Dr. Vladislav Zlatinov
Corresponding author :
Dr. Vladislav Zlatinov,
Central Veterinary Clinic
Chavdar Mutafov str, 25 B, Sofia, Bulgaria
E-mail: zlatinov_vet@yahoo.com
Key words : Total hip replacement, FHNO revision, Biomedtrix universal hip system, BFX, CFX
Abstract
This a case report of successful revision of femoral head and neck ostectomy (FHNO) with hybrid BioMedtrix (Boonton, NJ) total hip replacement (THR) system, in a 7 years old mix dog. The revision indications in the case were chronic pain and functional impairment after previous excision arthroplasty for severe coxo-femoral arthritis. The weight of the patient (43kg), incomplete resection of the femoral neck and concomitant orthopaedic condition (elbow osteoarthritis) could had been contributing factors for the FHNO bad outcome. A preoperative computer tomographic (CT) study was used for underlaying cause exploration and planning the replacement arthroplasty. The time window between the two surgeries was unusually long- three years. This had caused serious morphological alterations and made the surgery of upmost technical difficulty. Nevertheless, the revision of FHNE to THR produced marked clinical improvement and return to normal activity within 3 months after surgery.
Introduction
THR is a salvage procedure involving replacement of a diseased pelvic acetabulum and femoral head with implants. Common diseases which necessities this advanced bionic surgery are osteoarthritis, secondary to hip dysplasia or trauma, aseptic femoral head necrosis, acute or chronic hip luxation, failed FHNO, irreparable acetabular or femoral head fracture.
Actually, the canine THR became commercially available since 1974 (Hoefle) and huge advancements in canine and feline THR have been made in the past 30 years. At the present, two cementless commercial systems are most popular, and several other under development1.
The Zurich Cementless Hip Prosthesis (Kyon, Switzerland) provides immediate fixation of the acetabular cup by a press-fit insertion (plus option for screw fixation); Locking screws are used for immediate fixation of the femoral stem, and on growth of bone provides long-term stability.
The BioMedtrix biologic fixation system (BFX) is a modular, press-fit bone ingrowth system with an unsecured acetabular component that provides the advantage of size compatibility with the components of the BioMedtrix cemented THR system (CFX). The advantages of application hybrid THR are discussed further in the case report.
Implants design and procedures in canine THR have been well reviewed in the literature. There are several studies reporting the functional outcomes and complications.2,3 Over- all excellent clinical results and reasonable (2-5%) major complications occurrence are reported by the experienced surgeons in the field.
Never mind the specific implant system used, the THR surgery should achieving the ultimate goal of relieving pain and improve the patient’s quality of life by returning normal limb function. Optimally, the functional effect and the integrity of the prosthesis should last for a lifetime. Serious complications- that could be met in the procedure should be avoided by precise surgery planning and perfect aseptic and surgical technique.
Femoral head and neck ostectomy (FHNO) is alternative low- cost salvage procedure. It intend to eliminate bone-to-bone contact of the diseased acetabulum and femoral head, through the formation of a pseudoarhrosis composed of non-painful fibrous connective tissue.
Published reports about outcome results after FHNO have been controversial. These ones based on gross veterinarian observations or client questionnaires, show encouraging improvement in clinical signs for the majority of dogs.
The more objective gait analysis data (available only recently4,5,6,7) didn’t reveal so optimistic results. Not ideal outcome in function was most evident in studies that did not rely only on owner satisfaction. Common residual dysfunctions after FHNO include: persistent lameness, restricted hip ROM , limb shortening, decreased stifle and hock angulation and muscle atrophy. The maximum functional recovery from the procedure may take up to 8 months6,7,8. Logically, the functional outcome of FHNO is affected by surgical technique, severeness of the disease, age, post op physical therapy and body weight 9. Several clinical trials suggest lack of constant results in dogs heavier than 18 kg.10,11,12 . The cause of the suboptimal outcome in larger dogs is still controversial. Some studies blame the bone-to-bone contact from inadequate excision or postoperative bone proliferation13,14; Others suggest that the bone contact is commonly found after FHNO and do not explain the different clinical outcomes15,16.
In cases of unacceptable pain relief, following FHNO, a revision osteotomy could be contemplated to correct a residual bone-to-bone contact, if present. A more aggressive ostectomy (including trochanter minor) or usage of muscle flaps “slings” modifications could be used to improve the outcome, again with unpredictable outcomes12,17. Another viable option could be conversion to THR18,19,20 . Nevertheless, revisions to THR were reported to yield good and pain-free function (Gofton, 1982; Liska et al. 2010, Fitzpatrick et al. 2012) many obstacles lay in front of successful procedure. The presence of unstructured fibrous tissue and altered anatomy at the surgery site complicates the surgery, and manipulation of a previous surgical site increases the risk of infection. After an excision, the acetabulum fills in with bone and the proximal femur remodels with bone resorption at the excision surface and sclerotic bone production in the medial proximal endoosteal surface. Complications are more likely after revision of FHNO, so dogs that are initially better candidates for a THR, should not be offered excision as an interim procedure.
Case report
A 7 years old female mix breed dog (43kg) was presented for consultation because of chronic left hind leg lameness. A femoral head and neck excision was accomplished 3 years ago, but the patient never show adequate pain-free recovery afterwards, despite persistent usage of anti-inflammatory medications.
Disease history
The patient had a history of previous surgeries (Fig.1-2)- left hip luxation was treated by toggle-pin reduction technique, five years ago. At the same traumatic incident, right intra articular ulnar fracture was diagnosed and osteosynthesis with neutralisation plate was applied. Despite the successful healing, degenerative joint changes developed gradually in the elbow afterwards.
In the previously luxated left hip, progression of severe degenerative changes and clinical deterioration towards severe disabling lameness were demonstrated after the treatment. This why, FHNO was accomplished 18 months after the primary trauma (Fig.3). Radiographic signs of osteoarthritis progression were noticed also in the opposite, right hip joint. The primary cause was hip dysplasia, but no painful clinical consequences were confirmed.
Clinical examination
At the clinical exam we found a moderate (II/IV) left hind leg lameness. (video1). At manipulation the hip demonstrated restricted ROM, with obvious pain and crepitation feeling in extension.We found considerable limb muscle atrophy. The opposite hip also had decreased ROM but no pain was elicited through extension.
A CT imaging was used for better evaluation of the FHNO failure (Video 2). Our clinical and imaging interpretation was- residual bone-to-bone contact, caused by suboptimal FHNO and caudal- distal “under-excised” femoral neck.
Dorsal displacement of the femur could have exaggerated the residual contact. Schiatic nerve adhesions were not supposed.
A revision with hip replacement arthroplasty was planned.
Planning and templating
Preoperatively, magnification-calibrated radiographic study of the femur and pelvis was accomplished. The approximate size of the acetabular cup and femoral stem were determined using acetate template overlaid on radiographs, but with doubts considering the real bone quality of both- the acetabular and femoral components.
Actually, the CT images played a crucial role in the detailed evaluation of the abnormal morphology, present 3 years post FHNO surgery.
Appreciating the femoral component, challenging technical problem was found. A severe proximal femoral canal sclerosis (much more obvious on CT images compared to the pre op X-rays)- Fig.5. This secondary changes always interfere with the well aligned, centralised process of reaming and broaching into the femoral canal. The eccentrically dense bone structure inevitably pushes the canal instruments out of the ideal position, increasing the risk for stem malposition and iatrogenic femoral fracture. This plus the advanced age was appreciated as risk factors for femoral shaft fracture, so a decision for the safer cemented femoral stem (CFX № 7) insertion was made. Because CFX stem have collar, laying against the proximal canal opening, plan was made to correct of the previous FHNO cut, lowering it.
Another technical issues were met, evaluating the pelvic component. A flattened, critically shallow acetabulum was found on the CT images, not clearly visible on the radiographs (hidden by the false hoarse bone proliferation). This made the precise cup sizing challenging. The CT (including 3D reconstruction) images, were used for analysis the real bone stock present in the “pseudo acetabulum” area.
The smallest possible cup (24 mmBFX) was templated but still without adequate dorsal bone engagement.
Fortunately, the Biomedtrix THR system offers an unique clinical solution in these difficult cases. Because of the cylindrically shaped press- fit anchoring mechanism , the Biomedtrix BFX cup may offer great stability properties if just adequate cranial and caudal bone contact is achieved. A rarely applied technique of medial acetabulum wall penetration, allows deeper cup insertion , increasing the stability of the implant-Fig.6. 
This stability is provided by the press-fit cranial and caudal cup edges flush. Logically, the technique demands ideal starting point of the acetabular reaming, because any offset may cause inadvertent dorsal bone loss or devastating acetabular fracture-Fig.7. No option for switching towards cemented cup would be present in these circumstances. So a plan for hybrid THR (BFX cup and CFX stem) was made. Excellent clinical results with hybrid Biomedtrix system were reported (Gemmill TJ, Vet surg, 2011).
Surgical protocol
Surgical approach
A standard cranio- lateral approach to the hip joint, including full tenotomy of the deep gluteal muscle, was used. The sciatic nerve was not exposed during the procedure. Advancing through the excessive fibrotic tissue formed at the previous surgical field was extremely challenging and time consuming. It included sharp and blunt tissue dissection. A serious haemorrhage was met from unrecognised arterial vessel in the caudo- distal part of the surgical area. Direct clamping was attempted but not possible, so gauze compression was applied, during the whole procedure.
The replacement arthroplasty was accomplished, following the algorithms and rules provided by the implants manufacturer (more detailed information could be found at http://biomedtrix.com). Only the important technical problems and solutions are described in the following surgery protocol.
A pelvic positioning device was placed underneath the patient, before the aseptic preparation.
Neck resection
A full external femoral rotation to 90 degrees was not possible in the case. The presence of diffuse inelastic fibrotic adhesions, restricted significantly the manipulation of the femur. Two assistants were used to improve the manipulation and retraction at the surgical site. Using a resection guide, aligned with the central axis of the femur, the remnant of the neck was resected according to the preplanned.
A blunt-tipped Hohmann retractor was used to elevate the proximal femur from the wound. Adequate but still more or less suboptimal passage to the canal was achieved.
Femoral canal preparation
Initial opening
The entry point was difficult to visualise because of the solid sclerotic bone, present in the trochanteric fossa. The femoral canal was entered with great care to the alignment, gradually starting with initial 3 mm pin and proceeding with 5 mm drill bit.
Canal preparation
The canal was opened and expanded through reaming of caudal and lateral femoral neck’s walls. Extremely hard cortical bone was found in the caudal and medial femoral neck area. It caused considerable resistance to consequent broaching process. It was physically demanding to resist the tendency of the broach to slide back into malalignment during reinsertion. Small crack fracture (about 3 mm bone fragment) was inevitably caused at the medial wall edge.
No margin of cancellous bone was preserved between the implant and the cortex in the case. Temporary gauze compression of the canal was used to restrict the bleeding, during the following procedure of acteabulum bed preparation. After the BFX cup insertion, the stem was fixed to the femoral canal, using gentamycin impregnated cement.(Biomedtrix 3 G veterinary bone cement) applied by improved pressurised technique (using cement restrictor). No stem centraliser was used in the case.
Acetabular preparation
Meyerding retractors were used to reflected fibrotic soft tissues away of the acetabulum. A Hohmann retractor tip was positioned ventro-caudally of the acetabulum, so a femoral shaft retraction was achieved through a lever arm effect. The visibility to the pelvis was quite satisfactory. An emphasis was put on NOT- starting the acetabular reaming in the dorsally migrated pseudo- acetabulum (nevertheless reliable landmarks were difficult to found). First, the reaming was started approximately 20 degrees to perpendicular, and afterwards changed to the desired cup insertion position. Sequentially larger reamers were used. Very careful and gradual medial wall penetration was accomplished, incrementally testing the acteabular depth with a trial cup. The size of the opening was reasonably big and the periosteum could not be preserved. The toggle pin from a previous surgery was retrieved during the procedure.
Аfter the BFX cup hammering, there was a feeling for solid, and good flushed cup component- Fig.8.
Post op radiographs evaluation
Excellent implants’ stability and reasonably good orientation were appreciated on the post op X- rays (Fig.9).
BFX cup- a mild negative inclination and moderate retroversion was noticed. There was an excellent incorporation within the acetabular bone.
CFX stem- excellently centered in the frontal plane , but caudally tipped in the saggital plane. There was good cement filling, except small cavity in near the medial femoral wall.
Comments
The caudo- distal stem deviation, was probably caused by restricted proximal femur manipulation and suboptimal canal passage availability. It had precluded good alignment broaching and stem insertion- Fig. 10. A potential negative effect of eccentrically placed stems (tip contacting the cortex) could be a creation of stress riser effect and increased risk of femoral fracture, especially if BFX stem is being inserted. The use of cement mold centraliser may had improved the stem orientation, but was unavailable in this case- Fig.11.
The small air defect in the cement was probably caused by leakage through the medial wall fragmentation caused intraoperatively.
Post operative care and follow up
Postoperative analgesia included NSAIDs for 4 weeks. The dog was discharged the next day after surgery, with owner instructions for strict cage rest: controlled leash walking only for 10 minutes, 2-3 times daily.
The patient was toe- touching for 5 days post op with gradual increase of the limb usage; real weight bearing 7 days after the surgery. Physiotherapy was restricted to passive range of motion (home exercise).
A close follow-up was performed by phone contact with the owner. Radiographs were repeated at 12 weeks post op- Fig. 12. They revealed good implants stability; a femoral cortex hypertrophy was noticed around the stem tip area. This was appreciated as physiological remodelling due to altered bone stress bearing.
Results
The patient revealed gradual , but consistent and sustained full clinical improvement. Unrestricted activity was allowed for 12 weeks, when normal (pain free) limb function was appreciated (Video 3). Increased left hind leg muscle mass was found even in this short post op period. Return to normal ROM was found at the recheck (Video 4). Very good perceived quality was reported by the owners.
CONCLUSIONS
Transforming of FHNO to THR is a challenging but viable treatment option, even in severely complicated cases. The Biomedtrix system offers great implants’ design advantages, including combination of hybrid elements; excellent BFX cup anchorage, even in deformed shallow acetabulums.
Difficulties and complications could be faced during the FHNO revisions. These met in this case were manageable, but a higher complication ratio could be expected in similar scenarios. The major causes are the profound morphological changes present after femoral head and neck excision, and the fibrotic adhesions restricting the optimal femoral manipulation during the procedure.
The veterinary professionals , should use FHNO technique wisely, taking into consideration its financial/clinical advantage and disadvantages. The excision arthroplasty should never be suggested as a temporary clinical relief in large breed dogs because more or less it disrupts the normal bio- mechanics, causes length discrepancy and have unpredictable pain relief, requiring prolonged rehabilitation or a revision surgery.
During initial discussions about treatment options, the owners should always be treated fare with evidence based approach and realistically expected results explained. This could protect many dogs from suboptimal functional results, following FHNO recommendation in inappropriate candidates.
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