Background and purpose
The trabecular metal tibial monoblock component (TM) is a relatively new option available for total knee arthroplasty. We have previously reported a large degree of early migration of the trabecular metal component in a subset of patients. These implants all appeared to stabilize at 2 years. We now present 5-year RSA results of the TM and compare them with those of the NexGen Option Stemmed cemented tibial component (Zimmer, Warsaw IN).
Patients and methods
70 patients with osteoarthritis were randomized to receive either the TM implant or the cemented component. RSA examination was done postoperatively and at 6 months, 1 year, 2 years, and 5 years. RSA outcomes were translations, rotations, and maximum total point motion (MTPM) of the components. MTPM values were used to classify implants as “at risk” or “stable”.
At the 5-year follow-up, 45 patients were available for analysis. There were 27 in the TM group and 18 in the cemented group. MTPM values were similar in the 2 groups (p = 0.9). The TM components had significantly greater subsidence than the cemented components (p = 0.001). The proportion of “at risk” components at 5 years was 2 of 18 in the cemented group and 0 of 27 in the TM group (p = 0.2).
In the previous 2-year report, we expressed our uncertainty concerning the long-term stability of the TM implant due to the high initial migration seen in some cases. Here, we report stability of this implant up to 5 years in all cases. The implant appears to achieve solid fixation despite high levels of migration initially.
Background and purpose After joint replacement, a repair process starts at the interface between bone and cement. If this process is disturbed, the prosthesis may never become rigidly fixed to the bone, leading to migration—and with time, loosening. Cox-2 inhibitors are widely used as postoperative analgesics, and have adverse effects on bone healing. This could tamper prosthesis fixation. We investigated whether celecoxib, a selective Cox-2 inhibitor, increases prosthesis migration in total knee replacement (TKR).
Methods 50 patients were randomized to either placebo or celecoxib treatment, 200 mg twice daily, for 3 weeks after TKR (NexGen; Zimmer). Maximum total point motion (MTPM) of the tibial component was measured after 2 years using radiostereometric analysis (RSA). In addition, range of motion, pain, and, subjective outcome were evaluated.
Results No differences in prosthesis migration, pain scores, range of motion, and subjective outcome were found after 2 years. Confidence intervals were narrow.
Interpretation It is unlikely that Celecoxib increases the risk of loosening, and it may be used safely in conjunction with TKR.
As the number of young patients receiving total hip arthroplasty increases, bone-saving implantations facilitating possible future revision, such as the CUT femoral neck prosthesis, are gaining importance. There have been few medium-term results reported for this prosthesis, however, and its migration pattern has not been analyzed.
Patients and methods
39 consecutive CUT femoral neck prostheses were implanted in 32 patients, mean age 37 (17–58) years, with symptomatic osteoarthritis and either less than 55 years of age or with an anatomic anomaly preventing implantation of a diaphyseal stem (n = 1). Patients were followed prospectively using routine clinical examination and radiostereometric analysis (RSA) at 6, 12, 26, and 52 weeks postoperatively and annually thereafter. This study evaluated the 5-year follow-up results.
The mean Harris hip score increased from 26 (3–51) points preoperatively to 84 (66–98), 86 (55–98), and 87 (47–98) points at 3, 12, and 60 months. 3 stems were revised: 1 after luxation following excessive subsidence due to an undersized component and 2 due to persistent strong thigh pain. 5-year survival was 95% (95% CI: 87–100). Initial migration varied widely in magnitude; median total tip migration was 0.42 mm (0.09–9.4) at 6 weeks, 0.92 mm (0.18–5.9) at 1 year, and 1.10 mm (0.13–6.4) at 5 years. Even after high initial migration, stabilization was achieved in 31 of the 35 RSA-evaluable implants. 3 prostheses showed progressive continuous migration throughout the entire follow-up period, and were considered to be loose, suggesting reduced long-term survival.
Currently, we cannot recommend the CUT femoral neck prosthesis as a routine treatment option in (young) patients requiring THA. The CUT prosthesis may not reach the 90% survival benchmark at 10 years, and the prosthesis is difficult to implant. If initial stabilization is achieved, however, aseptic loosening is unlikely. A good clinical outcome was seen in the surviving prostheses. We will continue to follow this patient group.
The objective of this study was to compare the early migration
characteristics and functional outcome of the Triathlon cemented
knee prosthesis with its predecessor, the Duracon cemented knee
prosthesis (both Stryker).
A total 60 patients were prospectively randomised and tibial
component migration was measured by radiostereometric analysis (RSA)
at three months, one year and two years; clinical outcome was measured
by the American Knee Society score and the Knee Osteoarthritis and
Injury Outcome Score.
There were no statistically significant differences in rotation
or translation around or along the three coordinal axes, or in the
maximum total point motion (MTPM) during the two-year follow-up.
The Triathlon cemented knee prosthesis has similar early stability
and is likely to perform at least as well as the Duracon cemented
knee prosthesis over the longer term.
Total knee replacement; Single radius; New design; Safety; RSA; TKR
Background and purpose
Short femoral stems have been introduced in total hip arthroplasty in order to save proximal bone stock. We hypothesized that a short stem preserves periprosthetic bone mineral density (BMD) and provides good primary stability.
We carried out a prospective cohort study of 30 patients receiving the collum femoris-preserving (CFP) stem. Preoperative total hip BMD and postoperative periprosthetic BMD in Gruen zones 1–7 were investigated by dual-energy x-ray absorptiometry (DXA), stem migration was analyzed by radiostereometric analysis (RSA), and the Harris hip score (HHS) was determined.
2 patients were excluded intraoperatively and 1 patient was revised due to a deep infection, leaving 27 patients for analysis. The mean HHS increased from 49 (24–79) preoperatively to 99 (92–100) after 2 years. DXA after 1 year showed substantial loss of BMD in Gruen zone 7 (–31%), zone 6 (–19%), and zone 2 (–13%, p < 0.001) compared to baseline BMD determined immediately postoperatively. The bone loss in these regions did not recover after 2 years, whereas the more moderate bone loss in Gruen zones 1, 3, and 5 partially recovered. There was a correlation between low preoperative total hip BMD and a higher amount of bone loss in Gruen zones 2, 6 and 7. RSA showed minor micromotion of the stem: mean subsidence was 0.13 (95% CI: –0.28 to 0.01) mm and mean rotation around the longitudinal axis was 0.01º (95% CI: –0.1 to 0.39) after 2 years.
We conclude that substantial loss in proximal periprosthetic BMD cannot be prevented by the use of a novel type of short, curved stem, and forces appear to be transmitted distally. However, the stems showed very small migration—a characteristic of stable uncemented implants.
Background and purpose
There is no standard for patient triage in total knee arthroplasty (TKA) based on joint functional characteristics. This is largely due to the lack of objective postoperative measurement of success in TKA in terms of function and longevity, and the lack of knowledge of preoperative metrics that influence outcome. We examined the association between the preoperative mechanical environment of the patients knee joint during gait and the post-TKA stability of the tibial component as measured with radiostereometric analysis (RSA).
37 subjects were recruited out of a larger randomized RSA trial. 3-dimensional gait analysis was performed in the preoperative week. Longitudinal RSA data were gathered postoperatively at 6 months and 1 year.
We found a statistically significant association between the pattern of the knee adduction moment during gait preoperatively and the total migration of the implant at 6 months postoperatively. A substantial proportion of the variability in the total postoperative tibial component migration (R2 = 0.45) was explained by a combination of implant type, preoperative knee joint loading patterns during gait, and body mass index at 6 months postoperatively. The relationships did not remain statistically significant at 1 year postoperatively.
Our findings support the hypothesis that preoperative functional characteristics of patients, and particularly joint loading patterns during activities of daily living, are important for outcome in TKA. This represents a first step in the development of predictive models of objective TKA outcome based on preoperative patient characteristics, which may lead to better treatment strategies.
Background and purpose
Rehabilitation of patients with transfemoral amputations is particularly difficult due to problems in using standard socket prostheses. We wanted to assess long-term fixation of the osseointegrated implant system (OPRA) using radiostereometric analysis (RSA) and periprosthetic bone remodeling.
51 patients with transfemoral amputations (55 implants) were enrolled in an RSA study. RSA and plain radiographs were scheduled at 6 months and at 1, 2, 5, 7, and 10 years after surgery. RSA films were analyzed using UmRSA software. Plain radiographs were graded for bone resorption, cancellization, cortical thinning, and trabecular streaming or buttressing in specifically defined zones around the implant.
At 5 years, the median (SE) migration of the implant was –0.02 (0.06) mm distally. The rotational movement was 0.42 (0.32) degrees around the longitudinal axis. There was no statistically significant difference in median rotation or migration at any follow-up time. Cancellization of the cortex (plain radiographic grading) appeared in at least 1 zone in over half of the patients at 2 years. However, the prevalence of cancellization had decreased by the 5-year follow-up.
The RSA analysis for the OPRA system indicated stable fixation of the implant. The periprosthetic bone remodeling showed similarities with changes seen around uncemented hip stems. The OPRA system is a new and promising approach for addressing the challenges faced by patients with transfemoral amputations.
Implant stability is considered vital to long-time implant survival in total hip arthroplasty (THA), since loose implants are reported to be a major cause of hip revision. There is an association between early implant micromotion and increased risk of revision. More implant-specific data are needed to establish acceptable levels of early implant movement.
Materials and methods
Thirty-five patients (36 hips) undergoing Charnley THA were followed with repeated clinical, radiographic, and radiostereometric analysis (RSA) over 5 years. Twenty-three patients attended 5 years postoperatively.
The patient group was well functioning based on the radiological and clinical evaluations. The stems constantly moved up to 5 years postoperatively, with subsidence, retroversion, and varus tilt, based on the RSA.
Continuous movement of the Charnley stem was observed up to 5 years postoperatively in a well-functioning patient group. The migration data presented herein could be useful when defining acceptable migration limits for certain types of cemented femoral stems.
RSA; Charnley; THR; Five-year follow-up; Migration pattern
Bioactive coating of uncemented total knee arthroplasty (TKA) is believed to increase bone ingrowth and enhance early fixation of the TKA. In a prospective randomized study using radiostereometric analysis (RSA) we examined migrations of the tibial implant, in an uncemented TKA with and without bioactive coating. The study was performed according to new RSA guidelines, and focus was put on some important methodological issues.
Materials and methods
Twenty-three patients with osteoarthrosis of the knee received an uncemented Duracon TKA either with bioactive (hydroxyapatite or periapatite) coating (+HA) or without bioactive coating (−HA). Patients had RSA examinations postoperatively and at 3, 6 and 12 months. Nine patients were excluded during the study resulting in 14 knees for final analysis.
At 12 months follow-up we found no significant differences in migrations between the two groups. However, in general the −HA group migrated more than the +HA group, and we found a significant larger variation in migration pattern in the −HA group. In the +HA group the tibia component stabilized after 6 months, whereas the −HA group showed continuous migration. Subsidence and posterior tilt were the main migration patterns in both groups.
Bioactive coating of TKA seems to enhance early stabilization of the tibia component. Similar results are found in previous studies.
Hydroxyapatite; Migration; Roentgenstereogrammetric analysis; Total knee arthroplasty; Tibial implant
In ankles with end-stage osteoarthritis or with total ankle replacement (TAR), radiographic landmarks based on joint surface morphology are usually obscured and thus inadequate for radiographic measurement. Furthermore, because of difficulty in reproducibly positioning the ankle for a standing radiograph, any radiographic measure to accurately describe ankle alignment needs to tolerate perturbations of ankle positioning in clinical radiographs. To identify a radiographic measure of antero-posterior (AP) tibial-talar alignment that meets those requirements, three candidate measures were compared by means of sensitivity to perturbations of ankle positioning.
Ten cadaver ankles had lateral radiographs taken while varying ankle position, at nine prespecified positions in the transverse plane and at seven positions in the sagittal plane. The AP tibial-talar alignment was quantified by three candidate measures. Sensitivity to changes of ankle position in each plane was then compared across the measures.
With the tibial axis-talar ratio (T-T ratio: the ratio into which the mid-longitudinal axis of the tibial shaft divides the longitudinal talar length), sensitivity to ankle positional changes in either plane was lowest, with errors associated with 10 degrees of ankle malpositioning being around 2.2%. The posterior line-talar ratio (P-T ratio: a similar ratio, but using the posterior longitudinal line of the tibial shaft) showed higher sensitivity in the transverse plane than the T-T ratio, though the associated errors in either plane were nearly comparable. The tibial axis-lateral process distance (T-L distance: the perpendicular distance from the tibial axis to the tip of the lateral talar process) showed highest sensitivity in both planes.
The T-T ratio tolerated perturbations of ankle positioning best among the tested measures. This measure is potentially applicable to clinical radiographic measurement when determining the AP tibial-talar alignment in ankles with articular degeneration or TAR. The P-T ratio also appears to have reasonable tolerance.
ankle; alignment; radiographic measurement; cadaver experiment
Background and purpose
In contrast to early migration, the long-term migration of hydroxyapatite- (HA-) coated tibial components in TKA has been scantily reported. This randomized controlled trial investigated the long-term migration measured by radiostereometric analysis (RSA) of HA-coated, uncoated, and cemented tibial components in TKA.
Patients and methods
68 knees were randomized to HA-coated (n = 24), uncoated (n = 20), and cemented (n = 24) components. All knees were prospectively followed for 11–16 years, or until death or revision. RSA was used to evaluate migration at yearly intervals. Clinical and radiographic evaluation was according to the Knee Society system. A generalized linear mixed model (GLMM, adjusted for age, sex, diagnosis, revisions, and BMI) was used to take into account the repeated-measurement design.
The present study involved 742 RSA analyses. The mean migration at 10 years was 1.66 mm for HA, 2.25 mm for uncoated and 0.79 mm for the cemented group (p < 0.001). The reduction of migration by HA as compared to uncoated components was most pronounced for subsidence and external rotation. 3 tibial components were revised for aseptic loosening (2 uncoated and 1 cemented), 3 for septic loosening (2 uncoated and 1 cemented), and 1 for instability (HA-coated). 2 of these cases were revised for secondary loosening after a period of stability: 1 case of osteolysis and 1 case of late infection. There were no statistically significant differences between the fixation groups regarding clinical or radiographic scores.
HA reduces migration of uncemented tibial components. This beneficial effect lasts for more than 10 years. Cemented components showed the lowest migration. Longitudinal follow-up of TKA with RSA allows early detection of secondary loosening.
AIM: To determine the feasibility and potential role of combining radiostereometric analysis (RSA), gait analysis and activity monitoring in the follow-up of fracture patients.
METHODS: Two patients with similar 41B3 tibial plateau fractures were treated by open reduction internal fixation augmented with impaction bone grafting and were instructed to partial weight bear to 10 kg for the first six postoperative weeks. Fracture reduction and fixation were assessed by postoperative computer tomographic (CT) scanning. Both patients had tantalum markers inserted intra-operatively to monitor their fracture stability during healing using RSA and differentially loaded RSA (DLRSA) at 6 and 12 wk postoperatively. Gait analyses were performed at 1, 2, 6, and 12 wk postoperatively. Activity monitors were worn for 4 wk between the 2 and 6 wk appointments. In addition to gait analysis, knee function was assessed using the patient reported Lysholm scores, and doctor reported knee range of motion and stability, at 6 and 12 wk postoperatively.
RESULTS: There were no complications. CT demonstrated that both fractures were reduced anatomically. Gait analysis indicated that Patient 1 bore weight to 60% of body weight at 2 wk postoperative and 100% at 6 wk. Patient 2 bore weight at 10% of body weight to 6 wk and had very low joint contact forces to that time. At 12 wk however, there was no difference between the gait patterns in the two patients. Patient 1 increased activities of moderate-vigorous intensity from 20 to 60 min/d between 2 and 6 postoperative weeks, whereas Patient 2 remained more stable at 20-30 min/d. The Lysholm scores were similar for both patients and did not improve between 6 and 12 wk postoperatively. DLRSA examination at 12 wk showed that both patients were comfortable to weight bear to 80 kg and under this weight the fractures displaced less than 0.4 mm. RSA measurements demonstrated over time fracture migrations of less than 2 mm in both cases. However, Patient 2, who followed the postoperative weight bearing instructions most closely, displaced less (0.3 mm vs 1.6 mm).
CONCLUSION: This study demonstrates the potential of using a combination of RSA, gait analysis and activity monitoring to obtain a comprehensive evidence base for postoperative weight bearing schedules during fracture healing.
Radiostereometric analysis; Gait analysis; Activity monitoring; Rehabilitation protocols; Lower limb trauma
Fractures of the talus in the elderly are rare and usually result from high-impact injuries, suggesting only minor age-related bone structure changes. However, total ankle replacement failures with age often result from talar subsidence, suggesting age-related bone loss in the talus. Despite a number of histological analyses of talar microarchitecture, the effects of age and sex on talar microarchitecture changes remain poorly defined.
The aim of this study was to analyze changes or differences in the trabecular microarchitecture of the talus with regard to (1) age and (2) sex.
Sixty human tali were harvested from 30 patients at autopsy of three different age groups (20–40, 41–60, 61–80 years). The specimens were analyzed by radiography, micro-CT, and histological analysis. Given that there was no difference between the left and right talus, static histomorphometric parameters were assessed in three regions of interest of the right talus only (body, neck, head; n = 30).
The talar body, neck, and head were affected differently by age-related changes. The greatest loss of bone volume with age was seen in the talar body (estimate: −0.239; 95% confidence interval [CI], −0.365 to −0.114; p < 0.001). In the talar neck (estimate: −0.165; 95% CI, −0.307 to −0.023; p = 0.025), bone loss was only moderate and primarily was the result of reduction in trabecular thickness (estimate: −1.288; 95% CI, −2.449 to −0.127; p = 0.031) instead of number (estimate: −0.001; 95% CI, −0.005 to −0.003; p = 0.593). Bone structure changes were independent of sex.
Age-related bone structure changes predominantly occur in the talar body, which poses a potential risk factor for total ankle replacement loosening. The moderate changes in the talar neck might explain the persistent low incidence of talar neck fractures with age.
Our findings suggest that before total ankle replacement implantation, careful patient selection with dual-energy xray absorptiometry evaluation may be necessary to reduce the risk of talar implant subsidence.
Background and purpose
Although a tourniquet may reduce bleeding during total knee replacement (TKA), and thereby possibly improve fixation, it might also cause complications. Migration as measured by radiostereometric analysis (RSA) can predict future loosening. We investigated whether the use of a tourniquet influences prosthesis fixation measured with RSA. This has not been investigated previously to our knowledge.
50 patients with osteoarthritis of the knee were randomized to cemented TKA with or without tourniquet. RSA was performed postoperatively and at 6 months, 1 year, and 2 years. Pain during hospital stay was registered with a visual analog scale (VAS) and morphine consumption was measured. Overt bleeding and blood transfusions were registered, and total bleeding was estimated by the hemoglobin dilution method. Range of motion was measured up to 2 years.
RSA maximal total point motion (MTPM) differed by 0.01 mm (95% CI –0.13 to 0.15). Patients in the tourniquet group had less overt bleeding (317 mL vs. 615 mL), but the total bleeding estimated by hemoglobin dilution at day 4 was only slightly less (1,184 mL vs. 1,236 mL) with a mean difference of –54 mL (95% CI –256 to 152). Pain VAS measurements were lower in the non-tourniquet group (p = 0.01). There was no significant difference in morphine consumption. Range of motion was 11° more in the non-tourniquet group (p = 0.001 at 2 years).
Tourniquet use did not improve fixation but it may cause more postoperative pain and less range of motion.
We have previously reported the short-term migration of cemented Hinek femoral components using radiostereometric analysis (RSA). We now report the mid-term migration. During the first 2 years after implantation the prosthesis subsided into varus and rotated internally. Between years 3 and 8 the prosthesis continued to rotate internally with the head moving posteriorly (0.07 mm/year, P=0.004). It also continued to fall into varus with the tip moving laterally (0.07 mm/year, P=0.04). The head (0.06 mm/year, P<0.0001), shoulder (0.04 mm/year, P=0.0001) and tip (0.04 mm/year, P=0.001) continued to migrate distally. There were two cases of failure due to aseptic loosening during the follow-up period. During the second year both of these had posterior head migration, which was abnormally rapid (>2 SD from the mean). We have demonstrated that a cemented implant has slow but significant levels of migration and rotation for at least 8 years after implantation. Our study confirms that implants with abnormally rapid posterior head migration during the second year are likely to fail.
Background and purpose
Lasting stability of cementless implants depends on osseointegration into the implant surface, and long-term implant fixation can be predicted using radiostereometric analysis (RSA) with short-term follow-up. We hypothesized that there would be improved fixation of high-porosity trabecular metal (TM) tibial components compared to low-porosity titanium pegged porous fiber-metal (Ti) polyethylene metal backings.
In a prospective, parallel-group, randomized unblinded clinical trial, we compared cementless tibial components in patients aged 70 years and younger with osteoarthritis. The pre-study sample size calculation was 22 patients per group. 25 TM tibial components were fixed press-fit by 2 hexagonal pegs (TM group) and 25 Ti tibial components were fixed press-fit and by 4 supplemental screws (Ti group). Stereo radiographs for evaluation of absolute component migration (primary effect size) and single-direction absolute component migration (secondary effect size) were obtained within the first postoperative week and at 6 weeks, 6 months, 1 year, and 2 years. American Knee Society score was used for clinical assessment preoperatively, and at 1 and 2 years.
There were no intraoperative complications, and no postoperative infections or revisions. All patients had improved function and regained full extension. All tibial components migrated initially. Most migration of the TM components (n = 24) occurred within the first 3 months after surgery whereas migration of the Ti components (n = 22) appeared to stabilize first after 1 year. The TM components migrated less than the Ti components at 1 year (p = 0.01) and 2 years (p = 0.004).
We conclude that the mechanical fixation of TM tibial components is superior to that of screw-fixed Ti tibial components. We expect long-term implant survival to be better with the TM tibial component.
Total disc replacements (TDRs) have been used to reduce pain and preserve motion. However, the comparison of polyethylene wear following long-term implantation to those tested using an in vitro model had not yet been investigated.
The purpose of this study was to correlate wear and damage patterns in retrieved TDRs with motion patterns observed in a clinically validated in vitro lumbar spine model. We also sought to determine whether one-sided wear and motion patterns were associated with greater in vivo wear.
This two-part study combined the evaluation of retrieved total disc replacements with a biomechanical study using human lumbar spines.
38 CHARITÉ lumbar artificial discs were retrieved from 32 patients (24 female, 75%) after 7.3 years average implantation (range: 1.8 to 16.1y). The components were implanted at L2/L3 (n=1), L3/L4 (n=2), L4/L5 (n=20), and L5/S1 (n=15). All the implants were removed due to intractable back pain and/or facet degeneration. In addition, they were removed due to subsidence (n=10), anterior migration (n=3), core dislocation (n=2), lateral subluxation (n=1), endplate loosening (n = 2), and osteolysis (n=1). In parallel, 7 new implants were evaluated at L4-L5 and 13 implants at L5-S1 in an in vitro lumbar spine model.
Retrieval analysis included evaluation of clinical data, dimensional measurements and assessment of the extent and severity of PE surface damage mechanisms. In vitro testing involved the observation of motion patterns during physiological loading.
For the retrievals, each side of the PE core was independently analyzed at the rim and dome for the presence of machining marks, wear, and fracture. 35 cores were further analyzed using MicroCT to determine whether the wear was one-sided, or symmetrically distributed. For the in vitro study the new implants were tested under physiologic loads (flexion-extension with a compressive follower preload) using a validated cadaveric lumbar spine model. The center of the prosthesis was 2 mm posterior to the mid-point of the vertebral body endplate in mid-sagittal plane. Motion patterns of the in vitro-tested implants were tracked using sequential video-flouroscopy.
Substantial variability was observed in the wear patterns of the retrievals. 15/35 retrieved cores (43%) displayed one-sided wear patterns. The median dome penetration was 0.2 mm (range: 0.06 to 0.9 mm) and the median penetration rate was 0.04 mm/y (range: 0.01 to 0.2 mm/y). No significant difference in penetration or penetration rate was observed between retrievals with one-sided and symmetric wear patterns (p >0.05). Significant correlations were observed between implantation time and penetration (rho = 0.46, p = 0.004) and penetration rate (rho = −0.48, p = 0.003). In the in vitro study, there was clear visual evidence of motion at both articulations in 8/20 implantations. In additional 8/20 cases, there was some evidence of motion at both articulations; however, the predominant motion occurred at the top articulation. In 4/20 implantations motion could be visually detected only at the top articulation. Core entrapment and pinching was observed in 7/20 cases as the segment was extended, and was associated with visual evidence of core bending or deformation in 5/20 cases.
total disc arthroplasty; total disc replacement; lumbar spine; CHARITÉ; degenerative disc disease; artificial disc; in vitro motion response; wear; surface damage; fracture; impingement; ultra; high molecular weight polyethylene; UHMWPE
Fusion of cervical spine in kyphotic alignment has been proven to produce an acceleration of degenerative changes at adjacent levels. Stand-alone cages are reported to have a relatively high incidence of implant subsidence with secondary kyphotic deformity. This malalignment may theoretically lead to adjacent segment disease in the long term. The prospective study analysed possible risk factors leading to cage subsidence with resulting sagittal malalignment of cervical spine. Radiographic data of 100 consecutive patients with compressive radiculo-/myelopathy due to degenerative disc prolapse or osteophyte formation were prospectively collected in those who were treated by anterior cervical discectomy and implantation of single type interbody fusion cage. One hundred and forty four implants were inserted altogether at one or two levels as stand-alone cervical spacers without any bone graft or graft substitute. All patients underwent standard anterior cervical discectomy and the interbody implants were placed under fluoroscopy guidance. Plain radiographs were obtained on postoperative days one and three to verify position of the implant. Clinical and radiographic follow-up data were obtained at 6 weeks, 3 and 6 months and than annually in outpatient clinic. Radiographs were evaluated with respect to existing subsidence of implants. Subsidence was defined as more than 2 mm reduction in segmental height due to implant migration into the adjacent end-plates. Groups of subsided and non-subsided implants were statistically compared with respect to spacer distance to the anterior rim of vertebral body, spacer versus end-plate surface ratio, amount of bone removed from adjacent vertebral bodies during decompression and pre- versus immediate postoperative intervertebral space height ratio. There were 18 (18%) patients with 19 (13.2%) subsided cages in total. No patients experienced any symptoms. At 2 years, there was no radiographic evidence of accelerated adjacent segment degeneration. All cases of subsidence occurred at the anterior portion of the implant: 17 cases into the inferior vertebra, 1 into the superior and 1 into both vertebral bodies. In most cases, the process of implant settling started during the perioperative period and its progression did not exceed three postoperative months. There was an 8.7° average loss of segmental lordosis (measured by Cobb angle). Average distance of subsided intervertebral implants from anterior vertebral rim was found to be 2.59 mm, while that of non-subsided was only 0.82 mm (P < 0.001). Spacer versus end-plate surface ratio was significantly smaller in subsided implants (P < 0.001). Ratio of pre- and immediate postoperative height of the intervertebral space did not show significant difference between the two groups (i.e. subsided cages were not in overdistracted segments). Similarly, comparison of pre- and postoperative amount of bone mass in both adjacent vertebral bodies did not show a significant difference. Appropriate implant selection and placement appear to be the key factors influencing cage subsidence and secondary kyphotisation of box-shaped, stand-alone cages in anterior cervical discectomy and fusion. Mechanical support of the implant by cortical bone of the anterior osteophyte and maximal cage to end-plate surface ratio seem to be crucial in the prevention of postoperative loss of lordosis. Our results were not able to reflect the importance of end-plate integrity maintenance; the authors would, however, caution against mechanical end-plate damage. Intraoperative overdistraction was not shown to be a significant risk factor in this study. The significance of implant subsidence in acceleration of degenerative changes in adjacent segments remains to be evaluated during a longer follow-up.
Cervical vertebrae surgery; Spinal fusion; Equipment failure analysis; Postoperative complications; Subsidence
The mechanism of failure of metal-on-metal (MoM) total hip arthroplasty (THA) has been related to a high rate of metal wear debris, which is partly generated from the head-trunnion interface. However, it is not known whether implant fixation is affected by metal wear debris.
Patients and methods
49 cases of MoM THA in 41 patients (10 women) with a mean age of 52 (28–68) years were followed with stereoradiographs after surgery and at 1, 2, and 5 years to analyze implant migration by radiostereometric analysis (RSA). Patients also participated in a 5- to 7-year follow-up with measurement of serum metal ions, questionnaires (Oxford hip score (OHS) and Harris hip score (HHS)), and measurement of cup and stem positions and systemic bone mineral density.
At 1–2 years, mean total translation (TT) was 0.04 mm (95% CI: –0.07 to 0.14; p = 0.5) for the stems; at 2–5 years, mean TT was 0.13 mm (95% CI: –0.25 to –0.01; p = 0.03), but within the precision limit of the method. For the cups, there was no statistically significant TT or total rotation (TR) at 1–2 and 2–5 years. At 2–5 years, we found 4 cups and 5 stems with TT migrations exceeding the precision limit of the method. There was an association between cup migration and total OHS < 40 (4 patients, 4 hips; p = 0.04), but there were no statistically significant associations between cup or stem migration and T-scores < –1 (n = 10), cup and stem positions, or elevated serum metal ion levels (> 7µg/L (4 patients, 6 hips)).
Most cups and stems were well-fixed at 1–5 years. However, at 2–5 years, 4 cups and 5 stems had TT migrations above the precision limits, but these patients had serum metal ion levels similar to those of patients without measurable migrations, and they were pain-free. Patients with serum metal ion levels > 7 µg/L had migrations similar to those in patients with serum metal ion levels < 7 µg/L. Metal wear debris does not appear to influence the fixation of hip components in large-head MoM articulations at medium-term follow-up.
Background and purpose
Plasma-sprayed hydroxyapatite (HA) is a successful coating for fixation of uncemented femoral stems. There may be alternative coatings with advantages in bone remodeling and transport of bone-active substances. We investigated whether an electrochemically deposited hydroxyapatite, Bonemaster (BM), might be a safe alternative in total hip arthroplasty. Our hypothesis was that the new coating would not be inferior to the conventional one.
Patients and methods
50 patients (55 hips) were included. The stem was tapered and porous-coated proximally. On top of the porous coating was either HA or BM. Patients were evaluated postoperatively and after 3, 6, 12, and 24 months to measure fixation by radiostereometric analysis (RSA), bone mineral density by dual-energy X-ray absorptiometry (DXA), and conventional radiography. Clinical evaluation was performed with Harris hip score and Oxford hip score, both preoperatively and after 2 years.
After 2 years, the stems had subsided 0.25 (HA) and 0.28 (BM) mm and there were no statistically significant differences between the groups in any direction, regarding both migration and rotation. The BM group retained significantly more bone than the HA group in Gruen zone 1 during the first 2 years. The Harris and Oxford hip scores were similar in both groups.
Electrochemically deposited hydroxyapatite on an uncemented stem does not appear to be inferior to plasma-sprayed HA regarding clinical and radiological results, bone remodeling, and micromotion after 2 years follow-up.
Background and purpose
In a previous radiostereometric (RSA) trial the uncoated, uncemented, Interax tibial components showed excessive migration within 2 years compared to HA-coated and cemented tibial components. It was predicted that this type of fixation would have a high failure rate. The purpose of this systematic review and meta-analysis was to investigate whether this RSA prediction was correct.
Materials and methods
We performed a systematic review and meta-analysis to determine the revision rate for aseptic loosening of the uncoated and cemented Interax tibial components.
3 studies were included, involving 349 Interax total knee arthroplasties (TKAs) for the comparison of uncoated and cemented fixation. There were 30 revisions: 27 uncoated and 3 cemented components. There was a 3-times higher revision rate for the uncoated Interax components than that for cemented Interax components (OR = 3; 95% CI: 1.4–7.2).
This meta-analysis confirms the prediction of a previous RSA trial. The uncoated Interax components showed the highest migration and turned out to have the highest revision rate for aseptic loosening. RSA appears to enable efficient detection of an inferior design as early as 2 years postoperatively in a small group of patients.
Background and purpose
Clinical results of total knee replacement (TKR) are inferior in younger patients, mainly due to aseptic loosening. Coating of components with trabecular metal (TM) is a new way of enhancing fixation to bone. We have previously reported stabilization of TM tibial components at 2 years. We now report the 5-year follow-up of these patients, including RSA of their TM tibial components.
Patients and methods
22 patients (26 knees) received an uncemented TM cruciate-retaining tibial component and 19 patients (21 knees) a cemented NexGen Option cruciate-retaining tibial component. Follow-up with RSA, and clinical and radiographic examinations were done at 5 years. In bilaterally operated patients, the statistical analyses included only the first-operated knee.
Both groups had most migration within the first 3 months, the TM implants to a greater extent than the cemented implants. After 3 months, both groups stabilized and remained stable up to the 5-year follow-up.
After a high initial degree of migration, the TM tibia stabilized. This stabilization lasted for at least 5 years, which suggests a good long-term performance regarding fixation. The cemented NexGen CR tibial components showed some migration in the first 3 months and then stabilized up to the 5-year follow-up. This has not been reported previously.
We evaluated the influence of CT-free or CT-based computer assisted orthopaedic surgery (CAOS) on the alignment of total knee prostheses (TK) and micromotion of tibial components. This randomised study compared 19 CT-free, 17 CT-based CAOS TK, and a matched control group of 21 conventionally placed TK. Using Roentgen stereophotogrammetric analysis (RSA) the migration was measured. The alignment and component positions were measured on radiographs. No significant difference in leg and tibial component alignment was present between the three groups. A significant difference was found for micromotion in subsidence, with the conventional group having a mean of 0.16 mm, compared to the CT-free group at 0.01 mm and the CT-based group at −0.05 mm. No clinical significant difference in alignment was found between CAOS and conventionally operated TK. More subsidence of the tibial component was seen in the conventional group compared to both CAOS groups at two year follow-up.
Background and purpose
Immediate implant stability is a key factor for success in cementless total hip arthroplasty (THA). Low bone mineral density (BMD) and age-related geometric changes of the proximal femur may jeopardize initial stability and osseointegration. We compared migration of hydroxyapatite-coated femoral stems in women with or without low systemic BMD.
Patients and methods
61 female patients with hip osteoarthritis were treated with cementless THA with anatomically designed hydroxyapatite-coated femoral stems and ceramic-ceramic bearing surfaces (ABG-II). Of the 39 eligible patients between the ages of 41 and 78 years, 12 had normal systemic BMD and 27 had osteopenia or osteoporosis. According to the Dorr classification, 21 had type A bone and 18 had type B. Translational and rotational migration of the stems was evaluated with radiostereometric analysis (RSA) up to 2 years after surgery.
Patients with low systemic BMD showed higher subsidence of the femoral stem during the first 3 months after surgery than did those with normal BMD (difference = 0.6, 95% CI: 0.1–1.1; p = 0.03). Low systemic BMD (odds ratio (OR) = 0.1, CI: 0.006–1.0; p = 0.02), low local hip BMD (OR = 0.3, CI: 0.1–0.7; p = 0.005) and ageing (OR = 1.1, CI: 1.0–1.2; p = 0.02) were risk factors for delayed translational stability. Ageing and low canal flare index were risk factors for delayed rotational stabilization (OR = 3, CI: 1.1–9; p = 0.04 and OR = 1.1, CI: 1.0–1.2; p = 0.02, respectively). Harris hip score and WOMAC score were similar in patients with normal systemic BMD and low systemic BMD.
Low BMD, changes in intraosseous dimensions of the proximal femur, and ageing adversely affected initial stability and delayed osseointegration of cementless stems in women.
In ankles with end-stage osteoarthritis or after total ankle replacement (TAR), radiographic landmarks based on joint surface morphology are usually obscured and thus inadequate for measurement. Two candidate measures for quantifying AP tibial-talar alignment without relying on those landmarks were identified in a corollary cadaver-based study. This study aimed to verify reliability and validity of those candidate measures.
On clinical radiographs of thirty-three non-arthritic and thirty-five arthritic ankles, the AP tibial-talar alignment was quantified by the two candidate measures; the tibial axis-talar ratio (T-T ratio: the ratio into which the mid-longitudinal axis of the tibial shaft divides the longitudinal talar length) and the posterior tibial line-talar ratio (P-T ratio: a similar ratio, but using the posterior longitudinal line along the tibial shaft). Two observers performed every measurement twice, in order to evaluate intra- and inter-observer reliability of the candidate measures. For non-arthritic ankles, the AP tibial-talar alignment was further determined by a control measure that directly quantifies orientation of the talar dome relative to the tibial shaft. Correlation of each candidate measure with the control measure was then evaluated for validity.
Measurement of the T-T ratio with arthritic ankles was highly reproducible with the coefficients of determination (R2) greater than 0.95, for either inter- or intra-observer. Correlation between this measure and the control measure was supported (R2 = 0.60, p < 0.0001). Reliability of the P-T ratio was also strong (R2 > 0.91), though both reliability and validity of this measure was relatively inferior to the T-T ratio.
The T-T ratio reliably and validly described the AP tibial-talar alignment on clinical radiographs, regardless of the condition of ankle joint surface. This measure appears to be a reliable radiographic measure for determining the magnitude of AP talar subluxation in ankles with articular degeneration or after TAR, and can facilitate clinical investigations.
ankle; alignment; radiographic measurement