Total Hip Replacement (THR) relieves pain and restores function for dogs with severe hip conditions. Careful candidate selection is vital, assessed through clinical tests, radiographs, and biomechanical analysis, particularly when using the Prime Hip system.

Indications for THR:

Hip dysplasia in large breeds
Chronic or recurrent hip luxation
Post-traumatic arthrosis
Failed femoral head ostectomy
End-stage osteoarthritis
Avascular necrosis (Legg-Calvé-Perthes in small breeds)

Evaluation:

Dogs are assessed based on gait, posture, pain, and joint stability (Ortolani, Barlow’s/Barden’s tests). Radiographic views—VD pelvic, frog-leg, yoga, medio-lateral femur, and lateral ileum—help evaluate hip structure and laxity (Distraction Index, DI).

Femoral Morphology Impact:

Deformities like genu valgum, coxa vara/valga, and torsional issues affect implant planning. The Prime Hip’s lateral plate-bolt design adapts to these variations better than cementless systems.

Contraindications:

Active infection, severe muscle wasting, immature skeleton, neurological deficits, and inflammatory arthritis may preclude THR.

Surgical Candidacy Checklist:

DI > 0.7, positive Ortolani/reducible hip, infection-free, normal lab values, owner consent, and a weight plan.

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Long-Term Outcomes

Success is measured by implant survival (>5 years), pain-free movement, stable radiographs, absence of complications, and improved quality of life. Most canine data span 3–8 years due to breed-specific longevity.

Radiographic Follow-Up:

Check for stable implant integration annually, looking for cortical bridging and absence of radiolucency.

Owner Satisfaction:

Over 92% reported improved quality of life at 6–12 months post-op.

MaxPetZ Clinical Data (2023–2025):

Survival: 96.1%
Dislocation: 2.8%
Infection: 1.3%
Loosening: 1.3%
Sciatic neurapraxia: 5.5% (all recovered)

Failures relate to early unsupervised activity, poor rehab, or bone quality.

Prime Hip vs Other Systems:

Prime Hip offers modular revision and better adaptability to femoral variations, with outcomes equal or superior to other leading systems.

Long-Term Risk Factors:

Poor bolt trajectory, suboptimal cup placement, excessive anteversion, radiolucency, delayed muscle recovery, premature activity, high BMI, and young age increase complication risk.

Annual Monitoring Recommended:

Regular imaging, gait videos, blood work, and owner surveys help detect issues early.

Future Directions:

Studies focus on longer-term follow-up, registry development, advanced AI for imaging, patient-specific implants, and biomechanical simulations.

Expanded Research Priorities:

Improved radiographic measurement tools, mapping bone integration, custom plates, and outcome tracking will drive innovation and predictability in THR for canine patients.

1. Introduction

 Advancements in implant design, surgical technique, and perioperative care have reduced the incidence of complications, but total hip replacement (THR) procedures still carry inherent risks. The Prime Hip system, utilising a lateral plate and modular bolt design, addresses many issues associated with intramedullary stems; however, biologic, mechanical, and technical failures remain possible. This chapter presents a comprehensive review of potential complications, organised by timeline and anatomical structure.

2. Classification of Complications

 Complications may be categorised based on timing and anatomical origin:

Intraoperative: Occurring during exposure, bone preparation, or implant seating.
Early Postoperative (0–6 weeks): Includes dislocation, infection, hematoma, or sciatic neuropraxia.
Mid-Term (6 weeks – 6 months): Involves aseptic loosening, muscle atrophy, subluxation, or implant toggle.
Late (>6 months): Chronic infection, wear-induced osteolysis, implant fracture, or pseudotumor formation.
Etiologic categories:

• Mechanical (malalignment, impingement)

• Biological (infection, osteolysis)

• Technical (improper seating, under-reaming)

3. Intraoperative Complications

 - Femoral Canal Blowout:

• Rare with Prime Hip due to lateral bolt-based fixation, though excessive bolt length or misaligned drilling are risk factors.

 - Acetabular Wall Perforation:

• More likely in coxa plana or revision cases (refer to Chapter 8, Case 2). Prevention involves conservative reaming and verifying wall thickness.

 - Sciatic Nerve Contusion:

• Associated with prolonged deep gluteal retraction or misplaced retractors. Prevention includes periodic repositioning of retractors and avoiding blind instrumentation.

 - Improper Cup Angle (ALO or Retroversion):

• Can result in dislocation or edge loading. Use intraoperative imaging for angular control.

4. Early Postoperative Complications (0–6 Weeks)

 - Dislocation:

• Typically linked to cup retroversion mismatch, soft tissue imbalance, or insufficient bolt-head tension. Managed by closed reduction or revision as indicated.

 - Infection (Superficial/Deep):

• Immediate antibiotic coverage and diagnostic evaluation are necessary; early debridement may be warranted.

 - Bolt Loosening or Toggle:

• Related to inadequate cortical engagement or incorrect bolt sizing. Surgical revision and upsizing may be required.

 - Hematoma or Seroma:

• Caused by inadequate hemostasis or excess dead space. Persistent or expanding collections should be evacuated.

 - Sciatic Neurapraxia:

• Presents with motor deficits and is generally self-limiting; supportive care recommended.

5. Mid-Term Complications (6 Weeks – 6 Months)

 - Aseptic Loosening:

• Frequently attributed to micromotion or failed osseointegration. Radiographic and clinical findings guide management, which may include revision.

 - Muscle Atrophy and Disuse Syndrome:

• Results from insufficient rehabilitation; addressed through targeted physiotherapy.

 - Subluxation or Edge Loading:

• Manifested by abnormal joint mechanics; revision may be considered depending on severity.

 - Implant Toggle or Noise:

• Indicates rotational instability, often due to sizing or alignment issues; evaluated radiographically.

6. Long-Term Complications (>6 Months)

 - Chronic Infection (Late-Onset):

• Diagnosis via laboratory and imaging studies; managed with staged explantation and antibiotics.

 - Osteolysis and Implant Wear:

• Caused by particulate debris, leading to bone loss; prevention includes implant selection and regular monitoring.

 - Implant Fracture:

• Uncommon with Prime Hip, but may occur with infection, osteopenia, or mechanical overload.

 - Pseudotumor Formation:

• Reactive masses identified on imaging; may require surgical intervention.

7. Diagnostic Approach to a Failing THR

 Evaluation should be systematic:

History: Assess symptom onset and progression.
Physical Exam: Evaluate for signs such as crepitus, swelling, limb asymmetry, and altered gait.
Imaging: Radiographs and advanced modalities can identify implant positioning and complications.
Laboratory Tests: Used to investigate infection.
Advanced Imaging: CT and MRI aid in assessment of implant and soft tissues.

8. Revision Strategies Based on Etiology

 Revision surgery is determined by failure type:

Aseptic Loosening: Upsize fixation components and address bone deficits.
Dislocation: Reevaluate component orientation and stability options.
Infection: Perform a staged procedure with antibiotic spacers.
Implant Toggle or Fracture: Replace failing hardware and reinforce as necessary.

9. Salvage Procedures and Prognosis

 When revision is not feasible, options include:

Excision Arthroplasty: For non-reconstructable cases.
Arthrodesis: Considered rarely due to functional limitations.
Amputation: Reserved for persistent pain or systemic compromise.

Prognosis is generally favourable if infection is absent and rehabilitation is effective; chronic infection or delayed intervention negatively affects outcomes.

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Rehabilitation and Long-Term Outcomes

 Postoperative rehabilitation is essential for optimising the long-term outcome after Total Hip Replacement (THR) with the Prime Hip implant. While surgery restores joint mechanics, recovery depends on soft tissue healing, progressive strengthening, and gradual activity resumption. This chapter describes a structured protocol, phases of recovery, and approaches to outcome monitoring.

1. Goals of Rehabilitation After THR

 A successful plan aims to:

Reduce complication risk, including dislocation or fracture
Promote bone ingrowth for stability
Encourage normal limb use and gait patterns
Minimise muscle atrophy and contracture
Restore full range of motion without compromising implant position
Support sustainable joint function

2. Immediate Postoperative Phase (0–14 Days)

 - Confinement to crate or small room with non-slip flooring.

Brief lead walks for basic needs only.
Daily incision monitoring.
Use collar to prevent interference with wound.
Pain management as indicated.
Initiate passive exercises under supervision if suitable.
Adjust caloric intake to reflect decreased activity.

3. Controlled Recovery Phase (2–8 Weeks)

 - Begin supervised lead walks; duration increased gradually.

Focus on symmetrical weight bearing.
Hydrotherapy may be introduced after incision healing.
Carpeted stairs permitted at six weeks.
Restrict high-impact activity.
Weekly assessments to monitor progress.

4. Advanced Functional Recovery (8–12 Weeks)

 - Gradual introduction of controlled off-leash activity.

Incorporate varied surfaces and simple agility tasks.
Strengthening exercises implemented.
Monitor for signs of overloading.
Radiographic follow-up at ten weeks.

5. Long-Term Return to Normal Function (>12 Weeks)

 - Unrestricted activity allowed for most dogs by 12–14 weeks.

Extended ramp-up for working/sporting animals.
Defined by restored gait, motion, and absence of dysfunction.
Avoid repetitive high-impact actions.

6. Rehabilitation Modalities

 - Hydrotherapy: Enables low-impact resistance training.

Laser therapy: May reduce inflammation and support healing.
Physiotherapy: Tailored exercises expedite recovery.
Cold/heat therapy: Utilised according to postoperative stage.
PROM and massage: Maintain mobility and circulation.

7. Monitoring Long-Term Outcomes

 - Scheduled radiographs and clinical evaluations to assess implant stability and function.

Ongoing owner observation encouraged.

8. Factors Affecting Prognosis and Implant Longevity

 - Favourable indicators: Early gait restoration, compliance with rehabilitation, absence of complications.

Risk factors: Excess weight, poor preoperative condition, malposition, and lack of adherence to recommendations.
Certain cases may warrant adjusted expectations or alternative implant choices.

Implant Systems – Evolution and Innovation

1. Historical Evolution of Total Hip Replacement in Veterinary Orthopedics

Total Hip Replacement (THR) in veterinary orthopedics has developed from adaptations of human orthopedic methods. The earliest THR systems used polymethylmethacrylate (PMMA) cement to secure femoral and acetabular components, following practices in human arthroplasty. Initial designs, such as cemented modular stems for large breed dogs with advanced hip dysplasia, provided pain management but experienced long-term loosening, infection, and limited customization. The veterinary field subsequently identified the requirement for systems adjusted to specific biomechanical characteristics in canine patients, including their quadrupedal gait, high joint loading, and diverse bone structure.

2. Overview of Contemporary Veterinary Hip Systems

Multiple total hip replacement systems are presently available for use in dogs. Examples include:

Biomedtrix Universal Hip (cemented and cementless variants)
KYON Zurich Cementless System or V-Art cementless hip system
BFX (Biologic Fixation) and CFX (Cemented Fixation) Modular Systems
Lyon Cementless Hip

Each system is designed according to specific principles; some focus on biological fixation, while others allow for easier component exchange during revision procedures.

3. Technical and Clinical Limitations in Traditional Systems

Conventional THR systems present several limitations:

Intramedullary fixation requires precise reaming, which may lead to cortical thinning or potential iatrogenic fractures.
Rigid implant sizing can restrict application in dogs with abnormal femoral shapes.
Cemented systems, though cost-effective, are associated with increased rates of aseptic loosening in active dogs.
In complex situations (such as coxa vara, severe femoral torsion, or pseudoacetabulum), traditional stems may necessitate femoral osteotomies or extensive contouring.

In response to these challenges, the Prime Hip system was developed to utilize lateral femoral cortex fixation.

4. Innovation Behind the Prime Hip System

The Prime Hip system does not rely on intramedullary fixation; instead, it implements a lateral locking plate system with a double-locking bolt mechanism. This design removes the need for intramedullary canal preparation, which helps preserve endosteal blood supply and reduces the risk of femoral fractures.

Key features of the system include:

A femoral plate with a pre-angled barrel set at 135 degrees to accommodate natural anteversion.
A hydroxyapatite-coated barrel to support osteointegration.
A double-locking bolt securing both into the barrel and the modular femoral head.
Compatibility with dual mobility cups and ceramic/polyethylene liners.

By laterally shifting the load-bearing axis and providing modular bolt lengths, the Prime Hip system is adaptable to anatomical variations such as coxa vara, coxa valga, and genu valgum, without compromising implant stability or joint function.

Femoral Head and Neck Ostectomy (FHNO or FHO)

Femoral head and neck ostectomy (FHNO) is a drastic and ultimate surgical intervention that is categorized as a rescue one, and it is not advised by orthopedic specialists at MaxPetZ hospitals.This procedure is employed to treat dogs in pain due to poor hip health in a bid to enhance their well-being, although the pain alleviation is not total, in cases where hip replacement is impossible.ls. This procedure is used to help dogs suffering in pain due to bad hips to improve their quality of life, by reducing the pain (not eliminating it completely) only when hip replacement is not an option. Bio-mechanical function is not kept as in the case with the total hip replacement surgery (THR). In this procedure (FHO) the femoral head (ball) is removed and in FHNO, the femoral head an neck is removed, which helps to create a separation between the pelvis and the femur to decrease bone on bone rubbing. Because of ignorance and nonexistence of technology/refined pathology, it was embraced by many vets without knowing the biomechanical and the ramifications that came with it.

FHO VS THR

Where on one hand using of the FHO as a procedure is only justified in case hip joint diesase leads to constant pain and there are no other methods or other methods have been ineffective.The procedure is recommended as such when there is financial constraint and other methods of treatment are not feasible or did not produce satisfactory results. The procedure is recommended as an option primarily when financial constraints are present. In patients, the degree of limb use may range from full use to limp continued after the surgery has been done.Most of the time FHO leads to limb shortening, limitation on hip joint motion, muscle wasting and cannot predict the degree of pain relief.treatment are not feasible or did not produce satisfactory results. The procedure is recommended as an option primarily when financial constraints are present. After surgery, the degree of limb use may vary from normal use to a continued limp, dependent on the patient. In most cases a FHO results in shortened limbs, restricted hip movement, muscle atrophy, and unpredictable pain relief.

In general, the larger the patient the less predictable the result. Older or larger dogs, who present with severe degenerative disease involving the hip joint, are expected to have much more favourable results with a total hip replacement, rather than a femoral head osteotomy. Rehabilitation after FHO may take 3-6 months and requires high level of client-patient compliance. Many factors are partially dependent on postoperative care and physical therapy. After FHO, physical therapy begins shortly after your pet’s sutures are removed.

One type of physical therapy for your pet to participate in following this procedure is swimming. This is because this exercise involves a movement that stretches the hip joint as well as the one that consolidates it. The period of time that is advised for each session depends on the type of physical therapy applied. This will enable the dog to have increase range of motion and strength.However, it is important to emphasise the fact that the outcomes of the FHO are unpredictable and, among other factors, are affected by the size of a patient and the postoperative and subsequent physiotherapy treatment .y. Out of the objective data thereby obtained, it can be seen that small dogs and cats also seem to have other issues which persist even after FHO.

In conclusion, it’s important that any time you are discussing any surgery – femoral head osteotomy (FHO) or total hip replacement (THR) – for your animal anytime, you should consider the pros and cons for those processes.Although there might be some situations when a FHO is acceptable for you, benefits resulting from the execution of a THR have to be discussed.The pros and cons of each procedure should be thoroughly explained to your surgeon before finalizing a choice.as physical therapy. Objective data results show that small dogs and cats also often continue to have problems after FHO.

In conclusion, anytime you are considering any surgery – whether it be a femoral head osteotomy (FHO) or total hip replacement (THR) – for your pet, it is highly recommended that you first carefully weigh the advantages and disadvantages of each surgery. While there may be instances where a FHO is acceptable for you, the advantages of a THR must be considered. Advantages and disadvantages of both procedures should be discussed with your surgeon prior to making any definitive decisions.

Comparison of Total Hip Replacement (THR) to Femoral Head Osteotomy (FHO)

Total Hip Replacement surgery is designed to enhance a dog's quality of life by providing a pain-free joint with normal biomechanics and function. When addressing hip pain, treatment options range from conservative medical management to surgical interventions. The most commonly offered surgical procedures include total hip replacement (THR) and femoral head osteotomy (FHO). At MaxPetZ, THR is generally preferred over FHO due to the superior outcomes associated with improved quality of life.

Advancements in technology, surgical instruments, and expertise have contributed to the success of THR in canine patients. Currently, more than 95 percent of dogs undergoing this procedure can expect to enjoy an active, pain-free lifestyle throughout their lifetime without recurrence of symptoms. Based on current evidence, we recommend considering total hip replacement as the first-line surgical treatment in most cases, reserving FHO for select situations.

Multiple studies have demonstrated that following a total hip replacement, patients—including dogs—exhibit higher limb loading, indicating better functional recovery. The following points summarize key findings from published research:

• The FHO procedure significantly alters the biomechanics of the hip joint.

• Limb shortening to varying degrees is a common outcome of FHO.

• Pain relief following FHO is unpredictable.

• Rehabilitation after FHO tends to be prolonged, especially when compared to THR.

• Both small dogs and cats do not necessarily achieve better results than larger dogs post-FHO.

• According to Gendreau and Cawley, only 37% of FHO cases reported excellent outcomes, while 26% were classified as good. Some discrepancies in perceived results may arise from subjective assessment versus objective measurement, with many patients achieving less than optimal limb function. The overall level of function following FHO may be unacceptably low given available alternatives.

• Veterinary orthopedic surgeons everywhere in the world, typically advise total hip replacement as the primary intervention to address hip pain and restore normal activity. FHO is generally considered a salvage procedure when THR is not an option. While THR offers significant benefits, some pet owners may face constraints that prevent them from pursuing this surgical option.

Case Study Related to THR

Total Hip Replacement (THR) a veterinary guide