*Corresponding author: Jaemin Jeong Department of Veterinary Surgery, College of Veterinary Medicine, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Korea Total hip replacement (THR) is a well-established surgical technique that restores the coxofemoral joint function in dogs and cats [1]. The procedure addresses severe conditions, including hip dysplasia, advanced osteoarthritis secondary to dysplasia, luxation of the hip joint, irreparable femoral head fractures, Legg-Calvé-Perthes disease, and necessary revisions after femoral head and neck osteotomies [1]. Clinical recovery after the THR procedure is generally excellent, with success rates ranging from 85 to 95% [2,3]. Despite the high success rates, the complication spectrum for THR is broad, ranging from 3.8% to 56%, encompassing aseptic loosening, luxation of the prosthesis, and femur fractures or fissures, with prosthesis dislocation emerging as the most prevalent complication [3-5]. Although these complications vary across institutions, most can be revised. Nevertheless, complete removal of all implants becomes imperative when THR revision surgery fails or in the presence of fractured implants [6].
The removal of implants that are well integrated into the bone presents a significant challenge [7]. Implants can be detached from the bone using various tools such as flexible-blade osteotomy, K-wire, or a stem extraction device. On the other hand, removing a well-fixed fractured femoral stem is more problematic than an intact femoral stem because the fractured femoral stem cannot be gripped by the extraction device, which would otherwise facilitate its removal. Consequently, a surgical approach may be necessary to perform the retrograde extraction of the fractured femoral stem through the femoral canal, detaching it from the bone [7,8].
Extended trochanteric osteotomy (ETO) is a surgical technique that involves partially cutting the circumferential femoral bone from the greater trochanter to the femoral shaft [9]. This technique enables greater detachment of a well-integrated bone-implant surface and allows for the retrograde extraction of the stem [7]. ETO is commonly used in revision THR surgeries and the extraction of well-fixed stems in human medicine, but it is rarely reported in veterinary medicine. This case report describes the ETO surgical technique and the clinical outcomes in a dog with a well-fixed fractured femoral stem after THR surgery.
A 5-year-old castrated male Border Collie weighing 28 kg presented for revision surgery because of a femoral stem fracture, which occurred subsequent to THR performed at a local animal hospital 2 years prior.
The physical examination revealed normal vital signs, and a body condition score (BCS) of 8 indicated overweight status. The orthopedic examination elicited pain and metal crepitus during the passive range of motion, with a 10% reduction in the thigh circumference measurement compared to the contralateral hindlimb. The radiographic evaluation identified a fracture in the neck region and a migration of the lateral bolt (Fig. 1). A #5 BFX lateral bolt stem (BioMedtrix LLC, USA) was in place with a +5 mm head, while a fracture was observed at the stem. The pre-anesthetic laboratory assessments, which included complete blood count, biochemistry, and electrolytes, were unremarkable.
Considering the patient’s clinical history and radiographic findings, it was suspected that the well-fixed stem had fractured. The absence of the neck portion, combined with established osteointegration, presented significant challenges to explanting the stem using the slap hammer. Consequently, the surgical plan included the application of ETO to remove the fractured stem. The patient was premedicated with midazolam (0.2 mg/kg intravenously [IV], Midazolam; Bukwang Pharm Co., Ltd.). General anesthesia was induced with propofol (6 mg/kg, IV, Anepol Inj; Hana Pharm Co., Ltd.) and maintained with isoflurane (Ifran Liq; Hana Pharm Co., Ltd.) in oxygen. Remifentanil (0.1-0.3 μg/kg/min, Remiva; Hana Pharm Co., Ltd.) and ketamine (5-10 μg/kg/min, Yuhan Ketamine; Yuhan Pharm Co., Ltd.) was administered by constant rate infusion for analgesia. Cefazolin (22 mg/kg, IV, Cefazoline injection 1 g; Chong Kun Dang Pharm Co., Ltd.) was administered 30 minutes before the incision and repeated every 90 minutes.
The patient was positioned in lateral recumbency and a standard craniolateral approach to the left hip joint was used. ETO was performed to facilitate the removal of the implant because of the well-fixed nature of the femoral component. Before conducting the osteotomy, a long 3.5 mm locking plate was pre-contoured from the greater trochanter to the distal third of the femur. The extent of the osteotomy was pre-determined by surgical planning to achieve appropriate exposure of the stem, with the caudal border defined by the linea aspera and the cranial border developed with multiple holes using a drill. The final width of the U-shaped osteotomy was approximately 30% of the femoral diameter, with the distal pole defined by a horizontal cut in the diaphysis of the femur (Fig. 2A-C). The well-fixed femoral stem was separated from the cancellous bone using a sharp osteotome and subsequently removed through a retro-impacting extraction technique. After stem explantation, the osteotomy was reduced using Kirschner wires and 2 double-loop cerclage wires without compromising the endosteal blood flow of the fragment. Subsequently, the pre-contoured locking plate was applied to the lateral side of the femur in bridging fashion. The acetabular cup, exhibiting polyethylene wear and the presence of metallic debris, was explanted using a sharp osteotome and a high-speed burr (Fig. 2D and E). Closure of the surgical site was performed routinely.
Radiographs obtained immediately after surgery revealed complete explantation of the THR prosthesis and proper stabilization of the femur with wires and a locking plate (Fig. 3A and B). Postoperative analgesia was managed with remifentanil during the first 6 hours, transitioning to meloxicam (0.2 mg/kg subcutaneously on day 1, followed by 0.1 mg/kg orally once daily from days 2 to 7). Amoxicillin-clavulanic acid (12.5 mg/kg, IV) and clindamycin (8.5 mg/kg, IV) were administered for 7 days and discontinued after a negative culture test. At 4 months postoperatively, the patient exhibited mild weight-bearing lameness. The radiographs confirmed complete bony union of the left femur without complications (Fig. 3C and D). The owner reported during a phone call follow-up that a similar gait pattern was maintained for up to 2 years after surgery.
In the present case, the absence of the neck portion of the stem caused by the fracture made removal using conventional methods, such as a slap hammer, challenging, necessitating the use of the ETO technique for successful removal.
ETO ensures adequate exposure of the femur and may address challenges that arise with the extraction of well-fixed femoral components using conventional techniques [8]. ETO limits the retraction of the surrounding tissues, minimizing the risk of damage to the sciatic and femoral nerves [7,10,11]. Furthermore, ETO has several advantages, including predictable recovery of osteotomy, reduced risk of intraoperative fractures and femoral perforations during the debonding process, and a less time-consuming process that facilitates the retrieval of fractured implants [7,10,11].
Nevertheless, complications associated with ETO include nonunion, migration, and intraoperative or postoperative fractures [8,11-13]. Based on a retrospective study in human medicine, the group that underwent ETO appeared to have a lower complication rate than the group that did not, showing a better prognosis in clinical and radiographic examinations. Furthermore, most patients who underwent ETO experienced a successful union of the osteotomized fragment [7,13,14]. Consistent with previous studies on humans, which reported average union times ranging from 3 to 3.9 months [10,11], the clinical union of the fracture site in the present case was observed at 4 months postoperatively.
Among THR implants, stem fractures tend to occur predominantly at the neck junction [7]. Obesity, high levels of activity, and insufficient osseous support in the proximal part of the stem are risk factors for implant fractures [1]. Stem fracture is primarily considered a result of chronic fatigue rather than a single traumatic event. Moreover, when the neck is inserted too long, the lever-arm effect increases the load on the neck, elevating the risk of fracture in the neck region of the stem [1]. In this case, the patient was overweight with BCS of 8, and a lateral bolt stem of size #5 was used. The #5 standard BFX stem is recommended for a maximum weight of 20.4 kg. Nevertheless, the use of a #5 lateral bolt stem in this patient is considered a major risk because of the relatively low area of the moment of inertia compared to a standard stem and the use of an undersized implant relative to the body weight. Furthermore, the proximal stem position, which places the bolt hole close to the trochanteric fossa, and an excessive neck length (+ 5) in this case might increase the risk of bending stress.
The limitations of this case report include being a single case and a lack of extended long-term follow-up of more than several years. Future retrospective studies based on a larger number of clinical cases will be needed to substantiate the utility of ETO in THR implant removal.
This report outlines an ETO procedure that facilitates the removal of fractured stem, which can pose challenges because of the loss of a graspable neck region. The application of ETO provides wide, safe exposure, and precise extraction of well-fixed cementless femoral components and reliable bone union.
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