Mid-Head Resection Research Articles

Does modularity of metal-on-metal hip implants increase cobalt: chromium ratio?

Blood metal ion levels are used in the surveillance of metal-on-metal (MoM) hip implants. Modular implants contain an extra source of metal debris that may affect the ratio of metal ions in the blood. This was a retrospective study of 503 patients with hip replacements made by a single manufacturer (Smith & Nephew, Warwick, UK) with the same bearing surface. There were 54 total hip arthroplasties, 35 Birmingham Mid-Head Resections and 414 hip resurfacings. Whole blood metal ion levels and their ratios were analysed to investigate the effect of a modular junction. The cobalt:chromium ratios were greater in the total hip arthroplasty group (mean 2.3:1) when compared to the resurfacings group (mean 1.3:1, p = <0.05) and Birmingham Mid-Head Resection group (mean 1.1:1, p = 0.11). This study demonstrated a trend for a higher cobalt:chromium ratio in patients with MoM total hip replacement that may be due to metal debris from the modular stem-head junction. Further work is required to correlate clinical data with retrieval analysis to confirm the effect of taper material loss on the cobalt:chromium ratio.

CORR Insights(®): frequent femoral neck osteolysis with Birmingham mid-head resection resurfacing arthroplasty in young patients.

Where Are We Now? Mid-head resection resurfacing arthroplasty is considered a viable hip-preserving procedure that allows bone preservation to patients with an abnormal femoral head morphology and/or poor bone quality. These bone issues are generally found in younger patients (typically younger than 55 years of age) with hip osteonecrosis. The mid-head resection resurfacing may offer an alternative to conventional hip arthroplasty implants. However, there are only a few small studies with short-term followup (mean, 2 years to 3.5 years) using this particular implant that have shown high survivorship rates of 97% or greater [1-3]. To the best of my knowledge, the study by Assad and colleagues presents the longest mean followup for these prostheses. The authors found an increased risk of osteolysis of the remaining femoral neck in these patients despite 100% survivorship at a mean 6-year followup (range, 3 years to 8 years). It appears that many of these hips (at least 16%) will ultimately fail due to osteolysis based on the findings of the present study. Patients who have not been followed closely should receive careful scrutiny. Where Do We Need to Go? Such a finding raises specific concerns about the safety of this hip-preserving operation. We must ensure that we maximize the survivorship of these prostheses, by following the correct indications. Assuming that these prostheses will continue being used, we must also identify risk factors that could potentially lead to failure. The authors did an exhaustive search for osteolysis or failure. Unfortunately, they were unable to identify any factors that would portend a poor result (having evaluated gender, age, height, preoperative Oxford Hip Scores, preoperative UCLA activity scores; size of implant head, cup, or stem; and radiographic parameters such as cup inclination, stem-shaft angle, or spot welding). Since this problem appears sporadic, but common, they no longer recommend using this device. Even though this is a small study (n = 47 patients), one cannot assume that a larger study would have been more useful to identify this prosthesis as a problem and more patients at risk might pose an undue risk for this larger population. However, larger retrospective series of patients may help identify risk factor that contribute to failure. Until more risk factors for increased osteolysis of these prostheses can be established, this alarming risk of osteolysis without symptoms necessitates a carefully constructed followup plan for all patients who have received these devices. Failure to do so may put these patients at risk. In fact, by the time their hips become symptomatic, these patients may have more severe osteolysis, making subsequent reconstructions more difficult and jeopardizing the functional results following reconstructions. How Do We Get There? Finding the specific risk factors of osteolysis will require several types of studies. If there are other centers with large patient cohorts, it would behoove them to analyze their data to determine who might be a “safe” population and who is at high risk and needs to be evaluated more frequently. Any retrospective study must be large in order to (1) appropriately analyze those patients with osteolysis and (2) determine if there are any patient- or surgery-related factors that may be associated with increased risk. This may require the collaboration of multiple high-volume institutions with surgeons who still perform these procedures, or analysis of a national registry where these procedures are being performed. All patients should be followed on a frequent basis with: (1) Histories and physicals, (2) metal ion analyses, and (3) multiple imaging modalities including MRI or ultrasound.

Frequent femoral neck osteolysis with Birmingham mid-head resection resurfacing arthroplasty in young patients.

Mid-head resection total hip resurfacing arthroplasty was promoted as an alternative to traditional total hip resurfacing for patients with poor femoral head bone quality or abnormal femoral head morphology, because those patients are at high risk of failure with traditional total hip resurfacing. It is a large-headed metal-on-metal device that uses a short, bone-conserving stem. Good performance of the implant has been reported at short-term followup, but no information on the implant performance in the mid- or long-term is available. In this study, we report (1) on the mid-term implant survivorship and hip scores in a single nondesigner surgeon series. Because of the occurrence of femoral neck osteolysis and pseudotumor in a subgroup of patients, we also investigated the following: (2) Were there any preoperative parameters that are associated with osteolysis? (3) Could we differentiate the osteolysis group from the others on the basis of implant component sizes, positions, and radiologic parameters? (4) Could we differentiate the osteolysis group from the others on the basis of metal ion levels? Between 2006 and 2011, one surgeon performed a total of 49 Birmingham Mid-head Resection total hip resurfacing arthroplasties in 47 patients. The general indications for this procedure were young patients who were considered suitable for hip resurfacing arthroplasty but had avascular necrosis, large cysts, or severe deformity of the femoral head. Clinical followup including Oxford Hip Score (OHS) and UCLA hip scores were available preoperatively and at a mean of 6 years (range, 3-8 years) on all patients (100%), radiographic followup on 45 of 47 (96%), MRIs on 18 (38%), and metal ion levels on 37 (79%). Mean age at surgery was 50 years. Spearman's correlation was used to test the association between femoral neck osteolysis and preoperative parameters, implant component sizes and positions, and blood metal ion levels. We found 100% survival. Patients' median OHS was 46 of 48 (range, 35-48) and UCLA 8 of 10 (range, 4-10). However, 16% of the hips (seven of 45) demonstrated osteolysis in the femoral neck. Of the preoperative parameters, the osteolysis was associated with low weight (r = -0.337, p = 0.031) and to a lesser degree with female sex (r = 0.275, p = 0.067). Radiologically, the osteolysis was strongly associated with the presence of a pseudotumor on MRI (r = 0.663, p = 0.004). We could not differentiate the osteolysis group from the rest of the cohort on the basis of the implant sizes or radiographic implant component positions. The cohort's median whole blood cobalt was 1.77 ppb (range, 0.18-10.27 ppb) and chromium 1.88 ppb (range 0.36-10.09 ppb). There was no difference in the metal ion levels between the osteolysis group and the rest of the cohort. The high rate of silently developing femoral neck osteolysis associated with this implant is concerning and is expected to cause a high rate of failure at longer followup. We have instituted a program of annual clinical and radiologic followup for this group of patients. We have stopped implanting this device and recommend against its use. Level IV, therapeutic study.

Femoral Neck Stress Shielding after Birmingham Mid Head Resection Hip Arthroplasty – Case Report and Literature Review

We describe the presentation of substantial neck thinning due to stress shielding about a well-fixed Birmingham Mid Head Resection femoral implant. Despite significant resorption of proximal periarticular bone adjacent to the modular femoral head, secondary bone remodeling about the implant stem and proximal femur has occurred and stress shielding has appeared to stabilize, resulting in a satisfactory clinical outcome to date. For total hip arthroplasty utilizing short femoral implants we recommend consideration of alternative design stems to reduce the risk of stress shielding.

The impact of proximal femoral morphology on failure strength with a mid-head resection short-stem hip arthroplasty.

Mid-head resection short-stem hip arthroplasty is a conservative alternative to conventional total hip replacement and addresses proximal fixation challenges in patients not suitable for hip resurfacing. It is unclear whether proximal femoral morphology impacts the ultimate failure load of mid-head resection implanted femurs, thus the aim of this study was to investigate the effect of native neck-shaft angle (NSA) and coronal implant alignment on proximal femoral strength. In total, 36 synthetic femurs with two different proximal femoral morphologies were utilized in this study. Of them, 18 femurs with a varus NSA of 120° and 18 femurs with a valgus NSA of 135° were each implanted with a mid-head resection prosthesis. Femurs within the two different femoral morphology groups were divided into three equal coronal implant alignment groups: 10° valgus, 10° varus or neutral alignment. Prepared femurs were tested for stiffness and to failure in axial compression. There was no significant difference in stiffness nor failure load between femurs implanted with valgus-, varus- or neutrally aligned implants in femurs with a NSA of 120° (p = 0.396, p = 0.111, respectively). Femurs implanted in valgus orientation were significantly stiffer and failed at significantly higher loads than those implanted in varus alignment in femurs with a NSA of 135° (p = 0.001, p = 0.007, respectively). A mid-head resection short-stem hip arthroplasty seems less sensitive to clinically relevant variations of coronal implant alignment and may be more forgiving upon implantation in some femoral morphologies, however, a relative valgus component alignment is recommended.

A two-year radiostereometric follow-up of the first generation Birmingham mid head resection arthroplasty.

During the first decade of the 21st century, metal-on-metal hip resurfacing became one of the main treatment options for younger, more active patients with osteoarthritis. However, as a result of the reported failure rate of both total hip replacement (THR) and resurfacing in patients with considerable loss of bone stock in the femoral head (e.g., in extensive avascular necrosis), other solutions have been sought for these patients. The short-stemmed Birmingham Mid Head Resection prosthesis (BMHR) combines a metal-on-metal articulation and a femoral neck preserving feature. In this study, radiostereometric analysis (RSA) was used to study migration of the BMHR femoral component in 13 hips. Translations and rotations were measured up to two years. Relative values showed no statistically significant migration. Absolute values demonstrated settling in occurring between zero and two months postoperatively in all directions studied. From two months to two years no significant migration occurred except for rotation around the x-axis of the femoral segment (p = 0.049). After initial settling-in, absolute values were low, indicating that there was no evidence of early migration or loosening of the components.

A biomechanical study of the Birmingham mid head resection arthroplasty: Effect of stem size on femoral neck fracture

The Birmingham mid head resection (BMHR) arthroplasty can be used as an alternative to conventional stemmed total hip arthroplasty in young patients unsuitable for hip resurfacing. This study investigated the effect of stem size on femoral neck fracture in the BMHR. Sawbones composite femurs were randomly allocated to one of the following groups: (1) unprepared femur with no prosthesis, (2) femur prepared with a Birmingham hip resurfacing (BHR) prosthesis, (3) femur prepared with a BMHR stem size 1 (BMHR-1) and (4) femur prepared with a BMHR stem size 3 (BMHR-3). Each femur was subjected to a compressive force using a materials testing machine until fracture of the femoral neck occurred. The highest force at fracture was in the unprepared femurs with a mean (±standard deviation) force at failure of 5.9 ± 0.2 kN. The mean force at failure for the femurs fitted with a prosthesis was 2.6 ± 0.4, 3.0 ± 0.4 and 3.5 ± 0.5 kN for the BHR, BMHR-1 and BMHR-3, respectively. Statistical analysis showed that the failure force for the unprepared femur was significantly (p<0.05) greater than that of the BHR, BMHR-1 and BMHR-3. There was a significant difference (p<0.05) between the force at failure for the BMHR-1 and BMHR-3, indicating that these two stem sizes have an effect on fracture force.

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.

A Biomechanical Comparison of Epiphyseal Versus Metaphyseal Fixed Bone-Conserving Hip Arthroplasty

The Birmingham Mid-Head Resection (BMHR) is a bone-conserving, short-stem alternative to hip resurfacing for patients with abnormal femoral head anatomy. The current study examines whether a bone-preserving femoral component that is fixed into the femoral neck metaphysis provides a mechanical advantage in terms of resisting femoral neck fracture in comparison with a conventional hip resurfacing implant in a human cadaveric femoral model. Femora with a BMHR femoral component failed at an average of 23% less load than those prepared with a conventional hip resurfacing component (mean and standard deviation, 5434 ± 2297 compared with 7012 ± 2619 N; p < 0.001). An uncemented, metaphyseal fixed, bone-conserving femoral implant does not provide superior mechanical strength or increased resistance to femoral neck fracture in comparison with a conventional hip resurfacing arthroplasty.

The Birmingham Mid-Head Resection Arthroplasty - Minimum Two Year Clinical and Radiological Follow-Up: An Independent Single Surgeon Series

We report the results of the Birmingham Mid-Head Resection Arthroplasty (BMHR) for patients with poor femoral head bone quality where standard hip resurfacing is contraindicated. This is a clinical and radiological follow-up of the first 35 consecutive procedures (34 patients, 16 male, 18 female) performed by an independent surgeon. The mean follow-up was 2.8 years (2.1 to 4.1) and no patients were lost to follow-up. The mean age at the time of surgery was 50.4 years (23.8 to 69.4). There were no failures. The mean HHS improved from 46.6 (25 to 70) pre-operatively to 96.1 (72 to 100) post-operatively. The mean OHS was 36.4 (19 to 53) pre-operatively and 14.2 (12 to 34) post-operatively. The mean WOMAC score was 45.6 (7 to 92) pre-operatively and 4.3 (0 to 28) post-operatively. The mean UCLA activity score was 4.5 (1 to 9) pre-operatively and 7.6 (5 to 10) post-operatively. Radiographic analysis did not show any adverse features such as stress shielding, loosening or femoral neck narrowing. The BMHR provides an excellent alternative to conventional total hip arthroplasty in patients with poor femoral head bone quality who are not suitable for standard resurfacing.

Is Mid-head Resection a Durable Conservative Option in the Presence of Poor Femoral Bone Quality and Distorted Anatomy?

High medium-term survivorship of hip resurfacing arthroplasty in young patients has led to its increased usage. To achieve high survival rates, selecting patients with appropriate proximal femoral morphology and bone quality is important. For patients with poor bone quality or abnormal morphology, the mid-head resection technique is an alternative, bone-conserving procedure but whether this technique results in acceptable complications and survival is unknown. We therefore assessed (1) implant survivorship of a mid-head resection device during short- and medium-term followup, (2) hip function, (3) adverse radiographic features emphasizing proximal stress shielding, and (4) complications. We retrospectively reviewed 164 patients (171 hips) who underwent reconstruction with the Birmingham Mid-Head Resection device (Smith and Nephew Orthopaedics Ltd, Warwick, UK) between 2003 and 2008. Patients were reviewed with hip outcome questionnaires, clinical examination, and radiographs. We report findings in 156 of these 171 hips with a minimum followup of 2 years (mean, 3.5 years, range, 2-7.5 years). They include three successive iterations based on the same design rationale. There were four revisions during this period, including two femoral failures, giving 3.5-year survivorships of 97.4% and 98.7% with revision or reoperation for any reason and femoral failure as the end points, respectively. No patient is currently awaiting revision. Average hip function was 98%, as assessed by Oxford hip score. Five of the 87 intermediate-iteration (V1) stems showed proximal femoral stress shielding, a phenomenon not observed in the other two iterations. Four patients had asymptomatic below-knee deep venous thrombosis and one had nonfatal pulmonary embolism, all of which resolved uneventfully. The mid-head resection technique can circumvent the need for a more invasive procedure such as standard THA in patients who would benefit from a conservative arthroplasty but do not possess good femoral head bone quality or morphology.

A Biomechanical Investigation of Implant Alignment and Femoral Neck Notching With the Birmingham Mid-Head Resection

The Birmingham Mid-Head Resection (BMHR) is a bone-conserving, short-stem alternative to hip resurfacing for patients with compromised femoral head anatomy. The current study examined the effect of coronal implant alignment and femoral neck notching on proximal femoral strength with the BMHR. Neither relative valgus nor varus implant alignment had a significant impact on femoral strength compared to neutrally aligned, matched, paired cadaveric specimens. A 5-mm superior neck notch significantly weakened BMHR-implanted synthetic femurs compared to unnotched controls, whereas a 2-mm notch did not significantly affect ultimate failure load. Relative valgus alignment had a protective effect on a full-cortical-thickness superior neck notch. Mid-head resection arthroplasty may be more forgiving to minor preparatory errors than a typical hip resurfacing.

The Effect of Component Alignment on Proximal Femoral Strength with the Birmingham Mid-Head Resection

The Birmingham Mid-Head Resection (BMHR) is a bone-conserving, short-stem femoral prosthesis designed for patients with compromised femoral head anatomy unsuitable for a traditional hip resurfacing arthroplasty. Similar to hip resurfacing, the BMHR preserves the femoral neck, however, it is not known if the femoral neck fracture risks associated with hip resurfacing pose the same risk to a mid-head resection arthroplasty. The current study examined the effect of coronal alignment on proximal femoral strength with the BMHR. Sixteen pairs of fresh-frozen cadaveric femurs were divided into 2 equal alignment groups. Individual pairs were divided into a control and a test specimen. A power analysis revealed 8 pairs each would be needed to detect an effect size of approximately 500 N (α = 0.05; β = 1-0.8; population SD 500 N). The first alignment group prepared test specimens in 10° of relative valgus alignment, while the second group prepared test femurs in 10° of relative varus. All control specimens were prepared with the implant aligned with the native neck-shaft angle of the femur. Femurs were tested in axial compression in single-leg stance. There was no significant difference between matched paired femurs prepared in varus alignment (mean 4324 N; SD 2207) compared to controls (mean 4114; SD 2153; P = .996). Likewise, there was no difference between femurs prepared in valgus alignment (mean 4623; SD 1608) and matched paired control specimens (mean 4761; SD 1290; P = .999). There was also no difference between control groups (P = .897). Femurs were well matched for BMD and anatomic parameters. The findings of the current study are in contrast to previous studies investigating implant alignment in hip resurfacing. A valgus aligned implant did not appear to strengthen, nor a varus implant weaken, proximal femoral strength compared to a neutrally aligned implant. Failure of the proximal femur implanted with a BMHR appears less sensitive to variations in implant alignment than a typical hip resurfacing.

Mid-Head Resection Technique for Complex Deformity

Summary:The mid-head resection technique uses a unique resection level in conservative hip arthroplasty, which preserves the distal part of the femoral head and neck and does not invade the medullary canal of the femur. It is useful in young patients with severe hip arthritis in the presence of poor