ABSTRACT: Intra-articular injections have been recommended as adjunctive treatment for patients with knee osteoarthritis (OA). The many anatomical-based approaches through which to administer therapeutic injections into the knee include the extended leg lateral and medial midpatellar portals and the bent leg anteromedial and anterolateral portals. Agreement about the most accurate approach is lacking. In “dry” knee OA—in which the knee does not have a clinically detectable effusion—the accuracy of intra-articular needle placement is less certain because confirmation of placement by aspiration is not possible. The accuracy of needle placement may have implications for the efficacy and safety of intra-articular injections of the knee. Several studies that used various subjects and methodologies have evaluated the accuracy of intra-articular knee injections. (J Musculoskel Med. 2012;29:114-117)
Intra-articular injections of corticosteroids or hyaluronate have been recommended for use in patients with moderate to severe osteoarthritis (OA) of the knee.1,2 Systematic reviews and meta-analyses suggest that intra-articular injections of corticosteroids provide short-term (about 1 to 4 weeks), clinically significant improvements in pain in patients with knee OA.3-6 Intra-articular injections of hyaluronate may provide longer-term (conservatively estimated as up to about 3 months) improvements in pain and function.7,8
Several palpation-based, anatomical landmark–guided approaches for the administration of therapeutic injections into the knee have been described, including the extended leg lateral midpatellar (LMP) and medial midpatellar (MMP) portals and the bent leg (flexed to 90°) anteromedial (AM) and anterolateral (AL) portals (Figure).9,10 Agreement about the most accurate approach through which to administer therapeutic intra-articular injections into the knee is lacking—practices appear to vary widely and choices ultimately depend on the preference of the clinician who is administering the injection.11
When an intra-articular effusion is present in patients with knee OA, the accuracy of needle placement has been suggested to be confirmed by the return of synovial fluid during joint aspiration.10 In the absence of an effusion (“dry” knee OA), however, the accuracy of intra-articular needle placement is less certain because confirmation of placement by aspiration is not possible.12
The accuracy of needle placement may have implications for the efficacy and safety of intra-articular injections of the knee, particularly of hyaluronate. It also may affect the diagnosis of joint-related pathologies, such as infective arthritis and crystal diseases.13,14
In this article, I review the evidence evaluating the accuracy of needle placement during intra-articular injections for dry OA of the knee using various anatomical portals. I establish whether the evidence supports the use of one particular approach from those available such that recommendations for the administration of intra-articular knee injections in clinical practice may be made.
A few studies that used various methodologies evaluated the accuracy of needle placement during intra-articular injections of the dry OA knee joint performed with anatomical landmark–guided approaches. Jackson and associates15 compared the accuracy of needle placement of 3 landmark-guided intra-articular injection approaches in a prospective series of 240 hyaluronate injections in 80 patients with symptomatic dry knee OA. Injections were administered by 1 orthopedic surgeon through 1 of 3 portals—AM, AL, or LMP—using a 21-gauge, 5.1-cm needle.
Each patient received 1 injection through each portal; thus, the potential for sampling bias was eliminated. Accuracy was determined by an acceptable gold standard of real-time fluoroscopic imaging with dispersion of contrast material within the joint space together with “coating” of the articular surfaces indicative of accurate needle placement.
LMP Approach Recommended
The LMP approach was significantly more accurate than the other approaches studied (intra-articular placement achieved on the first attempt 93% of the time, compared with 75% and 71% for the AM and AL approaches, respectively). The authors recommended the use of the LMP approach for intra-articular joint injections in patients with dry OA knee disease.
However, the order in which the injections were administered was not randomized. Therefore, an order effect could have confounded the results. Because injections were administered by a single clinician, the accuracy of the LMP approach should be evaluated in defined cohorts of clinicians to test the generalizability of this approach in clinical practice.
Accuracy and Severity Comparisons
In another study, Toda and Tsukimura10 compared the accuracy of intra-articular hyaluronate knee injections performed with the modified Waddell (an AM approach with manipulative ankle traction at 30° of knee flexion), seated AM (knee flexion to 90°), and extended leg superolateral patellar (SLP) approaches in 50 patients with dry OA of the knee of grade II, III, or IV severity on the Kellgren-Lawrence radiographic scale (equivalent to minimal, moderate, or severe joint changes, respectively16). Injections were performed by 1 orthopedic surgeon using a 23-gauge, 3.2-cm needle. Each patient received 1 injection (combined with contrast material) through each portal in a random order over a 3-week period. Accuracy was determined by postinjection radiographs; it was confirmed when contrast material was deemed to shape the outline of the suprapatellar pouch and meniscus.
Modified Waddell Approach Advocated
The overall accuracy rates for the modified Waddell, seated AM, and extended leg SLP approaches were 86%, 62%, and 70%, respectively. There were no significant differences in accuracy rates between approaches for patients classified with Kellgren-Lawrence scale grades II and III. The accuracy rate for the modified Waddell approach was significantly higher (100%) than those for the seated AM and extended leg SLP approaches (55% each) in patients with Kellgren-Lawrence scale grade IV changes. On the basis of these results, the authors advocated that clinicians change the approach used for hyaluronate injections according to the severity of knee OA and recommended the use of the modified Waddell approach in patients who have more severe OA changes of the knee.
In the Toda and Tsukimura study,10 all patients received an injection through each portal in a randomized fashion, which eliminated the potentially confounding influences of sampling bias and order effects. However, when the robustness of the findings and the validity of the conclusion are being considered, the following methodological flaws invite caution:
• The needle length (3.2 cm) may have been insufficient to allow for accurate intra-articular needle placement. Jackson and colleagues15 recommended a needle length of about 5 cm to clear periarticular structures and reach the intra-articular space.
• With small patient numbers in each Kellgren-Lawrence scale grade, the study probably was insufficiently powered to allow for valid subgroup analyses.
• Definitions of Kellgren-Lawrence scale grades are not specified; consequently, the external validity and generalizability of the results are limited. In addition, the Kellgren-Lawrence grading system may lack validity as a method of subgrouping the severity of knee OA because operational definitions and interpretations of its grades vary.17
Modified Bent Knee Approach Evaluated
In a recent study, Chavez-Chiang and associates9 evaluated the accuracy of a modified bent knee (knee flexion to 90°) AL approach (Mod-AL). They targeted the synovial membrane of the medial femoral condyle in 76 consecutive injections of corticosteroid with local anesthetic in patients with dry knee OA via a 21-gauge, 5.1-cm needle. Accuracy was determined using real-time ultrasonography (US) and defined as visualization of (1) the needle tip at the interface of the synovial membrane and cartilage, (2) the free flow of fluid into the intra-articular space, and (3) dilation of the intra-articular space with injected fluid. Injection via the Mod-AL approach had an accuracy rate of 97%.
Chavez-Chiang and associates9 suggested that the Mod-AL approach provides accuracy similar to that achieved with the LMP approach. They noted that the approach might be useful for patients who cannot lie down or transfer to an examination couch or extend their knee, such as some older, obese, or wheelchair-bound persons and those who have flexion contractures. Although the authors assumed parity between the Mod-AL and LMP approaches, the lack of a direct comparison limited the study’s usefulness.
Also, whether the injection and US were performed by the same or different physicians is not clear. If the accuracy was determined by same physician who administered the injection, the results could be subject to a degree of operator bias that could have inflated the accuracy rate. In addition, the characteristics of the clinicians who administered the injections are not described and their professional background and competence cannot be ascertained. These factors limit the generalizability of the study’s findings as well as its replicability.
Several other studies that used various subjects and methodologies have evaluated the accuracy of intra-articular knee injections. In a cadaver study, Esenyel and colleagues18 compared the accuracy of the bent knee AL and AM (5.1-cm needle) and extended leg LMP and MMP approaches. Cadaveric knees were injected with methylene blue, and accuracy was determined by surgical dissection and inspection of the needle tip and diffusion of the methylene blue.
Accuracy rates for the AL, AM, LMP, and MMP approaches were 85%, 73%, 76%, and 56%, respectively. There were no statistically significant differences among the AL, AM, and LMP approaches, but the MMP approach was significantly less accurate than the others. Esenyel and colleagues18 suggested that any of the AL, AM, and LMP portals could be used clinically.
Extended Leg Comparisons
Another study compared the accuracy of extended leg medial, midlateral, and superolateral approaches during US-guided intra-articular injections of corticosteroid, local anesthetic, and contrast agent via a 25-gauge, 3.8-cm needle into 126 dry OA knees.19 The accuracy rates were 95% and 100% for the midlateral and superolateral portals, respectively, compared with 75% for the medial portal.
A recent systematic review of accuracy rates of various intra-articular injection approaches for the knee joint found the extended leg SLP approach to be the most accurate (pooled accuracy, 91%), followed by the LMP (85%), AM (72%), and AL (67%) approaches.13 However, the review included studies that involved patient populations that had knee disorders with various causes, such as rheumatoid arthritis; patients admitted for arthroscopy; patients with effusions; and one cadaveric study. Therefore, that evidence supporting the SLP approach as the most accurate may not generalize specifically enough to patients who have dry knee OA.
The studies’ heterogeneity limits direct comparisons. Overall, however, the data that specifically evaluated the accuracy of various landmark-guided approaches for intra-articular injections of dry knee OA suggest that the LMP approach probably offers the most accurate route for the administration of injectable therapeutic agents into the intra-articular space of the knee. Data to support this assertion are limited, and further studies using multiple clinicians and validly defined subgroups of patients are required before any clear clinical recommendation can be made.
Other studies and reviews provide mixed results about the accuracy of knee joint injections through various anatomical portals such that clear evidence of the accuracy of one approach over any other remains equivocal. Therefore, the anatomical portals through which intra-articular injections of the knee are currently administered are likely to remain dependent on clinician preference unless clarification comes from future research.
Take Home Points
• Limited evidence suggests the lateral midpatellar portal to be the most accurate approach through which to administer intra-articular injections for “dry” knee osteoarthritis (OA).
• Additional limited evidence suggests that clinicians might alter their injection approach according to the severity of knee OA.
• Further studies to evaluate the accuracy of various injection approaches are required before any clinical recommendations can be made.