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Knee injuries under the Illinois Workers' Compensation Act represent significant liability for employers and insurers. This pamphlet provides a concise overview and analysis of common knee injuries to help employers and insurers estimate their exposure under the Act for compensable knee injuries.

The first step in analyzing a knee injury is a basic understanding of the anatomy of the knee. The diagram below illustrates the most frequently injured parts of the knee.

Other Knee Anatomy Links:  Melrose-Wakefield - Anatomy of Knee  Univ. of PA Interactive Knee

The menisci are bodies of cartilage which are attached to the top of the tibia. The articulating surface of the knee is formed by both femoral condyles which sit in the concave surfaces of the menisci. The lateral and medial menisci provide a smooth, lubricated cushion on which the femoral condyles glide when the knee is flexed and extended.

The patella, more commonly known as the kneecap, is a lens-shaped bone which protects the knee joint from frontal impacts. If depicted in the diagram below, the patella would cover the horseshoe shaped opening which exposes the anterior and posterior cruciate ligaments (bony structures of knee).

The cruciate ligaments provide one of the connections between the femur and tibia. The anterior and posterior ligaments hold the femoral condyle against the menisci from the inside of the joint as depicted.

The collateral ligaments (not depicted) attach to the sides of the knee (medially and laterally) and stabilize the knee from each side.

Strain Injuries
The most common type of knee injury involves a strain of the soft tissues in the knee. A strain occurs when muscle and ligamentous tissues are stretched beyond their normal range but no serious tear occurs. Usually, no significant permanency results. Occasionally, arthroscopic surgery will be performed on a petitioner and the final diagnosis will be strain with no internal derangement. Unfortunately, the Industrial Commission is likely to find more permanency under this circumstance simply because of the surgery.

Meniscal Injuries
Meniscal tears are the most frequently litigated type of knee injury. Traumatically induced meniscal tears are almost always associated with twisting injuries. It is important to verify a history of a twisting injury at work. If the petitioner does not describe a twisting motion as part of the accident, it should be considered suspicious.

Degenerative Conditions
Chondromalacia of the patella and meniscal tears are frequently degenerative in nature. After surgery, it is often helpful to obtain a videotape of the arthroscopic surgery which can be viewed by an independent physician. Experienced surgeons can tell by looking at the articular surfaces shown in the videotape whether the cartilage damage was caused traumatically or as a result of degenerative processes. Traumatically damaged cartilage looks shiny like the outside of an orange with a definite area of damage. Degenerative tissue looks frayed like the inside of an orange peel.

Condyle Injuries
Traumatic injuries to the condyle surfaces of the femur are usually associated with a severe blow to either side of the knee. If there is no history of a direct blow to the knee, injuries of this type should be deemed suspicious. Damage to the condyle structures of the joint can also be degenerative in nature. A videotape of the surgery can be powerful ammunition for an examining physician.

Knee Replacements
Knee replacements are almost always associated with degenerative conditions in the knee. A close examination of the petitioner's prior medical history is of utmost importance. It is critical to obtain a credible independent orthopedic opinion on the question of causation to defend such a claim.

Fractures
Fractures of the knee joint are probably the least problematic in terms of causation but can create significant disability if the fracture is located within the articular surface of the joint.

Independent Physicians
Selection of an independent physician is an art in itself. The most important factor to consider is the arbitrator who will be hearing the case. The arbitrator's biases for or against the IME physician and treating physician can be the decisive factor in the outcome of a case.

Permanency Evaluations
Knee injuries are generally valued based on a percentage of the petitioner’s affected leg. In Illinois, 100% of a leg is valued at 200 weeks of disability at the petitioner's permanent partial disability rate (PPD). The following grid summarizes the typical exposure as a percent of a leg based on reported Industrial Commission decisions from 1981 to 1994 for common knee injuries. It is submitted for reference purposes only and is not meant as a definite standard for evaluating exposure in an individual case. The true value of a workers' compensation injury is a function of numerous factors not reflected in the table below including but not limited to: 1) the arbitrator hearing the case, 2) the credibility of the players (Treating Physician, IME Physician and Petitioner), 3) documented preexisting conditions, 4) age and occupation of petitioner, and 5) permanent restrictions.

James M. Voelker Bank One Bldg., Suite 600 124 S.W. Adams St. Peoria, IL 61602 (309) 676-0400 Fax: (309) 676-3374 jvoelker@hrva.com