Background

Pseudotumours have been associated with metal-on-metal (MoM) hip replacements. We define it as a solid mass which may have cystic components that is neither neoplastic nor infectious in aetiology. The cause of a pseudotumour is not fully understood but could be due to excessive wear, metal hypersensitivity or due to an as-yet unknown cause.

Introduction: Metal on metal hip resurfacing arthroplasty-induced pseudotumours are a serious complication, which occur in 1.8% of patients who undergo this procedure in our institution. The aim of this study was to measure the 3D in vivo wear on the surface of resurfacing components revised for pseudotumour, compared to a control group.

Method: Thirty-six hip resurfacing implants were divided into two groups; 18 patients with a clinical and histopathological diagnosis of pseudotumour and 18 controls (revised for femoral neck fracture and infection). Three dimensional contactless metrology (Redlux^™ Ltd) was used to scan the surface of the femoral and acetabular components, to a resolution of 20 nanometers. The location, depth and area of the wear scar were determined for each component. A separate blinded analysis to determine the presence of absence of impingement was performed by one of the authors.

Results: The volumetric wear rate for femoral component of the pseudotumour group was 3.29 mm3/yr (SD5.7) and 0.79 mm3/yr (SD1.2) for the control group (p=0.005). In the pseudotumour group, the volumetric wear rate of the acetabular component was 2.5 mm3/yr (SD6.9) compared to 0.36 mm3/yr (SD0.80) for the control group (p=0.008). Edge-wear was detected in 89% of acetabular components in the pseudotumour group and 21% of those in the control group (p=0.01). Anterior or posterior edge-wear, consistent with impingement was present on the femoral components of 73% of patients in the pseudotumour group and 22% in the control group (p=0.01).

Discussion: This work demonstrates that implants revised for pseudotumour have significantly higher volumetric wear rates than controls. They also have a significantly higher incidence of edge-wear than controls. We suggest that a significant proportion of pseudotumours are associated with high concentrations of metal wear debris; however a minority may result from a hypersensitivity reaction to metal ions.

Introduction: Metal on metal hip resurfacing arthroplasty-induced pseudotumours are a serious complication, which occur in 4% of patients who undergo this procedure. The aim of this study was to measure the 3D in vivo wear on the surface of resurfacing components revised for pseudotumour, compared to a control group.

Method: Thirty-nine hip resurfacing implants were examined; these were sourced from our institutions prosthesis retrieval bank. They were divided into two groups; 22 patients with a clinical and histopathological diagnosis of pseudotumour and 17 controls. Patient demographics and time to revision were known. Three dimensional contactless metrology (Redlux™ Ltd) was used to scan the surface of the femoral and acetabular components, to a resolution of 20 nanometers. The location, depth and area of the wear scar was determined for each component. Volumetric wear was determined, along with the presence of absence of edge-loading. A separate blinded analysis to determine the presence of absence of impingement was performed by one of the authors. ANOVA was used to test for differences in wear and Fishers Exact test was used to compare the incidence of edge-loading between the groups.

Results: The volumetric wear rate for femoral component of the pseudotumour group was 4.7mm3/yr (SD3.5) and 1.7 mm3/yr (SD1.5) for the control group (p=0.03). In the pseudotumour group, the volumetric wear rate of the acetabular component was 3.5 mm3/yr (SD3.6) compared to 0.02 mm3/yr (SD0.07) for the control group (p=0.01). Edge-loading was detected in 74% of acetabular components in the pseudotumour group and 22% of those in the control group (p=0.01). Anterior or posterior edge-loading, consistent with impingement was present on the femoral components of 73% of patients in the pseudotumour group and 22% in the control group (p=0.01).

Discussion: This work demonstrates that implants revised for pseudotumour have significantly higher volumetric wear rates than controls. They also have a significantly higher incidence of edge-loading and impingement than controls. Edge-loading significantly increases wear. We suggest that pseudotumours are caused by high concentrations of metal wear debris, which have been shown to have a toxic effect on osteocytes and macrophages. This is the one of the first studies to demonstrate a clear link between pseudotumours and increased bearing surface wear. It is also the first to demonstrate that edge-loading, due to impingement, occurs in a significant number of patients who develop this condition. Improved implantation techniques and resurfacing designs may help avoid this serious complication of hip resurfacing.

Ion levels in the serum and urine of patients with metal-on-metal hip resurfacing implants can provide a means to monitor bearing wear. This presentation will discuss the current results, now out to 5 years for the Conserve Plus resurfacing. In particular, the effect of bilateral implantation on ion levels was examined

Forty-eight patients were studied. Forty-three of these cases were initially implanted with a unilateral resurfacing. Nine of these cases subsequently were implanted with a resurfacing implant on the contra-lateral side 4 to 48 months following the first implantation (staged implantations). Five cases had bilateral resurfacings done simultaneously. All surgeries were done in one institution by a single surgeon. Serum and urine samples were collected pre-operatively, and at 4 months, 12 months and annually thereafter. The samples were analysed for cobalt and chromium using atomic absorption spectrometry with a detection limit of 0.3 to 0.03ng/ml respectively. The data were compared between the groups and also correlated with UCLA activity scores, cup angle, BMI and component size.

All patients showed a rise in ions following implantation. The simultaneous bilateral levels were higher at all time periods compared with the staged bilaterals monitored at the same time point for the second hip, for example cobalt serum at 12 month uni = 2.24, simultaneous bilat = 2.53, staged bilat = 2.05ng/ml, and at 4 years uni = 1.20, simultaneous bilat = 2.93, staged bilat = 2.27ng/ml. There was no correlation between ion levels and UCLA activity score, gender, component size or cup angle (but only 4 hips had cups > 55 degrees).

Bilateral metal-on-metal hip resurfacings performed simultaneously resulted in higher levels of metal ions, particularly chromium, compared to staged implantations monitored at the same time periods. With the exception of a small number of outliers, the levels in this group of hip resurfacings were within the range of metal levels reported for other metal-on-metal total hips.

Femoral neck fracture is a common short-term hip resurfacing failure mode, but later term fractures are starting to be reported. The fracture pattern may indicate whether etiology is primarily mechanical or biological¹. This study evaluated fracture patterns in conjunction with histology to determine etiology in a varied group of hip resurfacings.

Central 3mm thick coronal slices were cut from each of 50 cemented and 2 cementless fractured femoral components (27 males, 25 females). Fracture patterns were grouped as: “edge to edge”, “inside head”, “outside” and “edge to outside”¹. Sections were decalcified and processed for routine histology to examine viability and remodelling. Bone viability was judged on the presence of osteocyte nuclei. Components were judged to be unseated if the cement mantle was more than twice the manufacturers recommended thickness. Histological and clinical data were correlated with fracture pattern.

Overall average time to fracture was 6 months (1–85 months). There were 25 “edge to edge”, 12 “inside head”, 4 “outside” and 11 “edge to outside” fractures, which occurred after a median of 2.0, 13, 1.5, and 2.0 months respectively. The majority of the heads were viable, and the fractures occurred through a region of healing bone involving one or both edges. Fifteen heads with a substantial proximal avascular segment fractured at the interface between necrotic and viable bone, typically inside the component. Eleven implants (21%) were considered unseated. All 4 “outside” fractures were found to be unseated. All “inside head” fractures were seated, but 83% (10/12) of them were found to be avascular. The latest failure (85 months) occurred in association with wear-induced osteolysis. Both cementless components fractured early with an “edge to outside” pattern and were found to be substantially avascular.

Avascular heads failed from one month to four years, usually inside the component. Viable heads tended to fracture early through an area of healing bone at or below the rim. Most fractures were technical failure-sand might be avoided with better patient selection and surgical technique.

Introduction: Management of Ficat stage III and IV hip osteonecrosis remains a formidable challenge in regards to long term care. We report a case of a hemiresurfacing arthroplasty lasting 23 years in a patient who received the implant for osteonecrosis associated with corticosteroid use following kidney transplantation. In 1981, a moderately obese, 27-year-old man presented with bilateral osteonecrotic collapse of the femoral heads secondary to heavy immunosuppressive corticosteroid therapy associated with a kidney transplant. The patient had suffered a loss of both kidneys after a bout of severe nephritis that resulted in replacement with a cadaver kidney in 1979. A cemented THARIES (total hip articular replacement with internal eccentric shells) metal-on-polyethylene resurfacing (Zimmer, Warsaw, Indiana) was implanted in the right hip in 1981. At 3 years post-operatively, the patient complained of acute, exacerbated pain in his right hip. The THARIES components were removed for acetabular and femoral loosening and replaced with a total hip replacement.

Surgery: The acetabular cartilage of the other hip was rated intraoperatively as Grade III (no or minimal acetabular cartilage involvement), and was deemed suitable for hemiresurfacing. A 50 millimeter custom cemented titanium shell (Zimmer, Warsaw, Indiana) was implanted using a lateral incision and a trans-trochanteric approach. The patient continued to be assessed by the surgeon on a regular basis, and returned to an active lifestyle while his kidney function continued to be regulated with corticosteroids and imoran. In 1989, eight years following hemiresurfacing, the left hip radiographs showed a reduced joint space, with further new bone in the acetabular fossa, and the patient continued to do well. UCLA hip scores were 9, 9, 10, and 7 for pain, walking, function and activity, respectively compared with 6, 6, 4, and 4 preoperatively. Radiographs taken at 18 years post-operatively showed further narrowing of the joint space, but the patient continued to be asymptomatic. At the 22-year clinic visit, the patient, now 50 years old, complained of slight groin pain, and some minor limitation in his activities, but was still able to walk without any method of support, and able to participate in recreational exercise including swimming, baseball, and weight lifting. The resurfacing hip was revised to a total hip at 23 years post-op and the specimen was submitted for implant retrieval analysis. This involved sectioning the component into three, 3-millimeter thick coronal slices, which were decalcified and routinely embedded in paraffin.

Results: Hematoxylin and Eosin stained sections showed that the bone within the head was osteopenic but viable with areas of healed old necrotic segments of trabeculae which were surrounded by appositional new bone with some focal areas of recently formed woven bone. A fibrous membrane ranging from a few microns to 1.8 millimeters in thickness was present along most of the cement interface and this contained scattered particle-filled macrophages. There were occasional osteoclastic resorption fronts of bone against this membrane, but osteoblasts were also occasionally seen lining the non-membrane surface. The resurfaced head and neck showed remarkable preservation of bone stock. Although there was minimal cement penetration into the bone, either because of lack of initial penetration or from fragmentation of the cement over the years, the component was functionally well fixed. The bone was viable and there were minimal effects of the small amount of titanium metal debris.

Discussion: Studies report osteonecrosis of the femoral head developing in approximately 11% of hips and 20% of patients receiving organ transplants and for young patients conservative methods need to be pursued. While the best choice of treatment for osteonecrosis is not universally agreed upon, the options are limited once collapse of the femoral head has occurred. Treatment for these patients should be based on the progression of the disease, the age of the patient, and the patient’s long-term needs. This patient had a hemiresurfacing and a metal-on-polyethylene resurfacing; the latter succumbed to polyethylene induced osteolysis, but the hemiresurfacing provided good clinical function in a young, normally active patient for 23 years. While it is recognized that hemiresurfacing is not suitable for every patient with osteonecrosis, it remains a treatment option for some patients.

We appraised whether deformity of the inferior limbs, routinely treated with external fixation (EF), can be corrected when synthesis with locked intramedullary nails is associated with the synthesis and what the indications are.

In all, 24 patients with a deformity of the inferior limbs treated between 1997 and 2003 were included in the study and divided into two groups: (1) patients with external fixation, average 23 years, deformity axial 20° (9–28°); and (2) patients with osteotomy and interlocked nailing. average 35 years, deformity axial 16° (10–25°). The indications for treatment with interlocked nail were set according to the following criteria: (a) possibility to correct the deformity with only restoration of the anatomical axis without necessity of lengthening; (b) previous use of EF; (c) EF refused by the patient, and (d) physeal closure.

In both groups complete correction of the deformity was achieved. In the group of patients treated with EF the time of consolidation was on average 5.5 months (range 4–8 months). In this group the time of consolidation proportionally increased to time required to effect a bone lengthening.

In the group of patients treated with osteotomy and nailing the times of consolidation were different with respect to age, to the side and the type of osteotomy and to the type of deformity. The time of consolidation was 7 months (range 3–12 months). The most rapid consolidation corresponds to the congenital deformities treated with oblique osteotomy.

Correction of deformities by osteotomy and interlocked nail introduces the advantage of not limiting joints and immediate correction of the angular and rotatory deformity. The indication for this technique is that there is no residual hypometry. In this case the treatment of choice is corticotomy and external fixation.