Between 1999 and 2002, we revised 72 hips in 69 patients using this technique (mean age 65years, 28 to 88). Fifty-six cases had aseptic loosening, 8 had infection (2 stages), 7 had peri-prosthetic fractures and 1 had a broken stem. The mean time to revision was 8.5years (1 to 21). Patients were assessed clinically and with the Oxford Hip Score (OHS) pre- and post-operatively. Fifty-seven patients also had acetabular revision. Four patients required femoral osteotomy to remove the old prosthesis. We used a mean of 1.8 (1 to 4) femoral heads per operation. Complications included 6 peri-operative femoral fractures diagnosed at operation and fixed successfully, 6 infections, 10 dislocations (2 were recurrent), one deep vein thrombosis, 2 pulmonary embolism and one gastrointestinal haemorrhage. The average blood transfusion was 1.8 units (0 to 9). The OHS improved from 45 (26 to 58) pre-operatively to 24.3 post-operatively (12 to 43). No hip has been re-revised for aseptic loosening at a mean follow-up of 32.7 months (16 to 51).
There is an increasing interest amongst surgeons and demand from patients for hip resurfacing. One concern regarding resurfacing is the incidence of femoral neck fracture post operatively. McMinn and Treacy report an incidence of 0.4% in their series, our finding was of an incidence of over four times as high (1.9%). We looked at our database of hip resurfacings and tried to identify the risk factors for fracture. We identified 11 fractures and compared these with 22 controls selected by choosing the cases performed by the surgeon immediately before and after the fracture case. We analysed their medical notes and x-rays. Statistical analysis was performed using a package in ™Excel. The implants were either Birmingham Hip (Midland Medical Technologies) or Cormet (Corin) resurfacings. No statistically significant correlation was found for sex, age or body mass index. We found that fracture was twice as likely in the presence of possible or probable osteopenia. We did not find that fracture was more likely to occur in patients with a previous diagnosis of Perthes, DDH, SUFE and avascular necrosis (AVN). We found patients with a superior overhang of the femoral component on the neck did not risk fracture, however we could not demonstrate that notching in itself increased the risk of fracture. There was no correlation with neck-shaft and stem-shaft angle or neck lengthening and offset and subsequent neck fracture. In 13 bilateral cases there was fracture in 3 (incidence 23%). Apart from one fracture that occurred at 18 weeks post-operatively all the others occurred before eight weeks. Five fractures occurred in patients who subsequently on histological analysis were found to have avascular necrosis. We conclude that bilateral surgery is probably unwise. That a superior overhang seems to protect against fracture as long as this is not at the expense of creating an inferior notch. Finally, we find AVN in a number of retrieved heads, what is the true incidence of AVN and does the approach adopted cause the avascular process and if so why do we see so few fractures?
Despite impressive overall results at one year, lower knee scores were associated with a surgeons ‘learning curve’. After this ‘learning curve’, increased surgical experience led to further improvement with 90% achieving an excellent result, 8% a good, 2% a fair and 0% a poor result.
Polyethylene wear remains an important cause of failure in knee replacements. Retrieval studies, simulators and simple X-ray methods produce wear data that may be inaccurate or unrealistic. We have developed an accurate RSA system for measuring wear in-vivo. Using this system we have found wear rate in a fixed bearing TKR to be about 0.1mm/yr[ Four Oxford uni-compartmental knee replacements, with excellent clinical results were studied ten years after implantation. RSA X-rays were taken in double leg stance with the knee in full extension and 15 and 30 degrees flexion. Following RSA calibration, silhouettes of the components on the stereo X-rays were extracted using a Canny edge detector and were matched to silhouettes projected using CAD models to determine the 3D component position. The average minimum thickness of the bearing was determined and was compared with the measured minimum thickness of 14 unused bearings to calculate linear penetration. The average linear penetration after average 10 years implantation (range 8.5 to 10.25 years) was 0.16 mm (SD 0.13 mm). The average penetration rate was 0.017 mm/year (SD 0.011 mm/year). The maximum linear penetration rate was 0.027 mm/year. The penetration rate is similar to that obtained in a retrieval study [
Increasing the width of the proximal section of a polished tapered stem enhances its rotational stability.
The Birmingham hip resurfacing (BHR) arthroplasty is a metal-on-metal prosthesis for which no medium- or long-term results have been published. Despite this, it is increasing in popularity as an alternative to stemmed prostheses for younger patients. Since the fixation of the socket is conventional, the major concern is long-term failure of the femoral component. This can be predicted by the use of roentgen stereophotogrammetric analysis (RSA). We have therefore undertaken such a study of the BHR femoral component over a period of two years. Twenty patients (22 hips) underwent a standard BHR procedure. Migration of the femoral component was measured by RSA at intervals of three, six, 12 and 24 months. At 24 months the total three-dimensional migration of the head was 0.2 mm. This was not statistically significant. Previous studies have shown that implants which loosen quickly have rapid early migration. Our results therefore suggest that the BHR femoral component is an inherently stable device which is likely to perform well in the long term.
The relative motion between a prosthesis, the cement mantle and its’ host bone during weight bearing is not well understood. Using Radiostereophotogrammetric Analysis (RSA), we examined the dynamically inducible micromotion that exists at these interfaces when an increased load is placed through the prosthesis. Dynamically inducible micromotion was measured in the femoral components of 21 subjects undergoing total hip replacement with polished Exeter stems. Two standing RSA studies were performed, at 3 and 12 months postoperatively. Firstly in double-leg stance, and secondly fully weight bearing through the operated hip. Subjects had no signs of clinical or radiological signs of loosening at 1 year. Significant micromotion was detected at the prosthesis-cement interface at 3 months. Similar patterns of micromotion were observed at 12 months. The prosthesis appeared to bend during single-leg stance weight bearing, however this accounted for less than half of the total observed movement. Conventional RSA studies were conducted at 3 months, 6 months and 1 year to confirm that the implants showed normal migration patterns. This study demonstrates that movement exists between the prosthesis and bone during cyclical weight bearing. This dynamically inducible micromotion probably occurs at the prosthesis-cement interface. It could account for the wear that is observed on the surface of retrieved secure prostheses. This may be a mechanism by which failure eventually occurs.
The aim of the study was to measure in-vivo the 10-year linear and volumetric polyethylene wear of a fully congruent mobile bearing unicompartmental knee arthroplasty (OUKA). We studied six OUKA’s that had all been implanted 10 years previously. Each patient was examined in even double leg stance at a range of knee flexion angles, in a calibration cage. A stereo pair of X-ray films was acquired for each patient at 0°, 15° and 30° of flexion. The films were analysed using an RSA style calibration and a CAD model silhouette-fitting technique. The position and orientation of each femoral and tibial component was found relative to each other and the bearing position inferred. Penetration of the femoral component into the original volume of the bearing was our estimate of linear wear. The volumetric wear is calculated from the measured linear wear and the known surface area of the bearing. In addition eight control patients were examined less than 3 weeks post-operation where no wear would be expected.and 30We studied seven OUKA’s that had all been implanted at least 10 years previously. A stereo pair of X-ray films was acquired for each patient at 0 Results: The control group showed no measured wear. The seven OUKA’s had an average maximum depth of linear penetration of 0.40 mm at a mean follow-up of 10.9 years. The linear wear rate was 0.033 mm/year. The volumetric material loss was 79.8 mm3. If a steady gradual material loss is assumed, 8 mm3 of UHMWPE was lost per year. Polyethylene particulate wear debris continues to be implicated in the aetiology of component loosening and implant failure knee following arthroplasty. The OUKA employs a spherical femoral component and a fully congruous meniscal bearing to increase contact area and theoretically reduce the potential for polyethylene wear. The results from this in-vivo study confirm that the device has low 10-year linear and volumetric wear in clinical practice. This may protect the device from component loosening in the long term.
The Birmingham reSurfacing Arthroplasty (BSA) is a metal on metal prosthesis with no published independent clinical studies. Despite this, it is increasing in popularity, especially as an alternative to stemmed prostheses in younger patients. This study presents the 1year migration results of the BSA femoral component using Roentgen Stereophotogrammteric Analysis (RSA). Twenty six subjects underwent a BSA, through the postero-lateral approach using CMW3G cement, with RSA marker balls placed intra-operatively. The femoral component migration was measured at intervals of 3, 6 and 12 months using the Oxford RSA system. Geometric algorhythms were used to identify the femoral component. The data was examined for distribution prior to analysis. All statistical analysis was performed using the t-test. The data was normally distributed. The 1 year migration results of the BSA femoral component are displayed below. All cemented implants migrate in vivo. The majority of cemented stemmed implant migration occurs within the first post-operative year. High rates of migration within the first post-operative year correlate with premature component failure in some instances. The BSA is a fundamentally different design to most cemented prostheses, despite this we know that very large migrations, those in excess of 2mm/year in any direction are generally regarded as poor indicators of long term outcome. These results suggest that the BSA femoral component is an inherently stable device as it does not migrate significantly within the first post-operative year. Only long-term independent clinical studies and continued RSA follow-up will enable a comprehensive evaluation of the device.
Before proceeding to longer-term studies, we have studied the early clinical results of a new mobile-bearing total knee prosthesis in comparison with an established fixed-bearing device. Patients requiring bilateral knee replacement consented to have their operations under one anaesthetic using one of each prosthesis. They also agreed to accept the random choice of knee (right or left) and to remain ignorant as to which side had which implant. Outcomes were measured using the American Knee Society Score (AKSS), the Oxford Knee Score (OKS), and determination of the range of movement and pain scores before and at one year after operation. Preoperatively, there was no systematic difference between the right and left knees. One patient died in the perioperative period and one mobile-bearing prosthesis required early revision for dislocation of the meniscal component. At one year the mean AKSS, OKS and pain scores for the new device were slightly better (p <
0.025) than those for the fixed-bearing device. There was no difference in the range of movement. We believe that this is the first controlled, blinded trial to compare early function of a new knee prosthesis with that of a standard implant. It demonstrates a small but significant clinical advantage for the mobile-bearing design.
This early study examines the influence of a wider shoulder on the 1 year migration of a cemented, polished, tapered stem, using RSA. Polished, tapered stems (PTS) have excellent 10 year survival rates. RSA studies have demonstrated that these devices subside about 1 mm / year. Small amounts of subsidence are beneficial in stabilising a stem. Stem rotation (measured as posterior head migration) within the cement mantle is probably a more important mechanism of failure than subsidence. Stems with a wider proximal portion are thought to better resist rotation. The CPS (Endoplus, UK) is such a device; here we compare its’ stability with that of the Exeter. 20 patients received the CPS-plus stem and underwent RSA examinations at 3, 6 and 12 months postoperatively. The Exeter 1 year migration data was used as a comparison. Both groups underwent a Hardinge approach with CMW3G cement. Both stems subsided about 1mm. The CPS showed less medio-lateral and A-P movement of the proximal stem than the Exeter over 1 year, as shown below: The CPS internally rotates less than the Exeter, as demonstrated by the smaller amount of posterior head migration. It has a lateral flare of the shoulder; making its cross-section wider than the Exeter’s, this probably accounts for its’ greater resistance to rotation. The CPS also undergoes less medio-lateral proximal stem migration. Its’ lateral shoulder flare is probably responsible for this axial subsidence, as it prevents the shoulder from moving laterally whilst subsiding over the calcar. A PTS with a broad proximal section is more stable, this may confer an increased survival advantage.
Results at one year (TMK first): AKSS(Knee) 91.6 / 84.1 (p=0.003), OKS 39.8 / 37.6 (p=0.006), ROM 104 / 104 (p=0.364), Pain (AKSS) 47.3 / 41.7 (p=0.01), Pain (OKS) 3.5 / 2.9 (p=0.006).
The Oxford hip score (OHS) is a patient-based instrument for assessment of outcome which is often used after total hip replacement, and the EuroQol 5D (EQ5D) is a patient-based generic questionnaire for health assessment. In an analysis of the outcome at one year of 609 revision hip replacements (RHRs), we compared the OHS and EQ5D scores, postoperative patient satisfaction and change in pain. About 25% of the operations were repeat RHRs. At one year, 57% of patients were very pleased with their operation. The correlation between preoperative and postoperative scores and change scores for the OHS and EQ5D was high. For both instruments the effect sizes were large, but the greater effect size of the OHS suggests that it is particularly sensitive to improvements after RHR. The effect scores of the OHS declined with the number of previous RHRs, while those for the EQ5D seemed less sensitive. Our results confirm the value of the OHS in assessing outcome after RHR.
Ultrasound examination has been recommended for the evaluation of acute haemorrhages into soft tissues or joints in haemophilic patients. We have reviewed the notes of all such patients admitted during one calendar year and find that in 47 separate admissions the ultrasound examination assisted management decisions on 27 occasions. The technique is described with an analysis of the ways in which ultrasound observations may influence the clinician.
