Biomechanics Lab - Clinical Studies

D. Rod Walters, DA, ATC

How effective is prophylactic bracing of the knee? How much more protection can be gained from the use of functional braces for prophylaxis? When deciding to use braces for prophylaxis, should they be custom-fitted, or conventional "off-the-shelf" types? Of interest to the practitioner are time lost to sport for athletes, cost to the insurance company, and pain and suffering of the patient. In the early 1970s, Nicholas and Castiglia of Lenox Hill Hospital (New York City) developed the Lenox Hill Derotation knee brace for professional football player Joe Namath1. From this the industry has blossomed.

In 1984, the American Academy of Orthopaedic Surgeons (AAOS) categorized knee braces three ways. Prophylactic knee braces are those devices designed to prevent or reduce the severity of knee injuries; rehabilitative braces are devices aimed to limit motion of injured knees or knees following surgical treatment; and functional knee braces are appliances designed to provide stability for unstable knees2.

Adequate protection of the knee requires an understanding of specific biomechanics and corresponding stressed tissue. Initially designed to restrain abnormal knee motions, knee braces have now progressed to provide functional stability3.

Protective and functional knee brace
Prophylactic lateral brace wear has been shown to decrease valgus force application to the knee joint4, which is often a cause of injury to the medial knee structures. At West Point, researchers concluded that knee injuries occurred with significantly reduced frequency in prophylactically braced football players compared to nonbraced players5. Albright et al further reported the effectiveness of prophylactic braces6.

Baker studied valgus force reduction with protective knee guards and functional knee braces7,8. Functional knee braces were expanded into the rehabilitation setting with the aggressive rehabilitation protocols of the 1980s1. Cawley stressed the importance of functional brace use in rehabilitation to restore a patient's confidence in activity.1 With the ACL-deficient patient, Beard reported that brace use resulted in fewer episodes of giving way with a perception of stability in the knee9.

The rationale for this effect is not fully understood9,10. By using leverage systems, functional braces control excessive movement of the tibia. Extension stops and posterior restraints are incorporated in the brace design to prevent hyperextension of the knee11. Brace designs that incorporate bilateral hinges and rigid shells were found to be more effective than unilaterally hinged designs in transmitting loads12
According to the report of the AAOS, functional braces help control unstable knee joints. Functional brace use did minimize "giving way" complaints. Properly fitted braces, used in conjunction with rehabilitation programs, are vital adjuncts in the treatment of knee instability1.

Beynnon reported functional knee braces as providing a protective strain-shielding effect on the anterior cruciate ligament13. Relative to preloading of the knee ligaments, Beynnon could not find increased strain to the anterior cruciate ligaments with functional braces14. Functional knee braces provide restraining influence to control abnormal displacements of the knee8 and decrease anterior tibial translation without associated contraction of the musculature of the lower extremity.

Surrogate studies have also exhibited the efficacy of functional bracing and the effective control of rotational forces producing injury to the intracapsular ligaments. Additionally, Erikson et al studied brace efficacy in reduction of forces along the knee ligaments in cadaver limbs. They found the braces decreased forces at the point of contact but did not significantly decrease stress along the anterior cruciate ligament15.

During the 1997 and 1998 seasons, I studied the incidence and severity of knee injuries among offensive linemen in a National Collegiate Athletic Association Division I institution. The goal was to retrospectively compare prophylactic bracing in two styles of knee braces: prefabricated lateral protective knee braces and custom-fitted functional braces. Due to the risk of injury from valgus loading of the knee in offensive linemen, my institution elected to provide prophylactic bracing to players in this position during contact activity.

Table 1. Player Characteristics
  1997 1998
Number 20 18
Mean age (months) 249 (range 217 to 266) 249 (range 221 to 274)
Mean body mass (pounds) 290 (range 210 to 335) 290 (range 231 to 340)
Average height (inches) 74.9 (range 72 to 77) 74.6 (range 73 to 76)
Game participation 4.95 (range 0 to 11) 74.6 (range 73 to 76)
Years of college participation 2.3 (range 0 to 4) 2.2 (range 0 to 4)
Brace type Single lateral upright prophylactic knee braces (DonJoy) Defiance custom fitted functional knee braces (DonJoy)
Days braces worn
(contact practice sessions)


During the 1997 season, prophylactic brace use by offensive linemen (offensive center, offensive guard, offensive tackle, and offensive tight end) was endorsed by the university coaching and medical team (certified athletic trainers and physicians). Certified athletic trainers instructed the subjects in proper application of the prefabricated prophylactic knee braces (DonJoy PKG-Protective Knee Guard) and compliance was monitored. Subjects used both the manufacturer's neoprene straps and elastic tape to secure braces to the lateral aspect of both lower extremities.

In the 1998 season, it was decided to provide custom-fitted functional knee braces (DonJoy Defiance) to all varsity offensive linemen and those freshmen offensive linemen receiving athletic scholarship aid. As nonscholarship student athletes progressed to their second year of participation in the football program, they were fitted with custom functional knee braces. Lineman positions were selected because anecdotal evidence and observation showed an inordinate number of injuries to offensive linemen due to other players falling across their knees.

Members of the offensive line were fitted bilaterally with custom functional knee braces by a single technician prior to the beginning of preseason conditioning drills. Each player was instructed individually in the proper application of the brace. Braces were worn for all contact practices. During each season, the sports medicine staff, including certified athletic trainers and board-certified orthopedic surgeons, monitored knee injuries. All injuries were recorded in the format of the NCAA's Injury Surveillance. After the season, the knee injuries were extracted and further classified according to the specific pathology involved and the severity of the injury.

In 1997, 20 subjects with a mean age of 249 months (20.75 years), mean body weight of 290 pounds, and average height of 74.9 inches were fitted with prefabricated prophylactic knee braces. Subjects averaged participation in 4.95 games during the study period and had 2.3 years of college football experience. All subjects wore bilateral protective knee braces in contact practice sessions and games (Table 1).

In 1998, 18 players were fitted bilaterally with custom functional knee braces. The average age was 249 months (20.75 years), mean body weight was 290 pounds, and average height was 74.6 inches. The study continued over two consecutive years, and thus many of the subjects were involved in both years' data. The average participation in games during the 1998 study period was 7.4 games with 2.2 years of experience (Table 1).
Table 2. Healthcare Costs
Player Days missed Pathology Severity Weeks
of treatment
Surgical costs Total Costs
1. 10 to 21 days MCL II 3 $2,475   $2,475
2. 22 days ACL III 30 $24,750 $18,000 $42,750
3. 22 days ACL III 30 $24,750 $18,000 $42,750
            Total $87,975
Player Days missed Pathology Severity Weeks
of treatment
Surgical costs Total Costs
1. 1 to 2 days MCL I <1 $815* (5 days) 0 $815
2. 1 to 2 days MCL I <1 $815* (5 days) 0 $815
            Total $1,630


Table 2 contains data regarding the injuries of the 1997 and 1998 seasons. In 1997, the isolated grade II medial collateral ligament sprain was treated aggressively with nonsurgical care. The patient returned to activity in 30 days, missing a total of 21 practice sessions. The grade III ACL tears were treated with arthroscopic surgical reconstruction using patellar tendon autograft. Both athletes were withheld from contact practice and conditioning activities for six months.
In 1998, the two grade I medial collateral ligament sprains were treated aggressively but nonoperatively. Patients were able to return to full activity within two days of the injury.

Economic Considerations
With more and more effort being placed on controlling medical costs, athletic administrators' concern about reimbursement for professional services continues to grow. This situation must be dealt with at all levels of athletic participation, from high school and college to professional sports. With the cases presented from the 1997 and 1998 seasons, we looked at actual costs of the injuries and the impact of prophylactic bracing as a prevention tool.

Review of Table 2 reveals the economic impact of knee injury and subsequent care to offensive linemen. The actual costs of the 1997 season include two surgical reconstructions of anterior cruciate ligaments totaling $45,795. The cost of care for knee injuries in 1998 fell to $1,630, due primarily to the lack of surgical cases. The cost to provide custom fitted prophylactic knee braces to offensive linemen for this project totaled $16,200 (30 braces at $540 each). Though a significant expenditure (the prefabricated braces had cost $75 each), the staff felt the investment was very prudent-especially in terms of injury prevention, quality of life for student athletes, and further prevention of time lost from activity.

This review of the literature provides evidence of the protective aspects of prophylactic knee braces to capsular structures of the knee. Likewise, functional knee braces are found to effectively control forces of the tibia, which can produce stresses and possibly injure the capsular and/or anterior cruciate ligaments. Regarding the choice of braces, clinicians have felt that custom braces are associated with improved fit and result in less brace migration. Regardless, the chosen brace should be one that can withstand the forces of the activity, especially those selected for contact activity. At this time, I feel it is prudent to recommend bracing for prophylaxis, and this is being done at many institutions with growing popularity.

A comprehensive study of all divisions of football regarding the prophylactic nature of knee bracing needs to be undertaken. The study should track injuries relative to all brace types for prophylaxis-including the lateral protective knee guards and functional knee braces. Many institutions embrace prophylactic concepts, and further information is needed to determine the cost-to-benefit ratio for brace use. If protective knee braces are selected, the different benefits afforded by custom-fitted versus the "off-the-shelf" brace styles need to be assessed.

D. Rod Walters, DA, ATC, is assistant athletic director for sports medicine at the University of South Carolina in Columbia.

Published in Biomechanics, 712: 57-61.

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