Surgical treatment of Canine Hip Dysplasia
In this article we will discuss some aspects of 5 surgical techniques used in the treatment of canine hip dysplasia.
First we will describe the instability of a dysplastic hip:
The bad conformation of the joint will cause the movement we see in the picture (lateral translation).
This pathological movement will worsen the hip conformation because the growing acetabulum needs the femoral head to be contained in its center so that it can grow to the correct form. It’s as if the femoral head molds the acetabulum. They are congruent forms.This movement (lateral translation) causes accelerated wear of the cartilage. It demands an extra-effort of some muscle groups that try to keep the femoral head centered inside the acetabulum. These muscles eventually fail to the overload and the situation becomes unbearable. The joint capsule is stretched over-and-over and lacerates. The excessive joint fluid (inflammatory) and the labrum deformation causes the joint to loose the negative pressure (like a plunger) that helps to keep together the 2 surfaces (in a normal hip) when distractive forces occur.The femoral head will move away from the center of the acetabulum and can (in the worst case scenario) luxate.
First we will discuss 3 surgeries that improve the femoral head coverage and the hip biomechanics. One of the key ideas about these surgeries is that the earlier we do them the better results we will have. Remember that the dogs clock runs faster than the human clock: 2 months gestation against 9 months in the humans, the hip is well developed at 9-10 months against 9-10 years of a human; growth stops at 12-18 months against 17-20 years in the human species. This is what we must have in mind when we make decisions regarding this disease. Every week counts.
Triple Pelvic Osteotomy
In this technique the acetabulum is freed and rotated to cover the femoral head. This new acetabular position is kept by surgical plate and screws. This will cause a better force distribution at the hip and equilibrate the muscles around the hip stopping the bad lateral translation (subluxating) movements and its consequences.
If the dog still has some growing to do (for example if it is 5 months old) the rest of the acetabular development will be better oriented by a femoral head in its center and not in a bad subluxated position.
The results with this technique have been consistent regarding the improvement of limb function in spite of the fact that the degenerative joint disease cannot be stopped.
Not all dogs are candidates to this surgical technique. The pre-surgical evaluation will determine if the acetabulum has the correct properties so that its rotation will cause better coverage of the femoral head. After the surgical procedure it is very important to respect a period of 6-8 weeks of confinement not allowing any running or jumping by the dog. The excessive stress on the implants could make them fail.
DARthroplasty (Dorsal Acetabular Rim plasty)
In this technique we will create an extension of the acetabulum by means of a bone graft. In this way we will augment the load transferring surface since the articular capsule underneath the graft will be transformed in fibrocartilage – the best approximation to hialine cartilage the organism can produce. Depending on the disease status it can be possible that the femoral head returns to the center of the acetabulum after this surgery. If the dog did not stop growing the rest of the growing process will be better oriented. In human medicine these techniques (Shelf techniques) have a well established history . In veterinary medicine there are few reports that gather information regarding its limits of application. Our experience with this technique ( more than 4 hundred hips operated) as left the surgical team, the owner and the dog very pleased with the results. The results have been consistent at improving the performance of the dysplastic hip in spite of the fact that the degenerative joint disease cannot be reversed. Only very serious dysplasia will exclude a dog from this surgical technique as opposed to the tighter selection criteria for the triple pelvic osteotomy. It is important to remind that these 2 techniques are geared towards younger animals, ideally before they finish growing up.After the DARthroplasty procedure it is very important to respect 6-8 weeks of confinement. The excessive stress transmitted to the graft could give it a suboptimal conformation when it fuses to the true acetabulum.
Juvenile Pubic Symphysiodesis
This technique originated from the discovery that: if we stop the growing at the pubic sinfisis we will cause rotation at the level of the acetabulum (similar to a triple pelvic ostetomy) improving femoral head retention.The surgical technique consists in cauterization of the pubic sinfisis growth plate. Some of the merits of the technique is it being less invasive than other options and requiring a shorter anesthesia period. The results reported in the literature are promising. One of the major short backs is that it has to be done before 5 months of age. Given the detection protocols established for hip dysplasia in many countries this will be a major limiting factor for this surgery.
Total Hip Replacement
It is a technique with reported good results of 90-95% in the hands of an experienced team.The prosthesis with greatest historical background is one in which we have cement between the bone and the implant – the cemented hip prosthesis. It has been reported that the best results will be obtained when it is used in dogs older than 4-5 years of age. Before this age there are concerns regarding the softness of the younger bone and the longevity of the hip implant. In the recent years various implants have been developed to give better bone anchorage, better longevity and that can be used in younger dogs. Procuring these goals new prosthesis have been developed, namely the non cemented , using noble materials like titanium alloys, and plasma coated with titanium and/or hidroxyapatite for better integration.
Femoral Head and Neck Resection
It consists in surgically removing the femoral head and neck. The body’s response is to densify the structures remaining around the hip, mainly the articular capsule, developing what has been called a “false articulation”. The reasons why this technique is considered a last option is the inconsistency of the functional results and of the duration of the recovery period (from surgery to good limb use). This does not mean that we do not obtain satisfactory results most of the time (especially when we are facing a very painful case of arthritis). It simply means that it s not consistent.
Some dogs will do well , some dogs will not.The majority of the dogs will improve the limb function , a considerable percentage will maintain some form of dysfunction regarding the limb use. In general terms the heavier the dog the greater the percentage of functional limitations. The time elapsed from the day of the surgery to good limb usage is variable and in some studies it can go up to 7-12 months. In our experience these long recovery periods are very infrequent.In our surgical center we frequently perform partial acetabular resection along with the femoral neck resection to avoid the post surgical complication of bone-on-bone contact which could give discomfort to the patient and worsen the results.