Two-year migration characteristics of a novel cementless femoral stem: a radiostereometric analysis and clinical outcomes study.

BACKGROUND: Radiostereometric analysis (RSA) is an established high precision tool enabling us to detect early implant migration in total hip arthroplasty. The aim of this study is to present the RSA and clinical results of a new cementless hip stem and to compare those with established benchmarks. METHODS: A total of 45 patients (46 hips) undergoing total hip arthroplasty were available for full radiographic and clinical assessment at 2 years post-operatively. Mean patient age was 69 (range 43-85) years and mean body mass index was 29 (range 21-38) kg/m2 . RSA was undertaken at day 1, 6 weeks, 6 months and 1 and 2 years post-operatively. Oxford hip score and EQ-5D-5L scores were recorded preoperatively and at the same other time points. Results were compared to published data of established implants. RESULTS: At 2 years, mean subsidence and retroversion were 0.61 mm (standard deviation 0.7 mm, range -0.19 to 3.06 mm) and 0.44° (standard deviation 0.81°, range 0.98 to 3.29°), respectively. Stem migration occurred primarily in the first 6 weeks with no detectable subsidence or rotation at 6 months or 2 years. Mean Oxford hip score and EQ-5D-5L improved from 18.6 to 44.7, and 69 to 86, respectively. There was one cup-only revision and no revisions for stem loosening. CONCLUSION: RSA serves as an accurate measure of femoral stem stability early in the post-operative period. Our data confirm that stability occurs as early as 6 weeks and is sustained at 2 years. The Paragon stem demonstrates stability parameters at 2 years that exceed other established benchmark implants.

Low wear of a second-generation highly crosslinked polyethylene liner: a 5-year radiostereometric analysis study.

BACKGROUND: A sequentially irradiated and annealed, second-generation highly crosslinked polyethylene (XLPE) liner was introduced clinically in 2005 to reduce in vivo oxidation. This liner design has also been shown to reduce wear in vitro when compared with conventional and first-generation crosslinked liners. To date, there is only one study reporting an in vivo wear rate of this liner at 5 years' followup. However, that study used measurements made from plain radiographs, which have limited sensitivity, particularly when monitoring very low amounts of wear. QUESTIONS/PURPOSES: What is the amount and direction of wear at 5 years using radiostereometric analysis (RSA) in patients who had THAs that included second-generation XLPE? METHODS: We prospectively reviewed 21 patients who underwent primary cementless THA with the same design of XLPE acetabular liner and 32-mm articulation. Tantalum markers were inserted during surgery and all patients had RSA radiographs at 1 week, 6 months, and 1, 2, and 5 years postoperatively. Femoral head penetration within the acetabular component was measured with UmRSA(®) software. One patient died and two had incomplete radiographs leaving 18 radiographic series for analysis. RESULTS: The mean amounts of proximal, two-dimensional, and three-dimensional head penetration between 1 week and 5 years were 0.018, 0.071, and 0.149 mm, respectively. The mean proximal, two-dimensional, and three-dimensional wear rates calculated between 1 year and 5 years were all less than 0.001 mm/year with no patient recording a wear rate of more than 0.040 mm/year. CONCLUSIONS: The head penetration of a second-generation XLPE liner remained low at 5 years and the wear rate calculated after the first year was low in all directions. This low level of wear remains encouraging for the future clinical performance of this material.

Stem micromotion after femoral impaction grafting using irradiated allograft bone: a time zero in vitro study.

BACKGROUND: A gamma irradiation dose of 15kGy has been shown to adequately sterilise allograft bone, commonly used in femoral impaction bone grafting to treat bone loss at revision hip replacement, without significantly affecting its mechanical properties. The objective of this study was to evaluate whether use of 15kGy irradiated bone affects the initial mechanical stability of the femoral stem prosthesis, as determined by micromotion in a comprehensive testing apparatus, in a clinically relevant time zero in vitro model of revision hip replacement. METHODS: Morselised ovine bone was nonirradiated (control), or irradiated at 15kGy or 60kGy. For each dose, six ovine femurs were implanted with a cemented polished taper stem following femoral impaction bone grafting. Using testing apparatus that reproduces stem loading, stems were cyclically loaded and triaxial micromotion of the stem relative to the bone was measured at the proximal and distal stem regions using non-contact laser transducers and linear variable differential transformers. FINDINGS: There were no significant differences in proximal or distal stem micromotion between groups for all directions (p≤0.80), apart for significantly greater distal stem medial-lateral micromotion in the 60kGy group compared to the 15kGy group (P=0.03), and near-significance in the anterior-posterior direction (P=0.08, power=0.85). INTERPRETATION: Using a clinically relevant model and loading apparatus, irradiation of bone at 15kGy does not affect initial femoral stem stability following femoral impaction bone grafting.

Wear of a 5 megarad cross-linked polyethylene liner: a 6-year RSA study.

BACKGROUND: One cross-linked polyethylene (XLPE) liner is manufactured using a lower dose of radiation, 5 Mrad, which may result in less cross-linking. The reported in vivo wear rate of this XLPE liner in patients undergoing THA has varied, and has included some patients in each reported cohort who had greater than 0.1 mm/year of wear, which is an historical threshold for osteolysis. Previous studies have measured wear on plain radiographs, an approach that has limited sensitivity. QUESTIONS/PURPOSES: We therefore measured the amount and direction of wear at 6 years using Radiostereometric analysis (RSA) in patients who had THAs that included a cross-linked polyethylene liner manufactured using 5 Mrad radiation. METHODS: We prospectively reviewed wear in 30 patients who underwent primary THAs with the same design of cross-linked acetabular liner and a 28-mm articulation. Tantalum markers were inserted during surgery and all patients had RSA radiographic examinations at 1 week, 6 months, 1, 2, and 6 years postoperatively. RESULTS: The mean proximal, two-dimensional (2-D) and three-dimensional (3-D) wear rates calculated between 1 year and 6 years were 0.014, 0.014, and 0.018 mm/per year, respectively. The direction of the head penetration recorded between 1 week and 6 years was in a proximal direction for all patients, proximolateral for 16 of 24 patients, and proximomedial for eight of 24 patients. CONCLUSIONS: The proximal, 2-D and 3-D wear of a XLPE liner produced using 5 Mrad of radiation was low but measurable by RSA after 6 years. No patients had proximal 2-D or 3-D wear rates exceeding 0.1 mm/year. Further followup is needed to evaluate the effect of XLPE wear particles on the development of long-term osteolysis.

The impact of tensioning device mal-positioning on strand tension during anterior cruciate ligament reconstruction.

BACKGROUND: In order to confer optimal strength and stiffness to the graft in Anterior Cruciate Ligament (ACL) reconstruction, the maintenance of equal strand tension prior to fixation, is desired; positioning of the tensioning device can significantly affect strand tension This study aimed to determine the effect of tensioning device mal-positioning on individual strand tension in simulated cadaveric ACL reconstructions. METHODS: Twenty cadaveric specimens, comprising bovine tibia and tendon harvested from sheep, were used to simulate ACL reconstruction with a looped four-strand tendon graft. A proprietary tensioning device was used to tension the graft during tibial component fixation with graft tension recorded using load cells. The effects of the tensioning device at extreme angles, and in various locking states, was evaluated. RESULTS: Strand tension varied significantly when the tensioning device was held at extreme angles (p < 0.001) or in 'locked' configurations of the tensioning device (p < 0.046). Tendon position also produced significant effects (p < 0.016) on the resultant strand tension. CONCLUSION: An even distribution of tension among individual graft strands is obtained by maintaining the tensioning device in an unlocked state, aligned with the longitudinal axis of the tibial tunnel. If the maintenance of equal strand tension during tibial fixation of grafts is important, close attention must be paid to positioning of the tensioning device in order to optimize the resultant graft tension and, by implication, the strength and stiffness of the graft and ultimately, surgical outcome.

Tibial interference screw fixation in anterior cruciate ligament reconstruction with and without autograft bone augmentation.

PURPOSE: Because tibial fixation of soft-tissue grafts in anterior cruciate ligament (ACL) reconstruction is problematic, this study aimed to develop a means of delivering bone graft evenly around tendon autograft and define any mechanical, radiologic, or histologic benefit using an ovine model. METHODS: A device to deliver bone graft evenly throughout the tibial tunnel was developed. Forty mature sheep underwent simulated quadruple hamstring tendon-ACL reconstruction by use of a bioresorbable interference screw, either with or without bone graft augmentation of the tibial tunnel. Endpoint data were derived at time 0 and after 6 weeks in vivo. Radiostereometric analysis provided quantitation of the translational characteristics; computed tomography evaluated tunnel volume, and measures of yield strength and stiffness were obtained. Sequential fluorochrome administration assessed bone formation, and light microscopy surveyed the biological response. RESULTS: Radiostereometric analysis highlighted differences in the translational characteristics of ACL-deficient knees when compared with intact knees. Reconstructed knees (with or without autograft) showed significantly greater translation when compared with unoperated knees at 6 weeks; autograft bone augmentation provided no benefit. Neither tunnel volume nor yield strength nor stiffness was improved with the addition of autograft bone. No untoward histologic responses were observed. Bone apposition rates were similar between treatment groups. An even distribution of bone graft throughout the tunnels was observed. CONCLUSIONS: This model has confirmed the ability of the bone graft-delivery system to evenly distribute bone graft throughout the tunnels. However, the study has failed to show improvement in stability or fixation strength after augmentation with autograft bone. CLINICAL RELEVANCE: The autograft bone-delivery system may provide a means of establishing an osteoconductive/inductive environment. At this early juncture (6 weeks), no benefit could be defined. Its use in combination with bone morphogenetic proteins or stem cells may provide more rapid fixation, rehabilitation, and reconstitution of bone volume within the tunnel.

Second-generation highly cross-linked X3™ polyethylene wear: a preliminary radiostereometric analysis study.

BACKGROUND: First-generation highly cross-linked polyethylene liners have reduced the incidence of wear particle-induced osteolysis. However, failed acetabular liners have shown evidence of surface cracking, mechanical failure, and oxidative damage. This has led to the development of second-generation highly cross-linked polyethylene, which has improved wear and mechanical properties and resistance to oxidation in vitro. Owing to its recent introduction, there are no publications describing its clinical performance. QUESTIONS/PURPOSES: We assessed early clinical wear of a second-generation highly cross-linked polyethylene liner and compared its clinical performance with the published results of hip simulator tests and with first-generation highly cross-linked polyethylene annealed liners. PATIENTS AND METHODS: Twenty-one patients were enrolled in a prospective cohort study. Clinical outcome and femoral head penetration were measured for 19 patients at 6 months and 1 and 2 years postoperatively. RESULTS: The median proximal head penetration was 0.009 mm and 0.024 mm at 1 and 2 years, respectively. The median two-dimensional (2-D) head penetration was 0.083 mm and 0.060 mm at 1 and 2 years, respectively. The median proximal wear rate between 1 and 2 years was 0.015 mm/year. CONCLUSIONS: The wear rate calculated was similar to the in vitro wear rate reported for this material; however, it was less than the detection threshold for this technique. Although longer followup is required for wear to reach a clinically quantifiable level, this low level of wear is encouraging for the future clinical performance of this material. LEVEL OF EVIDENCE: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Biceps tenodesis: a biomechanical study of fixation methods.

Rupture of the biceps tendon occurs predominantly in the middle-aged and elderly, being predisposed through bicipital tendinitis and rotator cuff lesions. Surgical repair may be an option for those requiring strength in supination. This study compared the initial fixation strength of keyhole tenodesis (n = 7) and interference screw fixation by use of cadaveric specimens. Two interference screws were evaluated (n = 7 x 2): the round-headed cannulated interference screw (RCI) and a bioresorbable screw (Sysorb). All specimens failed at the fixation site but one. This study found that overall there was a significant effect as a result of study group (keyhole vs Sysorb vs RCI, P =.034). The post hoc comparisons revealed that the keyhole was significantly stronger than the RCI screw (P =.033) but not significantly different compared with the Sysorb screw (P =.129). No significant difference was observed between the Sysorb and RCI screws (P =.762). Interference screw fixation failed by tendon slippage at the screw-tendon-bone interface; keyhole fixation failed by tendon splitting and slippage out of the restraining keyhole. Keyhole tenodesis may permit earlier postoperative mobilization when compared with tenodesis by use of interference screw fixation.

Bone blood flow response to surgical trauma.

The evolution of bone plate design has been with a view to reducing the interface contact between the plate and the underlying bone thereby limiting the perfusion deficiency that develops. Little consequence, however, has been attributed to the drilling of holes in the steps prior to bone plate application; the work present herein attempts to define the vascular response of bone to the trauma of drilling holes. Anaesthetized sheep underwent the creation of drill holes in both tibiae and metatarsi. Animals were then heparinized and euthanatized. Utilizing femoral cannula, perfusion of the vasculature ensued; spalteholz (India ink), disulphine blue and radiocontrast material (barium sulfate). Decalcified histology was performed and correlated with the perfusion studies. Regions of perfusion deficiency were observed immediately adjacent to, and removed from, the drill hole site. Radiographic images showed substantial haematoma formation and vascular disruption in the vicinity of the drill hole site. Histologically, blood vessels immediately adjacent and distal to the drill hole site, contained a proteinaceous/cellular material occluding the vascular space. Our findings support the proposal of a short-term obstruction in cortical blood flow which may contribute to later adaptational osteopaenia following bone plate application. We have observed an acute vascular insufficiency in cortical bone directly related to the trauma of drilling screw holes.