Perthes Disease

Perthes disease, formally known as Legg-Calve-Perthes disease, is an orthopedic condition characterized by avascular necrosis of the femoral head in dogs. The femoral head is the ball-shaped top of the thigh bone that articulates with the acetabulum of the pelvis to form the hip joint. In Perthes disease, the blood supply to the femoral head is disrupted, leading to ischemia and subsequent death of the bone tissue. As the necrotic bone weakens and collapses, the smooth articular surface of the femoral head degenerates, resulting in pain, inflammation, and progressive loss of normal hip joint function.

The condition predominantly affects young dogs of small and toy breeds, with clinical signs typically appearing between five and eight months of age during the period of rapid skeletal growth. Perthes disease is one of the most common orthopedic conditions in small breed puppies and represents a significant cause of hindlimb lameness in these dogs. The disease is named after the three physicians who independently described the analogous condition in human children in the early twentieth century: Arthur Legg, Jacques Calve, and Georg Perthes.

Perthes disease most commonly affects only one hip, with unilateral presentation accounting for the majority of cases. However, bilateral involvement occurs in an estimated 12 to 16 percent of affected dogs, with both femoral heads undergoing avascular necrosis either simultaneously or sequentially. When bilateral disease is present, the severity may differ between the two hips, with one side typically being more severely affected than the other. The bilateral form poses additional challenges for management and rehabilitation.

The impact of Perthes disease on an affected dog can range from mild intermittent lameness to severe, debilitating pain that significantly impairs mobility and quality of life. Without appropriate treatment, the condition progresses to degenerative joint disease of the hip with chronic pain and permanent functional impairment. However, with timely diagnosis and appropriate surgical intervention, the prognosis for dogs with Perthes disease is generally favorable, and most affected dogs can return to normal or near-normal function following treatment and rehabilitation.

The fundamental pathological process underlying Perthes disease is avascular necrosis, which refers to the death of bone tissue due to loss of its blood supply. The femoral head receives its vascular supply primarily through the lateral epiphyseal vessels that travel along the femoral neck and penetrate the bone through the epiphyseal plate region. In growing puppies, the epiphyseal plate is a zone of active cartilage growth that is particularly vulnerable to vascular disruption. Any compromise to these critical blood vessels results in ischemia of the femoral head, initiating the cascade of bone necrosis that characterizes the disease.

The precise cause of the vascular disruption in Perthes disease remains a subject of ongoing investigation, but several theories have been proposed. The most widely accepted theory involves a hereditary predisposition that affects the architecture or integrity of the blood vessels supplying the femoral head, making them susceptible to occlusion or compression. Hormonal influences during the period of rapid growth may contribute to changes in blood flow or vascular tone that precipitate ischemia. Mechanical factors, including conformational characteristics of the hip joint in small breed dogs, have also been suggested as potential contributing elements.

Once ischemia occurs, the pathological progression of Perthes disease follows a relatively predictable sequence. The initial phase involves necrosis of the subchondral bone and marrow elements within the femoral head, while the articular cartilage covering the surface may initially remain intact because it derives its nutrition primarily from synovial fluid rather than from the underlying blood supply. As the necrotic bone loses its structural integrity, microfractures and trabecular collapse begin to occur within the femoral head, leading to deformation and flattening of the normally spherical articular surface.

The body's reparative response to the necrotic bone involves revascularization and resorption of dead bone by osteoclasts, followed by the deposition of new bone by osteoblasts. However, this remodeling process occurs unevenly and is often incomplete, resulting in a femoral head that is irregularly shaped, flattened, and poorly congruent with the acetabulum. The loss of normal joint congruity produces abnormal mechanical stresses within the hip joint, triggering secondary degenerative changes including cartilage fibrillation, osteophyte formation, and joint capsule thickening. These degenerative changes constitute the secondary osteoarthritis that is the primary source of chronic pain in affected dogs.

Perthes disease demonstrates a strong breed predisposition, with the condition occurring almost exclusively in small and toy breed dogs weighing less than approximately twelve kilograms. Yorkshire Terriers are the breed most commonly affected and represent the largest single breed population in most clinical studies of the disease. Other breeds with well-documented predisposition include Miniature Pinschers, Toy and Miniature Poodles, West Highland White Terriers, Cairn Terriers, Manchester Terriers, Australian Terriers, Lakeland Terriers, Chihuahuas, and Pugs.

The hereditary basis of Perthes disease is well established, though the precise mode of inheritance has been debated. Early studies suggested an autosomal recessive inheritance pattern, while more recent genetic analyses have indicated a more complex inheritance involving multiple genes with variable penetrance. Research in Manchester Terriers and other breeds has provided evidence for a major gene effect with additional modifying genetic and potentially environmental influences. The genetic complexity of the condition makes it difficult to develop simple screening tests or to predict which individual dogs will be affected based on their pedigree alone.

The concentration of Perthes disease in small breed dogs raises important questions about the relationship between body size, growth characteristics, and susceptibility to femoral head avascular necrosis. Small breed dogs undergo a different growth trajectory compared to larger breeds, with a shorter period of rapid skeletal growth and earlier physeal closure. The vascular anatomy of the femoral head in small breed dogs may also differ from that of larger breeds in ways that increase vulnerability to ischemic events. Some researchers have hypothesized that the relatively high metabolic rate and rapid growth velocity of small breed puppies may place increased demands on the femoral head blood supply during the critical developmental window.

Breeding recommendations for the prevention of Perthes disease generally advise against breeding affected individuals and, when possible, their close relatives. However, the variable penetrance of the condition means that carriers without clinical disease can produce affected offspring, making elimination of the condition through selective breeding alone challenging. Breed clubs and registries can contribute to disease reduction by maintaining databases of affected individuals, promoting awareness among breeders, and supporting research into the genetic basis of the condition. Orthopedic screening of breeding stock, including radiographic evaluation of the hips in predisposed breeds, can help identify subclinical cases.

The clinical presentation of Perthes disease typically begins with a gradual onset of hindlimb lameness in a young small breed dog, usually between five and eight months of age. The lameness may initially be intermittent and mild, causing the dog to occasionally favor the affected leg or show stiffness after periods of rest. As the disease progresses, the lameness becomes more consistent and pronounced, with affected dogs bearing progressively less weight on the involved limb. In some cases, the onset of lameness may appear more acute, particularly if a pathological fracture or collapse of the weakened femoral head occurs in response to normal activity or minor trauma.

Pain on manipulation of the affected hip joint is one of the most consistent clinical findings. Extension, internal rotation, and abduction of the hip joint typically elicit a pain response, which may range from mild discomfort to vocalization and attempts to bite. The range of motion in the affected hip is often reduced compared to the normal side, with crepitus sometimes palpable during joint manipulation. Muscle atrophy of the thigh and gluteal musculature on the affected side develops relatively quickly due to disuse and can become quite pronounced, creating a visible asymmetry between the two hindlimbs.

As the disease advances, affected dogs may hold the leg in a flexed, adducted position and show marked reluctance to bear weight on the limb. In severe cases, dogs may become essentially non-weight-bearing on the affected leg, using only the opposite hindlimb for propulsion. Dogs with bilateral disease present with an altered gait affecting both hindlimbs, shifting their weight forward onto their forelimbs and exhibiting a characteristic short, stilted stride in the rear. Bilateral cases may be more difficult to recognize initially because the symmetry of involvement can mask the degree of impairment.

Behavioral changes associated with the pain of Perthes disease may include decreased activity level, reluctance to jump, play, or climb stairs, irritability when handled around the hindquarters, and changes in posture when sitting or lying down. Some dogs develop compensatory lameness in other limbs due to the abnormal weight distribution caused by favoring the affected leg. Young puppies with Perthes disease may fail to achieve normal developmental milestones in terms of activity level and physical capability, prompting owners to seek veterinary evaluation.

Diagnosis of Perthes disease is based on the combination of signalment, clinical findings, and diagnostic imaging. The typical presentation of a young small breed dog with progressive hindlimb lameness, pain on hip manipulation, and thigh muscle atrophy should raise strong suspicion for the condition. Radiography of the pelvis and hip joints is the primary diagnostic imaging modality and is usually sufficient to confirm the diagnosis in most cases.

Radiographic findings in Perthes disease vary depending on the stage of the disease at the time of presentation. Early radiographic changes include increased opacity or irregularity of the femoral head with widening of the joint space, reflecting the initial bone necrosis and joint effusion. As the disease progresses, more characteristic changes become apparent, including areas of radiolucency within the femoral head representing resorption of necrotic bone, flattening and irregularity of the femoral head contour, fragmentation of the femoral epiphysis, and shortening or thickening of the femoral neck. In advanced cases, severe deformation and collapse of the femoral head are evident, along with secondary degenerative changes including subchondral sclerosis, osteophyte formation, and acetabular remodeling.

Standard ventrodorsal radiographic positioning with the hindlimbs extended is used for initial evaluation, and a frog-leg lateral view may provide additional information about the extent and distribution of femoral head involvement. Comparison with the contralateral hip is valuable, even in apparently unilateral cases, to identify early subclinical changes in the opposite femoral head. It is important to note that very early stages of Perthes disease may not produce detectable radiographic changes, and a normal initial radiograph does not definitively exclude the diagnosis in a clinically suspect patient. Repeat radiography after two to four weeks may be necessary to identify progression.

Advanced imaging modalities can provide additional diagnostic information in cases where radiographic findings are equivocal or where detailed preoperative planning is needed. Computed tomography offers superior spatial resolution and three-dimensional assessment of the femoral head and can detect earlier and more subtle changes than conventional radiography. Magnetic resonance imaging is the most sensitive modality for detecting early avascular necrosis, as it can identify marrow edema and vascular changes before bone structural alterations become evident on radiographs. However, the need for general anesthesia and the higher cost of these advanced imaging techniques limit their routine use in clinical practice.

Surgical intervention is the definitive treatment for Perthes disease and is recommended for the majority of affected dogs. The standard surgical procedure is femoral head and neck ostectomy, commonly abbreviated as FHO. This procedure involves the surgical removal of the damaged femoral head and neck, eliminating the source of bone-on-bone pain within the degenerated hip joint. Following removal of the femoral head, a fibrous pseudoarthrosis forms between the femoral shaft and the acetabulum, creating a functional false joint that allows pain-free movement.

The FHO procedure is performed under general anesthesia with the dog positioned in lateral recumbency. A surgical approach to the hip joint is made through the lateral or craniolateral aspect of the thigh, with careful retraction of the surrounding musculature to expose the hip joint capsule. The joint capsule is incised, the round ligament is transected, and the femoral head is luxated from the acetabulum. An oscillating bone saw or osteotome is used to cut through the femoral neck at its base, removing the entire femoral head and neck as a single piece. The cut surface of the remaining femoral shaft is smoothed to remove any sharp edges that could impinge on surrounding tissues.

Proper technique during FHO is critical for achieving a good functional outcome. The osteotomy should be performed at the appropriate level and angle to ensure complete removal of the femoral neck and to create a smooth residual surface. Inadequate resection leaving a prominent femoral neck stump can lead to impingement, persistent pain, and poor limb function. Some surgeons interpose a portion of the deep gluteal muscle or joint capsule between the osteotomy site and the acetabulum to promote formation of a well-cushioned pseudoarthrosis. Intraoperative radiography may be performed to confirm adequate bone removal before surgical closure.

Total hip replacement represents an alternative surgical option that preserves normal joint mechanics by replacing the damaged femoral head and acetabulum with prosthetic components. Micro total hip replacement systems have been developed specifically for small breed dogs and can provide excellent functional outcomes. However, total hip replacement is a more complex, expensive procedure with a different risk profile compared to FHO and requires specialized surgical expertise and equipment. For most small breed dogs with Perthes disease, FHO provides reliable, cost-effective results and remains the procedure of choice.

Postoperative care and rehabilitation are essential components of the treatment plan for dogs that have undergone femoral head and neck ostectomy for Perthes disease. The goals of rehabilitation are to reduce postoperative pain and swelling, promote formation of a functional pseudoarthrosis, restore range of motion in the affected hip, rebuild muscle mass in the hindlimb, and return the dog to normal weight-bearing and activity. A structured rehabilitation program significantly improves the speed and completeness of functional recovery.

In the immediate postoperative period, pain management is a priority and typically involves a multimodal analgesic protocol including nonsteroidal anti-inflammatory drugs, opioid analgesics, and potentially gabapentin or other adjunctive pain medications. Cold therapy applied to the surgical site during the first 48 to 72 hours helps reduce swelling and discomfort. Strict rest with confinement to a small area or crate is recommended for the first one to two weeks to allow initial soft tissue healing, with only brief, controlled leash walks for elimination purposes.

Physical rehabilitation should begin as soon as the patient is comfortable, typically within the first few days after surgery. Early rehabilitation focuses on passive range of motion exercises performed by gently flexing and extending the hip joint through its comfortable range of movement several times daily. These exercises help prevent the formation of restrictive scar tissue and maintain joint mobility during the healing period. Gentle massage of the surrounding musculature can help reduce muscle spasm and improve local circulation.

As recovery progresses, the rehabilitation program is advanced to include active exercises that encourage the dog to use the operated limb. Controlled leash walks on level surfaces are gradually increased in duration and distance. Underwater treadmill therapy is an excellent rehabilitation tool that allows the dog to exercise the limb in a gravity-reduced environment, promoting muscle strengthening and normal gait mechanics while minimizing mechanical stress on the healing tissues. Swimming provides similar benefits and can be introduced once the surgical incision has fully healed. Most dogs achieve good to excellent functional recovery within six to twelve weeks following FHO surgery, though full muscle mass restoration and optimal gait may take several months to develop.

Conservative or non-surgical management of Perthes disease is generally considered inferior to surgical treatment and is typically reserved for specific situations where surgery is not immediately feasible or where the disease is detected at a very early stage. Non-surgical management may be considered in dogs with very mild clinical signs, in cases where financial constraints preclude surgical intervention, or as a temporary measure while surgical planning is underway. However, owners should be counseled that conservative management rarely results in the same level of functional recovery as surgical treatment.

The mainstay of conservative management is strict exercise restriction combined with analgesic and anti-inflammatory medication. Rest is intended to reduce mechanical stress on the weakened femoral head and minimize pain associated with weight-bearing on the affected limb. Nonsteroidal anti-inflammatory drugs provide pain relief and reduce inflammation within the hip joint. Additional analgesic agents such as gabapentin or tramadol may be incorporated into the pain management protocol as needed. Exercise restriction typically involves confinement to a small area with only brief, controlled leash walks for several weeks to months.

Physical therapy modalities may be employed as part of a conservative management approach to maintain muscle mass and joint range of motion while limiting weight-bearing stress. Passive range of motion exercises, massage, and cold or warm therapy can provide symptomatic relief and may help slow the progression of muscle atrophy. However, these measures do not address the underlying structural damage to the femoral head and cannot reverse the avascular necrosis process.

The limitations of conservative management should be clearly communicated to owners. The necrotic femoral head does not regenerate a normal blood supply or regain its structural integrity through rest alone. While some dogs may show temporary improvement in clinical signs with pain management and activity restriction, the underlying bone damage continues to progress in most cases, leading to worsening deformity of the femoral head and increasing degenerative joint disease. Dogs managed conservatively often develop chronic pain and progressive lameness that ultimately necessitates surgical intervention. For these reasons, surgical treatment is recommended as the preferred approach in the majority of cases.

The prognosis for dogs with Perthes disease that undergo femoral head and neck ostectomy is generally good to excellent. The vast majority of dogs achieve functional, pain-free use of the affected limb following surgery and appropriate rehabilitation. Studies evaluating long-term outcomes after FHO for Perthes disease have reported good to excellent results in approximately 85 to 95 percent of cases, with most dogs returning to normal or near-normal activity levels within several months of surgery.

Factors that influence the prognosis include the severity of femoral head damage at the time of surgery, the duration of clinical signs prior to surgical intervention, the presence of bilateral disease, the quality of the surgical technique, and the compliance with postoperative rehabilitation. Dogs that undergo surgery earlier in the disease course, before extensive secondary degenerative changes have developed, generally have faster recovery times and better functional outcomes. Similarly, dogs that participate in structured rehabilitation programs consistently achieve superior results compared to those that do not receive formal physical therapy.

Long-term follow-up of dogs that have undergone FHO for Perthes disease generally shows maintained functional outcomes years after surgery. The fibrous pseudoarthrosis that forms at the site of bone removal provides a stable, pain-free articulation that accommodates the normal activity levels of small breed dogs. While the operated limb may never achieve completely normal biomechanics compared to a native hip joint, the functional difference is typically imperceptible in daily activities. Some dogs may develop a mild mechanical lameness that becomes apparent only during strenuous exercise or in cold, damp weather conditions.

Dogs with bilateral Perthes disease that require FHO on both sides typically have a somewhat more guarded prognosis than those with unilateral disease, though outcomes are still generally favorable. When bilateral surgery is required, the procedures are usually staged, with the more severely affected hip treated first and the second hip addressed after recovery from the initial surgery. The rehabilitation period for bilateral cases is longer, and achieving optimal functional recovery may be more challenging, but most dogs ultimately achieve satisfactory outcomes with appropriate management.

Prevention of Perthes disease centers on responsible breeding practices aimed at reducing the prevalence of the condition in predisposed breeds. Because the disease has a strong hereditary component, the most effective preventive strategy is to avoid breeding dogs that have been diagnosed with Perthes disease and, when possible, to avoid breeding close relatives of affected individuals. Breeders of predisposed breeds should be educated about the condition and should incorporate orthopedic screening into their breeding programs.

Radiographic screening of breeding stock for evidence of Perthes disease or femoral head abnormalities can help identify affected or subclinically affected individuals before breeding decisions are made. Screening radiographs of the pelvis and hip joints should ideally be performed after skeletal maturity, which in small breed dogs typically occurs by approximately twelve months of age. The Orthopedic Foundation for Animals offers a registry for hip evaluations that can be used to document the orthopedic status of breeding dogs and to make screening results available to other breeders.

The genetic complexity of Perthes disease presents challenges for breeding programs aimed at disease elimination. The likely polygenic nature of the condition, combined with variable penetrance, means that phenotypically normal parents can produce affected offspring. Development of genetic tests that can identify carriers would represent a major advance in the prevention of Perthes disease, and research efforts in this area are ongoing. Until such tests become available, pedigree analysis combined with phenotypic screening remains the primary tool for breeders seeking to reduce the incidence of the condition.

Owners of small breed puppies should be aware of the possibility of Perthes disease and should seek prompt veterinary evaluation if their puppy develops hindlimb lameness, reluctance to bear weight on a rear leg, or signs of hip pain. Early diagnosis and treatment are associated with better outcomes, and any delay in seeking veterinary care can allow the disease to progress to a more advanced stage before intervention occurs. Veterinarians who regularly work with predisposed breeds should maintain a high index of clinical suspicion for Perthes disease when evaluating young small breed dogs with hindlimb lameness and should not dismiss such presentations as simple sprains or growing pains without appropriate diagnostic evaluation.