Orientation of the femoral component in surface arthroplasty of the hip. A biomechanical and clinical analysis

Two-Year Results of Ceramic-on-Ceramic Hip Resurfacing in an International Multicenter Cohort

BACKGROUND

Hip resurfacing arthroplasty (HRA) is a bone-conserving alternative to total hip arthroplasty. We present the 2-year clinical and radiographic follow-up of a novel ceramic-on-ceramic HRA in an international multicenter cohort.

METHODS

Patients undergoing HRA between September 2018 and January 2021 were prospectively included. Patient-reported outcome measures (PROMs) in the form of the Forgotten Joint Score, Hip Disability and Osteoarthritis Outcome Score Jr., Western Ontario and McMaster Universities Arthritis Index, Oxford Hip Score, and University of California, Los Angeles, Activity Score were collected preoperatively, and at 1 and 2 years postoperation. Serial radiographs were assessed for migration, component alignment, evidence of osteolysis or loosening, and heterotopic ossification formation.

RESULTS

The study identified 200 patients who reached a minimum 2-year follow-up (mean 3.5 years). Of these, 185 completed PROMs follow-up at 2 years. There was a significant improvement in Hip Disability and Osteoarthritis Outcome Score (P < .001) and Oxford Hip Score (P < .001) between the preoperative, 1-year, and 2-year outcomes. Patients had improved activity scores on the University of California, Los Angeles, Active Score (P < .001), with 45% reporting a return to high-impact activity at 2 years. At 1 and 2 years, the Forgotten Joint Score was not significantly different (P = .38). There was no migration, osteolysis, or loosening of any of the implants. No fractures were reported over the 2-year follow-up, with only 1 patient reporting a sciatic nerve palsy. There were 2 revisions, 1 for unexplained pain at 3 months due to acetabular component malposition and 1 at 33.5 months for acetabular implant failure.

CONCLUSIONS

The ceramic-on-ceramic resurfacing at 2 years postoperation demonstrates promising results with satisfactory outcomes in all recorded PROMs. Further long-term data are needed to support the widespread adoption of this prosthesis as an alternative to other HRA bearings.

Is there still an indication for the Birmingham Hip Resurfacing in femoral head osteonecrosis?

PURPOSE

Osteonecrosis of the femoral head (ONFH) is a progressive hip disease. Hip resurfacing arthroplasty (HRA) is a preferred surgical procedure among hip arthroplasty performed in young patients. The aim of this study is to show the long-term clinical and radiological results of HRA procedures performed for patients suffering from ONFH.

METHODS

Forty-five patients who underwent hip resurfacing with the diagnosis of femoral head osteonecrosis were included in the study. The Harris Hip Score (HHS) was used for clinical scoring of the patients. The blood chromium, cobalt, white blood cell (WBC) count, and CRP levels of patients were checked. Ultrasonography (USG) was performed for all patients at mid-term control checked for pseudo-tumours. For the radiological evaluation, acetabular inclination, stem shaft angle, prothesis-to-neck ratio, osteolysis zones, and heterotopic ossification were used.

RESULTS

The mean age of the patients was 46.6 ± 9.3 years, and the mean follow-up period was 11.83 ± 2.9 years. The mean HHS was 90.3 ± 12.8 for final follow-up. The mean WBC value was 8.2 109/L, mean CRP value was 6.3 mg/L, mean chromium value was 4.9 µg/L, and mean cobalt value was 1.8 µg/L. Inclination changing 0.2°(p = 0.788), stem shaft angle changing 0.7°(p = 0.424), and neck-to-prosthesis ratio changing 0.01°(p = 0.075). No pseudo-tumours were detected in any patients in USG examination.

CONCLUSION

HRA provides long-term implant survival and excellent clinical outcomes for end-stage ONFH patients with low complication rates.

Hueter Anterior Approach for Metal-on-Metal Hip Resurfacing Arthroplasty: 555 Cases at a Minimum Five-Year Follow-Up

BACKGROUND

Purpose of this study was to determine implant survivorship and resultant outcomes, including modes of failure, for metal-on-metal hip resurfacing through the Hueter anterior approach (HAA).

METHODS

Retrospective review of cases from 2006 to 2015, resulted in 555 metal-on-metal hip resurfacing via HAA, mean age 49.4 ± 6.9 years and mean BMI 28.1 ± 5.3. Kaplan-Meier curves were used to assess implant survivorship. Evaluation of technique was based on radiographic assessment of component position at 6 weeks. Patient-reported outcome measures were assessed using 12-Item Short Form Survey 12, University of California Los Angeles activity, Western Ontario and McMaster Universities Osteoarthritis Index, and hip disability osteoarthritis outcome scores.

RESULTS

At a mean follow-up of 9.18 years, survivorship was 95.0% at 5 years (95% CI: 93.2-96.8 years) and 92.5% at 10 years (95% CI: 90.0-95.0 years); men at 96.1% (95% CI: 94.3-97.9) and 93.8% (95% CI: 91.1-96.5), and women at 88.8% (95% CI: 81.9-95.7) and 85.6% (95% CI: 77.6-93.6), 5 and 10 years, respectively (P = .033). There were 37 revisions to total hips (7%) at a mean time of 3.3 years (SD 2.7). Indications for revision were aseptic loosening of acetabular (n = 12) and femoral component (n = 7) and pseudotumor (n = 6). Radiographic parameters were respectable and consistent, median acetabular inclination angle 41.2° and femoral stem shaft angle 137.7°. Patient-reported outcome measure scores significantly improved and remained stable at 2 and 5 years postoperatively.

CONCLUSION

Although choice of surgical approach should always be based on surgeon's technical expertise, this study has shown that HAA is safe and effective for hip resurfacing. Mindful attention to long-term metal ion exposure must still be considered.

A Comparative Cohort Study With a 20-Year Age Gap: Hip Resurfacing in Patients Aged ≤35 Years and Patients Aged ≥55 Years

Background

This single-center retrospective cohort study aimed to evaluate and compare implant survival and patient-reported outcome measures in 2 distinct age groups separated by 20 years who underwent hip resurfacing arthroplasty (HRA).

Methods

Between 2005 and 2014, 2042 HRAs were performed by a single-surgeon, and 75 and 377 hips from patients aged ≤35 years and ≥55 years, respectively, were included in this study. Implant survival was determined for all available hips. Clinical features and patient-reported outcome measures were collected.

Results

Seven hips were revised, 4 for aseptic loosening of one or both components, one for infection, one for accelerated wear and metallosis, and one for femoral neck fracture. There was no difference in all-cause 10-year revision, with 97.1% (95% confidence interval 80.9 to 99.6) and 99.6% (95% confidence interval: 97 to 99.9) survivorship in younger and older patients, respectively (P = .246). Preoperatively, younger patients were less active than older patients on the Lower Extremity Activity Scale (LEAS) or University of California, Los Angeles, activity scale, but at follow-up, younger patients outpaced older ones.

Conclusion

Original to our study was the isolation and comparison of 2 distinct age groups. With excellent results in disparate age groups, HRA can be applied to a broad patient demographic and is suitable for those patients who want to achieve a high activity level as defined by Lower Extremity Activity Scale or University of California, Los Angeles, scores.

Gait after Birmingham Hip Resurfacing: an age-matched controlled prospective study

Aims

The aim of this study was to assess the functional gain achieved following hip resurfacing arthroplasty (HRA).

Patients and Methods

A total of 28 patients (23 male, five female; mean age, 56 years (25 to 73)) awaiting Birmingham HRA volunteered for this prospective gait study, with an age-matched control group of 26 healthy adults (16 male, ten female; mean age, 56 years (33 to 84)). The Oxford Hip Score (OHS) and gait analysis using an instrumented treadmill were used preoperatively and more than two years postoperatively to measure the functional change attributable to the intervention.

Results

The mean OHS improved significantly from 27 to 46 points (p < 0.001) at a mean of 29 months (12 to 60) after HRA. The mean metal ion levels at a mean 32 months (13 to 60) postoperatively were 1.71 (0.77 to 4.83) µg/l (ppb) and 1.77 (0.68 to 4.16) µg/l (ppb) for cobalt and chromium, respectively. When compared with healthy controls, preoperative patients overloaded the contralateral good hip, limping significantly. After HRA, patients walked at high speeds, with symmetrical gait, statistically indistinguishable from healthy controls over almost all characteristics. The control group could only be distinguished by an increased push-off force at higher speeds, which may reflect the operative approach.

Conclusion

Patients undergoing HRA improved their preoperative gait pattern of a significant limp to a symmetrical gait at high speeds and on inclines, almost indistinguishable from normal controls. HRA with an approved device offers substantial functional gains, almost indistinguishable from healthy controls.

Cite this article: Bone Joint J 2019;101-B:1423–1430.

No added value for Computer-Assisted surgery to improve femoral component positioning and Patient Reported Outcomes in Hip Resurfacing Arthroplasty; a multi-center randomized controlled trial

Background

Computer Assisted Surgery (CAS) has proven to improve the accuracy in several orthopedic procedures. Therefore we used this technique to evaluate femoral component positioning in Hip Resurfacing Arthroplasty (HRA). The aim of this study was to evaluate imageless CAS compared to manually implanted femoral components and subsequently evaluates Patient Related Outcome Measures (PROMs). We hypothesized that the use of CAS optimizes the position of the femoral component and improves PROMs.

Methods

This is a multicenter, single-blinded, randomized, controlled trial of two groups. In the CAS group guiding of the femoral component was done with imageless navigation. In the Conventional (control) group the femoral component was placed manually according to the preplanned position. The primary outcome measure consists of a maximum of 3 degrees difference between the postoperative Stem Shaft Angle (SSA) and preplanned SSA. Secondary outcome measures consist of the Hip disability and Osteoarthritis Outcome Scale (HOOS), the Harris Hip Score (HHS) and Visual Analogue Scale (VAS) pain score.

Results

A total of 122 patients were randomized, 61 in the CAS group and 61 in the conventional group. There was no significant differences in accuracy of femoral implant position. The mean difference between the postoperative- and preplanned SSA was − 2.26 and − 1.75 degrees (more varus) respectively in the CAS and Conventional group. After surgery both groups show significant improvement in all PROMs compared to the baseline measurements, with no significant differences between the groups.

Conclusion

Our cohort indicates no benefit for the use of CAS in accuracy of placement of the femoral component in HRA compared to manual implantation. There are no clinical differences in PROMs after 1 year follow up. This study showed no added value and no justification for the use of CAS in femoral component positioning in HRA.

Trial registration

This trial is registered at ClinicalTrails.gov (https://clinicaltrials.gov/) on the 25th of October 2006: NCT00391937.

Level of incidence

Level IIb, multicenter randomized controlled trial.

Mechanical and numerical characterization of ceramic femoral components for hip resurfacing arthroplasty

Hip resurfacing arthroplasty may have distinct advantages for young and active patients, but large metal-on-metal bearings can be associated with increased wear, adverse tissue reactions and higher rate of implant loosening. Ceramic wear couples are a commonly used alternative to metals and therefore might be an alternative for hip resurfacing arthroplastys. The aim of this study was to evaluate the mechanical strength of femoral components made of an alumina-toughened zirconia composite by means of experimental testing and finite element analysis. For the mechanical characterization, ceramic femoral components (Ø: 48 mm) were tested under compression loading experimentally until fracture occurred or a maximum load of 85 kN was obtained. The femoral components were either loaded against a ceramic cup or a copper ring (outer diameter Ø: 7.0 mm). In addition, the complex geometry of the ceramic femoral component was simplified, and only the stem was loaded in a cantilever test until fracture. In addition, the fracture tests were numerically simulated to investigate the influence of additional loading conditions and geometric parameters, which were not experimentally tested. The experimental data were used for validation of the finite element analysis. None of the tested ceramic femoral components fractured at a compression load of 85 kN when they were loaded against a ceramic cup at an inclination angle of 45°. When the femoral components were loaded against a copper ring, the femoral components fractured at 29.9 kN at a testing angle of 45°. The fracture load was reduced when an angle of 30° and increased when an angle of 60° was simulated. Using an experimental cantilever test, the stem of the femoral component fractured at 1124.0 N. When the stem length was increased or the diameter was reduced by 10% in the finite element analysis, the fracture load was reduced. Decreasing the length or increasing the diameter led to an increase of the fracture load. The strongest influence was found for the reduction of the transition radius of the stem, with a decrease of the fracture load up to 27.2%. The analyzed femoral components made of alumina-toughened zirconia (ATZ) showed sufficient mechanical capability to withstand high loadings during unfavorable loading conditions. However, further biomechanical and tribological investigations are required before clinical application.

Mid- to long-term results of resurfacing hip arthroplasty in Japanese patients: a comparison of osteoarthritic vs non-osteoarthritic patients

Past reports showed good mid-term results of RHA for Japanese patients. However, few reports have compared the mid- to long-term results for RHA in Japanese patients with and without osteoarthritis. Therefore, this study investigated the mid- to long-term results of RHA in Japanese patients with osteoarthritis compared to those without. We conducted a retrospective review of a consecutive series of 92 hips in 80 patients (59 men and 21 women). The minimum follow-up period was 5 years. The JOA hip scoring system was used to clinically evaluate hip function. In the radiological assessment, stem-shaft angle, inclination of the acetabular component, postoperative complications, and adverse reactions around RHA were evaluated. The 10-year survival rate using the Kaplan-Meier method was investigated to compare patients with and without osteoarthritis. A significant difference was observed between the preoperative and postoperative JOA hip scores of either group. Also, the radiological assessment revealed no significant changes in either group. All three revision THAs were performed on patients in the only non-osteoarthritis group. In the osteoarthritis group, the 10-year survival rate was 94% (95% CI 81.8-100) in males and 100% (95% CI 100) for females; in the non-osteoarthritis group, the rate was 80% (95% CI 55.1-100) in males and 66.7% (95% CI 13.3-100) for females. In conclusion, this study showed good mid- to long-term clinical results for young Japanese osteoarthritis patients, with less satisfactory mid- to long-term results in patients without osteoarthritis.

Augmented Reality Based Navigation for Computer Assisted Hip Resurfacing: A Proof of Concept Study

Implantation accuracy has a great impact on the outcomes of hip resurfacing such as recovery of hip function. Computer assisted orthopedic surgery has demonstrated clear advantages for the patients, with improved placement accuracy and fewer outliers, but the intrusiveness, cost, and added complexity have limited its widespread adoption. To provide seamless computer assistance with improved immersion and a more natural surgical workflow, we propose an augmented-reality (AR) based navigation system for hip resurfacing. The operative femur is registered by processing depth information from the surgical site with a commercial depth camera. By coupling depth data with robotic assistance, obstacles that may obstruct the femur can be tracked and avoided automatically to reduce the chance of disruption to the surgical workflow. Using the registration result and the pre-operative plan, intra-operative surgical guidance is provided through a commercial AR headset so that the user can perform the operation without additional physical guides. To assess the accuracy of the navigation system, experiments of guide hole drilling were performed on femur phantoms. The position and orientation of the drilled holes were compared with the pre-operative plan, and the mean errors were found to be approximately 2 mm and 2°, results which are in line with commercial computer assisted orthopedic systems today.

Clinical accuracy and precision of hip resurfacing arthroplasty using computed tomography-based navigation

PURPOSE

To avoid malalignment of components during hip resurfacing arthroplasty (HRA), we used a computed tomography (CT)-based navigation system for guidance. This study aimed to evaluate the clinical accuracy and precision of HRA performed using the CT-based navigation systems.

METHODS

HRA was performed on 17 hips guided by the CT-based navigation systems. We measured cup alignment deviation, deviation of the stem position, and alignment from the plan by image matching between pre-operative and post-operative CT images.

RESULTS

Cup anteversion was within 5° of that in the plan in all cases. Cup inclination was within 5° of that in the plan in 82.4% and within 10° in all cases. The angular difference of the stem was within 5° in all cases, and the entry point of the stem was within 4 mm in all cases.

CONCLUSION

The CT-based navigation system for HRA guided accurate component placement according to the plan.

CUSTOMIZED GUIDE FOR FEMORAL COMPONENT POSITIONING IN HIP RESURFACING ARTHROPLASTY

Objective:

To prove the accuracy of a customized guide developed according to our method.

Methods:

This customized guide was developed from a three-dimensional model of proximal femur reconstructed using computed tomography data. Based on the new technique, the position of the guide pin insertion was selected and adjusted using the reference of the anatomical femoral neck axis. The customized guide consists of a hemispheric covering designed to fit the posterior part of the femoral neck. The performance of the customized guide was tested in eight patients scheduled for total hip arthroplasty. The stability of the customized guide was assessed by orthopedic surgeons. An intraoperative image intensifier was used to assess the accuracy.

Results:

The customized guide was stabilized with full contact and was fixed in place in all patients. The mean angular deviations in relation to the what was planned in anteroposterior and lateral hip radiographs were 0.5º ± 1.8º in valgus and 1.0º ± 2.4º in retroversion, respectively.

Conclusion:

From this pilot test, the authors suggest that the proposed technique could be applied as a customized guide to the positioning device for hip resurfacing arthroplasty with acceptable accuracy and user-friendly interface. Level of Evidence IV, Cases Series.

Mid-Term Results and Predictors of Patient-Reported Outcomes of Birmingham Hip Resurfacing

BACKGROUND

Birmingham hip resurfacing (BHR) is the only Food and Drug Administration approved resurfacing option currently available in the United States. While adequate BHR outcomes are established, there is a paucity of US-based literature demonstrating factors critical to improve patient reported outcomes (PROs). This study answers: (1) What is the implant survivorship in a large US cohort? (2) Which preoperative factors result in higher PRO scores over 5 years postoperatively?

METHODS

A retrospective 541 hip single-surgeon cohort with mean of 6.2 years follow-up (range 5-8.1) was collected. Preoperative patient/implant variables, including postoperative radiographic acetabular inclination and femoral component position, clinical outcomes, and follow-up PRO questionnaire information were collected. Validated PROs included the Hip Disability and Osteoarthritis Outcome Score (HOOS), Veterans Rand-12, and University of California Los Angeles (UCLA) activity. PROs were modeled with ordinary least squares then used to create nomograms.

RESULTS

Average patient age was 53 years with 391 (72%) males. Seven hips were revised, resulting in an overall survival of 98.8% at 5 years. Predictive modeling identified preoperative variables (sex, body mass index, smoking, and comorbidity) that had statistically significant associations with HOOS pain (P = .049), HOOS activities of daily living (P = .017), UCLA activity (P < .001), and Veterans Rand-12 physical (P < .001) PROs at latest follow-up. Nomograms predicted follow-up PROs using preoperative patient-specific variables.

CONCLUSION

This study documents excellent survival of the largest reported single-center cohort of BHRs in the United States with a mean 6.2 years follow-up. Multivariate modeling shows male nonsmokers with low body mass index, and no comorbidities will have less hip pain, better function in daily life, higher activity, and better general physical health after BHR arthroplasty.

Hip resurfacing arthroplasty in patients with varus deformity of the femoral neck-shaft angle

Hip resurfacing arthroplasty (HRA) in patients with a varus deformity of the femoral neck-shaft angle (NSA) is associated with poorer outcomes. Our experience has not reflected this. We examined the Oxford Hip Scores (OHS), Harris Hip Scores (HHS) and outcomes of patients with varus hips against a normal cohort to ascertain any significant difference. We identified 179 patients. Measurement of the femoral neck-shaft angle was undertaken from antero-posterior radiographs pre-operatively. The mean NSA was 128.5 degrees (SD 6.3). Patients with a NSA of less than 122.2 were deemed varus and those above 134.8 valgus. These parameters were consistent with published anatomical studies. The 'varus' cohort consisted of 23 patients, mean NSA 118.7 (range 113.6-121.5), mean follow-up 49 months (range 13-74). Mean OHS and HHS were 16 and 93.5 respectively. Complications included 2 cases of trochanteric non-union, but there were no femoral neck fractures, early failures or revisions. The 'normal' cohort consisted of 125 patients, mean NSA 128 degrees, mean follow-up 41 months (range 6-76). The OHS and HSS were 18.8 and 88.9 respectively. Complications included 5 trochanteric non-unions and 1 revision due to an acetabular fracture following a fall. Statistical analysis demonstrated no statistical difference between the cohorts' OHS (p=0.583) or HHS (p=0.139). Our experience in patients with a varus femoral neck has been positive. We have not yet experienced any femoral neck fractures, which we believe is in part due to the use of an uncemented femoral component and preservation of blood supply.

Biomechanical optimization of subject-specific implant positioning for femoral head resurfacing to reduce fracture risk

Peri-prosthetic femoral neck fracture after femoral head resurfacing can be either patient-related or surgical technique-related. The study aimed to develop a patient-specific finite element modelling technique that can reliably predict an optimal implant position and give minimal strain in the peri-prosthetic bone tissue, thereby reducing the risk of peri-prosthetic femoral neck fracture. The subject-specific finite element modelling was integrated with optimization techniques including design of experiments to best possibly position the implant for achieving minimal strain for femoral head resurfacing. Sample space was defined by varying the floating point to find the extremes at which the cylindrical reaming operation actually cuts into the femoral neck causing a notch during hip resurfacing surgery. The study showed that the location of the maximum strain, for all non-notching positions, was on the superior femoral neck, in the peri-prosthetic bone tissue. It demonstrated that varus positioning resulted in a higher strain, while valgus positioning reduced the strain, and further that neutral version had a lower strain.

Effect of surgical experience on imageless computer-assisted femoral component positioning in hip resurfacing--a preclinical study

Background

The clinical outcome of hip resurfacing (HR) as a demanding surgical technique associated with a substantial learning curve depends on the position of the femoral component. The aim of the study was to investigate the effects of the level of surgical experience on computer-assisted imageless navigation concerning precision of femoral component positioning, notching, and oversizing rate, as well as operative time.

Methods

Three surgeons with different levels of experience in both HR and computer-assisted surgery (CAS) prepared the femoral heads of 54 synthetic femurs using the Durom^TM Hip Resurfacing (Zimmer, Warsaw, IN, USA) system. Each surgeon prepared a total of 18 proximal femurs using the Navitrack® system (ORTHOsoft Inc., Montreal, Canada) or the conventional free-hand Durom^TM K-wire positioning jig. The differences between planned and postoperative stem shaft angle (SSA) and anteversion angle in standardized x-rays were measured and the operative time, not including the time for calibrating the CAS-system, was documented. Notching was evaluated by the three surgeons in a randomized manner. Oversizing was determined by the difference of the preoperative determined cap and the cap size advised by the CAS-system.

Results

CAS significantly reduced the overall mean deviation between planned and postoperative SSA in comparison with the conventional procedure (mean ± SD, 1 ± 1.7° vs. 7.4 ± 4.4°, P <0.01) regardless of the surgeon’s level of experience. The incidence of either varus or valgus SSA deviations exceeding 5° were 1/27 for CAS and 15/27 for the conventional method, respectively (P <0.001), corresponding to a reduction by 97%. Using CAS, the rate of notching was reduced by 100%.

Conclusions

The accuracy of femoral HR component orientation is significantly increased by use of CAS regardless of the surgeon’s level of experience in our preclinical study. Thus, imageless computer-assisted navigation can be a valuable tool to improve implant positioning in HR for surgeons at any stage of their learning curve.

Mid-term results of metal-on-metal hip resurfacing for treatment of osteoarthritis secondary to developmental dysplasia of the hip: a minimum of 8-years of follow-up

Background

Metal-on-metal resurfacing arthroplasty is an attractive alternative to conventional total hip arthroplasty in patients with osteoarthritis secondary to developmental dysplasia of the hip (DDH). The purpose of this study was to assess the mid-term clinical outcome and mid-term survivorship of Metal-on-metal resurfacing arthroplasty in patients suffering from osteoarthritis secondary to DDH.

Material/Methods

Between May 2003 and Dec. 2005, 15 operations using ASR™ and 19 using Corin were performed in 29 patients to treat advanced osteoarthritis secondary to DDHs. There were 6 males (20.7%) and 23 females (79.3%), with an average age of 47.2 years (range, 36–64 years). Clinical and radiographic results were observed. All patients were followed up at the 1^st, 2^nd, 3^rd, 6^th, and 12^th months after surgery and annually thereafter.

Results

The overall survival was 88.2% at a minimum follow-up of 8 years, but the survival was 91.2% after excluding the infections as the cause of component loosening and failure. The mean Harris hip score improved from 48.27±3.13 (range, 14–71) to 89.63±3.42 (range, 65–100) at latest follow-up. The flexion was from 75.14±8.05° to 107.21±9.34. Only 4 failed because of deep infection, femoral neck fracture, and aseptic loosening.

Conclusions

Metal-on-metal resurfacing arthroplasty showed perfect results at a minimum of 8-years of follow-up in our study, and may be a reasonable option for osteoarthritis secondary to developmental dysplasia of the hip (DDH).

Long-term outcome of a metal-on-polyethylene cementless hip resurfacing

Due to the well-documented problems surrounding metal-on-metal bearings, the use of hip resurfacing has declined. Since the potential benefits of hip resurfacing remain desirable, it may be beneficial to investigate the long-term outcome of hip resurfacings using metal-on-polyethylene in the 1980's. We report the long-term survivorship and modes of failure of a cementless metal-on-polyethylene resurfacing (n = 178) with different porous ingrowth surfaces. While acetabular loosening was absent, a high incidence of femoral failures (femoral loosening = 18.1%, osteolytic neck fracture = 21%) occurred despite using the same ingrowth surface for both components. Ongoing developments using the lessons learned from these previous generation components and utilizing modern low wear materials, e.g., cross-linked polyethylene, may lead to improved implants for future hip resurfacings.

Evaluation of a patient specific femoral alignment guide for hip resurfacing

A novel alternative to conventional instrumentation for femoral component insertion in hip resurfacing is a patient specific, computed tomography based femoral alignment guide. A benchside study using cadaveric femora was performed comparing a custom alignment guide to conventional instrumentation and computer navigation. A clinical series of twenty-five hip resurfacings utilizing a custom alignment guide was conducted by three surgeons experienced in hip resurfacing. Using cadaveric femora, the custom guide was comparable to conventional instrumentation with computer navigation proving superior to both. Clinical femoral component alignment accuracy was 3.7° and measured within ± 5° of plan in 20 of 24 cases. Patient specific femoral alignment guides provide a satisfactory level of accuracy and may be a better alternative to conventional instrumentation for initial femoral guidewire placement in hip resurfacing.

High incidence of pseudotumours after hip resurfacing even in low risk patients; results from an intensified MRI screening protocol

We intensified our screening protocol for the presence of pseudotumours in a consecutive series of patients with a hip resurfacing arthroplasty (HRA), to establish whether we should be alert to the presence of 'silent' pseudotumours. Patients categorised with high risk (11 hips) and low risk (10 hips) for pseudotumour development and a control group (23 hips) were screened with metal artefact reduction sequence (MARS) magnetic resonance imaging (MRI). The Anderson classification to grade any metal-on-metal (MoM) disease present on MARS-MRI images was used. In 15 out of 44 MRI scans pseudotumours were observed (34.1%), of which six were graded with mild (13.6%), eight with moderate (18.2%) and one with severe MoM disease (2.3%). Twelve pseudotumours were present in asymptomatic patients (27.3%). Metal ion levels were normal in 80% of the MARS-MRI screened patients. As a consequence of our intensified screening protocol, one patient was revised for pseudotumour formation and another patient was scheduled for revision. Silent pseudotumours were observed in all three groups. Before our intensified screening protocol was initiated, no pseudotumours were encountered in our cohort of 289 HRAs. We concluded that clinical outcomes and plain radiographs for screening MoM patients underestimates the presence of pseudotumours in MoM patients. The true clinical relevance of these pseudotumours is still unclear.

Reproducibility of radiographic assessment of femoral implant position after hip resurfacing arthroplasty: a pilot study

To determine whether femoral implant position can be reproducibly measured on plain digital radiographs, we prospectively studied 40 patients after hip resurfacing arthroplasty. Three observers performed double blinded randomized analysis of calibrated digital radiographs meeting strict quality criteria. The implant stem-shaft angle and femoral anteversion angle were measured by the trapezoid method of axis determination using OsiriX software. The upper and lower offset and the anterior and posterior offset were measured. The statistical analysis was performed using Pearson correlation tests (intra-observer reproducibility) and Fisher F tests (inter-observer reproducibility). Intra-observer reproducibility was very good for all parameters and all observers. Inter-observer reproducibility was excellent except for superior offset measurement. Thus, this study validates a radiographic method for assessing the femoral implant position in hip resurfacing. We believe this could be useful for future studies on hip resurfacing devices.

The First SICOT Oral Presentation Award 2011: imageless computer-assisted femoral component positioning in hip resurfacing: a prospective randomised trial

PURPOSE

The aim of the study was to evaluate the effects of imageless computer-assisted surgery (CAS) on the accuracy of positioning of the femoral component and on the short-term clinical outcome in hip resurfacing (HR) using a randomised prospective design.

METHODS

A total of 75 consecutive patients undergoing HR were randomly allocated to CAS and conventional implantation, respectively. Preoperatively and six months post-operatively standardised pelvic anteroposterior X-ray images, the total Western Ontario and McMaster Universities Osteoarthritis Index, the Harris Hip Score and the EQ-5D utility index were evaluated in a blinded manner. The primary end point of the study was a post-operative femoral component malpositioning in five degrees or more either varus or valgus absolute deviation from the planned stem shaft angle.

RESULTS

Patient demographics and algofunctional scores did not differ between the CAS and conventional implantation samples. Using CAS fewer femoral components were positioned in five or more degrees absolute deviation (4/37 vs 12/38, Fisher's exact p = 0.047; 95 % confidence interval for the primary end point's incidence difference: +3 %; +39 %); the respective incidences of five or more degrees of varus deviation were 0/37 vs 5/38. One conversion to a stemmed prosthesis (CAS group) was performed for periprosthetic femoral neck fracture. Radiological signs of superolateral femoral neck/implant impingement were observed in two cases (one CAS-based and one conventional implantation).

CONCLUSIONS

The accuracy of femoral HR component positioning was significantly improved using CAS. However, one major complication necessitated early revision in the CAS group at six months of observation. Apart from that adverse event no inter-group differences were observed for the short-term clinical outcome. Future studies need to address the clinical long-term relevance of CAS in HR.

Results of metal-on-metal hip resurfacing in patients 40 years old and younger

The prevalence of total hip arthroplasty in young patients is small but increasing. We analyzed the results of metal-on-metal hip resurfacing (MMHR) in patients aged 40 years or less. In total 74 operations were performed on 64 patients. Mean age at operation was 33.2 years. HHS averaged 92.3 points at latest follow-up, mean UCLA activity was 8.2. Patients with comorbidity evinced lower scores in HHS, in UCLA activity and in quality of life than patients without comorbidities. Eight revisions (10.8 %) were performed, of which seven due to adverse reaction to metal debris. Seven-year survival was 90.5 %. The functional outcome of hip resurfacing in this cohort was excellent, but overall survival was unsatisfactory. Further analysis is required to verify the role of hip resurfacing among young and active patients.

Radiological validation of a fluoroscopic guided technique for femoral implant positioning during hip resurfacing

PURPOSE

The positioning of the femoral cup in hip resurfacing is essential for the survival of the implant. We described a technique in 2005 to position the femoral cup guided by fluoroscopy independent of the approach performed. The main objectives were to study the positioning of the femoral components of the implant and the accuracy of the technique.

METHODS

Between 2003 and 2011 we conducted a prospective study of 160 consecutive hip resurfacings all operated with this fluoroscopic-guided technique. Three independent observers performed a radiographic analysis at the pre-operative planning stage and on postoperative radiographs using OsiriX software. The statistical analysis was based on comparison of two groups by Student's t test.

RESULTS

The entire implant was positioned in valgus, with an average of 7.816° valgus (p <0.001). All implants were positioned in neutral or anteverted with a mean of 1.98° (p <0.001). The risk of malpositioning on the antero-posterior plane was less than 1.41° with p <0.019. The risk of profile positioning error was lower than 0.80° with p <0.047.

CONCLUSION

This study validates a technique of femoral implant positioning for resurfacing. It is simple, precise and independent of the approach performed.

Computer navigation experience in hip resurfacing improves femoral component alignment using a conventional jig

BACKGROUND

The use of computer navigation has been shown to improve the accuracy of femoral component placement compared to conventional instrumentation in hip resurfacing. Whether exposure to computer navigation improves accuracy when the procedure is subsequently performed with conventional instrumentation without navigation has not been explored. We examined whether femoral component alignment utilizing a conventional jig improves following experience with the use of imageless computer navigation for hip resurfacing.

MATERIALS AND METHODS

Between December 2004 and December 2008, 213 consecutive hip resurfacings were performed by a single surgeon. The first 17 (Cohort 1) and the last 9 (Cohort 2) hip resurfacings were performed using a conventional guidewire alignment jig. In 187 cases, the femoral component was implanted using the imageless computer navigation. Cohorts 1 and 2 were compared for femoral component alignment accuracy.

RESULTS

All components in Cohort 2 achieved the position determined by the preoperative plan. The mean deviation of the stem-shaft angle (SSA) from the preoperatively planned target position was 2.2° in Cohort 2 and 5.6° in Cohort 1 (P = 0.01). Four implants in Cohort 1 were positioned at least 10° varus compared to the target SSA position and another four were retroverted.

CONCLUSIONS

Femoral component placement utilizing conventional instrumentation may be more accurate following experience using imageless computer navigation.

The effect of cup orientation and coverage on contact mechanics and range of motion of metal-on-metal hip resurfacing arthroplasty

Implant malpositioning has been identified as a factor associated with clinical failures of metal-on-metal hip resurfacings (MoMHRs). This study investigated the effect of cup orientation and cup coverage on the contact mechanics (incidence of edge-loading) and range of motion (ROM) of MoMHR. Three generic MoMHRs with differing amounts of cup coverage were considered at various orientations. Contact area and contact pressure at the bearing surface were predicted for each design using finite element (FE) method. The ROM was determined based on the geometry overlap. Edge contact was found at lower angles of inclination (65°) for lower coverage cup designs; however, they also provided the greatest ROM. Conversely, cups with greater coverage did not exhibit edge contact until the cup was more steeply positioned (75°), however ROM was reduced. This study enables both sets of variable to be considered in the design of metal-on-metal bearings in hip.

Design and primary application of computer-assisted, patient-specific navigational templates in metal-on-metal hip resurfacing arthroplasty

Total hip resurfacing arthroplasty is increasingly being used. One of its goals is to closely mimic the normal anatomy and normal biomechanics of the hip joint. Prosthesis location has a large impact on implant survival and patient function; but in conventional hip resurfacing arthroplasty, precise positioning sometimes cannot be achieved. We describe a novel method for ensuring accurate prosthesis implantation in hip resurfacing arthroplasty by means of 3-dimensional reconstruction and reverse engineering.

Hip resurfacing revision rates: radiological audit of risk factors

INTRODUCTION

We performed a retrospective radiological audit of the hip resurfacings carried out in our trust over a five-year period. Abnormal cup inclination angle (CIA) and stem shaft angle (SSA) are recognised risk factors for revision in hip resurfacing. Our aims were to identify the CIA and SSA for hip resurfacings in our trust, to determine the revision rate in a CIA of ≥60° and an SSA of >0° varus, thereby identifying a high risk group for close, long-term follow up.

METHODS

A total of 247 patients underwent hip resurfacing in our trust between April 2003 and March 2008. The CIA and SSA were recorded. Of the 247 patients, 26 were excluded as there were no appropriate radiographs and so results were analysed for 221 patients.

RESULTS

The mean CIA was 47.6°. Over a third of the patients (34%) had a CIA of >50° and 13% had >60°. The mean SSA was 1.4° varus. Over two-thirds of the patients (67%) had a varus SSA. There were six revisions but one was excluded as it was secondary to infection. The revision rate was 10% in patients with a CIA of ≥60° and 1% in those with a CIA of <60° (p=0.017), and 1% in a varus and 4% in a valgus SSA ((p)>0.05) respectively.

CONCLUSIONS

The measurement of the CIA and SSA in hip resurfacings has identified a high risk group for close long-term follow up. There is already a 10% revision rate in those patients with a CIA of >60°. Hip resurfacing may generate a large revision burden in the 'average' surgeon's hands and all hospitals/surgeons should review their radiological outcomes critically and identify those at risk of revision.

Radiographic evaluation of midterm failure rates following metal-on-metal hip resurfacing

This prospective study examined patient characteristics and radiographic findings for 89 subjects undergoing total hip resurfacing. Thirteen (14.6%) of 89 hips have required revision. Female sex, smaller implant size, and diagnosis of osteonecrosis were associated with lower device survival. No significant differences in acetabular cup angle and stem angle were observed between revised and nonrevised hips. Revision rates for the first 25 hips were 24% and 8% for the last 64 hips. Females accounted for 56% of subjects 1 to 25 and 23% of subjects 26 to 89. Despite representing only 33% of included subjects, females accounted for 62% of revision procedures. The lower device survival proportion in subjects 1 to 25 could not be attributed to acetabular or femoral component malpositioning and can likely be explained by a significantly higher proportion of females enrolled early in the study.

Radiology of the resurfaced hip

Hip resurfacing arthroplasty is an increasingly common procedure for osteoarthritis. Conventional radiographs are used routinely for follow-up assessment, however they only provide limited information on the radiological outcome. Various complications have been reported in the scientific literature although not all are fully understood. In an effort to investigate problematic or failing hip resurfacings, various radiological methods have been utilized. These methods can be used to help make a diagnosis and guide management. This paper aims to review and illustrate the radiographic findings in the form of radiography, computerized tomography (CT), magnetic resonance imaging (MRI), and ultrasound of both normal and abnormal findings in hip resurfacing arthroplasty. However, imaging around a metal prosthesis with CT and MRI is particularly challenging and therefore the potential techniques used to overcome this are discussed.

Avoiding short-term femoral neck fracture with imageless computer navigation for hip resurfacing

BACKGROUND

Femoral neck fracture in hip resurfacing has been attributed to technical error during femoral head preparation. In the absence of fracture, several radiographic findings have been speculated to increase the risk of femoral component failure.

QUESTIONS/PURPOSES

We examined whether (1) the use of navigation to reduce technical errors during femoral head preparation reduces the incidence of femoral neck fractures in the short-term followup period; and (2) alignment of the femoral component with the use of computer navigation reduces the incidence of femoral neck thinning, femoral stem radiolucencies, and stem migration.

METHODS

We retrospectively reviewed the first 100 Birmingham Hip Resurfacings performed in 94 prospectively followed patients between October 2005 and November 2007. We examined all radiographs on last followup. Eighty-six patients of the 94 patients had a minimum followup of 2 years (mean, 2.5 years; range, 2-4.1 years).

RESULTS

There were no cases of femoral neck notching, varus femoral component alignment, or femoral neck fractures in the series. Neck thinning of greater than 10% was observed in three patients and perimetaphyseal stem lucencies were noted in 10 patients. In three patients, the metaphyseal stem showed varus migration relative to the postoperative stem-shaft angle at latest followup. There was one revision to a total hip arthroplasty for deep sepsis. The overall survivorship at 4 years was 99%.

CONCLUSIONS

The use of imageless computer navigation to reduce technical errors in hip resurfacing may reduce the incidence of femoral neck fracture in the short-term. However, neck thinning, stem radiolucencies, and stem migration remain radiographic sequelae of hip resurfacing despite the use of navigation for placement of the femoral component.

Radiographic changes of the femoral neck after total hip resurfacing

INTRODUCTION

Significant femoral neck narrowing following hip resurfacing arthroplasty has been observed. Several factors contributing to the physiopathology of femoral neck narrowing have been suggested. The aim of this study was to evaluate the femoral neck radiographic changes observed after hip resurfacing at a minimum follow-up period of 5 years and to determine their causes.

PATIENTS AND METHODS

We conducted a prospective study of 57 hip resurfacing arthroplasties performed in 53 patients (30 men, 23 women) of mean age 49.2 years (32-65) at surgery. These patients were clinically reviewed (inguinal pain during walking, WOMAC and UCLA scores) at 2 years and radiographically examined at 1, 2 and 5 postoperative years. The accuracy of our computer-aided measurement method was 1mm. Measurement of femoral neck to implant ratio was performed to assess the amount of neck thinning at the femoral neck-implant junction (N/H) and midway between the implant and the inter-trochanteric line (N(1/2)H) on an AP radiograph. Neck-thinning greater than 10% was considered as significant. Any other radiographic morphologic change in the femoral neck was investigated. Metallic ion concentration in blood was measured. A uni- and multivariate analysis was performed to determine the correlation with radiographic changes.

RESULTS

In one third of the patients, femoral neck narrowing was greater than 1mm at 2 and 5 postoperative years. Such result corresponds to a mean decrease in neck to implant ratio (N/H) of 5.9% (range, 2.3 to 9.4) at 2 years and 8.3% (range, 2.5 to 23.8) at 5 years. At 5 postoperative years, an overall neck thinning greater than 10% was reported in 3 patients (with a 10- to 17-% increase in femoral neck narrowing between the 2nd and the 5th postoperative year). In one case, neck thinning was associated with fracture of the femoral stem managed with revision surgery during which femoral neck necrosis was confirmed. Neck thinning was, in these cases, circumferential to the neck-implant junction. There was no significant negative impact on clinical scores and no relationship could be established between neck thinning and factors such as BMI or patient activity. Moreover, neck thinning greater than 10% was reported in two cases after 2 postoperative years through the appearance of a localized femoral neck notching which was absent in the postoperative period, secondary to a femoroacetabular impingement.

DISCUSSION-CONCLUSION

Femoral neck narrowing used to be a common phenomenon after HR when polyethylene acetabular bearings were implanted thus inducing osteolysis secondary to PE wear debris. The incidence of such phenomenon has decreased but still occurs after HR when using a metal-on-metal bearing surface. It has an early occurence but stabilizes after 2 postoperative years. Changes in mechanical stress distribution in the neck region after hip resurfacing have been hypothesized to be a cause of neck thinning. Other aetiologies may be suggested. An overall evolutive femoral neck narrowing after 2 postoperative years should raise the suspicion of necrosis leading to a risk of loosening, fracture or implant failure. Therefore, radiographic monitoring should be conducted. The presence of femoral neck notching secondary to femoroacetabular impingement represents a differential diagnosis which conservative treatment is advocated in the absence of any associated symptoms.

Imaging of metal-on-metal hip resurfacing

Conventional radiography is the primary imaging modality to evaluate the condition of hip resurfacing implants and the preferred method of assessing implant stability over time. Radiographs assess the angle of inclination of the femoral and acetabular components, implant stability, and femoral neck narrowing. Ultrasonography detects solid or soft tissue masses adjacent to the implant. Magnetic resonance imaging (MRI) detects osteolysis and complications in the periprosthetic soft tissues such as wear-induced synovitis, periprosthetic collections, neurovascular compression, and quality of the muscle and tendons of the rotator cuff of the hip. For pain after hip resurfacing, early use of optimized MRI is recommended.

The effect of the cam deformity on the insertion of the femoral component in hip resurfacing

Surface arthroplasty simulations were generated using 3-dimensional computed tomographic scans from 61 consecutive patients presenting with idiopathic osteoarthritis to evaluate the change in femoral component positioning that would allow optimal alignment when resurfacing a cam-type deformity. Anatomical parameters were measured to quantify the influence of the deformity on the insertion technique of the femoral implant. A modified femoral head ratio was initially calculated from plain radiographs to define the severity of cam deformity in these patients. A severe deformity required more superior translation of the entry point and greater reaming depth to allow safe insertion with optimal implant alignment. This could be achieved while preserving the leg length, minimizing the component size, and maximizing the amount of host bone contact, although the horizontal femoral offset was reduced. These findings suggest that the femoral component can be safely inserted by modifying the surgical technique despite progressive deformity of the femoral head.

The future of hip resurfacing

With experience in metal-metal resurfacing, several opportunities to improve resurfacing technology have been identified. There is a need for better education on hip resurfacing in residency training programs. The majority of short-term complications associated with resurfacing are related to surgical technique or component position. Innovations to improve acetabular component position and femoral-acetabular mating are needed. Although the majority of high wear and adverse local tissue reactions (ALTR) can be prevented by proper component positioning, the variable exposure to metal particles and ions associated with metal-metal resurfacing components continues to be a concern and bearing surface technology will evolve.

Metal-on-metal hip resurfacing: a critical review

In this article, a concise review of the current literature on metal-on-metal hip resurfacing (MoMHR) is given. In contrast to conventional total hip arthroplasty, older age, female sex and small femoral head sizes predispose to failure. Neck fracture and metal wear-related complications account for the most frequent reasons for re-operations. Although the long-term consequences of metal ion release remain unknown, the increasing prevalence of soft tissue related problems with potentially devastating functional consequences in this younger patient group are of concern. Outcome after revision for metal wear related failure of MoMHR is poor. In our opinion, patients with this device should be managed in dedicated centers with facilities for data collection and monitoring. The majority of proposed advantages of MoMHR cannot be supported by the published evidence.

The biomechanical consequence of insufficient femoral component lateralization and exposed cancellous bone in hip resurfacing arthroplasty

Insufficient lateralization of the femoral component coupled with exposed reamed cancellous bone has been speculated to predispose to femoral neck fracture. The current study examined the effect of mediolateral implant position and exposed cancellous bone on the strength of the resurfaced proximal femur. Composite femurs were prepared in three configurations: (1) partial, with the implant placed at the native femoral head offset of the femur, partially exposing reamed cancellous bone; (2) proud, with a medialized implant exposing a circumferential ring of cancellous bone; and (3) complete, with a lateralized implant covering all reamed cancellous bone. Specimens were loaded to failure in axial compression. A finite element model was used to further explore the effect of exposed cancellous bone, cement mantle thickness, and relative valgus orientation on the strain distributions in the resurfaced femur. The proud group (2063 N) was significantly weaker than both the partial (2974 N, p=0.004) and complete groups (5899 N, p=0.001) when tested to failure. The partial group was also significantly weaker than the complete group when tested to failure (p=0.001). The finite element model demonstrated increasing levels of strain in the superior reamed cortical-cancellous bone interface with increasing degree of exposed cancellous bone. The condition of the femoral component medialized as the result of a thick cement mantle had the greatest detrimental impact on strain level in the superior reamed cancellous bone while a valgus oriented implant provided a protective effect. This study provides biomechanical evidence that exposed reamed cancellous bone significantly reduces the load-to-failure and increases maximum strains in the resurfaced proximal femur. The perceived benefit of reconstructing the femur to its native geometry may inherently weaken the proximal femur and increase femoral neck fracture risk if the femoral component is not sufficiently lateralized to cover all unsupported reamed cancellous bone. Relative valgus orientation of the implant may help to minimize the risk of neck fracture if reamed cancellous bone remains exposed following implant impaction.

Are component positioning and prosthesis size associated with hip resurfacing failure?

Background

Recent studies suggest that there is a learning curve for metal-on-metal hip resurfacing. The purpose of this study was to assess whether implant positioning changed with surgeon experience and whether positioning and component sizing were associated with implant longevity.

Methods

We evaluated the first 361 consecutive hip resurfacings performed by a single surgeon, which had a mean follow-up of 59 months (range, 28 to 87 months). Pre and post-operative radiographs were assessed to determine the inclination of the acetabular component, as well as the sagittal and coronal femoral stem-neck angles. Changes in the precision of component placement were determined by assessing changes in the standard deviation of each measurement using variance ratio and linear regression analysis. Additionally, the cup and stem-shaft angles as well as component sizes were compared between the 31 hips that failed over the follow-up period and the surviving components to assess for any differences that might have been associated with an increased risk for failure.

Results

Surgeon experience was correlated with improved precision of the antero-posterior and lateral positioning of the femoral component. However, femoral and acetabular radiographic implant positioning angles were not different between the surviving hips and failures. The failures had smaller mean femoral component diameters as compared to the non-failure group (44 versus 47 millimeters).

Conclusions

These results suggest that there may be differences in implant positioning in early versus late learning curve procedures, but that in the absence of recognized risk factors such as intra-operative notching of the femoral neck and cup inclination in excess of 50 degrees, component positioning does not appear to be associated with failure. Nevertheless, surgeons should exercise caution in operating patients with small femoral necks, especially when they are early in the learning curve.

Cortical strut allograft as an adjunct to plate fixation for periprosthetic fractures of the femur

The use of cortical strut allografts in the treatment of periprosthetic femoral fractures remain controversial. Complications such as infection and the potential transmission of disease remain concerns. A retrospective review at a tertiary-care hospital was completed of 21 patients who had sustained a periprosthetic femoral fracture and who were treated using a plate and a deep-frozen cortical strut allograft, between 1996 and 2007. The average age at the time of surgery was 80.3 years old and included 16 women and 5 men. Three patients were lost to follow-up and four died within a few weeks of discharge. The remaining 14 patients were evaluated clinically and radiographically with a mean follow-up of 3.2 years. Fracture union was observed in 13 patients, and integration of the graft occurred in 12 patients. One of the 14 patients developed a deep infection with Coagulase-Negative Staphylococcus, with a satisfactory outcome after surgical debridement and antibiotic treatment. There were no cases of fixation failure or plate rupture. At the final evaluation, the mean EQ-5D VAS score was 64 (ranging from 40-90 points) and the mean EQ-5D health state index adapted to Spanish value sets was 0.57. The mean Oxford Hip Score was 31.2. The results support the use of cortical allograft for these fractures to increase the likelihood of fracture healing and to improve the bone stock. We consider that cortical strut grafting is specially indicated for B1 and C fractures in which decreased bone density is present.

[Imageless computer navigation of hip resurfacing arthroplasty]

OBJECTIVE

Precise implantation of hip resurfacing arthroplasty by imageless computer navigation. Hence a malalignment of the femoral component, leading to early loss of the implant, can safely be avoided.

INDICATIONS

Coxarthrosis in patients with normal bone mineral density; only minor deformity of the femoral head that enables milling around the femoral neck without notching.

CONTRAINDICATIONS

Osteoporosis; large necrosis of the femoral head; metal allergy; small acetabular seat and corresponding wide femoral neck, leading to needless acetabular bone loss; pregnancy, lactation.

SURGICAL TECHNIQUE

Hip joint exposure by a standard surgical approach, bicortical placement of a Schanz screw for the navigation array in the lesser trochanter. Referencing of the epicondyles, the four planes around the femoral neck and head by use of the navigation pointer. Planning of the desired implant position on the touchscreen of the navigation device; a guide wire is inserted into the femoral head and neck using the navigated drill guide; navigated depth drilling is performed. The femoral head is milled using the standard instruments. The acetabular bone stock is prepared with the conventional instrumentation; high-viscosity cement is finger-packed on the reamed head and the femoral component is inserted. Hammer blows should be avoided to prevent microfractures. Verification of the implant position by the navigation device; displacement of the Schanz screw; joint reposition and closure of the wound.

POSTOPERATIVE MANAGEMENT

Standard postoperative management after hip arthroplasty.

RESULTS

The comparison of 40 navigated and 32 conventionally implanted ASR prostheses resulted in a significant reduction of outliers by use of computer navigation (navigated procedures: one outlier, conventional procedure: nine outliers; p<0.001). Accuracy of the navigation device was tested by analysis of planned and verified implant position: CCD angle accuracy was 1 degrees , antetorsion accuracy was 1 degrees , and offset accuracy was 1.5 mm. An ongoing computed tomography-based anatomic study proved a varus-valgus accuracy of the navigation device of 1 degrees .

Optimal acetabular orientation for hip resurfacing

Pseudotumours are a rare complication of hip resurfacing. They are thought to be a response to metal debris which may be caused by edge loading due to poor orientation of the acetabular component. Our aim was to determine the optimal acetabular orientation to minimise the risk of pseudotumour formation.

We matched 31 hip resurfacings revised for pseudotumour formation with 58 controls who had a satisfactory outcome from this procedure. The radiographic inclination and anteversion angles of the acetabular component were measured on anteroposterior radiographs of the pelvis using Einzel-Bild-Roentgen-Analyse software. The mean inclination angle (47°, 10° to 81°) and anteversion angle (14°, 4° to 34°) of the pseudotumour cases were the same (p = 0.8, p = 0.2) as the controls, 46° (29° to 60°) and 16° (4° to 30°) respectively, but the variation was greater. Assuming an accuracy of implantation of ± 10° about a target position, the optimal radiographic position was found to be approximately 45° of inclination and 20° of anteversion. The incidence of pseudotumours inside the zone was four times lower (p = 0.007) than outside the zone.

In order to minimise the risk of pseudotumour formation we recommend that surgeons implant the acetabular component at an inclination of 45° (± 10) and anteversion of 20° (± 10) on post-operative radiographs. Because of differences between the radiographic and the operative angles, this may be best achieved by aiming for an inclination of 40° and an anteversion of 25°.

Influence of bone density on the cement fixation of femoral hip resurfacing components

In clinical outcome studies, small component sizes, female gender, femoral shape, focal bone defects, bad bone quality, and biomechanics have been associated with failures of resurfacing arthroplasties. We used a well-established experimental setup and human bone specimens to analyze the effects of bone density on cement fixation of femoral hip resurfacing components. Thirty-one fresh frozen femora were prepared for resurfacing using the original instruments. ASR resurfacing prostheses were implanted after dual-energy X-ray densitometer scans. Real-time measurements of pressure and temperature during implantation, analyses of cement penetration, and measurements of micro motions under torque application were performed. The associations of bone density and measurement data were examined calculating regression lines and multiple correlation coefficients; acceptability was tested with ANOVA. We found significant relations between bone density and micro motion, cement penetration, cement mantle thickness, cement pressure, and interface temperature. Mean bone density of the femora was 0.82 +/- 0.13 g/cm(2), t-score was -0.7 +/- 1.0, and mean micro motion between bone and femoral resurfacing component was 17.5 +/- 9.1 microm/Nm. The regression line between bone density and micro motion was equal to -56.7 x bone density + 63.8, R = 0.815 (p < 0.001). Bone density scans are most helpful for patient selection in hip resurfacing, and a better bone quality leads to higher initial component stability. A sophisticated cementing technique is recommended to avoid vigorous impaction and incomplete seating, since increasing bone density also results in higher cement pressures, lower cement penetration, lower interface temperatures, and thicker cement mantles.

A custom-made guide-wire positioning device for hip surface replacement arthroplasty: description and first results

Background

Hip surface replacement arthroplasty (SRA) can be an alternative for total hip arthroplasty. The short and long-term outcome of hip surface replacement arthroplasty mainly relies on the optimal size and position of the femoral component. This can be defined before surgery with pre-operative templating. Reproducing the optimal, templated femoral implant position during surgery relies on guide wire positioning devices in combination with visual inspection and experience of the surgeon. Another method of transferring the templated position into surgery is by navigation or Computer Assisted Surgery (CAS). Though CAS is documented to increase accurate placement particularly in case of normal hip anatomy, it requires bulky equipment that is not readily available in each centre.

Methods

A custom made neck jig device is presented as well as the results of a pilot study.

The device is produced based on data pre-operatively acquired with CT-scan. The position of the guide wire is chosen as the anatomical axis of the femoral neck. Adjustments to the design of the jig are made based on the orthopedic surgeon's recommendations for the drill direction. The SRA jig is designed as a slightly more-than-hemispherical cage to fit the anterior part of the femoral head. The cage is connected to an anterior neck support. Four knifes are attached on the central arch of the cage. A drill guide cylinder is attached to the cage, thus allowing guide wire positioning as pre-operatively planned.

Custom made devices were tested in 5 patients scheduled for total hip arthroplasty. The orthopedic surgeons reported the practical aspects of the use of the neck-jig device. The retrieved femoral heads were analyzed to assess the achieved drill place in mm deviation from the predefined location and orientation compared to the predefined orientation.

Results

The orthopedic surgeons rated the passive stability, full contact with neck portion of the jig and knife contact with femoral head, positive. There were no guide failures. The jig unique position and the number of steps required to put the guide in place were rated 1, while the complexity to put the guide into place was rated 1-2. In all five cases the guide wire was accurately positioned. Maximum angular deviation was 2.9° and maximum distance between insertion points was 2.1 mm.

Conclusions

Pilot testing of a custom made jig for use during SRA indicated that the device was (1) successfully applied and user friendly and (2) allowed for accurate guide wire placement according to the preoperative plan.