Treatment of full thickness focal cartilage lesions with a metallic resurfacing implant in a sheep animal model, 1 year evaluation.

BACKGROUND: Full depth focal cartilage lesions do not heal spontaneously and while some of these lesions are asymptomatic they might progress to osteoarthritis. Treatment for these lesions is warranted and the gold standard treatment at younger age remains biological healing by cell stimulation. In the middle-age patient the success rate of biologic treatment varies, hence the surge of non-biological alternatives. Our objective was to evaluate the efficacy and safety of a metallic implant for treatment of these lesions with respect to the long-term panarticular cartilage homeostasis. METHODS: The medial femoral condyle of 16 sheep was operated unilaterally. A metallic implant was inserted in the weight-bearing surface at an aimed height of 0.5 mm recessed. Euthanasia was performed at 6 or 12 months. Implant height and tilt was analyzed using a laser-scanning device. Damage to cartilage surfaces was evaluated macroscopically and microscopically according to the Osteoarthritis Research Society International (OARSI) recommendations. RESULTS: Thirteen sheep were available for evaluation and showed a varying degree of cartilage damage linearly increasing with age. Cartilage damage of the medial tibial plateau opposing the implant was increased compared to the non-operated knee by 1.77 units (p = 0.041; 95% CI: 0.08, 3.45) on a 0-27 unit scale. Remaining joint compartments were unaffected. Implant position averaged 0.54 recessed (95% CI: 0.41, 0.67). CONCLUSIONS: Our results showed a consistent and accurate placement of these implants at a defined zone. At this position cartilage wear of opposing and surrounding joint cartilage is limited. Thus expanded animal and human studies are motivated.

Positive effect of removal of subchondral bone plate for cemented acetabular component fixation in total hip arthroplasty: a randomised RSA study with ten-year follow-up.

We hypothesised that the removal of the subchondral bone plate (SCBP) for cemented acetabular component fixation in total hip arthroplasty (THA) offers advantages over retention by improving the cement-bone interface, without jeopardising implant stability. We have previously published two-year follow-up data of a randomised controlled trial (RCT), in which 50 patients with primary osteoarthritis were randomised to either retention or removal of the SCBP. The mean age of the retention group (n = 25, 13 males) was 70.0 years (sd 6.8). The mean age in the removal group (n = 25, 16 males) was 70.3 years (sd 7.9). Now we have followed up the patients at six (retention group, n = 21; removal group, n = 20) and ten years (retention group: n = 17, removal group: n = 18), administering clinical outcome questionnaires and radiostereometric analysis (RSA), and determining the presence of radiolucent lines (RLLs) on conventional radiographs. RSA demonstrated similar translation and rotation patterns up to six years. Between six and ten years, proximal acetabular component migration and changes of inclination were larger in the retention group, although the mean differences did not reach statistical significance. Differences in migration were driven by two patients in the SCBP retention group with extensive migration versus none in the SCBP removal group. The significant difference (p < 0.001) in the development of radiolucent lines in the retention group, previously observed at two years, increased even further during the course of follow-up (p < 0.001). While recognising SCBP removal is a more demanding technique, we conclude that, wherever possible, the SCBP should be removed to improve the cement-bone interface in order to maximise acetabular component stability and longevity.

Fixation of a double-coated titanium-hydroxyapatite focal knee resurfacing implant: a 12-month study in sheep.

OBJECTIVE: Focal cartilage lesions according to International Cartilage Repair Society (ICRS) grade 3-4 in the medial femoral condyle may progress to osteoarthritis. When treating such focal lesions with metallic implants a sound fixation to the underlying bone is mandatory. We developed a monobloc unipolar cobalt-chrome (Co-Cr) implant with a double coating; first a layer of commercially pure titanium (c.p.Ti) on top of which a layer of hydroxyapatite (HA) was applied. We hypothesised that such a double coating would provide long-lasting and adequate osseointegration. DESIGN (MATERIALS AND METHODS): Unilateral medial femoral condyles of 10 sheep were operated. The implants were inserted in the weight-bearing surface and immediate weight-bearing was allowed. Euthanasia was performed at 6 (three animals) or 12 months (six animals). Osseointegration was analysed with micro-computer tomography (CT), light microscopy and histomorphometric analyses using backscatter scanning electron microscopy (B-SEM) technique. RESULTS: At 6 months one specimen out of three showed small osteolytic areas at the hat and at 12 months two specimens out of six showed small osteolytic areas at the hat, no osteolytical areas were seen around the peg at any time point. At both time points, a high total bone-to-implant contact was measured with a mean (95% confidence interval - CI) of 90.6 (79-102) at 6 months and 92.3 (89-95) at 12 months, respectively. CONCLUSIONS: A double coating (Ti + HA) of a focal knee resurfacing Co-Cr implant was presented in a sheep animal model. A firm and consistent bond to bone under weight-bearing conditions was shown up to 1 year.

Focal knee resurfacing and effects of surgical precision on opposing cartilage. A pilot study on 12 sheep.

BACKGROUND: Full thickness cartilage lesions (ICRS grade 3-4) and focal lesions of degenerative origin may progress to osteoarthritis (OA). Such focal lesions can be treated by metallic implants. We hypothesized that such treatment results in opposing surface cartilage damage that correlates with implant position (height) relative to the adjacent cartilage surface. This relationship was investigated using a sheep animal model. METHODS: Both medial femoral condyles of 12 sheep were operated. The implants, were inserted in the weight-bearing surface at different heights relative to the surrounding cartilage. Euthanasia was performed at 6 or 12 weeks. After retrieval, implant height was analyzed using laser scanning. Damage to the opposing tibial cartilage was evaluated macroscopically and microscopically according to the modified Mankin score. RESULTS: Twenty-two knees were available for evaluation and showed cartilage lesions ranging from severe damage (Mankin stage 11) to almost pristine conditions (Mankin stage 1). There was a strong correlation between implant height and cartilage damage. Standard deviation from the aimed implant height was 0.47 mm. CONCLUSIONS: Our results showed significant surgical imprecision and protruding implants imposed severe cartilage damage. We therefore suggest implants should be placed recessed (approx. 0.5 mm) below the surrounding cartilage in this animal model. These results encourage further studies of metallic implants yet the utmost precision regarding position is required.

The importance of adequate stem anteversion for rotational stability in cemented total hip replacement: a radiostereometric study with ten-year follow-up.

Progressive retroversion of a cemented stem is predictive of early loosening and failure. We assessed the relationship between direct post-operative stem anteversion, measured with CT, and the resulting rotational stability, measured with repeated radiostereometric analysis over ten years. The study comprised 60 cemented total hip replacements using one of two types of matt collared stem with a rounded cross-section. The patients were divided into three groups depending on their measured post-operative anteversion (< 10°, 10° to 25°, > 25°). There was a strong correlation between direct post-operative anteversion and later posterior rotation. At one year the < 10° group showed significantly more progressive retroversion together with distal migration, and this persisted to the ten-year follow-up. In the < 10° group four of ten stems (40%) had been revised at ten years, and an additional two stems (20%) were radiologically loose. In the 'normal' (10° to 25°) anteversion group there was one revised (3%) and one loose stem (3%) of a total of 30 stems, and in the > 25° group one stem (5%) was revised and another loose (5%) out of 20 stems. This poor outcome is partly dependent on the design of this prosthesis, but the results strongly suggest that the initial rotational position of cemented stems during surgery affects the subsequent progressive retroversion, subsidence and eventual loosening. The degree of retroversion may be sensitive to prosthetic design and stem size, but < 10° of anteversion appears deleterious to the long-term outcome for cemented hip prosthetic stems.

A circumferentially flanged tibial tray minimizes bone-tray shear micromotion.

Aseptic loosening of the tibial component is the major complication of total knee arthroplasty. There is an association between early excessive shear micromotion between the bone and the tray of the tibial component and late aseptic loosening. Using non-linear finite element analysis, whether a tibial tray with a circumferentially flanged rim and a mating cut in the proximal tibia could minimize bone-tray shear micromotion was considered. Fifteen competing tray designs with various degrees of flange curvature were assessed with the aim of minimizing bone-tray shear micromotion. A trade-off was found between reducing micromotion and increasing peripheral cancellous bone stresses. It was found that, within the limitations of the study, there was a theoretical design that could virtually eliminate micromotion due to axial loads, with minimal bone removal and without the use of screws or pegs.

A combined RSA and FE study of the implanted proximal tibia: correlation of the post-operative mechanical environment with implant migration.

There is strong evidence to suggest that inducible displacements, migration and implant loosening are closely related to the initial mechanical environment of the implanted tibia. If this is true, then it should be possible to predict the likelihood of implant migration using patient-specific finite element models. Finite element models of the proximal implanted tibiae were analysed based on pre-operative quantitative computed tomography data of four patients entered into a radiographic migration study. These four patients were also part of an radiostereometric analysis (RSA) study. A variety of load cases were analysed and the risk of bone failure determined for a 2 mm layer of bone immediately beneath the tibial tray. The results were compared with the RSA data measured 1 year post-operatively for each patient. For each patient, an appropriate load case was selected based on patient weight and on the varus-valgus migrations observed in the migration study. The two patients with press-fit implants were predicted to have the highest risk of failure and were found to migrate the most. The two patients with bonded implants (one HA coated and one cemented) were found to have a low risk of failure and these implants migrated the least. This study suggests that the degree of implant migration is dependent on the initial mechanical environment and can be determined using patient-specific finite element analysis.

A comparison of structural and mechanical properties in cancellous bone from the femoral head and acetabulum.

Mechanical interlock obtained by penetration of bone cement into cancellous bone is critical to the success of cemented total hip replacement (THR). Although acetabular component loosening is an important mode of THR failure, the properties of acetabular cancellous bone relevant to cement penetration are not well characterized. Bone biopsies (9 mm diameter, 10 mm long) were taken from the articular surfaces of the acetabulum and femoral head during total hip replacement. After mechanical and chemical defatting the two groups of bone specimens were characterized using flow measurement, mechanical testing and finally serial sectioning and three-dimensional computer reconstruction. The mean permeabilities of the acetabular group (1.064 x 10(-10) m2) and femoral group (1.155 x 10(-10) m2) were calculated from the flow measurements, which used saline solution and a static pressure of 9.8 kPa. The mean Young's modulus, measured non-destructively, was 47.4 MPa for the femoral group and 116.4 MPa for the acetabular group. Three-dimensional computer reconstruction of the specimens showed no significant differences in connectivity and porosity between the groups. Results obtained using femoral head cancellous bone to investigate bone cement penetration and fixation are directly relevant to fixation in the acetabulum.

A biomechanical study on fixation stability with twin hook or lag screw in artificial cancellous bone.

The twin hook has been developed as an alternative to the conventional lag screw to be combined with a barrelled side-plate in the treatment of trochanteric hip fractures. With two oppositely directed apical hooks introduced into the subchondral bone of the femoral head, the twin hook provides different stabilising properties to the lag screw. The femoral head purchase of the twin hook and the lag screw were compared in a biomechanical study using artificial cancellous bone, and responses to axial and torsional loading was determined. A distinct yield point in load and torque was noted for the lag screw, representing failure of the laminas supporting the threads. For the twin hook, gradual increase of load and torque occurred during impaction of the bone supporting the hooks. The peak loads and torques were higher for the lag screw, but were similar for both devices after 8 mm deformation. The stiffness was higher for the lag screw, but in counter-clockwise rotation the stiffness for the lag screw was negligible. The twin hook appeared to provide fixation stability comparable to that offered by the lag screw, but with conceivable advantages in terms of a deformation response involving bone impaction and gradually increasing stability.

Roentgen single-plane photogrammetric analysis (RSPA.) A new approach to the study of musculoskeletal movement.

We present a new approach for the accurate reconstruction of three-dimensional skeletal positions using roentgen single-plane photogrammetric analysis (RSPA). This technique uses a minimum of three markers embedded in each segment which allow continuous, real-time, internal skeletal movement to be measured from single-plane images, provided that the precise distance between the markers is known. A simulation study indicated that the error propagation in this approach is influenced by focus position, object position, the number of control points, the accuracy of the previous measurement of the distance between markers and the accuracy of image measurement. For reconstruction of normal movement of the knee with an input measurement error of SD = 0.02 mm, the rotational and translational differences between reconstructed and original movement were less than 0.27 degrees and 0.9 mm, respectively. Our results showed that the accuracy of RSPA is sufficient for the analysis of most movement of joints. This approach can be applied in combination with force measurements for dynamic studies of the musculoskeletal system.

Arch-shaped versus flat arthrodesis of the ankle joint: strength measurements using synthetic cancellous bone.

The aim of this study was to see if preservation of the arch shape of the ankle at arthrodesis contributes to stability. The ankle joint was simulated by paired blocks of a synthetic material corresponding to rheumatoid cancellous bone with low stiffness and strength. Flat end constructs with and without subchondral bone were compared with arch-shape constructs with and without subchondral bone. The pairs were fixed with two screws simulating an arthrodesis. These constructs were then tested to failure in four-point bending and torque. In four-point bending the subchondral bone increased the strength, regardless of shape. Stiffness was higher in the arch-shaped specimens but was not influenced by the subchondral bone. In torque, both arch-shape and subchondral bone increase the strength. Stiffness was increased by arch-shape but not subchondral bone. The results imply that the arch-shape and subchondral bone should be preserved when performing an ankle arthrodesis, especially in weak rheumatoid bone.

Appropriate questionnaires for knee arthroplasty. Results of a survey of 3600 patients from The Swedish Knee Arthroplasty Registry.

The Swedish Knee Arthroplasty Registry (SKAR) has recorded knee arthroplasties prospectively in Sweden since 1975. The only outcome measure available to date has been revision status. While questionnaires on health outcome may function as more comprehensive endpoints, it is unclear which are the most appropriate. We tested various outcome questionnaires in order to determine which is the best for patients who have had knee arthroplasty as applied in a cross-sectional, discriminative, postal survey. Four general health questionnaires (NHP, SF-12, SF-36 and SIP) and three disease/site-specific questionnaires (Lequesne, Oxford-12, and WOMAC) were tested on 3600 patients randomly selected from the SKAR. Differences were found between questionnaires in response rate, time required for completion, the need for assistance, the efficiency of completion, the validity of the content and the reliability. The mean overall ranks for each questionnaire were generated. The SF-12 ranked the best for the general health, and the Oxford-12 for the disease/site-specific questionnaires. These two questionnaires could therefore be recommended as the most appropriate for use with a large knee arthroplasty database in a cross-sectional population.

Radiostereometric analysis of distal radial fracture displacement during treatment: a randomized study comparing Norian SRS and external fixation in 23 patients.

In a randomized study, we included 23 osteoporotic patients with a distal radial fracture and loss of reduction after 1 week. The facture was re-reduced. In one group, a self-setting hydroxyapatite, Norian SRS, was injected into the fracture and the wrist was immobilized for 2 weeks with a dorsal splint (n 12). In the other group, the fracture was immobilized for 5 weeks with an external fixator (n 11). During the operation, the fracture fragments were marked with tantalum markers, so that loss of reduction during the immobilization and after mobilization could be studied with radiostereometric analysis (RSA). We found some recurrence of compression in the fracture in both groups during immobilization. After mobilization, the motion of the fracture, measured by displacement of the fragments along the longitudinal axis, was less than 2 mm, except in 3 cases treated with Norian SRS. A compression along the longitudinal axis of less than 2 mm is not likely to cause any problem in the long term. From the first to the last investigation, 7/12 patients with Norian SRS and 4/11 with external fixation lost more than 2 mm of the reduction along the longitudinal axis. We conclude that 5 weeks of immobilization is sufficient for healing with external fixation in this age group. This immobilization time might be reduced to 2 weeks for fractures treated with Norian SRS, but additional hardware should be used to ensure stability of the fracture system.

Radiographic measurement of femorotibial rotation in weight-bearing. The influence of flexion and extension in the knee on the extensor mechanism and angles of the lower extremity in a healthy population.

PURPOSE: A system for examination and measurement of the weight-bearing knee was developed earlier on examination equipment used for QUESTOR Precision Radiography (QPR), adapted to computed radiography and to a picture archiving and communication system. In this study the same system was used to develop a method to define "patellar variables" including measurements of the rotation of the femur and the tibia and the patellar translation, between semiflexion and extension, as well as the Q-angle. The aim of this study was to evaluate the reproducibility of these patellar variables and also to establish "normal" reference values for both the patellar variables and the variables in the original QPR system. MATERIAL AND METHODS: For evaluation of the reproducibility 10 volunteers with healthy knees were examined twice. To obtain the reference values, 80 volunteers with healthy knees, 10 females and 10 males within each decade between 20 and 59 years of age, were examined. RESULTS AND CONCLUSION: The reproducibility of the rotation of the femur and the tibia and of the Q-angle was 2--3 degrees (SD) and of the patellar translation about 3 mm (SD). The result from the healthy volunteers will be a useful tool for evaluation of disorders in the knee joint.

Femorotibial rotation and the Q-angle related to the dislocating patella.

PURPOSE: To compare the femorotibial rotation, the patellar translation, the hip-knee-ankle angle and the Q-angle in patients with a dislocation of the patella with those of healthy volunteers. Further, the clinically measured Q-angle was compared to that measured by radiography. MATERIAL AND METHODS: A system for measurement of patellar variables was previously developed and applied to 80 healthy volunteers. In the present study, 28 patients (20 women, 8 men) with dislocation of the patella were examined bilaterally. Fourteen patients had habitual dislocations (20 affected knees) and 14 patients traumatic dislocations (17 affected knees). In 20 patients the clinical Q-angle was measured bilaterally by an orthopaedic surgeon and in 9 of these patients also by a second independent orthopaedic surgeon. RESULTS: The most striking finding was that dislocating knees in both groups showed a smaller Q-angle than the healthy knees. Further, the habitual group showed greater relative rotation between the tibia and the femur and an increased patellar translation compared to the traumatic group and to the healthy volunteers. There was a poor correlation between clinical and radiographic measurements of the Q-angle and no correlation was found between two independent clinical measurements. CONCLUSION: Surgical operations aiming at decreasing the Q-angle should be challenged.

Methods for determining the accuracy of radiostereometric analysis (RSA).

The problem of determining the noise level in any measuring system remains urgent. Radiostereometric analysis (RSA) is a radiographic system of unique accuracy which has applications in areas where minute motions or no motion at all occurs. Examples are micromotion between endoprostheses and bone and in fracture healing. We have determined the accuracy of the RSA system as applied to a clinical series of spinal fusions, where the conditions for RSA were not optimal. Using the usual test-retest methodology on a phantom, we showed that its accuracy can be grossly overestimated in the individual case. We found considerable variations in the accuracy in the individual case, depending on the rigid-body configuration. The overall accuracy, expressed as 3-D "vectors" for rotation and translation, respectively, correlated with the condition number, a method for characterizing the marker configuration. Indeed, the condition number explained as much as 92% of the variation in overall rotation. This condition number, however, cannot be used to analyze the accuracy of one degree of freedom of rotation alone. Mathematical simulation of the accuracy in the individual case of the individual dimension, using in-house software, showed that the accuracy (95% confidence) varied between 0.4 and 4.6 degrees of rotation about the transverse axis, corresponding to a clinical stress series of extension and flexion.

Substantial disability 3 months after arthroscopic partial meniscectomy: A prospective study of patient-relevant outcomes.

To our knowledge, this is the first prospective study using validated questionnaires to assess patient-relevant outcomes after arthroscopic partial meniscectomy. Data from the Knee Injury and Osteoarthritis Outcome Score (KOOS), the SF-36 Medical Outcomes Study Short-Form Health Survey, and the Lysholm Knee Scoring Scale were available for 74 consecutive patients (50 males, 24 females; mean age, 45 years) with isolated meniscus tear (n = 47) or meniscus tear combined with cartilage damage (n = 27). At postoperative follow-up (mean, 14.4 weeks) significant improvement was seen, but despite only minor pain and other symptoms postoperatively, significant physical disability and handicap were reported. Postoperatively, 30% of patients were active in sports compared with 63% before injury. A sedentary lifestyle was reported by 38% compared with 9% before injury. We conclude that patient-relevant outcomes provide additional information and should be assessed after arthroscopic partial meniscectomy. We further suggest that preoperative information for the meniscectomy patient should include a realistic expected functional outcome.

Digital automated RSA compared to manually operated RSA.

The accuracy of digital Roentgen stereophotogrammetric analysis (RSA) was compared to the accuracy of a manually operated RSA system. For this purpose, we used radiographs of a phantom and radiographs of patients. The radiographs of the patients consisted of double examinations of 12 patients that had a tibial osteotomy and of double examinations of 12 patients that received a total hip prosthesis. First, the radiographs were measured manually with an accurate measurement table. Subsequently, the images were digitized by a film scanner at 150 DPI and 300 DPI resolutions and analyzed with the RSA-CMS software. In the phantom experiment, the manually operated system produced significantly better results than the digital system, although the maximum difference between the median values of the manually operated system and the digital system was as low as 0.013mm for translations and 0.033 degrees for rotations. In the radiographs of the patients, the manually operated system and the digital system produced equally accurate results: no significant differences in translations and rotations were found. We conclude that digital RSA is an accurate, fast, and user friendly alternative for manually operated RSA. Currently, digital RSA systems are being used in a growing number of clinical RSA-studies.

The introduction period of unicompartmental knee arthroplasty is critical: a clinical, clinical multicentered, and radiostereometric study of 251 Duracon unicompartmental knee arthroplasties.

One hundred twenty-eight consecutive knees were operated on with the Duracon unicompartmental knee arthroplasty. Of 111 knees, followed 3 years (range, 1-6 years), 109 knees were satisfactory. Two knees were revised because of progression of osteoarthritis and inexplicable pain. Radiostereometric analysis in 49 knees showed a migration of 0.6 mm after 2 years. The magnitude of migration was lower in comparison with published series. In a multicenter study comprising 4 other hospitals, there were 8 revisions in 123 operated knees. The reasons were loosening, subsidence, or fracture. These revisions were within 1 year and mostly related to operative technique. Unicompartmental knee arthroplasty is a demanding procedure that needs special experience and includes a risk of early failures during the introduction of a system.

Translation and validation of the Oxford-12 item knee score for use in Sweden.

The Oxford-12 Item Knee Score is a recently developed and validated patient-completed outcome measure designed specifically for use with knee arthroplasty in the United Kingdom. We have translated this questionnaire into Swedish and tested the validity and reliability of the translated version in a cross-sectional study by a postal survey to 1,200 randomly selected patients from the Swedish Knee Arthroplasty Register. Swedish versions of the WOMAC, Nottingham Health Profile, SF-36, SF-12, and the Sickness Impact Profile were employed in the validation process. We also tested feasibility and patient-burden parameters. The translated version appeared to be linguistically and culturally equivalent to the original version with good validity and reliability. Indirect measures of responsiveness indicated that it is at least as responsive to relevant knee arthroplasty patient states as the previously validated Swedish version of the WOMAC. Application of the translated questionnaire to this population is feasible with minimal imposed patient-burden. The Swedish translation of the Oxford-12 Item Knee Score is a valid and reliable tool for outcome studies on knee arthroplasty patients.