Global and Spatial Compartmental Interrelationships of Bone Density, Microstructure, Geometry and Biomechanics in the Distal Radius in a Colles' Fracture Study Using HR-pQCT

BACKGROUND

Bone parameters derived from HR-pQCT have been investigated on a parameter-by-parameter basis for different clinical conditions. However, little is known regarding the interrelationships of bone parameters and the spatial distribution of these interrelationships. In this work: 1) we investigate compartmental interrelationships of bone parameters; 2) assess the spatial distribution of interrelationships of bone parameters; and 3) compare interrelationships of bone parameters between postmenopausal women with and without a recent Colles' fracture.

METHODS

Images from the unaffected radius in fracture cases (n=84), and from the non-dominant radius of controls (n=98) were obtained using HR-pQCT. Trabecular voxel-based maps of local bone volume fraction (L.Tb.BV/TV), homogenized volumetric bone mineral density (H.Tb.BMD), homogenized μFEA-derived strain energy density (H.Tb.SED), and homogenized inter-trabecular distances (H.Tb.1/N) were generated; as well as surface-based maps of apparent cortical bone thickness (Surf.app.Ct.Th), porosity-weighted cortical bone thickness (Surf.Ct.SIT), mean cortical BMD (Surf.Ct.BMD), and mean cortical SED (Surf.Ct.SED). Anatomical correspondences across the parametric maps in the study were established via spatial normalization to a common template. Mean values of the parametric maps before spatial normalization were used to assess compartmental Spearman's rank partial correlations of bone parameters (e.g., between H.Tb.BMD and L.Tb.BV/TV or between Surf.Ct.BMD and Surf.app.Ct.Th). Spearman's rank partial correlations were also assessed for each voxel and vertex of the spatially normalized parametric maps, thus generating maps of Spearman's rank partial correlation coefficients. Correlations were performed independently within each group, and compared between groups using the Fisher's Z transformation.

RESULTS

All within-group global trabecular and cortical Spearman's rank partial correlations were significant; and the correlations of H.Tb.BMD-L.Tb.BV/TV, H.Tb.BMD-H.Tb.1/N, L.Tb.BV/TV-H.Tb.1/N, Surf.Ct.BMD-Surf.Ct.SED and Surf.Ct.SIT-Surf.Ct.SED were significantly different between controls and fracture cases. The spatial analyses revealed significant heterogeneous voxel- and surface-based correlation coefficient maps across the distal radius for both groups; and the correlation maps of H.Tb.BMD-L.Tb.BV/TV, H.Tb.BMD-H.Tb.1/N, L.Tb.BV/TV-H.Tb.1/N, H.Tb.1/N-H.Tb.SED and Surf.app.Ct.Th - Surf.Ct.SIT yielded small clusters of significant correlation differences between groups.

DISCUSSION

The heterogeneous spatial distribution of interrelationships of bone parameters assessing density, microstructure, geometry and biomechanics, along with their global and local differences between controls and fracture cases, may help us further understand different bone mechanisms of bone fracture.

Fast estimation of Colles' fracture load of the distal section of the radius by homogenized finite element analysis based on HR-pQCT

Fractures of the distal section of the radius (Colles' fractures) occur earlier in life than other osteoporotic fractures. Therefore, they can be interpreted as a warning signal for later, more deleterious fractures of vertebral bodies or the femoral neck. In the past decade, the advent of HR-pQCT allowed a detailed architectural analysis of the distal radius and an automated but time-consuming estimation of its strength with linear micro-finite element (μFE) analysis. Recently, a second generation of HR-pQCT scanner (XtremeCT II, SCANCO Medical, Switzerland) with a resolution beyond 61 μm became available for even more refined biomechanical investigations in vivo. This raises the question how biomechanical outcome variables compare between the original (LR) and the new (HR) scanner resolution. Accordingly, the aim of this work was to validate experimentally a patient-specific homogenized finite element (hFE) analysis of the distal section of the human radius for the fast prediction of Colles' fracture load based on the last generation HR-pQCT. Fourteen pairs of fresh frozen forearms (mean age = 77.5±9) were scanned intact using the high (61 μm) and the low (82 μm) resolution protocols that correspond to the new and original HR-pQCT systems. From each forearm, the 20mm most distal section of the radius were dissected out, scanned with μCT at 16.4 μm and tested experimentally under compression up to failure for assessment of stiffness and ultimate load. Linear and nonlinear hFE models together with linear micro finite element (μFE) models were then generated based on the μCT and HR-pQCT reconstructions to predict the aforementioned mechanical properties of 24 sections. Precision errors of the short term reproducibility of the FE analyses were measured based on the repeated scans of 12 sections. The calculated failure loads correlated strongly with those measured in the experiments: accounting for donor as a random factor, the nonlinear hFE provided a marginal coefficient of determination (R_m²) of 0.957 for the high resolution (HR) and 0.948 for the low resolution (LR) protocols, the linear hFE with R_m² of 0.957 for the HR and 0.947 for the LR protocols. Linear μFE predictions of the ultimate load were similar with an R_m² of 0.950 for the HR and 0.954 for the LR protocols, respectively. Nonlinear hFE strength computation led to precision errors of 2.2 and 2.3% which were higher than the ones calculated based on the linear hFE (1.6 and 1.9%) and linear μFE (1.2 and 1.6%) for the HR and LR protocols respectively. Computation of the fracture load with nonlinear hFE demanded in average 6h of CPU time which was 3 times faster than with linear μFE, while computation with linear hFE took only a few minutes. This study delivers an extensive experimental and numerical validation for the application of an accurate and fast hFE diagnostic tool to help in identifying individuals who may be at risk of an osteoporotic wrist fracture and to follow up pharmacological and other treatments in such patients.

Late dorsal tilt angulation of distal articular surface of radius in Colles' type of fracture at the end of the immobilization, can it be predicted?

BACKGROUND

The objective was to predict the late dorsal tilt angulation of distal articular surface of radius in Colles' type of fracture with radioulna index difference, age, sex of the patient and dorsal cortex comminution.

MATERIAL AND METHOD

Correlation between previously mentioned factors and the changing degree of dorsal tilt angulation of distal articular surface of radius were analyzed. Sixty three wrist radiographs of sixty two patients with Colles' type of fracture were evaluated for dorsal tilt angulation of distal articular surface, radioulna index before and after reduction and at the end of the immobilization, dorsal cortex comminution after reduction. The interobserver and intraobserver generalizability coefficients of the dorsal cortex comminution measurement method were analyzed.

RESULTS

Dorsal cortex comminution, age and sex of the patient were the predictors of the dorsal tilt angulation of distal articular surface of Colles' type of fracture at the end of the immobilization. Partial correlation coefficient for dorsal cortex comminution, age and sex were 0.177, 0.201 and -8.206 respectively. The generalizability coefficients were rated as substantial to excellent.

CONCLUSION

The late dorsal tilt angulation of distal articular surface of radius at the end of the immobilization can be predicted from size of dorsal cortex comminution, age and sex of the patients.

Assessing forearm fracture risk in postmenopausal women

A diverse array of bone density, structure, and strength parameters were significantly associated with distal forearm fractures in postmenopausal women, but most of them were also correlated with femoral neck areal bone mineral density (aBMD), which provides an adequate measure of bone fragility at the wrist for routine clinical purposes.

INTRODUCTION

This study seeks to test the clinical utility of approaches for assessing forearm fracture risk.

METHODS

Among 100 postmenopausal women with a distal forearm fracture (cases) and 105 with no osteoporotic fracture (controls), we measured aBMD and assessed radius volumetric bone mineral density, geometry, and microstructure; ultradistal radius failure load was evaluated in microfinite element (microFE) models.

RESULTS

Fracture cases had inferior bone density, geometry, microstructure, and strength. The most significant determinant of fracture in five categories were bone density (femoral neck aBMD; odds ratio (OR) per standard deviation (SD), 2.0; 95% confidence interval (CI), 1.4-2.8), geometry (cortical thickness; OR, 1.5; 95% CI, 1.1-2.1), microstructure (structure model index (SMI); OR, 0.5; 95% CI, 0.4-0.7), and strength (microFE failure load; OR, 1.8; 95% CI, 1.3-2.5); the factor-of-risk (applied load in a forward fall / microFE failure load) was 15% worse in cases (OR, 1.9; 95% CI, 1.4-2.6). Areas under receiver operating characteristic curves (AUC) ranged from 0.62 to 0.68. The predictors of forearm fracture risk that entered a multivariable model were femoral neck aBMD and SMI (combined AUC, 0.71).

CONCLUSIONS

Detailed bone structure and strength measurements provide insight into forearm fracture pathogenesis, but femoral neck aBMD performs adequately for routine clinical risk assessment.

Prediction of Colles' fracture load in human radius using cohesive finite element modeling

Osteoporotic and age-related fractures are a significant public health problem. One of the most common osteoporotic fracture sites in the aging population is distal radius. There is evidence in the literature that distal radius fractures (Colles' fracture) are an indicative of increased risk of future spine and hip fractures. In this study, a nonlinear fracture mechanics-based finite element method is applied to human radius to assess its fracture load as a function of cortical bone geometry and material properties. Seven three-dimensional finite element models of radius were created and the fracture loads were determined by using cohesive finite element modeling which explicitly represents the crack and the fracture process zone behavior. The fracture loads found in the simulations (731-6793 N) were in the range of experimental values reported in the literature. The fracture loads predicted by the simulations decreased by 4-5% per decade based only on material level changes and by 6-20% per decade when geometrical changes were also included. Cortical polar moment of inertia at 15% distal radius showed the highest correlation to fracture load (r(2)=0.97). These findings demonstrate the strength of fracture mechanics-based finite element modeling and show that combining geometrical and material properties provides a better assessment of fracture risk in human radius.

Is ulnar variance suitable for a parameter of Colles' fracture pre-operatively?

BACKGROUND

To evaluate ulnar variance (UV) as a parameter for Colles' fracture as a measure of the true length of the distal radius pre-operatively, we measured UV pre-operatively in 20 patients with Colles' fractures being treated surgically using the method of perpendiculars. Because the distal fragment is by definition dorsi-flexed, the dorsal edge of the most distal part of the radius is seen proximally and the volar edge of it is seen distally on true postero-anterior x-ray of the wrist.

METHODS

We measured three different UVs in x-rays. UVd is the distance from the dorsal edge of the distal radius to the distal end of the ulnar head. UVv is the distance from the volar edge of the distal radius to the distal end of the ulnar head. We calculated UVc using lateral x-ray of the wrist at the midpoint of the lunate fossa to describe the true length of the distal radius. We compared UVd with UVv or UVc in 20 patients as well as in 11 patients who had dorsal tilt over 15 degrees.

RESULTS

UVv was -3.8 +/- 2.5 mm (average+/-SD). UVd was 2.2 +/- 2.4 mm. UVc was 1.7 +/- 2.2 mm. Statistically, there was a significant difference between UVv and UVd (p < 0.0001). There was no statistically significant difference between UVd and UVc. However, in 11 cases with dorsal tilt over 15 degrees, UVd was 2.2 +/- 2.8 mm and UVc was 1.1 +/- 2.7 mm. There was a statistically significant difference between both groups (p = 0.003).

CONCLUSIONS

The length of the distal radius can be described by measuring UVd pre-operatively in Colles' fracture patient in general. However, the true length of the distal radius can not be described by measuring UVd pre-operatively in cases with marked dorsi-flexion of the distal fragment.

Do Kirschner wires maintain reduction of displaced Colles' fractures?

Fifty-three patients underwent closed reduction and longitudinal k-wiring of displaced Colles' fractures and were reviewed after a mean of 26 months. Radiographs taken at the time of injury, after reduction and k-wiring, and at fracture union were compared for radial shortening and dorsal angulation. Manipulation significantly improved fracture position (P<0.001). Dorsal angulation was successfully corrected by manipulation in 98%, and this position was maintained to fracture union in all cases. Seventy-three percentage of fractures manipulated for radial shortening >2 mm were adequately reduced, but 41% of these fractures subsequently lost position to malunite. In this group of patients, the mean radial shortening between reduction and fracture union was 1.6 mm. This did not correlate with Frykman Class or radial shortening at injury. Closed reduction and k-wire stabilisation is an attractive technique because it is relatively non-invasive compared with plating or external fixation. However, a degree of radial shortening between reduction and fracture union must be anticipated. Fractures reduced inadequately to allow for this loss of radial length, are more likely to malunite. This may compromise functional outcome.

[Treatment of AO type C2-C3 fractures of the distal end of the radius with external fixation]

OBJECTIVES

We evaluated the results of combined treatment with closed reduction, grafting, K-wires, and external fixation in patients with fractures of the distal end of the radius.

METHODS

Of 24 patients (15 males, 9 females; mean age 34 years; range 21-73), 16 patients had C2, eight patients had C3 fractures according to the AO classification. Three patients had open fractures, and four patients had signs of median nerve compression. Treatment included closed reduction, autologous grafting (16 cases) followed by fixation with 2 to 5 K-wires, and an external fixator. Clinical and radiographic results were assessed according to the Gartland-Werley's and Stewart's criteria, respectively, and degenerative changes to the Knirk-Jupiter's criteria. The mean follow-up was 35 months (range 25 to 52 months).

RESULTS

All of the 19 patients who were employed returned to preinjury working conditions in a mean of 3.5 months. Radial length was preserved to a great extent. The mean amount of collapse of the joint surface was 1.4 mm. The mean loss was 6.7% in radial inclination, and 17.6% in the volar tilt. According to the Stewart's criteria, the results were good, moderate, and poor in 12, nine, and three patients, respectively. Flexion-extension (75%), supination-pronation (70%), and radial-ulnar deviation (75%) were preserved to a great extent. Grip force amounted to 70% of the healthy side. According to the Gartland-Werley criteria, three patients had excellent, eight patients had good, 10 patients had moderate, and three patients had poor results. According to the Knirk-Jupiter's criteria, degenerative changes were slight in 11 patients, moderate in six patients, and severe in one patient. Six patients had no signs of degeneration. Complications included pin track infections (n=4), early transient reflex sympathetic dystrophy (n=2), and hypoesthesia along the superficial branch of the radial nerve (n=2).

CONCLUSION

Treatment of the distal end fractures of the radius (AO type C2-C3) with a combination of external fixation, grafting, and percutaneous K-wires provides almost normal radiologic and clinical parameters.

[The effect of long- or short-arm casting on the stability of reduction and bone mineral density in conservative treatment of Colles' fractures]

OBJECTIVES

We evaluated the effect of long- or short-arm casting on the stability of reduction and bone mineral density (BMD) in the forearm in patients treated conservatively for Colles' fractures (CF).

METHODS

Eighty-three patients (48 females, 35 males; mean age 53 years; range 30 to 76 years) with an isolated unilateral CF underwent closed reduction followed by a randomly assigned long-arm (n=44) or short-arm (n=39) casting. Fractures were classified according to the Frykman's system. After reduction, radiographs of both forearms were taken, on which radial height and inclination, and volar tilt were measured and assessed according to the criteria by Sarmiento et al. In the first week, BMD measurements were made on the unaffected side to obtain reference values from four sites of the forearm, namely ultradistal, 1/3 proximal, middle diaphysis, and total. Following removal of the casts (mean 45.3 days; range 40 to 55 days), radiographic and BMD assessments were repeated. Osteoporosis was defined according to the criteria of the World Health Organization.

RESULTS

The two casting groups were similar with respect to age, sex, Frykman's classification, involved side, and the dominant extremity. Osteoporosis was detected in 20% according to the T scores. All the sites in the fractured forearm showed density losses, but the difference was significant only in the middle diaphysis (p<0.05). No significant relationship was found between BMD losses and the cast type. Angular measurements showed significant deterioration after union; however, none was found to be related to the cast type (p>0.05).

CONCLUSION

Our results show that BMD losses and deterioration in reduction following treatment of CF occur irrespective of which type of casting is used.

Intra-articular fractures of the distal aspect of the radius

Intra-articular distal radius fractures are a heterogeneous group of injuries with different fracture patterns. The existing classification systems are helpful for describing the fractures but not for assessing their stability or for deciding which surgical approach to use. Patients who have a fracture with at least 1.0 mm of displacement of the articular surface may benefit from open surgical treatment. Improved diagnostic imaging with CT is helpful for fracture classification and surgical planning. The options for surgical treatment include limited open reduction and internal fixation, arthroscopically assisted internal fixation, and open reduction and internal fixation. The surgical approach is determined on the basis of the initial displacement of the fracture. Patients who have a displaced fracture of the volar rim may benefit from a volar approach; those who have a dorsally displaced fracture, from a dorsal approach; and those who have an impacted fracture such as a die-punch fracture, from a dorsal approach that provides better visualization of the articular surface. The long-term functional outcome is determined in part by the severity of the fracture as defined by the amount of comminution, the initial severity of displacement, and the number of fracture fragments. The accuracy of the reconstruction of the articular surface, with the goal of establishing congruency to within 1.0 mm, is also important in order to minimize the risk of late osteoarthrosis. Of all of the extra-articular parameters, restoration of the length of the radius is the most important for enhancing recovery of motion and grip strength and for preventing problems involving the distal radioulnar joint--the so-called forgotten joint in distal radial fractures.

[Orthopedic treatment of fractures of the lower extremity of the radius by the Judet technique. Anatomic results in function of the type of lesion: apropos of 280 cases]

PURPOSE OF THE STUDY

The authors evaluated the anatomical results and limits of the conservative treatment for displaced Colle's fracture.

MATERIAL AND METHODS

The anatomical results of 280 consecutive fractures were retrospectively analysed. Conservative treatment was performed according to Judet. Stability of the reduction was assessed for grade 0, 1, 2 of Kapandji's classification. Radiographical mean follow-up for all patient was three months (2 months to 8 years).

RESULTS

In 122 cases (64 per cent) mal-union was observed. Mal-union was due in 93.5 per cent of cases (114) to secondary displacement of the distal fragment and in 6.5 per cent (8 cases) to poor reduction. Secondary displacement was essentially posterior in the sagittal plane. The principal factors of instability were radial shortening superior to 3 mm (p = 0.005), patient age of 55 years of more (p = 0.004), metaphyseal comminution (p = 0.004) and degree of primary displacement in the frontal plane (p = 0.01). Stability after reduction was determined by crossing the distal fragment in relation to the anterior cortex of the proximal fragment. There were 10.5 per cent algodystrophies and 9 per cent median nerve paresthesiae which were avoided by 45 degrees of wrist flexion.

DISCUSSION

Judet's conservative treatment is indicated in extra-articular Colle's fractures (grade 0, 1, 2 of Kapandji's classification), after evaluation of factors of instability, secondary displacement and mal-union. Minor mal-unions may be well tolerated, and do not seem to affect wrist function with 3 mm of radial shortening and 10 degrees of radial glenoid posterior angulation on the sagittal plane.

Changes in cortical and trabecular bone in algodystrophy

We studied the pattern of bone loss in the hand of 77 patients with Colles' fracture using metacarpal morphometry, single photon absorptiometry and a radiographic scoring system. Forty-four patients had post-traumatic algodystrophy and the remainder served as controls. Both groups were immobilized in the same manner and for the same period of time and both showed loss of bone during immobilization. The loss of bone 7 weeks after fracture was significantly greater in algodystrophy than in controls both at cortical (P < 0.05) and at trabecular sites (P < 0.001). Recovery of bone occurred in the control patients by 19 weeks after fracture at cortical sites and by 31 weeks in trabecular bone. In contrast, the bone loss seen in patients with algodystrophy persisted for the 6-month duration of the follow-up, and up to 1 year in all nine patients studied for longer. These findings indicate that post-traumatic algodystrophy is associated with regional skeletal losses greater than those following uncomplicated fracture and may result in irreversible changes in the structure and thus the strength of the bony architecture.

Minor axial shortening of the radius affects outcome of Colles' fracture treatment

Functional disability after a Colles' fracture was correlated to the degree of axial shortening of the radius measured at the site of distal radioulnar joint. According to the sum of demerit points, the functional end result was unsatisfactory (fair or poor) in 4% of the patients with an acceptable anatomic result, in 25% of the patients with grade 1 shortening (corresponding to a shortening of 3 to 5 mm), and in 31% of the patients with grade 2 shortening (shortening of more than 5 mm). The results suggest that even a minor axial shortening of the radius, without concomitant malalignment of the articular surface, carries an increased risk of permanent disability.

Fixation not needed for undisplaced Colles' fracture

A series of 68 undisplaced or minimally displaced Colles' fractures was randomized into two groups undergoing treatment with either a plaster cast or an elastic bandage. Pain, function, grip strength, and range of motion were evaluated 1 year later. There was a difference in the functional outcome in favor of the patients treated with an elastic bandage, who did not have more fracture redislocations than those treated with a plaster cast.

Unequal decrease in bone density of lumbar spine and ultradistal radius in Colles' and vertebral fracture syndromes

We measured bone mineral density (BMD) at the lumbar spine (LS-BMD) and ultradistal radius (UDR-BMD) in 42 postmenopausal normal women and in 108 postmenopausal osteoporotic women (55 with vertebral fracture, 34 with Colles' fracture, and 19 with both fractures). By receiver operating characteristic analysis, LS-BMD was better than UDR-BMD (P less than 0.01) as an indicator of vertebral fracture; the converse was true for Colles' fracture (P less than 0.01). Although UDR-BMD and LS-BMD were lower in each of the three fracture groups than in controls (P less than 0.01), the pattern of bone loss differed (P less than 0.001, analysis of variance): with vertebral fracture, LS-BMD decreased relatively more than UDR-BMD; with Colles' fracture, UDR-BMD decreased relatively more than LS-BMD; and with both fractures, decreases in LS-BMD and UDR-BMD were similar. We conclude that both types of fracture are caused by excessive bone loss but the difference in bone loss at the two sites is a major factor in determining which will fracture.

Colles fracture: does the anatomical result affect the final function?

Thirty patients who had sustained a Colles' fracture at least four years previously were examined functionally and radiographically. Seventeen had a good radiological result and 13 were considered to have malunion. Functionally the displaced group performed significantly worse than the undisplaced group. We conclude that malunion of a Colles' fracture results in a weak, deformed, stiff and probably painful wrist.

Hypertrophic ulnar styloid nonunions

Eleven patients with chronic pain on the ulnar side of the wrist and roentgenographic evidence of a hypertrophic ulnar styloid nonunion were treated with subperiosteal excision of the nonunion fragment. This procedure relieved the localized pain without changing either radiocarpal or distal radioulnar joint stability.

The radiological deformity of Colles' fractures

The behaviour of the bony deformity in Colles' fractures and factors influencing this were prospectively investigated in 187 patients over the age of 55. Radiographic assessment was made throughout a 13-week period and during this time the deformity progressively recurred, even after the plaster cast had been removed. Radial length and radial deviation reverted virtually to their positions before reduction. Only those fractures with a volar tilt greater than -15 degrees when first seen showed any improvement. In all fractures the initial deformity clearly influenced the final radiological result whereas the quality of reduction was not of critical importance. The extent of dorsal comminution and quality of the bone influenced the final anatomical result in those fractures which were not manipulated.

External fixation of Colles' fractures. An anatomical study

In a prospective, controlled study 58 patients aged under 60 years with Colles' fractures were treated either by a forearm plaster or by the application of an external fixator. In 94% of those treated by a fixator it was possible to insert the distal pins of the frame into the fracture fragment, the fixation obtained being sufficient to forgo additional splintage. The external fixator proved more effective at holding the manipulated position, and the radiological loss of position during fracture union was minimal compared with that seen in patients treated in plaster.

Trabecular osteopenia in Colles' fracture

Bone density was measured in 23 postmenopausal women with Colles' fracture. Trabecular spine density was measured by quantitative computed tomography. The bone mineral density in the distal radius and in the diaphysis of the radius and ulna was measured by the gamma ray attenuation method. Compared with age-matched controls, the patients were found to have reduced trabecular bone mass in the spine and distal radius, but no osteopenia in the diaphysis of the radius and ulna. The mean age-corrected decrease was 0.7 SD in the spine and 0.5 SD in the distal end of the radius. The results suggest that patients with Colles' fracture have trabecular but not cortical osteopenia.

Study of triangular fibrocartilage of the wrist joint in Colles' fracture

Poor results in Colles' fracture may be due to tears of the triangular fibrocartilage at the wrist joint. A series of patients have been studied by arthrography of the wrist; some were operated on and the findings confirmed. A series of 60 patients was studied.