Anatomy & Physiology

Growth Plates

Cartilaginous zones at the ends of long bones where new bone tissue is produced during development. In dogs, growth plates close between 12 and 24 months depending on breed size.

Growth plates (epiphyseal plates) are areas of actively dividing cartilage cells located near the ends of long bones (femur, tibia, humerus, radius). They are the primary site of longitudinal bone growth in puppies and young dogs.

Why Growth Plates Matter

Growth plate cartilage is significantly weaker than mature bone and vulnerable to injury from repetitive high-impact forces. Damage to a growth plate before it closes can cause:

  • Premature closure of the plate, resulting in uneven bone length
  • Angular limb deformities if only one plate of a paired set closes early
  • Chronic pain and altered joint mechanics from cartilage disruption

Closure Timeline by Breed Size

Breed SizeApproximate Closure Age
Toy/Small (<25 lbs)8–12 months
Medium (25–50 lbs)12–14 months
Large (50–90 lbs)14–18 months
Giant (>90 lbs)18–24 months

These timelines are approximations. The distal radius (wrist) closes last in most breeds — an important practical consideration for sporting and agility dogs.

Exercise Implications

Before growth plate closure, puppies should avoid:

  • Repetitive long-distance running on hard surfaces
  • High-impact jumping (agility, frisbee, stairs repeatedly)
  • Forced sustained exercise beyond self-selected play duration

After growth plate closure is confirmed (radiographically if needed for athletic dogs), progressive loading is appropriate. Many sport dog veterinarians recommend baseline radiographs at 16–18 months in large and giant breeds before beginning high-impact training programs.

How Growth Plates Close

Closure (ossification) is triggered by rising estrogen and testosterone at puberty. This is one reason early spay/neuter (before 6 months) in large and giant breeds can delay closure — absent gonadal hormones allow plates to remain open longer, resulting in taller but sometimes less structurally sound frames. Current evidence supports waiting until 12–18 months for spay/neuter in breeds over 45 lbs.