Continuing Education Activity

The pes anserine describes a region where tendinous structures of the semitendinosus, gracilis, and sartorius muscles join to insert at the medial knee. The pes anserine bursa is sandwiched between the proximal medial tibia and the insertion point of the three tendons. Pes anserine bursitis is a clinical entity associated with pain at the medial knee and upper tibial region. A more generic term, pes anserine pain syndrome, has been applied to refer to medial knee pain, which may or may not include inflammation of the bursal sac. This article focuses on the clinical entity of pes anserine bursitis unless otherwise specifically stated. This activity describes the evaluation and management of pes anserine bursitis and highlights the interprofessional team's role in improving care for affected patients.

Objectives:

• Describe the anatomy of the pes anserine and its bursa.
• Identify underlying risk factors for developing pes anserine bursitis.
• Outline limb-threatening conditions that may mimic pes anserine bursitis.
• Explain a well-coordinated, interprofessional team approach to provide effective care to patients affected by pes anserine bursitis.

Introduction

Bursitis is the general term used to describe inflammation of any bursa. The bursae are cavitary structures lined with synovial tissue that cushions and assists during the motion of joints and muscles. Bursitis is usually accompanied by tenderness; however, swelling and redness may also be present.

Pes anserine bursitis is a clinical entity associated with pain at the medial knee and the proximal medial tibial region. A more generic term, pes anserine pain syndrome, has been applied to refer to medial knee pain, which may or may not include inflammation of the bursal sac. This article focuses on the clinical entity of pes anserine bursitis unless otherwise specifically stated.

Sartorius, gracilis, and semitendinous tendons insert roughly 5 cm distal to the medial knee joint line forming a structure that mimics the natatory membrane of the goose and hence is called "goosefoot" or pes anserinus in Latin. The 3 muscles are primary knee flexors and play a secondary role in tibial internal rotation with a resultant protective effect against rotation and valgus stress. There are thirteen bursae around the knee, one of them is the pes anserinus bursa. The pes anserinus bursa is situated immediately beneath the pes anserinus, separating it from the upper medial tibia. Usually, there is no communication between the pes anserinus bursa and the knee joint. [1][2]

In 1937, Moschcowitz was the first to describe pes anserinus bursitis changes when he reported the complaint of knee pain almost exclusively in females with pain complaint with ascending or descending stairs or rising from a seated position or difficulty with knee flexion. It is challenging to differentiate between pes anserine bursitis and tendinitis as both the tendons and bursa are anatomically close to each other. However, management is the same.

Etiology

As in other knee conditions, mechanical derangement, direct trauma, obesity, and overuse have all been implicated in developing pes anserine bursitis. Medial knee osteoarthritis is an early and common finding in patients with this condition. Diabetes mellitus was also reported in a significant proportion of patients with pes anserine bursitis.[3]

In particular, sports may make one prone to pes anserine inflammatory conditions, including long-distance running, basketball, and racquet sports.[4][5] Other conditions that can be encountered with the etiology of pes anserinus bursitis include bone exostosis, retraction of posterior thigh muscles, irritation of suprapatellar plica, medial meniscus injury, knee valgus malalignment, or even a foreign body reaction or infection.[6] Chronic bursitis has been reported in association with osteoarthritis or rheumatoid arthritis.[7][8]

Epidemiology

The exact frequency of this condition in the general population is unclear as there is extensive overlap with other knee conditions. However, in one large study of over 10,000 persons, pes anserine pain was prevalent in approximately one-third of 1% of these individuals. The association of pes anserine pain (but not necessarily bursitis) with concomitant osteoarthritis was noted in one study to be over 90%.[9] 

Additionally, anserine bursitis was reported to be more common in obese females with knee osteoarthritis.[1][10][11][8][12] It was supposedly more common in females because of them having a wider pelvis with more knee angulation and higher pressure on the area of anserine insertion.[13] Despite that it is more commonly encountered between 50-80 years of age, younger obese females still can be affected. Other associations include genu valgum and pes planus.[13]

Pathophysiology

Multiple reports suggest that pes anserine bursitis is more common in overweight middle-aged females. There is an established association of pes anserine pain with diabetes mellitus. In many patients with established knee osteoarthritis, the inflammation of the pes anserine bursae may not be the primary pathology but rather a sequela of earlier knee complications.[14] Mechanical derangement at the medial knee joint is surmised to cause localized inflammation to the surrounding tendinous structures. This may include medial meniscus protrusion and displacement of the medial collateral ligament. Subsequently, the anserine bursa may become inflamed as well.

History and Physical

Patients with pes anserine bursitis likely will complain of pain on the inside (medial aspect) of the knee, particularly with rising from a seated position, going upstairs, or sitting with their legs crossed. The semitendinosus, gracilis, and sartorius function in unison in the act of crossing one leg over the other; thus, this motion typically will elicit the pain seen in pes anserine bursitis.[13] Patients may also complain of posteromedial or midline knee pain, which makes it difficult to differentiate from a meniscal lesion or injury.

Additionally, there may be subjective complaints of muscle weakness and decreased range of motion of the knee joint. Tenderness is invariably present over at the insertion of the pes anserine tendons, “goose’s foot,” at the medial knee and upper medial tibia. Swelling may or may not be present due to edema or fluid collection at the site of insertion. In patients with osteoarthritis, the clinician should have heightened suspicion for the possibility of pes anserine pain.

On physical examination, the affected knee should initially be evaluated in full extension. Tenderness will likely be present in the medial knee joint and may extend along the proximal, medial tibial region. With knee flexion to 90 degrees, tenderness may be palpated along the medial tendinous structures of the pes anserine group as they travel to insert along the medial tibial region. The pes anserine bursa lies directly beneath the tendons at their insertion.

The patient can also present with neuropathic pain due to saphenous compression by pes anserinus bursitis. It can cause pain and paresthesia even in the lateral tibial region and simulates a tibial stress fracture.[15]

In 1985, a group of criteria was set by Larson and Baum to diagnose pes anserinus bursitis, which includes:

• Anteromedial knee pain, especially with ascending or descending stairs.
• Morning pain and stiffness that lasts more than an hour. 
• Difficulty in rising from a seated position or getting out of a car
• Local sensitivity and edema at the anatomical location of the anserine bursa[7]

Evaluation

Generally speaking, imaging does not assist with the diagnosis of pes anserine bursitis. However, plain knee radiographs are usually obtained to observe for any underlying bony abnormalities, including osteoarthritis.[16]

Ultrasonography may be used as an adjunct to evaluate other causes of localized swelling, including joint effusions. 

Magnetic Resonance Imaging (MRI): Though rarely indicated in an urgent setting, MRI may help assess for knee pathology and rule out alternative diagnoses.MRI scans can demonstrate fluid in the anserine bursa in cases of bursitis. However, fluid has been demonstrated in 5% of asymptomatic knees. Hence, its presence in imaging is not diagnostic.[17][18] Multiple studies have shown the axial imaging sequence essential for the differentiation of fluid collection, especially in semimembranosus bursa and Bakers cyst. Fluid collections in the structures anatomically close to the collateral ligament, such as bone cysts, meniscal cysts, and bursitis, would result in a more challenging differential diagnosis.[19][20]

Aspiration and fluid analysis: This has rarely been documented in the literature. When performed showed mononuclear cells or the absence of inflammatory cells and crystals.[21][22]

Treatment / Management

The basics of initial therapy for pes anserine bursitis include the usual typical recommendations for many musculoskeletal disorders, including rest, ice, and short-term nonsteroidal anti-inflammatory drug use (unless otherwise contraindicated based on the patient’s medical history). Additionally, in the setting of obesity and deconditioning, weight loss and muscle strengthening exercises (particularly the quadriceps muscle group) can help with the long-term resolution of symptoms.[23]

In patients with underlying osteoarthritis or occasionally associated conditions such as knee malalignment or pes planus, treatment may need to be directed at this entity as well. Steroid injections are reserved for refractory symptoms but may be used initially with severe pain or in patients with nocturnal pain symptoms. However, steroid injections risk complications such as subcutaneous tissue atrophy, skin pigmentation, and tendon tear.

Additional modalities for treatment include therapeutic ultrasound, physical therapy, and transcutaneous electrical nerve stimulation (TENS).[24]

Surgical intervention is usually reserved for cases that fail conservative treatment over long periods. Incision and drainage of the bursae can relieve the symptoms, but bursal excision has also been reported in the literature. Underlying conditions should be addressed, as in cases of exostosis that should be excised.

Differential Diagnosis

The differential diagnosis for a patient presenting with localized pain in the area of the pes anserine bursa is significantly broad and forms the main body of the topic.[13] A myriad of possibilities can be on the list, such as:

• Infectious pathologies such as septic bursitis or osteomyelitis.
• Gouty changes to the bursa. 
• Medial meniscus injuries and lesions or medial compartment osteoarthritis: both pathologies would present with medial joint line pain symptoms and signs, whereas symptoms from pes anserinus bursitis are more inferomedial.
• L3-L4 radiculopathy: This is most likely will be associated with lumbar pain with no tenderness to palpation of the anserine bursa.
• Medial collateral ligament injuries or lesions: history of trauma and Stress maneuvers with or without resultant instability or laxity would differentiate this etiology.
• In the setting of trauma, proximal tibia stress fracture from repetitive sports activities. Or in cases of intraarticular fractures, lipohemarthrosis may develop in the bursa. Also, free bodies that develop in the joint can migrate to the bursa.
• Other bursae inflammation, such as suprapatellar bursitis, should be in the differential diagnosis. The suprapatellar bursa is located in the midline between the prefemoral and suprapatellar fat pad and usually communicates with the knee joint apart from cases where suprapatellar plica is present. Prepatellar bursitis: this bursa is situated between the patella and the skin and would be encountered in people involved in more kneeling. Superficial infrapatellar bursitis: this bursa is located anterior to the patellar tendon and inferior to the subcutaneous fat or deep infrapatellar bursitis: this bursa is located deep to the distal patellar tendon and anterior to the proximal tibia. All suprapatellar, infrapatellar, and prepatellar bursae can be clearly visualized in the sagittal sequences of the MRI.
  • Also, semimembranosus bursitis, also known as semimembranosustibial collateral ligament bursitis and this bursa lies between superficial and deep layers of the medial collateral ligament at the anterosuperior aspect of the semimembranosus tendon. Hemorrhagic bursitis can develop following trauma or could be related to Osgood-Schlatter disease. Bursal fluid is a physiological finding as a result of overloading the extensor tendons in athletic individuals, especially long-distance runners and jumpers, and hence the challenge in the diagnosis.[25][26] 
  • As bursitis around the knee mentioned, others such as iliotibial bursitis: this bursa lies in the distal portion of the iliotibial band close to Gerdy's tubercle and proximal lateral tibia. An overload secondary to varus stress can result in iliotibial tendonitis and bursitis. However, this presents with pain in the anterolateral knee and can mimic lateral meniscus injuries or pathologies.
• Knee cysts are also part of the differential diagnosis, such as Baker's cyst, otherwise known as a popliteal cyst or gastrocnemius-semimembranosus recess. This bursa is communicated with the synovium and lies between the medial head of the gastrocnemius and semimembranosus muscles. It can be easily differentiated from other knee cysts due to its peculiar anatomical location. Bimodal age distribution (4 to 7) and (35 to 70) has been reported in the literature for Baker's cysts. It can be asymptomatic or large enough to compress the popliteal vein and cause deep vein thrombosis, or it can rupture acutely and present with a clinical picture similar to deep vein thrombosis.
• Meniscal cysts (cysts of the semilunar fibrocartilage): results from fluid extrusion into the parameniscal soft tissue secondary to a meniscal tear. Usually presents with pain, palpable mass, and occasionally locking. Meniscal cysts are more commonly medial than lateral and tend to recur after aspiration or excision unless the meniscal pathology is treated.
• Ganglions (intra-articular synovial cysts) can be in the joint capsule, periarticular ligament, or synovial tendon sheath. The absence of meniscal pathology would exclude meniscal cysts from ganglion differential.Synovial osteochondromatosis is characterized by intraarticular cartilaginous bodies with synovial metaplasia.
• Spontaneous osteonecrosis of the medial tibial plateau can also be among the differential diagnosis; however, this can be excluded radiologically.[27]
• Masses and space-occupying lesions, either benign, such as lipoma, hemangioma, giant cell tumor, myelolipoma, para-articular chondroma or osteochondroma, or synovial hemangioma. Or infectious such conditions as tuberculosis. Or even malignant tumors commonly detected in the knee, such as fibrous histiocytoma, liposarcoma, and synovial sarcoma. 

Added to the long list are: the varicose popliteal vein, popliteal aneurysm, and secular dilation of the popliteal vein can occasionally be a consequence of trauma. Less urgent pathology to include in the differential for pes anserine bursitis includes fat pad tenderness in overweight patients or fibromyalgia. In fibromyalgia patients, the pain is typically more symmetric and bilateral. Popliteal varicose vein, popliteal aneurysm, and secular dilation of the popliteal vein could all be due to trauma. Others include Osgood-Schlatter disease, dissecting osteochondritis, patellar tendinitis, synovial plica, muscle pain, patellofemoral syndrome, recurring patellar subluxation, patellar chondromalacia, lesion of the infrapatellar fat pad, patellar dysplasia, bi- or multipartite patella, or patellar fracture. Frequently, pain in the anserine region is part of the fibromyalgia syndrome.

Prognosis

The prognosis of most cases of pes anserine bursitis is a long-term resolution after limiting the inciting factors, including avoiding sports or repetitive activities that may worsen the patient’s pain. Duration of symptoms varies based on underlying conditions, including osteoarthritis, obesity, and deconditioning.[28]

Complications

Complications of pes anserine bursitis are rare but usually result from a lack of treatment. These can include increased pain and inflammation and subsequent weakening of the muscles and tendons around the knee joint.[29][28]

Deterrence and Patient Education

Patient education centers around preventing reinjury and proper steps to return to play for athletes. These include using proper form when training, hamstring stretching along with quadriceps strengthening, proper footwear for activity level and intensity, maintaining healthy body weight, and cautious return to competitive training and activity.

Pearls and Other Issues

Pes anserine bursitis refers specifically to the inflammatory condition of the bursal sac located between the muscular tendons (sartorius, gracilis, and semitendinosus) and their insertion at the proximal medial tibia. These three muscles act to help in the “cross-legged” position. Thus, any repetitive activity that requires this form of motion may exacerbate the symptoms of the condition.

Underlying osteoarthritis, obesity, and the female gender are risk factors for developing this syndrome.

Treatment of pes anserine bursitis is generally supportive, with steroid injections reserved for refractory cases.

Enhancing Healthcare Team Outcomes

Patients with pes anserine bursitis may be seen in all practice settings, from outpatient offices, urgent care centers, and emergency departments. Referral to a specialist is not often necessary unless the patient has another underlying condition that may be causing this syndrome or if there is unrelenting discomfort despite supportive measures.

Most data on diagnosis and treatment of pes anserine is derived from case series, relying heavily on expert opinions for direction and care goals. An interprofessional team approach involving clinicians, nurses, and physical therapists, all working collaboratively and engaging in open communication, will result in the best outcomes. [Level 5]