Next, the patients were instructed to place the knees at an angle of approximately 25° on a pillow and were then instructed to extend the knees, as follows: “Please extend your knee firmly and keep your heel off the bed.” Subsequently, we touched the quadriceps and said, “Please contract this muscle firmly.” There were no subjects who could not follow these instructions. This is the position used in the isometric quadriceps contraction method (Fig. 2-B). After manually confirming that the quadriceps muscle was in a state of isometric contraction with the knee extended and the heel off the surface of the bed, the anterior-posterior dimension was measured again (Fig. 3-B). The 2 anterior-posterior dimensions were then compared.
We also validated the reliability of ultrasonographic measurements of the anterior-posterior dimensions. To assess the intraobserver reliability, the surgeon of this study measured 6 healthy knees on 3 days at 1-week intervals. Three measurements were done on each day, and the mean values on the 3 days were compared. For interobserver reliability, 4 examiners measured 4 healthy knees each, 3 times per knee. The measurement order was randomly assigned. Reliability was assessed by calculating intraclass correlation coefficients.
Statistical analysis was performed using SAS 9.4 (SAS Institute). Significant differences were determined using the Mann-Whitney U test (p < 0.05).
Intra-Articular Injection Method and Accuracy Measurement
The skin was pierced at a point on the lateral side of the quadriceps tendon approximately 1 cm proximal to the superior margin of the patella. The needle tip was angled toward the suprapatellar bursa without ultrasound guidance. It was stopped when the surgeon sensed that the needle had pierced the synovial membrane of the suprapatellar bursa (Video 1). The target point for the needle was the measurement site of the anterior-posterior dimension, which is an area with relatively little obstruction (Fig. 3). Once the drug solution was injected, an ultrasound probe was used parallel to the needle to capture its image and confirm whether the solution diffused within the joint. A 25-G needle and 1% hyaluronic acid (low molecular weight, approximately 900 kDa) solution at a dose of 2.5 mL/injection (Artz [purified sodium hyaluronate]; Seikagaku) were employed.
We performed this procedure for both the non-activated quadriceps method and the isometric quadriceps contraction method. Prior to extending the knee, the skin puncture point was confirmed, because it becomes difficult to palpate the margin of the patella because of isometric contraction of the quadriceps. The percentages of accurate intra-articular injections within the 2 groups were compared. Statistical analysis was performed with the Fisher exact test using SAS 9.4.
There were no significant differences (p < 0.05) with regard to sex, age, or side between the isometric quadriceps contraction group and the non-activated quadriceps group (Table I). We found that the anterior-posterior dimension in the isometric quadriceps contraction method was significantly greater (p < 0.001) than that in the non-activated quadriceps method (Table II). Also, the success probability of the isometric quadriceps contraction method was higher than that of the non-activated quadriceps method (Table III).
TABLE I -
Differences Between the 2 Groups
||Isometric Quadriceps Contraction Group (N = 75)
||Non-Activated Quadriceps Group (N = 75)
||72.7 ± 8.3
||74.4 ± 6.6
*The values are given as the number of patients, with the percentage in parentheses. The p value was determined with use of the chi-square test.†The values are given as the mean and the standard deviation. The mean difference in years, with the 95% confidence interval, is −1.25 (−3.53 to 1.02). The p value was determined with use of the t test.
TABLE II -
Expansion of the Suprapatellar Bursa According to Injection Technique
||Anterior-Posterior Dimension* †
|Isometric quadriceps contraction
||2.1 ± 1.4 (2.0 [0 to 5])
||0.8 ± 0.7 (1.0 [0 to 2])
*The values are given as the mean and the standard deviation, in millimeters, with the median in parentheses and the range in brackets.†Significantly different at p < 0.001, determined with use of the Mann-Whitney U test.
TABLE III -
Comparison of Intra-Articular Injection Accuracies*
||No. with Success
|Isometric quadriceps contraction
*The p value between the 2 groups, determined with use of the Fisher test, was p = 0.0287.
When performing the isometric contraction method, the intraclass correlation coefficients of the sonographic measurements were 0.999 for intraobserver reliability and 0.935 for interobserver reliability (Tables IV and V). High reliability was thus obtained for both intraobserver and interobserver correlations.
TABLE IV -
Intraobserver Reliability of Ultrasonographic Measurement of the Anterior-Posterior Dimension of the Suprapatellar Pouch*
*The intraclass correlation coefficient was 0.999 (95% confidence interval, 0.995 to 1.000).†The value is given as the mean value of 3 measurements, in millimeters.
TABLE V -
Interobserver Reliability of Ultrasonographic Measurement of the Anterior-Posterior Dimension of the Suprapatellar Pouch*
*The intraclass correlation coefficient was 0.935 (95% confidence interval, 0.711 to 0.995).†The value is given as the mean value of 3 measurements, in millimeters.
The results of this study indicate that the suprapatellar bursa is likely to expand during isometric quadriceps contraction, improving the probability of successful intra-articular injections.
We believe that the isometric quadriceps contraction method is therapeutically effective and could reduce the risk of injection pain due to inaccurate injections into the synovial membrane, which has a large number of nerve endings4,6,7.
There are many reports providing evidence for the validity of ultrasound in detecting structural pathology20-22, and good agreement between ultrasonography and magnetic resonance imaging (MRI) in visualizing effusion and synovial hypertrophy with knee osteoarthritis has been shown23. The reliability in this current study, as shown by intraclass correlation coefficients, was also very high. Thus, ultrasound measurement is effective for evaluating the expansion of the suprapatellar bursa, which occurs as discussed below.
The quadriceps tendon becomes tense under isometric contraction; therefore, the space between the tendon and the femoral bone increases. The articularis genus muscle synchronously contracts with the quadriceps and lifts the suprapatellar bursa to a proximal position, preventing it from being entrapped in the patellofemoral joint24-28. Thus, the suprapatellar bursa can expand in this space under the quadriceps tendon. In addition, when subjects contract the quadriceps muscle, the patella is lifted to the proximal position. Tension on the patellar tendon and the patellar retinaculum moves the Hoffa fat pad toward the femoral condyles and intercondylar space, reducing the lumen of the tibiofemoral joint and patellofemoral joint. This moves the joint fluid to the suprapatellar bursa20,28.
Next we will look into difficult cases, such as obese patients. A large amount of subcutaneous fat makes it difficult to predict the distance that the needle must travel to reach the suprapatellar bursa. In such cases, accidental injection into the wrong tissues, such as the quadriceps tendon, suprapatellar fat pad, and prefemoral fat pad, may occur. There is also a risk of extra-articular injections when it is difficult for the physician to detect when the needle has pierced the suprapatellar bursa synovium.
The expansion of the suprapatellar bursa enables accurate injections even for individuals with a large amount of subcutaneous fat. The articularis genus muscle pulls the suprapatellar bursa up, which puts the synovium under tension25-29 and therefore makes it easier to determine when the needle tip has pierced it. As a result, the probability of successfully administering an intra-articular injection increases, and, conversely, the risk of administering an inaccurate injection is reduced.
When synovial fluid is present under the vastus lateralis and vastus medialis muscles30, movement of the fluid can be detected by palpation. Clinically, when patients have a large amount of synovial fluid, fluid can be aspirated without any special treatment. However, for patients with only a small amount of synovial fluid, the fluid was manually gathered into the suprapatellar bursa prior to performing aspirations.
This accumulation is difficult in cases in which the anterior-posterior dimension of the suprapatellar bursa is ≤2 mm. For subjects with little synovial fluid, isometric contraction of the quadriceps proved effective for concentrating the synovial fluid of the tibiofemoral joint and the patellofemoral joint into the suprapatellar bursa (Fig. 4).
On the basis of this mechanism, we believe that the isometric quadriceps contraction method can be utilized to reduce the risk of accidental injection into the fat pads surrounding the suprapatellar bursa and into the quadriceps tendon.
Maricar et al. gathered data from 23 previous studies with regard to the accuracy of intra-articular injections administered via various approaches14. According to their systematic review, the superolateral patellar approach without ultrasonography had a higher success rate (87%) than the medial midpatellar approach (64%) and the anterolateral joint line approach (70%). In their systematic review, Hermans et al. reported that the superolateral patellar approach resulted in the highest pooled accuracy of 91%15. These systematic reviews included patients in whom a substantial amount of synovial fluid was present. In our current study, the superolateral patellar approach was performed only for subjects with a suprapatellar bursa anterior-posterior dimension of ≤2 mm (minimal synovial fluid accumulation), which means that conditions were more difficult. Nevertheless, the results indicated that isometric contraction of the quadriceps led to a high success rate of 93.3%.
Lockman reported that confirmation by palpation was difficult for obese patients and other patients with a thick layer of subcutaneous fat; as a result, he developed an approach that used the apex of the patella and the femur as anatomical landmarks6. However, we could not find any previous studies of methods in which patients were directed to consciously contract the quadriceps and articularis genus muscles. The isometric quadriceps contraction method in the present study is a type of superolateral patellar approach, which was reported by Maricar et al. to have the highest success rate.
Park et al. reported that the success rate of intra-articular injections using the superolateral patellar approach was 83.7% without ultrasound guidance and 96.0% with ultrasound guidance11. The accuracy of the isometric quadriceps contraction method is near that of the ultrasound guidance method.
Ultrasound equipment is not always available. As a result, many physicians perform intra-articular injections without ultrasonography. When physicians rely only on the sense of touch, there are many subjects for whom it is difficult to ascertain whether the needle has entered the suprapatellar bursa. The use of the isometric quadriceps contraction technique allows for more accurate and successful intra-articular injections even for these subjects without using sonography.
One limitation of this study was that it was not an ideal randomized controlled trial; because of the quasi-randomization, randomness was not guaranteed. However, the background factors showed no bias between the 2 groups (Table I), and double-blinding was not applicable in this study because we compared the methods of injection. In light of the methodology and relatively small sample size of this current study, further studies with randomization and a larger sample size are needed.
In conclusion, the isometric quadriceps contraction method can expand the suprapatellar bursa and improve the accuracy of intra-articular injections. We believe that this method is a highly useful injection technique for knees with osteoarthritis without effusion.
Investigation performed at the Department of Orthopaedic Surgery, Wada Orthopaedic Clinic, Hirakata, Japan, and the Department of Orthopaedic Surgery, Kashiba Asahigaoka Hospital, Kashiba, Japan
Disclosure: There was no source of external funding for this study. The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJSOA/A73).
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