Comparison of Bone Removed During Total Hip Arthroplasty With a Resurfacing or Conventional Femoral Component : A Cadaveric Study

We sought to examine the amount of bone removed during total hip arthroplasty with a resurfacing femoral component, compared to with a conventional, stemmed femoral component, by using 6 male and 4 female cadaveric pelves with attached bilateral proximal femora. Using randomized assignment and order, a total hip arthroplasty with a resurfacing femoral implant was performed on one side, and total hip arthroplasty with a cementless, stemmed femoral implant was performed on the contralateral side. The relationship between native femoral head diameter and the implanted acetabular socket was on average within 2 mm for both procedures. No significant difference was observed in the amount of acetabular bone removed (9.8 g for hip resurfacing vs 8.8 g). However, a resurfacing component resulted in approximated 3 × less bone removal from the femur (25.8 g vs 75.1 g). This study shows that the preservation of femoral bone with a resurfacing femoral component does not result in an increased removal of acetabular bone when compared to the use of a conventional, stemmed femoral component.     

Removal of acetabular bone in resurfacing arthroplasty of the hip: a comparison with hybrid total hip arthroplasty

Resurfacing arthroplasty of the hip is being performed more frequently in the United Kingdom. The majority of these patients are younger than 55 years of age, and in this group the key benefits include conservation of femoral bone stock and the potential reduction in the rate of dislocation afforded by the larger resurfacing head. Early aseptic loosening is well recognised in patients younger than 55 years of age, and proponents of resurfacing believe that the improved wear characteristics of the metal-on-metal bearing may improve the long-term survival of this implant. There has been some concern, however, that resurfacing may not be conservative of acetabular bone.We compared a series of 33 consecutive patients who had a hybrid total hip arthroplasty with an uncemented acetabular component and a cemented femoral implant, with 35 patients undergoing a Birmingham hip resurfacing arthroplasty. We compared the diameter of the implanted acetabulum in both groups and, because they were not directly comparable, we corrected for patient size by measuring the diameter of the contralateral femoral head. The data were analysed using unpaired t-tests and analysis of covariance.There was a significantly larger acetabulum in the Birmingham arthroplasty group (mean diameter 56.6 mm vs 52.0 mm; p < 0.001). However, this group had a significantly larger femoral head diameter on the contralateral side (p = 0.03). Analysis of covariance revealed a significant difference between the mean size of the acetabular component implanted in the two operations. The greatest difference in the size of acetabulum was in those patients with a larger diameter of the femoral head. This study shows that more bone is removed from the acetabulum in hip resurfacing than during hybrid total hip arthroplasty, a difference which is most marked in larger patients.     

Femoral component neck fracture after failed hip resurfacing arthroplasty

Failure on the femoral side after third-generation metal-on-metal hip resurfacing arthroplasty is suggested to be easily treated with conversion to conventional total hip arthroplasty. Clinical results of conversion for failed hip resurfacing arthroplasty with the use of primary femoral implants confirmed this for a short-term follow-up. We present a case of the occurrence of a stemmed femoral implant neck fracture in a patient who was earlier treated for a failed hip resurfacing. We advise to consider acetabular revision in case of (suspected) acetabular metal damage and to use a stem component with a relative large neck diameter.     

Limited range of motion of hip resurfacing arthroplasty due to unfavorable ratio of prosthetic head size and femoral neck diameter

Background and purpose?Hip resurfacing arthroplasty is being used more and more frequently. The small ratio in size between the resurfaced femoral head and the relatively thick femoral neck raises the question of whether the range of motion is sufficient, particularly with regard to the high mobility required by younger patients. We analyzed motion in a CAD model.

Methods?Three-dimensional CAD models of the natural hip were created from CT scans and 8 designs of hip resurfacing prostheses (head diameter between 42 mm and 54 mm combined with a hemispherical cup) were implanted in a virtual sense. We simulated 3 different leg positions and the range of motion was evaluated, considering five different implant positions.

Results?The range of motion of the hip resurfacing designs analyzed was far below the range of motion of stemmed total hip prostheses. None of the resurfacing prostheses provided flexion movements of 90° without impingement. The average range of motion of hip resurfacing arthroplasty was 31–48° below the range of motion of a stemmed total hip replacement with 32-mm head diameter.

Interpretation?The range of motion of the hip resurfacing designs examined was substantially less than that of a conventional total hip prosthesis. Since impingement of the femoral neck on the acetabular component increases the risk of neck fractures, of dislocation and of subsequent implant loosening, the design and position of the implant should be considered before using hip resurfacing arthroplasty as a standard treatment for younger patients.     

Biomechanische Aspekte zur Implantatverankerung und Kinematik von Oberflächenersatzhüftendoprothesen

Hip resurfacing is undergoing a resurgence in orthopaedic surgery with an increasing number of implantations. The objective of this article is to present the biomechanical basics of implant anchorage as well as the kinematics of hip resurfacing implants.Today, fixation of the femoral component onto the prepared femoral head is mainly done using bone cement. Depending on the implant design, the bone structures beneath the femoral component can be exposed to stress shielding, followed by degradation of the bone density and subsequent initiation of implant loosening. However, the trabecular bone has the ability to adapt itself to the fixation peg, to additional cement pegs, and to the elastic properties of the femoral component as well.The acetabular component is mainly inserted into the bone stock without using cement. Provided that large prosthetic heads will be applied, thin-walled acetabular cups are crucial for bone-saving preparation of the acetabular bone stock. Nearly all hip resurfacing systems are currently based on metal-on-metal wear-bearing couples. The acetabular components are mainly designed as monoblock implants, which can make subsequent revision difficult.Kinematic analyses show a significantly lower range of motion of hip resurfacing implants compared with modern standard (stemmed) total hip replacement systems. This difference originates from the small ratio of the resurfaced femoral head diameter and the relatively thick neck of the femur. Impingement of the femur neck onto the rim of the acetabular component can result in subluxation, deformation of the bearing surfaces, femoral neck fracture, and impairment of the bony anchorage of the hip resurfacing implants.     

Total resurfacing for osteonecrosis of the hip

With the resurgence of metal-on-metal bearings, there is renewed interest in total hip resurfacing. A cementless acetabular component used for resurfacing with a wall thickness of fewer than 5 mm is comparable in size to acetabular components used for total hip replacement. The fixation of a porous-ingrowth acetabular component used for resurfacing has been shown to be reliable and durable. There are few clinical reports of total hip resurfacing that stratify results by diagnosis. However, available evidence indicates that the pain relief, function, and activity after total hip resurfacing for osteonecrosis are superior to the results reported for hemiresurfacing and similar to the results of total hip replacement. Femoral-side failure is the main issue occurring with total resurfacing for osteonecrosis, and the femoral side failure rate is higher than that of hemiresurfacing. There are no simple guidelines for the extent of femoral head necrosis that are compatible with successful resurfacing. Refined patient selection and surgical technique can improve the outcomes and durability of total hip resurfacing for osteonecrosis.     

THARIES resurfacing arthroplasty. Evolution and long-term results

The unsatisfactory results of total hip arthroplasty in the young patient led to the development of the concept of hip resurfacing. Total hip articular replacement by internal eccentric shells (THARIES) resurfacing was introduced in 1975, with the primary goal of bone stock preservation and the hope of increased durability in the young patient. Major changes in design and technique include thicker and more uniform acrylic layers, metal-backed flanged acetabular component, and reduction in femoral size for preservation of acetabular bone stock. Of the 584 hips (average patient age, 48 years) with one- to ten-year follow-up study, there have been 72 failures (revision rate, 12.3%) with 66 cases of loosening (nearly all beginning in or limited to the acetabular side), two neck fractures, and four sepses. Survivorship analysis revealed that the single most important factor related to prosthesis failure is age followed by diagnosis and experience of the surgeon. Osteoarthritis and rheumatoid arthritis were favorable categories with congenital dysplastic hip (CDH), osteonecrosis, and previous failed resurfacing being unfavorable categories. Experience has taught the importance in preserving acetabular bone stock, providing bone graft for socket coverage in severe dysplasia, and removing dead bone in osteonecrosis. While resurfacing did not solve the problems of the young patient, even those patients who failed often gained time for application of the newer techniques and materials. The femoral component infrequently failed. The head remained vascular. This leads the authors to conclude that the surface arthroplasty concept is a viable alternative to total hip arthroplasty and seems to be ideal for the application of porous technology.     

Metal-on-metal surface replacement: a triumph of hope over reason: affirms

Metal-on-metal hip resurfacing offers some potential for total hip arthroplasty (THA) in the young patient. However, short- and intermediate-term results of the currently available implants have failed to demonstrate advantage over conventional THA. The risks of femoral neck fracture or avascular necrosis have been disappointing early limitations of the procedure. The Australian Joint Registry reports a 5-year revision rate of all hip resurfacings of 3.8%, compared with conventional THAs at 2.8%, and a 9-year cumulative revision rate of 7.2% for hip resurfacings. Recent reports of femoral neck erosion and pseudotumors associated with resurfacing have raised concern about the survivorship of the procedure in some patients. Recently, the British Medicines and Healthcare Product Regulatory Agency issued an alert over adverse reactions associated with metal-on-metal THAs, with particular concern expressed about hip resurfacings. Acetabular bone stock may not be conserved when large-diameter femoral head components are used, depending on the surgical technique and implant design. In hip resurfacing, the minimum diameter femoral component avoids notching of the femoral neck; thus, larger diameter acetabular components may be necessary to accommodate the femoral component. Hip resurfacing is contraindicated in cases of avascular necrosis of the femoral head, especially with cysts >1 cm in diameter, with severe slipped capital femoral epiphysis, and in some posttraumatic arthroses; furthermore, the biomechanics of the resurfaced hip appear to be less reliably restored than with conventional THA. The hypothesis that resurfacing is a more conservative procedure than conventional THA remains unproven at this time. Given the documented intermediate failure rates of resurfacing, metal-on-polyethylene is the more successful implant choice.     

Birmingham hip resurfacing: is acetabular bone conserved?

Hip resurfacing is a bone-conserving procedure with respect to proximal femoral resection, but there is debate in the literature as to whether the same holds true for the acetabulum. We have investigated whether the Birmingham hip resurfacing conserves acetabular bone. Between 1998 and 2005, 500 Birmingham hip resurfacings were performed by two surgeons. Between 1996 and 2005 they undertook 700 primary hip replacements, with an uncemented acetabular component. These patients formed the clinical material to compare acetabular component sizing. The Birmingham hip resurfacing group comprised 350 hips in men and 150 hips in women. The uncemented total hip replacement group comprised 236 hips in men and 464 hips in women. Age- and gender-matched analysis of a cohort of patients for the sizes of the acetabular components required for the two types of replacement was also undertaken. Additionally, an analysis of the sizes of the components used by each surgeon was performed. For age-matched women, the mean outside diameter of the Birmingham hip resurfacing acetabular components was 2.03 mm less than that of the acetabular components in the uncemented total hip replacements (p < 0.0001). In similarly matched men there was no significant difference (p = 0.77). A significant difference was also found between the size of acetabular components used by the two surgeons for Birmingham hip resurfacing for both men (p = 0.0015) and women (p = 0.001). In contrast, no significant difference was found between the size of acetabular components used by the two surgeons for uncemented total hip replacement in either men or women (p = 0.06 and p = 0.14, respectively). This suggests that variations in acetabular preparation also influence acetabular component size in hip resurfacing.     

Painful impingement of the hip joint after total hip resurfacing: a report of two cases

Many patients undergoing total hip resurfacing arthroplasty present with reduced anterior femoral neck concavity as a part of the degenerative process. Painful hip impingement may develop or persist after hip resurfacing when the retained femoral neck abuts against the metallic acetabular component or the anterior acetabular bony wall. We report on two cases of painful postoperative hip impingement after hip resurfacing, in one of whom anterior neck-contouring osteoplasty restored pain-free range of motion (ROM). To restore natural hip ROM, surgeons performing hip total hip resurfacing arthroplasty should aim to reproduce the normal femoral head-neck offset ratio. Femoral head-neck offset restoration can be achieved by proper femoral component positioning (especially optimal translation), by femoral neck osteoplasty or by increasing femoral component head size appropriately.     

Changes in bone mineral density of the acetabulum, femoral neck and femoral shaft, after hip resurfacing and total hip replacement: two-year results from a randomised study

It is accepted that resurfacing hip replacement preserves the bone mineral density (BMD) of the femur better than total hip replacement (THR). However, no studies have investigated any possible difference on the acetabular side. Between April 2007 and March 2009, 39 patients were randomised into two groups to receive either a resurfacing or a THR and were followed for two years. One patient's resurfacing subsequently failed, leaving 19 patients in each group. Resurfaced replacements maintained proximal femoral BMD and, compared with THR, had an increased bone mineral density in Gruen zones 2, 3, 6, and particularly zone 7, with a gain of 7.5% (95% confidence interval (CI) 2.6 to 12.5) compared with a loss of 14.6% (95% CI 7.6 to 21.6). Resurfacing replacements maintained the BMD of the medial femoral neck and increased that in the lateral zones between 12.8% (95% CI 4.3 to 21.4) and 25.9% (95% CI 7.1 to 44.6). On the acetabular side, BMD was similar in every zone at each point in time. The mean BMD of all acetabular regions in the resurfaced group was reduced to 96.2% (95% CI 93.7 to 98.6) and for the total hip replacement group to 97.6% (95% CI 93.7 to 101.5) (p = 0.4863). A mean total loss of 3.7% (95% CI 1.0 to 6.5) and 4.9% (95% CI 0.8 to 9.0) of BMD was found above the acetabular component in W1 and 10.2% (95% CI 0.9 to 19.4) and 9.1% (95% CI 3.8 to 14.4) medial to the implant in W2 for resurfaced replacements and THRs respectively. Resurfacing resulted in a mean loss of BMD of 6.7% (95% CI 0.7 to 12.7) in W3 but the BMD inferior to the acetabular component was maintained in both groups. These results suggest that the ability of a resurfacing hip replacement to preserve BMD only applies to the femoral side.     

Thermal effects of cement mantle thickness for hip resurfacing

Hybrid hip resurfacing arthroplasty with uncemented acetabular and cemented femoral fixation is increasingly becoming popular as an alternative to total hip arthroplasty. There is concern about femoral neck fractures, and long-term survival has not yet been demonstrated. Thermal necrosis may be an important factor for neck fracture and will affect the viability of the femoral bone. This cadaveric study investigated the thermal effect of thick (1.5 mm, n = 3) and thin (0.5 mm, n = 3) cement mantles; 5 thermocouples were used to record temperature at the femoral bone/cement interface during hip resurfacing arthroplasty. The highest recorded temperatures were significantly higher when a thick cement mantle is used (45.4 degrees C), compared to a thin cement mantle (32.7 degrees C). To reduce the potential for thermal necrosis, the thin cement mantle technique is recommended.     

Surface replacement: A viable option for the right patient

Surface replacement of the hip was established in the 1970s as a bone preserving alternative to total hip replacement. However, problems with femoral neck fracture, osteolysis, and component loosening led to early failures and an abandonment of the procedure. The modern hip resurfacing has improved upon past results with new implant designs and materials. The benefits include the preservation of bone, lower dislocation rate, and more physiologic bone loading, factors which may lead to an ability for a higher activity level. National joint registry results find that a certain group of patients has greater survivorship with resurfacing than with total hip replacement. Therefore, we believe that surface replacement arthroplasty is a viable alternative in this subgroup of patients.     

Resurfacing arthroplasty for hip dysplasia: a prospective randomised study

In this prospective study a total of 80 consecutive Chinese patients with Crowe type I or II developmental dysplasia of the hip were randomly assigned for hip resurfacing arthroplasty (HRA) or total hip replacement (THR). Three patients assigned to HRA were converted to THR, and three HRA patients and two THR patients were lost to follow-up. This left a total of 34 patients (37 hips) who underwent HRA and 38 (39 hips) who underwent THR. The mean follow-up was 59.4 months (52 to 70) in the HRA group and 60.6 months (50 to 72) in the THR group. There was no failure of the prosthesis in either group. Flexion of the hip was significantly better after HRA, but there was no difference in the mean post-operative Harris hip scores between the groups. The mean size of the acetabular component in the HRA group was significantly larger than in the THR group (49.5 mm vs 46.1 mm, p = 0.001). There was no difference in the mean abduction angle of the acetabular component between the two groups. Although the patients in this series had risk factors for failure after HRA, such as low body weight, small femoral heads and dysplasia, the clinical results of resurfacing in those with Crowe type I or II hip dysplasia were satisfactory. Patients in the HRA group had a better range of movement, although neck-cup impingement was observed. However, more acetabular bone was sacrificed in HRA patients, and it is unclear whether this will have an adverse effect in the long term.     

Birmingham Mid-Head Resection hip arthroplasty in a young man with gigantism

The Birmingham Mid-Head Resection (Smith & Nephew Ltd, Warwick, United Kingdom) arthroplasty is a new bone-conserving procedure that, like hip resurfacing, is used in younger, active patients. We present the case of a young man with Sotos syndrome (cerebral gigantism) with associated extraordinary stature (height, 2.16 m; weight, 157 kg) who underwent Birmingham Mid-Head Resection arthroplasty. The large stature of this patient required a custom manufactured prosthesis (a femoral head 68 mm in diameter with an acetabular cup 76 mm in diameter). We believe this to be the largest metal-on-metal resurfacing articulation and hip arthroplasty reported to date.     

Resurfacing arthroplasty in osteonecrosis of the hip

Approximately 10% of the total hip replacements performed in the United States are for osteonecrosis. Resurfacing arthroplasty has received renewed interest, with several new designs being implanted worldwide. Proponents of resurfacing arthroplasty describe the advantages of bone conservation, preservation of joint mechanics, more physiologic loading of the bone, lower incidence of perioperative complications, and easier conversion to a secondary procedure if failure occurs. Critics recite previous poor results including high failure rates with femoral and acetabular loosening, osteonecrosis of the femoral head, femoral neck fracture, and loss of acetabular bone stock making the secondary revision procedure more difficult. This article attempts to clarify the advantages and disadvantages of the resurfacing concept as it applies to the treatment of osteonecrosis of the femoral head.     

全髋表面置换术和传统全髋置换术术后生物力学结构恢复的比较研究

目的比较全髋表面置换术（HRA）和传统全髋置换术（THA）后的下肢长度、股骨偏心距和髋臼偏心距等恢复的情况,确定HRA是否更有利于恢复髋关节的生物力学结构。方法选择单侧施行HRA或THA的股骨头坏死患者各20例（对侧髋关节均健康）。术前、术后摄等比例X线正位片,测量患者双髋的下肢长度、股骨偏心距和髋臼偏心距指标,与对侧髋比较患髋术后的改变。将HRA和THA术后改变的结果进行比较。结果 HRA组各项生物力学参数差值恢复明显比THA组更接近正常。术后HRA组和THA组患侧和健侧比较下肢长度差分别为（-2.1±1.1）mm和（3.5±2.6）mm（P〈0.05）,HRA组为轻度短缩而THA组为轻度延长;股骨偏心距差分别为（-1.8±1.4）mm和（3.1±1.9）mm（P〈0.05）,HRA组股骨偏心距降低,而THA组偏心距增加;髋臼偏心距分别为（1.6±1.8）mm和（-2.3±2.1）mm（P〈0.05）,THA组髋臼偏心距增加较大。结论 HRA可以更加精确地恢复股骨近端解剖结构,大直径股骨头假体增加了髋关节的稳定性,避免了THA容易导致的下肢延长和偏心距增加,有利于改善软组织张力。但HRA还是有轻度缩短下肢长度和股骨偏心距的倾向。     

Bone density adjacent to press-fit acetabular components. A prospective analysis with quantitative computed tomography

BACKGROUND: The status of periprosthetic bone stock is an important concern when revision total hip arthroplasty is undertaken. Remodeling of periprosthetic femoral bone after total hip arthroplasty has been studied extensively, and the phenomenon of femoral stress-shielding has been well characterized. Finite element analysis and computer-simulated remodeling theory have predicted that retroacetabular bone-mineral density decreases after total hip arthroplasty; however, remodeling of periprosthetic pelvic bone in this setting has yet to be well defined. This study was conducted to evaluate the short-term natural history of periacetabular bone-mineral density following primary total hip arthroplasty. METHODS: Periacetabular bone-mineral density was studied prospectively in a group of twenty-six patients who underwent primary hybrid total hip arthroplasty for the treatment of advanced osteoarthritis. Density within the central part of the ilium (directly cephalad to a press-fit acetabular component) was assessed with serial quantitative computed tomography. Baseline density was measured within the first five days following the total hip arthroplasty. Ipsilateral density measurements were repeated at an average of 1.28 years postoperatively. Density values at corresponding levels of the contralateral ilium were obtained at both time-points in all patients to serve as internal controls. RESULTS: Bone-mineral density decreased significantly (p< or =0.001) between the two time-points on the side of the operation. The mean absolute magnitude of the interval density reduction (75 mg/cc) was greatest immediately adjacent to the implant (p<0.001), but it was also significantly reduced (by 35 mg/cc) at a distance of 10 mm cephalad to the implant (p = 0.001). Relative declines in mean density ranged from 33% to 20% of the baseline values. No focal bone resorption (osteolysis) was detected at the time of this short-term follow-up study. With the numbers available, no significant interval alteration in bone-mineral density was found on the untreated (internal control) side (p> or =0.07). CONCLUSIONS: We suggest that the observed decline in bone-mineral density represents a remodeling response to an altered stress pattern within the pelvis that was induced by the presence of the acetabular implant. This finding corroborates the predictions of finite element analysis and computer-simulated remodeling theory. It remains to be seen whether this trend of atrophy of retroacetabular bone stock will continue with longer follow-up or will ultimately affect the long-term stability of press-fit acetabular components.     

Long term results of the Corin C-Fit uncemented total hip arthroplasty in young patients

Introduction  We conducted a prospective study to evaluate the long-term results after Corin C-Fit uncemented total hip arthroplasty in young patients with hydroxyapatite or porous coated components. Materials and methods  We prospectively followed 36 patients (38 hips) who had Corin C-Fit uncemented total hip arthroplasties by eight experienced consultant surgeons at two centres. The acetabular and femoral components were hydroxyapatite or porous coated. Results  The overall 10-year survival rate for the Corin C-Fit arthroplasty was 43%. The 10-year survivorship for the femoral implant was 56% and for the acetabular component 59%. Conclusion  The evidence presented in this study suggests that the Corin C-Fit uncemented total hip arthroplasty has one of the highest mid- and long-term failure rates for both femoral and acetabular components in the literature. We believe this implant should not be used and patients who have had this form of total hip arthroplasty should be kept under regular review.     

Assessment of Accuracy and Reliability in Preoperative Templating for Hip Resurfacing Arthroplasty

The current study investigated the accuracy and reliability of hip resurfacing component selection based on digital preoperative templating. Four surgeons made a template of preoperative radiographs on 2 occasions for acetabular and femoral components in 50 randomly selected hip resurfacing patients. Component selection reliability was variable among surgeons (κ = 0.16-0.73) and fair between surgeons (κ = 0.23-0.32). The average percentage of agreement for the acetabular component was 47% (range, 32%-64%) and for the femoral component was 54% (range, 38%-70%). Surgeons tended to underestimate implant size if the correct implant was not chosen (acetabular, 29%; femoral, 32%). Selection of an undersized femoral component may lead to femoral neck notching or varus implant alignment. This study emphasizes the need for intraoperative verification of preoperative templating results to ensure optimal implant selection in hip resurfacing.