Infection is always considered foremost in the differential diagnosis of the painful prosthetic joint. Signs and symptoms include fever, chills, night sweats, and pain at rest. A history of previous infection at the incision site, distant infections in the body, and recent invasive procedures (including dental, gastrointestinal, or urologic procedures) are all risk factors for infection of the prosthetic joint.
On physical examination, the wound and surrounding joint areas should be examined carefully for evidence of swelling, erythema, and drainage. Laboratory tests may show a leukocytosis, with an elevated ESR and CRP. When aspiration is indicated, Gram stain and cultures for aerobic and anaerobic organisms as well as acid-fast bacilli and fungal organisms are essential.
Radiographic findings suggestive of infection include periosteal new bone formation (Figure 13–2), endosteal scalloping, soft-tissue swelling, osteopenia, and premature loosening of the component. Infections are considered to be acute if diagnosed within 6 weeks of symptom onset. Acute infections can be treated with surgical irrigation, debridement, and exchange of the modular components. For infections that have persisted longer than 6 weeks, a two-stage reimplantation is currently the standard of care. The first stage surgery involves removal of all foreign material, including the prosthetic implant, methylmethacrylate, metal cables, plates, and screws. A 6-week course of intravenous antibiotics follows the first stage. After this initial treatment, joint aspiration is recommended following an antibiotic “holiday”; ie, the antibiotic is discontinued for a minimum of 2 weeks before joint aspiration is performed. Once there is no clinical evidence of infection, the ESR and CRP values have returned to their baseline levels, and the joint aspiration is negative for infection, the definitive second stage reimplantation surgery is performed. Reimplantation surgery is not undertaken until the infection has been eradicated.
On average, a well-implanted prosthesis remains viable for 10–25 years or more, depending on multiple factors, such as implant design, material, patient age, and activity level. Longevity of implant survival is improved with modern bearing surfaces, such as highly cross-linked polyethylene, because these have significantly lower wear rates compared with materials used in the past. The most common cause of prosthetic failure, however, is aseptic loosening.
The pain associated with aseptic prosthetic loosening is usually aggravated by weight-bearing activities, such as lifting objects or simply rising from a seated position. This pain can also be present immediately after surgery if there has been inadequate fixation of the prosthesis to the bone.
Patients with prosthetic loosening in the lower extremity are likely to have an antalgic gait or limp, and pain may be elicited with range of motion. There may also be more pain in the area of loosening with an active straight leg raise (raising the leg off the examination table with the knee fully extended), than with a passive straight leg raise.
The radiographic signs of prosthetic joint loosening include subsidence of the implant, cement or prosthetic fracture, debonding between the cement mantle and implant, and pedestal formation with a cementless femoral stem (Figure 13–3).
Aseptic loosening of the femoral implant with periprosthetic osteolysis, areas of debonding between cement mantle and implant.
Periprosthetic osteolysis (or bone resorption) is initiated by osteoclasts, which are stimulated by inflammatory mediators produced through the macrophage response to wear debris. Wear debris stimulates a foreign body inflammatory response, which leads to the bone resorption. Osteolysis manifests itself as a lucent area around the prosthesis on plain radiographs and is the most common cause for implant loosening. In the absence of loosening, osteolysis can still account for pain. Radiographs normally do not demonstrate osteolysis until the bone mass in the area of lucency has decreased by at least 30% (Figure 13–4).
Osteolysis (arrows) in the acetabulum seen on radiographic (A and B) and CT assessment (C).
Treatment of osteolysis may be expectant if the patient is asymptomatic or only mildly symptomatic. Revision arthroplasty is indicated if there is significant pain, dysfunction, or impending fracture.
Fracture around the implant is uncommon and is typically related to osteolysis, implant loosening, or trauma. There may be antecedent minor trauma, especially in patients with significant osteolysis. Standard radiographs almost always reveal the fracture (Figure 13–5).
Fracture of the bone around a prosthesis typically requires surgery, and surgical considerations include the quality of the bone, stability of the implant, and location of the fracture.
Prosthetic dislocation is most common at the hip and rare in the knee. Joint dislocation leads to pain, deformity, and loss of function. Standard radiographs are necessary to help confirm dislocation (Figure 13–6). Radiographic evaluation should always include two orthogonal views (eg, anteroposterior and lateral), since the diagnosis can be missed if only one view is obtained.
Prosthetic dislocation is treated with closed reduction under sedation, although open reduction may be required for patients in whom closed reduction is unsuccessful. Once the joint has been reduced, patients are counseled on activity modification to prevent further dislocation or subluxation. Revision surgery is indicated in cases of recurrent dislocation.
A common cause of referred pain to the lower limb is a spinal disorder. Nerve impingement in the cervical or lumbar spine can cause pain similar to that of a loose prosthesis. Indeed, tumors in the neck, shoulder, abdomen, or pelvis can also cause referred pain. Signs and symptoms of nerve root impingement include atrophy, weakness, paresthesia, and neuropathic pain. This pain is not normally aggravated by weight-bearing.
Pain caused by spinal stenosis is typically relieved by forward flexion or the assumption of a stooped, forward-leaning posture. CT and MRI of the spine are useful in arriving at the diagnosis. Treatment of spinal disorders includes both conservative and surgical measures. Depending on the diagnosis, there may be a role for activity modification, physiotherapy, core body strengthening activity, and pain management modalities. Patients whose symptoms are refractory to these conservative measures may require spinal decompression or fusion.
Bursae around prosthetic joints remain potential sites of inflammation and sources of pain after total joint arthroplasty. Patients with trochanteric, pes, patellar or anserine bursitis describe pain in the bursal region and localized tenderness to palpation.
The treatment approach to bursitis following joint arthroplasty is different to that of bursitis in a native joint. Following surgery, patients are less likely to have a capsular boundary between the bursa and the joint space. Thus, bursal injections are discouraged as contamination of the bursa is associated with an increased risk of joint infection. Use of a nonsteroidal anti-inflammatory medication and other multimodal therapy may help with resolution of the pain. Surgical intervention for bursitis refractory to conservative management has a variable outcome.
Neuroma or Chronic Regional Pain Syndrome
Any nerve transected at surgery may cause pain postoperatively. The infrapatellar branch of the saphenous nerve, normally cut with a midline incision during knee arthroplasty, can be a potential source of complaint. Symptomatic neuromas generally cause pain disproportionate to the physical examination and can lead to cutaneous hypersensitivity with dysesthesia, allodynia, and hyperalgesia.
Patients with chronic regional pain syndrome generally have pain that is diffuse. There may be associated joint stiffness, hyperhidrosis, and skin discoloration, along with motor disturbances such as weakness, spasm, and tremor. Local osteopenia can often be seen in the affected extremity on radiographs.
In the absence of another diagnosis, resection of the neuroma may be useful in patients with symptoms of at least 6 months duration and refractory to conservative treatment. In addition to the use of tricyclic antidepressant and anticonvulsant agents, physiotherapy modalities and sympathetic nerve block may offer relief to patients with chronic regional pain syndrome. Nevertheless, these conditions remain difficult to treat and usually require multimodal treatments.
Adverse Soft‐Tissue Reaction to Metal‐on-Metal Hip Resurfacing
Metal-on-metal hip resurfacing arthroplasty has undergone a resurgence as an alternative treatment option for young and active patients with significant hip osteoarthritis. The proposed potential advantages of metal-on-metal hip resurfacing arthroplasty over conventional total hip arthroplasty include bone conservation, greater implant stability, and easier revision surgery. Despite the satisfactory short-term implant survival, there is concern regarding the long-term biologic consequences of exposure to cobalt (Co) and chromium (Cr), the principal elements in the CoCr alloy used in the modern metal-on-metal bearings. One of the local adverse biologic responses is the occurrence of abnormal periprosthetic soft-tissue reactions, which have become popularly described as pseudotumors (Figure 13–7).
MRI scan with metal artifact reduction sequence showing a pseudotumor with both cystic and solid components in a patient with painful metal-on-metal hip replacement.
Pseudotumors can cause a wide spectrum of clinical presentations, including hip pain, lump/mass, and joint dislocation. These lesions are characterized histologically by the presence of T-lymphocytes and macrophages with extensive necrosis, often difficult to distinguish morphologically from a necrotic tumor, hence the term “pseudotumor.” However, these periprosthetic soft-tissue lesions have also been described by other names, such as bursae, cysts, inflammatory masses, or adverse reactions to metal debris. The association between the increased serum and hip aspirate metal ion levels suggests that pseudotumors are likely to represent a biologic response to the large amount of metal wear debris generated from excessive wear in vivo. Although the exact prevalence is unknown, it has been reported to be approximately 2%.
Clinicians need to be aware of the potential for pseudotumor development when evaluating patients with painful metal-on-metal hip resurfacing arthroplasty. Because patients with pseudotumors may have normal radiographs, further radiographic investigation using soft-tissue imaging modalities, such as ultrasound or MRI with metal artifact reduction sequence, is recommended to confirm the diagnosis. In the majority of patients with pseudotumors, the treatment is revision surgery to non-metal-on-metal total hip replacements.
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