Partial osteoarthritis
This form of disease involves one compartment before the other. Either the medial, lateral or patellofemoral compartment is involved before the other.

Causative factors
Bow legs, tibial and femoral intra articular fractures lead to medial compartment arthritis. Knock knees lead to lateral compartment arthritis.

Diagnosis
Pain is one sided. A squat test will confrm the localisation of pain to the inner or outer half. Tenderness is also in the same half while the other side is normal. Standing x rays are diagnostic.

Antero medial wear in medial compartment arthritis
A depression is seen in the medial tibial plateau as seen in the specimen

Treatment
Uni condylar replacement or osteotomy are the surgical alternatives in the young patient. A high tibial osteotomy is indicated for active males while a Unicondylar knee replacement is more suitable for a sedentary lady. Quality of pain relief is better with a replacement than an osteotomy.