The Philadelphia 76ers have been one of the NBA’s top teams in the 2020-21 team. Sixers big man Joel Embiid has been the catalyst for Philly’s success and emerged as the frontrunner for league MVP. Unfortunately, Embiid’s season took a scary turn on Friday when he limped off the court after hyperextending his left knee. An MRI was quickly scheduled to determine the extent of the damage and Sixers fan began fearing the worst.
To start, a hyperextended knee is not a true injury. The term hyperextension simply describes the nature of injury, indicating the involved joint was pushed beyond its normal range of motion. Multiple structures, including ligaments, the joint capsule, and menisci, can be damaged when the knee is forced into hyperextension. However, Embiid’s MRI showed all these structures intact and the final diagnosis is a bone contusion.
A bone contusion or bone bruise is an injury more complex than its name suggests and one that has been discussed multiple times on InStreetClothes.com. However, let’s review.
A bone bruise is not as simple as the more common soft tissue bruise or contusion. Bone tissue is covered by a thin layer known as the periosteum. The periosteum acts as layer of protection and surrounds blood vessels and nerves. Multiple layers sit beneath the periosteum, depending on the specific bone. These layers include harder compact bone that compromises the majority of the human skeleton and the porous spongy bone, often located at the end of long bones. The multiple levels of bone tissue surround and protect the innermost aspect of the bone, the bone marrow where red blood cell production occurs.
The layers of bone tissue can be damaged if overloaded or stressed following an assortment of stresses including a direct blow or a hyperextension. A fracture occurs if every layers of the involved bone fails. However if the damage is incomplete and is isolated to just one layer, it is classified as a bone bruise. There are multiple types of bone contusions. A subperiosteal hematoma or periosteal bruise develops when blood builds up under the outer layer of bone. An interosseous bone bruise is marked by deeper edema in the medulla of the bone where the bone marrow is contained. The final bone bruise classification is a subchondral bruise and occurs between bone and an area of cartilage.
For professional athletes, an interosseous bone bruise is the more common occurrence and likely what Embiid is managing. While the injury has to be considered a win for the Sixers, the body’s natural healing response for bone contusions needs time as it is repairs the injury just like a true fracture. In both injuries, specialized cells known as osteoblasts create and lay down new bony tissue at the injury site to repair the associated damage. The bone tissue will eventually return to its original strength once remodeling is complete.
Knee bone contusions can require a prolonged period of time to heal, especially if the patella (kneecap) is involved. The patella is classified as a sesamoid bone and sits within the tendon of the quadriceps muscle. This positioning allows the patella to increase the moment arm of the tendon, increasing the moment of torque and consequently improving range of motion. However, the patella touches multiple areas of the knee joint, particularly the femur, during this process. This repetitive bone-to-bone contact can delay the healing process and prolong recovery.
Multiple NBA players have missed time with injuries described as bone contusions of the knee, including big men Tim Duncan, DeMarcus Cousins, Domantas Sabonis, and Nikola Vucevic. Since the 2005-06 season, the average time lost for players 6’10” and up that suffer a bone contusion in the knee and are forced out of action is approximately two weeks or eight games though the variability remains high. The wide range is likely linked to the location of the accrued damage.
Further complicating the situation is Embiid’s injury history. The center has missed time with an assortment of injuries involving his left knee, including tendinitis and a torn lateral meniscus. As a result, look for Philadelphia to handle Embiid’s recovery conservatively and don’t be shocked if his absence extends beyond the initial two week timeline. Still, given Philadelphia’s previous luck with injury the final diagnosis has to be considered a win for Embiid and the Sixers.