Hip dysplasia in dogs
Part II: Treatment
MeSH keywords:dog, hip dysplasia, treatment
Canine hip dysplasia is a disease which can be both prevented and treated. Prevention in young dogs includes conservative measures and surgical procedures, which under certain conditions can prevent the manifestation of clinical signs. Treatment begins conservatively in all animals, usually with the administration of a combination of drugs and/or biological agents, as well as changes to the lifestyle and living conditions. Results are often satisfactory. However, when conservative treatment is insufficient in alleviating clinical signs, specialised surgical procedures are performed, which might offer a definitive solution to the problem.
In a clinical setting, the veterinarian is commonly being asked to suggest the appropriate solution for the problem of canine hip dysplasia (HD), either during the selection of breeder dogs or during treatment. The aim of the treatment is to reduce or eliminate pain and to improve or restore hind limb function. In young dogs in particular, the development of the disease could even be prevented.
Treatment options for this disease are classified as conservative and surgical, however selection of one does not exclude the other. On the contrary, on several occasions their combination leads to better results (Manley 2021).
Selection of treatment
Factors that affect the selection of treatment include the age of the dog on admission, the severity of clinical signs, the severity and type of radiological findings, the temperament and function of the animal, the simultaneous presence of another disease, orthopaedic or not, and finally the social, professional, and financial situation of the owner.
It is the first step in the treatment of HD, irrespective of the age of the presenting animal. It is comprised of a combination of actions, such as changes in daily activity and living conditions, drug and food supplement administration, as well as the application of rehabilitation protocols (Innes 2012).
Controlling body weight
It has been proven that overweight animals, especially at a young age, have increased weight-bearing forces applying stress on the hip joints, and if they are affected by HD this can accelerate the manifestation of degenerative lesions (Impellizeri et al. 2000). In order to prevent obesity, the owners should not provide ad libitum diet, but the amount of daily provided food should be equal to or up to 25% less than the amount recommended by the manufacturer (Smith et al. 2006) (Figure 1). If the dog is obese, a plan of diet and exercise should be constructed with the aid of the veterinarian, which should be followed consistently in order for the dog to acquire the appropriate body weight. It has been proven that weight loss in dogs contributes substantially to improvement of clinical signs of osteoarthritis (OA) (Kealy et al. 1992).
If the animals are of high risk, usually large breeds (e.g., Rottweiler, Golden Retriever, German Shepherd), it is recommended to provide a good quality diet for large breeds, regardless of body weight, even before the manifestation of clinical signs of HD. The diets of this category are low in caloric content and rich in ω3- and ω6-fatty acids, which have been proven to reduce the inflammatory and possibly degenerative response of chondrocytes during the development of ΟΑ (Kealy et al. 1992, Impellizeri et al. 2000, Smith et al. 2006, Hurst et al. 2009).
Closely monitored physical activity
Pre-emptively, in puppies of large breeds (which are predisposed to HD), at least until 8-9 months of age, even if they do not develop clinical signs of HD, it is recommended to avoid intense physical activity (e.g., running long distances, playing with a ball, pulling weights etc). Likewise, in dogs of any age with pain and lameness due to OA, controlled daily mild exercise is recommended. Controlled physical activity protects the hip joints from excess weight bearing stress, meanwhile the normal range of motion for the joints is preserved, as well as the mass and strength of the surrounding muscles, which are the necessary elements in order to increase stability in the joints and reduce pain. Therefore, swimming and walking on a short leash are considered to be ideal exercises, whereas movement on slippery surfaces, intense running and high jumps are best avoided (Beraud et al. 2010).
Nonsteroidal anti-inflammatory drugs (NSAIDs)
The spearhead in the conservative treatment of HD is the administration of NSAIDs. These drugs have anti-inflammatory and analgesic properties, quick onset of action and are very effective (Schulz 2013).
In general, NSAIDS inhibit the activity of cyclooxygenase (COX), an enzyme necessary for the synthesis of prostaglandins, which are produced as a side product of tissue damage in the joints and promote the inflammatory process and cause intens pain. There are at least two isoenzymes of COX. COX1 is a homeostasis enzyme and is necessary in various functions, such as renal perfusion, hepatic function and protection of the gastric mucosa. COX-2 is the inducible form of the enzyme and is expressed on the inflammation site (Sanderson et al. 2009) (Figure 2). In dogs, some NSAIDs are nonspecific inhibitors of COX activity, such as acetylsalicylic acid and ketoprofen, whereas others inhibit COX2, either preferably or selectively, such as carprofen, firocoxib, mavacoxib, meloxicam, robenacoxib, deracoxib, cimicoxib, grapiprant and enflicoxib (Table 1).
|Drug||Brand name||Dose||Long-term administration||Commercial availability in Greece|
|Carprofen||Rimadyl (Pfizer, USA) and generic products||2-4 mg kg-1 twice daily||YES|
|Firocoxib||Previcox (Merial, France)||5 mg kg-1 daily||YES||YES|
|Mavacoxib||Trocoxil (Pfizer, USA)||2 mg kg-1 monthly||YES||NO|
|Meloxicam||Metacam (Boehringer, Germany) and generic products||0,1 mg kg-1 daily||YES|
|Robenacoxib||Onsior (Novartis, Switzerland)||1-2 mg kg-1 daily||YES|
|Deracoxib||Deramaxx (Elanco, USA)||1-2 mg kg-1 daily||NO|
|Cimicoxib||Cimalgex (Vétoquinol, France)||2 mg kg-1 daily||YES||YES|
|Grapiprant||Galliprant (Elanco, USA)||2 mg kg-1 daily||YES||NO|
|Enflicoxib||Daxocox (Ecuphar NV, Belgium)||8 mg kg-1 once weekly, followed by 4 mg kg-1 weekly||YES||YES|
Side effects can emerge from NSAID administration; therefore, caution is recommended regarding dosing and duration of therapy (Sanderson et al. 2009, Canapp 2010, Innes 2010). The most common side effects of NSAIDs include anorexia, vomiting and diarrhoea. Furthermore, almost all NSAIDs can potentially affect platelet function, and a very common clinical sign is gastric haemorrhage, due to the potential of these drugs of predisposing to gastric ulcers (Innes 2012).Great care should also be given to the indications of each drug, regarding the age limit when administration can be started in young dogs.
The ΟΑ which is formed due to HD, was initially considered to be a disease that stemmed from the cartilage. Nowadays it is known that OA is a much more complicated disease with inflammatory mediators released from the cartilage, bones, neurons and the synovial lining (Goldring & Otero 2011). NSAIDs are not always sufficient, when they are used as the only therapy (Lascelles et al. 2008). For that reason, lately more effective treatments have been developed and published (Seidel et al. 2013) in order to eliminate pain due to OA in dogs, which has been associated with a new molecule, the nerve growth factor (NGF). The concentration levels of the NGF are increased in the affected joints, therefore it clearly plays a significant role in the manifestations of pain, by interacting with cells and tissues of the affected joint (Isola et al. 2011).
Monoclonal Anti-NGF antibodies are effective in eliminating pain, first by reducing the concentration levels of NGF in the joints, and second by preventing it from binding to specific receptors and activating them (Isola et al. 2011).
In our country, the first monoclonal antibody formulation recently became commercially available (bedinvetmab, Librela, Zoetis, USA), in injectable form. It is administered subcutaneously once a month and it can be combined with the use of NSAIDs.
The role of corticosteroids in the management of HD is controversial (Johnston & Budsberg 1997). Oral use is generally not recommended, whereas some suggest their use in acute manifestations of pain due to OA (Henrotin et al. 2005). Although they have not been sufficiently studied in dogs, compared to human medicine, the intra-articular injection of slow-release steroids appears to reduce inflammation and offer pain relief. For that reason, methylprednisolone acetate is administered (Depo-Medrol, Zoetis, USA) at 20 mg per animal followed by a second injection 3 weeks later or triamcinolone acetonide (Vetalog, Boehringer Ingelheim Vetmedica, Inc., USA) at 30 mg per animal single dose. There is some discomfort noted usually in the first 12 hours post injection. The analgesic and anti-inflammatory effect begins 24 hours post injection and can last for weeks to months. However, their use is recommended only in very advanced stages of OA, when other conservative treatments have failed (Canapp 2010, Innes 2010).
Another category of agents administered as a single drug or in combination with NSAIDs are chondroprotective agents. There is an extended period of time between onset of administration and onset of action. These agents do not have side effects and can be orally administered as food supplements or as a component of the diet (nutraceuticals). They include ω-3 and ω-6 fatty acids, the simultaneous inclusion of which in the diet appears to boost their effectiveness (Canapp 2010). The same category includes substances that are administered in injectable form, e.g., intramuscular or intra-articular formulations.
The combined oral administration of chondroprotective agents, such as low molecular weight chondroitin sulphate (basic building block of synovial cartilage) and glucosamine hydrochloride (affects chondrocyte metabolism), have been proven in vitro to delay the degradation of synovial cartilage, to stimulate the production of proteoglycans and to have mild anti-inflammatory effect on the joints (Setnikar et al. 1991, Canapp 2010).
Hyaluronic acid is a component of synovial fluid and contributes to the lubrication of the joints, reducing friction between anatomic structures and improving motility. In HD the viscosity of synovial fluid is reduced, because the concentration level of hyaluronic acid is 2-3 times lower. Hyaluronic acid is available as a dietary supplement, usually in combination with other chondroprotective agents, but for more immediate onset of action it is administered by intra-articular injection. High molecular weight hyaluronic acid formulations are preferable (e.g., Hylartin V, Zoetis, USA, approved for horses) (Canapp 2010). The intra-articular injection of the latter, in three doses in total of 10 mg per week have been reported to significantly improve clinically the dogs with moderate to mild OA, for a duration of up to 6 months. The intra-articular injection should be administered with the animal under deep sedation or anaesthesia after the site has been surgically scrubbed and disinfected. Intra-articular administration is not without complications, considering that the animal may develop intermittently pain and lameness, as well as septic arthritis (Canapp 2010, Innes 2010).
Glycosaminoglycan polysulphate (PSGAG) (Adequan Canine, Novartis, USA) is administered by intramuscular injection at 4 mg kg-1 of body weight, twice a week, for 4 weeks. This agent acts in the synovial fluid and articular cartilage and is considered to arrest the development of OA, by preserving the histological conformation of cartilage, stimulating the synthesis of endogenous glycosaminoglycan by chondrocytes, and inhibiting the action of catabolic enzymes which are released when inflammation is present. At the same time, it allows cartilage to retain more water so that it will be more durable against the formation of erosions. For optimal results, PSGAG should be used at the beginning of the disease (Innes 2010).
Other agents that are administered in HD with a chondroprotective effect, include the New Zealand green-lip mussel extract and the formulation Dasuquin (Nutramax Laboratories, USA) which contains avocado and soybean.
Moreover, botulinum toxin, as well as autologous platelet rich plasma (PRP) are administered by intra-articular injection (Canapp 2010, Innes 2010). The latter contains growth factors which influence in various ways the rebirth and reconstruction of destroyed cartilage and in many cases offer significant clinical improvement (Catarino et al. 2020).
In the previous years the use of stem cells has been investigated as part of the treatment of HD, however, there has been no scientific evidence thus far to substantiate any success. Nonetheless, this is a very promising scientific field which, according to expert opinion, may in the following years eventually offer genuine conservative treatment to canine HD and not merely symptomatic (Palmer Ross 2021).
Finally, it should not be overlooked that in the plan of care for the conservative management of HD acupuncture can also play a role in pain reduction, as well as several physiotherapy protocols, which are also used in the postsurgical rehabilitation of the animal patient.
The conservative treatment algorithm is briefly summarised in Figure 3.
As a reminder, two different age groups are presented with HD. The first includes young dogs less than 12 months of age, with pain and hip laxity during physical examination, and usually with no radiological signs of degenerative disease. The aim of surgical treatment in these dogs is to improve congruity between the articular surfaces of the hip joints, with the aim to prevent or reduce future degenerative lesions. The second group usually includes adult dogs, frequently over 2 years old, with clinical signs caused by secondary degenerative hip disease; during physical examination there is usually no laxity observed in the hip joints. The aim of surgical treatment in this group is pain relief and improvement or restoration of limb function (Pozzi 2008).
The age group of 1 to 2 years old usually are not presented to a veterinarian and this is because periarticular fibrosis forming around the hips due to joint instability reduces laxity as well as pain, and as a result there is a temporary improvement of the animals clinically, whereas the degenerative processes of OA have not yet developed to a clinically significant degree.
Various surgical procedures have been suggested at times, many of which have been abandoned, due to unsatisfactory long-term results or due to high complication rates. Surgical techniques are classified under three categories: procedures that prevent or limit disease progression, palliative or relieving, and salvage procedures (Fitzpatrick 2009).
Procedures that prevent or limit disease progression
Juvenile pubic symphysiodesis - JPS
This is a simple and effective surgical procedure, which is performed on young growing dogs in order to prevent the progression of HD and it consists of thermal necrosis and therefore premature closure of the growth plate of the pubic symphysis. With this procedure, there is a bilateral alteration in the angle of the acetabular fossa, thereby increasing coverage over the femoral heads, with the aim of the management of hip laxity and the prevention of OA.
Growth of the canine pelvis is symmetrical. However, after the surgically induced thermal necrosis of germinal chondrocytes of the pubic symphysis, the growth of the caudal segment of the pubic bone is arrested. This fact, in combination with normal growth in the dorsal segment of the pelvis, leads to lateral rotation of the dorsal acetabular rims (Figure 4).
In order for the procedure to succeed, it is of paramount importance to properly select the right candidates, which is done based on the following criteria:
a. Age of dogs. Diagnosis of HD should be established at the age of 15-16 weeks, so that JSP can be performed when the dogs are 16-18 weeks old. Therefore, the owners of dogs of breeds predisposed to HD should be performed about the disorder and this procedure, when the dog is admitted to the practice for the first vaccinations.
b. Physical examination. This includes visual gait assessment of the dog at both walk and trot in order to detect lameness (relatively uncommon for dogs this age) and the Ortolani test under anaesthesia, and by calculating the angle of reduction of subluxation (AR) and the angle of subluxation (AS).
c. Radiographic examination. It is recommended to obtain radiographs of the hip joints in several projections, including:
- Symmetric ventrodorsal projection of the pelvis with hind limbs extended.
- Ventrodorsal projection of the pelvis with dynamic forces placed on the femoral heads to drive them from the acetabulae (PennHIP view).
- Dorsoventral projection of the dorsal acetabular rims (DAR).
With the first projection, the distance is measured between the centre of the femoral head and the dorsal acetabular rim, whereas measuring the Norberg angle, which is more often used in adult dogs, has minimal diagnostic value. With the second projection the distraction index (DI) is calculated and with the third the position of the dorsal acetabular rim is assessed. Out of these projections, it is the second that is of highest diagnostic value in order to perform JPS. Then, based on these measurements, the degree of severity of the dysplasia is estimated and the potential result of the procedure can be evaluated according to the Tables 2 and 3, respectively.
|Degree of severity||AR||AS||DI||DARA||Centre of the femoral head|
|a||Minor||15°- 25°||0°- 5°||0.4 - 0.6||7°- 10°||Over DAR laterally 1 mm|
|b||Intermediate||26°- 35°||6°- 10°||0.61 - 0.75||7°- 12°||Over DAR laterally 2 mm|
|c||Major||36°- 45°||11°- 15°||0.76 – 0.9||10°- 12°||Over DAR laterally 2-3 mm|
|Excellent||Positive||15°- 25°||0°- 5°||Over DAR laterally < 1 mm||0.4 – 0.6||7°- 10°|
|Good toguarded||Positive||26°- 35°||6°- 10°||Over DAR laterally 1-2 mm||0.61 – 0.75||11°- 12°|
|Poor||Positive||36°- 45°||11°- 15°||Over DAR laterally > 2 mm||> 0.75||> 12°|
Surgical technique (according to our modifications for easier application in the clinical setting). With the animal in dorsal recumbency, a ventral midline incision extending 3-5 cm is made over the pubic symphysis, at the caudal aspect of the abdomen. The subcutaneous and fascial tissues are dissected, and a small caudal laparotomy is performed in order to introduce a wooden spatula in the pelvic cavity and the dorsal aspect of the pubic symphysis, which will protect soft tissue structures in the pelvis from the electrocautery. A small elevation of the muscles from the ventral surface of the pubic symphysis is applied, corresponding to 1/2 up to 2/3 of the cranial segment of the pubic symphysis which is comprised of cartilage, and thermal necrosis is applied to the symphyseal cartilage by monopolar electrocautery, pre-set at 40-50 Watt. The electrocautery electrode is inserted into the full thickness of the symphysis (up to the spatula) in consecutive intervals every 2 mm. Every entry point is cauterised for 10 sec by pressing the electrocautery button in coagulation mode (Figure 5). In order to prevent a thermal burn on the point of contact of the electrocautery grounding plate with the skin of the lumbar area, the grounding plate should be covered with a large amount of gel. Incision is closed routinely. Postoperative complications are not usually noted, except for the development of oedema on the surgical site. The effect of the procedure is evaluated radiographically 12-14 months later.
It is considered that JPS, after extensive preoperative assessment and within certain limitations, is a safe and effective surgical procedure in order to prevent HD. When JPS is required, it does not exclude any further steps of HD management (Manley 2007, Vezzoni 2007).
Triple pelvic osteotomy - TPO
TPO is a technically demanding procedure intended to eliminate hip subluxation prior to the development of secondary degenerative lesions. This is accomplished by rotating the acetabulae at an angle which offers full coverage over the femoral head, in order to increase the area of the articulating surfaces of the hip joint and to distribute the forces applied to the hind limbs during the load bearing phase evenly to the entire articulating surface of the acetabulum. This increases joint stability and prevents the manifestation of OA.
The selection of candidates is based on age, clinical signs and radiographic evaluation, just like in the previous procedure. Appropriate candidates in order to perform the procedure are young dogs 5-12 months of age, which are affected by HD without any or minimal radiographic findings of degenerative disease and relatively sufficient coverage of the femoral head by the acetabulum. During radiological evaluation, radiographs are obtained in various projections, such as:
a) Symmetric ventrodorsal projection of the pelvis with hind limbs extended, in order to search for degenerative lesions and measure the Norberg angle, and
b) Dorsoventral projection of the dorsal acetabular rim (DAR), in order to measure its slope.
The values of the measured angles based on which performing TPO is indicated should be for the angle of reduction of subluxation (AR) equal to 20°- 40°, for the angle of subluxation (AS) equal to 10°-30° and for the DAR angle equal to 8°-20°. The Norberg angle mainly has prognostic value and in particular, the wider it is the better the postoperative outcome will be.
Procedure(according to Slocum & Slocum (1998), minimally modified by the authors). In TPO the surgical approach of the pelvis is through three unilateral sites and rotation of the acetabulum to its new position is performed after partial osteotomy of the pubis, the ischium and the ilium (Figure 6).
The procedure begins with pubic osteotomy. Τhe corresponding hind limb is abducted and an incision is made through the skin, 5-6 cm in length, right over the pubis, vertical to the longitudinal axis of the dog and between the pectineus and gracilis muscle. The pectineus is isolated from the surrounding tissues and its insertion in the pubis is resected, in order to reveal the ventral aspect of the bone. With the aid of an oscillating saw or an osteotome and hammer, part of the pubis 1-2 cm in length is removed, which is properly preserved so that it can be used as a bone graft during iliac fixation, in the next stage of the procedure. Great care is demanded in order to prevent damaging of the blood vessels and nerves of the area and especially the obturator nerve, which passes dorsally through the obturator foramen. Closure of the surgical site is followed by the second stage of the procedure, i.e., pubic osteotomy.
The skin incision is made exactly over the ischial tuberosity and vertical to its axis, 5-6 cm in length. Then the obturator internus muscle is detached from the dorsal aspect of the ischium, as well as the semimembranosus and the quadratus femoris muscles from the ventral aspect and the obturator foramen is revealed. With the aid of an oscillating saw or a Gigli osteotome, osteotomy of the ischium is performed parallel to the longitudinal axis of the animal. To each side of the osteotomy and at 5 mm distance from the ischial tuberosity, two holes are drilled into the ischium and metallic sutures are inserted, which are not tightened, whereas the surgical site is not closed until the completion of the next part of the procedure.
With a lateral approach of the ilium and the resection of gluteus muscles from the body of the ilium and the ventral-rostral segment of the gluteal surface of the ilium, with an oscillating saw, iliac osteotomy is performed at the neck, directly behind the sacroiliac joint. Osteotomy should be perpendicular to the sagittal plane and the line, which passes through the dorsal segment of the ischial tuberosity is directed toward the edge of the bottom third of the iliac crest (Figure 7). With this method, the section of the pelvis which includes the acetabulum is exposed and with the aid of bone holding forceps, it is rotated to the new position and fixed in place with a specially designed osteosynthesis plate, which is placed on the body of the ilium (Figure 8). The rotation angle of the acetabulum depends on the severity of subluxation and is calculated by the average of the AR and AS. Usually, this equals 5° - 10° less than the AR. In recent years, there is a preference for selected plates to avoid rotating the acetabulum more than 20°-30°, because it has been proven that increased rotation does not offer more extensive coverage of the femoral head, whereas it limits the range of limb abduction. Afterward, there is layered closure of the ilium surgical site, tightening of the wire that was placed previously through the ilium and the incision at the level of the ischial tuberosity is sutured (Figure 9).
Postsurgical care includes limiting the dog’s physical activity for 10 days and then controlled exercise (walk on a short leash) for 6 weeks. Potential complications include loosening of the osteosynthesis and damage to the sciatic and obturator nerve (Slocum B & Slocum TD 1998). In cases of bilateral disease, the contralateral limb can undergo surgery in 4-6 weeks after the first.
In recent years, a modification of TPO has been suggested, the double pelvic osteotomy - DPO, which has the same indications as TPO. The difference between the two is that the second stage of the procedure is omitted, i.e., the osteotomy of the ischium, and the mandatory use of a bone plate with locking bone screws (Figure 10). Therefore, the overall procedure time is reduced and with a less negative impact on the animal, with a smoother post-surgical recovery phase. It is usually performed on dogs 5-8 months old, because the pelvic bones are more pliable (Vezzoni et al. 2010).
Other surgical procedures
The category of prophylactic surgical procedures includes femoral trochanteric osteotomy, femoral neck lengthening and dorsal acetabular rim arthroplasty. These techniques have been used in the past, however nowadays they are rarely performed, considering that on a long-term basis their results were deemed to be unsatisfactory (Anderson 2010).
Palliative relief or salvage procedures
These procedures are performed when particular reasons apply, either financial or of management (e.g., lack of free time on the owner’s side, inability for post-surgical care and support). Whatever the case may be, the owner must be informed about the fact that with these procedures any improvement in clinical signs is usually temporary.
This technique aims in relieving pain caused from the contraction of the pectineus muscle, the forces of which are relayed to the hip through the femoral bone and drive the femoral head laterally and dorsally, and finally these forces are applied to the dorsal acetabular rim (Figure 11). When the pectineus muscle function ceases due to this procedure, the femoral head settles deeper into the acetabulum. Therefore, the contact surface of the articular surfaces of the hip joint is increased, a fact which contributes to the smoother distribution of forces exerted on the joint. However, because instability remains in the hip joints, the progress of OA is not hindered and pain returns after varying time intervals. Therefore, any positive results of the procedure are considered to be temporary, and due to this fact pectineal myectomy is of little value in managing HD.
Procedure. The surgical approach is the same as that of the first stage of TPO, followed by myectomy of the pectineus muscle, which is preferred over myotomy, tenontotomy or tenontectomy which have also been described (Wallace 1971).
Denervation of the acetabulum
This procedure includes removal of the periosteum of the dorsal acetabular rim (Figure 12). By destroying the sensory nerve endings of the cranial gluteal and sciatic nerve, partial or complete analgesia of the acetabulum, pain relief and clinical improvement are immediately obtained. The results of the procedure, even though they are impressive, are most often temporary and unpredictable (Kinzel et al. 2002).
If it is required, the procedure is performed on both hips simultaneously in both of the techniques described above. The postoperative treatment is not different to that of a standard surgical procedure.
The surgeon will turn to such procedures, when findings of the diagnostic investigation exclude the possibility of a successful outcome for any of the prophylactic procedures, when the results of palliative procedures are unsatisfactory and when conservative management has failed or can no longer be applied. This category includes femoral head ostectomy and total hip replacement.
Femoral head ostectomy - FHO
With this procedure there is no longer any contact between the affected articular surfaces of the hip joint and a neoarthrosis is formed. Pain relief is achieved, however the range of motion of the hip joint is limited, surrounding muscle atrophy occurs and some mild lameness may remain.
The appropriate candidates for FHO are adult dogs, with clinical signs of OA and body weight up to 25 kg, for which conservative treatment is ineffective. Performing the procedure on young animals with HD is not preferable according to our approach, although it can be applied by some surgeons and this is due to two reasons. First, in a significant number of dogs with HD the clinical signs improve over time, perhaps because of the formation of the formation of periarticular fibrosis sufficient to stabilise the joint and secondly, during the process of healing post ostectomy a large bone callus can be formed resulting in roughness of the smooth surface of ostectomy and causing pain during motion. Most dogs with HD belong in large and giant breeds, with body weight over 25 kg. FHO can also be performed in these animals and in some cases, it may have acceptable clinical results (Farese 2006, Fitzpatrick 2009, Anderson 2010).
Procedure. FHO begins with a craniolateral approach to the hip joint without tenontotomy of the gluteus muscles and then with the aid of an oscillating saw or osteotome and hammer, the head and neck of the femur are excised (Figures 13 & 14). Then, if the ostectomy surface is not smooth, it is sufficiently rasped. Moreover, in case of extensive periarticular osteophytes their removal is recommended. Postoperatively it is suggested to begin immediately, but with initially mild use of the limb and passive range of motion movements, as well as to administer analgesics and to apply appropriate physiotherapy protocols in order to use the limb sooner and to prevent the manifestation of muscle atrophy (Krystalli et al. 2019).
Total hip replacement - THR
This is a technically demanding procedure, for which expensive equipment and expendable supplies are required, and is performed by experienced veterinarian specialists. There are several techniques, depending on the tool and implant manufacturer and they are classified into those in which bone cement is used, those in which bone cement is not used and into hybrid techniques (Figures 15, 16, 17). Procedure selection depends on breed, age and surgeon preference. THR is considered to be the procedure of choice for adult animals with severe clinical signs of OA, for which conservative treatment is ineffective and the absence of pain and lameness are required in order to preserve muscle mass and hip joint range of motion (Vezzoni et al. 2010).
Procedure. Regardless of the technique used for THR, a cranio-lateral approach of the hip joint is made, through which ostectomy of the femoral head and neck are performed, at a specific angle which is defined by a special surgical instrument. Then the appropriate preparations are made, first of the acetabular fossa and then of the femoral medullary cavity, with the aid of specialised rasps. The preparation is made in order to apply the implants of the artificial acetabulum and femoral shaft, either through press-fit technique, or with the aid of bone cement, or with the use of screws, according to the requirements of the implants. Finally, after the correct size of femoral head has been fixed onto the femoral shaft, so that perfect contact with the acetabulum is ensured, an evaluation is made of passive range of motion movements of the joint and the surgical site is sutured in layers.
Although the animals are usually capable of walking some hours post-surgery, restriction of physical activity is mandatory for the first 6 weeks. Radiographic evaluation is recommended at 6 weeks and 6 months post-surgery (Figure 18), whereas when there is indication for bilateral THR, the second procedure is performed 6-12 weeks later.
It is worthy of note that the success rate of the procedure is about 85%, considering that complications may occur, such as infection of the surgical site, septic or aseptic loosening, femoral fracture, luxation of the artificial hip joint and sciatic nerve damage. These complications are usually due to mistakes in technique, which can be done even by the most experienced surgeons. In order to manage complications, it is most common to remove the implant system and restore it, or the femur remains without the head forming a pseudoarthrosis at the level of the hip joint.
The algorithm of surgical options for HD is briefly summarised in Figure 19.
When treating HD, greater emphasis should be given on the prevention of its manifestations. The proper management and diet, which start from a very young age, as well as the early diagnosis of the disease (at the age of 15 weeks) are important and essential actions and require excellent cooperation of their owner with the veterinarian. Excluding prophylactic surgical procedures, which should be performed at the appropriate age, with the aid of the diagnostic findings, the management of HD always begins conservatively. The multitude of drugs, biologic agents and rehabilitation techniques, provide an arsenal for the veterinarian in order to control clinical signs and improve quality of life for both the dog and the owner. However, when symptomatic treatment is insufficient in ensuring these conditions are met, due to the development of OA, is the only case when the veterinarian turns to surgery, in order to perform palliative (in large dogs as the financially viable solution) or appropriate procedures.
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