Effect of bending direction on the mechanical behaviour of 3.5 mm String-of-Pearls and Limited Contact Dynamic Compression Plate constructs.

OBJECTIVE: To compare the bending properties of String-of-Pearls® (SOP) and Limited Contact Dynamic Compression Plate® (LC-DCP) constructs in orthogonal bending directions. METHODS: 3.5 mm SOP and LC-DCP plates were fixed to a bone model simulating a comminuted tibial fracture. Specimens were non-destructively tested in both mediolateral and craniocaudal bending for 10 cycles. Bending stiffness and total angular deformation were compared using parametric analyses (p <0.05). RESULTS: For both constructs, stiffness was significantly less when bending moments were applied against the thickness of the plates (mediolateral bending) than against the width (craniocaudal bending). When compared to the mediolateral plane, bending constructs in the craniocaudal plane resulted in a 49% (SOP group) and 370% (LC-DCP group) increase in stiffness (p <0.001). Mediolateral bending stiffness was significantly greater in the SOP than the LC-DCP constructs. Conversely, in craniocaudal bending, SOP constructs stiffness was significantly less than that of the LC-DCP constructs. The differences between the two constructs in total angular deformation had an identical pattern of significance. CLINICAL SIGNIFICANCE: This study found that SOP showed less variability between the orthogonal bending directions than LC-DCP in a comminuted fracture model, and also described the bi-planar bending behaviour of both constructs. Although not exhibiting identical bending properties in both planes, SOP constructs had a more homogenous bending behaviour in orthogonal loading directions. The difference between the SOP with a circular cross sectional shape compared to the rectangular shape of standard plates is probably responsible for this difference.

Reverse TPLO for asymmetrical -premature closure of the proximal tibial physis in a dog.

A 4.5-month-old, 13.8 kg, female neutered mixed breed dog was presented for evaluation of acute non-weight bearing right pelvic limb lameness. Radiographs revealed a tibial tuberosity avulsion fracture for which open reduction/internal fixation was performed. Asymmetrical premature closure of the cranial aspect of the proximal tibial physis ensued with a tibial plateau angle of -12°. Abnormal stifle biomechanics resulted in lameness and caudal cruciate ligament fraying. Tibial plateau levelling osteotomy was performed in standard fashion with the exception that the proximal tibial fragment was rotated cranioproximally to increase the tibial plateau angle from -12° to +5° (reverse tibial plateau levelling osteotomy). Normal healing and resolution of lameness followed and the dog remained clinically healthy 2 years postoperatively. This case report demonstrates that any change in proximal tibial anatomy, whether traumatic, iatrogenic or with therapeutic intent, can cause altered stifle biomechanics and should not be underestimated. Surgical management through corrective osteotomy can be used to restore adequate function.

In vitro mechanical evaluation of a limited contact dynamic compression plate and hybrid carpal arthrodesis plate for canine pancarpal arthrodesis.

OBJECTIVE: To compare the mechanical properties of pancarpal arthrodesis (PCA) constructs stabilized at 20° of extension using either a 3.5 mm limited contact dynamic compression plate (LC-DCP) or a 3.5/2.7 mm hybrid plate (HP). METHODS: Seven forelimb pairs were used from dogs of similar size. All soft tissues were removed except for supporting structures of the carpus and proximal metacarpal region. All plates were accurately bent to 20°, and then instrumented with two, 350Ω strain gauges applied at the level of the bend. Constructs were embedded in epoxy moulds then mounted onto a servo-hydraulic testing machine. Specimens were loaded for 10 cycles at 100N, 200N and 300N. Tenth cycle construct compliance (CC), maximum angular deformation (MAD), and peak plate strain (PPS) were compared using two-factor analysis of variance (ANOVA) and Student-Newman-Keuls post-hoc tests (p <0.05). RESULTS: Regardless of load, CC was 29% to 33% smaller in the HP than the LC-DCP group (p <0.03). In each group, the CC significantly increased with increasing loads (p <0.02). Mean MAD was 19% to 22% less in HP than LC-DCP constructs, with significant differences seen at 200N and 300N loads. In both groups, MAD was significantly greater with increasing loads (p <0.02). In addition, PPS was 37% to 43% smaller for HP than LC-DCP. CLINICAL SIGNIFICANCE: The mechanical advantages of the HP over the LC-DCP make it a viable alternative for PCA. Smaller CC, MAD and PSS of the HP may reduce the risk of implant failure and postoperative morbidity following PCA.