An otherwise healthy 17-year-old male presents to the ED after an ATV accident. He was riding at a low speed when he swerved to avoid a branch, lost control, forcing him to bail forward over the handlebars. He sustains a laceration to his knee during the fall, but suffers no other injuries. Exam of the right knee is notable for a 2.5 cm deep, jagged laceration (Figure 1), tenderness to the patella and a joint effusion, no palpable bony deformities, stable ligamentous exam, with the distal extremity neurovascularly intact. Radiographs of the knee are obtained:
The above radiographs demonstrate no evidence of fracture or dislocation; however, subcutaneous gas is visible in the region of the laceration. Given the depth and location of the injury, there is concern for traumatic arthrotomy. Orthopedics is consulted.
Knee injuries are a common reason for patient presentation to the emergency department, often with concomitant wounds adjacent to the joint. These injuries typically occur in young adult males, with common mechanisms including gunshot wounds, motor vehicle accidents, motorcycle accidents, or injury due to sharp objects. When there is concern for wounds entering the joint space, the saline load test (SLT) is used for further evaluation.
The knee contains the largest synovial joint cavity in the body. To perform arthrocentesis, the knee should be placed in approximately 15-20 degrees of flexion (often helpful to place a folded blanket or pillow in the popliteal fossa to aid in positioning); a medial or lateral approach may be used, but should enter at the superior third of the patella, with the needle aimed towards the intercondylar notch.
A systematic review by Daley, et al, in 2011 of needle entry location showed that the superolateral approach had the overall greatest success of 91%. In difficult cases, use of ultrasound has been shown to improve accuracy of intra-articular needle placement, a modality readily used and available in the ED.
How much is enough?
In examination of the saline load test, varying sensitivities have been reported using a range of infused volumes. Using an arthroscopy model with a 1 cm incision, Nord et al, showed that 95% sensitivity could be achieved using a volume of 155 cc, if tolerated by the patient. In the ED setting, potentially lower volumes may be used due to generally larger arthrotomy sizes. Konda, et al, demonstrated 94% sensitivity with a dynamic (moving the knee through flexion and extension) saline load test using a volume of 74.9 cc +/- 28.2 cc, but had a 9% false positive rate.
But don’t I need to inject that blue stuff?
A single study comparing injection of normal saline alone vs. methylene blue in patients undergoing routine knee arthroscopy showed instillation of methylene blue did not improve sensitivity in diagnosis of arthrotomy.
Is a picture alone worth a thousand words?
A retrospective study in 2013 compared the traditional SLT to CT scan identification of intra-articular air in evaluation of a traumatic arthrotomy. This study revealed that CT scan was more sensitive in detection of traumatic arthrotomy over the traditional SLT (100% vs. 92%). The additional benefit of performing a CT scan is detection of periarticular fractures, and in the study group, findings on CT scan in evaluation of traumatic arthrotomy altered management in 43% of patients.
What about pediatrics?
A prospective study of 87 pediatric patients with mean age 13.4 years +/- 3.0 years undergoing elective knee arthroscopy were studied. After a 5-mm superolateral arthrotomy site was made, the authors concluded that a minimum of 47 mL was required to detect 90% of the arthrotomies in this population. A limitation, however, is that all patients were anesthetized during joint injection, preventing assessment of patient comfort with this infused volume.
The patient undergoes saline load testing of the affected knee in the ED using 155 cc of intra-articular saline, with noted extravasation from the wound. He is placed in a splint, IV antibiotics are started, and he is taken to the operating room for irrigation and debridement. Intra-operatively, he is noted to have a 1 cm traumatic arthrotomy to the lateral joint capsule. The joint is thoroughly irrigated, he is continued on antibiotics, and was discharged home the following day without complication.
A great post by our EM colleagues at the Las Vegas Emergency Medicine Residency also reviewing this topic can be found here: http://www.lasvegasemr.com/foam-blog/knee-capsule-violation-bedside-rule-out-test
Take Home Points:
Knee injuries are common: when there is concern for joint violation, the saline load test can be used for further evaluation
If using anatomic landmarks, the superolateral approach may be the most successful, and in difficult cases, ultrasound can help improve success
Methylene blue does not add additional sensitivity over normal saline alone
CT scan can be used to identify traumatic arthrotomy, may have better sensitivity than the SLT, and adds evaluation of potential periarticular fractures not seen on plain radiographs
In general, wounds seen in the ED may require less overall volume due to larger arthrotomy size, but optimal volume is still unclear
Faculty Reviewer: Dr. Dina Gozman
Konda, SR., Davidovitch, RI., Egol, KA; “Open knee joint injuries: an evidenced-based approach to management”, Bulletin of the Hospital for Joint Diseases, Vol 72 No. 1, 2014
Thomsen, TW., Shen, S., Shaffer, RW., Setnik, GS; “Arthrocentesis of the knee”, New England Journal of Medicine, Vol 354 No. 19, May 2006
Nord, RM., Quach, T., Walsh, M., et al; “Detection of traumatic arthrotomy of the knee using saline solution load test”, Journal of Bone and Joint Surgery American Volume, Vol 91 No. 1, January 2009
Konda, SR., Howard, D., Davidovitch, RI., Egol, KA; “The saline load test of the knee redefined: a test to detect traumatic arthrotomies and rule out periarticular wounds not requiring surgical intervention”, Journal of Orthopedic Trauma, Vol 27 No. 9, September 2013
Metzger, P., Carney, J., Kuhn, K., Booher, K., Mazurek, M; “Sensitivity of the saline load test with and without methylene blue dye in the diagnosis of artificial traumatic knee arthrotomies”, Journal of Orthopedic Trauma, Vol 26 No. 6, June 2012
Konda, SR., Davidovitch, RI., Egol, KA; “Computed tomography scan to detect traumatic arthrotomies and identify periarticular wounds not requiring surgical intervention: an improvement over the saline load test” Journal of Orthopedic Trauma, Volume 27 No. 9, September 2014
Haller, JM., Beckmann, JT., Kapron, AL., Aoki, SK; “Detection of a traumatic arthrotomy in the pediatric knee using the saline solution load test”, The Journal of Bone and Joint Surgery, Vol 97 No. 10, May 2015
Konda, SR., Howard, D., Davidovitch, RI., Egol, KA; “The role of computed tomography in the assessment of open periarticular fractures associated with deep knee wounds”, Journal of Orthopedic Trauma, Vol 27 No. 9, September 2013
Daley, EL., Bajaj, S., Bisson, LJ., Cole, BJ; “Improving injection accuracy of the elbow, knee, and shoulder: does injection site and imaging make a difference? A systematic review” The American Journal of Sports Medicine, Vol 39 No. 3, March 2011
Daniels, EW., Cole, D., Phillips, SF.; “Existing evidence on ultrasound-guided injections in sports medicine”, Orthopaedic Journal of Sports Medicine, Vol 6 No. 2, February 2018