Limb Straightening and Osseointegrated Transcutaneous Amputation Prosthesis in a Dog with Angular Limb Deformity

Abstract

Objective

To report the successful implantation of an osseointegrated transcutaneous amputation prosthesis (OTAP) device following the correction of a distal tibia recurvatum with an intramedullary interlocking nail (ILN) in a 5-year-old Dachshund dog.

Study Design

Case report.

Results

A straight medullary canal was achieved with the opening wedge and stem impaction was performed with relative ease. Radiographic evidence (X-rays and computed tomography scan) 5 months postoperatively showed appropriate callus formation and osseointegration of the endoprosthetic stem, despite visible fissure lines remaining. Force-plate data showed symmetry in gait between prosthetic limb and the contralateral limb. A healthy stoma was achieved during the follow-up period, despite self-limiting skin retraction.

Conclusion

The usage of ILN to correct extreme limb deformity prior to OTAP placement led to greater ease of endoprosthesis impaction. Limb straightening preceding OTAP placement in a chondrodystrophic dog is feasible and no significant lameness was detected despite no surgical intervention to address tibial fissures.

Keywords

osseointegration - prostheses - orthopaedic surgery - small animal surgery - implants

Introduction

Limb amputation is frequently considered the treatment of choice for the management of unsalvageable distal extremity conditions like neoplasia, ischaemia, or traumatic injury in animals. In addition to being financially appealing to some owners, amputation is often recommended as dogs and cats are perceived to “do well on three legs,” enabling them to live pain or disease-free lives with minimal impact on mobility.[1]

While owners and veterinary professionals do not necessarily appreciate an overt decrease in quality of life or impact on their pet's well being, recent force plate data, kinetic, and kinematic studies show significant changes in ground reactive forces and gait in amputees.[2] [3] Changes in weight distribution over the remaining limbs also affect the vertebral column and accelerate the development of degenerative joint disease in those limbs.[4] It remains difficult to ascertain the benefits of prostheses in animals due to the lack of accurate assessment methods; however, extrapolation from human studies suggests that in addition to improving mobility, amputation prostheses in animals may also improve overall health and reduce pain.[5]

Socket prostheses are the most reported form of amputation prostheses in veterinary literature; however, they are associated with many complications including stump–socket interface irritation, pressure sores, infection, necrosis, poor fit, device failure, and poor patient acceptance.[6] Using transcutaneous osseointegrated devices eliminates the challenges associated with socket prostheses.[7] Small numbers of such cases are reported in veterinary medicine, including transcutaneous tibial implants by Drygas[8] and the intraosseous transcutaneous amputation prosthesis (ITAP) by Fitzpatrick et al.[9]

The main challenges associated with osseointegrated amputation prosthesis are maintaining healthy and infection-free bone–implant and skin–implant interfaces. The purpose of this report is to describe a case where the additional challenge of a short and recurved tibia in a chondrodystrophic dog was managed with opening wedge osteotomy to facilitate later osseointegrated transcutaneous amputation prosthesis (OTAP) placement. The additional length of straight medullary canal provided sufficient bone-implant contact to allow primary stability at the bone–implant interface, facilitating osseointegration.

Case Description

A 5-year-old female spayed Dachshund dog was referred to the reporting institution for OTAP following a right distal pes amputation due to dorsal metatarsal necrosis. Examination revealed a body condition of 6/9, absent distal pes with an intact calcaneus, and a well-healed amputation site. The amputation was performed at the referring hospital a year prior to presentation to the reporting institution, following which multiple variations of socket prosthesis were trialed unsuccessfully.

Radiography and computed tomography (CT) scans prior to surgery showed a 24-degree recurvatum, sagittal plane angular limb deformity (ALD) within a single center of rotation of angulation (CORA) with its axis positioned within the bounds of the cortices, approximately 29 mm from the joint surface ([Fig. 1]). With an inadequate straight medullary canal present to allow adequate intramedullary implant fixation, a staged surgical approach was elected to straighten the tibia before OTAP placement.

Fig. 1 Cranial opening wedge. Preoperative planning to identify the center of rotation of angulation (CORA) and joint angle difference of 24 (1a), 24-degree cranial opening wedge was planned along the CORA (1b). A 3 mm × 70 mm I-Loc device templated (C). Computed tomography image of cranial opening wedge using intramedullary interlocking nail immediately postoperatively (2a) and at 10 weeks postoperatively (2b).

Surgery Report

Opening Wedge Osteotomy

The dog was premedicated with 0.2 mg/kg of methadone and 3 µg/kg of medetomidine intravenously (IV) and induced with a total of 2 mg/kg of propofol titrated to effect. IV gastrointestinal support medications were administered prior to induction (1 mg/kg of maropitant, 0.5 mg/kg of ondansetron, and 1 mg/kg of esomeprazole). A total of 22 mg/kg of cephazolin antibiotic was given IV before surgery and repeated in 90-minute intervals. Multimodal analgesia was provided through local sciatic and femoral nerve blocks using 5% bupivacaine and 15 mg/kg of IV paracetamol.

Cranial opening wedge osteotomy was performed at the CORA identified on the tibia ([Fig. 1]). The medullary canals were aligned under fluoroscopy guidance, and a 70 mm × 3 mm Biomedtrix I-Loc interlocking nail was placed, entering from a location cranial to the stifle joint and extending through the talocrural joint into the talus. Bolts were placed only in the most distal and proximal holes in the talus and tibial metaphysis, respectively, and the wedge deficit was packed with demineralized bone matrix (Veterinary Tissue Bank Ltd, Wrexham, United Kingdom). The tibia was opened by 24 degrees. Appropriate healing was confirmed through CT images at 10-week postoperative, and the I-Loc was explanted ([Fig. 1]).

Osseointegrated Transcutaneous Amputation Prosthesis Placement

The dog was anaesthetized using the same anesthetic protocol as above for OTAP placement. A fish-mouth approach consisting of a horizontal elliptical incision was made along the distal tibia, and collateral ligaments of the tibia–tarsal joint were transected.[10] A transverse distal tibial osteotomy was performed, leaving approximately 5 cm of tibial amputation stump. A Kirschner wire was placed under fluoroscopy guidance and the medullary canal was reamed using 3.6- and 4.0-mm cannulated drill bits; the position was checked intermittently using fluoroscopy. The OTAP implant was shortened slightly after comparison with a three-dimensional (3D)-printed model of the tibia to ensure the implant did not interfere with the stifle joint surface. The stem was impacted under fluoroscopic guidance until the collar of the abutment was flush with the distal margin of the tibial stump. Excess distal soft tissues and skin were trimmed and fashioned around the distal abutment using 3–0 polydioxanone suture material.[10]

Postoperative pain relief and medications in the hospital included 0.1 mg/kg of meloxicam injection given subcutaneously, 0.2 mg/kg of IV methadone 4 hourly, 15 mg/kg of IV paracetamol 8 hourly, and 22 mg/kg IV of cephazolin 6 hourly overnight before continuing a week course of oral cephalexin at an equivalent dose.

Prosthesis Design

The intramedullary implant was a modification of those produced for human use (Osseointegration International Pty Ltd, North Ryde, New South Wales, Australia) and was 4 mm in diameter, comprising of a porous titanium alloy stem. Exoprostheses were 3D printed with polyethylene terephthalate glycol and a basket design was adopted to prevent self-traumatization of the skin–implant interface ([Fig. 2]). 3D-printed foot attachments comprised of polyurethane. There were two versions of exoprothesis; in the first version, the basket attachment and foot followed a straight trajectory. The final version was designed based on limb usage following the fitting of the first prosthesis and incorporated the standing tarsocrural joint angle derived from the contralateral limb.

Fig. 2 Diagram of the first (A) and final (B) endo- and exoprosthesis device. The final design (B) also features an alignment spacer that provides rotational alignment options and an offset exoprosthesis with a distal portion angled to mimic the standing tarsocrural joint angle of the contralateral limb.

Follow-up

The dog remained in the hospital for 4 days following OTAP placement. The stoma site was cleaned with saline and evaluated daily, then every other day and weekly for exudate, necrosis, and signs of infection until it was no longer exudative. Stoma dressing consisted of a nonadhesive foam contact layer that was secured using the abutment screw and cohesive bandages. These were removed and changed as the stoma site was being cleaned and evaluated. The stoma site was markedly effusive with moderate swelling at day 2 postoperatively. By day 10, there was minimal effusion and plantar skin retraction was observed. Generalized skin retraction was observed by 2 months postoperatively, which ceased by 6 months ([Fig. 3]).

Fig. 3 Stoma appearance at day 1 (1a), day 6 (1b), day 10 (1c), 2 months (2a and 2b), and 6 months (3a and 3b) postoperatively.

Immediate OTAP postoperative radiographs showed appropriate implant position and no evidence of cortical fractures or fissures ([Fig. 4]). The bone–implant interface was divided into seven zones and evaluated using the Osseointegration Group of Australia zonal analysis[11] ([Fig. 4]). Radiographs repeated at 6 months showed generalized thickening of the cortical bone, most prominently along zones 1 and 7. There were no signs of osteolysis or aseptic loosening in all seven zones. Narrowed peri-implant radiolucent line was observed at zones 1, 3, 6, and 7 ([Fig. 4]). A significant callus was present along the caudodistal tibia, where the bone was in contact with the abutment. CT at week 7 revealed a fissure along the craniolateral and caudolateral tibial cortices extending approximately 1.8 cm proximally from the distal tibia, and these fissures remained static when CT was repeated at 6 months ([Fig. 5]). No changes were made to recovery recommendations.

Fig. 4 Caudal–cranial radiographic projections of tibia immediate postoperatively depicting bone–implant interface sectioned according to the Osseointegration Group of Australia zonal analysis.[11] Comparison between radiographs taken immediately postoperatively (2a and 2b), 6 months (3a and 3b). Reduction in width of radiolucent lines along bone–implant interface observed (red circles). Caudodistal callus formation present at 6 months postoperatively (red arrow).

Fig. 5 Three-dimensional computed tomography (CT) bone reconstruction tibia at 7 weeks postoperatively, fissures (red arrow) are present along the distal tibia craniolaterally (1a) and caudally (1b). Transverse CT projections of fissures at 7 weeks proximally (2a) and distally (2b), and at 6 months proximally (2c) and distally (2d).

The exoprosthesis and foot attachment were fitted 2 weeks following surgery and were removed weekly by the owner for stoma site cleaning using saline solution. Limb usage was observed immediately following the attachment of exoprosthesis and foot. Force plate analysis was performed after 2 months and showed a symmetry index (SI) of 1.9, indicating no significant lameness (SI 0 = perfect symmetry, SI > 9 = significant lameness).[12]

Discussion

This is the first case to date to report on staged limb straightening and OTAP placement for a dog with ALD. An intramedullary interlocking nail (ILN) was chosen as it provided a pre-reamed canal for the eventual impaction of the stem. The minimal invasiveness of ILN is also advantageous for the preservation of surrounding soft tissue above and beneath the osteotomy. This leaves a healthy soft tissue bed to encourage osteogenesis during bone healing,[13] facilitating osseointegration.[14]

Closing wedges and cylindrical osteotomies were also considered, as they allow interfragmentary compression, providing stability and a stronger union;[15] however, additional limb length cannot be achieved with such techniques. Minimum implant length and diameter requirements are currently poorly described, although a small stem diameter has been associated with higher stem failure.[16] Given that medullary canal dimensions accepted only a 4 mm diameter stem during 3D templating in this dog, maximizing implant length was desired to optimize biomechanics.[17] A minimum 5- to 10-cm length has been previously proposed in human literature.[18] Due to the dog's limb conformation, templating for a cylindrical osteotomy led to a complete loss of medullary canal alignment; hence, it was considered unsuitable.

A single-stage procedure was theoretically feasible, as the customizability of the implant could potentially accommodate a peri-implant fixation component to aid in osteotomy healing. However, the outcomes of osseointegration in bones with wedge deficits have not been investigated. Based on the principles of osseointegration, a titanium stem could serve as a bridge across the osteotomy site, potentially eliminating the need for autogenous bone grafts or bone matrix to fill the wedge, improving healing.[19] Nonetheless, the impact of reduced cortical bone-to-implant contact on integration must also be considered.

The use of customized curved implants was reported for a radius in the case series by Fitzpatrick. When they compared osseous remodeling between the curved and straight implants, the lack of remodeling in the radius of that dog suggested potential stress dissipation by the curved implant.[9] Flexible cannulated reamers could facilitate curved implant placement but, unfortunately, while they allow reaming of bones with gradual curvature like in a radius, the acute bend in this tibia would risk a fracture through the caudal cortex. An alternative to limb straightening is the use of an implant system comprising of a short intramedullary component with cranial and medial locking plates as described in an ITAP case report on a small ruminant (Arabian Tahr).[20] However, there is a lack of evidence to support the use of peri-implant fixation in the long term, and it is generally avoided with the implant system used here, as it is perceived to be a risk factor for failure to achieve durable osseointegration in human studies.[10]

It is uncertain if, in our case, the mid-tibia fissures developed as a result of stem impaction during surgery or postoperative use, as immediate postoperative CT was not performed. Potential repair methods include using cerclage wires, as reported in a bilateral tibial transcutaneous prosthesis case.[8] While there are currently no guidelines on periprosthetic fracture management in this scenario, the recommendation in human literature is to avoid the placement of cerclages or bone grafts in cases of small and nonpropagating distal fractures.[21] Additionally, surgical intervention was not attempted to prevent disruption of healing between the dermis and bone, which is crucial for achieving a tight seal at the skin–implant interface.[22] Further studies should be conducted to compare the impact of periosteum disruption and fissuring on osseointegration.

The cause of asymmetrical bone growth along the caudodistal tibia is not confirmed but could be attributed to an increase in osteogenic activity to stabilize the fissures. Immediate limb usage resulting in early and dynamic loading, and changes in weight distribution could also have a role in this asymmetric callus formation. Early loading results in stronger peri-implant cortical bone,[23] while dynamic loading has been proven to cause asymmetrical bone deposition.[24] The lack of tarsocrural joint angulation in the first exoprosthesis resulted in caudal distribution of weight-bearing forces, which likely contributed to osseous remodeling and bone growth caudodistally as well.[25] Despite this, appropriate limb usage without detectable lameness was still achieved.

The finding of gait symmetry was consistent with an ovine study in 2011, where no significant differences between the contralateral and prosthetic limb were detected within 12 months of prosthesis placement. However, complete weight-bearing on the prosthetic limb was never achieved.[26] This suggests that despite observing appropriate and gradual improvements in weight-bearing and limb use, there is potential for an ongoing decrease in weight-bearing on the prosthetic limb in the long run. Further studies with longer follow-up periods are required to determine the long-term outcome of limb use in animals with OTAP.

A healthy and substantial skin–implant interface is critical for resisting infections[27] and continues to be a challenge in both human and veterinary osseointegration amputation prosthesis. In this case, a tight seal between skin and implant was readily achieved; however, skin retraction, while self-resolving, still occurred despite purse–string sutures used to immobilize the skin. To date, there remains no consensus on the best practice for maintaining the skin–implant interface or immobilization of the skin to prevent retraction. The ITAP device in the case series by Fitzpatrick was manufactured to feature a hydroxyapatite (HA) coated porous flange that provides a transcutaneous handle for dermal and subcutaneous tissue attachment;[9] however, due to skin breakdown at the HA surface in human trials, implant use in dogs and humans have not been reported again.[18] Immediate immobilization by only attaching skin to a porous-coated implant surface also proved to reduce retraction.[8] [28] Alternatively, increasing bone thickness at the skin–implant site also enhanced skin attachment.[29] Considering the tendency for skin to attach to porous-coated and textured surfaces, skin retraction in this study could have occurred due to initial attachment at the distal edge of the smooth abutment, instead of the porous OTAP stem proximal to the abutment. However, the goal of the Osseointegration Australia technique employed in this case was to establish a healthy stoma, regardless of skin adhesion.

In conclusion, this case demonstrated a solution for dogs with ALD or short amputation stumps, who would otherwise be unsuitable candidates for receiving an osseointegrated prosthesis. Failure to immobilize skin to implant potentially resulted in skin retraction; however, retraction in this case was self-resolving, required no additional intervention, and did not have an impact on the health of the stoma site during the follow-up period. Further studies are required to determine the overall benefit of OTAP and its impact on quality of life in recipient animals.

Conflict of Interest

None declared.

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Publication History

Received: 13 August 2024

Accepted: 05 February 2025

Article published online:
25 March 2025