The effects of the interosseous membrane and partial fibulectomy on loading of the tibia: a biomechanical study

Comparing Fibula Flap Insetting Techniques for Pediatric Oncologic Extremity Reconstruction

BACKGROUND

Extremity reconstruction in skeletally immature patients presents unique challenges in terms of operative technique, bone healing, and limb function. A variety of insetting techniques have been described, with no clearly superior option. The authors hypothesized that vascularized fibula flaps placed in the intramedullary space are associated with shorter union times and better functionality compared with onlay flaps.

METHODS

In a cohort study, the authors retrospectively reviewed the medical records of all pediatric patients who underwent fibula flap extremity reconstruction at a single center from 2001 through 2018. Comorbidities, complications, and outcomes were analyzed. Complete fibula union was based on radiographic evidence of significant cortical bridging.

RESULTS

Thirty-three patients (mean age, 13.6 years; range, 2 to 18 years) underwent pedicled ( n = 7) or free ( n = 26) fibula flap reconstructions in 12 upper extremities and 21 lower extremities. Median follow-up was 69.5 months (interquartile range, 16.3 to 114.6 months). Onlay and intramedullary fibula position compared with intercalary placement (median, 13.5 and 14.6 months versus 3.4 months; P = 0.002) were associated with longer time to complete bone union. Complications including allograft fracture ( P = 0.02) and hardware removal ( P = 0.018) were also associated with longer time to complete union and eventual conversion to megaprosthesis ( P = 0.02, P = 0.038). Thirty-two patients (97%) achieved full union and a functional reconstruction.

CONCLUSIONS

Fibula flap reconstruction is safe and effective for pediatric long-bone reconstruction. Longer fibula union times were associated with onlay and intramedullary fibula placement, allograft fracture, and hardware removal.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Anatomical Adaptation of Fibula and its Mechanism of Proximal Partial Fibulectomy Associated with Medial Compartment Knee Osteoarthritis

Objectives

To reveal the anatomical adaptation of the fibula and its relations to age and settlement of the medial tibial plateau, and to explore the mechanism of proximal partial fibulectomy in treating medial compartment knee osteoarthritis (OA).

Methods

A retrospective study was performed in the Third Hospital of Hebei Medical University. Weight‐bearing full‐leg anteroposterior (AP) radiographs of 280 adults (560 knees) obtained from 1 January 2018 to 31 October 2018 were enrolled according to our inclusion and exclusion criteria, including 157 men and 123 women, with an average age of 50.3 ± 14.8 years (range, 19–80 years). Radiographic severity of knee OA was assessed using Kellgren and Lawrence (K–L) grading. The settlement of the medial tibial plateau was evaluated using the medial proximal tibial angle (MPTA). Curvatures of the tibia and the fibula were measured as proximal tibial curvature (PTC), distal tibial curvature (DTC), proximal fibular curvature (PFC), and distal fibular curvature (DFC). Two orthopaedic surgeons performed all the radiological measurements for 30 randomly selected patients, and repeated the measurements 1 week later. Based on the satisfactory intra‐observer and inter‐observer reliabilities (ICC > 0.9), each parameter was analyzed in this study. Multivariable linear regression models were used to examine relations between radiological measurements and age.

Results

The mean MPTA, PTC, DTC, PFC, and DFC were 85.4° ± 2.8°, 176.2° ± 1.9°, 176.8° ± 1.8°, 176.8° ± 1.9°, and 177.0° ± 2.0°, respectively. Ninety‐three knees of K–L grade I were categorized as non‐knee OA, and 467 knees of K–L grades II–IV were categorized as knee OA. The MPTA, PTC, and PFC of the knee OA group were significantly smaller than those of non‐knee OA group (P < 0.05). The K–L grade of knee OA significantly increased with age (χ² = 182.169, P < 0.01). The multivariate linear regression analysis indicated that the MPTA and fibular curvatures were negatively correlated with age (the regression equation is age = 561.165–0.945 MPTA‐0.937 PFC‐0.959 DFC, P < 0.05), and the MPTA was negatively correlated with PFC (the regression equation is MPTA = 7.827 + 0.099 DFC, P < 0.05).

Conclusions

The proximal curve of the fibula increased in patients with medial compartment knee OA, and this change was positively correlated with age and settlement of the medial tibial plateau. This anatomical adaptation of the fibula was associated with greater fibular axial load and the pulling from the peroneus longus. The proximal partial fibulectomy procedure effected a receptive foot pronation to reduce KAM and rebalance the biceps‐proximal fibula–peroneus longus complex, consequently achieving medial compartment unloading.

The relative position of the human fibula to the tibia influences cross-sectional properties of the tibia

OBJECTIVES

The fibula transmits loads within the lower limb of hominids. The few studies of variation in the cross-sectional geometric (CSG) properties of the fibula have established differences in its rigidity among groups engaged in distinct habitual loading activities. This study adds to this research by considering the relationship between CSG properties and the anatomical position of the fibula relative to the tibia among groups with differences in documented activity patterns.

MATERIAL AND METHODS

We used pQCT scans taken at 50% of the length of the lower leg in 83 healthy young adult collegiate-aged individuals divided into five activity groups: runners, swimmers, cricketers, field hockey players, and non-athletes. We compared variation in calculated CSG properties against the distance between fibular and tibial centroids, as well as the angle of that plane relative to the plane of tibial I_max .

RESULTS

Tibial and fibular CSG properties vary with respect to the relative position of the two bones. Tibial CSG properties differ in concert with the relative angle of the fibula to tibial I_max , while fibular CSG properties differ with the distance between the elements. Fibulae are more posterior-medially positioned in groups engaged in terrestrial athletics than among swimmers.

DISCUSSION

The tibia and fibula experience different loads. The relative position of the two bones leads to compensatory differences in their CSG properties, perhaps due to increased resistance to bending in fibulae with greater distances from the tibia. Examinations of tibial CSG properties without considering the fibula limits interpretations about activity.

Utility of osteon circularity for determining species and interpreting load history in primates and nonprimates

OBJECTIVES

Histomorphological analyses of bones are used to estimate an individual's chronological age, interpret a bone's load history, and differentiate species. Among various histomorphological characteristics that can influence mechanical properties of cortical bone, secondary osteon (Haversian system) population density and predominant collagen fiber orientation are particularly important. Cross-sectional shape characteristics of secondary osteons (On.Cr = osteon circularity, On.El = osteon ellipticality) are considered helpful in these contexts, but more robust proof is needed. We sought to determine if variations in osteon shape characteristics are sufficient for accurately differentiating species, load-complexity categories, and regional habitual strain-mode distributions (e.g., tension vs. compression regions).

MATERIALS AND METHODS

Circularly polarized light images were obtained from 100-micron transverse sections from diaphyses of adult deer calcanei; sheep calcanei, radii, and tibiae; equine calcanei, radii, and third metacarpals (MC3s); chimpanzee femora; and human femora and fibulae. Osteon cross-sectional area (On.Ar), On.Cr, and On.El were quantified indiscriminately and in the contexts of load-complexity and regional strain-mode distributions.

RESULTS

On.Cr and On.El, when examined independently in terms of all data, or mean (nested) data, for each bone, exceeded 80% accuracy in the inter-species comparisons only with respect to distinguishing humans from nonhumans. Correct classification among the nonhuman species was <70%. When On.Cr and On.El were coupled together and with On.Ar in discriminant function analyses (nested and unnested data) there were high misclassifications in all but human vs. nonhuman comparisons.

DISCUSSION

Frequent misclassifications in nonhuman comparisons might reflect influences of habitual load complexity and/or strain-mode distributions, or other factors not accounted for by these two considerations.

Role of the fibula in the stability of diaphyseal tibial fractures fixed by intramedullary nailing

BACKGROUND

For tibial fractures, the decision to fix a concomitant fibular fracture is undertaken on a case-by-case basis. To aid in this clinical decision-making process, we investigated whether loss of integrity of the fibula significantly destabilises midshaft tibial fractures, whether fixation of the fibula restores stability to the tibia, and whether removal of the fibula and interosseous membrane for expediency in biomechanical testing significantly influences tibial interfragmentary mechanics.

METHODS

Tibia/fibula pairs were harvested from six cadaveric donors with the interosseous membrane intact. A tibial osteotomy fracture was fixed by reamed intramedullary (IM) nailing. Axial, torsion, bending, and shear tests were completed for four models of fibular involvement: intact fibula, osteotomy fracture, fibular plating, and resected fibula and interosseous membrane.

FINDINGS

Overall construct stiffness decreased slightly with fibular osteotomy compared to intact bone, but this change was not statistically significant. Under low loads, the influence of the fibula on construct stability was only statistically significant in torsion (large effect size). Fibular plating stiffened the construct slightly, but this change was not statistically significant compared to the fibular osteotomy case. Complete resection of the fibula and interosseous membrane significantly decreased construct torsional stiffness only (large effect size).

INTERPRETATION

These results suggest that fixation of the fibula may not contribute significantly to the stability of diaphyseal tibial fractures and should not be undertaken unless otherwise clinically indicated. For testing purposes, load-sharing through the interosseous membrane contributes significantly to overall construct mechanics, especially in torsion, and we recommend preservation of these structures when possible.

Structural differences in cortical shell properties between upper and lower human fibula as described by pQCT serial scans. A biomechanical interpretation

This study describes the structural features of fibula cortical shell as allowed by serial pQCT scans in 10/10 healthy men and women aged 20-40years. Indicators of cortical mass (mineral content -BMC-, cross-sectional area -CSA-), mineralization (volumetric BMD, vBMD), design (perimeters, thickness, moments of inertia -MIs-) and strength (Bone Strength Indices, BSIs; polar Strength-Strain Index, pSSI) were determined. All cross-sectional shapes and geometrical or strength indicators suggested a sequence of five different regions along the bone, which would be successively adapted to 1. transmit loads from the articular surface to the cortical shell (near the proximal tibia-fibular joint), 2. favor lateral bending (central part of upper half), 3. resist lateral bending (mid-diaphysis), 4. favor lateral bending again (central part of the lower half), and 5. resist bending/torsion (distal end). Cortical BMC and the cortical/total CSA ratio were higher at the midshaft than at both bone ends (p<0.001). However, all MIs, BSIs and pSSI values and the endocortical perimeter/cortical CSA ratio (indicator of the mechanostat's ability to re-distribute the available cortical mass) showed a "W-shaped" distribution along the bone, with maximums at the mid-shaft and at both bone's ends (site effect, p<0.001). The correlation coefficient (r) of the relationship between MIs (y) and cortical vBMD (x) at each bone site ("distribution/quality" curve that describes the efficiency of distribution of the cortical tissue as a function of the local tissue stiffness) was higher at proximal than distal bone regions (p<0.001). The results from the study suggest that human fibula is primarily adapted to resist bending and torsion rather than compression stresses, and that fibula's bending strength is lower at the center of its proximal and distal halves and higher at the mid-shaft and at both bone's ends. This would favor, proximally, the elastic absorption of energy by the attached muscles that rotate or evert the foot, and distally, the widening of the heel joint and the resistance to excessive lateral bending. Results also suggest that biomechanical control of structural stiffness differs between proximal and distal fibula.

Will My Tibial Fracture Heal? Predicting Nonunion at the Time of Definitive Fixation Based on Commonly Available Variables

BACKGROUND

Accurate prediction of tibial nonunions has eluded researchers. Reliably predicting tibial nonunions at the time of fixation could change management strategies and stimulate further research.

QUESTIONS/PURPOSES

We asked (1) whether data from medical records, fracture characteristics, and radiographs obtained at the time of fixation would identify features predictive of tibial fracture nonunion; and (2) whether this information could be used to create a model to assess the chance of nonunion at the time of intramedullary (IM) nail fixation of the tibia.

METHODS

We retrospectively reviewed all tibial shaft fractures treated at our center from 2007 to 2014. We conducted a literature review and collected data on 35 factors theorized to contribute to delayed bone healing. Patients were followed to fracture healing or surgery for nonunion. Patients with planned prophylactic nonunion surgery were excluded because their nonunions were anticipated and our focus was on unanticipated nonunions. Our cohort consisted of 382 patients treated with IM nails for tibial shaft fractures (nonunion, 56; healed, 326). Bivariate and multivariate regression techniques and stepwise modeling approaches examined the relationship between variables available at definitive fixation. Factors were included in our model if they were identified as having a modest to large effect size (odds ratio > 2) at the p < 0.05 level.

RESULTS

A multiple variable logistic regression model was developed, including seven factors (p < 0.05; odds ratio > 2.0). With these factors, we created the Nonunion Risk Determination (NURD) score. The NURD score assigns 5 points for flaps, 4 points for compartment syndrome, 3 points for chronic condition(s), 2 points for open fractures, 1 point for male gender, and 1 point per grade of American Society of Anesthesiologists Physical Status and percent cortical contact. One point each is subtracted for spiral fractures and for low-energy injuries, which were found to be predictive of union. A NURD score of 0 to 5 had a 2% chance of nonunion; 6 to 8, 22%; 9 to 11, 42%; and > 12, 61%.

CONCLUSIONS

The proposed nonunion prediction model (NURDS) seems to have potential to allow clinicians to better determine which patients have a higher risk of nonunion. Future work should be directed at prospectively validating and enhancing this model.

LEVEL OF EVIDENCE

Level III, diagnostic study.

The effect of intact fibula on functional outcome of reamed intramedullary interlocking nail in open and closed isolated tibial shaft fractures: A prospective study

BACKGROUND

Isolated tibial shaft (ITS) fracture with intact fibula is a common injury but records often fail to mention it. Our primary aim was to study the effect of the intact fibula in ITS fractures in closed and open injuries and that these fractures can unite without a primary fibulectomy.

MATERIALS AND METHODS

56 patients who sustained an ITS fracture with an intact fibula who underwent closed or open reduction and reamed intramedullary interlocking nailing (IM IL nail) for closed and open fractures between August 2008 and April 2014 were included in this study. Four patients were lost to followup. One patient died due to causes not related to the surgery. At the time of final followup, 51 patients with 51 ITS fractures were available for the analysis. There were 33 closed and 18 open fractures. Patients were followed up at 4 weekly intervals until radiological signs of union were noted. They were assessed for functional outcome using the IOWA knee and ankle score systems at the time of final followup.

RESULTS

The average time to union was 19.7 weeks. Closed fractures united in 17.7 weeks as compared to 23.5 weeks for open fractures (P < 0.05). A delay in union occurred in 6 patients (4 open) and in 3 patients fractures failed to unite (2 open). The functional outcome as per the knee score and ankle score evaluation system was 93.13 and 92.54, respectively. The knee scores were 93.81 and 91.8 for closed and open ITS fractures, respectively (P > 0.05). Similarly, the ankle scores were 94.96 and 88.1 for closed and open ITS fractures, respectively (P < 0.05).

CONCLUSION

ITS fracture with intact fibula is a common occurrence, and they can be treated safely with reamed IM nailing that provides good union rates and the excellent functional result even in open fractures.

Ankle sprains and instability

Ankle injuries are among the most common injuries presenting to primary care providers and emergency departments and may cause considerable time lost to injury and long-term disability. Inversion injuries about the ankle involve about 25% of all injuries of the musculoskeletal system and 50% of all sports-related injuries. Medial-sided ankle sprains occur less frequently than those on the lateral side. High ankle sprains occur less frequently in the general population, but do occur commonly in collision sports. Providers should apply the Ottawa ankle rules when radiography is indicated and refer fractures and more severe injuries to orthopedic surgery as needed.

Comparative morphometry of the antebrachial and crural interosseous membranes: preliminary study for the use of the crural interosseous membrane in the surgical repair of the antebrachial interosseous membrane tears

INTRODUCTION

Traumatic tears of the antebrachial interosseous membrane (AIOM) on its whole length are difficult to treat, particularly in the Essex-Lopresti syndrome. The number of ligamentoplasty techniques described in the literature witnesses the difficulty of its reconstruction and the absence of reliable and satisfying procedure. The aim of this study was to explore a new way of treatment, which consists in replacing the AIOM by the crural interosseous membrane (CIOM), harvested from the same patient.

MATERIALS AND METHODS

A morphometric study of the AIOM and CIOM has been conducted on both sides of 15 formalin preserved corpses (i.e. 30 AIOM and 30 CIOM). Studied data were: length of forearms and legs, length and width (at different locations) of the membranes, in situ and after harvesting, and orientation of their fibers. The thickness of membrane was also measured but only after harvesting.

RESULTS

Concerning the AIOM, the mean length was 13.3 cm in situ and 12.8 cm after harvesting. Its width was maximal at the union of middle and distal thirds with an average value of 1.7 cm in situ and 1.45 cm after harvesting. Mean thickness was 1 mm. Anterior fibers were oblique distally and medially (20.5° ± 0.95°), and posterior fibers were oblique distally and laterally (40° ± 3.4°). Concerning the CIOM, the mean length was 24.75 cm in situ and 23.9 cm after harvesting. Its width was maximal at the union of proximal and middle thirds with an average value of 2.3 cm in situ and 1.85 cm after harvesting. Mean thickness was 0.5 mm. Obliquity of its fibers was reverse of that of the AIOM: the anterior fibers were quite oblique distally and laterally (13° ± 2.6°), and the posterior fibers oblique were oblique distally and medially (24.2° ± 2.48°).

DISCUSSION

From these results, one may conclude that the largest length and width of the CIOM allow its use as substitute for the injured AIOM. The orientation of its fibers should necessitate either its reversal while using the same side or the use of the CIOM of the opposite side; its relative sharpness could signify that its biomechanical properties could be worse. A biomechanical study is necessary to evaluate how this new way of replacing the AIOM could resist to the strains imposed on the forearm.

Which ankle fractures require syndesmotic stabilization?

Syndesmotic ruptures associated with ankle fractures are most commonly caused by external rotation of the foot, eversion of the talus within the ankle mortise, and excessive dorsiflexion. The distal tibiofibular syndesmosis consists of the anterior inferior tibiofibular ligament, posterior inferior tibiofibular ligament, and interosseous ligament, and it is essential for stability of the ankle mortise. Despite the numerous biomechanical and clinical studies pertaining to ankle fractures, there are no uniform recommendations regarding the use of the syndesmotic screw for specific injury patterns and fracture types. The objective of this review was to formulate recommendations for clinical practice related to the use of syndesmotic screw placement.

The line of action in the tibia during axial compression of the leg

Compression of the leg induces bending in the tibia, which can lead to tensile failure of the bone in the midshaft. The purpose of this study was to determine the orientation of the compressive load vector in the human tibia. Five cadaveric lower extremities were instrumented with in situ 6-axis tibial and fibular load cells and subjected to quasistatic axial leg compression tests in two knee positions and nine ankle positions. For each test, the location and angle of the line of action were calculated at the tibial midshaft. The line of action was extended to the bone ends in order to determine the locations of the effective centers of pressure on the tibial plafond and tibial plateau. The effective center of pressure on the tibial plafond consistently migrated anteriorly in dorsiflexion, laterally in eversion, posteriorly in plantarflexion, and medially in inversion. An opposite pattern was observed on the tibial plateau. When the knee was flexed, the effective center of pressure was generally isolated to a small area in the posterior portion of the medial tibial condyle. The percentage of the axial load borne by the fibula varied from -8% to 19%, and was related to the inversion/eversion angle of the ankle (p<0.02), as well as the distance between the fibula and the axial load path at the midshaft (p<0.001). The line of action through the tibia appeared to follow the external load path to the extent allowed by the available joint contact surfaces.

Stress-induced spiculated periosteal reaction appearing as a malignant bone tumor: a case report

OBJECTIVE

The aim of this study was to describe the appearance of a rare occurrence of a spiculated periosteal reaction caused by stress injury and the subsequent diagnostic assessments. A proposed mechanism for the etiology of stress-induced periosteal reactions in this case is offered.

CLINICAL FEATURES

A 54-year-old female had ankle pain for 1 year. Radiographs revealed a spiculated periosteal reaction of the distal fibula. In light of the clinical history of prior breast carcinoma, the possibility of metastatic disease was entertained.

INTERVENTION AND OUTCOME

Scintigraphy and magnetic resonance imaging were used in the diagnostic evaluation of this patient. Malignancy was ruled out on the basis of the magnetic resonance imaging findings, and an etiology of a stress reaction was proposed based on the scintigraphic findings.

CONCLUSION

Stress-induced spiculated periosteal reactions are a rare occurrence. This case illustrates the role that advanced imaging plays in the assessment of a suspicious periosteal reaction.

Ankle syndesmosis injuries: anatomy, biomechanics, mechanism of injury, and clinical guidelines for diagnosis and intervention

Syndesmosis injuries are rare, but very debilitating and frequently misdiagnosed. The purpose of this clinical commentary is to review the mechanisms of syndesmotic injuries, clinical examination methods, diagnosis, and management of the injuries. Cadaveric studies of the syndesmosis and deltoid ligaments are also reviewed for further understanding of stress transmission and the roles of different structures in stabilizing the distal syndesmosis. External rotation and excessive dorsiflexion of the foot on the leg have been reported as the most common mechanisms of injury. The injury is most often incurred by individuals who participate in skiing, football, soccer, and other sport activities played on turf. The external rotation and squeeze tests are reliable tests to detect this injury. The ability of imaging studies to assist in an accurate diagnosis may depend on the severity of the injury. The results of cadaveric studies indicate the importance of the deltoid ligament in maintaining stability of the distal tibiofibular syndesmosis and the congruency of the ankle mortise. Intervention programs with early rigid immobilization and pain relief strategies, followed by strengthening and balance training are recommended. Heel lift and posterior splint intervention can be used to avoid separation of the distal syndesmosis induced by excessive dorsiflexion of the ankle joint. Application of a rigid external device should be used with caution to prevent medial-lateral compression of the leg superior to the ankle mortise, thereby inducing separation of the distal syndesmosis articulation. Surgical intervention is an option when a complete tear of the syndesmotic ligaments is present or when fractures are observed.

Mechanical contribution of the fibula to torsion stiffness in the lower extremity

The role of the fibula in rotational stability of the lower extremity, taking into account the intact knee joint and tibia, to the best of our knowledge, has not been investigated. A cadaver study was designed to determine the torque transfer down the lower extremity, with and without the fibula. Six fresh, frozen human cadaver legs were used. The knee joint was left intact and the foot disarticulated. An external rotation up to 5 degrees , coupled with axial compression, was applied to the femur passing through the knee joint in extension and down the lower extremity to the fixed distal end, where torque (N m) was measured via a load cell. Each specimen was further tested with the fibula, cut 4 cm from the distal end, and finally with the entire fibula disarticulated at the proximal end and removed. To achieve 5 degrees rotation, torques reached 1.82 N m (SD, 0.66 N m). When the fibula was cut, the torque reduced a small yet significant amount of 5%. With the entire fibula removed, the torque reduction was significant and more pronounced at 11%. The fibula provided a small yet significant role in torsion stability. From this study, where the biomechanical characteristics of the fibula is explicated, it is hoped that this information will have use in further understanding the biomechanical role of the fibula, especially, in relation to the altered mechanics associated with lower limb pathology involving a deficient fibula.

Regenerating the fibula with beta-tricalcium phosphate minimizes morbidity after fibula resection

The aim of this study was to assess the radiologic and clinical outcome when beta-tricalcium phosphate is used as a bone graft substitute to backfill the fibular defect that is created by harvesting the fibula. Fourteen patients who had fibula resections to be used as bone grafts for bone tumor resections were assessed radiographically. Callus formation bridging the beta-tricalcium phosphate was seen in 12 of 14 patients at an average of 1.4 months after surgery. In these 12 patients the beta-tricalcium phosphate mostly was absorbed and replaced by newly formed bone at an average of 9.3 months after surgery. In all children, beta-tricalcium phosphate was replaced by newly formed bone at an average of 3.2 months after surgery. Only one adult patient had complete regeneration of the fibula. Few patients had continuity between the regenerated fibula and the native fibula. In one patient in whom free vascularized fibula was harvested, regeneration of the fibula was not observed. Clinical functional outcome was not correlated with successful fibula regeneration and union with the native fibula, as determined using radiographs. The results of the study suggest that, in children, regeneration of the fibula by implanting beta-tricalcium phosphate into a bone defect can reduce morbidity of the fibula harvest sites.

Tibia fracture after fibula resection for distal peroneal bypass

The lateral approach to the distal peroneal artery has been used by vascular surgeons for 25 years. No complications specifically related to this approach have previously been reported. We reviewed 18 cases of peroneal bypass for limb salvage using the lateral approach with fibula resection and found that two of these cases had ipsilateral tibia fractures within 1 year of the bypass. Eight out of 18 cases were women, and two of these eight had tibia fracture. Both women suffered from osteoporosis. We conclude that tibia fracture is a possible complication of this approach, especially in elderly women with osteoporosis.

The role of fibular fixation in combined fractures of the tibia and fibula: a biomechanical investigation

OBJECTIVES

To determine whether adjunctive plating of the fibula with tibial fixation enhanced the stability of the construct under combined compressive and bending loads in simulated fractures of both the tibia and fibula.

METHODS

Each of twelve fresh cadaveric specimens (six pairs) with an intact knee, lower extremity, and foot was mounted on the table of a materials testing machine. An intramedullary (IM) rod locked in the distal femur allowed combined compression, and flexion, valgus bending, or varus bending loads to be transmitted from the actuator of the testing machine to the knee. Three displacement measurement transducers were mounted on the tibia at anterior, posterolateral, and posteromedial positions. Intact tibial deformations under load were measured. Then, in one specimen of each pair a 2 cm osteotomy was created near the tibial midshaft, which was stabilized with an external fixator. Tibial gap displacements were measured under the following conditions: (a) intact fibula, (b) osteotomized fibula, (c) fibula fixed with a plate, (d) fibula fixed with an Enders IM nail. In the other specimen of the pair, tibial fixation was performed with an interlocked unreamed IM nail, with the same successive stages of fibular fixation.

RESULTS

Osteotomy of the fibula significantly increased tibial defect motion when external fixation was used, and plating the fibula in this case significantly decreased motion. Using an Enders rod to stabilize the fibula instead of a plate, with tibial external fixation, produced smaller decreases in tibial defect site motion. With IM rod fixation of the tibia, osteotomizing the fibula had no effect on defect site motion or on its subsequent stabilization using a plate or IM rod.

CONCLUSION

Plating the fibula can decrease motion across a tibial defect, but only when less rigid (i.e., external) fixation is used.

Biomechanical analysis of nonreamed tibial intramedullary nailing after simulated transverse fracture and fibulectomy

A tibial shaft fracture model was created to study the effects of an intramedullary nail and partial fibulectomy on fracture loading. Cadaveric lower extremities were instrumented with strain gages and subjected to biomechanical testing. A nonreamed nail was inserted into each tibia using only the proximal locking screws. Each specimen was tested under six conditions: intact tibia; intact tibia with nail; fractured tibia with nail removed and fibula intact; fractured tibia with nail and fibula intact; fractured tibia with nail and partial fibulectomy; and fractured tibia with partial fibulectomy and nail removed. In the intact tibia the anterior cortices were in relative tension compared with the posterior cortex. After transverse fracture this relative tension was increased. Inserting the nail after fracture significantly increased anteromedial and anterolateral compressive strains and decreased posterior strains. Performing a partial fibulectomy in the fractured tibia with a nail had no significant effect on the strain patterns. These results confirm the relative anterior tension present in the intact tibia and demonstrate an increase in this anterior tension following transverse fracture. Performing a partial fibulectomy or inserting an intramedullary nail increased anterior compressive loading. This loading alteration may be responsible for the clinical success seen using these treatment methods.