Patellar Luxation and Cartilage Erosion in Dogs

Introduction 

Patellar luxation is one of the most frequently encountered orthopedic conditions in dogs. While diagnosis is often straightforward, the broader joint consequences are easy to underestimate. Increasing evidence shows that patellar luxation, particularly medial patellar luxation, is commonly accompanied by clinically significant cartilage erosion within the patellofemoral joint. This cartilage damage plays a central role in pain, inflammation, and long-term osteoarthritis and has direct implications for how and when we intervene clinically¹. 

How Maltracking Leads to Cartilage Damage 

Normal stifle function depends on smooth, centered tracking of the patella within the trochlear groove. When patellar alignment is lost, joint mechanics change immediately. Load is no longer distributed evenly across the articular surfaces. Instead, repetitive shear and compressive forces are concentrated in specific regions of the patella and trochlea. 

Over time, these abnormal forces explain why cartilage erosion develops even in dogs that appear clinically comfortable between episodes of luxation. Mechanical overload, rather than acute trauma, drives the degenerative process¹. 

Prevalence and Location of Cartilage Erosion 

Cartilage erosion is a common finding in dogs with medial patellar luxation. Nearly half of affected stifles show erosion of the patellar articular cartilage, and more than half show erosion of the femoral trochlear surface¹. These lesions are not randomly distributed. Damage most often affects the distolateral surface of the patella and the proximomedial trochlea, reflecting predictable contact points created by medial displacement of the patella. 

Severity increases with luxation grade. Dogs with higher-grade luxation show more extensive cartilage involvement, and in Grade IV cases, erosion often spans large portions of both articular surfaces rather than remaining focal¹. For clinicians, this highlights that advanced cartilage pathology is frequently present by the time severe luxation is identified. 

Clinical Factors Influencing Cartilage Severity 

Several patient-related factors influence the extent of cartilage erosion. Increasing age and higher body weight are associated with more severe cartilage damage. Duration of clinical signs also matters, with longer-standing luxation linked to greater erosion¹. 

One clinically important observation is that the degree of visible lameness does not reliably reflect the severity of cartilage damage. Dogs with mild or intermittent signs may still have substantial intra-articular pathology. This disconnect can easily lead to underestimation of disease severity if decisions are based on gait alone. 

Radiographic Findings and Their Interpretation 

Radiographic evaluation often reveals increased stifle soft tissue opacity in dogs with patellar luxation, even when the cranial cruciate ligament is intact². This finding is consistent with synovial thickening and joint effusion associated with inflammation and early degenerative change. 

In practice, increased soft tissue opacity should not be assumed to indicate cruciate disease in isolation. In dogs with patellar luxation, it more commonly reflects chronic joint irritation and evolving osteoarthritis related to abnormal patellar tracking². 

Implications for Surgical Decision-Making 

The presence of cartilage erosion has practical consequences for treatment planning. Dogs with higher luxation grades, greater body weight, or longer histories of clinical signs are more likely to have advanced cartilage damage, even if outward lameness appears limited. In these cases, delaying correction allows abnormal loading to persist, increasing the risk of progressive degeneration. 

Standard corrective techniques, including tibial tuberosity transposition, trochleoplasty, and soft tissue balancing, aim to restore alignment and reduce pathological contact forces. In most dogs, these approaches remain appropriate. However, some dogs develop significant patellofemoral cartilage erosion associated with maltracking rather than overt luxation. In selected cases, particularly reported in bulldogs, patellar groove replacement has been used to restore joint congruency and reduce abnormal loading of damaged cartilage³. While not a routine procedure, it reinforces the value of assessing cartilage health directly rather than relying solely on luxation grade. 

Key Takeaways 

Patellar luxation should be approached as a progressive joint disorder rather than a simple positional abnormality. Cartilage erosion is common, increases with time and severity, and may be present even when clinical signs are subtle. Integrating risk factors, radiographic findings, and awareness of underlying cartilage pathology supports better timing of intervention, more informed surgical planning, and clearer communication with owners about long-term joint health. 

References 

1. Kim HW, Kim YS, Kim WK, Kang KW, Kang BJ. Medial patellar luxation induces cartilage erosion in dogs: a retrospective study of prevalence and risk factors. Am J Vet Res. 2024;85(11).  

2. Hoenecke KE, Agnello KA, Stefanovski D, Massie AM. Increased radiographic stifle soft tissue opacity in dogs with patella luxation. Vet Surg. 2025;54(7):1417–1423.  

3. Vedrine B, Fernandes D. Patellar groove replacement in patellar maltracking with patellofemoral cartilage erosion in bulldogs. Can Vet J. 2024;65(11):1136–1140.