Patellar Desmopathy After Cruciate Surgery

Do We Care About That Thick Tendon?

This week I went down a rabbit hole on patellar tendinopathy/desmopathy after CCL surgery—because let’s be honest, we see it pretty frequently after TPLO.

But… does it actually matter?

Do we need to do anything about it?

Should it change how we rehab these patients?

What Actually Happens:

• We often see thickening, especially at the tibial insertion.

• On ultrasound: disrupted fiber pattern, hypoechoic zones, and increased cross-sectional area.

• Histologically, it’s not inflammatory—it’s tendinosis (degenerative change).

• It shows up in both naturally ruptured and post-surgical stifles—probably more than we realize.

Does the Type of Surgery Matter?

Absolutely!!

• TPLO increases the load on the patellar tendon by shortening the lever arm—so the tendon has to work harder.

  • According to Carey et al. VCOT 2005, Mattern et al. VRU 2006, 50-80% of dogs showed tendon thickening in the first 2–3 months post-op.

  • And joint inspection techniques also mattered. According to Owen et al. Vet Surg 2018, arthroscopy caused more patellar tendon thickening than arthrotomies.

• TTA is more tendon-friendly. The tendon changes tend to be less pronounced and can return closer to normal. Khun et al. VRU 2011 showed that the tendon thickeness increased in week 6 but returned to normal (not significantly different from week 0) in week 16.

• Extracapsular repairs or conservative management can still result in tendinopathy, particularly in chronic or overloaded cases.

  • Candela et al., 2025 (Frontiers) also showed 80% of dogs showed increased patellar tendon thickening in the first 2-3 months and while some reduction occurs over time, many tendons remain thickened at 8–10 months—they don’t return to normal thickness – so don’t tell your client that this will come back to normal thickness !

But… Does It Hurt?

Most of the time—no.

Many dogs show no clinical signs, even when the tendon looks abnormal on ultrasound—likely due to adaptation over time.

Still, in some cases you might see:

• Pain on palpation of patellar tendon

• Reluctance to fully flex the stifle, with a possible elastic end-feel

• Lameness without obvious joint effusion

That said, I still think synovitis, meniscal injury, or infection are more common causes of ongoing lameness after TPLO. 

But lameness due to patellar tendinopathy? Definitely possible.

So yes, I might reach for the ultrasound probe to check for core lesions or obvious fiber disruption before deciding if the tendon is the pain source.

A Cool Study I Found

Anggoro et al., 2024 (PLOS One) 

A live dog study evaluating patellar tendon tone/stiffness at different stifle angles, with muscle tone switched on/off using muscle relaxant.

Key takeaway:

• More flexion = higher tendon tone/stiffness

• Neutral stifle = lowest stiffness

So if the tendon is already adapting post-surgery, then loading it heavily—especially in deep flexion—might not be the best idea. Higher risk of additional injury!

So… What About Sit-to-Stand?

We all love prescribing sit-to-stand, but this got me thinking: 

Based on previous studies, patellar tendon continues to be thickened first 2-3 months after TPLO. Body is still working very hard to adjust new mechanical environment. So, in early post-op (like the first 4–6 weeks), is it really the best option?

➡️ Probably not, if it means deep flexion + pretty strong quad activation + repetition.

Instead, we might be better off with:

• Controlled ROM (avoiding bouncing at end-range) – like cavaletti

• Isometric quad work – like FL on box

• Straight-leg stance or gentle weight shifting

• Or even just sit with bum on box, instead of sit-to-stand!

Bottom Line:

Patellar tendinopathy is common, usually benign, but worth monitoring. Just because a tendon is thick doesn’t mean it’s painful. But if recovery is stalling—or palpation cause discomfort—it’s worth a closer look. 

After TPLO, if it already happened, it is unlikely that it will return to normal thickness. 

And think one more time before giving sit-to-stand exercise for your patient!

🔍 Not every thick tendon needs fixing, but every thick tendon needs context.