How Variable Are Achilles Allografts Used for Anterior Cruciate Ligament Reconstruction? A Biomechanical Study.

BACKGROUND: Allograft tendon used in anterior cruciate ligament reconstruction (ACLR) requires sterilization before implantation. Low-dose gamma irradiation is a means of sterilization that may minimize tissue damage. PURPOSE: To quantify the variability in mechanical properties between low-dose irradiated Achilles tendon allografts used for ACLR. STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 15 intact outer-third Achilles tendon allograft specimens were collected from the remains of full Achilles allografts used for intraoperative ACLR at a single hospital. All grafts were obtained from a single tissue bank and underwent proprietary disinfection and low-dose gamma irradiation (1.5-2.5 Mrad). Biomechanical testing was carried out to measure tendon elongation, failure location during tensile testing, maximum stress, maximum strain, and modulus of elasticity. The mean and standard deviation were calculated for each outcome measure, and the variability between specimens was calculated by the coefficient of variation (CV). The effect of donor age on graft material properties was examined by use of linear regression. One-way analysis of variance was performed to compare differences in the mechanical properties across failure locations. RESULTS: During cyclic testing, tendon elongation averaged 1.4% ± 1.6% with a CV of 118%. During failure testing, the maximum stress averaged 12.2 ± 4.1 MPa, maximum strain averaged 21.0% ± 6.3%, and modulus of elasticity averaged 95.5 ± 30.8 MPa. The CVs for maximum stress, maximum strain, and modulus of elasticity were 34%, 30%, and 32%, respectively. Ten tendons failed in the midsubstance and 5 failed at the tendon-bone enthesis. No differences were noted in mechanical properties between grafts that failed in the midsubstance versus those that failed at the enthesis. Donor age did not correlate with allograft elongation during cyclic load or any of the material property measures during failure testing. CONCLUSION: The variabilities in the material properties and graft elongation during cyclic loading of Achilles tendon allografts used in ACLR fall within the range of properties reported in the literature for other ACLR allografts. Material properties do not differ by donor age or graft failure location observed during failure testing. CLINICAL RELEVANCE: Surgeons should be aware that there exists considerable variation in the mechanical properties of Achilles allograft tendons used for ACLR. This variability is difficult to detect by tissue bank screening or the treating surgeon's inspection and may contribute to the heterogeneity in outcomes of allograft ACLR.

Suture number determines strength of rotator cuff repair.

BACKGROUND: Failure of surgical repair of a rotator cuff tear continues to be a clinical problem. For other tendon repairs, increasing the number of sutures improves both biomechanical performance and clinical outcomes. Several investigators have shown biomechanical advantages of double-row techniques but have used many more sutures than were used with the single-row techniques with which the double-row techniques were compared. The purposes of our study were to establish whether using a greater number of sutures would improve the biomechanical properties of a rotator cuff repair model, and whether using equal numbers of sutures would lead to equivalent results between single and double-row configurations. METHODS: Fresh-frozen sheep infraspinatus tendons underwent single-row repair with two, four, or six mattress sutures and double-row repair with use of four mattress sutures. Specimens were pretensioned at 10 N for one minute, then cycled from 10 to 180 N for 200 cycles at 0.2 Hz; this was followed by load to failure. Cyclic gap formation, failure load, and failure type were recorded. RESULTS: The four-suture single-row and four-suture double-row repairs had similar gap formation during cyclic testing, with no significant differences between them. Cyclic gap formation in the two-suture single-row group was 6.7 and 7.1 mm (97% and 109%) greater than that in the four and six-suture single-row groups after 200 cycles (p < 0.001). The average loads to failure of the two, four, and six-suture single-row groups were 274, 362, and 572 N (p < 0.0001). The average load to failure of the four-suture double-row group was 386 N, which was similar to the value in the four-suture single-row group (p = 0.58). CONCLUSIONS: In an ovine rotator cuff tendon repair model, increasing the number of sutures decreased cyclic gap formation and increased load to failure. Single and double-row repairs are biomechanically equivalent when the number of sutures is kept constant. CLINICAL RELEVANCE: The results of this study support the use of greater numbers of sutures in rotator cuff repair and disagree with the assertion that double-row repairs are biomechanically superior to single-row repairs.

Matched-pair total knee arthroplasty retrieval analysis: oxidized zirconium vs. CoCrMo.

Oxidized zirconium (OxZr) was introduced to serve as a ceramic surface for femoral components in TKA. The aim of this study was to compare retrieved OxZr components and corresponding PE inserts in matched comparison with conventional cobalt/chrome/molybdenum alloy (CoCrMo). Eleven retrieved posterior stabilized TKA with an OxZr femoral component were included. This included 6 implants from an earlier preliminary study. From a cohort of 56 retrieved TKA with conventional CoCrMo femoral components, pairs were matched according to duration of implantation, patient age, reason for revision, and BMI. Polyethylene inlays and femoral components were optically scored for in vivo damage. The average damage score of the tibial PE inserts was significantly lower with OxZr components (p=0.01). Mainly burnishing and scratches were found. The average wear score in the visual analysis of the femoral components was significantly lower for the OxZr as well (p=0.005). Femoral components made of OxZr were less sensitive to in vivo damage and corresponding PE inlays also showed less damage than CoCrMo components.

Retrieval analysis of femoral zirconium components in total knee arthroplasty: preliminary results.

Safety of oxidized zirconium (OxZr) in total knee arthroplasty (TKA) has been supported by biomechanical, clinical, and radiologic data. Retrieved OxZr femoral components and corresponding polyethylene (PE) inserts were examined to rule out patterns leading to early failure. Sixteen retrieved TKA with an OxZr femoral component were included. The PE inlays were analyzed applying an established scoring system for wear and surface damage. Femoral components were screened for scratching, pitting, delamination, and striations. The prostheses were in situ for 16.4 ± 11.9 months. The average wear and damage score for the tibial PE inserts was 36.0 ± 12.7. The average score in the visual analysis of the OxZr femoral components was 1.3 ± 1.3. The data presented in this study did not show major wear of the PE in TKA using OxZr components. In this cohort, there were no failures directly related to this implant.

Trunnion fracture of the anatomic medullary locking a plus femoral component.

Fracture of the neck of the femoral component after total hip arthroplasty is an infrequent complication. We present a report of 2 cases of trunnion fractures of fully porous-coated femoral stems (AML A Plus, DePuy International, Leeds, England), which had been implanted for 6 and 7 years after the index procedures. In both cases, failure emanated from a region where the trunnion had been intentionally grooved; and in both cases, the diameter of the trunnion was small, and evidence of corrosion contributing to the initiation of the failure was noted. Although this is the first report of trunnion fractures in this particular implant design, a close monitoring of prostheses with this specific trunnion should be considered. In addition, further analysis of clinical results and complications with this implant is warranted.

Contribution of mineral to bone structural behavior and tissue mechanical properties.

Bone geometry and tissue material properties jointly govern whole-bone structural behavior. While the role of geometry in structural behavior is well characterized, the contribution of the tissue material properties is less clear, partially due to the multiple tissue constituents and hierarchical levels at which these properties can be characterized. Our objective was to elucidate the contribution of the mineral phase to bone mechanical properties across multiple length scales, from the tissue material level to the structural level. Vitamin D and calcium deficiency in 6-week-old male rats was employed as a model of reduced mineral content with minimal collagen changes. The structural properties of the humeri were measured in three-point bending and related to the mineral content and geometry from microcomputed tomography. Whole-cortex and local bone tissue properties were examined with infrared (IR) spectroscopy, Raman spectroscopy, and nanoindentation to understand the role of altered mineral content on the constituent material behavior. Structural stiffness (-47%) and strength (-50%) were reduced in vitamin D-deficient (-D) humeri relative to controls. Moment of inertia (-38%), tissue mineral density (TMD, -9%), periosteal mineralization (-28%), and IR mineral:matrix ratio (-19%) were reduced in -D cortices. Thus, both decreased tissue mineral content and changes in cortical geometry contributed to impaired skeletal load-bearing function. In fact, 97% of the variability in humeral strength was explained by moment of inertia, TMD, and IR mineral:matrix ratio. The strong relationships between structural properties and cortical material composition demonstrate a critical role of the microscale material behavior in skeletal load-bearing performance.