The purpose of this study was to observe the effects of knee saver use in male collegiate baseball catchers on lower extremity kinematics during a deep crouch. The results demonstrate that knee saver use did not significantly decrease knee flexion during a deep crouch, failing to reject the null hypothesis. Under certain circumstances, notably those volunteers with greater knee flexion before knee saver use, knee flexion angles were increased with the knee saver product. Although knee savers reduced deep flexion in a subset of catchers, the difference is likely not clinically significant.
Prolonged squatting has been demonstrated to be a risk factor for meniscal injury and possibly osteoarthritis (5,6). The posterior horns of the menisci become impinged between the femur and tibia during deep flexion, potentially leading to injury over repetitive insult (7,8). According to Williams and Logan (8), flexion beyond 120° causes the medial femoral condyle to rise and move onto the posterior horn of the medial meniscus. Because of a lack of mobility of the posteriorhorn, the meniscus appears to be vulnerable to damage (9-12). All of our volunteers flexed well past 120 degrees and the knee saver device was unable to reduce flexion beyond this threshold. If deep squatting carries an inherent risk for meniscal injury, knee savers will not significantly decrease that risk unless they decrease the load on the knee joint through other mechanisms and that decreased load has an effect on meniscal impingement.
At one time the claim was made that knee savers can reduce the damage done to cartilage caused by prolonged and frequent crouching (4). A predisposition to osteoarthritis from deep squatting has been documented (5,13). Recent work by Hartmann et al. (6), however, demonstrated that deep squatting places less load on the knee joint than does quarter squatting or half squatting, with squatting at 90 degrees incurring the highest retropatellar compressive forces. These effects are due to the “wrapping effect,” functional adaptation, and soft tissue contact between the posterior thighs and calves. The wrapping effect occurs when flexion exceeds 90 degrees and is defined as a support comprising contact between the intercondylar notch and quadriceps tendon that results in decreased knee joint forces (14). Furthermore, contact between the soft tissues of the calves and posterior thighs acts to decrease knee joint forces beyond 130 degrees of knee flexion (15). In this regard, a knee saver device may assist in further reducing knee joint forces by increasing the contact area between the posterior thigh and calves, ensuring maximal unloading of the knee joint; this could explain why some of our volunteers experienced deeper squatting with the knee saver.
Contrary to popular belief that deep squatting is to blame for acute knee pain and long-term injury in baseball catchers, current literature suggests that deep squatting is protective of knee joint articular cartilage compared with quarter squatting and half squatting. We speculate that knee discomfort experienced by catchers is not a function of time spent squatting, but rather the abundant transitions through high knee joint load states when moving from standing to deep squat, and vice-versa, that a catcher experiences throughout a game and practice. If true, knee saver devices do nothing to affect the maximal knee joint forces incurred by catchers. Research is warranted to determine whether multiple complete motions through a squatting maneuver or prolonged squatting without vertical motion causes more knee joint discomfort. This study also showed an increased variability in the correlation of knee and hip flexion angles with the use of knee savers (Figure 4).
This result potentially indicates a disruption in the natural biomechanics of deep squatting, the implications of which are unclear. It has been shown, however, that squatting increases lumbar spine compressive forces beyond those of the true weight load (16). The increased variability in hip flexion angle may act to decrease or increase lumbar compression because the spine must adapt to keep the catcher in an effective position. Further speculation on the subject is beyond the scope of this manuscript.
Limitations in this study may serve as a roadmap for future efforts in assessing knee joint discomfort and injury in baseball catchers. Quadriceps and hamstring activation both affect knee joint forces and studying them with electromyography during a deep squat with and without knee saver devices is warranted. Further, quantitative load forces between the posterior thigh and calf, as well as between the buttock and knee saver, would greatly assist in defining the true efficacy of the product.
Each addition of comfort or safety equipment to a catcher’s uniform comes with a penalty to agility or speed. The decision to use a knee saver device appears to be a tradeoff between blunted mobility and the promise of decreased “stress” and discomfort on the knee joints. Based on our study, the knee saver devices do not decrease knee flexion enough to prevent potential meniscal injury, which would require reduction to below 120°. Further, although we did not take force measurements with the knee saver device, natural biomechanics are already at work to decrease knee joint forces during deep squats through the wrapping effect, functional adaptation, and soft tissue contact and loading through the posterior thigh and calf. It appears from our results that the risk that knee savers would in themselves harm an athlete physically is minimal. However, the purported benefits have yet to find scientific validation and may only represent the placebo effect.
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