Periprosthetic joint infection (PJI) is a catastrophic complication after total hip arthroplasty (THA). A key step in addressing this situation is timely and accurate diagnosis. Most currently available tests for diagnosing PJI are based on synovial fluid analysis and include synovial white blood cell count, polymorphonuclear cell percentage, leukocyte esterase strip test, and culture.1 Thus, aspiration is a key procedure for PJI diagnosis.
In contrast to the knee, localization of the hip may be hindered by both body habitus and the inherently deep location of this joint.2 Many centers rely on various imaging methods, including fluoroscopy,3–9 ultrasound,10–12 or, less commonly, computed tomography13 to obtain satisfactory rates of successful aspiration. However, these methods have several disadvantages. First, image-guided procedures require specialized instrumentation, a particular location, and specially trained technicians. The procedure for performing aspiration is also complicated. Second, guidance based on radiograph modalities such as fluoroscopy is harmful to both physicians and patients. Finally, there is an additional medical burden placed on patients. Given these aspects, simple anatomic landmark-guided aspiration seems to have advantages compared with image-guided aspiration.
The reason surgeons prefer image-guided aspiration is the belief that it has a higher success rate for hip aspiration.14 However, the aspirations in previous studies were performed in native hips. In subjects with hip prosthetics, it may be easier to distinguish whether the needle is in the right place due to the metal-on-metal sensation that can be appreciated as the needle contacts the neck of the prosthesis. Thus, this technique may have higher success rates in subjects with hip prosthetics than in those with native hips. Until now, no clinical studies that evaluated the results of simply using anatomic landmarks for aspiration and the detection of PJI have been published.
The purpose of this study was to investigate the feasibility of anatomic landmark-guided hip aspiration in the diagnosis of PJI by reviewing patients who underwent aspiration and evaluating the following aspects: (1) the aspiration failure rate, (2) the sensitivity and specificity of cultures, and (3) the incidence of complications.
Materials and Methods
Patient and Public Involvement
The research ethics board of the authors' institution approved this study. The authors retrospectively reviewed a total of 186 consecutive hip aspirations. All of these aspirations were performed by the first author (R.L.) as part of routine workup between April 2015 and December 2018. Patients with any suspicion of infection after THA, such as an acute onset of pain or persistent pain since surgery, an increased erythrocyte sedimentation rate and/or C-reactive protein level, or implant failure within 5 years after a primary THA without any reasonable explanation, were included. Patients with other implants, such as a spacer in the joint rather than a prosthesis, were excluded.
Hip Aspiration Procedure
The hip aspiration procedure is shown in Figure 1. The authors aimed to aspirate at the neck of the prosthesis. They located the y-axis of the puncture point approximately 2 to 3 cm lateral to the pulse of the femoral artery in the region of the inguinal ligament (Figure 1A). The x-axis was estimated by the pubic symphysis or the greater trochanter according to an anteroposterior radiograph of the hip joint (Figure 1B). The procedure was performed with the patient in the supine position, and iodine and alcohol were used for disinfection (Figure 1C). Topical infiltration of 2% lidocaine was performed for anesthesia, and the authors were careful not to inject lidocaine into the joint. After anesthesia was completed, a No. 20 spinal needle (0.9 mm × 90 mm) attached to a 10-mL syringe was used for aspiration. There would be resistance when the needle crossed the tough joint capsule before entering the articular cavity and a breakthrough sensation when the metal needle entered the articular cavity. A metal friction sensation caused by the metal needle contacting the lateral neck of the prosthesis provided assurance that the needle was in the right place. If the needle was not in the right place on the first attempt, then the direction of the needle tip was adjusted according to anatomic landmarks, and another attempt was made. After correct placement of the tip of the needle, aspiration was performed (Figure 1D). The needle was withdrawn slightly during aspiration to prevent the synovial membrane from being aspirated into the needle tip and occluding the needle lumen.
Hip aspiration procedure. The red circle represents the targeted aspiration area. The y-axis (red line) was located approximately 2 to 3 cm lateral to the pulse of the femoral artery (green line) in the region of the inguinal ligament area (A). The red circle represents the targeted aspiration area. The x-axis (red line) was estimated by the distance (green line) from the pubic symphysis (blue oval) or greater trochanter (blue circle) according to an anteroposterior radiograph of the hip joint (B). The widely disinfected area covered both the aspiration point (red X) and the landmark (pubic symphysis, blue oval; greater trochanter, blue circle) in case the direction of the needle required adjustment during the procedure. The proximal boundary of the sterilized area was parallel to the navel level, the distal boundary was approximately one-half of the length of the thigh, the contralateral boundary was approximately one-half the length of the contralateral lower abdomen, and the whole lateral thigh was sterilized (C). After surgical drapes were applied and topical anesthesia was administered, aspiration was performed (D).
A synovial white blood cell count, polymorphonuclear percentage, leukocyte esterase strip test, and culture were performed with the aspirated synovial fluid. If there was insufficient synovial fluid, 10 mL of saline was injected, and reaspiration was performed. Under this condition, only a culture was performed. The culture procedure was the same in cases of direct aspiration and saline lavage. The aspirated fluid was injected into a BACT/ALERT FA FAN (BioMérieux) blood culture system for anaerobic bacterial culture and a BACT/ALERT PF Pediatric FAN (BioMérieux) blood culture system for aerobic bacterial and fungal cultures. The samples were sent to the medical laboratory center of the authors' hospital as soon as possible. Each sample was inoculated for 14 days unless microorganisms were detected. The BACT/ALERT 3D blood culture system (BioMérieux) was used for culture, and a matrix-assisted laser desorption ionization-time of flight mass spectrometry system (VITEK-MS; BioMérieux) was used for microorganism identification.
Periprosthetic joint infection was diagnosed based on the modified Musculoskeletal Infection Society (MSIS) criteria, which were recommended at an international consensus meeting.1 The aspiration failure rate, incidence of complications, and results of the culture were recorded. Aspiration failure refers to the failure to aspirate any useful fluid for synovial tests, such as cultures, even with saline lavage. Complications refer to any complication related to the aspiration procedure, such as blood vessel or nerve injury.
For the statistical analysis, significance was defined as P<.05. The authors used the Mann–Whitney U test for continuous variables and the chi-square test for nonparametric categorical variables. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and related 95% CIs of the cultures were calculated. Statistical analyses were performed using Empower ( www.empowerstats.com; X&Y Solutions, Inc) and R ( http://www.R-project.org; The R Foundation).
General Information and Success Rate
The general information regarding the included cases is summarized in Figure 2. Of the 186 consecutive aspirations, aspiration failed in 7 cases (no useful fluid was aspirated, even with the use of saline lavage and reaspiration). The overall failure rate was 3.8% (7 of 186). One of these cases underwent successful aspiration 1 month later. Four patients underwent surgery without any further aspiration. The other 2 patients were lost to follow-up. Of the remaining 179 cases, 81 underwent saline lavage and reaspiration. The saline lavage rate was 45.3% (81 of 179).
General information regarding the included cases. Abbreviation: PJI, periprosthetic joint infection.
For the culture accuracy analysis, 4 patients who were lost to follow-up and 6 patients who had insufficient information to determine the presence of a hip infection according to the MSIS criteria were excluded. Thus, a total of 169 patients had a definitive diagnosis. There were 87 PJI cases and 82 non-PJI cases. The characteristics of the remaining patients are shown in Table 1. The spectrum of organisms involved in PJIs is shown in Table 2. The cross-tabulation of the cultures is shown in Table 3. The sensitivity, specificity, PPV, and NPV were 0.781 (95% CI, 0.678–0.860), 0.939 (95% CI, 0.857–0.977), 0.931 (95% CI, 0.841–0.975), and 0.802 (95% CI, 0.706–0.874), respectively.
Characteristics of 165 Patients With a Definitive Diagnosis
Spectrum and Relative Frequencies of Microbes Isolated From Patients With Periprosthetic Joint Infection
Cross-Tabulation of the Culture Results
Among the patients who underwent aspiration, no major complications, such as blood vessel or nerve injury, were observed after aspiration. All patients were satisfied with the procedure. Only 1 patient had a rapid progression of symptoms, including pain and local pyrexia, after aspiration.
Preoperative detection of PJI and the causative microbiological pathogen is crucial. Hip aspiration, which is traditionally performed under fluoroscopy or ultrasound guidance, is a key step. In the current study, the authors demonstrated that it may not be necessary to use image-guided techniques and that anatomic landmarks can also be used to obtain satisfactory results for both hip aspiration and culture.
A previous study reported success rates for lateral and anterior hip injections of 80% and 60%, respectively.15 Another study reported a 77.5% success rate when anatomic landmarks were used under direct visualization.16 However, the aspirations performed in both these studies involved patients with native hips. In the current study, the overall success rate of anatomic landmark-guided aspiration was 96.2% (179 of 186), which was much higher than the success rates in the abovementioned studies. These results may be because it may be easier to distinguish whether the needle is correctly placed in patients with hip prosthetics due to the metal-on-metal sensation that can be appreciated as the needle contacts the neck of the prosthesis. In terms of the current results, the satisfactory success rate demonstrated that anatomic landmark-guided hip aspiration was feasible.
For the remaining patients who had successful aspiration, the overall saline lavage rate was 45.3% (81 of 179), which was comparable to the saline lavage rate of 49% reported by Roberts et al,17 who used fluoroscopic guidance. This finding provides further evidence that the authors' technique is viable.
In previous studies, fluoroscopy-guided aspiration and culture was the most widely used technique for detecting the microbiological pathogens responsible for PJI. The sensitivity and specificity ranged from 50% to 93% and 88% to 100%, respectively.3,6–9,18–20 For ultrasound-guided aspiration and culture, the sensitivity ranges from 69% to 89%, and the specificity is approximately 94% for the diagnosis of PJI.11,12 Based on the data, for the 169 patients who had a definitive diagnosis, the sensitivity and specificity were 0.781 (95% CI, 0.678–0.860) and 0.939 (95% CI, 0.857–0.977), respectively. These findings were comparable to the results of the abovementioned studies and to the findings of a meta-analysis by Qu et al,21 in which the sensitivity and specificity of cultures were 0.72 (95% CI, 0.65–0.78) and 0.95 (95% CI, 0.93–0.97), respectively. Thus, when this aspiration technique was used, the most valuable test, culture, also had satisfactory results.
In addition, among all the patients who underwent aspiration, no major complications, such as blood vessel or nerve injury, were observed. All patients were satisfied with the procedure. This suggests that anatomic landmark-guided hip aspiration is a safe technique in the diagnosis of PJI. Only 1 patient had a rapid progression of symptoms, including pain and local pyrexia, after aspiration. However, no evidence indicates that this complication is related to aspiration technique (ie, the use of anatomic landmark-guided aspiration rather than image-guided hip aspiration). This patient had a sinus tract at the time of aspiration. The culture results revealed multiple infectious agents (Streptococcus pyogenes and Klebsiella pneumoniae). The authors believe that the high bacterial virulence may have been associated with the observed phenomenon.
There are several obvious advantages to nonimage-guided aspirations. For example, they do not require any special instrumentation, particular location, complicated aspiration procedure, or specially trained technicians. Accordingly, the medical burden on patients is also reduced. Moreover, there is no need for harmful radiological exposure, which is good for both patients and physicians.
Several recommendations for anatomic landmark-guided hip aspiration should be noted. First, the authors recommend wide disinfection with an iodine tincture and alcohol to avoid bacterial contamination (as shown in Figure 1C) because the direction of the needle may need to be adjusted according to the landmarks (the pubic symphysis and/or greater trochanter) during the procedure. Second, many previous studies have considered that the use of local anesthetics, such as lidocaine, may have antimicrobial activity and can lead to false-negative results.22,23 Thus, when administering local anesthetics, lidocaine should not be injected into the articular capsule. For this reason, the authors also change the syringe after local anesthesia is completed to avoid the potential effects of any residual lidocaine in the syringe on the culture results. Third, different from native hip aspirations, it is easy to determine the correct placement for aspiration in patients with joint prosthetics. When the tip of the needle is in the joint capsule, a metal-on-metal sensation can be appreciated. At that time, the needle is definitely located in the right place. If no fluid is aspirated, the case is considered a “dry tap,” and saline lavage can be performed. The metal neck of a prosthesis is different from hard bone, and the metal-on-metal sensation is crucial. The most common mistake for beginners is to mistakenly regard contact with hard bone as an indication of correct positioning at the metal neck of the prosthesis. Finally, in patients with relatively little joint fluid, the tip of the needle is likely to become obstructed by the synovial membrane. Thus, the authors recommend slightly withdrawing the needle to prevent the synovial membrane from being aspirated into the tip, or even moving the needle slightly up and down along the metal neck of the prosthesis to make it easier to obtain fluid.
There were several limitations of this study. First, this was a summary of 1 physician's experience with nonimage-guided hip aspiration. The authors did not use a control group to directly compare the outcomes of nonimage-guided aspiration with those of image-guided aspiration. Thus, the authors could only provide a descriptive conclusion. In addition, as mentioned previously, the conclusion of this study was drawn from 1 physician's experience. Although the homogeneity of the procedure for each patient could be guaranteed, deviations may exist among different surgeons. Moreover, the procedure time and number of aspiration attempts were not recorded in this retrospective study. Thus, the authors could not describe the learning curve for this technique. Future studies may be needed to answer these questions. Furthermore, the authors chose anterior hip aspiration rather than a lateral approach in their routine. They cannot draw any conclusions regarding which method can achieve better results. However, they believe that there is no absolute rule regarding which approach to use. For patients with anterior heterotopic ossification of the joint capsule, a lateral approach is a good alternative. However, for patients who have undergone complicated revisions and have no obvious greater trochanter landmark, an anterior approach seems to be a reliable method. Finally, obese patients may be difficult to aspirate. Because Asians tend to be thin, most of the patients in the current study had normal or overweight body mass indexes. Thus, currently, the authors cannot draw a clear conclusion regarding the success rate for obese patients or the suitable body mass index range for this anatomic landmark-guided hip aspiration technique. Future studies could focus on these issues.
Anatomic landmark-guided hip aspiration was a convenient method and could provide a satisfactory result for detecting PJI.
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Characteristics of 165 Patients With a Definitive Diagnosis
|Characteristic||PJI (n=87)||Non-PJI (n=82)||P|
| Female||37 (42.53%)||48 (58.54%)|
| Male||50 (57.47%)||34 (41.46%)|
|Age, mean (IQR), y||60.00 (51.00–70.00)||60.00 (55.00–69.00)||.641|
|BMI, median (IQR), kg/m2||24.56 (22.08–26.49)||24.17 (22.03–26.83)||.849|
|ESR, median (IQR), mm/h||48.00 (23.00–73.00)||14.50 (7.00–24.50)||<.001|
|CRP, median (IQR), mg/L||19.50 (10.00–37.00)||3.19 (1.00–10.71)||<.001|
Spectrum and Relative Frequencies of Microbes Isolated From Patients With Periprosthetic Joint Infection
|Organism||No. of cases|
|Staphylococcus epidermidis||24 (27.6%)|
|Staphylococcus aureus||9 (10.3%)|
|Streptococcus agalactiae||7 (8.0%)|
|Escherichia coli||4 (4.6%)|
|Enterococcus faecalis||4 (4.6%)|
|Enterococcus faecium||2 (2.3%)|
|Staphylococcus cephalus||2 (2.3%)|
|Staphylococcus lugdunensis||1 (1.1%)|
|Streptococcus pallidum/Streptococcus stomatica||1 (1.1%)|
|Streptococcus gordonii||1 (1.1%)|
|Acinetobacter baumannii||1 (1.1%)|
|Enterobacter cloacae||1 (1.1%)|
|Granulicatella adiacens||1 (1.1%)|
|Kocuria varians||1 (1.1%)|
|Micromonas micros||1 (1.1%)|
|Pseudomonas aeruginosa||1 (1.1%)|
|Staphylococcus auricularis||1 (1.1%)|
|Staphylococcus warneri||1 (1.1%)|
|Streptococcus pyogenes||1 (1.1%)|
|Multiple infections||8 (9.2%)|
|Negative culture||15 (17.2%)|
Cross-Tabulation of the Culture Results
|Modified MSIS criteria|