Set up for a rabbit who cannot twist or hop away safely
An old rabbit grooms less not from laziness but because arthritis, a stiff spine, dental pain, or extra weight makes the curl round to his sides and rear physically hard. Your grooming has to replace that missing reach without asking him to balance or bend. Work on the floor or on a low, stable surface covered with a towel or fleece so his feet grip, and keep him in his familiar pen area if that is where he is calmest.
Keep sessions short and end them while he is still relaxed. A soft rubber brush or a fine grooming mitt suits most senior coats better than a stiff slicker, which can scratch thin older skin. Have small scissors put away out of the session entirely; cutting a mat close to loose rabbit skin is a common way owners cause a wound, so mats are teased and brushed out, not snipped blindly.
Work the map of places he has stopped reaching
Start where he can still groom himself, his head, shoulders, and upper back, so the session begins with a familiar sensation. Then move deliberately to the neglected zones: the lower back just above the tail, the flanks, the belly edge he can no longer roll to reach, and around the rear and scent glands. Loose fur collects heavily in these areas during a moult, and a senior rabbit who swallows what he cannot clear, or who is groomed less by a partner, can carry a surprising felt of dead coat there.
Support his body with one hand while the other brushes, lift no more fur than the brush takes easily, and use your fingers to ease apart small tangles before brushing through them. Check the skin under every cleared patch for redness, flakes, tiny scabs, or lumps, and feel along the jaw and body for changes you would not spot by eye under a thick coat.
Treat the underside check as the real point of the session
The highest-value part of grooming a senior rabbit is what you find underneath. A rabbit who cannot reach his rear may develop a damp, soiled bottom, matted fur around the tail, or sore skin hidden under clean-looking top fur, and in warm weather a soiled rear puts him at serious risk from flies. If the underside is dirty, clean only that area with a damp cloth or a shallow, vet-advised wash of the rear alone, dry him thoroughly, and look for why it happened rather than treating it as a one-off mess.
Never immerse or bathe a whole rabbit: the stress, chilling, and risk of shock outweigh any coat benefit, and a senior rabbit tolerates chilling especially poorly. Trim overgrown nails in the same calm setup if he allows it, taking only tips and keeping him supported, because long nails change how an arthritic foot lands and worsen his reluctance to move.
Know which grooming finds mean a vet visit
Book a veterinarian promptly if you find skin that is broken or weeping, a lump that is new or growing, heavy dandruff with fur loss, a persistently soiled rear, mats you cannot clear without hurting him, or any change paired with eating less hay. Those are health findings, not grooming failures, and pain relief or dental care often restores a rabbit's own grooming more than extra brushing ever will.
Between your sessions, KinsLe's Care Teams lets you assign this rabbit's twice-weekly rear-end and coat checks to the family members who help you, with each completed groom marked by a timestamp, so the areas he cannot reach are checked on schedule even on days you are out.