Some vets tell people their dogs will be crippled by arthritis later unless they have surgery as soon as possible after a ligament injury. This is not true.  Don't let yourself be rushed into agreeing to surgery on the basis of false claims like this whose purpose is to sell surgery. Restricting activity carefully after ligament injury minimizes the risk of future DJD (Degenerative Joint Disease) or arthritis.  Careful restriction of activity during recovery is the foundation of a good recovery with the least possible risk of future arthritic problems whether or not a dog has had surgery.  
---- Ligament injuries leave the joint 'loose'. The bones are not properly restrained in the joint as they were prior to injury. If the dog puts pressure on the joint as he would with normal levels of activity, the bones' ends can bump and grind roughly against each other damaging the meniscus (please see the 'Meniscus' page here at this website for more on the meniscus). This further damage to the joint must be avoided by restricting activity carefully. Preventing excessive stresses from running, jumping, etc, will both avoid further damage to the joint and provide the conditions the body needs to build new stabilization for the joint. It is also important to avoid excessive low-stress activity. Long walks, even though low-stress, can cause damage to the fragile recovering stifle.
---- Conventional Stabilization Surgery temporarily stabilizes the joint while the new supporting tissue builds up. Sometimes this is necessary, but for most dogs simply carefully restricting the dog is all that is needed to have the stifle(knee) re-stabilize without the risks of surgery. A brace may be helpful in some cases.  There is more about braces on the FAQ page.  With careful restriction the injured stifle should show slow improvement during the 8 weeks just after the injury. If careful restriction is ineffective, then stabilization surgery is appropriate.  The re-stabilization will continue for many months, perhaps as long as a year or more, whether or not surgery is used. Being cautious during recovery will give the dog the best possible recovered stifle with the least possible risk of future arthritic trouble.
---- Many factors enter into whether a dog will have future arthritic problems with a joint that has suffered a ligament injury, including:
-- The degree of damage to the joint's components at the time of the injury and any further damage from inappropriate activity during the recovery.
-- The dog's genetic predisposition to arthritic problems.
-- Diet and lifestyle:  Being overweight and/or engaging in high-risk activities (such as play involving jumping and landing with a twist like jumping to catch balls or frisbees) predispose a dog to recurring injury and eventual arthritic problems.
Other factors being equal, dogs who have recovered from ligament injury using non-surgical Conservative Management and dogs who have recovered after conventional stabilizing surgery, and dogs who have bone-altering surgery are all equally at risk for future arthritic problems.
(Please see the page 'But the vet said...' for information on false/flawed claims and a journal article on ligament injury treatment research review). Whichever type of surgery is being recommended, often the surgeon will say to people "Your dog will be crippled with arthritis if he doesn't have this surgery."  This is a baseless claim. While I have heard of many vets using this argument to support their preference for the surgery they are selling, there is nothing solid to support this claim. No real research studies have compared Conservative Management of ligament injury to surgical treatment and found that surgery provides a decreased risk of arthritis. Proper restriction after injury which prevents further damage to the joint is what minimizes the risk of future arthritic problems, with or without surgery.
---- I think that many vets who honestly believe in surgical treatment's superiority are making the mistake of comparing their preferred surgery's long term outlook to allowing the dog to decide his own activity level rather than comparing surgical results to the restricted-activity recovery of proper conservative treatment. Their belief in surgery's superiority assumes that without surgery the dogs will be allowed to repeatedly over-stress and re-injure the leg.  Also, some vets are basing their opinions on the statements of surgeons who make self-serving claims which are not supported by objective studies. But while there are various explanations for the pro-surgery opinions you may hear, no one is basing a "Surgery-Prevents-or-Reduces-Arthritis" statement on scientifically done medical research demonstrating a superior outcome for surgery over non-surgical recovery with regard to future arthritic problems. There isn't any such research supporting such claims.  (Please see the page 'But the vet said....' here at this website.)
The Spinach Ploy -- Years ago some mothers would tell their children that their growth will be stunted if they did not eat their spinach.  This is the same tactic as the 'Arthritis Scare': -- State a frightening but baseless claim with conviction and depend on the recipients' respect for expert authority to win their compliance.  This tactic used to get a lot of spinach eaten and it gets a lot of ligament surgery sold now.  I'm not saying all the vets (or the mothers) are purposely being deceptive. They may really believe what they say. They may honestly think these things are true. But when you look for the evidence supporting the claim that rejecting surgery leads to arthritis, there isn't anything solid there.  
Increased future arthritic risk is a fact in all cases. 
All dogs who have ligament injuries are more likely to have arthritis in the injured joints in the future than dogs who have not had ligament injuries.   The fact is that having had a ligament injury leaves a dog with a less than perfect joint which is going to be more prone to develop arthritic changes as the years go by.
---- But dogs who recover using Conservative Management and dogs who recover with surgery as an aspect of their treatment are equally at risk for future arthritic problems. Proper restriction during recovery and avoiding high-risk activities after recovery, together with weight control, good nutrition, and joint-supporting supplements are what minimize the chances of future arthritic problems.
TPLO and Arthritis Risk
When TPLO was a new procedure years ago, vets who were selling TPLO almost universally claimed that TPLO prevented future arthritis.  The fact was that TPLO had not been around very long, so the dogs who had already had TPLO had not had time to develop arthritic changes in the joint.  The most charitable way to view those claims made then would be that they were optimistic.   But as the years went by it became clear that TPLO dogs were just as likely to have arthritis later as were dogs who had other kinds of surgery or non-surgical treatment.  Today, an honest surgeon will tell you that no surgery reduces arthritis risk.  But in spite of the fact that time has proven that TPLO does not reduce arthritis risk, many TPLO surgeons today will tell people that the surgery they sell eliminates or lessens the risk of future arthritic problems for the dog. They do this as part of their sales pitch for the hugely profitable TPLO.  There is no substance behind these claims.  Just as great a proportion of dogs who have TPLO develop arthritis in future years.   
---- None of the treatment options, including non-surgical recovery and all the surgical options, can lessen future arthritic changes in the joint.  
Meniscal Release
'Meniscal Release' is often done as part of a TPLO procedure.  'Meniscal Release' cuts the connection of part of the meniscus, removing it from what would be its functional position in a normal joint.  This decreases the risk of injury to the meniscus at the cost of removing the meniscus from being a functioning part of the joint.  'Meniscal Release' has been found to be a factor in dogs' increased development of Degenerative Joint Disease (DJD). There is more about 'Meniscal Release' on the page 'The Dog Meniscus' found on the navigation bar at left.
Here's a quotation from James M Fingeroth, DVM DACVS, who is a TPLO surgeon and advocate, regarding Meniscal Release.
<<"...Meniscal release was Dr. Slocum's proposed solution to eliminating the vulnerability of the medial meniscus. He recognized that even with TPLO one could not ensure the elimination of all translational motion between the femur and tibia in all joint angles and in all phases of stride and weight bearing. Joint biomechanics are far too complex for any single alteration to account for every facet of motion. His concept was to either transect the caudal meniscotibial ligament (allowing the caudal pole to retract caudally "out of the way" when the femoral condyle rolled past), or alternatively to transect the caudal horn of the medial meniscus itself allowing similar mobility to mimic the situation with the lateral meniscus. The choice of where to perform the release (ligament or meniscal horn) is dependent on the type of arthrotomy used. Meniscal release can be incorporated into either a conventional reconstructive procedure or a geometry modifying procedure. However, recent studies done in Germany have suggested that meniscal release may be ineffective at reducing the incidence of late meniscal tears, and moreover, may, like a spontaneous meniscal injury, actually result in increased arthrosis in the knee. This remains a controversial area and some surgeons are now abandoning the practice, while others continue to employ it.">>>
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As far as I can determine there is no reasonable basis for inferring that any of the surgeries would result in a joint less susceptible to arthritis than a joint which had recovered without surgery. On what basis could such a claim be made? I see none.
However, it's important to restrict the dog during recovery. If a dog were not restricted while supporting tissue developed (either after surgery or as part of non-surgical Conservative Management) then the dog would repeatedly re-injure the joint. This would damage the new supporting tissue as it tried to develop. The joint would never heal properly. Such a dog would certainly be more likely to have serious arthritic problems in that joint than a properly restricted dog.
To do all we can to minimize arthritic problems, I strongly recommend giving Glucosamine & Chondroitin daily to all dogs who have had ligament injury, regardless of treatment used in recovery. Not for a limited period but for the rest of the dog's life. This may be the most important thing we can do for long-term joint support.