OBJECTIVE:The aim of this study was to evaluate the biomechanical effects of transfixation pin positioning in acrylic columns of external skeletal fixators (ESF). STUDY DESIGN:Twenty-four type I acrylic ESF were built simulating a fracture gap-model. Transfixation pins were placed centric (n = 12) or eccentric at ¼ of the column diameter (n = 12) in the acrylic columns. Six constructs from each group were subjected to axial compression and four-point bending tests. Stiffness, yield load and mode of failure were recorded. RESULTS:Stiffness was not influenced by centring (p = 0.373), but it was higher in four-point bending than in axial compression (p < 0.001). Pin positioning had no influence on the yield (p = 0.535) and failure loads (p = 0.715) in axial compression, nor on the yield load in bending (p = 0.135). Eccentric pin positioning decreased failure loads by 28% in bending (p < 0.001). CONCLUSION:Eccentric position of transfixation pins within the acrylic columns alters the biomechanical properties of type I ESF constructs. While acrylic offers several advantages, when forming the columns, frame strength will be optimized if pins are centrally located.

Acrylic columns are commonly used in external skeletal fixators, especially for fracture management or trans-articular fixations. To the authors' knowledge, there are no studies demonstrating if the number or position of the transfixation pins influence the ultimate strength and stiffness of the acrylic column. The objective of this study was to evaluate the effects of the number and position of transfixation pins (concentric versus eccentric) on the strength and stiffness of acrylic columns placed in axial compression. We hypothesized that strength and stiffness of acrylic columns under axial compression would not be affected by the number or position of the transfixation pins through the column. Three different groups of 12 acrylic columns were constructed with 4, 6, and 8 pins. In each group, 6 columns were constructed with the pins placed concentrically and the remaining 6 columns with the pins placed eccentrically. Each column was then placed under axial compression using a biomechanical testing machine. No significant differences were observed in ultimate strength regarding the number or position of transfixation pins (P = 0.83 and P = 0.27, respectively). However, stiffness was significantly decreased for columns with 4 eccentric pins compared with columns with 6 and 8 eccentric pins (P < 0.01) and with columns with 4 concentric pins (P < 0.001). Although the effects of transfixation pins on the rigidity of acrylic columns do not appear to be clinically significant, these tests were performed only in compression and results might differ if complete external fixator systems are used with different models of testing. Future studies are recommended.

A 1-year-old athletic golden retriever dog was presented for a non-weight-bearing right pelvic limb lameness that occurred during a canicross race. Orthopedic examination revealed pain and inflammation of the right stifle joint. Radiographs showed a traumatic comminuted patellar fracture. Surgery was elected and a midsubstance patellar ligament rupture was also identified. Surgical management consisted of a combination of techniques for patellar fracture fixation and primary patellar ligament reconstruction. All orthopedic implants were removed secondary to implant failure. Postoperative 20-month radiographic follow-up revealed patella alta and non-union of the fracture. However, an excellent clinical outcome was achieved with a complete return to a high activity level. Key clinical message: Surgical stabilization of patellar fractures is usually a significant challenge. A return to apparent normal limb function was achieved in this dog suffering complex patellar fracture with concomitant patellar ligament rupture despite postoperative fracture non-union.

An 11 yr old female spayed shih tzu was referred for treatment of left ureterolithiasis with complete obstruction of the left ureter and pyonephrosis. A ureteral stent was placed surgically to relieve the obstruction and pyonephrosis was treated with antibiotics. Three and a half years following stent placement, the patient developed an abscess on the left flank with chronic purulent discharge. Diagnostic imaging confirmed the presence of a left uretero-cutaneous fistula and renal abscess. A left ureteronephrectomy was performed. The dog was euthanatized 4 mo later for cardiac insufficiency unresponsive to medical treatment. This is the first report of a uretero-cutaneous fistula and renal abscessation as a complication of ureteral stenting in a dog.

With acrylic external-fixation frames for fracture repair the acrylic columns can be contoured to allow greater versatility in the placement of transfixation pins, thus minimizing damage to the surrounding soft tissue and making mandibular and transarticular fixation easier. However, contouring affects the stiffness and ultimate strength of the construct under axial compression. In this study, polymethylmethacrylate columns 21 mm in diameter angled at 0 degrees, 30 degrees, 45 degrees, 60 degrees, or 90 degrees with clamps were constructed. For each angulation group, pins 3.2-mm long were placed in 6 columns, 2 pins at each end, 1.5 cm from each other, and 6 columns had no pins. Each column was allowed to polymerize for a minimum of 10 min, then was placed in a biomechanical-testing machine, the load cell at the bottom end of the column and the actuator on top, with a preload of 10 to 12 N to prevent slippage. The columns underwent axial loading at a rate of 8 mm/s until catastrophic failure occurred. Data on force and deformation were collected every 0.025 s. Both stiffness and ultimate strength of the column decreased significantly (P < 0.01), up to 77% and 70%, respectively, with each increase of angulation. The columns with pins were significantly less stiff (P < 0.05) than those without pins at angulations of 45 degrees and 60 degrees. However, the columns with pins did not show significant differences in ultimate strength from the columns without pins at any of the angulations. The point of failure was always at the angle of the column, demonstrating that in axial compression the weakest point is not the pin-acrylic interface when pins are eccentrically located within the column.

This study reports short- and long-term clinical outcomes following excision arthroplasty in 7 small breed dogs with shoulder pathology. Lameness and pain were scored before surgery, and reassessed at short- and long-term follow-ups with measurements of range of motion (ROM), scapulo-humeral angles of extension (EA) and flexion (FA), and muscle girth (MG) of the operated and contralateral limbs. All dogs improved clinically for lameness and pain. Range of motion, EA, and FA of the operated limb were not significantly different compared with the contralateral limb at short-term follow-up, but ROM and EA were significantly decreased at long-term examination. Muscle girth was not significantly different than the contralateral limb. Radiographic re-evaluations showed bony proliferation around osteotomies without interosseous union in most dogs and all owners were satisfied with the surgery outcome. Excision arthroplasty seems to be an effective treatment for chronic shoulder pathologies in small dogs. Range of motion and EA were decreased and a mild lameness remained present at long-term follow-up.

A 6-month-old neutered male pot-bellied pig was presented for an obstructive urethral stone which was successfully removed by percutaneous cystolithotomy (PCCL). The pig recovered well although suspected urethral spasms and pollakiuria persisted for 2 weeks after surgery. The owner reported a good urine stream 2 months after discharge. This novel minimally invasive approach provided excellent visualization and allowed complete evaluation of the lower urinary tract. Percutaneous cystolithotomy holds great promise for the future treatment of various lower urinary tract disorders in this species.