1. Radiological Findings

Based on the provided hand X-ray examinations, the following features are observed:

• Significant bony fusion at the distal interphalangeal (DIP) joint level: In the left middle finger DIP joint, the joint space is absent or abnormally narrowed, and there is continuity of trabecular bone across the joint surface.
• Changes in skin texture: Clinically, the dorsal skin of the distal finger shows no obvious creases, suggesting severely limited joint mobility.
• Phalangeal morphology: The affected finger may be slightly shorter than other fingers on the same hand, and there is no obvious cartilaginous space at the joint.

2. Potential Diagnoses

Taking into account the patient's history (present since childhood or congenital, with no obvious history of trauma) and current radiological findings, the following diagnoses or differential diagnoses may be considered:

1. Congenital bony fusion of interphalangeal joints (Symphalangism): A common radiographic finding is the fusion of the joint surfaces and loss of joint space, often with minimal pain. Although distal interphalangeal joints are less commonly affected, it is not impossible.
2. Post-traumatic ankylosis of the DIP joint: If there is a history of trauma or infection, it can lead to bony ankylosis of the distal interphalangeal joint. However, since the patient has no obvious history of trauma or infection, this is relatively less likely.
3. Secondary degenerative joint disease: Usually observed in older individuals or where there is repeated joint stress. For a 32-year-old patient with involvement of only a single joint, this possibility is relatively low.

3. Final Diagnosis

Considering the patient's age, clinical manifestations (finger stiffness, absence of skin creases over the joint), and the X-ray findings of bony fusion in the distal interphalangeal joint, the most likely diagnosis is:

Congenital symphalangism of the distal interphalangeal joint (congenital interphalangeal ankylosis).

If further confirmation is needed, a family history investigation or genetic testing can be performed to determine any congenital or hereditary factors. However, in most cases, clinical imaging and history are sufficient for diagnosis.

4. Treatment Plan and Rehabilitation

4.1 Treatment Strategies

• Non-surgical treatment: If DIP joint ankylosis does not affect daily function, surgical intervention is generally unnecessary. If the patient only has limited range of motion and mild pain or functional impairment, it can be managed with observation and appropriate protection during daily activities.
• Surgical treatment (rare): If there is severe functional limitation or cosmetic concerns, arthroplasty or other corrective surgeries may be considered, although outcomes can be limited.

4.2 Rehabilitation and Exercise Prescription

Because movement of the distal interphalangeal joint has a relatively minor impact on overall hand function, the primary goal of rehabilitation is to maintain the flexibility of other joints and overall hand function. The following progressive plan may be considered:

• Range of motion exercises:
  • Encourage flexion and extension exercises of healthy finger joints (other than the DIP joints), such as flexion and extension in warm water, fingertip-to-palm movements, etc.
  • Each session can last about 5–10 minutes, and be performed 2–3 times a day, consistently.
• Strength training:
  • Use a grip ball or soft stress ball to gently squeeze and relax, gradually increasing hand muscle strength.
  • Initially, choose a low-resistance option (e.g., soft sponge ball), and perform 10–15 repetitions per set for 2–3 sets, with a 2-minute rest between sets.
• Coordination and fine motor training:
  • Recommended training includes piano-like fingertip tapping, pinching small objects, or using chopsticks to pick up beans, to maintain finger flexibility and coordination.
  • Gradually increase the frequency and duration of exercises as tolerated.
• Daily living advice:
  • Avoid excessive force or sudden weight-bearing actions to reduce the risk of further injury to the DIP joint.
  • Use warm protective gear and moderate heat therapy in cold weather to help relieve stiffness.

Throughout the rehabilitation process, training frequency, intensity, and methods should be adjusted individually, and each session should be gradually extended to suit the patient's specific condition. If persistent pain or significant functional decline occurs, seek medical review in a timely manner.