• Acute tendinitis is seen mostly in young people.
• Chronic tendinitis is usually in middle aged people.
Complete tear is weirdly common in old people. In autopsy, you'll find that a lot of the cadavers over the age of 60 have wearing and even tears in the tendons of the supraspinatus and the long-head of biceps.

They all involve 3 basic pathological processes which are wear, tear, and repair:
• Wear (degeneration): usually due to overuse and consequently seen often with advanced age. You find minute tears and scarring in the cuff with fibrocartilaginous and/or calcium deposits.
• Tear (trauma and impingement): mostly in the supraspinatus ligament due to lifting a heavy weight or a fall on an extended arm. Tears are more likely if the cuff is already degenerate.
• Repair (vascular reaction): the repair process itself will cause congestion and pain.

In the young patient ‘repair’ is vigorous; consequently, healing is relatively rapid but (because the repair process itself causes pain) it is accompanied by considerable distress. The older patient has more ‘wear’ but less vigorous ‘repair’; healing will be slower but pain less severe. Thus acute tendinitis (which affects younger patients) is intensely painful but rapidly better; chronic tendinitis (a middle group) is only moderately painful but takes many months to recover and may be complicated by partial tears; and a complete tear (which generally occurs in the elderly) becomes painless soon after injury, but never mends.

Partial tears are not easily detected, even on direct inspection of the cuff. Continuity of the remaining cuff fibres permits active abduction with a painful arc, making it difficult to tell whether chronic tendinitis is complicated by a partial tear. If the diagnosis is in doubt, pain can be eliminated by injecting a local anaesthetic into the subacromial space. If active abduction is now possible the tear must be only partial. If active abduction remains impossible, then a complete tear is likely.

.

Total elbow arthroplasty

The stages of human life

From 'Atlas of human anatomy and surgery,' 1831-1854

.

Myositis Ossificans (MO)

It's a type of heterotopic ossification that develops within a muscle and is known to occur following muscle injury or bone fracture. It remains unclear why MO occurs, but it can develop at any site of muscle injury.

MO may be palpable as early as four to five days after a quadriceps contusion but may take several weeks to develop. Early symptoms include persistent pain and swelling that does not appear to be resolving. Later symptoms include a worsening of pain with activity or swelling, early morning or night pain, and decreasing range of motion after two to three weeks. If MO is suspected, plain radiographs or ultrasound should be obtained. Two to four weeks are typically needed for MO to become visible on plain radiographs.

It's histology is similar to osteosarcoma, even though it's benign and does not evolve into a malignant tumor. It's one of those "don't touch" lesions that are diagnosed radiologically & clinically alone, and don't need a histopathological study because it will only confuse you more.

Also called skeletal "leave alone" lesions. They are so characteristic radiographically, that further diagnostic tests such as a biopsy are unnecessary and can be frankly misleading and lead to additional unnecessary surgery. Thus a radiologic diagnosis should be made without a list of differential possibilities.