A pelvic kinematic approach for calculating hip angles for active hip disarticulation prosthesis control.

BACKGROUND: Control system design for a microprocessor-controlled hip-knee-ankle-foot (HKAF) prosthesis is a challenge since hip disarticulation amputees lack the entire leg and, therefore, only have pelvis movement as user-guided input. This research proposes a method for determining hip joint angles from pelvis movement in a control system for the next generation of powered prostheses. METHOD: Three-dimensional pelvic motion and stance time of 10 transfemoral (TF) prosthetic users were used to identify important features and to develop an algorithm to calculate hip angles from pelvis movement based on correlation and linear regression results. The algorithm was then applied to a separate (independent) TF group to validate algorithm performance. RESULTS: The proposed algorithm calculated viable hip angles during walking by utilizing pelvic rotation, pelvic tilt, and stance time. Small angular differences were found between the algorithm results and motion capture data. The greatest difference was for hip maximum extension angle (2.5 ± 2.0°). CONCLUSIONS: Since differences between algorithm output and motion data were within participant standard deviations, the developed algorithm could be used to determine the desired hip angle from pelvis movements. This study will aid the future development of gait control systems for new active HKAF prostheses.

Spontaneous resolution of asymptomatic alumina matrix composite ceramic liner dissociation: a case report.

BACKGROUND: Total hip arthroplasty(THA)is widely used to treat end-stage hip disorders. Ceramic-on-ceramic total hip prostheses are widely used because of their durability. Alumina matrix composite (AMC), known as the fourth-generation ceramics, reduces implant fracture and wear rate compared to their predecessors. However, ceramic acetabular liner dissociation is a complication that necessitates revision of the AMC prostheses. To date, only few cases of AMC liner dissociation have been reported and all of which have been treated with revision surgery. Therefore, the prognosis of non-operated AMC liner dissociation remains unknown so far. CASE PRESENTATION: A 57-year-old man with avascular necrosis of the femoral head was treated with THA, wherein a Pinnacle® (DePuy, J&J, Warsaw, IN) acetabular cup and AMC liner were implanted. Intraoperative examination confirmed proper seating of the liner, whereas the initial postoperative radiograph revealed liner dissociation. The patient refused surgical revision due to the absence of symptoms and was discharged and followed-up. The patient made an uneventful recovery, and radiographic follow-up at 6-month post-operation showed that the liner was re-seated to its right position. No clinical or radiographic anomaly was found at the 15-month of postoperative follow-up. CONCLUSIONS: Here, we report an unprecedented case of AMC ceramic liner dissociation with spontaneous resolution. This case shows that ceramic liner dissociation could be asymptomatic, and careful postoperative examination of the patient is important. Spontaneous resolution is possible, but the underlying mechanism and the eligible patient to benefit from it must be investigated. Before clarifying these questions, revision surgery should be the first-line treatment.

Pregnancy and parturition after hip arthroplasty.

BACKGROUND: The indications for total hip arthroplasty (THA) have become more widespread. Of the patients receiving a THA, some will be women with child-bearing potential. There has been little research into the effects of pregnancy and parturition on THA, and the effect of THA on pregnancy and parturition. METHODS: A systematic search in different database, to December 2020, was performed to define the effects of pregnancy and parturition on THA, and the effect of THA on pregnancy and parturition. Seven suitable studies were identified. RESULTS: Following a THA, there appear to be no harmful effects on subsequent pregnancies with regards to either the health of the mother or baby. There is no increase in pregnancy complications, or difficulties in labour arising from the THA. Some women and their obstetricians may opt for a pre-emptive Caesarian section, but there is no scientific basis for this line of action. The state of pregnancy in turn appears to have no harmful effects on the THA. CONCLUSION: Further research will be useful to better understand which materials and which types of prostheses to use in young women of childbearing age to ensure maximum safety for pregnancy and childbirth.

Comparison of different fixation techniques for periprosthetic fractures: a biomechanical study of a new implant.

INTRODUCTION: The ideal treatment method for periprosthetic fractures is controversial due to the risks of current methods. Single-cortex screw fixation in prosthesis may lead to implant failure. Therefore, we aimed to develop an implant that lowers the risk for complications. For this study, we designed and tested two new implant models. The first model was a plate with a combination of U nails and cerclage holes. The second model was a U nail plate with a screw, which combines a plate screw with U nail (staples). Our study aimed to compare the stability of two newly designed implants with classical treatment modalities. We used 27 (in 3 groups) artificial bone models and 9 different test models. METHODS: The ISO 7206-4:2010 (E) standards were used for 27 bones in nine groups tested under laboratory conditions. In our study, we examined nine different groups. In group 1, hip the prosthesis was extracted, and a revision femoral stem was embedded. In group 2, periprosthetic fractures were repaired with a plate and cable. In group 3, periprosthetic fractures were repaired with a plate and stapler. In group 4, periprosthetic fractures were repaired with a plate and stapler cable. In group 5, periprosthetic fractures were repaired with a plate stapler and screw. Groups 6 and 7 were the control groups. Group 6 was the only artificial bone group, and group 7 was the prosthesis embedded bone group. Group 8 was periprosthetic fractures treated with unicortical screw fixation with cerclage, and group 9 was periprosthetic fractures treated with unicortical screw fixation. Axial loading was applied to the bones. The yield strength of the system was determined by loading the synthetic bone models with a constant compression speed of 5 mm/min through the centre of motion using the Geratech SH 2000 testing system. During the tests, load and displacement values were recorded, and the stiffness of the models was calculated based on those values. RESULTS: According to our results, the greatest durability was found in the revision hip prosthesis group (1511 N), and the weakest performance was found in the plate with the stapler implant group (163N). When comparing the data of groups according to compression, significant differences were found in group 2 with groups 1, 4, 5, and 7; group 3 with group 1; group 8 with groups 1 and 5; and group 9 with 1, 5, 7, and according to breakage, significant differences were found in group2 with groups 1, 3, 5, and 7; group 3 with group 1; group 8 with groups 1 and 5; and group 9 with groups 1, 5, and 7 (p<0.001). DISCUSSION: The revision hip prosthesis treatment for periprosthetic fractures showed the best performance, followed by the plate with stapler screw. In older patients, U nail-augmented implants may be a good alternative for periprosthetic fractures. Unicortical screw and cerclage wire combination fixation results were unsatisfactory results in this study. CONCLUSION: This is an experimental study, so further studies, especially patient-specific studies, should be made to expand the findings of this study.

Course of Metal Ions after a Revision of Malfunctioning Metal-on-Metal Total Hip Prostheses.

The present research evaluated the course of cobalt and chromium in the blood and urine after the revision of metal-on-metal with a ceramic-on-polyethylene total hip arthroplasty. Seven patients were enrolled for hip prosthesis revision owing to ascertained damage of the implant. Metals in the blood and urine were evaluated before and after the hip revision. The double measurement before the total hip revision revealed high levels of metal ions (on average, 88.1 µg/L of cobalt in the blood, 399.0 µg/g of creatinine cobalt in the urine, 46.8 µg/L of chromium in the blood, and 129.6 µg/g of creatinine chromium in the urine at the first measurements), with an increasing trend between the first and second dosage. Within a week after the hip revision, the levels of metal ions significantly decreased by approximately half. Four to six months after the operation, the cobalt levels were found near to the reference values, whereas the chromium levels reached 25% of the values measured before the revision. The revision of malfunctioning metal-on-metal implants produced a dramatic decrease of metal ions in biological fluids, although it did not completely rescue the chromium level.

Numerical prediction of temperature elevation induced around metallic hip prostheses by traditional, split, and uniplanar gradient coils.

PURPOSE: The paper presents a computational study for the estimation of the temperature elevation occurring in a human subject carrying metallic hip prostheses when exposed to the magnetic field produced by gradient coils. METHODS: The simulations are performed through validated numerical codes, which solve the electromagnetic and thermal equations applied to a high-resolution anatomical human model. Three different sets of gradient coils (traditional, split and uniplanar) are considered to evaluate the maximum steady-state temperature elevation in the human body. This result is then rescaled to take into account the waveform of the signal, the duty-cycle and the duration of the scan. RESULTS: Several exposure situations obtained by changing the patient's position are analyzed, finding temperature elevations on the order of some degrees. CONCLUSION: The results are of possible concern and provide evidence of the need for further specific investigations aimed at assuring the safety of potential patients carrying metallic hip implants. Magn Reson Med 74:272-279, 2015. © 2014 Wiley Periodicals, Inc.

Predictivity and fate of metal ion release from metal-on-metal total hip prostheses.

Blood metal ion levels in 72 patients with large head metal-on-metal hip arthroplasty were studied to determine the correlation between the values measured in whole blood and urine. Urinary cobalt and chromium levels of 30µg and 21µg, respectively, adjusted to creatinine were found to correspond to the 7µg/l cut-off value that has been accepted in whole blood. Cobalt and chromium levels in whole blood and urine both significantly correlated with increased acetabular component inclination angle over 50 degrees and pain scores. There was no correlation with socket anteversion angle or femoral head diameter. The data support the use of urinary measurement of metal ions adjusted to creatinine to monitor patients with large head metal-on-metal total hip arthroplasty.

Mid-term study of bone remodeling after femoral cemented stem implantation: comparison between DXA and finite element simulation.

This five-year prospective study was designed to investigate periprosthetic bone remodeling associated with two cemented stem models, ABG-II (Stryker) and VerSys (Zimmer), randomly implanted in patients older than 75 years. The sample consisted of 64 cases (32, ABG-II; 32, VerSys). Inclusion criterion was diagnosis of osteoarthritis recommended for cemented total hip arthroplasty. Besides clinical study, Finite Element (FE) simulation was used to analyze biomechanical changes caused by hip arthroplasty. Bone Mineral Density (BMD) measurements showed a progressive increase in bone mass throughout the entire follow-up period for both stems, well correlated with FE results except in Gruen zones 4, 5, 6 for ABG-II and in zones 4, 5 for VerSys, denoting that remodeling in those zones does not depend on mechanical factors but rather on biological or physiological ones.

Restoring Hip Joint Anatomy With the Robotic Arm-Assisted System in Hip Fractures: Expanding the Applications for Hip Surgery.

Total hip arthroplasty (THA) has improved the life quality of osteoarthritic patients, yet challenges persist. The robotic arm-assisted system, integrated into THA, aims to refine implant positioning, enhance precision, reduce errors, and restore the hip joint's anatomy, including hip center, femoral offset, and limb length. We present the first use of the system for the treatment of a subcapital femoral neck hip fracture. A 62-year-old female suffering a left subcapital hip fracture underwent THA using the robotic arm-assisted system. After acetabular registration, accurate component placement was achieved, and a 9-mm limb length discrepancy was addressed. The patient had an unremarkable recovery with a reported Harris hip score of 96.5 at 18 months postsurgery. Robotic-guided navigation in THA, as showcased in this case, ensures accurate implant positioning by restoring the anatomical features of the hip joint. Its potential extends beyond conventional applications, hinting at future use in trauma, revision, and oncology cases. While promising, future adaptations should consider soft tissue dynamics to ensure joint stability and overall success.

The Insertion of Threaded Acetabulum Components: Indications According to Specific Acetabulum Anatomy and Methods to Avoid Pitfalls.

New-generation threaded acetabulum components have been used in total hip arthroplasty (THA) with good outcomes. We have extensively used the EcoFit® SC cup (Implantcast, Buxtehude, Germany) in our practice. In this report, we present some major complications related to the use of this implant, as well as insights regarding the surgical technique to avoid such adverse effects. Furthermore, we attempt to describe certain contraindications for using threaded cups in THA, taking into account specific patient anatomy and intraoperative acetabulum preparation. We have observed acetabulum roof and posterior wall fractures, as well as incomplete placement of the component. Ensuring the meticulous preparation of the peripheral rim of the acetabulum is crucial to prevent incomplete placement since threaded components have a larger diameter than that of the reamers used to prepare the acetabulum. Additionally, when dealing with the acetabula where the posterior or anterior walls have thinned, it is advisable to refrain from using a threaded cup to avoid the risk of intraoperative fractures caused by the torque forces exerted during implant insertion.

Fracture Of An Exeter™ V40™ Stem Through The Insertion Guide Hole And Revision Using Cement-In-Cement Technique.

Fracture of the Exeter™ V40™ stem is uncommonly reported in the literature. The cement-in-cement femoral revision is a described technique for revising well-cemented femoral components during revision hip arthroplasty. We present our experience using this technique in managing a fractured Exeter™ V40™ stem. There have been 24 reported Exeter™ V40™ stem fractures: 12 at the body and 12 at the neck. 3 of the reported fracture at the neck cases have occurred at the superior aspect of the neck-shaft junction which is an unusual site for failure of this stem. Our patient's fracture pattern matches this unusual presentation. This report has added to the limited evidence indicating the area around the insertion guide hole as a potential site through which stem fracture may begin and propagate inferiorly. The cement-in-cement technique may be successfully employed in managing Exeter™ V40™ stem fractures, without need for extended trochanteric osteotomy or cortical window.

Carbon-Ion Radiotherapy Using Metal Artifact Reduction Computed Tomography in a Patient with Prostate Cancer with Bilateral Hip Prostheses: A Case Report.

Carbon-ion radiotherapy (CIRT) for prostate cancer is both safe and efficacious; beam range calculations use relative stopping power ratio, which is derived from computed tomography (CT) values. However, hip prostheses are made of high atomic number materials and show severe artifacts on CT images. Therefore, it is not possible to accurately calculate dose distribution for CIRT in patients with prostate cancer with hip prostheses. Here, we describe the management of a 77-year-old man with prostate cancer who had previously undergone bilateral hip replacement. CIRT, in combination with androgen deprivation therapy, was recommended as definitive treatment for prostate cancer. Planning CT, magnetic resonance (MRI), and CT images with metal artifact reduction (MAR) were acquired for CIRT planning. MRI and MAR images were superimposed on the planning CT to delineate target volume and organs at risk. The radiation treatment plan consisted of a total dose of 51.6 Gy (relative biological effect) to be delivered in 12 fractions over 3 weeks, and the patient was irradiated in the supine and prone positions with a vertical beam, on alternating days. CIRT was completed as scheduled. No adverse events were observed during treatment or at 3 months after treatment initiation. While we show that CIRT may be a treatment option for patients with prostate cancer with bilateral hip prostheses, further studies are needed to evaluate treatment efficacy and late toxicity and to determine how CIRT can be administered to patients with prostate cancer with bilateral hip prostheses.

Could Short Stems THA Be a Good Bone-Saving Option Even in Obese Patients?

Short femoral stems, with preservation of the femoral bone stock, are commonly used in recent years for hip replacement in younger and more active patients. Obesity is increasingly spreading even in the younger population. The aim of this case-series study is to evaluate short stems compared to traditional hip prostheses in the obese population. A total of 77 consecutive patients with a BMI greater than or equal to 30 Kg/m2 were enrolled in this prospective study and were divided into two groups: 49 patients have been implanted with short stems while 28 patients were implanted with traditional stems. All the patients were treated for primary osteoarthritis or avascular necrosis and all the stems were implanted by the same surgeon using a posterior approach. Clinical (Harris Hip Score­HHS, Western Ontario and McMaster Universities Osteoarthritis Index­WOMAC, visual analogue scale­VAS, 12-item Short Form Health Survey­SF-12) and radiographic outcomes were recorded. Radiological evaluations were carried out by three different blinded surgeons. A statistical analysis was performed (chi-square, t-test, Wilcoxon Rank Sum Test, 2-factor ANOVA). At a mean follow-up of 42.6 months both groups showed a marked improvement in pain and in the clinical scores between pre- and post-surgical procedures (p < 0.05) with no significant differences between the two groups at last follow-up (p > 0.05). The radiological evaluations, with high concordance correlation between the three blinded surgeons (ICC consistently >0.80), showed good positioning and osseointegration in all cases, with no significant differences in the restoration of the joint geometry and complications. No revisions were recorded during the follow-up period. In conclusion, short stems appear to be a good option for bone preservation even in obese patients, showing comparable results to traditional implants.

Results of the short neck-retaining stem prostheses CFP with a minimum follow-up of 10 years. / Resultado del vástago corto con preservación del cuello femoral CFP con un seguimiento mínimo de 10 años.

BACKGROUND AND OBJECTIVE: Bone-preserving implants in primary total hip arthroplasty have become an increasingly popular treatment choice, especially short stems. Currently there are many models with morphological and biodynamic differences, among which stand out the neck-retaining systems, but there are not many studies with a long-term follow-up of these systems. The objective of this study is to retrospectively analyze the results of the Collum Femoris Preserving (CFP) short neck-retaining stem system with a minimum follow-up of 10 years. MATERIAL AND METHODS: Between 2001 and 2010, 175 prostheses with a CFP stem were performed in 157 patients in our hospital. All patients were operated on by a single surgeon. The mean age at the time of surgery was 56.47 years (range 22-77). RESULTS: 175 prostheses have been evaluated with a minimum follow-up of 10 years and a mean of 13.89 years (range 10-19), with 16 cases having been lost. During the follow-up there were 8 polyethylene replacements, 2 cup replacements due to loosening, 2 osteosynthesis due to fracture without loosening, and 5 stem replacements: 1 due to chronic infection, 2 due to fracture and 2 due to aseptic loosening. CONCLUSIONS: As far as we know, this is the first follow-up work on a short stem implanted in our country with a minimum of 10 years of follow-up. The replacement of this stem due to aseptic loosening has been 2/159 and, therefore, survival for this reason is 98.75% at 10 years.

MINIMA Short Stem Versus Standard Profemur (TL) Stem in Primary Total Hip Replacement: A Comparative Study.

BACKGROUND: The objective of our study was to compare a novel squared section, tapered design - with four conicity - short stem, the MINIMA® short stem with the cementless Profemur® TL standard femoral stem in primary total hip arthroplasty (THA) in terms of functional outcomes, radiologic evaluation and other peri-operative and post-operative data. MATERIAL AND METHODS: This is a comparative study including 46 patients undergoing primary THA. In 23 patients, the MINIMA® short stem was used. These patients were matched with another 23 patients in whom a cementless Profemur® TL standard femoral stem was used. The levels of the pain were evaluated according to the Visual Analog Scale/Numerical Rating Scale (VAS/NRS). The functional and clinical evaluation of the patients was performed with Harris Hip Score (HHS), Charnley's Hip score, EuroQol (EQ-5D)-(EQ-100), Patient Health Questionnaire (PHQ-9), and neuropathic pain questionnaire (DN-4). The rest of the comparison data included demographic data, the American Society of Anesthesiologists score (ASA), Charlson Index score, the pre-operative diagnosis, radiographic evaluation, the days of hospitalization, the operating time, incision length, blood loss, and blood transfusion requirements and complication rates. RESULTS: The two cohorts had comparable results regarding all patients' peri-operative data. The radiographic assessment revealed considerable higher levels of femoral offset and femoral subsidence for the MINIMA group, but within acceptable limits for both cohorts. The majority of the functional and other scores did not give strong prominence to one specific femoral stem. CONCLUSION: Our comparative study underlined the efficacy of the MINIMA® short stem, due to the fact that it revealed comparable and, in some cases, relatively better short-term outcomes compared with the TL standard femoral stem. Yet, more well-designed long-term research is required in order to further establish its effectiveness.

MRI only in a patient with prostate cancer with bilateral metal hip prostheses: case study.

OBJECTIVE: To outline a practical method of performing prostate cancer radiotherapy in patients with bilateral metal hip prostheses with the standard resources available in a modern general hospital. The proposed workflow is based exclusively on magnetic resonance imaging (MRI) to avoid computed tomography (CT) artifacts. CASE DESCRIPTION: This study concerns a 73-year-old man with bilateral hip prostheses with an elevated risk prostate cancer. Magnetic resonance images with assigned electron densities were used for planning purposes, generating a synthetic CT (sCT). Imaging acquisition was performed with an optimized Dixon sequence on a 1.5T MRI scanner. The images were contoured by autosegmentation software, based on an MRI database of 20 patients. The sCT was generated assigning averaged electron densities to each contour. Two volumetric modulated arc therapy plans, a complete arc and a partial one, where the beam entrances through the prostheses were avoided for about 50° on both sides, were compared. The feasibility of matching daily cone beam CT (CBCT) with MRI reference images was also tested by visual evaluations of different radiation oncologists. CONCLUSIONS: The use of magnetic resonance images improved accuracy in targets and organs at risk (OARs) contouring. The complete arc plan was chosen because of 10% lower mean and maximum doses to prostheses with the same planning target volume coverage and OAR sparing. The image quality of the match between performed CBCTs and MRI was considered acceptable. The proposed method seems promising to improve radiotherapy treatments for this complex category of patients.

Long-term results of the custom- made hip endoprostheses Evolution K® and Adaptiva®: A prospective cohort study.

The aim of our study is to evaluate clinical long-term results and determine changes in periprosthetic bone density of the custom-made hip prostheses Evolution-K ® and Adaptiva ® . Periprosthetic bone density were evaluated by means of DEXA (LunariDXA- Prodigy® bone densitometer) with a long-term follow-up of 16 (15-18) years (Evolution-K®) in 24 patients and 13 (13-15) years (Adaptiva®) in 41 patients. Evolution- K® had a survival rate of 92% and yielded 79/100 points in Harris Hip Score, a mediocre result. Adaptiva® had a survival rate of 99% and achieved a good score of 88/100 points. Bone density measurements demonstrated the greatest loss of bone density in the proximal regions of interest (ROI) for both prosthesis types (Evolution-K®: -25.8% ROI 1, -40.3% ROI 7; -8.3% ROI 2, -10.4% ROI 6; Adaptiva®: -29.8% ROI 7, -6.8% ROI 6, +14.3% ROI 3, +3.1% ROI 4). Adaptiva® yielded a good clinical result as compared to Evolution-K® with only average clinical results. Both prostheses clearly showed signs of "stress shielding". Here, the Adaptiva® achieved reduced bone density loss as compared to the Evolution-K®.

Cemented versus cementless bipolar hemiarthroplasty for femoral neck fractures in the elderly.

The management of femoral neck fractures remains controversial. Treatment options include a wide variety of internal fixation methods, unipolar or bipolar hemiarthroplasty or total hip replacement.We carried out a systematic review of the available literature to detect differences between cemented and cementless fixation of bipolar prostheses in treating femoral neck fractures in patients aged 60 years or older.Thirteen studies involving a total of 1561 bipolar hemiarthroplasties (770 cemented and 791 uncemented) were identified. Uncemented hemiarthroplasty was associated with significantly lower blood loss (p < 0.0001), shorter operative time (p < 0.0001), less infection (p = 0.03) and lower risk of heterotopic ossification (p = 0.007). On the other hand, patients with cemented hemiarthroplasty suffered significantly less postoperative thigh pain than those with cementless implantation (p < 0.00001).The existing evidence indicates that uncemented bipolar hemiarthroplasty offers shorter operative time, less blood loss, lower local complications and a similar rate of systemic complications and reoperations as compared to cemented implantation. Cite this article: EFORT Open Rev 2021;6:380-386. DOI: 10.1302/2058-5241.6.200057.

Biological Monitoring of Metal Ions Released from Hip Prostheses.

The aim of this study was to evaluate the levels of As, Be, Bi, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Se, Tl, V, and Zn, by inductively coupled plasma-mass spectrometry (ICP-MS) in the urine of two groups of patients with two different types of metal-on-metal (MoM) total hip prostheses (ASR DePuy®, group A, 25 patients; total Met-Met System Lima®, group B, 28 patients). The determination of metals reflected a steady-state release (group A: 9 years after surgery and group B: 6 years after surgery). The results obtained confirmed the increase of Co and Cr urinary levels in both group when compared with the reference values for the general population adopted by the Italian Society of Reference Values (SIVR). In particular, Co and Cr levels exceeded the threshold values in urine, respectively, of 30 µg and 21 µg, adjusted to creatinine based on the threshold in whole blood of 7 µg/L proposed by the Medicines and Healthcare Products Regulatory Agency (MHRA). Regarding the other investigated metals, significantly higher values were found in Group A than in Group B. These differences could be due to the type of hip prosthesis implanted, the longer period of time since the implantation, as well as many other factors such as diet, age, drug consumption, physical activity, or presence of dental fillings. The continuous monitoring over the years of metal concentrations in patients carrying a prosthesis could be useful to better identify the sources of these metals.

Geometric Variations of Modular Head-Stem Taper Junctions of Total Hip Replacements.

Taper degradation in Total Hip Replacements (THR) has been identified as a clinical concern, and the degradation occurring at these interfaces has received increased interest in recent years. Wear and corrosion products produced at the taper junction are associated with adverse local tissue responses, leading to early failure and revision surgery. Retrieval and in-vitro studies have found that variations in taper design affect degradation. However, there is a lack of consistent understanding within the literature of what makes a good taper interface. Previous studies assessed different design variations using their global parameters assuming a perfect cone such as: taper length, cone angle and diameters. This study assessed geometrical variations of as-manufactured head and stem tapers and any local deviations from their geometry. The purpose of this study was to provide a greater insight into possible engagement, a key performance influencing parameter predicted by Morse taper connection theory. This was achieved by taking measurements of twelve different commercially available male tapers and six female tapers using a coordinate measurement machine (CMM). The results suggested that engagement is specific to a particular head-stem couple. This is subject to both their micro-scale deviations, superimposed on their macro-scale differences. Differences in cone angles between female and male tapers from the same manufacturer was found to create a predominately proximal contact. However, distally mismatched couples are present in some metal-on-metal head-stem couples. On a local scale, different deviation patterns were observed from the geometry which appeared to be linked to the manufacturing process. Future work will look at using this measurement methodology to fully characterise an optimal modular taper junction for a THR prosthesis.