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Single photon emission computerized tomography and conventional computerized tomography (SPECT/CT) for evaluation of patients after anterior cruciate ligament reconstruction: a novel standardized algorithm combining mechanical and metabolic information

  • Michael T. Hirschmann
  • Dominic Mathis
  • Faik K. Afifi
  • Helmut Rasch
  • Johann Henckel
  • Felix Amsler
  • Christopher R. Wagner
  • Niklaus F. Friederich
  • Markus P. Arnold
Experimental Study

Abstract

Purpose

The purpose of this study was to introduce a novel standardized algorithm using SPECT/CT, which promises the potential combined assessment of the biology of the joint in particular the bone-graft-fixation complex and the 3D tunnel placement in patients after ACL reconstruction. Its clinical application and inter- and intra-observer reliability should be critically evaluated.

Methods

A novel SPECT/CT localization scheme consisting of 13 tibial, 9 femoral and 4 patellar regions on standardized axial, coronal and sagittal slices is proposed. The tracer activity on SPECT/CT was localized and recorded in 25 consecutive patients using a 3D volumetric and quantitative analysis software. The inter- and intra-observer reliability was assessed for localization and tracer activity. The tunnel position was assessed in 3D-CT using standardized frames of reference. The inter- and intra-observer reliability (OR) of the measured distances were calculated (ICC).

Results

The localization scheme for tracer uptake analysis was useful and easily applicable in all 25 knees. It showed very high inter-OR and intra-ORs for all regions (ICC > 0.80). Tibial and femoral tunnel position measurements showed strong agreement between the readings of the two observers; the ICCs for the position, angulation, length and entry point of the femoral tunnel were >0.88 (intra-OR) and >0.86 (inter-OR). The ICC for the position of the tibial tunnel (angulation, length and entry point) was >0.79 (intra-OR) and >0.74 (inter-OR).

Conclusions

The SPECT/CT algorithm presented is highly reliable and clinically feasible. Combining the 3D-mechanical information on tunnel placement and attachment areas and the 3D metabolic data will be helpful in evaluating patients with pain after ACL reconstruction.

Keywords

SPECT/CT Anterior cruciate ligament reconstruction Diagnostics 3D-CT Tracer uptake distribution 3D volumetric analysis 

Introduction

3D-CT is used to accurately evaluate the tunnel placement in patients after ACL reconstruction [1, 6]. Single photon emission computerized tomography and conventional computerized tomography (SPECT/CT), which is obtained as a hybrid imaging modality, promises the potential assessment of the biology of the joint and particularly the bone-graft-fixation complex [6, 19].

To date, SPECT/CT has only been scarcely used in orthopaedic patients [3, 8, 9, 11, 15, 16, 17, 19]. Due to its combination of metabolic, structural and mechanical information, it offers a new dimension for patients with sports-related problems. In patients after ACL reconstruction, SPECT/CT could elucidate the questions why ACL grafts fail as a number of problems such as tunnel position, mechanical axes, tunnel widening and biological problems could be simultaneously evaluated [3, 8, 9, 11, 15, 16, 17, 19].

However, neither a standardized algorithm for evaluating patients after ACL reconstruction nor a specific localization scheme characterizing tracer activity in these patients has been reported. SPECT/CT, which accurately merges single photon emission computerized tomography (SPECT) and computerized tomography (CT) into a single imaging modality, is able to accurately allocate the metabolic activity in a region of interest to specific anatomical areas [8, 9]. With the introduction of a standardized SPECT/CT algorithm including a localization and grading scheme, specific pathological tracer uptake patterns and distributions could be identified. After relating these to graft and tunnel position, it might be possible to predict failure of an ACL reconstruction. It further leads to a better understanding of the biology of ACL graft integration [6].

The purpose of the present study was to introduce a novel standardized SPECT/CT algorithm in these patients and evaluate its clinical applicability, utility and inter- and intra-observer reliability. The proposed algorithm further strives to improve the evaluation of patients after ACL reconstruction [6]. In addition, data collection and comparison of clinical studies using SPECT/CT might be facilitated. The hypothesis was that the proposed diagnostic algorithm using SPECT/CT is highly reliable and easily clinically applicable.

Materials and methods

99mTc-HDP-SPECT/CT images of 25 consecutive patients after ACL reconstruction were prospectively collected and evaluated. The study was approved by the local ethical committee. SPECT/CT was performed using a hybrid system (Symbia T16, Siemens, Erlangen, Germany) that is equipped with a pair of low energy, high-resolution collimators, a dual-head gamma camera and an integrated 16-slice CT scanner (collimation of 16 × 0.75-mm).

All patients received a commercial 700 MBq, Tc-99 m HDP injection (CIS Bio International Sur Yvette, France). Planar scintigraphic images were taken in three phases, the perfusion phase (immediately after injection), the blood pool phase (from 1 to 5 min after injection) and the delayed metabolic phase (at least 2 h after injection). SPECT/CT was performed in the delayed phase with a matrix size of 128 × 128, an angle step of 32 and a time per frame of 25 s 2 h after injection.

Data were processed by interactive reconstruction on a work platform (Syngo, Siemens Erlangen, Germany). Images were displayed in orthogonal axial, coronal and sagittal planes. The CT protocol was modified according to the Imperial Knee Protocol [5].

Tracer uptake analysis

The tracer activity on SPECT/CT was noted using a specialized software (IntroSPECT, OrthoImagingSolutions Ltd., London, UK), which allows a 3D volumetric quantitative analysis of SPECT data as previously published [10]. The localization of the tracer activity was recorded on a standardized localization scheme developed for use in patients after ACL reconstruction (Fig. 1). This scheme defines 13 tibial, 9 femoral and 4 patellar volumes to accurately map the whole examination volume for detecting zones of increased activity. The anatomical area (femur, tibia and patella) is indicated with capital letters (F, T and P). The femur (F) is divided into nine zones that include one shaft and eight distal femoral zones. Each distal femoral zone is represented with a number (1-lateral, 2-medial) and 2 small letters (a-anterior, p-posterior and i-inferior, s-superior). The tibia (T) is divided into 13 zones that include each six proximal and distal tibial regions and one shaft region. Each tibial zone is represented with a number (1-lateral, 2-medial, 3- mid zone) and two small letters (a-anterior, p-posterior and i-inferior, s-superior). The patella (P) is divided into four zones (superomedial, superolateral, inferomedial and inferolateral). The tibial and femoral tunnels are measured as a whole and the entry and exit volume.
Fig. 1

The ‘Bruderholz’ localization scheme for the Tc-99 m HDP-tracer activity in patients after ACL reconstruction (Femur F, Tibia T, Patella P, 1 medial, 2 lateral, 3 central, a anterior, p posterior, i inferior, s superior)

Mean, standard deviation, minimum and maximum of intensity grading for each area of the localization scheme were recorded. Mean and maximum values were used to calculate the intra- and inter-OR. Two orthopaedic surgeons with more than 3 years experience in ACL reconstruction interpreted the SPECT/CT findings. Both observers performed the analysis in all patients three times with 1-week interval between interpretations in random order. All observers were blinded to the results from previous observations. In a previous pilot study, the variability of measurements between each observer and between the measurements of each observer was ±5 % of the measured values.

Measurement of tunnel position and attachment areas

For all measurements, a customized software, which is able to reconstruct three-dimensional images from CT data, was used (Robins3D, London, UK).

Orientation of tibial and femoral tunnels was assessed in relation to the anatomical knee axis. The femoral tunnel entry position was determined in mm distance on 3D-CT in relation to the Blumensaat`s line (anterior–posterior and high–low; Figs. 2 and 3). The tibial tunnel position was determined in mm distance on 3D-CT in relation to the anterior–posterior tibial plateau length and distance to the medial tibial spine (Figs. 2 and 4). The tibial and femoral tunnel length was measured. Two orthopaedic surgeons performed the measurements three times in random order. Both were blinded to results from previous observations. In a previous pilot study, the variability of measurements between each observer and between the measurements of each observer was ±3° and ±2 mm.
Fig. 2

Illustration of performed measurements indicating tibial and femoral tunnel position (1-anatomical femoral axis, 2-transepicondylar axis, 3-anatomical tibial axis, 4-tibial condylar axis, 5 + 6- medial and lateral tibial spine, 7-mid-tibial spine axis, 8-tibial and femoral tunnel exit, 9 + 10-Blumensaat's line)

Fig. 3

Illustration of the 3D-CT determination of femoral tunnel position, orientation and angulation in a patient after ACL reconstruction indicating an anatomical femoral tunnel position

Fig. 4

Illustration of the 3D-CT determination of tibial tunnel position, orientation and angulation in a patient after ACL reconstruction indicating a slightly anterior tibial tunnel position

Statistical analysis

Data were analysed using SPSS 16.0 (SPSS, Chicago, USA). Sample size was calculated according to the reported estimates for reliability studies using intra-class correlation coefficients (ICCs) [22].

The intra- and inter-observer reliability of the localization scheme, grading of the tracer intensity and tunnel position measurements were determined by calculating the intra-class correlation coefficients (ICC) for single measures using a two-way random effects model. Intra-observer reliability was calculated comparing first with second and second with third measurement of each observer. Inter-observer reliability was calculated by comparing each measurement of the two observers separately. We classified an ICC higher than .75 as ‘excellent’, between 0.40 and 0.75 as ‘fair’ to ‘good’ and below 0.40 as ‘poor’ [22].

Results

The localization scheme was useful and easily applicable in all 25 knees. All regions with tracer uptake were present in the localization scheme, and the 99mTc—HDP tracer uptake could be located to specific anatomical regions in all cases. The localization scheme as well as the intensity grading method showed high inter- and intra-observer reliabilities for all regions (tibia, femur, patella and femoral/tibial bone tunnels).

The ICCs are presented in Tables 1 and 2. Figures 2, 3, 4 and 5 show the application of the ‘Bruderholz’ localization scheme and an example measuring the tracer activity in 3D.
Table 1

Inter- and intra-observer reliability (intra-class correlation- ICC) of 99mTc-HDP-SPECT/CT activity using the localization scheme for tibia and femur volumes

Location

Type

Intra-observer reliability

Inter-observer reliability

Obs. 1

Obs. 2

Obs. 1–Obs. 2

M1–M2

M2–M3

M1–M2

M2–M3

M1

M2

M3

F1sa + 1sp

Max

0.913

0.993

0.972

0.988

0.994

0.923

0.964

Mean

0.973

0.994

0.967

0.997

0.998

0.986

0.987

F1ia + 1ip

Max

0.787

1.000

0.997

0.980

0.919

0.871

0.863

Mean

0.856

0.995

0.983

0.998

0.972

0.901

0.897

F2sa + 2sp

Max

0.979

0.997

0.996

0.996

0.994

0.978

0.986

Mean

0.963

0.990

0.969

0.994

0.992

0.982

0.978

F2ia + 2ip

Max

0.950

0.989

0.970

0.998

0.964

0.966

0.978

Mean

0.951

0.997

0.987

0.995

0.991

0.963

0.961

F1sa + 2sa

Max

0.962

0.987

0.990

0.991

0.987

0.979

0.980

Mean

0.986

0.997

0.993

0.992

0.997

0.995

0.978

F1sp + 2sp

Max

0.912

0.998

0.993

0.991

0.978

0.919

0.951

Mean

0.887

0.929

0.832

0.885

0.977

0.884

0.902

F1ia + 2ia

Max

0.825

0.998

0.951

0.994

0.883

0.931

0.934

Mean

0.920

0.991

0.968

0.980

0.986

0.917

0.919

F1ip + 2ip

Max

0.972

0.980

0.936

0.937

0.980

0.936

0.955

Mean

0.941

0.997

0.948

0.986

0.994

0.903

0.918

T1sa + 1sp

Max

0.980

0.989

0.987

0.989

0.998

0.992

0.992

Mean

0.990

0.993

0.995

0.997

0.991

0.985

0.986

T1ia + 1ip

Max

0.970

0.996

0.962

0.995

0.985

0.980

0.958

Mean

0.962

0.992

0.845

0.975

0.984

0.938

0.978

T1as + 1ai

Max

0.991

0.997

0.954

0.999

0.955

0.991

0.993

Mean

0.959

0.974

0.939

0.979

0.962

0.981

0.961

T1ps + 1pi

Max

0.983

0.999

0.982

0.988

0.972

0.992

0.981

Mean

0.991

0.996

0.982

0.995

0.991

0.992

0.994

T2sa + 2sp

Mean

0.972

0.989

0.991

0.991

0.984

0.981

0.977

Std

0.961

0.994

0.974

0.977

0.971

0.952

0.947

T2ia + 2ip

Max

0.972

0.981

0.997

0.983

0.977

0.992

0.986

Mean

0.953

0.960

0.906

0.970

0.989

0.950

0.959

T2as + 2ai

Max

0.972

0.994

0.949

0.994

0.951

0.975

0.979

Mean

0.975

0.942

0.950

0.980

0.954

0.950

0.939

T2ps + 2pi

Max

0.978

1.000

0.984

0.996

0.979

0.983

0.981

 

Mean

0.974

0.988

0.979

0.985

0.982

0.965

0.972

T3sa + 3sp

Max

0.969

1.000

1.000

1.000

1.000

0.970

0.970

Mean

0.939

0.998

0.993

0.992

0.988

0.934

0.938

T3ia + 3ip

Max

0.957

0.991

0.984

0.997

0.975

0.966

0.965

Mean

0.973

0.996

0.951

0.995

0.999

0.979

0.981

T3as + 3ai

Max

0.952

1.000

1.000

1.000

0.997

0.957

0.957

Mean

0.958

0.982

0.984

0.995

0.976

0.952

0.942

T3ps + 3pi

Max

0.973

1.000

0.999

1.000

0.995

0.979

0.979

Mean

0.983

0.998

0.998

0.997

0.997

0.982

0.986

Tsa1 + sa2 + sa3

Max

0.963

0.997

0.992

0.952

0.995

0.969

0.908

Mean

0.918

0.990

0.995

0.991

0.987

0.919

0.911

Tsp1 + sp2 + sp3

Max

0.984

0.988

0.991

0.993

0.993

0.993

0.998

Mean

0.974

0.996

0.992

0.996

0.986

0.983

0.983

Tia1 + ia2 + ia3

Max

0.955

0.995

0.988

0.998

0.990

0.973

0.960

Mean

0.986

0.994

0.931

0.983

0.990

0.963

0.970

Tip1 + ip2 + ip3

Max

0.973

0.991

0.993

0.981

0.991

0.979

0.959

Mean

0.934

0.990

0.904

0.993

0.994

0.987

0.988

Table 2

Inter- and intra-observer reliability (intra-class correlation ICC) of 99mTc-HDP-SPECT/CT measurements for patellar and tibial/femoral tunnel volumes

Location

Type

Intra-observer reliability

Inter-observer reliability

Obs. 1

Obs. 2

Obs. 1–Obs. 2

M1–M2

M2–M3

M1–M2

M2–M3

M1

M2

M3

P1s

Max

0.855

0.973

0.973

0.981

0.999

0.793

0.783

Mean

0.883

0.991

0.991

0.990

0.997

0.841

0.823

P2s

Max

0.938

0.998

0.993

0.996

0.998

0.908

0.911

Mean

0.972

0.997

0.990

0.997

0.994

0.950

0.956

P1i

Max

0.723

0.991

0.998

0.995

0.997

0.724

0.720

Mean

0.837

0.980

0.977

0.968

0.985

0.872

0.861

P2i

Max

0.757

1.000

0.992

0.992

0.965

0.879

0.881

Mean

0.916

0.974

0.988

0.959

0.971

0.960

0.942

tun.fem.

Max

0.934

0.999

0.989

0.995

0.802

0.870

0.864

Mean

0.877

0.996

0.993

0.991

0.803

0.929

0.943

tun.tib.

Max

0.989

0.997

0.996

0.998

0.923

0.925

0.922

Mean

0.992

0.993

0.987

0.996

0.883

0.904

0.900

Overall mean

Max

0.935

0.994

0.983

0.990

0.971

0.942

0.941

Mean

0.946

0.987

0.963

0.984

0.976

0.947

0.947

In addition, the overall mean of all measurements (femur, tibia, patella and tunnels) is given

Fig. 5

Application of the SPECT/CT measurements and localization in a patient with pain after ACL reconstruction showing increased tracer activity within the tibial tunnel

The overall means of all measurements (Table 2) do not show systematic differences between the intra-observer reliability of the two observers, of the comparison of first with second and second with third measure nor between inter-observer reliability between the first, second and third measure. No differences are seen also in the rating of maximum and mean intensity values. For the measurement of localization of the tibial and femoral tunnels, there was strong agreement between the readings of the two observers; the ICC for the position of the femoral tunnel entry point was 0.876 (intra-observer reliability) and 0.858 (inter-observer reliability). The ICC for the position of the tibial tunnel entry was 0.793 (intra-observer reliability) and 0.743 (inter-observer reliability). The inter- and intra-observer reliability of tibial and femoral tunnel position, angulation and length (ICCs) are presented in Table 3.
Table 3

Inter- and intra-observer reliability of tibial and femoral tunnel position, angulation and length (ICCs)

 

Intra-observer reliability

Inter-observer reliability

 

Obs. 1

Obs. 2

Obs. 1–Obs. 2

 

M1–M2

M1–M2

M1

M2

Angulation femoral tunnel ap

0.934

0.935

0.915

0.937

Angulation femoral tunnel lateral

0.973

0.982

0.983

0.941

Angulation femoral tunnel axial

0.946

0.988

0.944

0.959

Femoral tunnel length

0.934

0.979

0.958

0.929

Anterior distance femoral tunnel entry to Blumensaat's line x

0.936

0.876

0.858

0.915

Anterior distance femoral tunnel entry to Blumensaat's line y

0.900

0.905

0.863

0.870

Anterior distance femoral tunnel entry to Blumensaat's line z

0.962

0.947

0.930

0.941

Tibial tunnel angulation ap

0.953

0.958

0.917

0.932

Tibial tunnel angulation lateral

0.936

0.959

0.897

0.853

Tibial tunnel angulation axial

0.957

0.911

0.840

0.907

Tibial tunnel length

0.982

0.964

0.917

0.913

Distance tibial tunnel centre to midpoint tibial spines

0.950

0.935

0.957

0.922

Tibial tunnel exit to mid-tibial spine x

0.951

0.958

0.912

0.913

Tibial tunnel exit to mid-tibial spine y

0.793

0.892

0.743

0.758

Tibial tunnel exit to mid-tibial spine z

0.977

0.893

0.907

0.960

Discussion

Evaluation of patients after ACL reconstruction using SPECT/CT promises the benefit of combining anatomical 3D-CT assessment of the tunnel placement and orientation of the graft with information on joint biology. In particular, information on the loading history of the joint, which is influenced by the laxity of the ACL graft (loose versus too tight), can be obtained [6, 7, 10].

The most important findings and implications of the present study were threefold:

Firstly, a high inter-observer and intra-observer reliability was found for grading and localization of the tracer activity independent of the regions (femur, tibia, patella, femoral and tibial tunnels) investigated. The localization scheme used proved to be a valuable, consistent and useful tool in characterizing tracer activity in patients after ACL reconstruction. With our previously introduced methods, which enable 3D volumetric quantitative measurements and localization of tracer uptake, we are able to identify specific tracer uptake patterns and intensity values correlating with certain pathologies. This is the first study dealing with the use of SPECT/CT evaluating patients after ACL reconstruction.

Secondly, characterization of femoral and tibial tunnel position and orientation in relation to the anatomical knee alignment in 3D reconstructed CT images, which are an inherent part of the SPECT/CT data, offer important additional information to the surgeon for revision surgery. Only if the cause of failure of ACL reconstruction, whether it is tunnel widening, malposition of the graft, chronic synovitis or problems with degradation of biointerference screws is correctly identified, revision surgery could adequately address it [2, 4, 14, 20, 21].

To date, only few studies intended to describe the tunnel position or characterize the ACL graft attachment sites using 3D-CT more in detail [1, 6, 12, 13, 18].

Purnell et al. [18] were the first to describe the bony anatomy of ACL femoral and tibial attachment sites using 3D-CT in a cadaver study.

Basdekis et al. [1] compared the positioning of femoral tunnels in double-bundle ACL reconstruction with the native ACL attachment site using 3D CT. The angle between the longitudinal axis of the attachment site and the axis of the femur was measured. The length and width of the attachment site and the distance to the cartilage margins were measured [1]. They highlighted the clinical benefit of 3D evaluation of the tunnel position including quantification of angles, diameters and distances [1].

Inoue et al. [12] found that 3D-CT is a useful method to quantify femoral tunnel positioning after anatomical double-bundle ACL reconstruction as it allows visualization of any axis and measurement of any structure. Tunnel outlet locations were identified on translucent 3D-CT images in relation to standardized frames of Ref. [12]. The images were evaluated with regards to bone tunnel angles of each tunnel in the coronal, sagittal and axial plane [12]. They concluded that this translucent 3D-CT imaging technique, which is able to view bone cortex and tunnels simultaneously, is useful to evaluate outcome after ACL reconstruction [12].

Iriuchishima et al. [13] evaluated the tunnel position and investigated the relationship between anatomically placed ACL graft and the intercondylar roof using 3D-CT. The problem of all these studies is that the knees were only visualized in 3D, but measurements were widely performed in 2D. The novelty of our study is that we used SPECT/CT and hence added a new dimension of diagnostics to the analysis. In a previously published case report, it has been demonstrated the clinical value of SPECT/CT in combined evaluation of tunnel position and metabolic information [6]. However, an overwhelmingly convincing 3D classification system for ACL tunnel position has not yet been established.

Major limitations of all these studies are the fact that the CT images have not been adequately aligned and orientated to standardized frames of reference before measurements. However, only a reliable method of orientating these images results in reproducible and clinically meaningful data sets. A reliable standardized method to orientate 3D-CT images in relation to frames of reference has been reported recently [9]. The clinical significance of the measured angles and distances has also to be shown.

The important issue of radiation dose has been addressed implementing a low-dose SPECT/CT protocol, which is based on the Imperial Knee CT protocol [5]. Based upon our results, we propose the use of the SPECT/CT algorithm in patients with persistent pain after ACL reconstruction.

In summary, using this proposed SPECT/CT algorithm including anatomical localization and grading of tracer uptake patterns and evaluation of tunnel position and orientation, it might be possible to predict failure of ACL reconstruction. It will further lead to a better understanding of the biology of ACL graft integration.

Conclusion

The SPECT/CT algorithm presented is highly reliable and clinically feasible. Combining the 3D-mechanical information on tunnel placement and attachment areas and the 3D metabolic data will be helpful in evaluating patients with pain after ACL reconstruction.

Notes

Acknowledgments

We greatly thank the Deutsche Arthrose Hilfe e.V, Saarlouis, Germany as well as the Alwin-Jäger-Stiftung, Aschaffenburg, Germany for supporting our research and Jürg Schmutz, Bruderholz for his illustrative work.

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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Michael T. Hirschmann
    • 1
  • Dominic Mathis
    • 1
  • Faik K. Afifi
    • 1
  • Helmut Rasch
    • 2
  • Johann Henckel
    • 3
  • Felix Amsler
    • 4
  • Christopher R. Wagner
    • 5
  • Niklaus F. Friederich
    • 1
  • Markus P. Arnold
    • 1
  1. 1.Department of Orthopaedic Surgery and TraumatologyKantonsspital BruderholzBruderholzSwitzerland
  2. 2.Institute of Radiology and Nuclear MedicineKantonsspital BruderholzBruderholzSwitzerland
  3. 3.Imperial College LondonLondonUK
  4. 4.Amsler ConsultingBaselSwitzerland
  5. 5.OrthoImagingSolutions Ltd.LondonUK

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