Percutaneous Screw Fixation of Incomplete Ossification of the Humeral Condyle in Three Dogs (Four Elbows)
ABSTRACT
Transcondylar screw fixation was performed using a minimally invasive percutaneous technique on three dogs (four elbows) diagnosed with incomplete ossification of the humeral condyle. The technique was performed using an aiming device in all four elbow joints and assisted by intraoperative fluoroscopy in one. All screws were successfully placed on first attempt and no elbow joint required repositioning of the transcondylar screw. On immediate postoperative radiographs, median transcondylar screw angulation was 2.9° and median percentage of screw eccentricity relative to the theoretical center of the humeral condyle was 14%. No short-term postoperative complications (<1 mo) were observed. The surgical technique described is a feasible option for surgical management of incomplete ossification of the humeral condyle in dogs that allowed accurate transcondylar screw placement and orientation.
Introduction
Separate centers of ossification appear within the canine humeral condyle at a mean (± standard deviation) of 14 ± 8 days of age and normally fuse at 70 ± 14 days.1 Failure of the lateral and medial portions of the humeral condyle to completely fuse in the immature dog is characterized by the presence of a fissure in the sagittal plane within the condyle, referred to as incomplete ossification of the humeral condyle (IOHC).2,3
Treatment of IOHC involves prophylactic placement of a transcondylar screw, either fully or partially threaded, applied either as a position screw or in lag fashion.2,4,5 Autogenous bone grafting can also be used in conjunction with a transcondylar screw.6 Several studies have looked at the outcome and complications of transcondylar screw placement in dogs with IOHC, but there are few reports describing surgery, which includes the choice of surgical approach and placement of screw.2,4–7
Transcondylar screw placement by an open lateral or medial approach remains a popular stabilization method.2,4–6 Although an arthrotomy does not have to be necessarily performed, these approaches facilitate screw placement by direct observation of articular surfaces and evaluation of humeral condyle size, minimizing the risk that the implant may penetrate the articular cartilage. However, open fixation techniques are invasive. Reported wound-related complication rates using open techniques ranged from 22.2 to 62%.6,7 Correct screw placement can be challenging. The complex three-dimensional anatomy of the elbow joint and relatively small size of the humeral condyle in dogs complicates implant placement.8,9 Anatomical landmarks and safe corridors for accurate screw placement have been described for dogs.10 A single case report mentioned briefly the use of an aiming device to assist screw placement in stabilization of IOHC in a dog.11
In humans, percutaneous screw or pinning fixation of humeral condyle fractures using intraoperative fluoroscopy has increasingly gained importance in recent years.12,13 A fluoroscopic guided closed reduction and internal fixation technique of fractures of the lateral portion of the humeral condyle has been successfully reported in dogs.14 We are unaware of any studies reporting a percutaneous screw fixation technique of IOHC in dogs. The purposes of this case report are to describe the surgical technique, to evaluate screw positioning on immediate postoperative radiographs, and to present short-term postoperative complications on three dogs (four elbows) treated with this procedure.
Case Report
Prophylactic percutaneous screw fixation for stabilization of IOHC was performed on three dogs (four elbows) referred to University College Dublin Veterinary Teaching Hospital (UCDVTH) between November 2012 and March 2013. All dogs had immediate postoperative radiographs available and had been followed up for at least 1 mo after surgery. Data retrieved from the medical records included signalment; body weight; presenting complaints; duration of lameness; clinical signs on admission; concomitant injuries; details of radiographic, computed tomography (CT), and arthroscopic examinations; implants and modes of application (position screw or screw inserted in lag fashion); surgical time per elbow (from incision of the skin to closure of the skin incisions); short-term postoperative complications; and resolution of lameness. Immediate postoperative elbow joints radiographs were used to document accuracy of screw positioning.
Anesthesia was induced in all dogs with propofola (2 mg/kg IV) after sedation with acepromazineb (0.05 mg/kg intramuscularly) and morphinec (0.02 mg/kg intramuscularly). Prophylactic potentiated amoxicillind (20 mg/kg IV) was administered at the time of induction. All dogs were intubated, and anesthesia was maintained with isofluranee in oxygen. Fluidsf (10 mL/kg per hr IV) were administered during the entire procedure until complete recovery from anesthesia.
Dogs were routinely prepared for aseptic surgery of one or both forelimbs. Each dog was placed in dorsal recumbency with the affected limb up. All procedures were performed by a board-certified veterinary surgeon. A 1-cm skin and subcutis incision was performed 0.5-cm distal to the lateral epicondyle with retraction provided using Gelpi self-retaining retractors. An aiming deviceg was used for transcondylar screw placement (Figure 1). The aiming device trocar type was first seated percutaneously on the exit site for the fixation screw located 0.5-cm distal to the most cranial part of the medial epicondyle. Next, the drill guide tip was placed on the planned entry site located 0.5-cm distally to the most cranial part of the lateral epicondyle and compression was placed across the bones by squeezing and locking the device (Figure 2).
Citation: Journal of the American Animal Hospital Association 53, 1; 10.5326/JAAHA-MS-6246
Citation: Journal of the American Animal Hospital Association 53, 1; 10.5326/JAAHA-MS-6246
When intraoperative fluoroscopy was used, a 2-mm transcondylar trocar tipped bone pinh was placed before screw placement on the planned entry site using the 2-mm drill sleeve until the pin entered in contact with the aiming device trocar tip. Although the trocar tip pin is designed to cut the bone, care must be exercised to avoid heat necrosis during insertion. The aiming device was then unlocked and removed, and intraoperative fluoroscopyi was used to directly assess the position of the pin in the craniocaudal and mediolateral planes. If necessary, pin placement was adjusted and rechecked using fluoroscopy. When appropriate position of the pin was achieved, the aiming device was then re-inserted over the pin, locked, and the pin was removed. These manipulations were performed to avoid superimposition of the aiming device with the pin on mediolateral fluoroscopy images.
Standard lag screw technique was then used. The appropriate drill sleeve for the intended drill bit was then inserted on the drill guide tip. The drill bit was inserted through the drill sleeve and used for full-depth drilling of the humeral condyle (i.e., lateral and medial portions of the condyle). Full-depth drilling was achieved when the tip of the drill bit was in contact with the aiming device trocar tip. Next, a glide hole was performed through the lateral portion only. The aiming device was then unlocked and removed. A large, double-point, speed-lock bone reduction forceps was applied percutaneously to achieve compression on the IOHC site during insertion of the lag screw. The bone forceps was placed, such as the pointed ends did not interfere with the placement of the screw. Bone depth was measured using depth gauge and screw was selected to match the exact length measured. The screw was then inserted into the hole and tightened until the head of the screw contacted the underlying bone. The bone forceps was unlocked and removed.
The incision was then closed routinely. A wound dressing was applied on the surgical site. Postoperative radiographs of the elbow joint, including mediolateral and craniocaudal views, were obtained in all cases. Meloxicamj (0.1 mg/kg body weight orally once daily) was administered for 3 wk after a loading dose of 0.1 mg/kg subcutaneously the day of surgery. Instructions were given to the owners for care of the incision and strict exercise restriction consisting in confinement and short leash walking. The owners were also instructed to schedule a recheck appointment at the author's institution at 2 and 4 wk after surgery.
Immediate postoperative radiographs of elbow joints were used to document accuracy of screw placement within the humeral condyle. All measurements were evaluated independently on three separate occasions by the author using an image processing applicationk. The mean value of the three measurements was used for descriptive data, reported as median and range. The data recorded from review of the craniocaudal view included: transcondylar screw angulation (TSA) relative to a line between the epicondyles (degrees) (Figure 3); trans-cortical engagement of the transcondylar screw (yes or no).15 The data recorded from review of the mediolateral view included: condylar radius (CR) defined as the radius of the circle that outlined the caudal aspect of the subchondral bone of the groove of the humeral trochlea (in mm); screw eccentricity (SE) measured as the distance between the center of the circle defining the humeral trochlea and the center of a second circle following the head of the screw (in mm) (Figure 4). The center of the circle defining the humeral trochlea was also defined as the theoretical center of the humeral condyle (CenterHC). A ratio termed the screw eccentricity to condylar radius (SE:CR) was then calculated from the above measurements in order to normalize measurements across case sizes. This ratio provided an objective assessment of the positioning of the screw relative to the CenterHC. A SE:CR ratio of 0 indicated perfect superimposition of the center of the head of the screw with the CenterHC.
Citation: Journal of the American Animal Hospital Association 53, 1; 10.5326/JAAHA-MS-6246
Citation: Journal of the American Animal Hospital Association 53, 1; 10.5326/JAAHA-MS-6246
Short-term postoperative complications were defined as complications occurring <1 mo following surgery. Seroma was defined as a fluid-filled swelling at the wound site with no evidence of heat, discharge, or fistula. Surgical site infection was defined as a purulent discharge or a fistula associated with the wound diagnosed by cytology and/or bacterial culture.
Results
Three dogs (four elbows) treated for IOHC were included. Breeds were springer spaniels (n = 2) and a Labrador retriever (1). Two dogs were sexually intact males and one was a spayed female. Median age on admission was 3 yr (range, 0.75 to 5 yr) and median body weight was 22 kg (range, 14 to 32 kg) (Table 1).
CT, computed tomography; FMCP, fragmentation of the medial portion of the coronoid process; HCF, humeral condylar fracture; M, male; SF, spayed female; +, positive finding; −, nothing abnormal detected; N/A, not applicable or not performed.
referred for HCF, no radiography were available before HCF and referral (not included in this case report).
All dogs presented with a history of varying forelimb lamenesses. Median duration of lameness before admission was 12 wk (range, 1 to 16 wk). Cases 1 and 3 had unilateral intermittent weight-bearing lameness and bilateral pain on internal rotation, flexion, and direct digital pressure of the lateral epicondyle. Cases 2 presented for an acute nonweight bearing lameness of the left forelimb with crepitus and a severely decreased range of motion, suggestive of an elbow fracture (not included in this study). This dog's contralateral limb (right) had signs similar to cases 1 and 3 without any associated lameness.
Diagnosis of IOHC (in all dogs), concomitant fragmentation of the medial coronoid process (in case 3), and fracture of the lateral portion of the humeral condyle in one elbow (in case 2 but not included in this case report) were made on the basis of CT examination (in cases 1 and 2) and on results of elbow arthroscopy (in case 3) (Table 1). Bilateral IOHC was evident on CT in case 1. In case 2, bilateral IOHC was also suspected, but no radiographs were performed by the referring veterinarian before fracture of the lateral portion of the humeral condyle in the left elbow and referral. In case 3, only radiographs of the left elbow obtained from the referring veterinarian were available and were suggestive of fragmentation of the medial coronoid process. Preoperative CT examination was not performed in this dog for financial reasons and the owners only chose immediate left elbow arthroscopy investigation during which medial coronoid process fragmentation was confirmed and a transcondylar fissure consistent with IOHC was observed.
Overall, four prophylactic percutaneous screw fixation surgeries in three dogs were performed because one dog (case 1) was treated bilaterally. The surgical technique was performed using an aiming device in all four elbows with concurrent intraoperative fluoroscopy in one. Two attempts were necessary in the case 2 to ensure correct pin placement on fluoroscopy images before screw insertion. In this case, suboptimal positioning of the pin on first attempt was based on incorrect placement of the aiming guide and this mistake was not recognized initially. Stabilization of IOHC was performed using 3.5-mm cortical (three elbows) or 4-mm cancellous (case 1) screws. Screws were placed in a lag fashion in all cases (Table 2). Case 3 had concomitant fragmentation of the medial coronoid process treated by fragment removal and curettage under arthroscopy. Case 2 also underwent fracture repair of the lateral portion of the left humeral condyle by an open reduction and internal fixation technique during the same anesthetic time. Median surgical time for percutaneous screw fixation per elbow was 35 min (range, 20 to 50 min).
+, performed; ±, medial coronoid process fragment removal and curettage; N/A, not applicable or not performed.
humeral condylar fracture repair (not included in this case report).
No intraoperative complications occurred. All screws were successfully placed on first attempt and no elbow joint required repositioning of the screw. On immediate postoperative radiographs, median TSA was 2.9° (range, 1.2 to 7.3°), median CR was 10.1 mm (range, 6.7 to 13.4 mm), median SE was 1.1 mm (range, 0.9 to 4.5 mm), and median SE:CR ratio was 0.14 (range, 0.09 to 0.34) (Table 3). All four screws were engaging the medial cortex with two or three threads protruding.
CR, condyle radius of the humeral condyle; SE, distance between the centre of the head of the screw and the centre of the humeral condyle; SE:CR, ratio between SE and CR; TSA, transcondylar screw angulation; Y, yes; N/A, not applicable or not performed.
Lameness completely resolved in two dogs (cases 1 and 2). Mild persistent left front limb lameness (same intensity as before surgery) was observed in case 3, which was treated surgically for both IOHC and fragmentation of the medial coronoid process. No short-term postoperative complications were observed in any of the four elbows joints treated prophylactically using the percutaneous screw fixation technique described.
Discussion
The author describes a minimally invasive surgical approach for transcondylar screw fixation of IOHC in dogs. Data from this study could demonstrate that percutaneous screw application using an aiming device is a feasible and successful technique based on immediate postoperative radiographic assessment of screw positioning and orientation. Additionally, no short-term postoperative complications were reported.
In the case series presented here, signalment of dogs was similar to previous reports.2,5,7,16–18 An aiming device was used to guide insertion of the transcondylar screw stabilizing IOHC. This device has multiple applications in orthopedic surgery because it accurately locates the entry and exit points of a pin or drill hole on the far side of a bone or fractured bone fragment. Use of similar aiming devices has been previously reported in dogs for application of a bilateral external fixator frame to a fractured tibia, humeral transcondylar screw fixation for surgical repair of IOHC, and Toggle Rod stabilization technique for coxofemoral luxation.11,19,20 Accurate placement of the device is the most critical part using the technique presented here. Therefore, cautious aiming device placement is necessary to prevent subsequent inaccurate orientation and positioning of the transcondylar screw.
In dogs with fracture of the lateral portion of the humeral condyle, an attempt should be made to angulate the screw parallel to the epicondylar line (TSA) to minimize the chance of intracondylar fracture gap formation. If the screw hole is not perpendicular to the fracture gap, then shear forces can be introduced when tightening the screw leading to formation of a gap at the fracture site.10,15 The author suggests that similar objective should be reached for transcondylar screw fixation of IOHC. Using the anatomical landmarks described in this study for positioning the aiming device, acceptable orientation of the transcondylar screw (1.2° to 7.3°, with a median of 2.9°) can be achieved with a percutaneous approach, which is comparable to open approach technique in dogs with fracture of the lateral portion of the humeral condyle.15 By a percutaneous approach, it may be difficult to place the screw at the appropriate transcondylar angle without the use of an aiming device.
In dogs, anatomical landmarks for positioning the transcondylar screw within the humeral condyle have been defined.10 The screw is aimed from craniodistal to the lateral epicondyle to exit the bone medially at a similar point halfway between the epicondyle and the humeral condyle articular surfaces. In the present study, aiming device tips were placed 0.5-cm distally to the most cranial parts of both lateral and medial epicondyles. Screw eccentricity to condylar radius ratio was calculated to establish the position of the center of the screw relative to the CenterHC. Ideal SE:CR ratio is 0. The SE:CR ratio measured on the postoperative radiographs ranged from 0.09 to 0.34 (median, 0.14). To our knowledge, no study has established the requirements for acceptable positioning of a transcondylar screw relative to the CenterHC. However, the author considered the maximal value of 0.34 obtained in case 2 as being acceptable. The significance of 34% eccentricity of the screw relative to the CenterHC is subjective, but the smallest distance (safe distance) measured on the mediolateral view between the shaft of the screw and the humeral condyle articular surfaces was 5.9 mm in this dog, which represented 1.69 times the diameter of the 3.5-mm screw used (5.9 mm/3.5 mm = 1.69).
The larger diameter screw is recommended for prophylactic stabilization of IOHC in dogs to reduce the possibility of implant failure.10 In our study, 3.5-mm cortical and 4-mm cancellous screws were used. Median diameter of the humeral condyle was 20.2 mm. Thus, the use of a 3.5-mm screw would occupy ∼17% of the humeral condyle diameter whereas a 4-mm screw would occupy ∼20%. Data from this study suggests that larger screws could have been used relative to the average bone size measured (25 to 30% of the bone diameter).21 However, anatomical constraints of the humeral condyle in dogs (central intercondylar notch) and possible damages to the humeral condyle articular surfaces during insertion of a larger screw may complicate such a recommendation.
To ensure optimum screw purchase in the bone, the transcondylar screw must be sufficiently long that at least one thread protrudes from the medial cortex.15
Humeral condyles with IOHC have a dense cancellous bone that is cortical-like, particularly in older dogs.10 Stability of the IOHC site may be significantly decreased if the threads of the screw are not fully engaged within the medial cortex. Of the four transcondylar screws placed in this report, all engaged the medial cortex with two or three threads protruding, suggesting that surrounding soft tissue structures on the planned entry site of the screw did not affect appropriate screw length measurements.
On clinical re-examination, lameness resolved completely in two dogs and mild persistent lameness (same intensity as before surgery) was observed in one dog even though function was not directly assessed. Outcome assessment was limited to immediate postoperative radiographic evaluation and short-term postoperative complications (<1 mo following surgery). Functional outcome was not assessed because two of the three dogs had concomitant injuries, thus making functional outcome assessment specific to treatment of IOHC difficult. Seroma formation and surgical site infection were the most commonly encountered complications in one large previous retrospective study.7 Of the seventy-nine elbows with IOHC treated using a transcondylar screw, forty-nine (62%) developed wound-related complications. Also, transcondylar screw in lag fashion significantly reduced the incidence of surgical site infection whereas no significant risk factors were identified for development of seroma postoperatively. In the present report, all screws were inserted in lag fashion. Additionally, the author assumes that due to the minimally invasive approach, there is less disruption of the surrounding soft tissues, which may account for the lack of wound-related complications.
Other potential advantages of the surgical technique reported here include that the surgeon has more precise control over the planned exit site on the far side of the bone and, therefore, the risk that the implant may penetrate the articular surfaces is lessened. Potential disadvantages include the inability to visualize articular surfaces, size of the humeral condyle, and implant placement. These disadvantages can be minimized through the use of intraoperative fluoroscopy. Fluoroscopic guidance was used in only one of the four surgical procedures performed. Use of intraoperative fluoroscopy, although deemed beneficial for real-time assessment of implant position, was not a prerequisite to perform the surgical procedure. Furthermore, the benefits of intraoperative fluoroscopy should be carefully weighed against long-term insidious health effects of ionizing radiation and the additional anesthetic and surgical time required during the procedure.
This report is subject to a number of limitations, including its retrospective design and the small number of cases evaluated. Also, assessment of screw positioning within the humeral condyle on postoperative radiographs is not an exact measurement because of limitation of conventional radiographic imaging of a three-dimensional structure. The humeral trochlea does not have a precisely circular profile, so the definition of the circle of the humeral trochlea is merely approximate and a certain degree conditioned by the subjective appraisal of the examiner.
Conclusion
Percutaneous screw fixation using an aiming device is a feasible option for surgical management of incomplete ossification of the humeral condyle in dogs that allowed accurate transcondylar screw placement and orientation. The technique described should be considered as a viable alternative for clinical management of IOHC in dogs.
Aiming deviceg; 2.5-mm, 3.1-mm, 3.5-mm, and 3.9-mm drill sleeves; 2.5-mm and 3.5-mm drill bits; and 3.5-mm screwdriver. This “C-shaped” device is composed of stainless steel, has a trocar point on one end, and is supplied with drill sleeves that can be easily interchanged on the other end for insertion of drill bits or pins. Seven drill sleeve diameters are available, including 1.6-mm, 2.0-mm, 2.3-mm, 2.5-mm, 3.1-mm, 3.5-mm, 3.9-mm, and 4.5-mm.
Intraoperative photograph showing the percutaneous approach to the lateral portion of the humeral condyle (case 3). The aiming deviceg tips were seated percutaneously 0.5-cm distally to the most cranial parts of both medial and lateral epicondyles. A hypodermic needle was used to identify the joint surface in the lateral compartment of the elbow joint.
Craniocaudal radiographic view of a surgically repaired right incomplete ossification of the humeral condyle using a 3.5-mm cortical screw (case 1) representing the maximal transcondylar screw angulation (transcondylar screw angulation; 7.3°) in this case series.
Mediolateral radiographic view of a surgically repaired right incomplete ossification of the humeral condyle using a 3.5-mm cortical screw (case 1) showing the distance (defined by the green line) between the center of the head of screw (defined by the blue circle) and the center of the humeral condyle (CenterHC) (defined by the red circle) that defines the screw eccentricity. The condylar radius (yellow line) is also represented.
Contributor Notes
