investigated the efficiency of autologous bone grafting in a well-vascularised muscle environment, and additionally when isolated from the muscle and connected only to the bony environment. We designed a reproducible animal model producing a stable 3cm middiaphyseal bone and periosteal defect on sheep femurs and created a foreign-body membrane with a temporary poly-methylmethacrylate spacer. The foreign-body membrane had the outer dimension of the removed bone segment. We then ascertained the bony regeneration potential within the bone defect using autologous cancellous bone graft. Regeneration of bone is enhanced considerably by an autologous foreign-body membrane that separates the interfragmentary space from the muscular environment. This effect is independent of the autologous bone graft. The results suggest that bone behaves like a compartment that protects its specific humoral or its cellular environment, or both. Regeneration of bone can be enhanced by compartmentalisation of the bone defect.

Long-term effects of saw osteotomy versus random fracturing on bone healing and remodeling in a sheep tibia model

This article is about the evaluation of possible differences in biomechanical or histomorphological properties of bone healing between saw osteotomy and random fracturing after 6 months. A standardized, 30 degrees oblique monocortical saw osteotomy of sheep tibia was carried out, followed by manual fracture completion of the opposed cortical bone. Fixation was performed by bridge plating (4.5 mm, LCDCP, broad). X-rays were taken immediately after surgery and at the end of the study. Polychrome fluorescent staining was performed according to a standardized protocol in the 2nd, 4th 6th, 10th, 14th, 18th, 22th and 26th week. Ten sheep were comprehensively evaluated. Data for stiffness and histomorphology are reported. The average bending stiffness of the operated bone was higher (1.7 (SD 0.3) with plate (MP) vs. 1.5 without plate) than for the intact bone (1.4 (SD 0.2), though no significant differences in bending stiffness were observed (P>0.05). Fluorescence staining revealed small numbers of blood vessels and less fragment resorption and remodeling in the osteotomy gap. Bone healing after saw osteotomy shows a very close resemblance to 'normal' fracture healing. However, vascular density, fragment resorption, fragment remodeling, and callus remodeling are reduced at the osteotomy.

Prospective outcomes of comminuted periarticular metacarpal and phalangeal fractures treated using a titanium plate system

PURPOSE

The purpose of this study was to prospectively evaluate clinical results for open reduction and internal fixation of unstable metaphyseal fractures of the metacarpal and phalangeal bones using a miniature titanium plate.

METHODS

Fifty-one consecutive patients with periarticular fractures with metaphyseal comminution and displacement were enrolled. Intra-articular involvement with a split or depression fracture was identified in 22 hands. Minimum follow-up was 1 year. There were 37 male and 14 female patients; average age was 38 years (range, 14-63). Of the 51 fractures, 15 were open; 8 of these had additional soft tissue injury, involving neurovascular injury in 4 and extensor tendon injury in 6. The average duration from injury to surgery was 6 days (range, 2-40 days).

RESULTS

Bone union was successfully achieved in all patients over an average period of 2.6 months. The final range of total active motion (%TAM) was excellent (>85%) for 26, good (70%-84%) for 17, fair (50%-69%) for 5, and poor (<49%) for 3. Postoperative complications occurred in 5 patients, including fracture redisplacement in 2, a collapse or absorption of the condylar head in 2, and superficial infection due to hardware exposure in one. Subsequently, 2 of these patients had malrotation deformities or osteoarthritic changes in the injured finger. Plates were removed in 30 cases, and additional surgery was required in 20 cases. Postoperative grip strength averaged 87% of the contralateral side. Statistical analysis revealed that patient age was significantly correlated with %TAM of the injured finger at 1-year follow-up (p < .01), and intra-articular (p < .05) and phalangeal bone (p < .01) involvement, as well as associated soft tissue injury (p < .05), significantly affected the range of finger motion.

CONCLUSIONS

Despite the technical demands of plating for comminuted metacarpal and phalangeal fractures, the low-profile titanium plate system was highly effective in maintaining anatomic reduction. The postoperative complication rate was relatively low, and the objective outcomes approached a reasonable level at 1-year follow-up.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

A review of locking compression plate biomechanics and their advantages as internal fixators in fracture healing

Metallic implants are often involved in the open reduction and internal fixation of fractures. Open reduction and internal fixation is commonly used in cases of trauma when the bone cannot be healed using external methods such as casting. The locking compression plate combines the conventional screw hole, which uses non-locking screws, with a locking screw hole, which uses locking head screws. This allows for more versatility in the application of the plate. There are many factors which affect the functionality of the plate (e.g., screw placement, screw choice, length of plate, distance from bone, etc.). This paper presents a review of the literature related to the biomechanics of locking compression plates and their use as internal fixators in fracture healing. Furthermore, this paper also addresses the materials used for locking compression plates and their mechanical behavior, parameters that control the overall success, as well as inherent bone quality results.

Torsional stability of intramedullary compression nails: tibial osteotomy model

BACKGROUND

Studies comparing intramedullary compression nailing to conventional dynamized intramedullary nailing contend that better clinical outcomes of intramedullary compression techniques result from greater rotational stability of fracture or osteotomy sites. However, there appears to be no experimental evidence that rotational stability is improved with intramedullary nail compression. This study evaluated the effect of intramedullary nail compression on cadaveric and composite tibial fragment rotation above and below a mid-tibial transverse osteotomy.

METHODS

Twelve composite and four matched pairs of human cadaveric tibiae were randomized into either a compression group or a non-compressed dynamized group. A bi-axial servo-hydraulic testing machine applied 5Nm of internal and external torque (2Nm/s) under constant axial loads of 375N and 750N. Rotation along each tibia and at the osteotomy site was recorded from the trajectories of infrared emitting diodes rigidly attached along the tibial shaft.

FINDINGS

In comparison to dynamized nails, intramedullary nail compression significantly reduced the rotation at the osteotomy site in both human (8.9 degrees reduction; P=0.007) and composite tibiae (2.5 degrees reduction; P=0.039) under 750N of axial load. A similar result was noted for simulated half-body weight loads (375N) for both composite (3.0 degrees reduction; P=0.009) and human tibiae (10.5 degrees reduction; P=0.003).

INTERPRETATION

Intramedullary nail compression more effectively reduced tibial fragment rotation about a mid-tibial osteotomy than conventional dynamized intramedullary nails because intramedullary nails created more osteotomy site compression than the application of body weight to tibiae instrumented with dynamized intramedullary nails.

Locking plate technology and its applications in upper extremity fracture care

Locking plate technology has been a major advance in fracture care. These plates afford a stronger construct and have been useful in cases where the bone is osteoporotic and unicortical fixation or distal periarticular fracture fixation is necessary. Disadvantages include fixed angle screw fixation and inability to compress at the fracture site; however, the use of a combination of compression and locking screws allows for both fracture compression with cortical screws and stronger fixation with locking screws. Future studies will refine the indications and overall efficacy in the use of this technology.

Indikation zur Entfernung von Tibiamarknägeln

BACKGROUND

Tibial nail removal has been suggested as a routine procedure for both symptomatic and asymptomatic patients. The aim of this study was to define guidelines for the removal of tibial nails.

PATIENTS AND METHODS

A retrospective study on the isolated removal of 69 tibial nails after fracture consolidation was done. A review of the patient charts and radiographs was performed. Forty-four patients (64%) were available for the follow-up interview.

RESULTS

Preoperatively, 26 patients (59%) had local complaints. Of these 26 patients, 73% reported an improvement, and 8% reported an aggravation of their local complaints. Of the 18 patients who were asymptomatic before surgery, 17% reported long-term complaints at follow-up.

CONCLUSION

We conclude that routine removal of tibial nails should be discussed critically in asymptomatic patients.

Effect of lacunocanalicular architecture on hydraulic conductance in bone tissue: implications for bone health and evolution

Bone tissue health depends largely on efficient fluid and solute transport between the blood supply and cells that are the living component of the tissue. We hypothesized that the lacunocanalicular hydraulic network, which is defined by the pericellular fluid space that is common to all bone tissue, is optimized to transport fluid and solutes between the blood supply and bone cells. An analytical study was carried out to evaluate the effect of osteonal architecture, including the osteon diameter, number of annular lamellar regions, and number and length of canalicular channels, on fluid transport between the blood supply and bone cells. On the basis of this analysis, we conclude that osteon size is limited to the distance over which fluid and solutes can be transported efficiently between the blood supply and cells. This analytic model suggests that hydraulic conductivity is highest in lamellar regions closest to the Haversian canal (HC) and decreases with increasing distance from the blood supply, reaching a plateau after the fifth lamella (169 micro m radius). Furthermore, an increase in the diameter of the HC, or a decrease in the length of canaliculi, reduces the hydraulic conductivity within the lacunocanalicular network. Applying the principle of minimal expenditure of energy to this analysis, the path distance comprising five or six lamellar regions represents an effective limit for fluid and solute transport between the blood supply and cells; beyond this threshold, hydraulic resistance in the network increases and additional energy expenditure is necessary for further transportation. This suggests that transport is optimized to meet metabolic demands concomitant with a minimal expenditure of energy. This fundamental new insight into bone structure and physiology may provide a new basis of understanding for tissue engineering, bone physiology in health and disease, and evolutionary biology.