Good nutrition is important in healing and maintaining health. 
Opinions differ on diet, but it is certain that you should not be feeding your dog cheap grain-based kibble.
There are many supplements which are used to promote joint health & recovery from injury. 
There are many opinions about the best diet for dogs. I feed some meals of cooked stews made with meat & veggies, some meals of raw chicken and other raw meats, and some meals of high-Meat-protein, low-carbohydrate, no-grain kibble.  Some people favor an all raw diet. Others exclusively use packaged dry dog foods ('kibble'). Some of these kibbles are much better than others. 
        The cheap dog kibbles are mostly grain. These grain-based kibbles do have the amount of protein their labels say they have, but it is not the right kind of protein for dogs.  Proteins are made up of amino acids.  Different sources of protein contain different types of amino acids in different amounts.  Grains do not provide the correct types and balance of amino acids for dogs.  Dogs require 22 amino acids (the building blocks that make up proteins).  Dogs can synthesize 12 of these amino acids.  The remaining ones - called 'essential amino acids' - must be consumed.  Some of the essential amino acids are not present in proteins from grains.  A deficiency in any of the essential amino acids can cause health problems.  Meat, fish, and eggs are the best sources of high-quality protein for healthy, happy dogs.  If you give your dog a diet high in meat-protein, some of the protein will be used as calories, some used to build and repair the body, and any excess will be excreted.
        Dogs bodies have been designed by nature to thrive on the high-protein, meat-based diet of a carnivore. They won't prosper best on a high-carbohydrate grain-based diet any more than you would if you tried to live on a diet of grass that your horse would thrive on.  As omnivores we humans can make better use of carbohydrates / grains in our diet than dogs can.  We need to feed our dogs a diet that suits their digestive systems rather than a diet that would work for us.  Dog foods which contain at least some meat-source protein together with grain may prevent or delay the negative health consequences that would result from a total absence of the essential amino acids lacking in grains, but the best diet for dogs clearly should be based on meat, fish, & eggs.  Not grains.  
        Grains contain large amounts of carbohydrates. Much lower amounts of carbohydrates can be useful for a dog, but high levels of carbs in grain-based diets lead to weight gain and nutritional deficiencies.
"If no one on earth had ever seen a dog, and a dog arrived from another planet in a flying saucer, and we were wondering what food to offer, the dog's sharp teeth and short digestive system and other physical traits would clearly be saying  'This is a carnivore. His nutritional needs will best be met with meat.'"
Some vets will tell you that too much protein will cause kidney disease or other health problems. This is not true. It used to be widely believed in the past, but now is known to be untrue. 
If your dog has a kidney disease,  please see Mary Straus's 'DogAware' website.
Owners report that their dogs with arthritic problems improved greatly when grain was removed from their diets.  Chronic skin problems are also reported to be resolved by removing grains from dogs' diets, as well as other health problems.  It may be that some dogs are genetically more strongly predisposed to have arthritic & other health problems when fed a lot of grain and other carbohydrates.  It is certainly true that dogs do not need grain in their diet and that grains are not an ideal food for dogs.
There are now a number of no-grain dog foods available.  It is important in choosing among them to consider protein sources & protein percentages.  Simply being a no-grain food is not good enough. 
'No-grain' has become trendy, so some kibble makers are selling new products in which they have simply switched from grain to another carbohydrate.   It is possible for a kibble to be no-grain but have too little animal protein and/or low quality animal protein.  Look at the ingredients listed on the bag.  By law these must be listed in order of percentage in the kibble.  The first named ingredient being the thing there is most of in the kibble, etc.  However, be wary.  Some manufacturers will break down ingredients listed so as to give a false impression.  For instance, if a kibble is mostly rice with only a little meat, the ingredients list should in honesty read:
 "Rice(brewers rice/rice broken pieces/rice hulls/ground rice), chicken meal," --- etc etc
but the manufacturer knows many people look to see what the first named ingredient is on the bag, so he breaks out the various rice items as separate ingredients, letting him put 'chicken' first, thus:
"Chicken, brewers rice, rice pieces, rice hulls, ground rice," --- etc etc
Or, the manufacturer could use multiple non-meat ingredients to let him keep chicken as the first listed ingredient while the proportion of chicken in the kibble is actually small:
"Chicken, brewers rice, rice pieces, corn, wheat, ground brown rice, rice powder, beat pulp," --- etc etc.
A kibble could have a dozen non-meat ingredients which added together comprised more than 90% of the kibble's weight, but if no single one of the non-meat ingredients were more than a chicken proportion of 8%, the chicken would be listed as the first ingredient.
Seeing high quality meat sources (such as chicken, turkey, chicken meal, etc) as the first several ingredients, and high protein percentages overall, are the indicators of a good quality no-grain kibble.  
-- Seeing one or two low quality protein sources (like "poultry by-product meal") followed by non-meat ingredients, and a lower protein percentage overall, indicates a low quality kibble.
---- Here are the kibbles I like best:
--The Natura company which makes 'Innova' brand kibble has a no-grain kibble named 'Evo'.  Great for adult dogs, but not recommended for puppies.
-- Champion Petfoods makes 'Orijen'.  A great adult kibble, and for puppys, 'Orijen Puppy' is the best there is. 
--The Wellness company makes a good grain-free kibble  called 'Core'.
Here is a link to a dogfood analysis and review website:
Homemade meals which include a variety of meats and veggies are good.  Raw meat meals are good.  A high-quality, no-grain, high-Meat-protein, low-carb commercial dog food is also good choice.  Using a good quality kibble for at least part of a dog's diet insures that you aren't missing some necessary nutrient in your home-made food.  Here is a link to the Orijen 'White Paper' on dog nutrition which is extensive and well worth reading if you want to be better informed on dog nutrition.
http://www.orijen.ie/acatalog/ORIJEN_White_Paper(09).pdf


Losing Weight
Serendipitously, when I stopped using grains and reduced all carbohydrates I found that dogs were much less inclined to put on excess weight.  Many dogs who have ligament injuries are overweight dogs.  It is important to get their weight down as part of recovery and for avoidance of future joint problems.

'Diet' dog foods
are marketed to appeal to humans.  The kibble makers who sell these cut back on the more nutritious meat protein and animal fat components and put in more carbohydrate fillers so that the food bowl can be just as full but the dog will have more filler (corn meal etc) in the same volume and less high quality meat protein & other preferable ingredients.  The food appeals to humans who would feel bad about feeding Fido less, but this is not good for Fido.  It is much better to simply feed him less of a top quality food.


Supplements 
 ----
There are different opinions about the various joint supplements.  The foundational supplements for joints are  Glucosamine & Chondroitin. There are many manufacturers of these supplements. There is no reason to prefer supplements marketed especially for animals.  It is fine to use human-grade supplements.  You can find them at most places that sell vitamins.  Supplements are also available through catalog and internet sale.  Vets sell joint supplements but there is usually a high markup on the price.

There are now dry dog foods which include Glucosamine & Chondroitin.  The amounts included are very small relative to what a dog should be getting.  Supplement tablets are the best way to provide appropriate dosages.  I often hear from people that their vets have recommended dosage amounts that I believe are less than optimum.  Here's the amounts which I, and many other people, have used for years with good effect.
Recommended Daily Joint Supplement Dosages:
Glucosamine
500mg per 25 lbs of body weight ( 20mg/lb)
Chondroitin
400mg per 25 lbs of body weight.
You can safely give more so you don't have to split tablets.  Just give however many tablets it takes to be at or over those dosages. These are very safe supplements. 
---- Many supplements' front labels say something like "1500mg Glucosamine" when this is the amount in what they consider a serving, rather than per tablet.  Be sure you are calculating properly to give the right amount.  For instance, if there are 3 tablets per serving and a serving is 1500mg, then each tablet is 500mg. 
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Mary Straus's website "DogAware" is a valuable resource. Her page on diet and joint supplements is:
http://www.dogaware.com/health/arthritissupps.html
As you read about people's reported results with supplements, remember that people may see what they want to see, and may mis-attribute good results. There is very little solid research evidence supporting the vast majority of the various supplements that are promoted. But it is also true that a lack of solid evidence is not proof that a supplement is ineffective.