Charcot osteoarthropathy of the knee secondary to neurosyphilis: a rare condition managed by a challenging arthrodesis

Abstract

The Charcot joint or neuropathic osteoarthropathy was first described as an arthritic sequela of neurosyphilis (tabes dorsalis). It results in significant joint destruction and instability. Nowadays, it is a very rare condition and represents a considerable challenge to the orthopaedic surgeon. The authors describe the case of a patient diagnosed with neurosyphilis who was requested an orthopaedic consultation for an enlarged and unstable knee. The diagnosis of Charcot knee was made and based on the clinical and radiographical findings combined with the patient’s medical history. Knee arthrodesis was the surgical treatment chosen to preserve the limb and only succeeded at second attempt. At 4 years of follow-up, it proved to be an effective surgical treatment. In this article, we focus on the importance of early recognition of joint changes in these patients in order to prevent irreversible joint loss.

Background

In 1868, the French neurologist Jean-Marie Charcot noted a pattern of articular bone destruction and absent peripheral sensation in patients with tertiary syphilis. This osteoarthropathy was named Charcot joint disease after him.

Any disease-causing peripheral neuropathy or a central nerve lesion may lead to Charcot osteoarthropathy. It is thought that the loss of proprioception and deep sensation ultimately leads to progressive joint degeneration, inflammation and destruction secondary to repetitive unrecognised trauma.¹ In contemporary western societies, it is most often caused by diabetes. It is seen most commonly in the foot and ankle. Other less common sites of involvement may include the knee, hip, shoulder and spine.

Since the beginning of penicillin’s mass production in 1942, the incidence of syphilis decreased dramatically.² Nowadays, expanded screening, prompt diagnosis and effectiveness of treatment all combine to easily treat syphilis in its primary stage.

In this article, the authors describe the case of a patient with a form of tertiary syphilis (neurosyphilis or ‘tabes dorsalis’) who insidiously developed a destructive osteoarthropathy of the knee and underwent through a succession of orthopaedic procedures that finally resulted in a stable and painless limb.

Case presentation

The authors present a 55-year-old patient admitted in the infectious diseases department of the hospital for treatment of an upper respiratory tract infection who was requested an orthopaedic consultation. He complained of swollen right knee and limitation on walking in the previous eighteen months. When questioned he reported a history of disregarded warm and painful knee that lasted for a period of 3 months when his knee symptoms started. No investigations were made on his knee during the last 2 years. He had been diagnosed tertiary syphilis 12 years before and was followed in Infectious Diseases consultation on a irregular basis. The patient recognised having had genital erosions two decades before which he neglected and never received medical care at that time. He denied having being submitted to antibiotic treatment for those lesions. His medical history was otherwise unremarkable.

At the clinical examination, the patient presented a peripheral neuropathy with bilateral hypoesthesia in a stocking-and-glove pattern. His proprioception was impaired and there was a positive Romberg test. There was a bilateral reduced muscle strength, showing full range of motion with a bilateral decrease in muscle activation, graded 4/5. The patient presented a valgus deformity of the right knee which was painless (figure 1). The examiner observed an enlarged knee with marked ligamentous laxity at stress testing. There was evident crepitus from within the joint. The peripheral pulses were normal but the deep tendon reflexes of lower limbs were absent. He had a body mass index of 22 and the ankle:brachial blood pressure index was normal.

Figure 1.

Patient knees when firstly examined by the orthopaedic surgery consultants.

Investigations

Laboratory tests revealed normal serum white cell count and erythrocyte sedimentation rate. A knee radiograph was requested (figure 2): it showed advanced fragmentation of the knee joint, with almost complete disappearance of the lateral femoral condyle, subluxation, fragmentation, bony destruction and the presence of periarticular bone formation.

Figure 2.

First radiographs of patient’s right knee.

This clinical picture in the context of a confirmed tertiary syphilis along with the imagiological findings allowed the authors to establish the diagnosis of neuropathic osteoarthropathy of the knee, stage 3 of Eichenholtz.³

Treatment

After careful consideration, the patient was submitted to a knee arthrodesis by using a compression external fixator in a monoaxial parallel construct. Under general anaesthesia, a long medial parapatellar approach was used. The patella was removed and the cancellous bone used as autograft. Femur and tibia osteotomy were made and the knee was realigned. A careful debridement of all synovial tissue and scarred capsule was made. The bony defects were filled with autograft. There was extensive subchondral sclerosis and the surgeon noticed that femur and tibia bone extremities did not bleed despite no tourniquet was used. The surgical procedure was otherwise unremarkable and the result was satisfactory (figures 3 and 4).

Figure 3.

Postoperatory view of the Charcot knee submitted to arthrodesis.

Figure 4.

Postoperatory radiographs of the Charcot knee.

The patient experienced a favourable postoperative evolution and was discharged with a non-weight bearing status. After 7 months, there was radiological evidence of knee fusion (figure 5). However, 2 weeks before being scheduled to remove the external fixation, he suffered a fall resulting in a distal femur fracture (figure 6). The compressive external fixator was removed and the fracture was managed with a unilateral external fixator.

Figure 5.

Radiographs 7 months after the index arthrodesis.

Figure 6.

Radiographs showing distal femur fracture suffered by the patient before removing the external fixator.

After 4 months, there was radiological evidence of fracture consolidation and the external fixator was removed. The patient lower limb was then placed in a cast cylinder. Weeks later, he started complaining of knee pain. The cast was removed and the knee showed inflammatory signs and movement at the arthrodesis site. The X-ray confirmed complete resorption of the arthrodesis and revealed a pseudarthrosis.

The clinical picture at this point was subject of debate and multidisciplinary deliberation. Amputation and rearthrodesis were now the main surgical options. The chief surgeon chose to do a rearthrodesis, which was again performed with a compressive external fixator. Intraoperatively, the surgical team observed marked synovial proliferation and heterotopic ossification, which was removed. The postoperative period was uneventful and the patient was discharged. The patient was regularly observed by an orthopaedic surgeon with no significant postoperative complications. Eight months after the rearthrodesis, there was radiological evidence of knee fusion and the external fixator was removed.

Outcome and follow-up

This second arthrodesis proved to be a successful procedure as the clinical and radiographical re-evaluations showed a consolidated arthrodesis and a satisfied patient. He experienced no further complications.

The follow-up at 4 years after the second arthrodesis showed a 60-year-old patient with a painless and stable limb with an X-ray showing a completely fused knee joint (figure 7).

Figure 7.

Radiographs with evidence of knee fusion, 8 months after the rearthrodesis and 21 months after the index arthrodesis.

Discussion

Sir William Osler stated that ‘the physician who knows syphilis knows medicine’. The disease is often unrecognised or partially treated by the empirical use of antibiotics. Therefore, patients with tertiary or neurological syphilis frequently present with non-classic signs and symptoms.⁴ Loss of deep sensation and proprioception of this patient probably contributed to poor joint protection and undetected microtrauma, leading his knee to a silent osteoarthropathy. The early stages of a warm and painful knee and exsudation into the joint were undetected and then followed by a painless disorganisation of articular structures.

The presented patient was diagnosed in this late stage of a painless knee with absent deep tendon reflexes. The knee X-ray confirmed an advanced stage of articular destruction (stage 3 of Eichenholtz classification). Arthrodesis is the recommended operative treatment when instability and joint destruction is significant, as was the case of this patient. It is essential that the osteolytic stage of disease has ceased prior to surgical intervention.⁵ If osteolysis is more active than osteoblastic activity, the process of bone consolidation will be compromised. Full weight-bearing can only be allowed when there is evidence of a solid fusion. Clinical union may be difficult to assess; therefore, union is determined mainly radiologically.

The neuropathic joint has been particularly resistant to fusion, as illustrated by the failure of the first arthrodesis of the patient, having evolved to a pseudarthrosis. Arthrodesis of a Charcot joint can fail due to a variety of reasons including inadequate fixation, persisting infection, deficient bone stock and lack of solid bony contact. It has been recommended a complete synovectomy as the synovium is hypothesised to interfere with normal bone metabolism.⁶ To the best of the authors knowledge, this is the first case of a knee arthrodesis that evolved to a pseudarthrosis which achieved fusion after a second attempt using the same surgical technique.

Arthroplasty of a Charcot joint has commonly been avoided at all costs, due to the increased risk of complications when performed on a neuropathic knee. However, if well succeeded, arthroplasty can significantly improve the symptoms of a Charcot knee joint. Kim et al⁷ performed constrained knee arthroplasty in 17 out of 19 Charcot knees. Only 53% presented satisfactory outcomes at a mean follow-up of 5 years. Parvizi et al⁸ presented a case series of 40 Charcot knees and only four were submitted to a knee arthroplasty. Vince et al⁹ performed a constrained knee arthroplasty in a Charcot knee secondary to tertiary syphilis and the patient experienced dislocation and infection of the prosthesis. The implants had to be removed. More recently, Liu et al¹⁰ reported a bilateral total knee arthroplasty within a short period of time in a patient with neuropathic arthropathy of both knees associated with ‘tabes dorsalis’. They conclude that this cause of Charcot knee should not be considered a contraindication to arthroplasty, as long as patients are selected for surgery after the osteolytic phase has ceased.

The predisposition of the Charcot knee to postoperative complications requires many months of careful observation. That is why the patient was followed regularly in orthopaedic consultation during the 4 years. Surveillance within the primary care setting is the key of management to promote early detection and prevent Charcot osteoarthropathy. All at-risk patients should undergo regular review of their joints by general practitioners, neurologists and infectious disease specialists, who are often the main caregivers of these patients.

Learning points.

• Neurosyphilis is still a reality in the 21st century despite penicillin is widely available since the 1940s.

• A large weight-bearing joint as the knee can be insidiously destroyed by neurosyphilis and a high suspicion index is the key to prevent irreversible joint damage.

• Arthrodesis of a neuropathic knee arthropathy is a challenging procedure but results in a stable lower limb when joint repair is not possible.

• When diagnosed early, a knee arthroplasty can restore joint activity in a short period of time, although technically demanding in neuropathic patients.