Erik McDonald

Tibial plateau fracture repairs augmented with calcium phosphate cement have higher in situ fatigue strength than those with autograft.

Objectives: This study compared the biomechanical fatigue strength of calcium phosphate augmented repairs versus autogenous bone graft (ABG) repairs in lateral tibia plateau fractures. Methods: Eight matched pairs of tibias (six male, two female; age, 75 ± 14 years) were harvested from fresh-frozen cadavers. Reproducible split-depression fractures were simulated and repaired by an orthopaedic traumatologist using a lateral tibial plateau plate. One tibia from each donor was randomly assigned to either calcium phosphate (Callos; Acumed, Hillsboro, OR) or ABG as augmentation. The femoral component of a hemitotal knee arthroplasty was attached to the actuator of a servohydraulic press and centered above the repair site. Cyclic, physiological compression loads were applied at 4Hz starting with a maximum load of 15% body weight and increasing by 15% body weight every 70,000 cycles. Loading conditions were determined from calculations of weight distribution, joint contact area, and gait characterization from existing literature. Repair site depression and stiffness were measured at regular intervals. Specimens were then loaded to failure at 1 mm/min. Results: Calcium phosphate augmented repairs subsided less and were more stiff during the fatigue loading than were ABG repairs at the 70,000, 140,000, and 210,000 cycle intervals (P < 0.03) All repairs survived to 210,000 cycles. The average ultimate load of the calcium phosphate repairs was 2241 ± 455 N (N = 6) and 1717 ± 508 N (N = 8) for ABG repairs (P = 0.02). Conclusion: Calcium phosphate repairs have significantly higher fatigue strength and ultimate load than ABG repairs and may increase the immediate weightbearing capabilities of the repaired knee.

Comparison of a multifilament stainless steel suture with FiberWire for flexor tendon repairs — an in vitro biomechanical study

Our goal was to investigate and compare the mechanical properties of multifilament stainless steel suture (MFSS) and polyethylene multi-filament core FiberWire in flexor tendon repairs. Flexor digitorum profundus tendons were repaired in human cadaver hands with either a 4-strand cruciate cross-lock repair or 6-strand modified Savage repair using 4-0 and 3-0 multifilament stainless steel or FiberWire. The multifilament stainless steel repairs were as strong as those performed with FiberWire in terms of ultimate load and load at 2 mm gap. This study suggests that MFSS provides as strong a repair as FiberWire. The mode of failure of the MFSS occurred by the suture pulling through the tendon, which suggests an advantage in terms of suture strength.

Comparison of a New Multifilament Stainless Steel Suture with Frequently Used Sutures for Flexor Tendon Repair

PURPOSE To investigate the mechanical properties of some common suture materials currently in use and compare them with a new multifilament stainless steel suture. METHODS We investigated the mechanical properties of 3-0 and 4-0 Fiberwire, 3-0 Supramid, 3-0 Ethibond, and a new 3-0 and 4-0 multifilament stainless steel suture. All suture material was tested in a knotted configuration and all but the Supramid was tested in an unknotted configuration. We measured the load, elongation at failure, and stiffness during both tests. RESULTS The 4-0 multifilament stainless steel showed the least elongation, whereas the 3-0 multifilament stainless steel withstood the highest load of any material in both the knotted and unknotted tests. There was no difference in stiffness between the 3-0 and 4-0 multifilament stainless steel when untied; however, the 3-0 multifilament stainless steel was stiffer when tied. Soaking in a saline solution had no significant effect on the ultimate load, elongation at failure, or stiffness of any of the sutures. The 3-0 Fiberwire and 3-0 Ethibond required at least 5 throws to resist untying. CONCLUSIONS Multifilament stainless steel exhibited promising mechanical advantages over the other sutures tested. More research is needed to determine how this material will affect the clinical outcomes of primary flexor tendon repair. CLINICAL RELEVANCE With a secure attachment to the tendon, the multifilament stainless steels lower elongation and better knot-holding ability may result in a higher force to produce a 2-mm gap and a higher ultimate tensile strength in a tendon repair.

Comparison of Completely Knotless and Hybrid Double-Row Fixation Systems: A Biomechanical Study

PURPOSE The purpose of this study was to compare the biomechanical performance of a completely knotless double-row repair system (SutureCross Knotless Anatomic Fixation System; KFx Medical, Carlsbad, CA) with 2 commonly used hybrid double-row repair (medial knot-tying, lateral knotless) systems (Bio-Corkscrew/PushLock [Arthrex, Naples, FL] and Spiralok/Versalok [DePuy Mitek, Raynham, MA]). METHODS Fourteen pairs of fresh-frozen cadaveric shoulders were harvested, the supraspinatus tendons were isolated, and full-thickness supraspinatus tears were created. One of each pair was repaired with the completely knotless system, and the contralateral side was repaired with either of the hybrid systems. The repairs were then subjected to cyclic loading followed by load to failure. Conditioning elongation, peak-to-peak elongation, ultimate load, and mechanism of failure were recorded and compared by use of paired t tests. Seven additional shoulders were tested to determine the effect of refrigeration storage on the completely knotless system by use of the same mechanical testing protocol. RESULTS For the completely knotless repair group, 11 of 14 paired specimens failed during the cyclic loading period. Only 1 of 14 hybrid repair systems had failures during cyclic loading, and both hybrid repair systems had statistically lower conditioning elongation than the completely knotless repair group. The mean ultimate load of the SutureCross group was 166 ± 87 N, which was significantly lower than that in the Corkscrew/PushLock (310 ± 82 N) and Spiralok/Versalok (337 ± 44 N) groups. There was an effect of refrigeration storage on the peak-to-peak elongation and stiffness of the SutureCross group; however, there was no difference in ultimate tensile load or conditioning elongation. CONCLUSIONS The completely knotless repair system has lower time-zero biomechanical properties than the other 2 hybrid systems. CLINICAL RELEVANCE The SutureCross system has lower time-zero biomechanical properties when compared with other hybrid repair systems. Clinical outcome studies are needed to determine the significance.

Analysis of a knotless flexor tendon repair using a multifilament stainless steel cable-crimp system.

PURPOSE To compare the biomechanical and technical properties of flexor tendon repairs using a 4-strand cruciate FiberWire (FW) repair and a 2-strand multifilament stainless steel (MFSS) single cross-lock cable-crimp system. METHODS Eight tests were conducted for each type of repair using cadaver hand flexor digitorum profundus tendons. We measured the required surgical exposure, repair time, and force of flexion (friction) with a custom motor system with an inline load cell and measured ultimate tensile strength (UTS) and 2-mm gap force on a servo-hydraulic testing machine. RESULTS Repair time averaged less than 7 minutes for the 2-strand MFSS cable crimp repairs and 12 minutes for the FW repairs. The FW repair was performed with 2 cm of exposure and removal of the C-1 and A-3 pulleys. The C-1 and A-3 pulleys were retained in each of the MFSS cable crimp repairs with less than 1 cm of exposure. Following the FW repair, the average increase in friction was 89% compared with an average of 53% for the MFSS repairs. Six of the 8 MFSS specimens achieved the UTS before any gap had occurred, whereas all of the FW repairs had more than 2 mm of gap before the UTS, indicating that the MFSS was a stiffer repair. The average UTS appeared similar for both groups. CONCLUSIONS We describe a 2-strand multifilament stainless steel single cross-lock cable crimp flexor repair system. In our studies of this cable crimp system, we found that surgical exposure, average repair times, and friction were reduced compared to the traditional 4-strand cruciate FW repair. While demonstrating these benefits, the crimp repair also produced a stiff construct and high UTS and 2-mm gap force. CLINICAL RELEVANCE A cable crimp flexor tendon repair may offer an attractive alternative to current repair methods. The benefits may be important especially for flexor tendon repair in zone 2 or for the repair of multiple tendons.

Effect of mini-fragment fixation on the stabilization of medial malleolus fractures.

BACKGROUND: Oblique fractures of the medial malleolus can arise from the application of axial force at various anatomic positions of the ankle, including supination-external rotation, pronation-external rotation, or pronation abduction. Although a variety of techniques exist to provide fixation of horizontal medial malleolus fractures, the optimal technique and pattern for internal fixation remains unclear. The aim of this study was to evaluate the mechanical properties of four different fixation methods for fractures of the medial malleolus. METHODS: Identical oblique osteotomies were created in synthetic distal tibiae using a jig. The specimens were divided into four fixation groups: contoured 2.0 mm mini-fragment T-plate, figure-of-eight tension band wire, construct two parallel 4.0 mm cancellous screws, and two divergent 4.0 mm cancellous screws. The specimens were tested using offset axial tension at 10 mm/min until 2 mm of joint line displacement. RESULTS: The average stiffness in tension and force at 2 mm of joint line displacement of the plate construct was significantly greater than any of the other constructs (p < 0.05), whereas the average stiffness in tension of the other three groups were not significantly different from each other (p > 0.05). CONCLUSION: Using a contoured 2.0 mm mini-fragment T-plate as the method of fixation resulted in an at least 25% stiffer construct during tension and required at least 24% more force for 2 mm of joint line displacement when compared with more traditional methods of fixation in an osteotomy model of an oblique medial malleolus fracture. LEVEL OF EVIDENCE: V, therapeutic study.

A biomechanical comparison of ipsilateral and contralateral pedicle screw placement for modified triangular osteosynthesis in unstable pelvic fractures.

Objectives: Iliosacral fixation of unstable pelvic fractures does not produce enough stability to allow for immediate postoperative weight bearing. Triangular osteosynthesis creates additional resistance to vertical displacement and rotation. A disadvantage is the loss of the L5/S1 motion segment. We propose a modification of the standard triangular osteosynthesis construct in which the contralateral S1 pedicle is used. As the ipsilateral L5 pedicle is unavailable for fixation in a saw-bones composite pelvic model, we compared ipsilateral and contralateral S1 pedicle screw constructs. We hypothesized that ipsilateral and contralateral S1 pedicle screw constructs would demonstrate no difference in displacement or rotation. Methods: Seven saw bones pelvic models were tested. A 5-mm vertical fracture gap was created through the left sacrum while the pubic symphysis was completely dissociated. Each pelvis was tested sequentially in 4 triangular osteosynthesis configurations: ipsilateral S1 screw with anterior plate, contralateral S1 screw with anterior plate, contralateral S1 screw without anterior plate, and ipsilateral S1 screw without anterior plate. Specimens were cyclically loaded from 100–200 N at 0.25 Hz for 25 cycles and then loaded up to 300 N at 10 mm/min while displacement and rotation at the sacral and pubic fracture sites were measured. Results: There was no difference in any of the displacement measures between ipsilateral and contralateral constructs. When comparing rotation, the contralateral configuration experienced significantly less rotation than the ipsilateral configuration with and without the anterior plate applied. Conclusions: Within the limitations of the current model, contralateral S1 constructs for modified triangular osteosynthesis were biomechanically equal to ipsilateral constructs in preventing displacement and superior in preventing rotation.

Geometry of Proximal Humerus Locking Plates

Objectives: Proximal humerus fractures are commonly treated with open reduction and internal fixation with periarticular locking plates. This study compared the geometry of proximal humerus locking plates screw distribution, amount of bone–screw interface, and the volume the screws occupy within the humeral head, as well as how leaving the screws short of the articular surface affects these measures. Methods: Locking plates from 7 manufacturers were applied to foam humerus models. The entry and exit hole of each screw trajectory was digitized using a 3-dimensional motion tracking system. A trajectory for each screw was modeled, as well as the volume enclosed by the screw trajectories. The following outcome metrics were calculated: the bone–screw interface, the volume enclosed by the screws, and the effect of leaving the screws short of the articular surface. Results: Biomet had the most bone–screw interface (7259 mm2), whereas Zimmer had the least (3982 mm2). The original Synthes plate had the largest screw volume, occupying 31.5% of the humeral head, whereas Smith & Nephew and Zimmer had the lowest volumes, occupying 21.2% and 12.6%, respectively. Leaving the screws 15 mm short of the articular surface resulted in the most reduction in volume for the Depuy plate (50%) and the least reduction for the new version of the Synthes plate (29%). Conclusions: Many different manufactured periarticular locking plates exist to stabilize a proximal humeral fracture. Clinicians need to be familiar with the different plate configurations, screw lengths, and trajectories, which affect potential biomechanical performance and can optimize fracture site maintenance.

Mechanical behaviour of low-cost dynamic compression plates correlates with manufacturing quality standards

PurposeThis study compares the mechanical properties of low-cost stainless steel dynamic compression plates (DCPs) from developing-world manufacturers, adhering to varying manufacturing quality standards, with those of high-cost DCPs manufactured for use in the developed world.MethodsStandard-design ten-hole DCPs from six developing-world manufacturers and high-cost DCPs from two manufacturers in the developed world were studied. Nine plates from each manufacturer underwent mechanical testing: six in four-point monotonic bending to assess strength and stiffness and three in four-point bending fatigue. Statistical comparisons of the group means of monotonic bending test data were made, and a qualitative comparison was performed to assess failures in fatigue.ResultsLow-cost DCPs from manufacturers with at least one manufacturing quality standard had significantly higher bending strength and fewer failures in fatigue than did those from low-cost manufacturers with no recognised quality standards. High-cost DCPs demonstrated greater bending strength than did those in both low-cost groups. There were no differences in stiffness and fatigue failure between high-cost DCPs and those low-cost DCPs with quality standards. However, high-cost DCPs were significantly less stiff and had fewer fatigue failures than low-cost DCPs manufactured without such standards.ConclusionSignificant differences were found in the mechanical properties of ten-hole DCP plates from selected manufacturers in the developing and developed worlds. These differences correlated with reported quality certification in the manufacturing process. Mechanical analysis of low-cost implants may provide information useful in determining which manufacturers produce implants with the best potential for benefit relative to cost.

Biomechanical Evaluation of a Cable-Crimp System Designed for Repair of Tendons and Ligaments in the Hand

The goal of this study was to evaluate the biomechanical properties of an alternative method for connecting sutures using a crimp and to compare this method with a knot connection. Multifilament stainless steel suture (3-0 USP size) was connected by means of knot tying or crimp application and compared with FiberWire (3-0 USP size) connected by knot tying. Ultimate tensile strength (UTS) and stiffness were tested on a servohydraulic testing machine. The total UTS of the crimped constructs was significantly stronger and stiffer than the knotted groups, although the strength per strand was not statistically significant. Crimps offer an alternative method for connecting sutures. They have mechanical advantages over knot tying and allow the connection of multiple suture strands as well as the additional advantage of attaching both sides of the repair independently. This may provide precise pretensioning and potentially reduced surgical exposure.