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Practice fi rst on a spare or broken knee joint before attempting this procedure.
Ring locks, also known as drop locks due to the gravity-operated nature of the locking mechanism, are easily one of the most popular style of knee joint used on KAFOs in the United States. They are so popular because they are simple, easy to use, inexpensive and versatile.
One of the things about ring locks is that, theoretically, they always fall to the locking point when in a vertical, or standing, position. This is part of the design, but if you require that the rings stay in the unlocked position until a locked knee is desired, then you have a decision to make. You can either order the knee joints with ball bearing lock retainers already installed (Becker Orthopedic offers this service for a small upcharge) or you can install them yourself.
For the uninitiated, ball bearing lock retainers are a method for keeping the drop locks temporarily suspended above the point where the ring lock prevents fl exion of the hinge. A spring loaded ball bearing is implanted into the joint head so that it partly protrudes above the surface, preventing the lock from progressing over the point where the hinge folds. Because the ball bearing is spring loaded, it is easily overcome be pushing it downward with just a little force. Many patients fi nd them useful and convenient.
Installing them yourself can be easier said than done. I've seen quite a few perfectly good knee joints destroyed by inattentive or overzealous technicians who drilled a little too deeply. Armed with bit of foreknowledge, however, you will find that installing a lock retainer into a ring lock can actually be fun. Okay, not fun per se, but at least you won't waste time or knee joints during the undertaking.
The right tools
To install ball bearing lock retainers you will need a few basic tools. You will need the obvious...