Pes anserine syndrome in post knee arthroplasty. A rare case report

Abstract

Pes anserine syndrome is a cause of inferomedial knee pain. It occurs in patients with diabetes mellitus, osteoarthritis, rheumatoid arthritis and in overweight patients. It is a challenge to identify the causes of knee pain following knee replacement surgery. We present a case report of pes anserine syndrome in a 79-year-old female who had undergone knee arthroplasty 13 years prior. She was pain free until one year ago when her knee pain resurfaced without any symptoms of infection or history of trauma. She was successfully treated with a combination of stretching exercise and steroid local steroid injection. We want to highlight that such common condition as pes anserine syndrome, could occur in total knee arthroplasty, and should be considered as one of the possible diagnosis.

1. Introduction

Knee arthroplasty is one of the most successful procedures in orthopedics. The number of this procedure is increasing over the years worldwide. From the National Joint Replacement Registry of Australia, an increment of 3.5% for total knee arthroplasty has been reported in 2016.¹ The main goal of knee joint replacement is to eliminate pain and to correct the mechanical axis of the lower limb. Despite the glorious outcome of total knee surgery, managing the complication is a true challenge for surgeons. Revision surgery would be a catastrophic experience to patient.

Thus, it is important to identify the causes of knee pain after total knee arthroplasty. Evaluation of a painful total knee joint encompasses four important aspects; clinical assessments, laboratory blood investigations, imaging and joint fluid analysis. Even after all these investigations have been performed, it may still be a challenge to make an accurate diagnosis underpinning the origin of pain.²

In this paper, we present an uncommon case report of pes anserine syndrome (PAS) in the knee of a patient 13 years after joint replacement surgery with normal radiological findings. This report aims to highlight the importance of a systematic approach to investigate the possible causes of knee pain following knee replacement surgery. Proper clinical examinations, laboratory blood investigation, imaging including radiological and ultrasound would help to exclude a range of possible causes before subjecting the patient to more invasive investigations. If pain is the only indication for revision especially with an unclear diagnosis, the impact to the patient may potentially be catastrophic.

2. Case report

A 79-year-old lady with underlying diabetes mellitus and dyslipidemia had undergone joint replacement surgery of the left knee 13 years ago. She was satisfied with the knee until one year ago, where she complained of progressively worsening left knee pain. She had no fever nor other joint pain or stiffness. There was no history of trauma and denied straining both knees. Her daily activities were disrupted due to the knee pain and she required a walking stick for mobility. The pain was exacerbated by climbing up and going down the stairs and was relieved by rest.

On examination of the left knee, there was no swelling of the knee, the skin surrounding of the area was not erythematous nor there was any sinus or other signs of infection. There was no effusion, and the knee was not warm. There was tenderness over the inferomedial aspect of the left knee. She demonstrated a full range of motion of the left knee (5–120°) (Fig. 2, Fig. 3, Fig. 4).

Fig. 2.

The clinical picture of both knees in standing. Arrow shows the area of tenderness.

Fig. 3.

Clinical pictures show the active flexion and extension of the knees. Arrow shows the localised tenderness and area of palpation.

Fig. 4.

Clinical picture in front view. Arrow shows the location for palpation and tenderness.

Radiological findings revealed a total knee prosthesis in situ with no evidence of implant loosening with no increase opacity or lucency over the tender area (Fig. 1). The blood parameters including C-reactive protein and white cell count were also within normal limits.

Fig. 1.

The radiological imaging of anterior-posterior and lateral of both knees post knee joint replacement surgery, showed no area of lucencies that would suggest aseptic loosening.

The condition failed to improve with the quadriceps and hamstring muscles strengthening and range of motion of the knee exercises supervised by the physiotherapist for six months, thus we proceeded with ultrasound of the left knee. The ultrasound showed irregularity and the presence of osteophytes at the medial knee joint with synovitis changes over the pes anserine site. To confirm the diagnosis, a diagnostic steroid injection was administered over the pes anserine site. The procedure was done under aseptic technique and ultrasound guidance using a 20 G needle to inject the affected site with a solution of 1 mL of 40 mg/mL of triamcinolone acetonite and 4 mL of 5 mg/mL. Immediately post-injection, the inferomedial anterior left knee pain was reduced. We advised the patient to continue physiotherapy to strengthen the quadriceps and hamstring muscles and to maintain the range of motion of the knee. During our subsequent follow up at two months, six months and a year, the patient was pain free was able to ambulate unaided.

3. Discussion

Knee pain following arthroplasty is usually a diagnostic dilemma for surgeons. Patients sometimes presented to the clinic with the non-specific complaint of knee pain and unremarkable findings on the radiographs. There are many causes of pain in arthroplasty. Sofka et al. stated that joint instability is the most common causes of knee pain especially after more than five years after surgery. Most of the cases required surgical revision.³ However, before diagnosing joint instability as cause of knee pain, which leads to mechanical loosening of the implant, it is important to systematically examine the patient. Pes anserine syndrome is a possible causes of knee pain post arthroplasty.

A systematic and holistic approach when dealing with knee pain following total knee replacement is important. The key is to determine the origin of the pain. Wilson et al. divided the causes of the knee pain in total knee replacement into joint-related and non-joint related causes. The examples of joint-related causes such as infection, osteolysis (synovitis or microfracture), mechanical instability due to loosening implant and failure of the component, patellar clunk syndrome or synovial pinching syndrome. Non-joint causes of post-operative knee pain included neurological or vascular diseases, reflex sympathetic dystrophy and inflammation of the surrounding soft tissue (tendinitis or bursitis).² A full history, thorough clinical examinations, relevant laboratory blood investigation, and radiological imaging must be included in the work up as well.

Pes anserine is referred to as conjoint tendon, which consists of sartorius, gracilis and semitendinous tendons and is inserted 5cm distal to the medial portion of the knee. It comes from the Latin word “goosefoot”.⁴ The conjoint tendon is important as the primary flexor of the knee, and as secondary internal rotator of the knee. It protects the knee against rotation and valgus stress.

Moschcowitz in 1937 first reported about “pes anserine syndrome” as knee pain found in women, especially when going upstairs and downstairs, standing up from chair and difficulty on flexing the knee. Pes anserine syndrome is a condition where a patient complains of pain over the inferomedial aspect of the knee. It is inflammation of the bursa or the pes anserine tendon.⁵

Pes anserine syndrome has been reported to occur in an overweight patient, long-distance runner, patients with underlying diabetes mellitus, and in osteoarthritis or rheumatoid arthritis. Helfenstein et al. explained that the etiology of this syndrome includes trauma, infection, bone exostosis, pes planus, genu valgum and damage to the medial meniscus.⁴ Muhammad et al. documented that knee pain due to osteoarthritis is commonly associated with pes anserine syndrome but it is usually neglected.⁶ However, to the authors’ knowledge, not many authors have reported on PAS after long period after knee joint replacement.

The pathogenesis of PAS remains a controversial as many studies do not indicate whether the symptoms are related to true bursitis or fasciitis over the conjoint tendon or at its insertion. However, some authors documented that panniculitis does occur at this site, which is usually found in the obese. Mechanical stress to the area most likely contribute to bursitis.⁷

Most literatures described that such syndrome would benefit from extensive physiotherapy approaches such as stretching exercise, transcutaneous electriral nerve stimulation, and ultrasound. An analgesic such as non-steroidal anti-inflammatory drugs is the first-line of treatment. Intrabusal injection of local anesthesia with the mixture of steroids is the second line treatment.⁷ Sarifakioglu et al. discovered that a combination therapy of physiotherapy and steroid injection is more effective in treating PAS.⁸ In terms of duration of the physiotherapy that was required post steroidal injection, no proper study was conducted. However, Deborah et al. found out that patient comorbidities play a significant role rather than the duration or approach in rehabilitation for the patient post knee replacement.⁹

In our patient, she underwent total knee replacement for severe osteoarthritis, and the operation was considered successful as the patient was pain-free for more than 10 years. Her comorbidities were diabetes mellitus with no history of trauma or over excessive used of the knee after the operation. In view of the long pain period after knee arthroplasty, aseptic loosening of implant was our first differential diagnosis, but the radiological imaging showed no obvious evidence of loosening implant. Infection was dismissed as all blood parameter including white cell count, leucocyte differential and C reactive protein were all in normal range. After failed therapy with analgesia and physiotherapy management for six months, we proceeded with non-invasive imaging; ultrasound of the knee, which showed inflammation of the pes anserinus. Thus, we then proceeded with a diagnostic steroid injection to the site and the patient is now pain-free for subsequent one year follow up.

4. Conclusion

Pes anserine syndrome is one of the possible causes of knee pain post joint replacement surgery. With systematical examination, we could avoid subjecting the patient to expensive and invasive procedures including revision of arthroplasty. Treatment should only be initiated after diagnosis is confirmed. Even though the etiology behind PAS it is still controversial, theoretically, it would be caused by overuse. It is considered as a diagnosis of exclusion diagnosis of knee pain. The combination therapy of physical exercise and steroid injection would benefit the patient in treating such disease.

5. Conflicts of interest

The authors whose names are listed immediately below certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.

Appendix A. Supplementary data

The following is the supplementary data to this article: