Bending properties of stainless steel dynamic compression plates and limited contact dynamic compression plates

Single cycle to failure in bending of three standard and five locking plates and plate constructs

Objective: To evaluate the biomechanical properties of standard and locking plates in bending. We hypothesised that titanium (Ti) constructs would have the greatest deformation and that String of Pearl (SOP) constructs would have the greatest strength and stiffness, and would behave differently compared to plates alone.

Methods: Dynamic compression plates (DCP), stainless steel (SS) limited contact (LC)-DCP®, Ti LC-DCP, locking compression plates (LCP), 10 mm and 11 mm advanced locking plate system (ALPS 10 / 11), SOP and Fixin plates were evaluated individually and as constructs applied to a validated bone model simulating a bridging osteosynthesis. Bending stiffness and strength were compared using one-way ANOVA with post hoc Tukey, and un-paired t-test (p <0.05).

Results: The SOP plates had significantly greater stiffness than all other plates Ti LCDCP, ALPS 10 and Fixin plates had significantly lower stiffness than all other plates. The SOP constructs had the highest mean bending stiffness, and strength that was significantly different from only the Ti LC-DCP, ALPS 10 and Fixin constructs. The ALPS 10 constructs had the lowest mean bending stiffness, and strength that was significantly different from only ALPS 11 and SOP constructs. Comparison of bending structural stiffness of plates versus constructs showed a significant difference in all plate pairs except for the DCP and ALPS 10.

Clinical relevance: Due to differing plate construct properties inherent to these diverse implant systems, identical approaches to fracture management and plate application cannot be applied.

Presented at the 38th Annual Conference of the Veterinary Orthopedic Society, Snowmass, CO, USA March 6, 2011 (Mark S. Bloomberg Memorial Research Award recipient).

Fatigue Analysis of Plates Used for Fracture Stabilization in Small Dogs and Cats

OBJECTIVE

To evaluate the fatigue life of stacked and single, veterinary cuttable plates (VCP) and small, limited contact, dynamic compression plates (LC-DCP).

STUDY DESIGN

In vitro biomechanical study.

METHODS

Fracture models (constructs; n = 8) were assembled for each of 6 groups all with 8-hole plates: 2.0 mm LC-DCP; 2.4 mm LC-DCP; single 1.5/2.0 mm VCP; stacked 1.5/2.0 mm VCP; single 2.0/2.7 mm VCP; and stacked 2.0/2.7 mm VCP. Plate(s) were secured to 2 polyvinylchloride pipe lengths, mounted in a testing system with a custom jig, and subjected to axial loading (10-100 N) for 1,000,000 cycles at 10 Hz or until failure. Differences in number of cycles to failure among groups were compared. Failure mode was determined.

RESULTS

All LC-DCP and single VCP constructs failed before 1,000,000 cycles. Stacked 2.0/2.7 mm VCP constructs withstood 1,000,000 cycles without failure. ANOVA and Fisher's least significant difference tests demonstrated significantly more cycles to failure for the stacked 1.5/2.0 mm VCP and stacked 2.0/2.7 mm VCP compared with the single 1.5/2.0 mm VCP, single 2.0/2.7 mm VCP, 2.0 mm LC-DCP, or 2.4 mm LC-DCP. Constructs that failed did so through a screw hole adjacent to the gap.

CONCLUSION

Stacked VCP constructs have greater fatigue lives than comparably sized LC-DCP or single VCP constructs. Plates with 2.4 mm screws were not significantly different from the comparable construct with 2.0 mm screws.

CLINICAL RELEVANCE

Although these data reveal that stacked VCP create a superior construct with respect to cyclic fatigue, surgeons must decide whether this is a clinical advantage on a case-by-case basis.

In vitro biomechanical comparison of a plate-rod combination-construct and an interlocking nail-construct for experimentally induced gap fractures in canine tibiae

OBJECTIVE

To compare structural properties of a plate-rod combination-bone construct (PRCbc) and interlocking nail-bone construct (ILNbc) by use of an experimentally induced gap fracture in canine tibiae.

SAMPLE POPULATION

12 paired canine tibiae.

PROCEDURE

Specimens were implanted with a plate-rod combination consisting of a 3.5-mm, limited-contact, dynamic-compression plate combined with an intramedullary rod or 6-mm interlocking nail. Ostectomy (removal of 10-mm segment) was performed. Paired constructs were loaded for bending, compression, or torsion measurements (4 constructs/group). Compliance was determined by fitting regression lines to the load-position curves at low (initial compliance) and high (terminal compliance) loads.

RESULTS

Bending compliances did not differ significantly between constructs. For the ILNbc, initial compliance was greater than terminal compliance in compression and torsion. Initial compliance and terminal compliance for the PRCbc were similar in compression and torsion. Initial compliance in compression and torsion was greater for the ILNbc, compared with initial compliance for the PRCbc. Maximum deformations in bending and compression were similar between constructs; however, maximum torsional angle was significantly greater for the ILNbc, compared with values for the PRCbc.

CONCLUSIONS AND CLINICAL RELEVANCE

The study documented that for an experimentally induced gap fracture in canine tibiae, a plate-rod combination is a significantly less compliant fixation method in torsion and compression, compared with an interlocking nail. Considering the deleterious effects of torsional deformation on bone healing, a plate-rod combination may represent a biomechanically superior fixation method, compared with an interlocking nail, for the treatment of dogs with comminuted tibial diaphyseal fractures.

Internal fracture fixation

Over the past decade, many improvements to small animal internal fracture fixation have been developed, including improved fixation techniques and a more diverse selection of implants. The understanding that appropriate fixation selection is based on a plethora of biologic, mechanical, and clinical factors has also emerged. Classically, the methods of internal fracture fixation have used pins, wires, screws, and plates to rigidly stabilize fractures that have been anatomically reduced with significant disruption to the biologic fracture environment. Newer methods attempt to minimize trauma to the soft tissues surrounding a fracture and promote biologic osteosynthesis using such implants as interlocking nails and plate-rod fixations. This review provides an overview of both the traditional and current principles of small animal internal fracture fixation.

In vitro mechanical evaluation on the use of an intramedullary pin-plate combination for pantarsal arthrodesis in dogs

OBJECTIVE

To compare the biomechanical properties of pantarsal arthrodesis achieved with a dorsal bone plate-alone (BPA) or pin-plate combination (PPC).

SAMPLE POPULATION

8 pairs of cadaver canine tarsi.

PROCEDURE

Within a pair, 1 tarsus was arthrodesed by use of a 13-hole 3.5-mm broad dynamic compression bone plate applied to the dorsal aspect of the tarsus; the paired tarsus received an identical plate similarly applied, with the addition of an intramedullary pin filling approximately 40% of the tibial medullary canal, spanning the tibiotarsal joint. Plates were instrumented with strain gauges proximal and distal to the solid portion of the plate. Specimens were mounted on a servo-hydraulic testing machine and loaded at 20%, 40%, and 80% of body weight for 10 cycles at 1 Hz. Construct compliance, angular deformation, and plate strain were determined during the 10th cycle.

RESULTS

PPC specimens were less compliant than BPA specimens at all loads and had significantly less angular deformation than BPA specimens at loads of 40% and 80% of body weight. Tibiotarsal gauge microstrain was significantly less in PPC specimens, compared with BPA specimens, regardless of loads. Maximal strains were 33.5% to 40.5% less in PPC than BPA specimens.

CONCLUSIONS AND CLINICAL RELEVANCE

For pantarsal arthrodesis in dogs, our results indicate that the PPC construct is biomechanically superior to the BPA construct. By improving construct stability, addition of an intramedullary pin to the traditional BPA technique may lessen implant-related complications and improve plate fatigue life. A subsequent decrease in postoperative morbidity may occur with little addition of time or complexity to the surgical procedure.