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RFS - Clinical Vignette

Vague Posterior Knee Discomfort in a Soccer Player

A Clinical Vignette

Schroeder, Allison MD; Onishi, Kentaro DO

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American Journal of Physical Medicine & Rehabilitation: April 2020 - Volume 99 - Issue 4 - p e46-e49
doi: 10.1097/PHM.0000000000001248



A 24-yr-old male soccer player presented with a 7-yr history of left posterior knee “looseness.” He first noticed left knee symptoms 7 yrs ago on the day after a soccer match. He could not recall a traumatic injury. When he initially sought medical attention, he was told that he had “sprained his anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL),” based on magnetic resonance imaging. He completed a course of physical therapy. Seven years later, after improving minimally, he represented to a sports medicine physician with continued left knee discomfort. The patient described the pain as a constant, dull ache, 3/10, but his biggest complaint was this feeling of “instability” and looseness. His knee would “buckle” 3–4 times a week but would never fully give way. His pain worsened with ambulation and running, and he avoided playing soccer. He had tried nonsteroidal anti-inflammatory drugs, bracing (custom Ossur rebound PCL brace), activity avoidance, and had recent physical therapy (focusing on stretching and quadriceps strengthening while avoiding hamstring strengthening). There was no history of ligament sprain or family history of connective tissue disease.

What is the likely diagnosis based on history?

On which tests will you focus when conducting your physical examination?

Physical examination showed nonantalgic gait and bilateral pes planus. There was no discoloration, swelling, or tenderness to palpation, and active and passive range of motion was full and nonpainful of the knees bilaterally. Ligamentous testing was negative except for a posterior drawer grade 1 and posterior sag grade 1 on the left. Patellar grind, McMurray's, Apley's, bounce home tests, and Wilson's test were all negative bilaterally. Dial test was negative at both 30 and 90 degrees of knee flexion (see Table 1 for description of knee examination special tests). In addition, he had reverse KT-1000 arthrometer testing completed at 90 degrees revealing a side-to-side difference of +3 mm (right = 3 mm and left = 6 mm). He had less than 4 Beighton criteria.

Description of common tests performed during the knee physical examination


The differential diagnosis included PCL sprain or tear, posterolateral corner injury, injury to the posterior horn of the medial or lateral meniscus, osteochondral defect, patellar subluxation or dislocation, and patellofemoral pain syndrome.

Posterior cruciate ligament pathology was at the top of the differential, given a history of vague posterior knee pain, which is commonly reported in PCL injuries, and positive posterior drawer and sag sign, indicating posterior displacement of the tibia on the femur, were seen on physical examination. The differential also included posterolateral corner injury; however, the dial test was negative and isolated injury to the posterior lateral corner is rare.

Injury to the posterior horn of the medial or lateral meniscus could result in posterior knee pain, but we would expect an abnormality on physical exam with McMurray's, Apley's, or the bounce home test. The meniscofemoral ligaments, including the ligament of Humphrey and Wrisberg, are intimately associated with the PCL, and theoretically and esoterically lead to posterior knee pain, although isolated injury of these structures has never been reported.

Osteochondral defect, which is most commonly located in the knee on the posterior lateral aspect of the medial femoral condyle, was also a possibility, as patients can complain of vague pain and instability. However, diagnosis of Osteochondral defect is more common in younger patients with an open physis and is often accompanied by recurrent joint swelling and a positive Wilson's test.

Patellar subluxation or dislocation could present with the chief complaint of knee looseness or instability, but the patient had not witnessed or reported any of these episodes. Patellofemoral pain syndrome is often described with vague complaints of pain, but patellar grind was negative; this diagnosis is common and may also be contributing to symptomatology.

What is the best way to further evaluate this patient? Is additional imaging beyond the magnetic resonance imaging obtained 7 yrs ago necessary because there was no new injury mechanism?


X-rays of the left knee, including a weight bearing view, were completed to rule out traumatic injury and evaluate for arthritis and showed mild medial tibiofemoral compartment joint space narrowing. Magnetic resonance imaging to evaluate the soft tissue structures including the menisci and ligaments showed intact menisci, medial collateral ligament, lateral collateral ligament, ACL, and PCL. Although the PCL was intact, the musculoskeletal radiologist noted a “stable buckling” of the PCL fibers. An 8 × 7 × 6-mm cystic lesion abutting the posteromedial margin of the distal 1/3 of the PCL was also noted. The posterior lateral corner was intact on magnetic resonance imaging.


The patient was evaluated by several orthopedic surgeons before referral to our musculoskeletal sports ultrasound clinic after he continued with symptoms despite physical therapy. Although the patient requested surgical intervention to “tighten” his PCL, this was deemed unnecessary and unlikely to be beneficial by the orthopedic surgeon.

Sonographic examination in our clinic using a 15–6 MHz linear array transducer (GE E9, Chicago, IL) was performed with the patient in the prone position. The PCL was visualized in the oblique sagittal plane in the posterior knee region, just medial to the popliteal artery. The fibers of the PCL appeared intact but were slightly lax with a “kinked” nature (Fig. 1A), in comparison with the contralateral side. A cystic structure (measuring approximately 5 × 5 × 3 mm) was visualized superficial to the medial side of the PCL (Fig. 1).

Ultrasound image with transducer is being held in the oblique longitudinal axis to visualize the lax/“kinked” PCL with overlying cyst (A, using linear transducer) with needle coming from distal to proximal to inject prolotherapy superficial to the PCL (B, using curvilinear transducer).

The working diagnosis was PCL sprain with adjacent PCL cyst. His symptoms of vague knee pain and looseness were more likely emanating from the lax PCL rather than the small adjacent cyst.

After additional physical therapy without improvement, risks, benefits, and the experimental nature of a sonographically guided injection of dextrose hyperosmolar solution to treat PCL laxity were discussed with the patient and he elected to proceed. The injection of the left knee was performed from a distal to proximal in-plane approach with the patient in the prone position and the 9–2 curvilinear array transducer oriented in the oblique sagittal plane while visualizing the PCL and ganglion cyst slightly medial and superficial to the PCL. Extra care was taken to avoid the popliteal artery, which lies slightly superficial and lateral to the PCL. After local anesthesia, the soft tissues en route to the target were anesthetized using a 27-gauge 1.5-in needle, and then the superficial aspect of the cyst was fenestrated 10 times with a 25-gauge 3.5-in needle and less than 1 ml of a mixture of 1 ml of 50% dextrose, 2 ml of sterile water, and 2 ml of 1% lidocaine was injected (Fig. 1B). After cyst fenestration and injection, the needle tip was advanced deep to the posterior knee capsule, where 2 ml of the injectate was injected at the superficial aspect of the PCL without significant resistance and with excellent sonographic flow. After injection, the patient was made toe-touch weight bearing with crutches for 1 wk without bracing.

The patient reported gradual clinical improvement with more than 50% improvement in the bothersome feeling of looseness at 1 mo, and repeat sonographic examination showed decompression of the cyst, but small changes in gross PCL structure are difficult to assess sonographically. The patient inquired about an additional prolotherapy injection. However, given concern for overtightening the PCL, additional prolotherapy injection was not performed at this time. At 7 wks, he noted 80% improvement in knee looseness and KT-1000 testing (completed by the same provider as the initial measurement) revealed a 1-mm side-to-side difference (compared with a 3-mm side-to-side difference on initial evaluation). He reported no episodes of knee buckling and no limits to his daily activities, but unfortunately, he was not yet able to return to sport because of an ankle injury.

Injuries to the PCL are infrequently reported in isolation, which may be due to both a poor understanding of the injury and resultant missed diagnosis.1 The PCL primarily limits posterior tibial translation and patients commonly report disability rather than discomfort, complaining of vague symptoms, such as unsteadiness.1,2 Isolated PCL injuries often heal spontaneously, and the best method of treatment is debatable, with conservative treatment preferred for low-grade injuries and surgical treatment preferred for higher-grade injuries.1,3,4 Conservative treatment of isolated PCL injuries initially consists of activity modification and symptom management, bracing for stability, and physical therapy for stretching and strengthening of the quadriceps. One nonsurgical option for the treatment of musculoskeletal conditions, including ligament injury, is dextrose hyperosmolar therapy or prolotherapy. Although evidence is limited, the use of prolotherapy has been used to treat ACL and patellar ligament injury.5,6 Because prolotherapy is presumed to “tighten” ligaments through stimulation of the inflammatory cascade and proliferation, theoretically, the clinician must take care not to “overtighten” the PCL and cause biomechanical abnormalities.7,8 In our case, we used reverse KT-1000 arthrometer measurements (which have been used to measure PCL laxity) to show that injection of dextrose hyperosmolar solution can lead to decreased PCL laxity without causing overtightening.9

We report a case of successful treatment of symptomatic PCL laxity and adjacent PCL cyst with a single sonographically guided injection of dextrose hyperosmolar prolotherapy, and this treatment option can be considered when there is no improvement of symptoms with physical therapy and when surgery is unlikely to be successful. This study conforms to all CARE guidelines and reports the required information accordingly (see Supplemental Checklist, Supplemental Digital Content 1,


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5. Hauser RA, Lackner JB, Steilen-Matias D, et al: A systematic review of dextrose prolotherapy for chronic musculoskeletal pain. Clin Med Insights Arthritis Musculoskelet Disord 2016;9:139–59
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8. Jensen KT, Rabago DP, Best TM, et al: Response of knee ligaments to prolotherapy in a rat injury model. Am J Sports Med 2008;36:1347–57
9. Hewett TE, Noyes FR, Lee MD: Diagnosis of complete and partial posterior cruciate ligament ruptures. Stress radiography compared with KT-1000 arthrometer and posterior drawer testing. Am J Sports Med 1997;25:648–55

Musculoskeletal Ultrasound; PCL Injury; Sports Medicine

Supplemental Digital Content

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