Canine-fractures Of The Proximal Femoral Physis In Dogs

November 1996 Vol.18, No. 11

Continuing Education Article

FOCAL POINT ★Interfragmentary compression for physeal fractures in dogs is the surgical treatment of choice, although good results have been achieved with multiple-pin fixation.

KEY FACTS ■ Proximal femoral physeal fractures only occur in immature animals because the physis must be open for trauma to occur. ■ Physical examination following proximal femoral physeal fracture should evaluate all body systems because of the correlation of these fractures with physical trauma. ■ Because some dogs have minimal fragment displacement following a fracture, radiography and careful evaluation of the physis are important for accurate diagnosis. ■ Age at the time of injury is critical for prognosis; younger dogs have a greater chance of developing degenerative joint disease.

Fractures of the Proximal Femoral Physis in Dogs Auburn University

Kansas State University

D. M. Tillson, DVM, MS

R. M. McLaughlin, DVM, DVSc J. K. Roush, DVM, MS

T

he proximal femoral physis is a common site of fractures in immature dogs. Synonyms for fractures of the proximal femoral physis include capital physeal fracture, capital epiphyseal fracture, slipped capital epiphysis, and proximal femoral epiphyseal separation.1–7 Fractures of the proximal femoral physis are most commonly Salter-Harris type I or II fractures, which account for 16% of all physeal fractures.1,2,8–10 Complications of proximal femoral physeal fracture and its repair include degenerative joint disease, deformity and osteonecrosis of the femoral head and neck, subluxation or luxation of the coxofemoral joint, fracture nonunion, fixation failure, infection, and sciatic nerve impingement.1,4,6,11–13 This article reviews information pertinent to fractures of the proximal femoral physis in dogs. The anatomy and blood supply of the coxofemoral joint and the anatomy of the normal physis are reviewed. Treatment and repair options are presented, and complications associated with fracture repair and healing are discussed.

ANATOMY OF THE CANINE COXOFEMORAL JOINT The joint between the os coxae and the proximal femur is a synovial or diarthrodial joint with a ball-and-socket configuration.14 The joint consists of a joint cavity, joint capsule, synovial fluid, articular cartilage, and underlying bone.14 The os coxae is formed by fusion of the ilium, ischium, pubis, and acetabular bones at 12 weeks of age.14,15 The femoral head is anchored into the acetabulum by the round ligament (ligament of the head of the femur), surrounding joint capsule, and transacetabular ligament.14 In immature dogs, the coxofemoral joint develops in a normal manner as long as all forces acting on the hip are balanced and neutral to accommodate congruency between the acetabulum and femoral head.15 Instability between the femoral head and acetabulum leads to incongruency and degenerative joint disease.15,16 BLOOD SUPPLY TO THE CANINE FEMORAL HEAD The arterial supply to the coxofemoral joint and proximal femur has been

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Figure 1— The vascular supply of

the proximal femur comes primarily from the lateral (Lat) and medial (Med ) circumflex femoral arteries. The cranial and caudal gluteal (CG ) arteries also contribute to the blood supply. (A) Lateral view of the blood supply to the proximal femur. (B) Ventrodorsal view of the blood supply to the proximal femur. Note how the fine branches of the vessels anastomose and form a comprehensive vascular network. Care should be taken during surgical repair to minimize iatrogenic trauma to the blood supply. a = artery, Asc = ascending, br = branch, Des = descending, Ext = external, LCF = lateral circumflex. (Illustrated by Lisa Makarchuk, Auburn University.)

Figure 1A

Figure 1B

studied extensively because of the high frequency of traumatic and degenerative diseases affecting the canine coxofemoral joint and the importance of the canine coxofemoral joint as a model for human studies. Knowledge of the blood supply to both an immature and a mature canine coxofemoral joint is important for these studies and for surgical repair of proximal femoral physeal fractures. The proximal femoral blood supply has been studied by evaluating the extraosseous, intracapsular, and intraosseous components.17–20 The medial and lateral circumflex femoral arteries (branches of the deep femoral and femoral arteries, respectively) provide a majority (about 70%) of the extraosseous blood supply to the proximal femur and the coxofemoral joint.11,14, 17–22 The caudal gluteal, cranial gluteal, and iliolumbar arteries also contribute to the proximal femoral blood supply18,20 (Figure 1). The intracapsular blood supply is a continuation of extraosseous vessels within the coxofemoral joint capsule. The intracapsular vessels form a vasVASCULAR SUPPLY ■ FEMORAL ARTERIES ■ COXOFEMORAL JOINT

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Figure 2—The physis has a distinct orientation and can be divided into zones based on the activity of the cells in each layer. The reserve zone is beneath the epiphyseal bone and is followed by the zone of proliferation, zone of hypertrophy, and zone of endochondral ossification. (Illustrated by Lisa Makarchuk, Auburn University.)

cular ring or retinaculum at the base of the femoral neck.11,17,18 The dorsal retinacular artery supplies a majority of the proximal femoral epiphysis as a single vessel or as a part of a vascular arcade with the ventral retinacular artery.17 Retinacular vessels course along the femoral neck in an intracapsular, extraosseous position as they cross the physis and penetrate the femoral epiphysis. The intraosseous blood supply of the proximal femur has been studied in mature dogs and is composed of terminal branches of metaphyseal and epiphyseal arteries supplying endosteum and cancellous and cortical bone.19 Retinacular vessels pass through the epiphyseal cartilage and become epiphyseal vessels that anastomose and arborize, providing blood to the entire epiphysis.17 In immature dogs, the intraosseous arteries of the epiphysis and metaphysis are separated by the physis. Normally, the physeal barrier is not breached until after maturity, when anastomosis of epiphyseal and metaphyseal vessels can occur.17,20,21 Trauma such as a physeal fracture compromises the physeal barrier, and metaphyseal vessels thus cross and revascularize the epiphysis.7,23

The round ligament, which originates in the ventral acetabulum and inserts on the medial aspect of the femoral epiphysis, helps to maintain coxofemoral joint congruency, but does not contribute to the blood supply of the proximal femur.14 Histologic, vascular, and angiographic studies of dogs have not found evidence of significant vascular supply to the proximal femoral epiphysis from vessels in the round ligament.17,18,20 Similarly, vessels in the round ligament do not contribute to revascularization of the proximal femoral epiphysis after experimental fracture repair.7,23 Retinacular vessels supplying the femoral epiphysis are exposed along the femoral neck, predisposing them to compression and obstruction from increased intraarticular pressure. Increased intraarticular pressure from joint effusion or trauma has been hypothesized to cause vascular tamponade, which can result in pathologic damage to the femoral head.17,24,25 Measurement of the accumulation of a radiolabeled phosphorus (P32) during experimental studies on the proximal femoral circulation found that puppies had decreased uptake as intraarticular pressures increased.17 Traumatic injury with rigid fracture fixation results in revascularization from

PHYSEAL ZONES ■ ROUND LIGAMENT ■ RETINACULAR VESSELS

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metaphyseal vessels crossing the fractured physis,7,23 suggesting that revascularization could not occur without partial or complete physeal closure. Similar vascular patterns are described in the osteoarthritic hip joint of mature dogs, where anastomosing networks of epiphyseal and metaphyseal vessels have developed as a response to chronic injury.26 Such findings suggest a standard vascular response to acute or chronic trauma affecting the coxofemoral joint. Clinical management of fractures of the proximal femoral physis should take into consideration the blood supply to the femoral head and neck. Gentle tissue handling during the surgical approach to the coxofemoral joint for fracture repair is important to avoid iatrogenic damage to branches of the medial and lateral circumflex femoral arteries.18 While a craniolateral approach is used by many surgeons, the craniolateral approach using a trochanteric osteotomy27 has been recommended.7,19,23,28 Regardless of the approach used to expose the fracture, accurate anatomic reduction and rigid fracture stabilization are recommended to promote rapid revascularization of the proximal epiphysis.7,23

ANATOMY OF THE CANINE PHYSIS The function and normal anatomy of the physes (growth plates) of the long bones have been well established. The canine femur has three physes: the proximal femoral physis, the physis of the greater trochanter, and the distal femoral physis.15,29 The proximal femoral physis and the physis of the greater trochanter begin as a single physis that divides as a result of the pull of the gluteal muscles on the greater trochanter.15 Longitudinal growth of the proximal femur and femoral neck occurs from the proximal femoral physis. Histologically, the physis has a distinctive orientation (Figure 2). It is divided into four sections: reserve zone, zone of proliferation, zone of hypertrophy, and zone of endochondral ossification.30 The reserve zone (germinal or resting zone) is on the epiphyseal side of the physis. The function of this zone is not clear but is believed to be one of nutritional storage for later utilization.30 The zone of proliferation is where cell division for physeal growth occurs.30 The zone of hypertrophy is an area of abrupt change. The chondrocytes become five times larger, lose their glycogen stores, and start showing signs of cellular death.30 This zone, which is believed to be the weakest area of the physis, is where physeal fractures classically occur, although this finding has been disputed in dogs.9,31 The zone of endochondral ossification is where degenerative chondrocytes are calcified and incorporated into metaphyseal bone.30 No blood vessels exist in the hypertrophic zone of the physis, the results of which are very low oxygen tension and anaer-

obic depletion of glycogen stores within the chondrocytes.30 These metabolic stresses may be the stimulus for the changes undergone by the chondrocytes in the zone of hypertrophy.30

CLASSIFICATION OF PHYSEAL FRACTURES Fractures involving the physis (growth plate) were classified by Salter and Harris.9 Such classification provides information on the prognosis for fracture healing and subsequent growth abnormalities. Salter-Harris type I fractures involve only the physis. Type II fractures involve the physis and a portion of the metaphysis. Type III fractures involve the physis, the epiphysis, and usually the articular surface. Type IV fractures involve the physis, metaphysis, and epiphysis. Type V fractures are nondisplaced and crush the cells in the proliferative zone, resulting in premature physeal closure. Application of the Salter-Harris classification system and management of physeal fractures in veterinary medicine have been described.8 Type I or II physeal fractures should heal rapidly with minimal chance of future growth abnormalities; however, clinical experience reveals that this often is not the case. Indeed, the proximal femur was recognized as an exception to the classification system: . . . the prognosis for future growth is excellent unless the epiphysis involved is totally covered by cartilage (for example, upper end of the femur).9 Physeal fractures are classically reported to occur through the zone of hypertrophy; but 76% of naturally occurring physeal fractures in dogs involved a portion of the proliferative zone, possibly resulting in a higher than expected number of poor results after surgical intervention.9,31 As mentioned, fractures of the proximal femoral physis account for 16% of reported physeal injuries in dogs. In two studies, the fractures were overwhelmingly (91% and 96%) Salter-Harris type I or II fractures.1,10 The physis is weaker than bone, tendon, ligament, or the fibrous joint capsule complex.9,14,32 Inherent weakness in the zone of hypertrophy makes the physis a likely point of failure when fracture forces are applied to an immature limb. Growth abnormalities after physeal fracture may depend on whether the affected physis has reached physiologic closure. Occurring before radiographic closure, physiologic closure denotes the end of growth from the physis. Despite the potential for no further growth, the physis is still inherently weak. Physeal fracture occurring after physiologic closure should not result in growth abnormalities. Radiographic closure

NORMAL ANATOMY ■ SALTER-HARRIS CLASSIFICATION ■ RADIOGRAPHY

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begins with radiographic evidence of narrowing or obliteration of the physeal line, which occurs at approximately 6 to 11 months of age.29,33

DIAGNOSIS AND CAUSATIVE FACTORS Most cases of proximal femoral physeal fractures in animals are reported in dogs, although fractures are reported in other species.11,34–37 The fracture only occurs in immature animals because the physis of the proximal femur must be open for fracture to occur. The average age of dogs that sustain fracture to this area is 5.6 months.1,6 No breed or sex distribution has been reported, although fracture in Labrador retrievers was more prominent in one report.2,6,11 Most dogs present with a history or physical findings of acute trauma. In contrast, children develop slipped capital femoral epiphyses from the chronic trauma of normal activities.38–40 Causative factors in dogs are not clearly understood. Shearing and avulsion forces are reported to be the cause of most physeal fractures.9,10 The fact that the round ligament remains intact in most cases of proximal femoral physeal fracture supports speculation that this fracture is an avulsion fracture created after severe and sudden abduction of the rear leg.32,41–43 Because of the correlation between proximal femoral physeal fractures and physical trauma, the physical examination should evaluate all body systems.1 Thoracic radiographs and an electrocardiogram should be obtained before general anesthesia and surgical intervention.44 Clinical history may include acute onset of partial or non–weight-bearing lameness in the rear leg, reluctance or inability to stand or move, and observation of the traumatic event. Specific

Figure 3A

Figure 3B Figure 3— These radiographs taken before

surgery show a Salter-Harris type I fracture of the canine proximal femoral physis. (A) The lateral view fails to show the physeal fracture definitively. (B) The ventrodorsal view is important to provide adequate visualization of the fracture.

orthopedic findings may include slight swelling or bruising of the coxofemoral area, shortening of the injured leg attributable to dorsocranial pull of the gluteal muscles, and pain and crepitus during palpation or range of motion (especially extension) of the coxofemoral joint. Diagnostic differentials include hip dysplasia (coxofemoral laxity and subluxation), coxofemoral luxation, femoral neck fractures, pelvic fractures, sacroilial luxations, and proximal femoral shaft fractures. Radiographs are needed to confirm a diagnosis. Dogs tend to have significant displacement of the femur from the epiphysis, as opposed to the mild displacement or slips reported in children. 38 Some dogs, however, have minimal fragment displacement. Therefore, good-quality radiographs and careful evaluation of the physis are important for accurate diagnosis. Standard lateral and ventrodorsal views of the coxofemoral joint are needed because a single radiographic view does not provide adequate visualization of the proximal femur (Figure 3). A ventrodorsal frog-legged view distracts the fracture and may aid in making a diagnosis. As previously indicated, a majority of these fractures are Salter-Harris type I or II.1,10

MANAGEMENT OPTIONS Early techniques for treating fractures of the proximal femoral physis focused on external coaptation. Schroeder-Thomas splints, Stader apparatus, and Ehmer or non–weight-bearing slings have been used but are no longer accepted as appropriate treatment options.11,42,45,46 Because there are no acceptable methods of external fixation or coaptation, internal fracture fixation is recommended for dogs. The goals of internal

PHYSICAL TRAUMA ■ CLINICAL HISTORY ■ EARLY TREATMENT TECHNIQUES

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fracture fixation are accurate beyond into the joint.47,52 The articuanatomic reduction; rigid fracture lar surface should be inspected carestability to promote rapid fracture fully with a curved surgical instruhealing; early return to function and ment in areas where the surgeon’s activity; and, in the case of articular vision is limited.47,54,55 Once the surfractures, preservation of a normal, geon is satisfied with the fracture repain-free joint.44,47 Experimental and duction and stability, the pins can be clinical use of threaded or smooth bent and cut below the trochanter. pins, screws placed with or without The joint should then be lavaged generation of interfragmentary comwith sterile saline and closed in a pression, or combinations of pins routine fashion. If a greater troand screws have been reported and chanteric osteotomy was performed, are currently considered the staples the trochanter must be secured with of fracture repair of the proximal a tension band and the incision femoral physis.32,41,48–51 closed in a routine fashion47,52 (Figure The hair on the femur should be 4). clipped from the dorsal midline, Lag-screw repair can be percontinuing down the leg until distal formed in a similar manner. 1,4,6,7,32,47,53,54 to the stifle. The dorsal extent of A hole should be drilled in the clipped area can be extended for the femoral neck either from the Figure 4— This ventrodorsal radiograph epidural administration of anesthettaken after surgery shows a fractured proxi- fracture surface or from beneath the ics or analgesics if desired. A hang- mal femoral physis repaired by placing greater trochanter. The thread hole ing leg preparation is used, and the multiple pins from below the greater in the femoral neck must be overleg is draped for sterile surgery. Peri- trochanter. Careful evaluation during surgi- drilled to create a glide hole that aloperative antibiotics should be ad- cal repair is required to ensure that the pins lows compression to be generated ministered before a skin incision is do not penetrate the articular surface. Here across the fracture line by using the made and continued every 2 hours the radiographic positioning suggests that lag- screw principle. The fracture for the duration of the surgical pro- one pin may have penetrated beyond the should be reduced, a drill sleeve cedure. A craniolateral approach articular surface. placed in the glide hole, and a thread with or without a trochanteric oshole drilled in the epiphysis. The teotomy is recommended. 28 Alsurgeon is cautioned against penethough the approach is a matter of clinician preference, trating the articular surface.54 The depth of the thread a trochanteric osteotomy has been suggested as being hole can be measured and the epiphysis tapped. The less disruptive to the blood supply of the proximal femeasured screw length should be reduced by 2 mm to mur.7,19,23 ensure the screw tip does not penetrate the articular surMultiple small pins are commonly used for fracture face or strip the threads after hitting the bottom of the repair.1,4,6,47,52–54 The pins can be placed through the thread hole.32 The appropriate-length screw should be femoral neck in either a retrograde or normograde fashinserted and tightened, lagging the epiphysis back onto ion.47,52,54–56 Retrograde placement involves inserting the the femoral neck. Fracture reduction and stability can pins from the metaphyseal fracture surface and exiting be evaluated and the articular surface examined to conthe lateral femur distal to the greater trochanter. Norfirm that the screw has not protruded into the joint. mograde placement involves inserting the pins from the Placement of a single small pin in addition to the lag lateral femur distal to the trochanter up the femoral screw has been recommended to provide a second point neck and exiting at the fracture site. Regardless of the of epiphyseal fixation and counteract rotational forces method of placement, the pins should be retracted unon the epiphysis6,54,55 (Figure 5). Other reports have til they are flush with the fracture surface. Pins can be suggested that the undulating nature of the fracture bed placed in either a parallel or diverging manner.47,52,54–56 and the compression achieved by the lag screw are suffiThe width of the epiphysis should be estimated and cient to prevent rotation.6,11,41,54 Once the surgeon is the pins marked so that the surgeon can reduce the fracsatisfied with the fracture reduction and stability, the ture and advance the pins the estimated distance into joint can be lavaged with sterile saline and closed in a the epiphysis to avoid penetration of the articular surroutine fashion. If a greater trochanteric osteotomy was face.47,52,55,56 The joint should be subjected to a gentle performed, the trochanter should be secured with a tenrange of motion to ensure that no pins are protruding sion band and the incision closed in a routine fashion. PIN FIXATION ■ LAG-SCREW REPAIR ■ JOINT PRESERVATION

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Another method is the articular lag-screw technique, which uses screws placed in lag fashion.5 To perform this repair, the femoral epiphysis is removed from the acetabulum by severing the round ligament. The epiphysis should be reduced and secured to the femoral neck by placing a small pin in the fovea capitis. Doing so allows visualization of the entire femoral head to help ensure accurate anatomic reduction of the fracture. After reduction, a 1.5-mm drill bit should be used to drill a thread hole through the epiphysis and approximately 25 to 30 mm deep into the femoral neck (Figure 6). After drilling the thread hole, the epiphyseal portion is overdrilled with a 2-mm drill bit. A countersink should be used so that the screw head is set well below the surface of the articular cartilage. A 20-mm long, 2-mm screw should be placed and gently tightened, with a second 2mm screw placed in a similar manner. Screw placement should avoid the weight-bearing surface of the coxofemoral joint. The articular surface can be palpated to ensure that the screw heads are adequately countersunk below the joint surface. Once the surgeon is satisfied with the fracture reduction and stability, the joint should be lavaged with sterile saline and closed. Joint capsule closure is important for joint stability because the round ligament was severed. If a trochanteric osteotomy was performed during the approach, transposition of the trochanter to a more caudal and distal position tightens the gluteal muscles and provides additional joint stability.23,57 Each of the repairs discussed has advantages and disadvantages. Clinician experience plays

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Figure 5—This ventrodorsal radiograph taken after surgery shows repair of a proximal femoral physis via a single lag screw. A small pin has been added as a second point of fixation to prevent rotation of the epiphysis around the bone screw.

Figure 6—This ventrodorsal radiograph taken after surgery shows repair of a fractured proximal femoral physis by placing two small screws from the articular surface. The screw heads are countersunk beneath the level of the articular cartilage to avoid damage to the acetabular cartilage.

a large role in determining the type of fixation selected. Multiple-pin fixation of proximal femoral physeal fractures is widely described in veterinary surgical texts.47,52,54–56 The procedure has been reported to be technically easier than lag-screw fixation. 6 Multiple-pin fixation also is cited as the least likely method of repair to cause premature physeal closure47,55,56 because the procedure does not generate compressive force across the fracture line, which can result in cessation of physeal growth. The importance of this is questionable because premature physeal closure apparently occurs despite the meth- od of fixation used, probably because both the zone of hypertrophy and the zone of proliferation are involved, thereby predisposing the physis to premature closure.11,31 Visualization of the femoral epiphysis is limited, which can make accurate anatomic reduction difficult.52,54 Fracture line distraction may occur during pin placement in the epiphysis. 4 Care must be exercised to avoid unreco g n i z e d penetration of the pins into articular cartilage.47 Multiple-pin fixation does not meet the criteria for rigid fracture fixation and can possibly lead to decreased bone formation and increased bone resorption.32 Multiple diverging pins have been found to be significantly weaker against tensile forces than other methods of repair. 43 Fracture of the soft metaphyseal or epiphyseal bone can occur while bending the pins.55 Despite these drawbacks, multiple pins have provided a method of stable fixation with acceptable clinical results.1,6,11 Lag-screw repair provides rigid fracture fixation and interfragmentary compression, which promote early epi-

ARTICULAR LAG-SCREW TECHNIQUE ■ FRACTURE LINE DISTRACTION ■ STABILITY

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physeal revascularization.7,49,51 Lag-screw fixation also has been reported to be a simple surgical technique.32 Premature physeal closure can occur with interfragmentary compression; but, as previously noted, fracture trauma has likely predisposed the physis to premature closure.11 As with multiple pins, visualization of the femoral head is limited during reduction and fixation, thus increasing the difficulty and requiring the surgeon to evaluate the reduction carefully as well as check whether a screw extends beyond the articular surface of the cartilage.47,52 There may be minimal bone purchase by screw threads in the proximal femoral epiphysis because it is a thin, caplike piece of bone.4,5,47,52,56 Iatrogenic fracture of the femoral neck repaired with lag-screw fixation has been reported, and fracture of the epiphysis during lag-screw placement or tightening can occur.11 Articular lag-screw fixation allows complete visualization of the femoral capitis and thus helps with accurate fracture reduction.5 There is rigid fracture fixation and compression across the fracture line, which allows rapid epiphyseal revascularization.7,13,23 The surgical technique is reported to be simpler and less time-consuming than traditional methods of repair.5 Problems associated with premature physeal closure as a result of interfragmentary compression have been addressed. With this method, a greater amount of damage occurs to the articular cartilage with varying degrees of degenerative joint disease, although proper placement and countersinking places the screw heads in a non–weight-bearing area and beneath the articular cartilage, thereby allowing implant coverage with fibrocartilage.5,13,23 Tensile forces that may distract the fracture are eliminated when the round ligament is severed.5,23,43 Severing the round ligament, however, necessitates strict attention to joint stabilization during closure. Coxofemoral joint destabilization created by severing the round ligament was believed to be a complicating factor in four cases of failed repair in which articular screws were used.13 In vitro biomechanical evaluations of various repair options for proximal femoral physeal fractures have been performed. Fracture repair with one or two small pins was found to equal the original physeal strength when tested in shear, while repair with three pins significantly exceeded original strength.58 A second study found that two pins were significantly weaker than the original physis while a single lag screw exceeded original physeal strength.59 Comparison using diverging small pins, a single lag screw, and two screws placed from the articular surface revealed no significant difference in strength or stiffness when tested in shear, but found pins to be significantly weaker and hence less able than other repair methods to maintain fracture re-

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duction against distracting (tensile) forces.43 The inability to neutralize this fracture force with diverging pins could complicate fracture healing. Radiographs should be obtained after surgery to assess fracture reduction and implant placement. Multiple views (lateral, ventrodorsal, and frog-legged ventrodorsal) may be required to ensure that no implant protrusion beyond the joint surface has occurred. Fracture healing has been reported to occur within 3 to 6 weeks after surgical repair.7,23,32 We, however, do not routinely obtain radiographs until 8 weeks after surgery and then repeat the radiographs in 4 weeks if there are questions about the healing. Sudden worsening of clinical progress any time after surgery warrants radiographic evaluation. During the postoperative period, distinctive radiographic changes are common with this type of fracture; as discussed later, such changes should not be overinterpreted. Immediate postoperative care consists of pain management and exercise restriction. Epidural administration of analgesics may eliminate the requirement for additional postoperative analgesia; otherwise, systemic analgesics should be administered. When taking the dog for a walk after surgery, a supportive sling under the abdomen should be used for support and to prevent slipping or falling, which could disrupt the fracture repair. Although we do not use it, a non–weight-bearing sling on the affected limb has been recommended.47,51 Home care should include strict cage confinement and exercise restriction, gentle range-of-motion therapy, and use of a supportive sling during the first week of ambulation. Cage confinement, with only short walks for urination and defecation, should be enforced until radiographs confirm the fracture has healed. If the fracture repair fails, salvage options exist. Femoral head and neck excision can be done when the fracture repair is too expensive for the owner, the fracture occurred several weeks before diagnosis, articular cartilage damage occurs to the proximal femur or acetabulum, fracture comminution exists, the surgeon is not experienced with repair procedures, or referral to a surgical specialist is not possible. During femoral head and neck excision, the femoral epiphysis is removed; however, the surgeon must also remove the femoral neck to ensure pain-free pseudoarthrosis.52,60 Total hip replacement is another salvage option after the dog has reached skeletal maturity.60 This procedure can be done for dogs with working or athletic potential or when femoral head and neck excision is not a valid option. Expense, however, may be a limiting factor in the decision for total hip replacement. Because both procedures are salvage options, they should not be considered the first choice of treatment for dogs with fractures of the proximal femoral physis.11

TENSILE FORCES ■ BIOMECHANICAL EVALUATION ■ SALVAGE OPTIONS

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COMPLICATIONS Degenerative joint disease is the most common complication reported in dogs after a fracture of the proximal femoral physis has been repaired, regardless of the procedure used.1,6,11 Radiographic changes consistent with degenerative joint disease were present in all dogs, but degenerative changes were more severe in dogs younger than 4 to 6 months of age at the time of injury.1,6 Dogs with ipsilateral limb injuries were more likely to develop coxofemoral degenerative joint disease.1 Technical errors or inadequate fracture reduction were apparently related to the most severe cases of degenerative joint disease. 6,11 Mild articular cartilage changes were found after experimental repair using articular lag screws, with severe cartilage damage in one dog after implant loosening and migration.23 The effects of concurrent injuries and age on the development of degenerative joint disease have been reported; but the influence of developmental orthopedic diseases, such as hip dysplasia, is unknown. Owners should be counseled about the high frequency of degenerative joint disease after a fractured proximal femoral physis has been repaired; however, it should be stressed that radiographic degenerative changes after fracture repair have not correlated with decreased limb function or activity levels.6,11,49 Femoral neck narrowing (apple coring) was observed in radiographs in 38% to 100% of dogs that underwent fracture repair of the proximal femoral physis.1,7,23 There was no correlation between femoral neck thinning and the intervals before or after surgery.1 Experimental repair showed significant decreases in femoral neck thickness 4 weeks after surgery compared with 2 or 8 weeks after surgery.23 Partial restoration of femoral neck width at 8 weeks after surgery suggests that femoral neck thinning is part of the normal reparative process.23 Similar findings have been reported in other experimental cases.7 Femoral neck thinning should not be overinterpreted during the postoperative period. A dog progressing in a manner consistent with the postoperative interval should be managed by reinforcing exercise restrictions and frequent radiographic monitoring of the fracture repair. Surgical intervention is warranted if improvement does not occur or if discomfort increases. Remodeling of the proximal femur should continue as the fracture matures. Premature physis closure apparently is a more significant problem in dogs that are young at the time of injury. A trade-off between interfragmentary compression and rigid fixation across the fracture site and the potential for continued growth from the physis must be balanced; and in doing so, several findings should be considered. In children, closed pinning of slipped capital

physes resulted in significantly earlier physeal closure— an average of 10.2 months earlier than the nonpinned side.61 In naturally occurring canine physeal fractures, 76% of the fractures examined involved both the proliferative and hypertrophic zones of the physis.62 Experimental studies evaluating epiphyseal revascularization after fracture repair of the proximal femoral physis found that the revascularization was primarily from metaphyseal vessels that crossed the fractured growth plate. Such findings suggest that irreparable damage to the proximal femoral physis occurs when it is fractured, which predisposes it to premature closure. Dogs younger than 4 to 6 months of age at the time of fracture had more severe degenerative changes in the coxofemoral joint, thus supporting the hypotheses that the proximal femoral physeal fracture itself results in premature closure and that the growth potential remaining and not the repair method used influences the prognosis.1,6 Other complications include failure of fracture reduction, nonunion, collapse of the fracture repair, resorption of the femoral head and neck, penetration of the coxofemoral joint by the implant, and infection.1,4,6,11 Technical failures are frequently associated with these complications.1,6,11 Severe lameness in one dog 5 years after repair was attributed to compression of the sciatic nerve by a nonneoplastic mass arising from the healed femoral neck.12 Femoral head and neck excision resolved the lameness.

PROGNOSIS The prognosis varies according to age, presence of concurrent injuries, and successful early surgical stabilization. A good prognosis for normal limb function has been reported.11,47,52 Using a more restrictive definition of success (development of coxofemoral joint degenerative changes) has suggested a guarded prognosis, particularly in dogs younger than 6 months of age at the time of injury.6 Despite radiographic changes, limb function was not reported to be severely compromised in these dogs.6 Dogs with concurrent orthopedic injuries had increased chances of subsequent degenerative joint disease, which suggests a guarded prognosis.1 CONCLUSION Fractures of the proximal femoral physis are common in young dogs with the potential for severe degenerative changes and pathologic damage to the coxofemoral joint. Anatomic considerations for repair include preservation of the proximal femoral blood supply and the extent of damage to the proximal femoral physis. Anatomic reduction and rigid stabilization are important factors in achieving rapid and uncomplicated frac-

DEGENERATIVE JOINT DISEASE ■ APPLE CORING ■ PROGNOSIS

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ture healing. Traditional methods of external coaptation for fracture management have been replaced by open reduction and internal fixation. Use of interfragmentary compression is recommended, although good results have been achieved using multiple-pin fixation. The decision as to which repair method is to be used should be based on patient signalment, fracture classification, presence of concurrent injuries, and clinician preference and experience. The prognosis for return to function after surgical repair is guarded to good, with the best results in dogs older than 6 months of age at the time of fracture. Femoral head and neck excision remains an option for selected canine patients or if the primary fracture fixation fails. Early repair, accurate reduction, and stable fixation help to maintain the coxofemoral joint and have achieved good clinical results.

About the Authors Dr. Tillson is affiliated with the Department of Small Animal Surgery and Medicine, College of Veterinary Medicine, Auburn University, Auburn, Alabama. Drs. McLaughlin and Roush are with the Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas. Drs. Tillson, McLaughlin, and Roush are Diplomates of the American College of Veterinary Surgeons.

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