Quasi-static mechanical evaluation of canine cementless total hip replacement broaches: effect of tooth design on broach and stem insertion.

BACKGROUND: Biomedtrix BFX® cementless total hip replacement (THR) requires the use of femoral broaches to prepare a press-fit envelope within the femur for subsequent stem insertion. Current broaches contain teeth that crush and remove cancellous bone; however, they are not particularly well-suited for broaching sclerotic (corticalized) cancellous bone. In this study, three tooth designs [Control, TG1 (additional V-grooves), TG2 (diamond tooth pattern)] were evaluated with a quasi-static testing protocol and polyurethane test blocks simulating normal and sclerotic bone. To mimic clinical broaching, a series of five sequential broach insertions were used to determine cumulative broaching energy (J) and peak loads during broach insertion. To determine the effect of broach tooth design on THR stem insertion, a BFX® stem was inserted into prepared test blocks and insertion and subsidence energy and peak loads were determined. RESULTS: Broach tooth design led to significant differences in broaching energy and peak broaching loads in test blocks of both densities. In low density test blocks, TG1 required the lowest cumulative broaching energy (10.76 ±0.29 J), followed by Control (12.18 ±1.20 J) and TG2 (16.66 ±0.78 J) broaches. In high density test blocks, TG1 required the lowest cumulative broaching energy (32.60 ±2.54 J) as compared to Control (33.25 ±2.16 J) and TG2 (59.97 ±3.07 J).  During stem insertion and subsidence testing, stem insertion energy for high density test blocks prepared with Control broaches was 14.53 ± 0.81 J, which was significantly lower than blocks prepared with TG1 (22.53 ± 1.04 J) or TG2 (19.38 ± 3.00 J) broaches. For stem subsidence testing in high density blocks, TG1 prepared blocks required the highest amount of energy to undergo subsidence (14.49 ± 0.49 J), which was significantly greater than test blocks prepared with Control (11.09 ±0.09 J) or TG2 (12.57 ± 0.81 J) broaches. CONCLUSIONS: The additional V-grooves in TG1 broaches demonstrated improved broaching performance while also generating press-fit envelopes that were more resistant to stem insertion and subsidence. TG1 broaches may prove useful in the clinical setting; however additional studies that more closely simulate clinical broach impaction are necessary prior to making widespread changes to THR broaches.

Methodology for performing biomechanical push-out tests for evaluating the osseointegration of calvarial defect repair in small animal models.

Push-out tests are frequently used to evaluate the bone-implant interfacial strength of orthopedic implants, particularly dental and craniomaxillofacial applications. There currently is no standard method for performing push-out tests on calvarial models, leading to a variety of inconsistent approaches. In this study, fixtures and methods were developed to perform push-out tests in accordance with the following design objectives: (i) the system rigidly fixes the explanted calvarial sample, (ii) it minimizes lateral bending, (iii) it positions the defect accurately, and (iv) it permits verification of the coaxial alignment of the defect with the push-out rod. The fixture and method was first validated by completing push-out experiments on 30 explanted murine cranial caps and two explanted leporine cranial caps, all induced with bilateral sub-critical defects (5.0 mm and 8.0 mm nominal diameter for the murine and leporine models, respectively). Defects were treated with an autograft (i.e., excised tissue flap), a shape memory polymer (SMP) scaffold, or a PEEK implant. Additional validation was performed on 24 murine cranial caps induced with a single, unilateral critically-sized defect (8.0 mm nominal diameter) and treated with an autograft or a SMP scaffold.•A novel fixture was developed for performing push-out mechanical tests to characterize the strength of a bone-implant interface in calvarial defect repair.•The fixture uses a 3D printed vertical clamp with mating alignment component to fix the sample in place without inducing lateral bending and verify coaxial alignment of push-out rod with the defect.•The fixture can be scaled to different calvarial defect geometries as validated with 5.0 mm bilateral and 8.0 mm single diameter murine calvarial defect model and 8.0 mm bilateral leporine calvarial defect model.

Evaluation of a self-fitting, shape memory polymer scaffold in a rabbit calvarial defect model.

Self-fitting scaffolds prepared from biodegradable poly(ε-caprolactone)-diacrylate (PCL-DA) have been developed for the treatment of craniomaxillofacial (CMF) bone defects. As a thermoresponsive shape memory polymer (SMP), with the mere exposure to warm saline, these porous scaffolds achieve a conformal fit in defects. This behavior was expected to be advantageous to osseointegration and thus bone healing. Herein, for an initial assessment of their regenerative potential, a pilot in vivo study was performed using a rabbit calvarial defect model. Exogenous growth factors and cells were excluded from the scaffolds. Key scaffold material properties were confirmed to be maintained following gamma sterilization. To assess scaffold integration and neotissue infiltration along the defect perimeter, non-critically sized (d = 8 mm) bilateral calvarial defects were created in 12 New Zealand white rabbits. Bone formation was assessed at 4 and 16 weeks using histological analysis and micro-CT, comparing defects treated with an SMP scaffold (d = 9 mm x t = 1 or 2 mm) to untreated defects (i.e. defects able to heal without intervention). To further assess osseointegration, push-out tests were performed at 16 weeks and compared to defects treated with poly(ether ether ketone) (PEEK) discs (d = 8.5 mm x t = 2 mm). The results of this study confirmed that the SMP scaffolds were biocompatible and highly conducive to bone formation and ingrowth at the perimeter. Ultimately, this resulted in similar bone volume and surface area versus untreated defects and superior performance in push-out testing versus defects treated with PEEK discs. STATEMENT OF SIGNIFICANCE: Current treatments of craniomaxillofacial (CMF) bone defects include biologic and synthetic grafts but they are limited in their ability to form good contact with adjacent tissue. A regenerative engineering approach using a biologic-free scaffold able to achieve conformal fitting represents a potential "off-the-shelf" surgical product to heal CMF bone defects. Having not yet been evaluated in vivo, this study provided the preliminary assessment of the bone healing potential of self-fitting PCL scaffolds using a rabbit calvarial defect model. The study was designed to assess scaffold biocompatibility as well as bone formation and ingrowth using histology, micro-CT, and biomechanical push-out tests. The favorable results provide a basis to pursue establishing self-fitting scaffolds as a treatment option for CMF defects.

Double Tension Slide Technique as a Novel Repair for Distal Biceps Tendon Tear: A Biomechanical Evaluation.

Background A comparative biomechanical analysis of two distal biceps tendon repair techniques was performed: a single suture tension slide technique (TST) and two suture double tension slide (DTS) technique. Methodology Ten matched pairs of fresh frozen human cadaveric elbows (20 elbows) were randomly separated into two cohorts for distal biceps tendon repair. One cohort underwent the TST, and the other underwent the DTS technique. The tendon was preconditioned with cyclic loading from 0° to 90° at 0.5 Hz for 3,600 cycles with a 50 N load. The specimens were then loaded to failure at a rate of 1 mm/s. The difference in the load to failure between the groups was analyzed using the Student's t test. The mode of failure was compared between groups using the chi-square test. All p-values were reported with significance set at p < 0.05. Results Overall, 77.8% of the included matched pairs demonstrated greater load to failure in the DTS group. The mean load to failure in the DTS group was 383.3 ± 149.3 N compared to 275.8 ± 98.1 N in the TST group (p = 0.13). The DTS specimens failed at the tendon (5/9), suture (3/9), and bone (1/9). The TST specimens failed at the tendon (4/9) and suture (5/9) only. There was no significant difference in failure type between groups (p = 0.76). Conclusions DTS demonstrates a similar to greater load to failure compared to TST with a trend towards statistical significance. The redundancy provided by the second suture has an inherent advantage without compromising the biomechanical testing.

Distal Biceps Tendon Repair Using a Double Tension Slide Technique.

Distal biceps tendon ruptures are thought to be secondary to an acute forceful eccentric load on a degenerative tendon. Nonoperative treatment following rupture leads to significantly decreased forearm supination and elbow flexion strength. There are several techniques described in the literature for repair. This article describes, with video illustration, distal biceps tendon repair using a double tension slide technique with 2 No. 2 high-tension nonabsorbable composite sutures.

Clamping soft biologic tissues for uniaxial tensile testing: A brief survey of current methods and development of a novel clamping mechanism.

Biologic tissues are complex materials that come in many forms and perform a variety of functions. They vary widely in composition and mechanical properties, and determination of the mechanical properties of tissues is of interest to those trying to engineer tissues to restore missing function. In performing experiments to characterize the mechanical properties of biologic tissues, there is no single solution to clamping tissues or tissue engineered constructs for mechanical testing. Various clamping techniques have been developed over the past few decades to address the difficulty of imposing appropriate boundary conditions on particular soft tissues during mechanical testing. Two criteria for a successful clamping mechanism are (i) prevention of test specimen slippage, and (ii) prevention of test specimen failure outside the gage region. Herein we present a novel clamping mechanism design developed for the mechanical testing of abdominal wall tissue as an example. This design incorporates pins with serrated clamps to successfully decrease the occurrence of test sample slippage while reducing imposed stress concentrations at the clamping sites. This design was evaluated by performing 40 uniaxial tensile tests on rat abdominal wall muscles using strain rates of 1% per second or 10% per second. Load and displacement data were acquired at the grips. The clamping area on the tissue sample was marked with India ink to track potential slippage of the sample during testing. Ultimate tensile strength and the corresponding stretch were calculated when the maximum load was achieved. With fine-tuning of the torque applied to the clamping grips, the success rate of the tensile tests reached over 90%.