Abstract
Objective:
To investigate the value of MRI in comparison to single photon emission computed tomography (SPECT)/CT in patients with painful hip arthroplasties.
Methods:
A prospective, multi-institutional study was performed. Therefore, 35 consecutive patients (21 female, 14 male, mean age 61.8 ± 13.3 years) with 37-painful hip arthroplasties were included. A hip surgeon noted the most likely diagnosis based on clinical examination and hip radiographs. Then, MRI and SPECT/CT of the painful hips were acquired. MRI and SPECT/CT were assessed for loosening, infection, fracture, tendon pathology and other abnormalities. Final diagnosis and therapy was established by the hip surgeon after integration of MRI and SPECT/CT results. The value of MRI and SPECT/CT for diagnosis was assessed with a 3-point scale (1 = unimportant, 2 = helpful, 3 = essential).
Results:
Loosening was observed in 13/37 arthroplasties (6 shaft only, 6 cup only, 1 combined). Sensitivity, specificity, positive predictive value and negative predictive value for loosening of MRI were 86%/88%/60%/100% and of SPECT/CT 93%/97%/90%/100%, respectively. MRI and SPECT/CT diagnosed infection correctly in two of three patients and fractures in two patients, which were missed by X-ray. MRI detected soft tissue abnormalities in 21 patients (6 bursitis, 14 tendon lesions, 1 pseudotumor), of which only 1 tendon abnormality was accurately detected with SPECT/CT. All 5 arthroplasties with polyethylene wear were correctly diagnosed clinically and with both imaging modalities. MRI and SPECT/CT were judged as not helpful in 0/0%, as helpful in 16%/49% and essential in 84%/51%.
Conclusion:
In patients with painful hip arthroplasty SPECT/CT is slightly superior to MR in the assessment of loosening. MRI is far superior in the detection of soft tissue, especially tendon pathologies.
Advances in knowledge:
To our knowledge this is the first prospective, multiinstitutional study which compares MRI with SPECT/CT in painful hip arthroplasties. We found that MRI is far superior in the detection of soft tissue pathologies, whereas SPECT/CT remains slightly superior regarding loosening.
Introduction
Total hip arthroplasty (THA) is the most commonly implanted arthroplasty followed by knee and shoulder joint.1 In the United States, 277,200 primary total hip arthroplasties were performed in 2017 according to the American Joint Replacement Registry 2017 Annual Report.2 With increasing life expectancy and elderly population it is projected that 572,000 hip arthroplasties will be performed in the United States in 2030.3 According to the Swedish arthroplasty register, approx. 12–13% of arthroplasties need hip revision surgery due to loosening, infection, periprosthetic fracture or other reasons.4 Besides imaging with radiographs and planar bone scintigraphy, advanced cross-sectional imaging techniques like CT, MRI and hybrid imaging with single photon emission computed tomography/CT (SPECT/CT) are increasingly used for the evaluation of painful hip arthroplasties.5–9 Since MRI overcame the limitations of artifacts caused by metallic implants with implementation of dedicated metal artifact reduction sequences, it is now possible to adequately evaluate bone and soft tissue abnormalities around hip arthroplasties.10,11 SPECT/CT combines the high sensitivity of SPECT for increased bone metabolism and the morphologic information of CT in one exam.12 Thus, in recent years MRI and SPECT/CT became promising tools for the evaluation of painful hip arthroplasties. However, in this era of medical cost consciousness, it would benefit the surgeon to have an algorithm for ordering more expensive advanced imaging studies when trying to determine the etiology of pain after hip arthroplasty surgery.
To our knowledge, SPECT/CT and MRI has not been compared yet directly in patients with painful hip arthroplasties. Thus, the purpose of our study was to investigate the diagnostic value of MRI in comparison to SPECT/CT in patients with painful hip arthroplasties.
Material and methods
Study design
In total, 35 consecutive patients with 37 painful hip arthroplasties were prospectively enrolled in this study (21 female, 14 male, mean age 61.8 years, range 32–83). All patients were evaluated by a specialized orthopedic hip surgeon with more than 20 years of experience in hip surgery. Inclusion criteria consisted of patients older than 18 years, who presented in outpatient clinic with painful THA at least 1 year after implantation. Furthermore, in all patients conventional radiographs of the pelvis (anteroposterior) and axial views of the affected hips, MRI and SPECT/CT images were acquired. Mean time interval between SPECT/CT and MRI was 3.2 days. No interventions were undertaken between MR and SPECT/CT imaging. Exclusion criteria were patients with contraindications for MRI imaging (severe claustrophobia, non-MR compatible devices), pregnant females and patients under age of 18. Oral and written informed consent was obtained from all participants before enrolment. The study was approved by the local ethics committee ENKZ 2015–179.
Clinical assessment
After inclusion in the study and detailed clinical investigation including radiographs, the orthopedic surgeon was asked to give the most likely diagnosis responsible for the painful hip arthroplasty before MR and SPECT/CT were acquired. Final diagnosis was established by the same orthopedic surgeon after integration of clinical examination and all imaging modalities (radiographs, MR, SPECT/CT). This final assessment served as reference standard.
Radiographs
Conventional radiographs were acquired in all patients in standard anteroposterior and axial views. The plain film findings with comparison to previous X-rays were incorporated in the initial clinical diagnosis prior to MRI and SPECT/CT. For loosening, polyethylene wear, fractures and other findings established criteria were used as outlined below.5,13
SPECT/CT imaging protocol
Dual phase planar and SPECT/CT images of the pelvis and both femurs including the whole arthroplasty were obtained. The radiotracer 99mTc-3,3-diphosphono-1,2-propanedicarboxylic acid (99mTc-DPD) (Teceos, Behringwerke AG, Marburg) was injected intravenously (mean activity 668 MBQ, range 608–730). Early phase planar images of the hips were obtained 5 min after injection (matrix 256 × 256 pixels, field of view: 40 cm) with a hybrid SPECT/CT system with a built-in flat panel CT component (BrightView XCT; Philips Healthcare, Best, The Netherlands). Planar late-phase images of the hips were obtained three hours after radiotracer injection (matrix 256 × 256 pixels, field of view 40 cm). Subsequently, SPECT/CT of the hips was acquired. SPECT was performed in step-and-shoot mode with 64 projections and a frame time of 20 s (SPECT frame format 128 × 128). CT images were acquired with an isotropic voxel size of 1 × 1 × 1 mm (CT slice thickness 1 mm, matrix 512 × 512 mm) with 30 mA and 120 kV and reconstructed with iterative filters. SPECT images were reconstructed with an iterative three-dimensional ordered subsets expectation maximization algorithm (Astonish, Philips). SPECT and CT images were fused automatically with dedicated software (Extended Brilliance Workspace; Philips Healthcare) and reformatted in coronal and sagittal planes.
MRI protocol
All patients were examined on a 1.5 T MR Scanner (Magnetom Aera, Siemens Healtheneers, Erlangen, Germany) using a 18-channel body matrix coil and a 32-channel spine coil. Metal artifact reduction sequence (MARS) were used which allows to reduce the size and intensity of susceptibility artifacts from magnetic field distortion. The detailed protocol and sequences are shown in Table 1.
Table 1. .
MR protocol sequence description Pat No
| Sequence | TIRM | T1 | T1 | T2 | PD |
|---|---|---|---|---|---|
| TE | 3900 | 500 | 520 | 3550 | 3880 |
| TR | 42 | 8 | 7.9 | 85 | 26 |
| Orientation | Coronal | Coronal | Axial | Axial | Sagittal |
| Slice thickness | 4 mm | 3 mm | 4 mm | 4 mm | 3 mm |
| Slices | 30 | 30 | 65 | 65 | 35 |
| Matrix | 384 × 384 | 512 × 512 | 320 × 320 | 384 × 384 | 448 × 448 |
| Field of view | 370 × 370 | 370 × 370 | 220 × 220 | 220 × 220 | 260 × 260 |
| Receiver bandwith (Hz/Pixel) | 395 | 391 | 391 | 352 | 399 |
| Echo train length | 25/slice | 131/slice | 59/slice | 9/slice | 49/slice |
| Acquisition time (min.) | 4:58 | 4:25 | 5:10 | 5:30 | 4:50 |
TE, echo time; TR, repetition time.
SPECT/CT imaging evaluation
SPECT/CT image where reviewed and reported by a doubly board certified radiologist and nuclear medicine physician specialized in musculoskeletal radiology and with 14 years of experience in musculoskeletal SPECT/CT, blinded to the results of MRI.
Loosening was diagnosed according to the combined SPECT/CT criteria published by Dobrindt et al with a combination of increased uptake around the stem or cup together with lucencies.14
Infection was diagnosed in cases with significantly higher vascularity around the arthroplasty in the early phase images and increased uptake in late phase images.
Periprosthetic fractures were diagnosed in cases with linear increased uptake corresponding to fracture lines in CT.
Other findings: Polyethylene wear was diagnosed if the head of the arthroplasty was eccentric in combination with osteolyticlesions in the femur or acetabulum.
MRI evaluation
MR images were reviewed and reported by a specialized musculoskeletal radiologist with 15 years of experience in musculoskeletal radiology, blinded to SPECT/CT results.
Loosening was diagnosed if a layer of hypointense signal intensity on T1 weighted images and intermediate to high signal intensity on short-tau inversion recovery- and intermediated-weighted images around the implant with a thickness over 2 mm was present.15,16
Infection was defined as an increased amount of fluid in the prosthetic joint or in the presence of abscess like formations in the soft tissues.
Periprosthetic fractures were diagnosed if linear T1 weighted hypointense signal alterations of the cortex, trabecular bone, or both, with surrounding bone marrow oedema, were present.7
Other findings: the periprosthetic soft tissues were evaluated for bursitis and other extracapsular fluid and/or debris collection (e.g. pseudotumors or infection) as well as for tendon pathology such as tendon rupture, tendinosis or tenosynovitis. The iliopsoas tendon was evaluated for signs of impingement and/or tendinopathy (idiopathic or related to contact with the cup, fixation screw or retained cement): fluid in iliopsoas bursa and/or abnormal signal of the tendon.6,15 Polyethylene wear was diagnosed in cases of decentration of the arthroplasty head in craniolateral direction combined with synovitis and/or osteolysis.
Value of SPECT/CT and MR
After final clinical decision making, the surgeon judged MRI and SPECT/CT regarding their importance for his final diagnosis and usefulness for decision making with a 3-point scale: 1 – unimportant, 2 – helpful to 3 – essential.
Results
Patients
The 37 arthroplasties of the 35 included patients showed the following characteristics: 21 left and 16 right sided arthroplasties were affected. The majority of arthroplasties were cementless (n = 32) and five were hybrid cemented. Mean age of THA was 7.6 years (SD 8.2 years). In two cases an acetabular reconstruction using an acetabular reinforcement ring with hook was present. Two patients had bilateral painful hip arthroplasties. 19 patients complained about pain at rest with increasing pain under mechanical load and 16 had pain only under mechanical load. In addition, one patient also complained about crepitation. Only two patients had limited range of motion with restricted hip flexion <90 degrees. Summary of patient information and results of clinical and imaging assessment is shown in Tables 2 and 3.
Table 2. .
Summary of patient information and results of clinical and imaging assessment
| Pat. No | Side | Diagnosis based on clinical investigation and x-ray | Diagnosis based on MRI | MR Value | Diagnosis based on SPECT CT | SPECT CT value | Final diagnosis | Further procedure |
|---|---|---|---|---|---|---|---|---|
| 1 | Left | Shaft loosening | Shaft loosening | 3 | Shaft loosening | 3 | Arthroplasty loosening | Arthroplasty exchange |
| 2 | Left | Shaft loosening Gruen zone one suspected | Shaft loosening suspected | 2 | Nothing abnormal detected | 3 | Myalgia gluteus and piriformis muscles | Physiotherapy |
| 3 | Left | Cup loosening suspected | Cup loosening, Bursitis iliopsoas, fracture pubic bone | 3 | Cup loosening fracture pubic bone | 3 | Cup loosening, fracture pubic bone | Cup exchange |
| 4 | Right | Insertional tendinopathy gluteus medius | Insertional tendinopathy abductor muscles | 3 | Nothing abnormal detected | 2 | Insertional tendinopathy | Physiotherapy |
| 5 | Left | Prosthesis loosening, Polyethylene wear | Shaft loosening, Polyethylene wear, bursitis iliopsoas | 3 | Shaft loosening, Polyethylene wear | 2 | Arthroplasty loosening, polyethylene wear | Arthroplasty exchange |
| 6 | Right | Low grade infection | Infection, tear of abductor muscles | 3 | Low grade infection | 3 | Low grade infection suspected | Arthroplasty exchange versus second opinion |
| 7 | Left | Shaft loosening Gruen zone 1–2 | Shaft loosening | 3 | Shaft loosening | 2 | Shaft loosening | Shaft exchange or conservative |
| 8 | Right | Neuralgia parestehtica suspected | Nothing abnormal detected | 3 | Nothing abnormal detected | 3 | Unclear | Physiotherapy |
| 9 | Left | Shaft loosening Gruen zone 1–2,7 and Polyethylene wear | Cup loosening, polyethylene wear, bursitis iliopsoas, gluteal muscle atrophy | 3 | Cup loosening, polyethylene wear | 2 | Cup loosening and Polyethylene wear | Cup exchange |
| 10 | Right | Unclear | Bursitis ischiofemoralis | 3 | Nothing abnormal detected | 2 | Unclear | Wait patiently |
| 11 | Left | Unclear; ectopic ossifications; Impingement | Gluteal muscle atrophy | 2 | Nothing abnormal detected | 3 | Unclear | Lumbar spine evaluation |
| 12 | Left | Cup loosening and implant failure with dislocation of the femoral head, polythylene wear | Cup loosening and polyethylene wear | 2 | Cup loosening, polyethylene wear | 3 | Cup loosening, polyethylene wear | Cup exchange |
| 13 | Left | Pseudotumor | Pseudotumor | 3 | Nothing abnormal detected | 2 | Pseudotumor | Arthroplasty exchange |
| 14 | Left | Shaft loosening | Shaft loosening | 3 | Shaft loosening | 3 | Shaft loosening | Shaft exchange |
| 15 | Left | Unclear corticalis hypertrophia; shaft loosening suspected | Insertional tendinopathy abductor muscles | 3 | Shaft loosening | 2 | Lumbar disc hernia | Physiotherapy hip, lumbar spine surgery |
| 16 | Right | Psoas irritation, shaft loosening Gruen zone 1–2, 7 | Abductor tendon tear | 3 | Nothing abnormal detected | 2 | Abductor tendon tear, posas irritation, bursitis iliopectinea | Injection bursa iliopectinea |
| 17 | Left | Shaft loosening suspected | Shaft loosening | 3 | Beginning shaft loosening, foreign body granuloma | 3 | Beginning shaft loosening | Wait patiently |
| 18 | Right | Cup loosening | Cup loosening | 2 | Cup loosening | 3 | Cup loosening | Cup exchange |
| 19 | Left | Iliotibialis tract irritation, | Iliopsoas tendinopathy | 3 | Nothing abnormal detected | 3 | Iliopsoas tendinopathy | Hip arthroscopy |
| Right | Abductor insufficiency | Partial abductor tendon tear | 3 | Nothing abnormal detected | 3 | Partial abductor tendon tear | Physiotherapy | |
| 20 | Left | Insertional tendinopathy tuber ischiadicum, iliopsoas irritation | Scar tissue trochanter major | 3 | Nothing abnormal detected | 2 | Tuber ischiadicum irritation | Injection tuber ischiadicum |
| 21 | Right | Iliopsoas tendinopathy and reactive bursitis | Slight overlaying cup, iliopsoas tendon friction | 3 | Nothing abnormal detected | 2 | Slight overlaying cup, lumbago | MRI lumbal spine, physiotherapy |
| Left | Iliopsoas tendinopathy and reactive bursitis | Iliopsoas tendinopathy and friction | 3 | Nothing abnormal detected | 2 | Iliopsoas tendinopathy | MRI lumbal spine, physiotherapy | |
| 22 | Left | Arthroplasty loosening | Irritation of the iliotibial band | 3 | Nothing abnormal detected | 2 | Myalgia | Physiotherapy |
| 23 | Right | Insertional tendinopathy gluteus medius, and major trochanter | Abductor tendon tear | 3 | Nothing abnormal detected | 2 | Abductor tendon tear | Surgery—refixation |
| 24 | Right | Insertional abductor tendinopathy and partial rupture | Shaft loosening | 3 | Slight cup overlaying | 3 | Unclear | Physiotherapy |
| 25 | Left | Haft loosening Gruen zone one and Rectus femoris, Iliopsoas irritation | Shaft loosening, Bursitis iliopectinea | 2 | Cup loosening suspected | 3 | Cup loosening, bursitis iliopectinea | Cup exchange and injection bursa iliopectinea |
| 26 | Right | Low grade infection, ischiofemoral impingement | Abductor tendon tear | 3 | Nothing abnormal detected | 2 | Ischiofermoral impingement | Diagnostic hip puncture followed by arthroplasty exchange |
| 27 | Left | Prosthesis loosening | Bursitis iliopectinea | 3 | Nothing abnormal detected | 2 | Abductor atrophy | Physiotherapy |
| 28 | Left | Insertional tendinopathy rectus femoris and bursitis iliopectinea | Nothing abnormal detected | 3 | Nothing abnormal detected | 3 | Myalgia | Physiotherapy |
| 29 | Right | Shaft loosening Gruen zone 7 | Shaft loosening with polyethylene wear | 3 | Polyethylene wear | 3 | Polyethylene wear | Physiotherapy |
| 30 | Left | Muscular dysbalance, proximal shaft loosening | Early arthroplasty loosening, infection | 3 | Infection | 2 | Early arthroplasty loosening, low grade infection | Arthroplasty exchange |
| 31 | Left | Cup and/or shaft loosening, polyethylene wear | Arthroplasty loosening, greater trochanter fracture, polyethylene wear | 2 | Cup loosening, polyethylene wear, greater trochanter fracture | 3 | Arthroplasty loosening, polyethylene wear, greater trochanter fracture | Arthroplasty exchange and trochanter re-fixation |
| 32 | Right | Iliopsoas irritation, shaft loosening Gruen zone 1, 7 | Shaft and cup loosening, acetabular screw in the pelvis adjacent to iliac vessels | 3 | Acetabular screw in the pelvis | 2 | Irritation iliopsoas | Cup exchange |
| 33 | Right | Insertional tendinosis | Nothing abnormal detected | 3 | Beginning shaft loosening | 3 | Enthesopathy | Stimulating X-ray therapy or cutaneus femoris lateralis nerve release |
| 34 | Right | Prosthesis loosening and muscle contractures | Scar tissue between trochanter major and abductor muscles | 3 | Nothing abnormal detected | 3 | Muscle irritation | Physiotherapy |
| 35 | Right | Acetabular lesion | Tumor relapse | 3 | Tumor subacetabular, loosening shaft | 2 | Arthroplasty loosening and tumor relapse | Biopsy, surgery |
Table 3. .
Absolute numbers of pathologies found suspected in X-ray, SPECT/CT, MRI and final diagnosis
| Clinical diagnosis with X-ray | SPECT/CT | MRI | Final diagnosis | |
|---|---|---|---|---|
| Loosening | 20 | 13 | 16 | 13 |
| Infection | 3 | 2 | 2 | 2 |
| Fracture | 0 | 2 | 2 | 2 |
| Tendinopathy/tear | 11 | 1 | 9 | 9 |
| Bursitis | 3 | 0 | 6 | 2 |
SPECT, single photon emission computed tomography.
Loosening
Isolated shaft loosening was suspected after clinical investigation and radiographs in 17/37 (45.9%), with MR in 12/37 (32.4%) and with SPECT/CT in 8/37 (21.6%); and isolated cup loosening in 8/37 (21.6%), 7/37 (18.9%), 7/37 (18.9%), respectively. According to the reference standard loosening was confirmed in 13 arthroplasties. Sensitivity, specificity, positive predictive value and negative predictive value for shaft loosening, cup loosening and combined loosening of shaft and cup are shown in Table 4. Polyethylene wear was suspected clinically in five patients and visible in all five patients in MR and SPECT/CT and also confirmed as final diagnosis (Figure 1).
Table 4. .
Performance of different modalities regarding shaft and cup loosening
| Sensitivity | Specificity | PPV | NPV | |
|---|---|---|---|---|
| MRI overall | 86% | 88% | 60% | 100% |
| MRI cup | 86% | 97% | 90% | 100% |
| MRI shaft | 86% | 80% | 50% | 100% |
| SPECT CT overall | 93% | 97% | 90% | 100% |
| SPECT CT cup | 100% | 100% | 100% | 100% |
| SPECT CT shaft | 86% | 93% | 80% | 100% |
NPV, negative predictive value; PPV, positive predictive value; SPECT, single photon emission computed tomography.
Figure 1. .
A 68-year-old female patient. 28 years old asymptomatic arthroplasty on the right side and symptomatic 33 years old arthroplasty on the left side. Radiographs (A) show decentration of the arthroplasty head (long arrow) as a sign for polyethylene wear and a radiolucent rim around the shaft (short arrow) as sign for shaft loosening. Planar late phase bone scintigraphy image (B) and fused coronal SPECT/CT (G) show slightly increased uptake around the shaft (short arrows) and polyethylene wear (long arrow). Coronal TIRM (D, F) and T1 images show effusion with chronic synovitis (F) caused by polyethylene wear (arrow). Radiographs (C) after arthroplasty exchange. SPECT, single photon emission computed tomography.
Infection
Infection was initially suspected by the surgeon in 3/37 (8.1%) arthroplasties, on MRI in 2/37 (5.4%) and with SPECT/CT in 2/37 (5.4%) (both the same cases). Eventually, infection was confirmed in two arthroplasties (5.4%) as described in the previous MRI and SPECT/CT findings and excluded in one arthroplasty. One further arthroplasty was diagnosed with joint infection which was false negative in MRI and SPECT/CT.
Fractures
One fracture of the greater trochanter was not visible on radiographs, but detected on MRI and SPECT/CT and finally treated operatively (Figure 2). In one patient a fracture of the pubic bone was not visible on radiographs but diagnosed with MRI and SPECT/CT.
Figure 2. .
An 84-year-old female patient with 8 years old arthroplasty and pain. Radiographs (A) without evicence for fracture. Early phase (c), late phase (D), coronal CT (G) and fused SPECT/CT (H) with fracture of the greater trochanter (arrow) and increased linear uptake (arrows). MRI with coronal TIRM (E) and T1 (F) also showing the greater trochanter fracture (arrow). Radiographs (B) after fixation of trochanter and cup exchange. SPECT, single photon emission computed tomography.
Soft-tissue disorders
MRI: abductor tendon tears or tendinitis were suspected clinically in 11/37 (29.7%) arthroplasties, on MRI in 12/37 (32.4%), with SPECT/CT in 0/37 (0%) and confirmed in 8/37 (21.6%). Psoas tendinopathy was suspected by the surgeon before MR/SPECT/CT imaging in 5/37 (13.5%) arthroplasties, with MRI in 3/37 (8.1%), with SPECT/CT in 1/37 (2.7%) and finally confirmed in 4/37 (10.8%). In one case where an overlaying cup was diagnosed, iliopsoas tendinopathy was identified as well (Figure 3). Bursitis was suspected by the surgeon in 3/37 (8.1%) arthroplasties, on MRI in 6/37 (16.2%) and with SPECT/CT in 0 (0%) and finally confirmed in 2 out of 37 (5.4%).
Figure 3. .
A 74-year-old female patient with 9 year old arthroplasty and pain in the left groin. Radiograph (A) without signs of loosening. Planar bone scintigraphy (C) and SPECT/CT (D) without signs for loosening but screw protrusion in the pelvic soft tissues (arrow). Axial (E) and sagittal (F) T1 MR images showing conflict of psoas tendon with cup rim causing deviation and tendinopathy (arrows). Radiographs (B) after cup exchange. SPECT, single photon emission computed tomography.
Conclusions and proposed treatment
Based on the diagnosis, surgery was indicated in 14 arthroplasties to change either the cup (six patients), shaft (two patients) or both (six patients). In addition, one hip arthroscopy and one abductor tendon refixation were indicated. Conservative treatment/ physiotherapy was recommended in 15 arthroplasties. Additionally, in two patients no specific therapy was recommended and in one patient further evaluation of the spine was adviced. Corticosteroid infiltrations were recommended and performed in three trochanteric or iliopectinea bursae and external radiation therapy in one case with enthesiopathy.
Value of SPECT/CT and MR
The value of MRI and SPECT/CT for clinical decision-making was judged by the surgeon as not helpful in 0% (both modalities), as helpful in 16.2 and 48.6% and essential in 83.8 and 51.4%, respectively (Figure 4).
Figure 4.
Impact of SPECT/CT and MRI for final diagnosis as judged by the refering orthopedic surgeon. SPECT, single photon emission computed tomography.
Discussion
In this first direct comparison between MRI with MARS protocol and SPECT/CT in patients with painful hip arthroplasties, we showed that both modalities provide complementary information. SPECT/CT might serve as reference standard for loosening, positioning of the components and visualization of osteolysis and bone structure. However, SPECT/CT is clearly limited in the diagnosis of soft tissue and tendon abnormalities. MRI excels SPECT/CT for the detection of bursitis, pseudotumors and tendinopathy. Iliopsoas tendinopathy is observed in about 4.3% patients presenting with painful hip arthroplasty, but substantially higher in our study population (13.5%).17 Abductor (gluteus medius and minimus) tendon tears and greater trochanteric bursitis can cause lateral hip pain after hip replacement and can be assessed by ultrasound or MRI.18,19 No difference was seen in MRI and SPECT/CT regarding the diagnosis of infection. However, since only two infected arthroplasties were observed in this study no representative insights could be obtained. Of note, infection after hip arthoplasty is difficult to diagnose on imaging alone and typically combines serologic testing of inflammatory markers (sedimentation rate and c-reactive protein), a diagnostic aspiration of the joint as well as possible biopsy for microbiological testing.
SPECT/CT in the work-up of painful hip arthroplasties is increasingly used due to wider availability of SPECT/CT scanners in larger hospitals. Nevertheless, studies are still sparse. Dobrindt et al investigated 23 patients with painful hip arthroplasties and reported that the cause of pain could be identified with SPECT/CT in 13 of 18 cases.14 Loosening was correctly assessed in all cases. In that paper the authors provided combined SPECT/CT criteria for loosening of the acetabular and femoral component, which we also used in our study. Tam et al described in their review article useful criteria for abnormalities causing pain after hip arthroplasties, such as infection, periprosthetic fractures, heterotopic ossifications and polyethylene wear.20 Berber et al investigated SPECT/CT in 15 patients with painful hip arthroplasties and showed that SPECT/CT changed the management decision in 13 patients (68%) while loosening was the most frequent SPECT/CT diagnosis.21 Arican et al reported superiority of SPECT/CT over planar/ SPECT in 20 hip arthroplasties with sensitivities of 94.1 and 93.3% for loosening of the femoral component and 89.4 vs 57.8% for the acetabular component.22 With the newest generation of SPECT/CT scanners implementation of metal artifact suppressed diagnostic CT becomes available for improved evaluation of bone and soft tissue structures around the metal implants.12 Further important information of SPECT/CT can be obtained if three-dimensional reconstructions and measurements of the component positions are provided as shown in a recent study.23 Implementation of quantification and reconstruction algorithms such as xBone SPECT/CT in daily routine bone and joint SPECT/CT imaging are further promising tools for the assessment of painful arthroplasties.24
Interestingly, Robinson et al compared MRI with metal artifact reduction sequences with CT in 50 patients with painful arthroplasty. In that study, MRI was superior in pseudotumor detection (50% detection rate versus 22% with CT) and classification of pseudotumors.25 For high risk patients including high serum cobalt, high cup inclination of more than 45° and female gender, the incidence of pseudotumors is up to 59 vs 0% in low risk patients based on MARS-MRI.26 For the identification of osteolysis, CT had a clearly higher detection rate (30%) compared to MR (8%). Furthermore, Robinson showed that CT was unreliable for the assessment of muscle atrophy. These authors concluded that CT is an unsuitable substitute for MR regarding soft tissue abnormalities associated with hip arthroplasties.
Other studies which investigated the usefulness of MRI and related adverse local tissue reaction after hip arthroplasty reported a sensitivity of 86.4% and specificity of 60.2%.27 Nowadays MARS-MRI provides a good tool to overcome artifacts of metal implants especially in orthopaedic surgery and traumatology in comparison to MRIs.28 This sequence has broadened the indications and usefulness in diagnostics. Therefore, lower magnetic strengths are required (1.5 T), shorter echo spacing, short-tau inversion recovery for fat suppression, spin echo instead of gradient echo as well as smaller water-fat shift and thinner slices.29 Further research is focusing on newer sequences which include slice-encoding metal artifact correlation and view-angle tilting turbospin echo MR, which show even higher resolution and reduces metal artifact significantly in comparison to the normal turbospin echo MRI.30–32
In our study MRI with metallic artifact reduction protocol provided slightly more value to the surgeon for the diagnosis and clinical decision-making than SPECT/CT. This result represents the opinion of experienced hip surgeons in one institution only and might be biased by individual and institutional preference. Our results might help in the selection of advanced imaging and are in line with the proposed imaging flowchart published recently12: if conventional radiography is inconclusive and clinical examination favors a soft tissue pathology such as tenderness over the abductors or trochanteric bursa as the pain generator in patients with hip arthroplasties MARS-MRI or ultrasound might be the best second line imaging modality. If loosening, periprosthetic fractures or heterotopic calcifications are suspected, SPECT/CT might be the better imaging modality (Figure 5).33 Similar findings were described in girdlestone arthroplasty with higher specificity and equivalent sensitivity for SPECT/CT compared with MRI (SPECT/CT sensitivity 90% specificity 94% respectively 90 and 87% for MRI.34 Because of the complimentary information obtained by both techniques, the concurrent use might be necessary in some patients. MRI may also be contraindicated in patients with severe claustrophobia, metallic implants such as cardiac pacemakers or stimulators, which is not uncommon in this population.A limitation of our study was the relatively small sample size. Another limitation was that only one reader assessed the MRI images and SPECT/CT images, respectively. Hence, the final diagnosis might be biased on the readers’ experience. However, as both readers were highly specialized, we are convinced that a multireader setup would not substantially improve our results.
Figure 5. .
Diagnostic algorithm for painful hip arthroplasty adopted from van den Wyngaert et al.; * followed by dedicated radionuclide infection imaging if required.12
In conclusion, in patients with painful hip arthroplasties SPECT/CT is slightly superior to MRI in the assessment of loosening. However, only MRI detects soft tissue pathologies such as abductor or psoas tendon lesions accurately and its value to the surgeon was rated higher compared to SPECT/CT. The hip surgeon should likely initially evaluate the painful hip with plain radiographs and laboratory serologic testing. If the diagnosis is still elusive, this generalized approach of loosening versus soft-tissue pathology should be considered when ordering advanced imaging studies.
Key points
There is an increasing number in hip arthroplasty revision surgeries.
The diagnosis of prosthesis infection or loosening include conventional imaging as well as hip puncture, however the importance of magnetic resonance imaging and SPECT/CT is increasing.
Based on our study, SPECT/CT is still slightly superior to MRI in the assessment of loosening, however MRI is far superior in the detection of soft tissue pathologies and was found to give more informative value to the orthopaedic surgeron.
Contributor Information
Henrik C. Bäcker, Email: henrik.baecker@sports-med.org.
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Klaus Strobel, Email: klaus.strobel@luks.ch.
REFERENCES
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