Advanced quantitative 3D imaging improves the reliability of the classification of acetabular defects.

INTRODUCTION: Classifying complex acetabular defects in revision total hip arthroplasty (THA) by means of conventional radiographs comes with significant limitations. Statistical shape modelling allows the virtual reconstruction of the native pelvic morphology, hereby enabling an analytic acetabular defect assessment. Our objective was to evaluate the effect of advanced imaging augmented with analytic representations of the defect on (1) intra- and inter-rater reliability, and (2) up- or downscaling of classification scores when evaluating acetabular defects in patients undergoing revision THA. MATERIALS AND METHODS: The acetabular defects of 50 patients undergoing revision THA were evaluated by three independent, fellowship-trained orthopaedic surgeons. Defects were classified according to the acetabular defect classification (ADC) using four different imaging-based representations, namely, standard radiographs, CT imaging, a virtual three-dimensional (3D) model and a quantitative analytic representation of the defect based on a statistical shape model reconstruction. Intra- and inter-rater reliabilities were quantified using Fleiss' and Cohen's kappa scores, respectively. Up- and downscaling of classification scores were compared for each of the imaging-based representations and differences were tested. RESULTS: Overall inter-rater agreement across all imaging-based representations for the classification was fair (κ 0.29 95% CI 0.28-0.30). Inter-rater agreement was lowest for radiographs (κ 0.21 95% CI 0.19-0.22) and increased for other representations with agreement being highest when using analytic defect models (κ 0.46 95% CI 0.43-0.48). Overall intra-rater agreement was moderate (κ 0.51 95% CI 0.42-0.60). Intra-rater agreement was lowest for radiographs (κ 0.40 95% CI 0.23-0.57), and highest for ratings including analytic defect models (κ 0.64:95% CI 0.46-0.82). Virtual 3D models with quantitative analytic defect representations upscaled acetabular defect scores in comparison to standard radiographs. CONCLUSIONS: Using 3D CT imaging with statistical shape models doubles the intra- and inter-rater reliability and results in upscaling of acetabular defect classification when compared to standard radiographs. This method of evaluating defects will aid in planning surgical reconstruction and stimulate the development of new classification systems based on advanced imaging techniques.

Intra-Articular Hyaluronic Acid Injections Less Than 6 Months Before Total Hip Arthroplasty: Is It Safe? A Retrospective Cohort Study in 565 Patients.

BACKGROUND: Intra-articular hyaluronic acid (IAHA) can be injected into an osteoarthritic hip joint to reduce pain and to improve functionality. Several studies report IAHA to be safe, with minor adverse effects that normally disappear spontaneously within a week. However, intra-articular corticosteroids prior to total hip arthroplasty (THA) have been associated with increased infection rates. This association has never been investigated for IAHA and THA. We aimed to assess the influence of IAHA on the outcome of THA, with an emphasis on periprosthetic joint infection (PJI). METHODS: At a mean follow-up of 52 months (±18), we compared complication rates, including superficial and deep PJIs, of THA in patients who received an IAHA injection ≤6 months prior to surgery (injection group) with that of patients undergoing THA without any previous injection in the ipsilateral hip (control group). One hundred thirteen patients (118 hips) could be retrospectively included in the injection group, and 452 patients (495 hips) in the control group. RESULTS: No differences in baseline characteristics nor risk factors for PJI between the 2 groups were found. The clinical outcomes in terms of VAS pain scores (1.4 vs 1.7 points, P = .11), modified Harris Hip Scores (77 vs 75 points, P = .09), and Hip disability and Osteoarthritis Outcome Scores (79 vs 76 points, P = .24) did not differ between the injection group and the control group. Also, complications in terms of persistent wound leakage (0% vs 1.2%, P = .60), thromboembolic events (0% vs 0.6%, P = 1.00), periprosthetic fractures (1.7% vs 1.2%, P = .65), and dislocations (0% vs 0.4%, P = 1.00) did not differ. However, in the injection group there was a higher rate of PJIs (4% vs 0%, P < .001) and postoperative wound infections (9% vs 3%, P = .01), compared to the control group. CONCLUSION: Our findings suggest that IAHA performed 6 months or less prior to THA may pose a risk for increased rates of PJI. We recommend refraining from performing THA within 6 months after IAHA administration.

Two Different Methods to Measure the Stability of Acetabular Implants: A Comparison Using Artificial Acetabular Models.

The total number of total hip arthroplasties is increasing every year, and approximately 10% of these surgeries are revisions. New implant design and surgical techniques are evolving quickly and demand accurate preclinical evaluation. The initial stability of cementless implants is one of the main concerns of these preclinical evaluations. A broad range of initial stability test methods is currently used, which can be categorized into two main groups: Load-to-failure tests and relative micromotion measurements. Measuring relative micromotion between implant and bone is recognized as the golden standard for implant stability testing as this micromotion is directly linked to the long-term fixation of cementless implants. However, specific custom-made set-ups are required to measure this micromotion, with the result that numerous studies opt to perform more straightforward load-to-failure tests. A custom-made micromotion test set-up for artificial acetabular bone models was developed and used to compare load-to-failure (implant push-out test) with micromotion and to assess the influence of bone material properties and press-fit on the implant stability. The results showed a high degree of correlation between micromotion and load-to-failure stability metrics, which indicates that load-to-failure stability tests can be an appropriate estimator of the primary stability of acetabular implants. Nevertheless, micromotions still apply as the golden standard and are preferred when high accuracy is necessary. Higher bone density resulted in an increase in implant stability. An increase of press-fit from 0.7 mm to 1.2 mm did not significantly increase implant stability.

Pinnacle® modular metal-on-metal articulation in primary total hip arthroplasty: mid-term results of 195 cases.

Studies concerning Pinnacle® modular metal-on- metal (MoM) total hip arthroplasty (THA) show better results than for most other MoM THAs. The goal of this study was to report on the revision rate, clinical outcome and metal ion levels regarding this specific prosthesis. Retrospectively selected patients were evaluated clinically, and Visual Analogue Score for pain (VAS), Harris Hip Score (HHS) and Hip disability and Osteoarthritis Outcome Score (HOOS) were determined. Blood metal ion levels were measured. 195 patients were included (mean follow-up 6.4 years). MoM related revision was performed in 5.1%. Clinical outcome was good, with a mean VAS of 6.7 out of 100, HHS of 88.9 and HOOS of 80.7. Five year survival was 96.6%, eight year survival decreased to 90.0%. No correlation could be found between metal ion levels and outcome. Although clinical outcome was good, overall survival of the Pinnacle® MoM is unacceptably low compared to MoP survival.

Outcome of custom-made IMP femoral components of total hip arthroplasty: a follow-up of 15 to 22 years.

A total of 1659 primary THAs using a cemented custom-made intra-operative manufactured prosthesis (IMP)-stem were studied. The end point for survival was defined as revision of the stem for any reason. Revision arthroplasty was performed in 49 cases. The IMP-stems had a revision free 20-year survival rate of 95.5%. Revisions were performed mainly because of aseptic loosening. There were no drawbacks like increased infection risk due to the prolonged surgical time needed for the intra-operative production of the stem. These data provide evidence that the cemented IMP-stem is able to provide good long-term results.

A modified custom-made triflanged acetabular reconstruction ring (MCTARR) for revision hip arthroplasty with severe acetabular defects.

The treatment of extensive acetabular bone loss and pelvic discontinuity in revision total hip arthroplasty remains challenging. We report our preliminary experience with the modified custom-made triflanged acetabular reconstruction ring (MCTARR) in the management of such situations. The MCTARR is a custom-made metal reinforcement ring with a trabecular surface to encourage bone ingrowth and a bulky trabecular metal augmentation to fill the acetabular defects, designed to achieve initial and long-term stability. A custom-made drilling jig is used to achieve optimal screw positioning. The clinical and radiological short-term follow-up (10-58 months) of our first six cases treated with this new technique show acceptable to good results. None of the reconstructions failed or had to be revised. Clinical results were satisfactory. Radiographs showed good screw positioning. The custom-made acetabular drilling jig and the reconstruction of the acetabulum with a titanium porous structure are of added value in the treatment of severe acetabular bone loss and pelvic discontinuity with custom-made triflanged components.

Pinnacle revision cup in acetabular surgery results at 2 to 5 years.

Uncemented revision cups are widely used in revision hip arthroplasty; they have shown good results. We report the the short term outcome with the cementless Pinnacle revision cup. All acetabular revisions using a Pinnacle revision cup between January 2007 and March 2010 were included. In March 2012, clinical scores were determined and the latest radiographs were assessed. Revision and radiographic signs of loosening were reported as failure of the cup. Ths study included 117 patients (118 revision cups) with a follow-up between two and five years. Five cups failed (4%). The median modified Harris Hip Score was 64 (range : 18-91). Survival rates of the Pinnacle revision cup are good in the short term follow-up. This implant appears as a safe and reliable solution for small to moderate acetabular defects.

The morphological variation of acetabular defects in revision total hip arthroplasty-A statistical shape modeling approach.

Classification and evaluation of acetabular defects remain challenging and are primarily based on qualitative classification methods. That is because quantitative techniques describing variations of acetabular defects and accompanying bone loss volume are not available. This study introduces a new method based on statistical shape models (SSMs) to quantitively describe acetabular defects. This method is then applied to 87 acetabular defects to objectively describe the variations in acetabular defects typically encountered during revision total hip arthroplasty. The absolute bone loss volume, relative bone loss volume, and relative bone loss surface area with respect to the SSM-based pre-diseased anatomy were used to quantify the acetabular bone defects in different segments of the acetabular surface. The absolute bone loss volume of the average defect shape was equal to 37.0 cm3 . The first three principal modes, accounting for 62% of the total shape variation, were found to represent variations in acetabular defect morphology. The first, second, and third principal modes described, respectively, the size of the bone defects, the difference between superomedially and superolaterally migrated defects, and the degree of involvement of the posterior or anterior column. The developed SSM and the introduced approach could be used to create automated and unbiased classification methods based on quantitative data. Moreover, the proposed model and the underlying data provide the basis for a quantitative design approach where the shape and size of new acetabular implants are determined according to clinical variation present in acetabular defects.

Acoustic analysis to monitor implant seating and early detect fractures in cementless THA: An in vivo study.

The initial stability of cementless total hip arthroplasty (THA) implants is obtained by an interference fit that allows osseointegration for a long term secondary stability of the implant. Yet, finding the insertion endpoint that corresponds to an appropriate initial stability is currently often based on a number of subjective experiences of the orthopedic surgeon, which can be challenging. In order to assist the orthopedic surgeons in their pursuit to find this optimal initial stability, this study aims to determine whether the analysis of sound that results from the implant insertion hammer blows can be used to objectively monitor the insertion process of cementless THA implants. An in vivo study was conducted. The experimental results revealed vibro-acoustic behavior sensitive to implant seating, related to the low frequency content of the response spectra. This sensitive low-frequency behavior was quantified by a set of specific vibro-acoustic features and metrics that reflected the power and similarity of the low-frequency response. These features and metrics allowed monitoring the implant seating and their convergence agreed well with the endpoint of insertion as determined by the orthopedic surgeon. Intraoperative fractures caused an abrupt and opposite change of the vibro-acoustic behavior prior to the notification of the fracture by the orthopedic surgeon. The observation of such an abrupt change in the vibro-acoustic behavior can be an important early warning for loss of implant stability. The presented vibro-acoustic measurement method shows potential to serve as a decision supporting source of information as it showed to reflect the implant seating.

Development of an Instrument to Assess the Stability of Cementless Femoral Implants Using Vibration Analysis During Total Hip Arthroplasty.

OBJECTIVE: The level of primary implant fixation in cementless total hip arthroplasty is a key factor for the longevity of the implant. Vibration-based methods show promise for providing quantitative information to help surgeons monitor implant fixation intraoperatively. A thorough understanding of what is driving these changes in vibrational behavior is important for further development and improvement of these methods. Additionally, an instrument must be designed to enable surgeons to leverage these methods. This study addresses both of these issues. METHOD: An augmented system approach was used to develop an instrument that improves the sensitivity of the vibrational method and enables the implementation of the necessary excitation and measurement equipment. The augmented system approach took into account the dynamics of the existing bone-implant system and its interaction with the added instrument. RESULTS: Two instrument designs are proposed, accompanied by a convergence-based method to determine the insertion endpoint. The modal strain energy density distribution was shown to affect the vibrational sensitivity to contact changes in certain areas. CONCLUSION: The augmented system approach led to an instrument design that improved the sensitivity to changes in the proximal region of the combined bone-implant-instrument system. This fact was confirmed both in silico and in vitro. Clinical Impact: The presented method and instruments address practical intraoperative challenges and provide perspective to objectively support the surgeon's decision-making process, which will ensure optimal patient treatment.

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 degrees 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.

Comparison of intra-articular injections of hyaluronic acid and corticosteroid in the treatment of osteoarthritis of the hip in comparison with intra-articular injections of bupivacaine. Design of a prospective, randomized, controlled study with blinding of the patients and outcome assessors.

BACKGROUND: Although intra-articular hyaluronic acid is well established as a treatment for osteoarthritis of the knee, its use in hip osteoarthritis is not based on large randomized controlled trials. There is a need for more rigorously designed studies on hip osteoarthritis treatment as this subject is still very much under debate. METHODS/DESIGN: Randomized, controlled trial with a three-armed, parallel-group design. Approximately 315 patients complying with the inclusion and exclusion criteria will be randomized into one of the following treatment groups: infiltration of the hip joint with hyaluronic acid, with a corticosteroid or with 0.125% bupivacaine.The following outcome measure instruments will be assessed at baseline, i.e. before the intra-articular injection of one of the study products, and then again at six weeks, 3 and 6 months after the initial injection: Pain (100 mm VAS), Harris Hip Score and HOOS, patient assessment of their clinical status (worse, stable or better then at the time of enrollment) and intake of pain rescue medication (number per week). In addition patients will be asked if they have complications/adverse events. The six-month follow-up period for all patients will begin on the date the first injection is administered. DISCUSSION: This randomized, controlled, three-arm study will hopefully provide robust information on two of the intra-articular treatments used in hip osteoarthritis, in comparison to bupivacaine. TRIAL REGISTRATION: NCT01079455.

Percutaneous in situ cementation of a loose femoral stem.

This case report describes a patient with aseptic loosening of the femoral component of her total hip arthroplasty 33 years after the initial implantation. The patient was treated with a percutaneous cementation technique using Cortoss (Orthovita, Malvern, Pa) synthetic cortical bone void filler.

Complete slippage of capital femoral epiphysis: total hip arthroplasty with custom-made stem.

Slipped capital femoral epiphysis occurs in adolescents, most often shortly after the onset of puberty. In patients suffering form renal osteodystrophy, the incidence is higher and the condition usually occurs at a younger age. Metabolic changes induce weakening of the bone, which makes the hip joint vulnerable. The initial treatment consists of phosphate-restricted diet, lanthanum carbonate, cinacalcet (a calcimimetic), calcium carbonate and oral calcitriol, aiming at restoration of bone quality. The use of several surgical treatment options has been reported. In this case, which was diagnosed at a later age because no radiographic work-up was performed in the patient's homeland, the only possible treatment option was a total hip arthroplasty. The use of a commercially available femoral stem was impossible because of the abnormal anatomy of the proximal femur. This patient was treated with a custom stem prosthesis manufactured intraoperatively. Six weeks post surgery, HHS and VAS were improved. Ten weeks post surgery a fracture of the femoral diaphysis was treated with revision surgery using a 20 cm long custom-made stem. At 12 weeks post surgery progressive physical therapy is being instituted. Timely detection of slipped capital femoral epiphysis is a cornerstone of adequate management. In this specific case, the diagnosis was missed and salvage treatment required total hip arthroplasty with a stem prosthesis adapted to the patient's anatomy.

Comparison of Constrained Acetabular Components and Dual Mobility Cups in Revision Total Hip Arthroplasty: A Literature Review.

Recurrent instability remains a common cause of failure after revision total hip arthroplasty (THA). Dual mobility (DM) cups and designs with constrained acetabular liners (CAL) have both been developed to help overcome this challenge. The aim of this report is to compare safety and efficacy outcomes of both designs based on the literature. A comprehensive literature review including published evidence on the results of DM and CAL in revision THA was performed and summarized. Available literature focusing on overall survival, dislocation, loosening, intra-prosthetic dislocation (IPD), and functional outcomes were analysed. Forty-six reports including an evaluation of 5,617 total hips were evaluated were included in the review. The included studies were divided into two distinct groups based on implantation approach: i) CAL (n=15) and ii) DM (n=31). The DM group had higher overall survival rates (94.7% vs. 81.0%), lower dislocation rates (2.6% vs. 11.0%), and lower acetabular loosening rates (1.0% vs. 2.0%) compared to the CAL group. IPDs were reported in 6 studies (mean rate, 0.6%). No differences in functional outcomes were identified due to incomplete reports. Our observations reveal that designs with CAL have poorer outcomes as compared to DM cups in revision THA. Currently, the use of DM seems more appropriate since they offer lower rates of dislocations, loosening and re-revisions in the short- and mid-term. Concerns regarding the potential of increased wear in a younger, high-demand population require additional data and evaluation by long-term studies for the DM design.

Accurate reconstructions of pelvic defects and discontinuities using statistical shape models.

Treatment of large acetabular defects and discontinuities remains challenging and relies on the accurate restoration of the native anatomy of the patient. This study introduces and validates a statistical shape model for the reconstruction of acetabular discontinuities with severe bone loss through a two-sided Markov Chain Monte Carlo reconstruction method. The performance of the reconstruction algorithm was evaluated using leave-one-out cross-validation in three defect types with varying severity as well as severe defects with discontinuities. The two-sided reconstruction method was compared to a one-sided methodology. Although, reconstruction errors increased with defect size and this increase was most pronounced for pelvic discontinuities, the two-sided reconstruction method was able to reconstruct the native anatomy with higher accuracy than the one-sided reconstruction method. These findings can improve the preoperative planning and custom implant design in patients with large pelvic defects, both with and without discontinuities.

The Use of a Vibro-Acoustic Based Method to Determine the Composite Material Properties of a Replicate Clavicle Bone Model.

Replicate bones are widely used as an alternative for cadaveric bones for in vitro testing. These composite bone models are more easily available and show low inter-specimen variability compared to cadaveric bone models. The combination of in vitro testing with in silico models can provide further insights in the evaluation of the mechanical behavior of orthopedic implants. An accurate numerical representation of the experimental model is important to draw meaningful conclusions from the numerical predictions. This study aims to determine the elastic material constants of a commonly used composite clavicle model by combining acoustic experimental and numerical modal analysis. The difference between the experimental and finite element (FE) predicted natural frequencies was minimized by updating the elastic material constants of the transversely isotropic cortical bone analogue that are provided by the manufacturer. The longitudinal Young's modulus was reduced from 16.00 GPa to 12.88 GPa and the shear modulus was increased from 3.30 GPa to 4.53 GPa. These updated material properties resulted in an average natural frequency difference of 0.49% and a maximum difference of 1.73% between the FE predictions and the experimental results. The presented updated model aims to improve future research that focuses on mechanical simulations with clavicle composite bone models.

To cement or not to cement acetabular cups in total hip arthroplasty: a systematic review and re-evaluation.

INTRODUCTION: Total Hip Arthroplasty (THA) in the treatment of primary osteoarthritis of the hip has evolved to a very safe and cost-effective intervention with revision rates below 5% after 10 years. To this day, however, controversy remains on whether or not to cement the acetabular cup. METHODS: A comprehensive PubMed search of the English literature for studies published between 2007 and 2018 was performed. Studies comparing the clinical (revision rate, functionality), radiological (wear) or economic (cost) differences between cemented (cemented stem with cemented cup) and hybrid (cemented stem with uncemented cup) prostheses for primary osteoarthritis of the hip were identified as eligible. RESULTS: A total of 1032 studies were identified whereof twelve were included for qualitative synthesis. All studies concerning the risk of revision were based on registry data, covering a total of 365,693 cups. Cemented prostheses had a similar or lower risk of revision compared to hybrid prostheses in every study, but performed slightly worse on functionality and quality of life. While cemented prostheses were the cheapest option, hybrids were the most cost-effective. DISCUSSION: The widespread preference for cementless fixation of the acetabulum cannot be explained by a superior survival of cementless or hybrid models. Irrespective of age, cemented fixation of the acetabulum remains the gold standard to which other techniques should be compared.

Relation between subject-specific hip joint loading, stress distribution in the proximal femur and bone mineral density changes after total hip replacement.

In the prediction of bone remodelling processes after total hip replacement (THR), modelling of the subject-specific geometry is now state-of-the-art. In this study, we demonstrate that inclusion of subject-specific loading conditions drastically influences the calculated stress distribution, and hence influences the correlation between calculated stress distributions and changes in bone mineral density (BMD) after THR. For two patients who received cementless THR, personalized finite element (FE) models of the proximal femur were generated representing the pre- and post-operative geometry. FE analyses were performed by imposing subject-specific three-dimensional hip joint contact forces as well as muscle forces calculated based on gait analysis data. Average values of the von Mises stress were calculated for relevant zones of the proximal femur. Subsequently, the load cases were interchanged and the effect on the stress distribution was evaluated. Finally, the subject-specific stress distribution was correlated to the changes in BMD at 3 and 6 months after THR. We found subject-specific differences in the stress distribution induced by specific loading conditions, as interchanging of the loading also interchanged the patterns of the stress distribution. The correlation between the calculated stress distribution and the changes in BMD were affected by the two-dimensional nature of the BMD measurement. Our results confirm the hypothesis that inclusion of subject-specific hip contact forces and muscle forces drastically influences the stress distribution in the proximal femur. In addition to patient-specific geometry, inclusion of patient-specific loading is, therefore, essential to obtain accurate input for the analysis of stress distribution after THR.

Per-operative vibration analysis: a valuable tool for defining correct stem insertion: preliminary report.

BACKGROUND: Defining the stem insertion end point during total hip replacement still relies on the surgeon's feeling. When a custom-made stem prosthesis with an optimal fit into the femoral canal is used, the risk of per-operative fractures is even greater than with standard prostheses. Vibration analysis is used in other clinical settings and has been tested as a means to detect optimal stem insertion in the laboratory. The first per-operative use of vibration analysis during non-cemented custom-made stem insertion in 30 patients is reported here. MATERIALS AND METHODS: Thirty patients eligible for total hip replacement with uncemented stem prosthesis were included. The neck of the stem was connected with a shaker that emitted white noise as excitation signal and an impedance head that measured the frequency response. The response signal was sent to a computer that analyzed the frequency response function after each insertion phase. A technician present in the operating theatre but outside the laminated airflow provided feed-back to the surgeon. RESULTS: The correlation index between the frequency response function measured during the last two insertion hammering sessions was >0.99 in 86.7% of the cases. In four cases the surgeon stopped the insertion procedure because of a perceived risk of fracture. Two special cases illustrating the potential benefit of per-operative vibration analysis are described. CONCLUSIONS: The results of intra-operative vibration analysis indicate that this technique may be a useful tool assisting the orthopaedic surgeon in defining the insertion endpoint of the stem. The development of a more user-friendly device is therefore warranted.