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

Pantarsal arthrodesis in cats using orthogonal plating

Case series summary Pantarsal arthrodesis (PTA) was performed in seven tarsi of six cats, using orthogonal (dorsal and medial) veterinary cuttable plates (VCPs) without postoperative external coaptation. Short-term outcomes, arthrodesis progression and complications were assessed using a retrospective review of case notes (veterinary examination) and radiographs. Long-term outcomes were assessed via owner questionnaire (Feline Musculoskeletal Pain Index [FMPI]). Mean angle of PTA was 136° (range 116-166°). Intraoperative complications were recorded in two cases, both involving failure of the drill bit during drilling for calcaneotibial screws. Postoperative complications were encountered in a case of bilateral single-session PTA. These included gastrocnemius myotendinopathy on the right, and long-term protrusion of a screw head from the skin on the left. Both complications were resolved surgically, through resection of the implicated gastrocnemius tendon of insertion and removal of the plate, respectively. FMPI assessment was performed for all six cats a mean of 8.8 months (range 6-16 months) following surgery. Mean score for the first part (assessing ability to perform normal activities) was 92.2% (range 80.9-97.1%). Mean score for the second part (owner perception of pain) was 95.8% (range 87.5-100%). Mean overall score (mean score for parts 1 and 2 combined) was 92.3% (range 81.6-97.4%). PTA may be performed in cats using orthogonal VCPs to treat severe tarsal injuries. It may be prudent to avoid single-session bilateral PTA in cats. Relevance and novel information This case series documents a novel technique as an alternative for PTA in cats with talocrural injuries. Long-term outcome and complications presented in this case series are evaluated and discussed.

Feline pantarsal arthrodesis using pre-contoured dorsal plates applied according to the principles of percutaneous plate arthrodesis

Objective: To describe the surgical technique for pantarsal arthrodesis (PTA) in cats according to the principles of percutaneous plate arthrodesis with application of a pre-contoured dorsal plate, without external coaptation and to report the long-term clinical outcome.

Materials and methods: Retrospective review was performed of all cats treated by percutaneous plate application using a new pre-contoured dorsal plate for PTA between 2008 and 2011. Inclusion criteria were clinical and radiographic records plus clinical follow-up to at least six weeks. Data recorded included signalment, indication for surgery, postoperative care, and complications encountered. Radiographs were assessed for arthrodesis progression and complications. Outcome was assessed using an owner questionnaire.

Results: Eleven cats were treated for tarsal injuries and met the inclusion criteria. Mean age was 86 ± 45 months, weight 4.50 ± 0.92 kg. The only major short-term complication encountered was wound dehiscence requiring sedation and re-suturing. In the medium-term (23.3 months ± 11.6 months) eight out of nine cats returned to normal activity and one cat showed intermittent lameness. Long-term (34.3 months ±17.5 months) radiographic evaluation was performed in seven out of nine cats; six manifested complete arthrodesis and one sustained plate breakage. Based on owner questionnaire, all nine cats returned to normal activity in the long-term, even the case with plate breakage.

Conclusion: Based on our results, PTA using a custom pre-contoured dorsal plate is a suitable salvage surgery for treatment of severe tarsal injuries in cats.

The effect of external coaptation on plate deformation in an ex vivo model of canine pancarpal arthrodesis

Objectives: Since external coaptation is applied clinically to prevent plate failure during healing in canine pancarpal arthrodesis (PCA), we tested the hypothesis that external coaptation does not significantly reduce plate strain in an experimental ex vivo model of canine PCA.

Methods: Ten thoracic limbs from healthy Greyhounds euthanatized for reasons un- related to the study were harvested and the carpus was stabilised with a dorsally applied 2.7/3.5 mm hybrid PCA plate. The strain in the plate adjacent to the most distal radial screw hole (R4) and the radial carpal bone (RCB) screw hole was measured as the limbs were loaded axially to a load that approximated that of controlled walking. Each limb was tested with and without external coaptation in place.

Results: Mean strain amplitude at the RCB was –177.2 με (± 20.78) without external coaptation. Following cast application, strain reduced significantly to –34.7 με (± 9.84) (p <0.002). Mean strain at R4 was –89.4 με (± 22.10) without external support and –66.9 με (± 10.74) following application of a cast. This reduction in recorded strain was not statistically significant.

Clinical significance: The application of a cast to the distal portion of the limb significantly reduced strain in the 2.7/3.5 mm hybrid PCA plate, but the magnitude of the measured strain was low, suggesting that fatigue damage is unlikely to accumulate as a result of this type of loading and that external coaptation may not be necessary to prevent fatigue failure of the plate.

Ex vivo biomechanical comparison of a 3.5 mm locking compression plate applied cranially and a 2.7 mm locking compression plate applied medially in a gap model of the distal aspect of the canine radius

OBJECTIVE

To compare a medially applied 2.7 mm locking compression plate (LCP) to a cranially applied 3.5 mm LCP in a cadaveric distal radial fracture gap model.

STUDY DESIGN

In vitro mechanical testing of paired cadaveric limbs

SAMPLE POPULATION

Paired radii (n = 8) stabilized with either a 2.7 mm LCP medially or a 3.5 mm LCP cranially.

METHODS

Simulated distal radial comminuted fractures were created and stabilized with an LCP plate on the cranial surface in 1 limb, and on the medial surface in the contralateral limb. Gap stiffness, gap strain, and failure properties were compared between cranial and medial plate positions. Limb constructs were axially loaded, cyclically through 4 conditions that allowed mediolateral or craniocaudal bending at walk and trot loads, before monotonic failure loading. The effects of plate position on mechanical variables were assessed using paired t-tests.

RESULTS

Gap stiffness was greater for cranial plate constructs than medial plate constructs for axial loading with mediolateral bending, but lower with craniocaudal bending. However, in loading that facilitated craniocaudal bending the medial plate construct also had bending apparent in the mediolateral direction. Gap strains for the different conditions followed similar trends as stiffness. Cranial plate constructs had significantly higher monotonic stiffness, yield, and failure loads.

CONCLUSION

The larger, cranially applied LCP was biomechanically superior to the smaller, medially applied LCP in our distal radial fracture gap model, however the medial plate was superior to the cranial plate in cyclic loading allowing craniocaudal bending.

In vitro mechanical evaluation of medial plating for pantarsal arthrodesis in dogs

OBJECTIVE

To compare the bending properties of pantarsal arthrodesis constructs involving either a commercially available medial arthrodesis plate (MAP1) or a specially designed second-generation plate (MAP2) implanted in cadaveric canine limbs and evaluate the effect of calcaneotibial screw (CTS) augmentation on the structural properties of both constructs.

SAMPLE POPULATION

5 pairs of canine hind limbs.

PROCEDURES

Within pairs, specimens were stabilized with an MAP1 or MAP2 and loaded to 80% of body weight, with and without CTS augmentation. Compliance, angular deformation (AD), and plate strains were compared.

RESULTS

Construct compliance and AD did not differ between plates. Maximum plate strain was lower in the MAP2 than in the MAP1 (difference of approx 30%). Augmentation with a CTS reduced compliance, AD, and strains in MAP1 constructs but had no effect on those variables in MAP2 constructs.

CONCLUSIONS AND CLINICAL RELEVANCE

Because of lower peak strains, the MAP2 may be less susceptible to failure than the MAP1. Furthermore, CTS augmentation was unnecessary with MAP2s, which could minimize intra- and postoperative morbidity. Compared with what is known for dorsal plates, MAP2 constructs were associated with approximately 35% less AD. As a result of improved local stability, one might anticipate earlier fusion of the talocrural joint with an MAP2. In addition, plate peak strain was approximately 3.5 times lower in MAP2s than in dorsal plate constructs, which should result in greater fatigue resistance. The use of MAP2s may be a better alternative to both MAP1s and dorsal plates and could contribute to lower patient morbidity.