Manual impaction, with a mallet and introducer, remains the standard method of installing cementless acetabular cups during total hip arthroplasty (THA). This study aims to quantify the accuracy and precision of manual impaction strikes during the seating of an acetabular component. This understanding aims to help improve impaction surgical techniques and inform the development of future technologies. Posterior approach THAs were carried out on three cadavers by an expert orthopaedic surgeon. An instrumented mallet and introducer were used to insert cementless acetabular cups. The motion of the mallet, relative to the introducer, was analyzed for a total of 110 strikes split into low-, medium-, and high-effort strikes. Three parameters were extracted from these data: strike vector, strike offset, and mallet face alignment.Aims
Methods
Cementless acetabular components rely on press-fit fixation for initial stability. In certain cases, initial stability is more difficult to obtain (such as during revision). No current study evaluates how a surgeon’s impaction technique (mallet mass, mallet velocity, and number of strikes) may affect component fixation. This study seeks to answer the following research questions: 1) how does impaction technique affect a) bone strain generation and deterioration (and hence implant stability) and b) seating in different density bones?; and 2) can an impaction technique be recommended to minimize risk of implant loosening while ensuring seating of the acetabular component? A custom drop tower was used to simulate surgical strikes seating acetabular components into synthetic bone. Strike velocity and drop mass were varied. Synthetic bone strain was measured using strain gauges and stability was assessed via push-out tests. Polar gap was measured using optical trackers.Aims
Methods
The hip's capsular ligaments (CL) passively restrain extreme range of motion (ROM) by wrapping around the native femoral head/neck, and protect against impingement and instability. We compared how CL function was affected by device (hip resurfacing arthroplasty, HRA; dual mobility total hip arthroplasty, DM-THA; and conventional THA, C-THA), and surgical approach (anterior and posterior), with and without CL surgical-repair. We hypothesized that CL function would only be preserved when native head-size (HRA/DM-THA) was restored. CL function was quantified on sixteen cadaveric hips, by measuring ROM by internally (IR) and externally rotating (ER) the hip in six functional positions, ranging from full extension with abduction to full flexion with adduction (squatting). Native ROM was compared to ROM after posterior capsulotomy (right hips) or anterior capsulotomy (left hips), and HRA, and C-THA and DM-THA, before and after CL repair. Independent of approach, ROM increased most following C-THA (max 62°), then DM-THA (max 40°), then HRA (max 19°), indicating later CL engagement and reduced biomechanical function with smaller head-size. Dislocations also occurred in squatting after C-THA and DM-THA. CL-repair following HRA restored ROM to the native hip (max 8°). CL-repair following DM-THA reduced ROM hypermobility in flexed positions only and prevented dislocation (max 36°). CL-repair following C-THA did not reduce ROM or prevent dislocation. For HRA and repair, native anatomy was preserved and ligament function was restored. For DM-THA with repair, ligament function depended on the movement of the mobile-bearing, with increased ROM in positions when ligaments could not wrap around head/neck. For C-THA, the reduced head-size resulted in inferior capsular mechanics in all positions as the ligaments remained slack, irrespective of repair. Choosing devices with anatomic head-sizes (HRA/DM-THA) with capsular repair may have greater effect than surgical approach to protect against instability in the early postoperative period.
The hip joint capsular ligaments (CL) passively restrain extreme range of motion (ROM) by wrapping around the native femoral head, and protect against impingement, edge loading wear and dislocation. This study compared how ligament function was affected by device (hip resurfacing arthroplasty, HRA; dual mobility total hip arthroplasty, DM-THA; and conventional THA, C-THA), with and without CL repair. It was hypothesized that ligament function would only be preserved when native anatomy was preserved: with restoration of head-size (HRA or DM-THA) and repair. Eight normal male cadaveric hips were skeletonised, retaining the hip capsule. CL function was quantified by measuring ROM by internally (IR) and externally rotating (ER) the hip in six functional positions, ranging from full extension with abduction to full flexion with adduction (squatting). Native ROM was compared to ROM after posterior capsulotomy and HRA, and C-THA and DM-THA, before and after surgical CL repair. ROM increased most following C-THA (max 62°), then DM-THA (max 40°), then HRA (max 19°), indicating later engagement of the capsule and reduced biomechanical function with smaller head-size. Dislocations also occurred in When HRA was combined with repair, native anatomy was preserved and ligament function was restored. For DM-THA with repair, ligament function depended on the movement of the mobile bearing resulting in near-native function in some positions, but increased ROM when ligaments were unable to wrap around the head/neck. Following C-THA, the reduced head-size resulted in inferior capsular mechanics in all positions as the ligaments remained slack, irrespective of repair. Choosing devices with anatomic head-sizes (resurfacing or dual-mobility) and repairing the capsular ligaments may protect against instability in the early postoperative period.
The hip joint capsular ligaments passively restrain extreme range of motion (ROM), protecting the native hip against impingement, subluxation, edge loading and dislocation. This passive protection against instability would be beneficial following total hip arthroplasty (THA), however the reduced femoral head diameter postoperatively may prevent a wrapping mechanism that is essential to capsular ligament function in the native hip. Therefore we hypothesized that, post-THA, the reduced femoral head size would prevent the capsular ligaments protective biomechanical function. In vitro, THA was performed through the acetabular medial wall preserving the entire capsule, avoiding targeting a particular surgical approach. Eight fresh-frozen cadaveric hips were examined and capsular function was measured by internally/externally rotating the hip in five positions ranging from full extension with abduction, to full flexion with adduction. Three head sizes (28, 32, 36 mm) with three neck lengths (restored native 0, +5, +10 mm) were compared.Background
Methods
The hip joint capsule passively restrains extreme range of motion protecting against impingement, dislocation and possibly edge loading. These functions would be advantageous following total hip arthroplasty (THA) however the degree of capsular excision, preservation and/or repair greatly varies between surgeons/approaches. Therefore, we asked: how does THA affect capsular ligamentous biomechanics? Which factors have the biggest influence? For this laboratory based, cadaveric model, THA was performed through the acetabular medial wall, thus preserving the entire hip capsule. A previously published testing rig was used to measure capsular function by internally and externally rotating the hip in each of five hip positions (standing, sitting, gait heel strike, and two impingement risk positions, full flexion with adduction & extension with abduction). N=8 hips were tested both before and after THA allowing for repeated measurements between the native and replaced hip. The ROM before the capsule engaged increased following THA Following THA, the capsular ligaments were no longer able to wrap around the smaller femoral head thereby limiting their ability to restrain excessive hip movement. The anterior capsule is affected less than the posterior, and may benefit from being preserved length. A repair to the posterior capsule should compensate for the reduced THA head size in order to restore function.
The current, most popular recommendation for cup orientation, namely the Lewinnek box, dates back to the 70's, that is to say at the stone age of hip arthroplasty. Although Lewinnek's recommendations have been associated with a reduction of dislocation, some complications, either impingement or edge loading related, have not been eliminated. Early dislocations are becoming very rare and most of them probably occur in “outlier” patients with atypical pelvic/hip kinematics. Because singular problems usually need singular treatments, those patients need a more specific personalised planning of the treatment rather than a basic systematic application of Lewinnek recommendations. We aim in this review to define the potential impacts that the spine-hip relations (SHRs) have on hip arthroplasty. We highlight how recent improvements in hip implants technology and knowledge about SHRs can substantially modify the planning of a THR, and make the «Lewinnek recommendations» not relevant anymore. We propose a new classification of the SHRs with specific treatment recommendations for hip arthroplasty whose goal is to help at establishing a personalized planning of a THR. This new classification (figures 1 and 2) gives a rationale to optimize the short and long-term patient's outcomes by improving stability and reducing edge loading. We believe this new concept could be beneficial for clinical and research purposes.
In approximately 20 years, surgical treatment of femoro-acetabular impingement (FAI) has been widely accepted, and its indications refined. However, the current approach of the disease prevents a good understanding of its pathophysiology, and numerous uncertainties remain. Comprehending inter-individual spine-hip relations (SHRs) can further clarify the pathophysiology of impingement, and explain occasional surprising mismatch between clinical assessment and imaging or intraoperative findings. The rational is simple, the more the spino-pelvic complex is mobile (sagittal ROM) and the more the hip is protected against hip impingement but would probably become at risk of spine-hip syndrome if the spino-pelvic complex comes to degenerate. Grouping patients based on their spine-hip relation can help predict and diagnose hip impingement, and assess the relevance of physiotherapy. With the proposed new classification of FAIs, every patient can be classified in homogeneous groups of complexity of treatment. The primary aim of this paper is to raise awareness of the potential impact that the spine-hip relations have on the hip impingement disease. Two new classifications are proposed, for FAIs and SHRs that can help surgeons in their comprehension, and could be beneficial in clinical and research areas.
Optimal results from uncemented total hip arthroplasty (THA) requires the prosthesis to obtain initial stability, restoration of biomechanics, bone contact along the ingrowth surface and uniform stress transfer to the proximal femur. Anatomic variation within the population makes this difficult to reproduce in every patient. To achieve optimal fit and fill of the proximal femur, options are reshaping the canal or creating an implant which precisely fits the patient's anatomy. The former increases bone loss and risks weakening the supporting bone, creating areas of stress concentration or shielding. Computer assisted design-computer assisted manufacture (CAD-CAM) femoral components were designed to overcome these issues. We present the long term results of CAD-CAM femoral components used in primary THA. This was a prospective study looking at a consecutive, single surgeon series of THA's. Patients were reviewed pre operatively then at 6 weeks, 3 and 12 months post operatively and then yearly. Clinical as well as radiological review was performed at each visit and Harris Hip Score (HHS), Oxford Hip Score (OHS) and Western Ontario McMaster's (WOMAC) scores were calculated. Kaplan-Meier survival analysis was performed.Introduction
Methods
The variability of the endosteal geometry after removal of the femoral component can make proximal fit difficult to achieve with an ‘off the shelf’ prosthesis. Whatever the anatomy of the proximal femur, it is important to achieve immediate stability, preserve bone stock and protect the femur from cortical defects which can lead to subsequent fracture. In revision Total Hip Arthroplasty (THA) this requires a large inventory of modular components. The use of custom computer-assisted design-computer-assisted manufacture (CAD-CAM) components negates this need. Little has been published on the use of custom-made components in revision THA. We report the results of a cohort of patients who underwent revision THA using CAD-CAM femoral components. A prospective study was performed between 1991 and 1998. A consecutive series of patients who had revision THA using custom components were assessed clinically and radiologically. The design of the femoral components was governed by the existing femoral bone stock. Patients were reviewed pre operatively then at 6 weeks, 3months and 12 months postoperatively and then annually. Radiographs were assessed at each visit and Oxford, Harris and WOMAC hip scores were calculatedIntroduction
Methods
Metal on metal hip resurfacing arthroplasty (MoM HR) has the highest revision rates according to the UK National Joint Registry. Revisions for lesions associated with soft tissue necrosis (pseudotumors) have been associated with poor outcomes. There is a relative paucity of information on early revision of painful HR prostheses. We present the results of a series of patients who underwent early revision of painful MoM HR procedures. This prospective study involved a consecutive series of patients undergoing revision of HR to THA. The diagnoses leading to revision are discussed. Clinical and radiological assessments were performed pre operatively as well as 6 weeks, 12 months postoperatively and yearly thereafter. Pre and post operative Harris Hip Score, Oxford Hip Score and WOMAC scores were calculated. Patient satisfaction was assessed using a visual analogue scale.Introduction
Methods
There is no consensus on the ideal management of young, active patients with disabling coxarthrosis. Within this group, patients with femoral head defects secondary to cysts or avascular necrosis pose particular challenges. Resurfacing arthroplasty is contraindicated and the results of traditional total hip arthroplasty are suboptimal in this group. The BMHR was designed to offer a bone conserving option for these patients. We report the outcome of this device in the short term. This prospective study examines the clinical and radiological outcome of a consecutive series of patients treated with the BMHR arthroplasty. All patients had femoral head defects and disabling hip pain. Patients were reviewed pre operatively and then at 6 weeks, 12 weeks, and 1year post operatively and then yearly. Oxford, Harris and WOMAC hip scores were calculated at each review. Radiological assessment was also performed at each follow up.Introduction
Methods
The National Joint Registry has recently identified failure of large head metal on metal hip replacements. This failure is associated with the high torque at the interface of standard modular taper junction leading to fretting and corrosion. A number of manufacturers produce mini spigots, which in theory, provide a greater range of motion as the neck head junction is reduced. However, the relative torque to interface ratio at this junction is also increased. In this study we investigated hypothesis that the use of small spigots (minispigots) will increase wear and corrosion on modular tapers. Wear and corrosion of spigots were compared in-vitro when loaded with a force representative of the resultant force passing through the hip. The heads (female tapers) were made of cobalt-chrome-molybdenum (CoCrMo) and the stems (male tapers) of titanium alloy (Ti). Commercially available tapers and heads were used. The surface parameters & profiles were measured before & after testing. Electrochemical static and dynamic corrosion (pitting) tests were performed on minispigots under loaded and non-loaded conditions.Introduction
Methods
Patients with osteochondrodysplasia frequently require Total Hip Arthroplasty at a younger age, as a result of early degenerative disease of the hip joint. The outcome of Modular Total Hip Arthroplasty in this group of patients has been reported previously. In this retrospective study we evaluated the outcome of custom made (CADCAM) Total Hip Arthroplasty in patients with osteochondrodysplasia. Between 1974 and 2009, twenty one CADCAM Total Hip Arthroplasty procedures were performed in fourteen patients in our institution. There were eight female and six male patients, with the mean age at time of surgery of 40.95 years (20 to 78). The patients were followed up clinically and with the Harris hip score for a mean of 7.12 years (0.5 to 17 years). Four of the twenty-one hips (23.8%) required revision surgery at a mean of 11.54 years (6.5 to 17 years); one required it for aseptic loosening of the femoral component; one required complete revision of the acetabular component; one required exchange of acetabular liner; and one was for symptomatic non-union of a lesser trochanter avulsion. This study shows encouraging clinical outcomes of custom made (CADCAM) Total Hip Arthroplasty in patients with osteochondrodysplasia,
Total hip replacements have shown great benefits to patients through relief of pain and restoration of function. However, because of the extensive variation in the size and shape of the femoral canal, especially for the situation encountered in the revision hip arthroplasty, standard uncemented hip systems with a limited number of sizes are unable to provide an accurate fit in every case. This study showed clinical results of 112 primary total hip replacements and 158 revision total hip replacements, using custom made CAD-CAM (Computer Aided Design-Computer Aided Manufactured) hip prostheses inserted between 1992 and 1998. For primary hip replacements, the implants were designed to produce proximal line-to-line fit with the femoral bone and to provide optimal biomechanical environment of the hip. The stem was HA coated, 53 males and 58 females were included. Mean age was 46.2 years (range 24.6yrs - 62.2 yrs). The average duration of the follow up was 24 years (10 – 17 years). The mean Harris Hip Score (HHS) was improved from 42.4 to 90.3, mean Oxford Hip Score (OHS) was improved from 43.1 to 18.2 and the mean WOMAC hip score was improved from 57.0 to 11.9. There was 1 revision due to failure of the acetabular components but there were no failures of the femoral components. In the whole follow-up period, the survival of the femoral stem alone was 100%. For revision hip replacements, the implants were designed using our design strategies of graduate approach to different revision situation based on Paprosky's classification of femoral bone defect. The implants were HA coated; some of them had distal cutting flutes. A total of 158 patients (97 males and 61 females) who had operation between 1991 and 1998 were followed up, among them 138 cases were due to aseptic loosening, 6 cases were periprosthetic fractures and 14 cases were infection. The average age was 63.1 years (range 34.6 – 85.9 years). The minimum follow up was 10 years (range 10 – 12 years). The mean Harris Hip Score was improved from 44.2 to 89.3, mean Oxford Hip Score was improved from 41.1 to 18.2 and the mean WOMAC hip score was improved from 52.4 to 12.3 respectively. 6 cases required further revision surgery, among them 3 were due to aseptic implant loosening, the overall survivorship at ten years was 97%. The CAD-CAM hip stems are able to provide optimal implant fixation and restore hip function for every patient regardless their original femoral shape, bone condition and biomechanics of the hip. The excellent medium to long term clinical results justifies the use of CAD-CAM custom hip stems.
We report a prospective study of clinical data collected pre, intra and post operation to remove both cup and head components of 118 failed, current generation metal on metal (MOM) hips. Whilst component position was important, the majority were unexplained failures and of these the majority (63%) had cup inclination angles of less than 55 degrees. Poor biocompatibility of the wear debris may explain many of the failures. Morlock et al reported a retrospective analysis of 267 MOM hips but only 34 head and cup couples (ie most were femoral neck fractures) and without data necessary to define cause of failure. The commonest cause of failure in the National Joint Registry (NJR) is unexplained.SUMMARY
BACKGROUND
We present the medium to long term clinical results of 112 Uncemented custom Computer Assisted Design Computer Assisted Manufactured (CAD-CAM) total hip arthroplasties performed between 1992 and 1998 in 111 patients. Fifty three males and 58 females were included. Mean age was 46.2 years (range 24.6yrs - 62.2 yrs). Average duration of follow up was 156 months (120 – 204 months). The mean Harris Hip Score (HHS) improved from 42.4 to 90.3, mean Oxford Hip Score (OHS) improved from 43.1 to 18.2 and the mean WOMAC hip score improved from 57.0 to 11.9. There was 1 revision due to failure of the acetabular components but there were no failures of the femoral components. There were no revisions for aseptic loosening. The worst case survival in this cohort of custom femoral components at an average 13 year follow up (range 10-17 years) was 98.2% (95% Confidence interval 95% to 99%). Survival of the femoral component alone was 100%. These results are comparable with the best medium to long term results for femoral components used in primary total hip arthroplasty (THA) with any means of fixation.
There were ten revisions. Kaplan-Meier analysis showed survival of 96.5% (95% confidence interval 94.7 to 98.4) at 7 years taking revision for any cause as the end-point. There was a 3.9 times higher failure rate in women compared to men.
Wear measurements of 100 explanted hips have been carried out on a Taylor Hobson 365 Roundness Machine using the LIRC Wear Protocol. It was found that 50% of explanted cups were wearing less than 5 μm/year and 60% of components were wearing less than 10 μm/year. Wear tests on hip joint simulators predict wear rates between 2 and 8 μm/year. However, 6% of cups are wearing faster than 100 μm/year, with 16% of cups have wear patches deeper than 100 μm and that 4% have a wear patch deeper than 300 μm.
Cup position is an important factor, all of the high wearing components are outside the Lewinick’s Box, however it is shown that mal position is does not always lead to extreme wear. Further analysis is taking place to calculate the size of the contact patch between head and cup (based on patient data and biomechanics) and the proximity of the contact patch to the edge of the cup.
There were ten revisions. Kaplan-Meier analysis showed survival of 96.5% (95% confidence interval 94.7 to 98.4) at 7 years taking revision for any cause as the end-point. There was a 3.9 times higher failure rate in women compared to men.
