I needed a new knee op just from kicking a ball.
"My knee problem started out of the blue. I was walking my dogs on Hampstead Heath, North London, one winter's morning in 2013, and tried kicking a ball for them.
Suddenly, I felt a sharp pain in the back of my right knee - it was as if someone was pushing a finger hard into the skin. Thankfully, I could still walk.
Then, I noticed my knee starting to feel tight and some swelling. I thought I'd pulled a muscle so was shocked when, later, a specialist confirmed it was osteoarthritis - after all, I don't have signs of the disease in other joints.
Initially, I visited an acupuncturist. If possible, I think it's healthier to let the body deal with a problem before medication.
Sadly, that didn't work, so I visited my doctor, who referred me to a leading knee specialist, who I saw in February 2014. He quickly diagnosed osteoarthritis caused by wear and tear and suggested a partial knee replacement. X-rays and an MRI scan confirmed his diagnosis.
By then, my knee had started to affect my acting. I was appearing in Other Desert Cities, an American play at The Old Vic, and had to wear a knee support.
My agent watched a performance one night and said: "You've really got into your part and have an American swagger". But I was using my shoulders to walk and divert tension away from my knee.
It remained painful until I had the op at London's Princess Grace Hospital in August 2014. First, though, I had to reduce my blood pressure to be fit for theatre.
I'd smoked until I was 50 and after I quit, I had mild hypertension so took blood pressure tablets to reduce it. But when my heart was checked prior to the operation, my pressure was slightly too high again. To bring it down, I was advised to give up wine until after the op.
I loved white Burgundy but realising the effects it was having on my system, decided to give up for three months. And I never returned to it, although I do allow myself a couple of beers some evenings.
Work commitments meant I had to delay having the op. As well as finishing the play at The Old Vic, I was contracted to appear in Downton Abbey and a BBC production with Hayley Mills. Once they finished, I went into hospital during the first week of August 2014.
I worried about the op because I hadn't had one since 1980 - while taking part in a sword fight on stage, the little finger on my left hand was nearly severed. My opponent missed my blade and hit my hand, slicing the tendon in the finger. I underwent a serious operation to knit my finger together, the pain was excruciating.
For the partial knee op, I was advised not to believe I could deal with the pain. It was important I took some relief until it had recovered, which I needed because it did hurt - there are countless nerve ends around that part of the leg.
I was admitted on a Saturday morning at 8am. Staff like to get you up and about as quickly as possible. First, I used a zimmer frame, then two crutches and, finally, just one. But I couldn't leave hospital until I'd made a right angle with my knee joint and, believe it or not, successfully been to the loo, because morphine, which I took for pain relief, can cause constipation. Luckily, I passed the tests.
Within 10 days, I'd ditched my crutches and was back walking my dogs. Then in October, I appeared in the play Jonah and Otto in London. I started rehearsing for it seven weeks after the op - too quick.
On average, it's supposed to be around 16 weeks recovery, but it was about eight months before the flexibility I wanted had fully returned.
The physio I saw for three months after the op said I'd become active too soon. I'd wanted to walk and drive and was behind the wheel two weeks after leaving hospital and this hindered my recovery.
I took morphine for about 11 days after the operation. But, of course, it's very addictive so I only used it when the pain was too much. I also took prescription painkillers and used these for a month.
Thankfully, I don't have any pain now but do feel some nerve deadness on the right side of my knee, not that it restricts movement. I can kick the ball like before so my dogs are pleased! The only thing I tend to avoid is kneeling on it.
I'm back walking like before, which is my way of keeping fit. I visited a gym until I was 40 but then didn't have the time or desire to continue. For me, walking for one or two hours a day is perfect.
In terms of diet, I'm a vegan. I gave up meat seven years ago after watching a film, Earthlings, and seeing what happened in slaughterhouses.
I'm glad I've changed my diet. Now, I don't suffer acid indigestion, my stomach feels more settled, I'm more alert and don't get sleepy in the afternoon."
AS TOLD TO RICHARD WEBBER
Between July and October, Peter is appearing in Young Chekhov at The National Theatre. He's the UK ambassador for Animals Asia (animalsasia.org) and patron of Dr Hadwen Trust, a non-animal medical research charity (drhadwentrust.org)
PARTIAL KNEE REPLACEMENT
Mr Ali Bajwa, consultant orthopaedic surgeon at Princess Grace Hospital, says: "More than 70,000 knee replacement operations are performed in the UK annually - 90% are total knee replacement, the rest partial.
"Modern artificial knee replacements are metal alloy. A metal lining is fixed at the end of the thighbone and on top of the shin bone and a plastic spacer is fitted in between. The natural joint lining produces the lubricant fluid needed for the artificial joint.
"The surgery involves removing damaged cartilage and bone before placing artificial pieces in the knee. It lasts about 90 minutes but within a few hours the patient is back in their room. We emphasise moving the joint straightaway and taking a few steps with a physio's help using a walking aid.
"A stay usually ranges from two to four days. Partial knee replacement compared to total knee offers a faster recovery, less complication risk, shorter hospital stay, a smaller incision and, perhaps, better function overall because most of the soft tissues are better preserved.
"The downside is the risk of needing a further operation in 10 years as any joint replacement won't last for ever.
"Walking after a knee replacement starts almost immediately, although it takes a couple of weeks before the patient is walking unaided. Overall, recovery takes three to four months."
It felt tight and swollen - I thought I'd pulled a muscle but it was actually osteoarthritis
SITCOM Right, in Ever Decreasing Circles
MARQUESS In Downton with Lady Rose
ME & MY BODY: PETER EGAN