A 65-year-old man underwent a left cementless total hip arthroplasty for degenerative osteoarthritis using a large, cylindrical, cobalt–chrome stem. The postoperative course was uneventful, and the patient had a pain-free interval after the procedure.
The patient presented 3 years later with a dull, isolated, aching pain in the anterolateral thigh. He had no history of recent trauma, systemic illness, or back symptoms. The discomfort was localized to a specific area on the femur that correlated well with the location of the prosthetic stem tip. Palpation of the hip and thigh did not reproduce the pain, which began on initiation of activities and increased with continued activity. However, it was relieved at rest and after walking five blocks. There was no pain at night.
The patient has experienced pain on and off since the operation. The discomfort increased over time and became severe enough for the patient to use a cane.
Results of the neurovascular assessment of the lower extremities were normal. Active and passive ranges of motion did not suggest implant instability. Lumbar, spine, and knee radiographs were normal. Radiographs of the pelvis, hip, and femur revealed good acetabular and stem position and no signs of fracture. The bone–prosthesis interface demonstrated multiple endosteal spot welds. There was mild calcar atrophy and proximal stress shielding, which were more apparent compared with previous radiographs, but there was no evidence of implant migration, progressively increasing lucent lines, or femoral thickening. Levels of serum inflammatory markers were normal. Activity modification, antiinflammatory medications, and the use of a cane were unsuccessful in improving the patient’s symptoms 4 years after the initial procedure.
Thigh pain is a recognized problem after cementless primary total hip arthroplasty (THA). The reported incidence ranges from 1.9% to 40.4%. Loosening is the most common cause of pain in most THA patients. The main clinical symptom of a loose femoral component is thigh pain, and THA patients occasionally have severe pain. A thorough diagnostic evaluation is essential.
Typically, the pain is localized to the anterolateral aspect of the midthigh at the level of the stem tip. The cause of pain in patients with well-fixed implants remains controversial, but contributing factors include bone type, larger stem size, uncemented femoral components, straight femoral stem design, stem material composition, femoral component instability, and loosening.
After other causes (e.g., infection, stress fracture, spinal problems) have been ruled out, the most accepted hypothesis for the development of thigh pain in patients with well-fixed, adequately aligned, and correctly sized uncemented THAs is that microfactures cause abnormal thigh bone stresses at the tip of the femoral component. These stresses probably result from a mismatch in the flexural rigidity (i.e., resistance to bending) between the patient’s bone–stem construct and the bare bone. The flexural rigidity of a stem is related to stem morphometry and material composition, and both factors have been postulated as the primary cause of thigh pain. Flexural rigidity (EI) is determined by the elastic moduli (E) times the area moment of inertia (I).
The differences in currently used materials and fixation surfaces do not appear to affect outcomes as much as the differences in geometric design. Thigh pain has been observed more frequently with anatomically shaped designs and cylindrical, diaphyseal-filling stems ( Fig. 70.1 ). However, no uncemented THA design is completely free of it, and enigmatic thigh pain continues to be a complication after apparently successful cementless THAs. In most cases, the pain is mild and tolerable, and nonoperative treatment is successful. In some cases, however, the pain is refractory and disabling, and surgical intervention may be required.
Indications and Contraindications
Thigh pain in the setting of a well-fixed, adequately aligned THA should be thoroughly evaluated before proceeding with treatment. All possible causes of thigh pain must be investigated systematically. A detailed history and careful physical examination, which usually provide the most valuable information, should be followed by laboratory and radiographic studies. The diagnosis of idiopathic thigh pain can be made only after the clinical, radiographic, and laboratory evaluations confirm that the prosthesis is well fixed and correctly positioned and that all other potential sources of pain have been excluded. In some cases, a bone scan may show intense uptake at the tip of the device with a normal uptake everywhere else.
After all other causes of thigh pain have been ruled out; initial treatment should always be nonoperative. These measures should be continued for at least 18 to 24 months before considering surgical intervention. Activity modification, the use of ambulatory assistive devices to limit weight bearing on the affected leg, and antiinflammatory and analgesic medications must be used. Ineffective nonoperative measures may require operative treatment.
Surgical treatment includes revision of the femoral component and involves significant morbidity. Revision of the femoral component in managing idiopathic thigh pain remains controversial. Cortical strut grafting with cerclage wiring has been used with excellent results in revision THA to supplement host bone after aseptic loosening of the femoral component. However, grafting a loose femoral component may not resolve the problem. If the implant remains loose, the solution is to achieve stable fixation through revision of the femoral component to a different model or a cemented stem. We favor cortical strut grafting in patients with refractory thigh pain with an aseptic, well-fixed prosthesis after unsuccessful judicious nonoperative treatment, particularly in very old or medically complicated patients.
The fresh-frozen diaphyseal femoral allografts should be prepared from selected cadaver donors under sterile conditions ( Fig. 70.2 ). The allografts are not subjected to treatment with any chemical agents and are prepared using a slow freeze-drying cycle. This method allows preservation of most of the osteogenic factors present in cadaveric bone. Morselized allograft bone may be used around the periphery of the cortical graft to increase bony contact and accelerate integration of the graft ( Fig. 70.3 ).
A Midas Rex diamond wheel cutting tool (Medtronic, Fort Worth, Tex.) may be required to sculpt the diaphyseal allograft strut to make it conform to the native femur in certain patients. Fixation of the allograft strut can be obtained with Luque wire cerclage (Zimmer, Warsaw, Ind.) or various types of cables.
Anatomy and Approaches
The hip is exposed with an extensile lateral approach to the femoral shaft. There is no internervous or intermuscular plane because the dissection splits the vastus lateralis muscle. This approach can be extended proximally or distally to expose almost the whole femur. Numerous perforating branches of the profunda femoris artery may be encountered during the approach. If damaged, these vessels must be ligated or coagulated.
Examination and Imaging
The physical examination should include a complete neurovascular assessment of the lower extremity to exclude spinal pathology. Passive and active ranges of motion can be used to assess stability. The pain can usually be isolated in the anterolateral thigh at the level of the stem tip.
Radiography is the first imaging procedure used in the evaluation of thigh pain, which should include plain radiographs of the pelvis, hip, and femur. They should be compared with previous radiographs because pathologic signs may be subtle and progress slowly. Implant fixation is assessed to exclude loosening. Kinov and colleagues found a correlation between radiologic changes and thigh pain, suggesting implant micromotion and migration in some hips. Reliable criteria for loosening of cementless implants are implant subsidence or migration with or without radiolucency around the entire porous-coated portion of the stem. Reliable criteria for osteointegration are the absence of reactive lines around the porous surface and endosteal spot welds of trabecular bone from the host to the prosthesis. Less reliable criteria include calcar atrophy as a result of stress shielding and the absence of a pedestal, which indicates a stable stem tip. The presence or absence of radionuclide uptake alone in imaging procedures is of no clinical value in diagnosing infection or loosening ( Fig. 70.4 ). In confusing cases, a bone scan could be obtained with collimation of the hip.