A 6-month-old 4.2-kg (9.3-lb) sexually intact male Miniature Dachshund was referred for assessment and correction of a deformity of the distal aspect of the left pelvic limb. Lameness of the affected limb was observed after intense exercise. The deformity was clinically characterized by varus of the distal portion of the tibia (ie, pes varus). Results for the rest of the patient's physical and orthopedic examination were unremarkable.
The dog was sedated for diagnostic imaging. Orthogonal (caudocranial and mediolateral) radiographic views of both pelvic limbs were obtained. A CT scan was performed with images obtained in the dorsal, sagittal, and transverse planes, and a 3-D reconstructed image of the affected limb was created by use of simulation softwarea (Figure 1). Measurements of the proximal and distal joint orientation lines, mechanical axis of the tibia, and CORA for the affected limb were performed on digital radiographs as previously described.1,2 The findings confirmed that varus, procurvatum, and internal torsion of the distal portion of the left tibia were present (Figures 2 and 3).
To assess the varus deformity, proximal and distal joint orientation lines and the mechanical axis of the tibia were first plotted on the caudocranial radiograph of the unaffected limb, and the mechanical medial proximal tibial angle and the mechanical medial distal tibial angle were measured. These angles were then plotted on the caudocranial radiograph of the affected limb to draw proximal and distal mechanical axis lines of the unaffected bone on the affected bone. The site where the proximal and distal mechanical axis lines intersected was the CORA. The acute angle created by these 2 intersected axes corresponded to the degree of deformity that required correction (Figure 2). The procurvatum was similarly assessed by measuring the mechanical cranial proximal tibial angle and the mechanical cranial distal tibial angle on the unaffected limb and then plotting these angles and axes on the affected tibia (Figure 3). These measurements were cross-checked by CT examination with previously reported techniques.3 The degree of tibial torsion was determined from transverse CT images by measurement of the angle created between the caudal transcondylar axis proximally and the cranial surface of the tibia distally.3 The measurements for the unaffected right tibia were as follows: mechanical medial proximal tibial angle, 91.9°; mechanical medial distal tibial angle, 94.4°; mechanical cranial proximal tibial angle, 93.7°; mechanical cranial distal tibial angle, 80.2°; and tibial torsion, 5.8°. Preoperative differences between the right and left tibias at the CORA were 27.3°, 14.0°, and 4.3° in the dorsal, sagittal, and transverse planes, respectively.
All treatment options were discussed with the client, and consent was provided to proceed with surgical correction through a novel TSO procedure. The patient was premedicated with methadoneb (0.2 mg/kg [0.09 mg/lb], IV) and medetomidinec (8 μg/kg [3.6 μg/lb], IV), and general anesthesia was induced with propofold (4 mg/kg [1.8 mg/lb], IV) and maintained with isofluranee in oxygen. Preoperative analgesic treatments included epidural administration of morphinef (0.15 mg/kg [0.07 mg/lb]) and bupivacaineg (0.7 mg/kg [0.32 mg/lb]) and IV administration of methadoneb (0.2 mg/kg). An antimicrobial (cefuroxime,h 20 mg/kg [9.1 mg/lb], IV) was administered 30 minutes prior to the first incision and every 90 minutes for the duration of the procedure.
The patient was positioned in dorsal recumbency, and the entire left pelvic limb was aseptically prepared for surgery. One surgical assistant held the paw and femur so that the tibia was kept parallel to the table surface throughout the procedure; this was done to aid stabilization of the limb and provide an accurate reference for the surgeon. The first incision was made through the skin and subcutaneous fascia over the lateral aspect of the limb approximately halfway between the tarsal and stifle joints. A transverse fibular osteotomy was performed with a microsagittal saw bladei after retraction of soft tissue with Hohmann retractors.
A craniomedial approach to the tibia was performed from the middle of the tibial diaphysis down to the cranial aspect of the tarsus. Cranial exposure of the tibiotarsal joint allowed accurate observation of the joint angle and location. This improved implant placement and helped avoid violation of the articular surface. Distal tibial osteotomy was performed with a 12-mm dome osteotomy saw blade.j The size of saw blade was selected on the basis of previously published recommendations.4 Briefly, the blade with the smallest diameter was selected for which the diameter of the blade was still greater than the width of the bone, in both the dorsal and sagittal planes, at the level of the proposed osteotomy. The bone width measured on preoperative radiographs was 10.8 mm in the dorsal plane and 7.4 mm in the sagittal plane, leading to selection of the 12-mm blade.
The starting location on the tibia for the saw blade was chosen on the basis of measurements made on preoperative radiographs. Circles were drawn around the CORA with a 12-mm radius (matching that of the saw blade) to mimic the desired osteotomy location in the dorsal and sagittal planes. On the caudocranial radiograph, the proximal points where the circle bisected the medial and lateral cortices of the tibia were identified. On the mediolateral radiograph, the proximal point where the circle bisected the cranial cortex was identified. For each of these 3 points, the distance to the most craniodistal point of the tibial cochlea was measured. This point on the tibial cochlea was located during surgery, the 3 described distances were measured on the tibia, and the saw blade was positioned on the cranial aspect of the tibial cortex in line with the 3 points. The insertion angle of the saw blade relative to the long axis of the tibia was calculated by use of a previously reported formula.4 A surgical assistant used a goniometer during surgery to aid the surgeon's alignment of the saw blade, and the cut was completed to create proximal and distal segments.
The distal segment was rotated counterclockwise (to correct the varus) with a slight external rotation (to correct the internal torsion) and cranially (to correct the procurvatum). The distal segment was to be rotated relative to the proximal segment in the transverse, dorsal, and sagittal planes at distances determined by use of the following formula:
where a is the angle between the proximal and distal mechanical axes at the CORA in the respective plane and r is the radius of the saw blade. A caliper was used to measure these distances during surgery.
Initial stabilization was achieved with a 1.4-mm Kirschner wire inserted through the lateral aspect of the distal portion of the fibula, through the lateral cortex of the distal tibial fragment, across the osteotomy, and through the medial cortex of the proximal tibial fragment. Rigid fixation across the osteotomy site was accomplished with two 2.0-mm locking compression plates.k A 4-hole plate was placed cranially and secured with four 2-mm cortical screws, and a 6-hole plate was placed medially and secured with five 2.0-mm cortical screws. All screws were nonlocking. Limb alignment was deemed appropriate during surgery, and there was no impingement to stifle joint or tarsal joint range of motion. An allograftl of canine cancellous bone chips (1 cm3 of freeze-dried fine [< 1 mm] pieces) was packed adjacent to the medial side of the osteotomy. The incisions were closed routinely. Radiographic and CT assessments were performed immediately after surgery and revealed satisfactory limb alignment and implant positioning. Intraoperative photographs and immediate postoperative radiographs are provided (Figure 4). Single-energy metal artifact reduction was used to remove artifacts caused by the implants during CT imaging. Postoperative differences between the right and left tibias at the CORA were 2.6°, 6.5°, and 0.6° in the dorsal, sagittal, and transverse planes, respectively.
For analgesia, a transdermal fentanyl patchm (1.5 μg/kg/h [0.68 μg/lb/h]) was applied immediately after surgery and maintained for 3 days afterward. Prior to the fentanyl patch being deemed active in this dog on the basis of pain score assessments5 (12 hours after application), methadoneb (0.2 mg/kg, IV) was administered every 4 hours. Treatment with meloxicamn (0.1 mg/kg [0.045 mg/lb], PO, q 24 h) was initiated the evening following surgery. A soft, padded, compressive bandage was applied for 48 hours; on removal of the bandage, a small volume of serosanguineous discharge from the craniomedial surgical incision was noted; because of concerns about surgical site contamination, treatment with cephalexino (17 mg/kg [7.7 mg/lb], PO, q 12 h) was initiated. The patient was discharged from the hospital 4 days after surgery. Instructions for initial postoperative care given to the owners included routine incision care, continued administration of cephalexin (for a total of 10 days) and meloxicam (for a total of 4 weeks), and confinement of the patient in a crate for 6 weeks. Exercise was restricted to 10-minute walks with the dog on a leash, beginning 4 times daily for 6 weeks and then gradually increasing on-leash activity for another 6 weeks.
An individual certified as a specialist by the Royal College of Veterinary Surgeons performed clinical assessments on the day the dog was discharged from the hospital and 2, 6, 12, and 24 weeks after surgery. At each assessment, subjective lameness grade, stability of the osteotomy, joint range of motion, and signs of pain on examination were assessed and recorded. Lameness was evaluated on a scale of 0 to 5 as previously described6 and graded as moderate (3/5) at the time of discharge (4 days after surgery) and mild (1/5) at the 2-week follow-up, with no lameness (0/5) present at any of the subsequent examinations. Mild discomfort was detected on manipulation of the limb on the day of hospital discharge but was not found at any of the recheck examinations. Tarsal joint range of motion of the left pelvic limb was the same as that of the contralateral limb, and the osteotomy was palpably stable throughout all postoperative assessments. Although meloxicam administration was recommended for 4 weeks, the clients continued to give the medication until the bottle was empty, resulting in administration for 5 weeks. The instructions for strict crate rest and exercise restriction were not followed by the owners; however, no clinically important consequences were observed, and no additional analgesic medication was needed. Radiographic and CT assessments revealed satisfactory alignment and no disruption of the implants 6 weeks after surgery; osseous union had developed by 12 weeks after surgery. Photographs and selected radiographic images obtained during follow-up visits are provided (Figure 5). A telephone interview with the owner 30 months after surgery revealed the patient remained free of lameness or signs of pain in the treated limb.
Center of rotation of angulation
True spherical (dome) osteotomy
Toshiba Aquilion Prime 160 Slice, version 7, Canon Medical Systems Corp, Ōtawara, Japan.
Martindale Pharmaceuticals Ltd, Romford, England.
Domitor, Vetoquinol UK Ltd, Towcester, England.
Abbott Laboratories Ltd, Maidenhead, England.
Isoflo, Abbott Laboratories Ltd, Maidenhead, England.
Martindale Pharmaceuticals Ltd, Romford, England.
Marcain, AstraZeneca, Luton, England.
Zinacef, GlaxoSmithKline, Uxbridge, England.
Platinum Series Micro Sagittal Saw, Whittlemore Enterprises, Rancho Cucamonga, Calif.
DomeSaw blade, Matrix Orthopedics Inc, Twin Falls, Idaho.
LCP, DePuy Synthes, West Chester, Pa.
Veterinary Tissue Bank Ltd, Wrexham, Wales.
Duragesic, Janssen-Cilag Ltd, High Wycombe, England.
Metacam, Boehringer Ingelheim, Bracknell, England.
Therios, Ceva Animal Health Ltd, Amersham, England.
Fox DB, Fasanella FJ, Tomlinson JL. Comparison of osteotomy techniques for the correction of antebrachial angular limb deformities in the dog: investigation of a novel dome osteotomy saw blade (abstr), in Proceedings. 37th Annu Conf Vet Orthop Soc 2010;20.
Fitzpatrick N, Nikolaou C, Ochoa J, et al. True spherical dome osteotomy using a novel blade design in a dog with an antebrachial growth deformity: planning and execution of technique (abstr), in Proceedings. 38th Annu Conf Vet Orthop Soc 2011;22.
Fitzpatrick N, Egan P. Clinical outcome of antebrachial growth deformity treated using true spherical osteotomy and internal fixation in 47 canine limbs (abstr), in Proceedings. 42nd Annu Conf Vet Orthop Soc 2015;27.
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