Hi Jenny
Sound like you are progressing well to make a fist after 4 weeks. Keep working on it gently . In my case I believe what movement I had after 6 weeks was what I would finish up with . The "catching" sounds like a bit of trigger finger which is not uncommon after Dupuytren's surgery. Unfortunately after surgery nerves and tendons may not sit in the same position as prior to surgery. You may find after a while things settle down and the catching may subside. It is a bit unclear did your surgery take in the finger and the palm? Is this your First surgery? I've had 15 odd surgeries including grafts and back in 2007 I had a repeat surgery and within 4 weeks I had numerous nodules appear and a keloid . I was going to Germany and saw Prof. Seegenschmiedt then in Essen and had radiotherapy . (Received treatment for 5 consecutive days of 3 Gy total 15 Gy. ) Did the trick they all disappeared. Keliods are also treated with radiotherapy. Surgery sometimes starts the clock ticking towards the next surgery as in my case. Also you did not mention your age. These days the first option rather than surgery is PNF or NA as it is called in the States. Regards.

Edited 10/17/15 14:20

Hi again it sounds as though you had a cord connecting the two fingers within the web which prevents one from fully spreading the fingers apart. Do you have contraction in the other hand if so what degree % are you at. Use a simple protractor to take a measurement . I never used a splint after surgery as my fingers were straight. The case of PNF is different and a night splint is worn to prevent the fingers making a fist whilst sleeping. The putty you are using is good to build up the strength .Don't over do it at this stage. Are you applying a Scar Gel which helps reduce the scar tissue. Scar tissue in itself also restricts movement. In Germany there is a product called Narben Gel Brand Name "Scar Soft" Gel for Scars- Packet states made in following countries Germany/Belgium/Thailand- is made of natural herbs and a silicone. Check what is available at your chemist for reducing the scar tissue.
Check out the list on the top left window "Treatment"re list of Doctors in UK that carry out NA.

Edited 10/17/15 15:13

After my surgery 18 months ago ( palm , span between thumb and index finger , ring , middle and index finger , I was told that some patients are more likely to get scar tissue than others . Once the initial incisions had started to heal I used "Bio-Oil" daily and continued with the "putty" . Unfortunately in my case I have a feeling like ( rolled up cardboard in my index finger) , and the scars are very prominent in cold weather . I still think that having the operation was the only option although initially I did regret going ahead, my hand by now would have been like a "claw" without . It will/can take many months to feel back to some kind of normality , I found that it took nearly a year for the grip on my left hand to be as my right hand .

Waiting for Xiaflex injections on my right hand now !!

Best of luck