Laceration: Given the sharp object and the location on the back of the lateral malleolus, a laceration is the most straightforward and likely diagnosis. The sharp edge of the object would easily break the skin, leading to a cut.

Abrasion: If the object was sharp but the impact was glancing or the skin was scraped against a rough surface, an abrasion could result. This would be less severe than a laceration but still a common injury from a sharp object.
Puncture Wound: Depending on the shape and size of the sharp object, a puncture wound could occur if the object penetrated the skin deeply enough. This would be a concern for potential internal damage or infection.

Compartment Syndrome: Although less likely, compartment syndrome is a serious condition that could arise from significant trauma to the area, including a deep laceration or puncture wound. It's crucial to monitor for signs of compartment syndrome, such as severe pain, pallor, paresthesia, poikilothermia, and pulselessness, as it requires immediate medical intervention.
Osteomyelitis or Septic Arthritis: If the wound penetrates to the bone or joint, there's a risk of osteomyelitis (bone infection) or septic arthritis (joint infection). These conditions are serious and require prompt antibiotic treatment and possibly surgical intervention.
Tendon or Ligament Injury: The area around the lateral malleolus contains important tendons and ligaments. A sharp object could potentially damage these structures, leading to significant functional impairment.

Foreign Body Reaction: If a piece of the sharp object broke off and remained in the wound, it could lead to a foreign body reaction, which might cause chronic inflammation, infection, or other complications.
Nerve Damage: While less common, depending on the depth and location of the wound, there's a possibility of nerve damage. This could result in numbness, tingling, or weakness in the foot or ankle area.