The purpose of this study was to evaluate a high flex porous tantalum metal monoblock component system implanted through a MIS technique.

A fellowship trained surgeon proficient in MIS surgery performed 109 consecutive TKAs in 95 patients. Patients were implanted with a tantalum monoblock tibia and a fiber-metal cruciate-retaining high flex femur through a MIS midvastus approach. Ninety uncemented porous tantulum monoblock patellae and 19 cemented all polyethylene patellae were implanted.

Knee Society scores and Knee Society radiographic scores were calculated in all patients. Follow-up for a minimum of 2 years was performed in 109 knees. The average follow up was 39 months. Sixty-six percent of the patients were female and 34% male. The average age was 66 years. The average preoperative Knee Society Knee score was 36. The average preop Knee Society Functional Score was 46. Osteoarthritis was the primary diagnosis in 104 knees. Rheumatoid arthritis and Hemophilia was the diagnosis in two knees each.

The average Knee Society Knee Score improved to 89. The average Knee Society Function score improved to 86. 106 of the knees were rated good or excellent and three knees were rated poor. Two patellar revisions were performed for loose components and one for patellar misalignment. One patella fracture occurred that required ORIF. One femoral component was revised for loosening. There were nonprogressive radiographic lucencies demonstrated on 4 tibial components. One tibial component was rated loose. There were radiographic lucencies on 5 femoral components, all nonprogressive. There were two uncemented tantalum patellar components with stable radiolucencies.

Early results in 109 consecutive porous tantalum metal tibial and high flex cruciate-retaining femoral components implanted through an MIS midvastus approach have a high rate of success at a minimum followup of two years.

Bone mineral density (BMD) and bone mineral content (BMC) have not been previously assessed in unicompartmental knee replacement (UKR). We studied the early bone changes beneath the uncemented Oxford medial UKR. Our hypothesis was that this implant should decrease the shear stresses across the bone-implant interface and result in improved BMD and BMC beneath the tibial component. Using the Lunar iDXA and knee specific software we developed 7 regions of interest (ROI) in the proximal tibia and assessed 38 patients with an uncemented Oxford UKR at 2 years. We measured the replaced knee and contralateral unreplaced knee using the same ROI and compared the BMD and BMC. The initial precision study in 20 patients demonstrated high precision in all areas. There were 12 males and 16 females with an average age of 65.8 years (46–84 years). ROI 1 and 2 were beneath the tibial tray and had significantly less BMC (p=0.023 and 0.001) and BMD (p=0.012 and 0.002). ROI 3 was the lateral tibial plateau and this area also had significantly less BMC (p=0.007) and BMD (p=0.0001). ROI 4 and 5 immediately below the tibial keel had no significant change. These changes were independent of gender and age. These results were surprising in that the universal loss of BMC and BMD suggested that bone loading of the proximal tibia was not improved even after a UKR. The better BMD and BMC adjacent to the keel confirms other studies that show improved bone in-growth around keels and pegs in the uncemented tibial component. A prospective longitudinal study has been developed to compare BMD and BMC changes over time to see whether these changes are dynamic

Aims: To prospectively study the optimum fixation of the tibial component in patients younger than 65 years, where the mode of fixation is randomized. Methods: 35 patients (mean age 56 years, range 29 to 64) were operated with the Profix (Smith& Nephew) TKA due to gonarthrosis grade III to V. The patients were randomly allocated to fixation of the tibial component with cement (Group C) (n=6), uncemented fixation with hydroxyapatite coating (HA) without screws (Group HA−) (n=14), or uncemented fixation with HA coating and with screws (Group HA+) (n=15). Radiostereometry (RSA) was performed postop., 3, 12 and 24 months postop. Results: There were no complications or revisions during the follow-up. Up to 3 months the cemented implants migrated the least and the HA- group the most (P = 0.009 – 0.036). From 3 to 24 months however, the implants in all three groups displayed very small migration, magnitudes well below the detection limit of RSA, and there were no differences between the three groups. Conclusions: The uncemented tibial component displays relatively large migration within the first 3 months compared to the cemented implant, and uncemented fixation without screws have larger migration than when screws are used. This larger initial migration for the uncemented fixation probably is due to “setting-in” of the prostheses. However, if the uncemented HA-coated implant “survives” this early period, the results of the present study indicate a good long term prognosis, even in designs where no screws are used for additional stability

Purpose: To investigate the effect that gender may have on the RSA defined migration pattern of cemented and uncemented tibial components in total knee arthroplasty (TKA). Method: 70 patients with primary osteoarthritis of the knee were randomized to receive a Nexgen uncemented Trabecular Metal (TM) monoblock tibial component (n=37; 20 female; mean age=66 years; mean BMI=32) or cemented cobalt chrome modular tibial cmponent (n=33; 19 female; mean age=65 years; mean BMI=33). The same design of posterior stabilized tibial component was used in all cases. Four experienced knee surgeons followed a standardized surgical technique (PCL resection, patella resurfacing, RSA bead placement in poly-ethylene and tibia) and post-operative protocol (CPM as tolerated, no drains, WBAT). Within 4 days of surgery and at 6, 12 and 24 months post-operatively patients underwent bi-planar x-rays. RSA analysis was performed with MB-RSA (MEDIS, Leiden). Results were reported as maximum total point motion, and 6 degrees of freedom translations and rotations. A repeated measure ANOVA was used to test for differences and all statistical analysis was performed using Minitab V.14 (Minitab Inc, State College, PA, USA). Results: Highly significant differences were seen in the migration patterns in females between the TM and cemented tibial components. Females with the TM implant tended to rotate internally (0.29° vs. −0.16°, p< 0.0001), tilt posteriorly (−0.49° vs. 0.01°, p< 0.0001) and subside (−0.357mm vs. 0.00mm, p< 0.0001) compared with the female subjects with the cemented implant. In the male group, only subsidence was different between the TM and cemented groups (−0.344mm vs. −0.01mm, p< 0.0001). Conclusion: Uncemented TM implants in females tended to tilt posteriorly, rotate internally and subside. Uncemented implants in males tended only to subside. The increased tilting and rotation detected in females could be due to lower BMD or to mismatching between the shape of the female proximal tibial and the tibial component. These results may have implications for the current use of uncemented implants in females and for future design of uncemented implants for the female population

Purpose: To investigate the association between pre-operative gait patterns and the RSA defined migration migration pattern of cemented and uncemented tibial components post total knee arthroplasty (TKA). Method: 43 patients with primary osteoarthritis of the knee underwent Optotrack gait analysis in the week before TKA surgery. Three-dimensional net external knee joint moments and angles were calculated with inverse dynamics. The variability in subject gait patterns was captured with a set of discrete scores that represented weightings on objectively-extracted features of the gait waveform data using principal component analysis. The subjects were randomized to receive the uncemented Nexgen Trabecular metal Monoblock tibial component (n=22; mean age=66 years; mean BMI=32) or the modular cemented cobalt chrome tibial component (n=21; mean age=65 years; mean BMI=33). Both groups were posterior-stabilized and used the same design femoral component. Four experienced surgeons followed a standardized surgical technique and postoperative protocol. Within 4 days of surgery and at 6 months post-operatively, patients had bi-planar knee x-rays taken. RSA analysis was performed with MB-RSA (MEDIS, Leiden). RSA results were reported as maximum total point motion, translations and rotations at 6 months. Spearman’s rank correlations were used to examine the relationship between the first three principle component (PC) scores for each gait variable and the RSA metrics (P< 0.05). Results: There was a highly significant correlation between MTPM and the first principal component (PC) of the knee adduction moment, which represented the overall magnitude of moment during the stance phase of the gait cycle (r=0.459, P=0.005). Higher preoperative knee adduction moment magnitudes were associated with greater MTPM postoperatively. Internal rotation of the components was correlated with the second PC of internal/external rotation moment at the knee, which represented the magnitude of the moment at load acceptance (r=0.341, P=0.042). Greater knee internal rotation moments at load acceptance preoperatively were associated with higher internal rotation postoperatively. Conclusion: The amount of postoperative migration of the tibial component in TKA was found to be correlated with preoperative gait patterns, particularly to the magnitude of the knee adduction moment.. These results suggest that surgical success and prosthesis survivorship may be dependent on the preoperative mechanical environment of the knee joint (i.e., gait)

Initial fixation affects ingrowth of uncemented tibial components. Previous studies assessed initial fixation, however most used limited one-dimensional motion measurements. Therefore, a three-dimensional micro-motion and migration analysis was performed to compare initial fixation of four different tibial tray configurations: 1) Keeled component 2) Non-keeled component (post but no keel) 3) Keeled component with screws 4) Non-keeled component with screws. Osteonics series 7 000 tibial trays (identical to Scorpio design) with and without standard keels were obtained. The 30 mm posts were left intact. The components were implanted without cement into twenty-four fresh-frozen cadaveric tibiae. Specimens were loaded through matched femoral components via two separate loading conditions: 1) sinusoidal medial load from 200 to 2 200 N at 0.5 Hz and 2) sinusoidal torsion load from −5 Nm to +5 Nm at 0.5 Hz with constant 1 200 N axial load. Motion data were collected from reference cubes and transducers rigidly attached to the trays, during 3 000 cycles of loading. Rigid-body mechanics were used to calculate the motion of a wire-frame computer model. Comparisons were made of micro-motion and migration magnitudes. A keel did not significantly decrease micromotion or migration under medial or torsion loading compared to a post alone (p=1.04). The addition of four cancellous screws decreased motion (p< .05) regardless of the presence of a keel under medial loading. No significant differences were noted under torsional load for any tray configuration. A keel did not enhance initial fixation compared to screws or a post alone. Screws enhanced fixation under axial offset loading in all constructs. Screw fixation did not affect motion under torsion loads perhaps due to the limited magnitude of torque transmitted across the unconstrained femoral-tibial articulation. Based on these data, initial fixation of uncemented tibial implants should include screw fixation to counter the effects of offset axial loads

Introduction Cemented fixation of the tibial component is the standard treatment for patients older than 65 with long-standing excellent results. Whether cemented fixation is best even for younger patients is still debated, and if uncemented fixation is chosen, the question remains as to whether screws are necessary as an adjunct. We present the results of a prospective randomized study comparing cemented and two modes of uncemented fixation. Methods Thirty-five patients (mean age 56 years, range 29 to 64) were operated with the Profix (Smith& Nephew) TKA for gonarthrosis grade III to V. At the operation, the patients were randomly allocated to fixation of the tibial component with cement (Group C, n=6), uncemented fixation with hydroxyapatite (HA) coating without screws (Group HA, n=14), or uncemented fixation with HA coating and with screws (Group HA+, n=15). The implants and tibiae were prepared for RSA with tantalum markers. RSA was performed post-operatively, three, 12 and 24 months post-op. Results There were no complications or revisions during the follow-up. For all three types of fixation the migration was larger during the initial three months, after which the migration leveled off. At three months, subsidence and tilting of the implant was significantly larger for group HA- compared to group C (P = 0.009 − 0.036), with the migration for group HA+ in between. This difference between the groups persisted up to 24 months. When examining the migration from three to 24 months, the implants in all three groups displayed very small migration, magnitudes well below the detection limit of RSA. There were no differences in magnitude of migration between the three groups between three and 24 months. Conclusions The uncemented tibial component displays relatively large migration within the first three months compared to the cemented implant, and uncemented fixation without screws has larger migration than when screws are used. This larger initial migration for the uncemented fixation probably is due to “setting-in” of the prostheses. However, if the uncemented implant “survives” this early period, the results of the present study indicate a good long term prognosis, even when no screws are used for additional stability. This is important, since osteolysis frequently has been observed in relation to screws in the proximal tibia. One reason for the stable fixation of the uncemented implants may be the use of HA-coating. 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

Introduction. Initial stability of the tibial component influences the success of uncemented total knee arthroplasty. In uncemented components, osseointegration provides long-term fixation which is particularly important for the tibial component. Osseointegration is facilitated by minimising bone-implant interface micromotion to within acceptable limits. To investigate initial stability, this study compares the micromotion and initial seating of two uncemented hydroxyapatite-coated tibial components, the Genesis II and Profix. This is the first stability comparison of two hydroxyapatite-coated tibial components. Methods. Six components of each type were implanted into synthetic tibias by a single orthopaedic surgeon. Good coverage was achieved. No screws or articular inserts were used. Initial seating was measured using ImageJ software at five areas on each tibia. Tibias were transected and their proximal section implanted into a molten alloy parallel to horizontal. Dynamic mechanical testing was performed using a hydraulic 858-Bionix machine. Prostheses underwent unilateral axial point-loading of 700N cyclically applied four times. The load was applied to three locations approximating femoral loading points. The loading cycle was repeated six times at each point, allowing micromotion to be recorded at three contralateral locations. Micromotion was measured by optical lasers. After dynamic testing, two tibial components of each type were removed with claw pliers while measuring the force required on the 858-Bionix machine. Implant under-surfaces were photographed for wear. Results. The micromotion readings allowed a directional (subsidence or lift-off) movement profile to be constructed. The absolute micromotion recordings demonstrated areas experiencing the most micromotion. Micromotion was not significantly different between components (P>0.05). Absolute micromotion during posterolateral loading was significantly different (P<0.05). Loading points producing the most absolute micromotion were antero- and centrolateral in Genesis II prostheses and anteromedial and posterolateral in Profix prostheses. The areas which showed the greatest absolute micromotion were anteromedial in Genesis II prostheses and posteromedial and posterolateral in Profix prostheses. Average absolute micromotion did not exceed 75μm. Initial gap ranged from 535–633 μm in Genesis II prostheses and 631–799 μm in Profix prostheses. Initial gap did not significantly correlate with either prosthesis. Pullout force was significantly different (P<0.0001), requiring less than 75N for Profix prostheses and greater than 150N for Genesis II prostheses. Wear was seen anteromedially in all Profix components. In Profix prostheses the only loading point to consistently produce liftoff was anteromedially. Conclusions. Average micromotion is not significantly different in Genesis II and Profix trays during point loading central condylar areas in synthetic tibias. With posterolateral loading the Genesis II was significantly more stable. Unilateral loading demonstrated a pivot type micromotion pattern about the tibial stem in both designs. Seating was not a significant factor influencing micromotion, presumably while the initial gap is small (<800μm). The deficit of an anteromedial peg in the Profix prostheses predisposes to liftoff when this point is loaded. Using a force approximating that of walking, distributed through typical femoral loading points, results in micromotion in both designs at a level not expected to prevent osseointegration

Aims

The primary aim of the study was to compare the knee-specific functional outcome of robotic unicompartmental knee arthroplasty (rUKA) with manual total knee arthroplasty (mTKA) for the management of isolated medial compartment osteoarthritis. Secondary aims were to compare length of hospital stay, general health improvement, and satisfaction between rUKA and mTKA.