clock menu more-arrow no yes mobile

Filed under:

Injury analysis: A detailed discussion of Isaiah McKenzie’s shoulder injury

In the first of two installments, we take a look at McKenzie’s shoulder injury.

NFL: Buffalo Bills Minicamp Rich Barnes-USA TODAY Sports

BAM!! That’s how quick it happened last Tuesday. A thunderous hit from teammate Jordan Poyer flattened Buffalo Bills wide receiver Isaiah McKenzie towards the end of practice. Trainers quickly rushed to his aid, assessing his left shoulder, eventually taken off for further assessment.

NFL reporter Ian Rapoport later reported that McKenzie was sent off to get an MRI to assess the severity of the injury.

Few injuries are well timed with regards to time missed, but this injury does not make the Bills’ decision any easier considering the versatility that McKenzie brings to the offense and special teams. Complicating the matter is his direct competition, Marquez Stevenson is also working through a head injury from Saturday and prior right foot injury against the Chicago Bears.

Below is a detailed breakdown of the suspected injury McKenzie is dealing with, and the potential timeline he faces. In part two, we’ll discuss how the injury affects the roster decisions for cut-down day.


The AC joint is important in the shoulder as this is where the top of the acromion articulates with the clavicle. The AC joint is vital to shoulder motion due to the fact that as the arm is elevated, the acromion that attaches to the scapula begins to elevate. As the scapula begins to elevate, the articulation between the acromion and clavicle begin to move as the clavicle begins to rotate up and out of the way to allow for flexion and abduction required for overhead movement.

An example of the AC joint

Essentially, the clavicle acts as a strut does in a car, providing support at the thorax while allowing for mobility within the shoulder. If the AC joint is sprained, this limits the ability to elevate the shoulder, which could make catching the ball, blocking, or shedding tackles very difficult.

The injury

  • It’s known that McKenzie is dealing with a left shoulder injury that required an MRI to assess the severity of the injury.
  • It’s known that he’s wearing a sling to support the area while it’s healing.
  • Further reports from head coach Sean McDermott noted that he was between day-to-day and week-to-week, which is an odd descriptor as it has historically been one or the other. This has historically been 1-2 weeks missed for day-to-day and 2+ weeks for week-to-week in my observations.
  • What isn’t known is the specific injury. The fact that he’s possibly day-to-day rules out any sort of fracture, especially a collarbone fracture.

Possible injuries

This leaves injuries of the soft tissue variety including labrum, rotator cuff, or AC joint sprain.

There is a possibility that he could be dealing with a rotator cuff tear or labrum injury if he attempted to brace his fall with an outstretched arm. This isn’t publicly known at this time. This would cause the force to go up through the humeral head and either force the head of the humerus in such a way to partially tear the rotator cuff muscles. This force could also partially or fully dislocate the humeral head from the socket, tearing the rim of the labrum. However, Sean McDermott stated that this is not a long-term injury, which could rule out both options.

Reports indicate that McKenzie was hit hard but did not specify that he attempted to brace the fall. I suspect that he did not have time to anticipate the hit, which led to him falling directly onto the point of the left shoulder. This is the bony portion of the shoulder felt at the top when palpating.

This type of direct impact is a common mechanism of injury for an AC joint sprain. This can also occur due to a direct blow to the shoulder or fall on an outstretched hand or elbow, causing stress through the shoulder.


There isn’t a firm timeline but, again, McDemott noted this isn’t a long-term injury, suggesting under 4 weeks.

Looking at the available video and pictures, it appears as though McKenzie is dealing with a Grade I-II AC joint sprain. These injuries are unfortunately common with values ranging anywhere from 30 percent of all shoulder injuries in the NFL to upwards of 40 percent in the NCAA.

Example of AC joint sprain severities

Looking at the available pictures and video available so far, McKenzie does not have any visible deformity of the shoulder, specifically around the collarbone area. There would be a step deformity and could be seen under the shirt in most cases. This is not a determining factor, but can be a clue as to the specific injury.

In the video below, McKenzie is eating and while the video was about his masking fine, there is no sling on. This further suggests that the sling may be for comfort and support when walking around rather than sitting down, especially if he wished to use his other hand to eat or drink.

Using a sling following AC joint sprains is common and used for comfort, but are not recommended to use for a long duration so as to avoid shoulder stiffness.

On Saturday, it was further confirmed the injury is an AC joint sprain when WROC-TV’s Thad Brown filmed some of the warm ups above and a Twitter user noted that McKenzie was out of the sling, but was not moving the left shoulder much.

Referencing back to Rapoport’s tweet, the MRI was performed not only to assess the severity of the likely AC joint, but to assess if there was further damage to the other structures within the shoulder. While there isn’t an MRI machine in the building—only the Cincinnati Bengals are known to have one in their facility—there is an imaging center a stone’s throw from the Bills’ facility that a player can be quickly sent to for further assessment.

Now that we’ve analyzed the injury to Isaiah McKenzie’s shoulder it’s time to discuss the implications for the team’s roster—found here in part two of this analysis.