Klinische Wochenschrift
Klin. Wochenschr. 57, 763-767 (1979)
© Springer-Verlag 1979
Loss and Recovery of Trabecular Bone in the Distal Radius Following Fracture - Immobilization of the Upper Limb in Children* U. Etsasser 1'**, P. Rfiegsegger1, M. Anliker 1, G.U. Exner 2, and A. Prader 2 1 Institute for Biomedical Engineering, University and Federal Institute of Technology Zfirich 2 Department of Pediatrics and Pediatric Surgery, University of Z/irich
Dynamik von Spongiosaverlust und -erholung im distalen Radius nach Immobilisation der oberen Extremit~it bei Kindern Zusammenfassung. Durch die Anwendung eines Spezialscanners mit 125I als Strahlenquelle wird der menschliche Radius computertomographisch analysiert. Parameter ftir Spongiosa und Compacta k6nnen an einem metaphysfiren und diaphys/iren Met3ort separat bestimmt werden. Mit dieser Technik wurden Anderungen der Knochenmineralisation nach Immobilisation wegen einer Fraktur an der oberen Extremit/it bei 23 Kindern bestimmt. Eine Immobilisationsperiode von 3 6 Wochen ftihrte zu einer Abnahme der Spongiosadichte bis zu 44% (Mittelwert 16%) im distalen Radius, wfihrend keine signifikanten Anderungen an der Compacta der Diaphyse festzustellen waren. Eine rasche Remineralisation der Spongiosa konnte beobachtet werden, jedoch war diese bei einigen Patienten 6 Monate nach Gipsentfernung noch nicht vollstfindig. Sehliisselwiirter: Fraktur tertomographie (CT)
Spongiosadichte
Compu-
Summary. Computed tomography of the human radius is performed using a special purpose scanning device which incorporates a radionuclide (125I) as radiation source. Parameters describing the trabecular bone and the compact bone are determined at a distal and a diaphyseal measuring site respectively. Using this measurement technique changes in bone mineralization in the radius were studied in a * This work has been supported in part by the Swiss National Science Foundation ** Present address: Radioisotopes Division, MRC Clinical Research Centre, Harrow, Middlesex HAl 3UJ, England Oj,fprint requests to ." Pro[" Dr. A. Prader (address see p. 767)
group of 23 children following immobilization of an upper limb for fracture healing. An immobilization period of between three to six weeks resulted in a reduction of the relevant parameter value of up to 44% (mean 16%) in the distal part of the radius, whereas no significant change could be seen in the diaphyseal part of the same bone. Rapid remineralization of trabecular bone is indicated by the increase of the corresponding parameter value at a rate of up to several percent per week. However, in some of the patients studied complete normalization was not attained during the first six months following cast removal. Key words: Fracture tomography (CT)
Trabecular bone - Computed
Loss and recovery of bone mineral after fracture has previously been investigated in adults and children using photon absorptiometry [e.g., 7, 9, 1012, 17]. Other bone mineral measurement methods in clinical use include radiography [16] and bone biopsy [8]. With the exception of bone biopsy none of these techniques allow for a selective measurement of trabecular bone mass or density. However, trabecular bone is expected to show changes in mineralization earlier and these changes to be more pronounced than in cortical bone. Thus, measurements of bone mineral parameters for trabecular bone should be more sensitive than the total mineral content as assessed by photon absorptiometry. Bone mineral measurements using computed tomography (CT) are based on the evaluation of the distribution of the linear attenuation coefficients of the tissues within a bone cross section, thus allowing for the selective analysis of areas containing trabecular bone and bone marrow. We have applied a CT
U. Elsasser et al. : Trabecular Bone Following Fracture-Immobilization
764
technique first described by Riiegsegger etal. [13], which uses a special purpose scanner equipped with a low energy photon source (~25I) instead of the X-ray tube used in commercial CT systems. The method is r e f e r r e d t o a s g a m m a - r a y
computed
tomography
(?-CT). This technique allows the quantitative determination of the mean linear attenuation coefficient of various regions within a bone cross section with a r a d i a t i o n d o s e o f less t h a n t w o m r a d .
Subjects and Methods Twenty-three children (nine girls and 14 boys) treated with plaster cast immobilization for fracture of the forearm, fracture of the humerus or luxation of the elbow were studied. The subjects are distributed according to the fracture site as shown in Table 1. Neither duration of immobilization nor mean age differed significantly between the groups formed according to the fracture site. None of the patients showed signs of any other illness before or during the study. Details of the technique and instrumentation used in this study and preliminary results have been reported previously [24, 13]. Measurements are made for the radius only; measurement sites were determined relative to ulna length and are situated 10% and 33% of ulna length proximal to the styloid process of the ulna. By evaluating the radiographs of the fractured limb any interference between measuring site and fracture zone was excluded. Figure 1 displays four computer tomograms representing reconstructed images of cross sections through the metaphyseal and diaphyseal parts of the fractured and of the uninjured forearm of one of the patients. Each image is based on a matrix of 128 x 128 local linear attenuation coefficients. From the distributions of the linear attenuation coefficients the following two parameters can be computed: 1. TBD (Trabecutar Bone Density) ; defined as the mean linear attenuation coefficient (cm-1) of a 50% core area in the cross section of the radius at 10% ulna length. This region of the radius consists of trabecular bone and bone marrow.
Fig. 1, Tomograms and corresponding parameter values in both forearms of a t ll/2-year-old boy who had sustained a fracture of the left elbow. Immobilization by a plaster cast lasted 3 weeks, the measurements shown were carried out immediately after cast removal. Measuring sites on the radius are 10% and 33% of ulna length proximal to the styloid process of the ulna. The tomograms also show the muscIe atrophy of the injured arm
2. BD (Bone Density); defined as the mean linear attenuation coefficient (cm ~1) of the total cross section of the radius at 33% ulna length. This part of the radius consists of compact bone and bone marrow. The deviation of either TBD or BD of the fractured from the healthy arm is expressed as A(%)
fractured - healthy healthy
100.
Table 1. Differences between TBD and BD of the radius of the injured and healthy arm n
Site of fracture
Age
Duration of immobilization
ATBD °
(years)
(weeks)
(%)
7
Proximal or middle third of radius and/or ulna
2-+SD range
9.3_+ 2.7 6.4... 14.9
4.0+ 1.2 3 ...6
-16.4+ 13.2 - 1.5.. -44.0
9
Radius -loco classico-
2+_SD range
10.4+ 2.2 7.8... t3.2
3.6-+0.6 3 ...5
Fracture site interference
7
Distal humerus and/or luxation of elbow
)?+SD range
9.8-+ 3.2 6.6...15.7
4.0+_ 1.2 3 ...6
-16.6+_ I1.5 - 4.4.. -38.0
a
pb
A BD"
p~
(%)
Klin. Wochenschr. 57, 763-767 (1979)
© Springer-Verlag 1979
Loss and Recovery of Trabecular Bone in the Distal Radius Following Fracture - Immobilization of the Upper Limb in Children* U. Etsasser 1'**, P. Rfiegsegger1, M. Anliker 1, G.U. Exner 2, and A. Prader 2 1 Institute for Biomedical Engineering, University and Federal Institute of Technology Zfirich 2 Department of Pediatrics and Pediatric Surgery, University of Z/irich
Dynamik von Spongiosaverlust und -erholung im distalen Radius nach Immobilisation der oberen Extremit~it bei Kindern Zusammenfassung. Durch die Anwendung eines Spezialscanners mit 125I als Strahlenquelle wird der menschliche Radius computertomographisch analysiert. Parameter ftir Spongiosa und Compacta k6nnen an einem metaphysfiren und diaphys/iren Met3ort separat bestimmt werden. Mit dieser Technik wurden Anderungen der Knochenmineralisation nach Immobilisation wegen einer Fraktur an der oberen Extremit/it bei 23 Kindern bestimmt. Eine Immobilisationsperiode von 3 6 Wochen ftihrte zu einer Abnahme der Spongiosadichte bis zu 44% (Mittelwert 16%) im distalen Radius, wfihrend keine signifikanten Anderungen an der Compacta der Diaphyse festzustellen waren. Eine rasche Remineralisation der Spongiosa konnte beobachtet werden, jedoch war diese bei einigen Patienten 6 Monate nach Gipsentfernung noch nicht vollstfindig. Sehliisselwiirter: Fraktur tertomographie (CT)
Spongiosadichte
Compu-
Summary. Computed tomography of the human radius is performed using a special purpose scanning device which incorporates a radionuclide (125I) as radiation source. Parameters describing the trabecular bone and the compact bone are determined at a distal and a diaphyseal measuring site respectively. Using this measurement technique changes in bone mineralization in the radius were studied in a * This work has been supported in part by the Swiss National Science Foundation ** Present address: Radioisotopes Division, MRC Clinical Research Centre, Harrow, Middlesex HAl 3UJ, England Oj,fprint requests to ." Pro[" Dr. A. Prader (address see p. 767)
group of 23 children following immobilization of an upper limb for fracture healing. An immobilization period of between three to six weeks resulted in a reduction of the relevant parameter value of up to 44% (mean 16%) in the distal part of the radius, whereas no significant change could be seen in the diaphyseal part of the same bone. Rapid remineralization of trabecular bone is indicated by the increase of the corresponding parameter value at a rate of up to several percent per week. However, in some of the patients studied complete normalization was not attained during the first six months following cast removal. Key words: Fracture tomography (CT)
Trabecular bone - Computed
Loss and recovery of bone mineral after fracture has previously been investigated in adults and children using photon absorptiometry [e.g., 7, 9, 1012, 17]. Other bone mineral measurement methods in clinical use include radiography [16] and bone biopsy [8]. With the exception of bone biopsy none of these techniques allow for a selective measurement of trabecular bone mass or density. However, trabecular bone is expected to show changes in mineralization earlier and these changes to be more pronounced than in cortical bone. Thus, measurements of bone mineral parameters for trabecular bone should be more sensitive than the total mineral content as assessed by photon absorptiometry. Bone mineral measurements using computed tomography (CT) are based on the evaluation of the distribution of the linear attenuation coefficients of the tissues within a bone cross section, thus allowing for the selective analysis of areas containing trabecular bone and bone marrow. We have applied a CT
U. Elsasser et al. : Trabecular Bone Following Fracture-Immobilization
764
technique first described by Riiegsegger etal. [13], which uses a special purpose scanner equipped with a low energy photon source (~25I) instead of the X-ray tube used in commercial CT systems. The method is r e f e r r e d t o a s g a m m a - r a y
computed
tomography
(?-CT). This technique allows the quantitative determination of the mean linear attenuation coefficient of various regions within a bone cross section with a r a d i a t i o n d o s e o f less t h a n t w o m r a d .
Subjects and Methods Twenty-three children (nine girls and 14 boys) treated with plaster cast immobilization for fracture of the forearm, fracture of the humerus or luxation of the elbow were studied. The subjects are distributed according to the fracture site as shown in Table 1. Neither duration of immobilization nor mean age differed significantly between the groups formed according to the fracture site. None of the patients showed signs of any other illness before or during the study. Details of the technique and instrumentation used in this study and preliminary results have been reported previously [24, 13]. Measurements are made for the radius only; measurement sites were determined relative to ulna length and are situated 10% and 33% of ulna length proximal to the styloid process of the ulna. By evaluating the radiographs of the fractured limb any interference between measuring site and fracture zone was excluded. Figure 1 displays four computer tomograms representing reconstructed images of cross sections through the metaphyseal and diaphyseal parts of the fractured and of the uninjured forearm of one of the patients. Each image is based on a matrix of 128 x 128 local linear attenuation coefficients. From the distributions of the linear attenuation coefficients the following two parameters can be computed: 1. TBD (Trabecutar Bone Density) ; defined as the mean linear attenuation coefficient (cm-1) of a 50% core area in the cross section of the radius at 10% ulna length. This region of the radius consists of trabecular bone and bone marrow.
Fig. 1, Tomograms and corresponding parameter values in both forearms of a t ll/2-year-old boy who had sustained a fracture of the left elbow. Immobilization by a plaster cast lasted 3 weeks, the measurements shown were carried out immediately after cast removal. Measuring sites on the radius are 10% and 33% of ulna length proximal to the styloid process of the ulna. The tomograms also show the muscIe atrophy of the injured arm
2. BD (Bone Density); defined as the mean linear attenuation coefficient (cm ~1) of the total cross section of the radius at 33% ulna length. This part of the radius consists of compact bone and bone marrow. The deviation of either TBD or BD of the fractured from the healthy arm is expressed as A(%)
fractured - healthy healthy
100.
Table 1. Differences between TBD and BD of the radius of the injured and healthy arm n
Site of fracture
Age
Duration of immobilization
ATBD °
(years)
(weeks)
(%)
7
Proximal or middle third of radius and/or ulna
2-+SD range
9.3_+ 2.7 6.4... 14.9
4.0+ 1.2 3 ...6
-16.4+ 13.2 - 1.5.. -44.0
9
Radius -loco classico-
2+_SD range
10.4+ 2.2 7.8... t3.2
3.6-+0.6 3 ...5
Fracture site interference
7
Distal humerus and/or luxation of elbow
)?+SD range
9.8-+ 3.2 6.6...15.7
4.0+_ 1.2 3 ...6
-16.6+_ I1.5 - 4.4.. -38.0
a
pb
A BD"
p~
(%)
