In our forensic casework it’s not unusual for all parties to acknowledge that a mishap occurred, but disagree on the cause or severity of injuries claimed to be associated with the event. In this article, we discuss injury causation investigations through the example of an incident in which the plaintiff was struck by merchandise falling from a retail display shelf.
Falling Merchandise: Injury Causation Analysis - Expert Investigation
Biomechanics is the science that deals with the time and space response characteristics of biologic solids, fluids and viscoelastic materials to imposed internal and external forces. In more general terms, biomechanics is the science of how the human body responds to applied external and internal forces.
There are three primary modes of loading: tension (pulling), compression (squeezing), and shear (sliding). They can occur alone, or in combination. All other modes of loading are combinations of these three basic modes. For example, in bending, the material on the outside of the bend experiences tension, while that on the inside of the bend experiences compression.
In the context of a forensic investigation, a qualified biomechanical engineer can examine diagnosed injuries and determine if the requisite forces were generated within the incident to cause the injuries claimed. Through reverse engineering, injury causation can be determined.
Description of Retail Incident
On the day of the incident, the plaintiff was shopping for a modular plastic drawer. The incident product was a 2-drawer unit located on a shelf 56 inches from the ground; it weighed 10.67 pounds and was 22 in. long, 18 in. wide and 26 in. high.
The plaintiff reached up with both hands to grab the drawer unit from the shelf when the item fell and struck her. She covered her head and face with her arms, and the unit struck her arms. The unit also struck her leg and foot. She was bleeding from her left leg as a result of the incident, but she did not fall to the ground and did not lose consciousness.
Following the incident, the plaintiff reported pain in her neck and left shoulder. She went to the Emergency Room on the day after the incident.
Description of Injuries
Through subsequent medical examinations, the plaintiff was diagnosed with the following shoulder pathologies:
- Left shoulder acromioclavicular (AC) joint arthrosis
- Left shoulder impingement
- Left shoulder high grade articular surface and intrasubstance partial tearing of the supraspinatus tendon
- Right shoulder AC joint arthrosis
- Right shoulder impingement syndrome
- Right shoulder biceps tendinitis
- Right shoulder rotator cuff (supraspinatus) tear.
Anatomy of the Shoulder
The shoulder is a complex joint system consisting of three distinct joints: the sternoclavicular joint, acromioclavicular joint, and glenohumeral joint (see figure below). The glenohumeral joint is made up of the glenoid fossa and the head of the humerus; it is the “ball-and-socket” joint that is commonly referred to as the shoulder joint.
Investigation & Findings
A biomedical engineer from Robson Forensic was retained to determine if the incident generated the necessary mechanisms to cause the diagnosed shoulder pathologies.
- Arthrosis - also known as osteoarthritis, is the degeneration and loss of the articular cartilage that covers the joint surfaces of each bone. Arthrosis is a chronic condition that is caused by wear and tear over time. The plaintiff’s bilateral acromioclavicular joint arthrosis is a chronic pathology that is not consistent with an acute injury from the subject incident.
- Shoulder impingement - characterized by a narrowed space between the inferior surface of the acromion and the superior aspect of the humeral head. This condition is non-acute in nature and can be caused by several factors, including anatomical anomalies in the acromion, subacromial spurs, and osteoarthritis. The plaintiff’s diagnosed bilateral shoulder impingement is consistent with her diagnosis of AC arthrosis and is not consistent with an acute injury from the subject incident.
- Biceps tendinitis - a chronic condition often associated with other chronic shoulder pathologies such as shoulder impingement and arthrosis. The plaintiff’s right biceps tendinitis is consistent with the presence of her other chronic shoulder pathologies and is not consistent with an acute injury from the subject incident.
- Rotator cuff tear - Traumatic tears of the supraspinatus tendon (one of the four rotator cuff tendons) occur due to compression and shear forces due to impingement of the tendon between the humeral head and acromion. This mechanism is typically caused by a superiorly-directed force through an abducted arm, like a fall. The plaintiff’s raising of her arms in the manner described in her testimony involves flexion, not abduction, and would not generate the compression and shear forces to either left or right supraspinatus tendons necessary to cause her diagnosed tears.
Through the course of their analysis our expert found that the plaintiff’s pathologies were not consistent with the forces generated in the incident. As a result of our expert’s involvement in the matter, our client reached a favorable settlement.
Biomechanical Analyses of Injury Causation
Biomechanical experts at Robson Forensic offer a scientific approach to injury causation analysis. Forensic biomechanical investigations can be applied to various scenarios where the cause of an injury is in dispute, such as motor vehicle crashes, sports and workplace events, and falls.
By combining principles of engineering and physics with an understanding of injury biomechanics, our experts can determine whether an injury is consistent with the physical evidence and descriptions of an event. Our experts can also help elucidate whether an injury resulted from a defective product or device, and whether it could have been prevented.
Dr. Arslanoglu has nearly 30 years of engineering experience in academia and industry. He is an experienced research engineer/scientist with a strong track record of theoretical and computational mechanics, medical product development and research, and management of pre-clinical studies. Prior to joining Robson Forensic, Dr. Arslanoglu was a Senior Research Engineer with Orthofix Spine in their R&D Department. His forensic practice focuses on orthopedic and musculoskeletal biomechanics with respect to injuries related to vehicle crashes, falls, workplace and recreational injuries, and medical device and implant failures.