Comparison of multistage versus one-stage destabilization of a type II external fixator used to stabilize an oblique tibial osteotomy in dogs

Comparison of radiographic scoring systems for assessment of bone healing after tibial plateau leveling osteotomy in dogs

Introduction

Accurate radiographic assessment of bone healing is vital in determining both clinical treatment and for assessing interventions aimed at the promotion of bone healing. Several scoring systems have been used to evaluate osteotomy changes following tibial plateau leveling osteotomy (TPLO). The goal of this study was to compare the ability of five radiographic scoring systems to identify changes in bone healing following TPLO over time (Aim I), and to evaluate the influence of limb positioning on TPLO osteotomy scoring (Aim II).

Materials and methods

Phase I-A randomized, blinded, prospective study was conducted using similarly positioned postoperative TPLO radiographs from seven dogs taken immediately postoperatively, 6-weeks, and 8-weeks postoperatively. Ten reviewers assessed the radiographs, and five different scoring systems were tested for each set including three previously published ones, a Visual Analog Score (VAS), and a subjective 11-point scale. For each system, responses for 6-week postoperative were compared to 8-week postoperative. Scores were judged as correct (=showing an increase in score), incorrect (=decrease in score), or unchanged (=same score). Phase II-An international group of 39 reviewers was asked to score radiographs from three dogs, taken in different positions, using the VAS grading system. Scores were averaged and comparisons were made for each set.

Results

Phase I-The VAS system identified the greatest number of sets correctly (76%), with the least unchanged scores (15%), and 9% incorrect scores. Phase II-All three patients had an increase in the average difference between VAS-scores for differently positioned radiographs compared to similarly positioned radiographs. The magnitude of change between different positions far exceeded the magnitude of comparison of the similarly positioned radiographs from the 6- and 8-week time point.

Discussion/Conclusion

The VAS system appears to be the most appropriate of the tested systems to identify small changes in bone healing. In addition, the positioning of postoperative TPLO radiographs makes a substantial difference in the healing score that is assigned. Care must be undertaken when performing postoperative radiographs in both the clinical and research setting to ensure accurate assessment of bone healing.

Treatment of tibial shaft fractures in sheep using interlocking nails, Schanz screws and type I external fixators

This paper presents the results of a study of the treatment of transverse tibial shaft fractures in six sheep with the use of interlocking nails and type I extemal fixators. During surgery, tibial osteotomy was performed to induce an experimental fracture which was stabilized using a type I extemal fixator. Osteosynthesis was monitored for nine weeks by performing clinical tests, observing the degree of lameness and subjecting the patients to weekly radiological examinations. After nine weeks, the animals were euthanized, and samples of bone callus were sampled for histopathological analyses. Weight bearing on the fractured limb began on day 2 to 4 after treatment. Limb function was fully restored around five weeks after surgery. Radiograms taken during the observation period revealed gradual hyperplasia and progressing mineralization of bone callus at different stages of healing. The histopathological picture of the bone callus was characteristic of the phase of bone turnover and remodeling.

Late dynamization by reduced fixation stiffness enhances fracture healing in a rat femoral osteotomy model

OBJECTIVES

This study evaluated the effect of late dynamization on callus stiffness and size in a rat diaphyseal femoral osteotomy model. It was hypothesized that late dynamization, after bony bridging, would enhance healing.

METHODS

The external unilateral fixator was dynamized by removal of the inner fixator bar at either 3 weeks (D3 group) or 4 weeks (D4 group) postoperation. After 5 weeks, the rats were euthanized and healing was evaluated by biomechanical and densitometric methods. Published data of control groups, constant rigid (R group), and flexible fixation (F group) were included for comparison.

RESULTS

Enhanced healing was observed in both the 3- and 4-week dynamized groups compared with the constant flexible and constant rigid fixation. Late dynamization after both 3 and 4 weeks postoperation led to a stiffer callus (percent flexural rigidity relative to the intact side and elastic modulus) with a smaller callus bone volume compared with the F group. Both late dynamized groups (D3 and D4) had a similar flexural rigidity and bone mineral density as that of the R group. However, the D4 group had a significantly greater elastic modulus and significantly smaller callus bone volume compared with the R group suggesting increased remodeling occurred in the D4 group indicative of more advanced healing.

CONCLUSIONS

Late dynamization enhanced fracture healing in this animal model compared with a constant rigid or constant flexible fixation. Although results of the small animal study cannot directly be transferred to humans, these results indicate that once bony bridging has occurred, dynamization may accelerate bone remodeling processes.

Biomechanics of external fixation and limb lengthening

Surgeons who use external fixators for foot and ankle conditions need to understand the biomechanical principles to ensure good outcomes. Fixators can be used for fracture fixation, correction of contractures, distraction osteogenesis, and distraction arthroplasty. A two-ring fixator with wire fixation remains the gold standard with which all other frames are compared. Small changes in mechanical characteristics can have major implications on new bone or cartilage formation.

Treatment of canine and feline diaphyseal radial and tibial fractures with low-stiffness external skeletal fixation

The healing of 62 cases of radial and tibial fractures treated with low-stiffness Kirschner-Ehmer external skeletal fixation frames (frame types 1a, 1a plus intramedullary pin [1aIMP], 1b and 2b) was evaluated. The mean time to clinical union was 65 days. All cases treated with 1b, 2b or 1aIMP frames healed. Four of 25 cases treated with 1a frames failed to heal due to premature pin loosening; these failures were in heavier patients than 1a cases which healed (P=0.041). Complications occurred in 40 of 62 cases, and were more common in cases treated with type 2b frames. Pin loosening was the most frequent complication (35 cases) and most commonly involved the most proximal pin (P<0.001). In type 2b frames, full pins loosened more frequently than half pins (P<0.001). This study indicates that canine and feline fractures can heal readily when treated with these frames, suggesting that more rigid type 2a or type 3 frames are unnecessary in the majority of cases. Increased morbidity compared with the use of more rigid frames need not be expected, but 1a frames should be avoided in heavier patients.

Evaluation of a nontoxic rigid polymer as connecting bar in external skeletal fixators

OBJECTIVE

To investigate the mechanical characteristics of a nontoxic, low-cost, rigid polymer (RP) and to compare the structural and mechanical properties of a full-frame external skeletal fixator (ESF) with either RP connecting bars, polymethylmethacrylate (PMMA) connecting bars, or stainless-steel (SS) clamps and connecting bars.

STUDY DESIGN

In vitro mechanical evaluation.

METHODS

Mechanical properties were assessed using an in vitro bone fracture model with a bilateral uniplanar ESF (type II). Identical ESF were built with connecting bars using RP (n = 8), PMMA (n = 8), and SS connecting bars and clamps (System Meynard; n = 3). Nondestructive mechanical tests were performed in uniaxial compression (AC) and craniocaudal (CC) 4-point bending, as well as fatigue AC. Composite stiffness for each specimen and for each loading mode was calculated from 6 replicate measures using the slope of the load displacement curve at small displacements.

RESULTS

RP, PMMA, and SS ESF constructs yielded mean +/- SD composite stiffness values of 227 +/- 15, 381 +/- 30, and 394 +/- 9 N/mm in AC and of 35 +/- 2, 24 +/- 2, and 15 +/- 0 N/mm in CC, respectively.

CONCLUSIONS

Structural and mechanical properties of RP are satisfactorily rigid and fatigue resistant for its use as a connecting bar in ESF.

CLINICAL RELEVANCE

RP connecting bars in an ESF are a reliable, versatile, nontoxic and inexpensive option for the veterinary surgeon.