Roger Clarke, BVSc, MRCVS, FACVSc, Registered Veterinary Specialist, Small Animal Surgery
Indications
There are currently two main surgical procedures to prevent or modify the progress of hip dysplasia in young dogs, Juvenile pubic symphysiodesis and triple pelvic osteotomy. Triple pelvic osteotomy (TPO) is performed at a later age (8 to 10 months) and the awareness of the owners to the dangers of hip dysplasia is greater at this time. In my practice, TPO is currently the most popular and successful operation for minimising the onset of devastating arthritis and pain caused by hip dysplasia 1 2 3.
To achieve the best results, there is a very short 2-month period in the life of the dog, when it is best to perform this operation; this is when the bone is mature enough to hold the screws and implants firmly and yet immature enough to continue growing and undergo acetabular re-modeling following the surgery. This occurs between 8 to 10 months of age for most large breed dogs. Although the operation works best in young growing dogs, there have been cases recorded of dogs operated upon at up to three years of age that have benefited markedly from a TPO procedure.
Hip Dysplasia in these young growing dogs is diagnosed by a combination of radiography and hip laxity. Distraction radiographic techniques such as the Penn-Hip®4 technique developed at The University of Pennsylvania can be used, but it is often very obvious that the dog will have severe subluxation (Ortolani sign) when the dog is examined under general anaesthesia.
The size of the dog is also important; TPO cannot be easily performed on dogs less than 20 kg in weight due to the relatively fixed size of the currently available implants. Fortunately the management of hip dysplasia in small breed dogs is much easier in small breed dogs compared to the larger breeds.
Diagnosis and evaluation
Because of the short period available to perform successful surgery, the owner's veterinarian should advise their clients to have susceptible pups evaluated for joint laxity under deep sedation at approximately 8 to 9 months of age. Radiographs can be performed at this age, but may seem normal on appearance unless distraction techniques are used. The older 'traditional' recommendations of delaying hip radiographs to 18 month or 2 years of age will rule out TPO as an option to prevent HD, because by 2 years of age the problem will be well established if present and degenerative joint changes will rule out any benefits. Pain due to sub-luxation and early DJD are usually seen between 6 to 12 months of age in severe cases of HD, but may not be apparent for up to 2 years of age in less severe cases. If the diagnosis is left until clinical signs of hip dysplasia develop, the secondary changes of DJD will have already commenced and the benefits of the TPO will be markedly reduced.
Any dog which is of a susceptible breed, has the characteristic 'sailor's gait' of rolling hind limbs, is reluctant to exercise normally, becomes lame after exercise or shows pain when getting up or down, jumping into cars or going up steps, should receive a thorough clinical orthopaedic examination which includes palpation of the hips under general anaesthesia and distraction radiography of the hip joints. The traditional extended leg ventral-dorso view may show sub-luxation and a shallow acetabulum with the presence of inflammatory changes in the bone around the joint capsule (osteophytes/episiophytes) and around the cranial and caudal margins of the acetabular rim. However in many cases the radiographic appearance may be normal and the presence of hip dysplasia will be detectable by palpable sub-luxation of the hip only.
The Ortolani maneuver, performed correctly, can give the operator an indication of the angle of subluxation and relocation and an indication of the depth of the acetabulum. This also is a guide to degree of rotation of the pelvic segment that will be necessary to perform a successful TPO. Anaesthesia is necessary to perform this procedure with any degree of confidence. This palpation technique takes practice and it is helpful to also use a distraction radiographic technique that demonstrates this luxation of the joint. There are several techniques available but the most reliable are the PennHip® technique or evaluation of the dorsal acetabular rim using the DAR radiographic view as described by Slocum & Devine. 5
My experience with the TPO has been that many dogs with totally subluxated hips can be helped if they are operated on when young enough and if there are no degenerative joint changes. However, if the initial radiographs show a significant degree of sub-luxation in conjunction with degenerative joint changes, this may rule out any benefits from a TPO and your recommendation should be for medical management followed by a total hip replacement when medical management no longer is effective.
How does a TPO work?
TPO works by altering the alignment of the acetabulum in relation to the femoral head so that the head is forced more deeply into the acetabulum as the dog walks. In the young dog, the bones are still malleable enough to re-model; the acetabulum deepens due to the increased weight bearing pressure from the femoral head. The femoral head also develops more normally in response to these forces and because it is not constantly slipping in and out of the acetabulum as the dog walks. The degenerative changes of hip dysplasia are due to the constant laxity and subluxation of the hip joint, and these changes can be avoided or minimised if the operation is performed at the correct time. Many operated dogs live a relatively normal life. They should be sterilised and not used for breeding, as hip dysplasia is an inherited disease.
What can go wrong?
The most common complications are damage to the sciatic and obturator nerves during the surgical osteotomy. These are rare but can occur even in experienced hands. The other complications are failure of the implants to hold in the soft immature bone or infection of the operative site. These complications are also rare and can be minimised by confining the dog and the use of prophylactic antibiotics.
TPO Plates-what is available?
There are several brands available:
1. Mathys (Swiss) makes a TPO plate that is based on a normal DCP bone plate with a 45-degree angle of twist. They come in 4 sizes and left and right angles.
2. Slocum Enterprises (USA) makes the most commonly used plate and this plate is available in three angles, 40 degrees, 30 degrees and 20 degrees and left and right sides. A French company has now produced a similar TPO plate. Slocum has produced calculated evidence that the plate developed by him is 27% more resistant to torsional bending than a 1 cm Mathys plate.6
3. Recently, an eight-hole adjustable TPO plate (Stealth, Robert L. Rooks) has been introduced. All the above plates must be imported unless you live in USA. Several authors have suggested that the use of the TPO procedure should be avoided where plates with extreme angles of rotation are required7 8 9 10 . The more extreme the angle of rotation of the acetabulum, the more risk there is of interference between the femoral neck and the dorsal acetabular rim. In addition there is an increased chance of ventral luxation of the hip. Dejardin and co-workers 7,8 have shown that the ideal angle appears to be 20 degrees, however I have used 30 and 40-degree plates with some success in severe cases of sub-luxation and each case needs to be judged on its merits.
How is a TPO done?
The surgical procedure is well described in most modern texts and journals 11,12,13 and basically involves three pelvic osteotomies, at the pubis, the ischium and the shaft of the ilium. The surgical approaches are not difficult, but there are several precautions that need to be taken to protect the sciatic nerve and obturator nerve during the osteotomy. The surgeon attempting this operation for the first time would be well advised to seek advice from a more experienced surgeon in the procedure and to practice on a cadaver several times BEFORE attempting surgery on a live animal. I will not attempt to describe the surgical procedure in this paper. In my opinion the best surgical description is in the text "Current Techniques in Small Animal Surgery", fourth edition. Eds MJ Bojrab, GW Ellison, B Slocum. 1998, Williams & Wilkins, Baltimore.
If TPO is not a suitable procedure--what procedures can be recommended?
Juvenile pubic symphysiodesis14, 15,16,17,18,19
DARthroplasty Slocum & Devine 20
Denervation of the dorsal acetabular rim - Dr Sylvia Kinzel
BOP shelf arthroplasty 21 now discredited.
Total Hip Replacement
References
1. Hohn R B, Janes J M: Pelvic osteotomy in the treatment of canine hip dysplasia. Clin Orthop 62:70, 1969.
2. Slocum B, Devine Slocum T. Pelvic Osteotomy. In: Current Techniques in Small Animal Surgery, fourth edition. MJ Bojrab, GW Ellison, B Slocum. 1998, p 1159-1165.
3. McLaughlin RM et al. Force plate analysis of Triple Pelvic Osteotomy for the treatment of Canine Hip Dysplasia. Vet Surg 20, 5:291-297, 1991.
4. Smith G K et al., New concepts of coxofemoral joint stability and the development of a stressradiographic method for quantitating hip joint laxity in the dog. J Am Vet Med Assoc 196:59, 1990.
5. Slocum B, Devine T. Dorsal acetabular rim radiographic view for evaluation of the canine hip. J Am Anim Hosp Assoc 26:289, 1990.
6. Slocum B, Devine Slocum T. Pelvic Osteotomy. In: Current Techniques in Small Animal Surgery, fourth edition. MJ Bojrab, GW Ellison, B Slocum. 1998, p 1163.
7. Rasmussen L M et al., Preoperative variables affecting long-term outcome of triple pelvic osteotomy for treatment of naturally developing hip dysplasia in dogs. JAVMA Vol 213, No.1 July 1:80, 1998.
8. Graehler R A et al., The effects of plate type, angle of ilial osteotomy, and degree of axial rotation on the structural anatomy of the pelvis. Vet Surg 23:13-20, 1994.
9. Dejardin L M et al., The effect of triple pelvic osteotomy on hip force in dysplastic dogs: a theoretic analysis Vet Surg 25:114-120, 1996.
10. Dejardin L M et al., The effect of triple pelvic osteotomy on the articular contact area of the hip joint in dysplastic dogs: an in vitro experimental study Vet Surg 27:194-202, 1998.
11. Slocum B, Devine Slocum T. Pelvic Osteotomy. In: Current Techniques in Small Animal Surgery, fourth edition. MJ Bojrab, GW Ellison, B Slocum. 1998, p 1159-1165.
12. Schultz K S, Dejardin L M. Surgical Treatment of Canine Hip dysplasia. In: Textbook of Small Animal Surgery, third edition. Ed Douglas H Slatter. 2002, p 2033-2042.
13. McLaughlin R M et al. Force plate analysis of Triple Pelvic Osteotomy for the treatment of Canine Hip Dysplasia. Vet Surg 20, 5, 291-297, 1991.
14. Matthews et al: Effect of pubic symphysiodesis on acetabular rotation and pelvic development in guinea pigs. Am J Vet Research 57:1427,1996.
15. Dueland et al: Effect of age-sequenced pubic symphysiodesis in dysplastic pups. Proceedings, 8th Annual ACVS Symposium, 1998, page 8.
16. Swainson et al: Effects of pubic symphysiodesis on pelvic development in the skeletally immature greyhound. Vet Surg 29: 178, 2000.
17. Patricelli et al: Juvenile pubic symphysiodesis on dysplastic puppies at 15 and 20 weeks of age. Proceedings, 10th Annual Symposium ACVS, 2000, p17.
18. Dueland et al: Effects of pubic symphysiodesis in dysplastic puppies. Vet Surg 30:201, 2001.
19. Patricelli et al: Canine pubic symphysiodesis; Evaluation of electrocautery dose response by histologic examination and temperature measurement. Vet Surg 30:261,2001.
20. Slocum B, Devine Slocum T. DARthroplasty. In: Current Techniques in Small Animal Surgery, fourth edition. MJ Bojrab, GW Ellison, B Slocum. 1998, p 1168-1170.
21. Jensen D J, Sertl G O. Sertl shelf arthroplasty (BOP procedure) in the treatment of canine hip dysplasia. Vet Clin N Am May 1992, p 683-701.