There is ongoing debate on the benefits of fixed versus mobile bearing Unicompartmental Knee Replacement (UKR). We report the results from a randomised controlled trial comparing fixed and mobile bearing of the same UKR prosthesis. Forty patients were randomized to receive identical femoral components and either a fixed or mobile bearing tibial component. At 6.5 years follow-up 37% of the mobile bearing design had been revised and 14% for the fixed bearing design. The main reasons for revision were pain and loosening. These results were compared with data from The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) that show a cumulative percent revision of 24.2% for the mobile bearing Preservation UKR at 6.5 years. All locally explanted mobile bearings were examined microscopically, and 83% demonstrated significant backside wear. Constraint on the undersurface of the bearing coupled with a congruent upper surface may have contributed to the excessive revision rate. This is the first randomised controlled trial examining mobile and fixed variations of the same UKR prosthesis and shows this design of UKR with the mobile bearing has an unacceptably high revision rate and patients with this knee design should be closely monitored.
The aim of this study was to compare a single-incision minimally invasive (MI) posterior approach with a standard posterior approach in a double-blind prospective randomised controlled trial. A pilot study was carried out to assess the efficacy of the MI approach. Primary total hip replacements meeting the inclusion criteria were randomised to either the MI approach or the standard posterior approach. Patients were blinded to allocation. Patients were scored by a blinded physiotherapist pre-operatively, at Day 2, 2 weeks and 6 weeks. The primary outcome measure was function, assessed using the Oxford hip score, SF-12 questionnaire, Iowa score, 6-minute walk test and the number of walking aids required after 2 and 6 weeks post-operatively. Secondary outcomes were complication rates, patient satisfaction, soft tissue trauma and radiographic analysis.Aim
Method
In conclusion we found significantly reduced wear for aluminumoxide heads compared to cobalt chrome heads which could be beneficial for young and active patients.
We have conducted a prospective, observational clinical trial of 34 patients with dual compartment osteoarthritis of the knee treated with a 2/3 Knee.
Exclusion criteria included obesity, inflammatory arthritis and a fixed flexion deformity >
10 degrees. Subjective outcome measures included Oxford Knee Scores (OKS) and EQ-5D Scores. RSA beads were implanted at surgery to detect loosening, micro-motion and prosthesis wear. Gait analysis was conducted at 1 year post op in a subgroup of patients.
The patients have recorded Significant improvement in their Oxford Knee Scores at 6 months (mean reduction all patients: 17.3, resurfaced 20). Early RSA results have not detected Significant migration to indicate early loosening. Gait analysis has shown that patients return to approximate normal rather than pre-operative gait.
It is essential that patients undergo primary patella resurfacing to prevent crepitus and associated anterior knee pain. A study comparing clinical outcomes of 2/3 Knee vs TKA is underway at our institution.
Minimum follow-up was 3 years in group 1 and 1.5 years in group 2. There were 3 dislocations in group 1, and none in group 2. There were 2 re-operations in both groups. The relative improvement in WOMAC scores was significantly greater in group 2 at 3 months and 1 year (P<
0.05).
Patients were scored pre-operatively and followed up prospectively. The only special instruments required are two large curved Hohmann retractors and an angled cup introducer.
Forty-two percent of patients were male. Mean age was 68.9 years (42–90) and BMI 26 (14–39). Average operation time was 64.1 minutes and anaesthetic time 92.5 minutes. Mean fall in haemoglobin in the first 24 hours was 2.3g/dl. Mean incision length was 7.4cm. Follow-up was a minimum of one year (range 12–29 months). There was a highly statistically significant improvement in WOMAC and SF-36 scores at three and 12 months post-operatively (p<
0.0001). Early medical complications occurred in 12 patients, including two superficial infections, all of which resolved. There were no peri-prosthetic fractures and importantly, no dislocations. There were two re-operations: one revision for cup displacement and one washout for deep infection.
In our clinical series, over 30% of patients experienced paraesthesia and some experienced a burning dysaesthesia in the distribution of the LFCN.
In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.
The reported revision rate of total hip arthroplasties (THAs) due to wear and osteolysis is around 10% at 10 years. However, the actual rate is probably higher: the incidence of osteolysis is reported to be 10% to 45%. Apart from design improvements, improved or new materials and/or and combinations are important in reducing particle-induced osteolysis, especially in young and active patients. Wear reduction of up to 40% after inert gas sterilisation of polyethylene (PE) has been demonstrated, both in vitro and in vivo. An effective means of providing further increases in wear resistance is to cross-link PE extensively. Early clinical results of non-melt-annealed PE at three years showed wear reduction of up to 85% compared to inert gas radiation-sterilised PE. In hip joint simulator investigations, bearings with a ceramic ball-head articulating against a composite cup demonstrated wear rates similar to those of ceramic-ceramic bearings. The wear particles are benign. Clinical data collected over two years suggest no disadvantages compared to the standard articulation controls. The wear resistance of alumina-alumina articulation has been enhanced. In-vitro investigation demonstrated that even with a cup inclination of 60° the wear rate is not increased. The effect of micro-separation of the artificial joint is also minimised. Several prospective multi-centre alumina-alumina studies have shown no additional complications with this articulation. However, alumina is a brittle material with an inherent risk of fracture. The addition of 25% zirconia to alumina (ZTA) in the manufacturing process improves its fracture resistance, increasing its strength by more than 50%, while maintaining its other properties. The wear properties of ZTA are even better than that of alumina, especially in micro-separation articulation mode. Highly cross-linked and optimised PE and composite technology are promising concepts in address wear particle-induced osteolysis.
The mean vectorial migration was 0.31 and 0.24 mm and change in inclination 0.2° and 0.2° for the groups. (p>
0.8) Harris Hip Score was 92/96 and the radiological and clinical performance was equal after 2 years.
Post operative stability is of paramount importance to obtain bone in growth and a tight interface in uncemented implants. Although hemispherical press fit cups are widely used different opinions exists according optimal fixation and a variety of principles are preferred. Lab studies show better stability if a cup is augmented by screws or pegs. However, cups with screws and holes increases penetration of joint fluid, pressure and particles to the interface with a risk for osteolyses. HA coating is in many studies favourable to obtain a quick in growth but is by many regarded unnecessary or even a risk for increased wear. This RSA studie was done to investigate stability and wear in cups with different fixation.
Mann-Whitneys U-test was used on signed values for evaluation of group differencies.
Wear was 0.45 mm proximally and in total 0. 6 mm without any sign of differences between the HA and porous coated groups. HA coated cups had less radiolucent lines after 2 years. (p=0.01)
In clinical Orthopaedic research we often need better tools for follow up investigations and evaluation of new methods. One alternative is Radiostereometric analyses (RSA) which can be used for high precision measurements of migration, micro movements and wear. Since developed 25 years ago it has now been used in a few thousand patients and made into a comprehensible computerized, PC based system. Recent development has made it much faster, more accurate and user friendly enough for more common use. RSA can basically measure 3D movements between rigid bodies as bone or implants and is used for many sorts of applications as bone growth, fracture healing, joint kinematics, bone elasticity, spinal fusion etc where a high accuracy is needed. It has, however, mostly been used for research in hip and knee arthroplasty since early migration has been found a good predictor for later implant failure. As also wear in artificial joints can be accurately measured the technique is definitely a useful tool for implant research.
With modern digital x-ray technique we obtain an in vivo precision of about 50 microns longitudinally, 80 horizontally and 200 sagittaly, for rotations 0.1°–0.3°depending on direction, (95% confidence limit).
Some general findings are: In cemented stems the loosening starts at the stem-cement interface and the cement mantles are very well fixed to bone, loosening being a secondary phenomenon. A low temperature curing, non-vacuum mixed cement had equal fixation to bone and stem as a standard vacuum mixed. Some stem designs move a lot inside the cement, possibly with a big risk for cement fractures and abrasion. Especially subsidence and retro version seems ominous. Repeatedly HA coating has shown excellent implant stability, in the same range as cemented components and better than porous coated ones. We have found good and reproducible stability with impaction grafting in both acetabulum and femur using both cemented and uncemented non tapered implants. Structural grafts seem to imply increased migration. Wear has been increased with non irradiated plastic components, in younger patients, if cement contains ZrO as opacifier and together with unstable cemented stems. No correlation has been found between wear and HA coating, head or stem material or weight but decreased wear found for high cross-linked plastics. RSA has been a big asset for Implant research over the years. With the more stable implants and modern bearings of today a high accuracy method is even more needed for to measure fixation and wear, or the actual results will be lost in a lot of noise. The new focus and interest in synergistic effects of implant micro movements, interface stress, hydrostatic pressure and particles for the development of osteolyses is a new area were RSA should be a useful tool to study inducible implant movements and fixation quality in vivo.