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In Street Clothes

Covering sports injuries from the perspective of a certified athletic trainer and backed by analytics.

Breaking Down Bone Contusions

The 2016-17 NBA season is nearly a quarter of the way through and injuries are already piling up. The total number of games missed due to injury or illness is slightly up from last season, despite a dip in total injuries sustained during the preseason and regular season. As of November 25, NBA teams had surrendered 781 games to injury for the 2015-16 season, 56 more than last year’s total at the same time. The elevated total is even more surprising considering the number of injuries requiring surgery and the subsequent games lost are down. Instead the time lost to seemingly “minor injuries” like sprains and strains is on the rise. It may be a sign teams are being more conservative with their approach to these types of ailments and it will be interesting to see if the trend continues through the remainder of the first quarter of the year.

One specific “minor” injury that has been particularly problematic so far this season is the bone contusion. Multiple players including Michael Carter-Williams, Derrick Favors, Chandler Parsons, and most recently, Marvin Williams have all missed time with bone contusions.

While it seems a bit silly that a bruise or contusion would keep an NBA player on the sidelines, the injury tends to be more complex than its name suggests. When most people think of the term bruise, it is in conjunction with a soft tissue contusion. However, like their name suggests, bone bruises involve one of the underlying layers of bone and not just muscle or fat.

Bone is a multilayered tissue with each specific layer varying in thickness and consistency. The thin, outer layer is the periosteum that protects the bone and surrounds nerves and blood vessels. Below that sits the harder compact bone that compromises the majority of the human skeleton. The next layer of bone is the less dense spongy bone. Spongy bone or cancellous bone is often located at the end of long bones and, like its name suggests, is porous. These layers protect the innermost aspect of the bone, the bone marrow, which is involved in red blood cell production.bone-layers

The various layers of bone tissue can be damaged when overloaded or stressed, like after a fall or with a direct blow. If every layer of the effected bone is damaged, the bone is considered fractured or broken. However if the damage is limited to one layer, it is classified as a bone bruise. A subperiosteal hematoma or periosteal bruise develops when blood builds up under the outer layer of bone while 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, which develops between an area of cartilage and the bone tissue below.

For professional athletes, an interosseous bone bruise is the most commonly suffered classification of bone contusion. Unfortunately for the affected individual, the body’s natural healing response does not differentiate between a bone bruise and a fracture, repairing both in a similar fashion. In both injuries, specialized cells known as osteoblasts must create and lay down new bony tissue to fill in the gaps created during the injury. While the new tissue will eventually return to its original strength, it does take time to complete and a player can be sidelined for a surprisingly lengthy amount of time.

Patellar bone contusions are even more complicated due to the biomechanics of the kneecap. The kneecap or patella is embedded within the tendon of the quadriceps muscle group. This somewhat unusual location enables the patella to increase the moment arm of the tendon, increasing the moment of torque and consequently improving range of motion. However, as it moves, the kneecap comes in contact with multiple areas of the knee joint, particularly the femur. This repetitive bone-on-bone contact can negatively impact healing and prolong the rehab process.

The total number of games lost to bone contusions this is season is over three times higher than last year and twice has high as the 2014-15 campaign. The number will continue to rise with Favors, Parsons, and Williams all expected to remain sidelined for the immediate future. It’s likely the increase is simply a coincidence evaluated in a small sample size due to the unpredictable manner in which bone contusions occur. However time will tell if bone contusions, along with other supposedly “mild” injuries, continue to shape this season’s injury rate as the season progresses.