Common Shoulder Injuries in American Football Athletes.

American football is a collision sport played by athletes at high speeds. Despite the padding and conditioning in these athletes, the shoulder is a vulnerable joint, and injuries to the shoulder girdle are common at all levels of competitive football. Some of the most common injuries in these athletes include anterior and posterior glenohumeral instability, acromioclavicular pathology (including separation, osteolysis, and osteoarthritis), rotator cuff pathology (including contusions, partial thickness, and full thickness tears), and pectoralis major and minor tears. In this article, we will review the epidemiology and clinical and radiographic workup of these injuries. We also will evaluate the effectiveness of surgical and nonsurgical management specifically related to high school, collegiate, and professional football athletes.

Supramolecular design of self-assembling nanofibers for cartilage regeneration.

Molecular and supramolecular design of bioactive biomaterials could have a significant impact on regenerative medicine. Ideal regenerative therapies should be minimally invasive, and thus the notion of self-assembling biomaterials programmed to transform from injectable liquids to solid bioactive structures in tissue is highly attractive for clinical translation. We report here on a coassembly system of peptide amphiphile (PA) molecules designed to form nanofibers for cartilage regeneration by displaying a high density of binding epitopes to transforming growth factor beta-1 (TGFbeta-1). Growth factor release studies showed that passive release of TGFbeta-1 was slower from PA gels containing the growth factor binding sites. In vitro experiments indicate these materials support the survival and promote the chondrogenic differentiation of human mesenchymal stem cells. We also show that these materials can promote regeneration of articular cartilage in a full thickness chondral defect treated with microfracture in a rabbit model with or even without the addition of exogenous growth factor. These results demonstrate the potential of a completely synthetic bioactive biomaterial as a therapy to promote cartilage regeneration.

The anterior deltoid's importance in reverse shoulder arthroplasty: a cadaveric biomechanical study.

BACKGROUND: Frequently, patients who are candidates for reverse shoulder arthroplasty have had prior surgery that may compromise the anterior deltoid muscle. There have been conflicting reports on the necessity of the anterior deltoid thus it is unclear whether a dysfunctional anterior deltoid muscle is a contraindication to reverse shoulder arthroplasty. The purpose of this study was to determine the 3-dimensional (3D) moment arms for all 6 deltoid segments, and determine the biomechanical significance of the anterior deltoid before and after reverse shoulder arthroplasty. METHODS: Eight cadaveric shoulders were evaluated with a 6-axis force/torque sensor to assess the direction of rotation and 3D moment arms for all 6 segments of the deltoid both before and after placement of a reverse shoulder prosthesis. The 2 segments of anterior deltoid were unloaded sequentially to determine their functional role. RESULTS: The 3D moment arms of the deltoid were significantly altered by placement of the reverse shoulder prosthesis. The anterior and middle deltoid abduction moment arms significantly increased after placement of the reverse prosthesis (P < .05). Furthermore, the loss of the anterior deltoid resulted in a significant decrease in both abduction and flexion moments (P < .05). CONCLUSION: The anterior deltoid is important biomechanically for balanced function after a reverse total shoulder arthroplasty. Losing 1 segment of the anterior deltoid may still allow abduction; however, losing both segments of the anterior deltoid may disrupt balanced abduction. Surgeons should be cautious about performing reverse shoulder arthroplasty in patients who do not have a functioning anterior deltoid muscle.

Biologic and pharmacologic augmentation of rotator cuff repairs.

As rotator cuff repair techniques have improved, failure of the tendon to heal to the proximal humerus is less likely to occur from weak tendon-to-bone fixation. More likely causes of failure include biologic factors such as intrinsic tendon degeneration, fatty atrophy, fatty infiltration of muscle, and lack of vascularity of the tendons. High failure rates have led to the investigation of biologic augmentation to potentially enhance the healing response. Histologic studies have shown that restoration of the rotator cuff footprint during repair can help reestablish the enthesis. In animal models, growth factors and their delivery scaffolds as well as tissue engineering have shown promise in decreasing scar tissue while maintaining biomechanical strength. Platelet-rich plasma may be a safe adjuvant to rotator cuff repair, but it has not been shown to improve healing or function. Many of these strategies need to be further defined to permit understanding of, and to optimize, the biologic environment; in addition, techniques need to be refined for clinical use.

Efficacy of preoperative home use of 2% chlorhexidine gluconate cloth before shoulder surgery.

HYPOTHESIS: Deep infection after shoulder surgery is a rare but devastating problem. This study tested the hypothesis that the home application of a 2% chlorhexidine gluconate cloth before shoulder surgery would be more efficacious than a standard shower of soap and water at decreasing the preoperative cutaneous levels of pathogenic bacteria on the shoulder. MATERIALS AND METHODS: This randomized, prospective study evaluated 100 consecutive patients undergoing shoulder surgery. Patients were randomly assigned to use 2% chlorhexidine gluconate-impregnated cloths (treatment group) or to shower with soap and water before surgery (control group). Cutaneous cultures were taken from the patients'shoulders in the preoperative holding area. Patients were monitored for 2 months postoperatively for clinical signs of infection. RESULTS: In the treatment group vs the control group, the overall positive culture rate was 66% vs 94% (P = .0008), and the positive culture rate for coagulase-negative Staphylococcus was 30% vs 70% (P = .0001). The positive culture rate for Propionibacterium acnes was 46% in the treatment group vs 58% in the control group (P = .32). No infections occurred in any patients at a minimum of 2-months after surgery. DISCUSSION: The use of the 2% chlorhexidine cloth was effective at decreasing overall bacterial culture rates before shoulder surgery and was particularly effective at decreasing the quantity of coagulase-negative Staphylococcus, a known causative agent of postoperative shoulder infections. CONCLUSION: Use of chlorhexidine impregnated cloths prior to shoulder surgery may be a useful adjunct to presently used infection prevention strategies.

Elbow Dislocations in the National Football League: Epidemiology and Management.

Background Currently, it is not known how the combined osseous and ligamentous injury of a traumatic elbow dislocation in a National Football League (NFL) athlete affects management and return to play. In this study, we aimed to describe the epidemiology, management, and return to play for elbow dislocations in NFL athletes. Methodology This is a descriptive observational study. A retrospective review of all elbow dislocations between 2000 and 2014 (15 seasons) was performed using the NFL Injury Surveillance System (NFLISS). Results Over 15 NFL seasons, 82 elbow dislocations were recorded in the NFLISS. Among players who reported surgery (n = 5), players missed an average of 73.8 days of play. Among those who did not report surgery, players missed an average of 36.1 days. The overall incidence was 0.26 dislocation events per 10,000 athlete exposures. The majority of these injuries occurred during regular-season games, in defensive linebackers and linemen, during tackling contact with another player, and most commonly on a running play. Conclusions This study demonstrates that an elbow dislocation is not a career-ending or season-ending injury in an NFL cohort. Information regarding incidence, positions affected, whether surgical management is utilized, and return to play will help players who sustain and physicians who treat these injuries in elite football athletes understand the impact of their injuries.

Pectoralis Major Injuries in the National Football League.

BACKGROUND: Pectoralis major (PM) injuries are rare, primarily occurring in males during athletic activity. In the current literature, these injuries have not been well described in National Football League (NFL) athletes. HYPOTHESIS: The incidence of PM injuries will be low in NFL athletes, with athletes missing significantly more time after injuries requiring operative management. STUDY DESIGN: Cohort study. LEVEL OF EVIDENCE: Level 4. METHODS: All documented PM injuries were retrospectively analyzed using the NFL Injury Surveillance System over a 15-season period. The data were analyzed by season, session, position, activity, and contact type at the time of injury. Additionally, the incidence, treatment, and days missed as a result of injury were assessed. RESULTS: Over 15 consecutive seasons, there were a total of 211 PM injuries. Of these injuries, 132 were classified as strains and 79 as ruptures. The incidence of strains was 0.41 per 10,000 athlete-exposures, compared with 0.25 per 10,0000 athlete-exposures for ruptures (P < 0.01). Players with PM ruptures treated operatively missed significantly more days than players treated nonoperatively (146.7 ± 55.0 vs 77.2 ± 72.9; P < 0.01). CONCLUSION: NFL athletes miss significantly more time after operative compared with nonoperative management of PM ruptures. CLINICAL RELEVANCE: PM injuries are rare, with the current literature lacking description of these injuries in NFL athletes. The paucity of data limits physicians from providing adequate counseling and expectations for athletes with this injury. This research represents the largest study assessing PM injuries in NFL athletes.

Biomechanical analysis of bursal-sided partial thickness rotator cuff tears.

BACKGROUND: Treatment of partial thickness supraspinatus tendon tears is controversial with no clearly defined treatment algorithms based on severity of tears. This study aims to evaluate the relationship between depth of partial thickness tears and strain. METHODS: Bursal-sided partial thickness tears were created at 1 mm increments in depth at the anterior portion of the supraspinatus tendon to 3/4 tendon width on ten fresh-frozen shoulder specimens. The supraspinatus muscle was dynamically loaded from 0-50N, and strain recorded at both the anterior and posterior portions of the tendon. RESULTS: Strain in the intact posterior portion increased monotonically with tear depth and supraspinatus force. Strain in the torn anterior portion decreased with increasing tear thickness and loading force. At 60% thickness tear, strain was significantly higher (P = 0.023) in the intact posterior portion compared to intact tendon. As the tear thickness exceeded 50% tendon thickness, the strain in the intact tendon rapidly increased nonlinearly. CONCLUSIONS: Biomechanical results herein suggest increasing potential for tear propagation in the transverse plane with increasing depth of tears, and biomechanically supports repairs of grade III (>50% thickness).

The negative impact of anterior cruciate ligament reconstruction in professional male footballers.

BACKGROUND: Soccer is one of the most common international sports in which ACL injuries occur, with previous studies reporting high return-to-play rates following ACL reconstruction (ACLR). Return-to-play analysis fails to take into consideration how effective a player remains once returning to competition. The aims of this study are to provide a large-scale international analysis of return-to-play and player performance statistics among professional soccer athletes following ACLR. METHODS: Using publicly available sources, professional soccer athletes who have undergone ACLR between the 1996 and 2015 seasons were identified. Player metrics including statistical performance, recovery time, and return-to-play rates were analyzed both before and after reconstruction. Furthermore, player performance statistics during each of three consecutive seasons post-ACLR were compared. RESULTS: A total of 176 athletes who underwent ACLR were included in this study. The return-to-play rate was 93.2% (164 athletes). Cumulative post-surgical statistical analysis of ACLR players demonstrated fewer games/season, minutes/season, minutes/game, goals/season, and more fouls/season following ACLR (p < 0.04). Analysis of player performance statistics suggests that athletes do not return to their baseline number of games/season and minutes/game until two and three seasons post-ACLR, respectively. At three seasons post-ACLR, athletes are still starting fewer games/season and scoring fewer goals/90 min (p < 0.04). CONCLUSION: Return-to-play rate is high following ACLR; however, athletes exhibit poorer statistical performance, especially in the first few seasons upon return. Our data shows that athletes continue to start fewer games/season and score fewer goals/90 min at three seasons post-ACLR.

Muscle contribution to elbow joint valgus stability.

Repetitive valgus stress of the elbow can result in excessive strain or rupture of the native medial ulnar collateral ligament (MUCL). The flexor-pronator mass (FPM) may be particularly important for elbow valgus stability in overhead-throwing athletes. The aim of this study was to identify the relative contribution of each muscle of the FPM--that is, the flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), flexor carpi radialis (FCR), and pronator teres (PT)--and of the extensor-supinator mass, including the extensor carpi ulnaris (ECU), extensor digitorum communis (EDC), extensor carpi radialis longus and brevus, and brachioradialis, to elbow valgus stability at 45 degrees and 90 degrees of elbow flexion angles. Eight fresh-frozen elbow specimens (mean age at death, 73.75 +/- 14.07 years) were tested. With the skin and subcutaneous tissue removed but all muscles left intact, each individual muscle of the FPM and extensor-supinator mass was loaded at 3 levels of force. During loading, strain on the MUCL and the kinematics of the elbow were measured simultaneously. Kinematic measurements were later repeated when the MUCL was fully cut. At 45 degrees and 90 degrees of elbow flexion, individual loading of the FCU, FDS, and FCR caused significant relief to the MUCL whereas the PT produced no significant change. Furthermore, of these flexor muscles, the FCU provided the greatest MUCL relief at both 45 degrees and 90 degrees . In contrast, loading of the ECU at 45 degrees of elbow flexion produced a significant increase in MUCL strain. All FPM muscles caused significant elbow varus movement at both 45 degrees and 90 degrees when loaded individually. At 90 degrees , the FCU created more motion than both the FCR and PT but not the FDS, and the FDS created more motion than the PT. The EDC and ECU created significant valgus movement at 45 degrees and 90 degrees , which became insignificant when the MUCL was transected. Our study suggested that the FCU, FDS, and FCR may function as dynamic stabilizers, with the FCU being the primary stabilizer for elbow valgus stability, incorporating with the MUCL for all tested joint configurations. Our findings also suggest that the ECU and EDC increased MUCL strain and elbow valgus movement at both 45 degrees and 90 degrees .

Superior Labrum Anterior-Posterior Tears in the National Football League.

BACKGROUND: Shoulder disorders are common in football players, with up to 50% of National Football League (NFL) recruits reporting a history of shoulder injuries. Superior labrum anterior-posterior (SLAP) tears are an entity with well-described detrimental effects on return to play in overhead-throwing athletes but with minimal data in contact athletes. PURPOSE: To identify the incidence, predisposing factors, and effect of SLAP tears in NFL athletes and prospects as well as the treatment patterns of NFL team physicians. STUDY DESIGN: Descriptive epidemiology study. METHODS: This study was a comprehensive analysis of SLAP tears in elite football players using a dual approach: (1) SLAP injuries recorded in the NFL Injury Surveillance System from 2000 to 2014 were evaluated by player position, type of play, days/games lost, and surgical intervention; (2) NFL Scouting Combine athletes from 2003 to 2011 with prior SLAP repair were evaluated for draft success, and drafted athletes were compared with matched controls for career length and performance scores. RESULTS: SLAP tears represented a small portion (3.1%) of shoulder injuries in NFL athletes from 2000 to 2014, occurring most commonly in offensive linemen (28%). Surgically treated SLAP tears (42%) resulted in more days missed than did nonoperatively managed tears (140.2 vs 21.5 days; P < .001) and more games missed (8.4 vs 2.6 games; P = .003). SLAP repairs were also rare in NFL Combine athletes (n = 25 of 2965 athletes), with most having been performed in offensive linemen (32%). As compared with control NFL Combine athletes without SLAP tears, those drafted into the NFL with prior SLAP repair played significantly fewer games (33.7 vs 48.3; P = .049) and had fewer game starts (19.6 vs 35.4; P = .036). CONCLUSION: In this comprehensive analysis of SLAP tears in elite football players, it is clear that these injuries have the potential to cause significant detriment to an athlete's career.

Different roles of the medial and lateral hamstrings in unloading the anterior cruciate ligament.

INTRODUCTION: Anterior cruciate ligament injuries are closely associated with excessive loading and motion about the off axes of the knee, i.e. tibial rotation and knee varus/valgus. However, it is not clear about the 3-D mechanical actions of the lateral and medial hamstring muscles and their differences in loading the ACL. The purpose of this study was to investigate the change in anterior cruciate ligament strain induced by loading the lateral and medial hamstrings individually. METHODS: Seven cadaveric knees were investigated using a custom testing apparatus allowing for six degree-of-freedom tibiofemoral motion induced by individual muscle loading. With major muscles crossing the knee loaded moderately, the medial and lateral hamstrings were loaded independently to 200N along their lines of actions at 0°, 30°, 60° and 90° of knee flexion. The induced strain of the anterior cruciate ligament was measured using a differential variable reluctance transducer. Tibiofemoral kinematics was monitored using a six degrees-of-freedom knee goniometer. RESULTS: Loading the lateral hamstrings induced significantly more anterior cruciate ligament strain reduction (mean 0.764 [SD 0.63] %) than loading the medial hamstrings (mean 0.007 [0.2] %), (P=0.001 and effect size=0.837) across the knee flexion angles. CONCLUSION: The lateral and medial hamstrings have significantly different effects on anterior cruciate ligament loadings. More effective rehabilitation and training strategies may be developed to strengthen the lateral and medial hamstrings selectively and differentially to reduce anterior cruciate ligament injury and improve post-injury rehabilitation. CLINICAL RELEVANCE: The lateral and medial hamstrings can potentially be strengthened selectively and differentially as a more focused rehabilitation approach to reduce ACL injury and improve post-injury rehabilitation. Different ACL reconstruction procedures with some of them involving the medial hamstrings can be compared to each other for their effect on ACL loading.

The NFL Orthopaedic Surgery Outcomes Database (NO-SOD): The Effect of Common Orthopaedic Procedures on Football Careers.

BACKGROUND: Injuries are inherent to the sport of American football and often require operative management. Outcomes have been reported for certain surgical procedures in professional athletes in the National Football League (NFL), but there is little information comparing the career effect of these procedures. PURPOSE: To catalog the postoperative outcomes of orthopaedic procedures in NFL athletes and to compare respective prognoses and effects on careers. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Athletes in the NFL undergoing procedures for anterior cruciate ligament (ACL) tears, Achilles tendon tears, patellar tendon tears, cervical disc herniation, lumbar disc herniation, sports hernia, knee articular cartilage repair (microfracture technique), forearm fractures, tibial shaft fractures, and ankle fractures were identified through team injury reports or other public records. Game and performance statistics during the regular season were collected before and after surgery. Statistical analysis was performed with significance accepted as P < .05. RESULTS: A total of 559 NFL athletes were included. Overall, 79.4% of NFL athletes returned to play after an orthopaedic procedure. Forearm open reduction and internal fixation (ORIF), sports hernia repair, and tibia intramedullary nailing (IMN) led to significantly higher return-to-play (RTP) rates (90.2%-96.3%), while patellar tendon repair led to a significantly lower rate (50%) (P < .001). Athletes undergoing ACL reconstruction (ACLR), Achilles tendon repair, patellar tendon repair, and ankle fracture ORIF had significant declines in games played at 1 year and recovered to baseline at 2 to 3 years after surgery. Athletes undergoing ACLR, Achilles tendon repair, patellar tendon repair, and tibia IMN had decreased performance in postoperative season 1. Athletes in the Achilles tendon repair and tibia IMN cohorts recovered to baseline performance, while those in the ACLR and patellar tendon repair cohorts demonstrated sustained decreases in performance. CONCLUSION: ACLR, Achilles tendon repair, and patellar tendon repair have the greatest effect on NFL careers, with patellar tendon repair faring worst with respect to the RTP rate, career length after surgery, games played, and performance at 1 year and 2 to 3 years after surgery.

Preexisting Rotator Cuff Tears as a Predictor of Outcomes in National Football League Athletes.

BACKGROUND: A preexisting rotator cuff tear may affect the draft status and career performance of National Football League (NFL) players. HYPOTHESIS: Preexisting rotator cuff tears decrease a player's draft status, performance, and longevity in the NFL. STUDY DESIGN: Retrospective cohort study. LEVEL OF EVIDENCE: Level 3. METHODS: Medical reports of prospective NFL players during the NFL Scouting Combine from 2003 to 2011 were evaluated to identify players with a previous rotator cuff tear. Athletes were matched to control draftees without documented shoulder pathology by age, position, year drafted, and round drafted. Career statistics and performance scores were calculated. RESULTS: Between 2003 and 2011, 2965 consecutive athletes were evaluated. Forty-nine athletes had preexisting rotator cuff tears: 22 athletes underwent surgical intervention for their tear and 27 were treated nonoperatively. Those with a rotator cuff tear were significantly less likely to be drafted than those without a previous injury (55.1% vs 77.5%, P = 0.002). The 27 drafted athletes with preexisting rotator cuff tears started significantly fewer games (23.7 vs 43.0, P = 0.02) and played significantly fewer years (4.3 vs 5.7, P = 0.04) and significantly fewer games (47.1 vs 68.4, P = 0.04) than matched control athletes without rotator cuff tears. CONCLUSION: Athletes with a preexisting rotator cuff tear were less likely to be drafted and had decreased career longevity.

Does the Level of Cervical Disc Herniation Surgery Affect Performance-based Outcomes in National Football League Athletes?

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: The aim of this study was to determine whether the level of a cervical disc herniation (CDH) procedure will uniquely impact performance-based outcomes in elite athletes of the National Football League (NFL). SUMMARY OF BACKGROUND DATA: Comparative assessments of postsurgical outcomes in NFL athletes with CDH at different levels are unknown. Further, the surgical decision-making for these types of injuries in professional football athletes remains controversial. METHODS: NFL players with a CDH injury at a definitive cervical level were identified through a review of publicly available archives. Injuries were divided into upper- (C2-C4) and lower-level (C4-T1) CDH. The impact on player outcomes was determined by comparing return to play statistics and calculating a "Performance Score" for each player on the basis of pertinent statistical data, both before and after surgery. RESULTS: A total of 40 NFL athletes met inclusion criteria. In the upper-level group, 10 of 15 (66.6%) players successfully returned to play an average of 44.6 games over 2.6 years. The lower-level cohort had 18 of 25 (72%) players return to play with an average of 44.1 games over 3.1 years. There was no significant difference in the rate of return to play (P = 0.71). Postsurgical performance scores of the upper and lower-level groups were 1.47 vs. 0.69 respectively, with no significant difference between these groups (P = 0.06). Adjacent segment disease requiring reoperation occurred in 10% of anterior cervical discectomy and fusion patients. In 50% of foraminotomy patients, a subsequent fusion was required. CONCLUSION: A uniquely high percentage of upper-level disc herniations develop in NFL athletes, and although CDH injuries present career threatening implications, an upper-level CDH does not preclude a player from successfully returning to play at a competitive level. In fact, these athletes showed comparable postsurgical performance to those athletes who underwent CDH procedures at lower cervical levels. LEVEL OF EVIDENCE: 4.

Pre-existing lumbar spine diagnosis as a predictor of outcomes in National Football League athletes.

BACKGROUND: It is currently unknown how pre-existing lumbar spine conditions may affect the medical evaluation, draft status, and subsequent career performance of National Football League (NFL) players. PURPOSE: To determine if a pre-existing lumbar diagnosis affects a player's draft status or his performance and longevity in the NFL. STUDY DESIGN: Cohort study; Level 3. METHODS: The investigators evaluated the written medical evaluations and imaging reports of prospective NFL players from a single franchise during the NFL Scouting Combine from 2003 to 2011. Players with a reported lumbar spine diagnosis and with appropriate imaging were included in this study. Athletes were then matched to control draftees without a lumbar spine diagnosis by age, position, year, and round drafted. Career statistics and performance scores were calculated. RESULTS: Of a total of 2965 athletes evaluated, 414 were identified as having a pre-existing lumbar spine diagnosis. Players without a lumbar spine diagnosis were more likely to be drafted than were those with a diagnosis (80.2% vs. 61.1%, respectively, P < .001). Drafted athletes with pre-existing lumbar spine injuries had a decrease in the number of years played compared with the matched control group (4.0 vs. 4.3 years, respectively, P = .001), games played (46.5 vs. 50.8, respectively, P = .0001), and games started (28.1 vs. 30.6, respectively, P = .02) but not performance score (1.4 vs. 1.8, respectively, P = .13). Compared with controls, players were less likely to be drafted if they had been diagnosed with spondylosis (62.37% vs. 78.55%), a lumbar herniated disc (60.27% vs. 78.43%), or spondylolysis with or without spondylolisthesis (64.44% vs. 78.15%) (P < .001 for all), but there was no appreciable effect on career performance; however, the diagnosis of spondylolysis was associated with a decrease in career longevity (P < .05). Notably, 2 athletes who had undergone posterior lateral lumbar fusion were drafted. One played in 125 games, and the other is still active and has played in 108 games. CONCLUSION: The data in this study suggest that athletes with pre-existing lumbar spine conditions were less likely to be drafted and that the diagnosis is associated with a decrease in career longevity but not performance. Players with lumbar fusion have achieved successful careers in the NFL.

In vivo load sharing among the quadriceps components.

Knee extension is always performed with coordinated contractions of multiple quadriceps muscle components; however, how the load is shared among them under normal and pathological conditions is unclear. We hypothesized that: the absolute moment generated by each quadriceps component increases with the total knee extension moment; the relative contribution and its dependence on the total knee extension moment are different for different quadriceps components; and the centrally located large vastus intermedius (VI) is favored by the central nervous system at low levels of activation. Electrical stimulation was used to activate each quadriceps component selectively in six human subjects. The relationship between the knee extension moment generated by an individual quadriceps component and the corresponding compound muscular action potential (M-wave) over various contraction levels was established for each quadriceps component. This relationship was used to calibrate the corresponding EMG signal and determine load sharing among quadriceps components during submaximal isometric voluntary knee extension. The VI contributed the most (51.8-39.6%) and vastus medialis the least (9.5-12.2%) to knee extension moment (P<0.05). As the knee extension moment increased, the relative contribution of the VI decreased (P=0.017) while the relation contribution of the vastus lateralis and medialis increased (P

In vivo and noninvasive load sharing among the vasti in patellar malalignment.

PURPOSE: It is not clear how the knee extension torque is distributed quantitatively among the lateral and medial vasti in patellofemoral pain (PFP) patients with patellar malalignment, which was investigated in vivo and noninvasively in ten PFP patients and eleven controls. We hypothesized that the vastus medialis oblique (VMO) and vastus medialis longus (VML) of PFP patients contribute less to knee extension than that in controls. METHODS: Electrical stimulation was used to activate each vastus component selectively. The relationship between the knee extension torque generated by each individual vastus component and the corresponding compound muscle action potential (M-wave) was established over different contraction levels, which was used to calibrate the corresponding voluntary EMG signal and determine torque ratios of VMO/VL (vastus lateralis), VMO/VML, VML/VL and (VMO+VML)NL during voluntary isometric knee extension. RESULTS: The VMO and VML of PFP patients contributed significantly less to knee extension than their counterparts in controls. The combination of VMO and VML generated comparable amount of extension torque as the VL in the controls, while it produced significantly lower extension torque than that of the VL in the PFP patients. In addition, the VMO/VL was lower than VMO/VML and VML/VL in both PFP and control groups. CONCLUSIONS: Compared to controls, the VMO and VML in the PFP patients contributed significantly less to the knee extension torque. The approach can be used to investigate load sharing among quadriceps muscles in vivo and noninvasively, in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.

Multiaxis muscle strength in ACL deficient and reconstructed knees: compensatory mechanism.

PURPOSE: It is unclear how muscle strength in tibial rotation and knee abduction change following anterior cruciate ligament (ACL) injury and reconstruction. Such strength changes are likely, considering the oblique orientation of the ACL and the constraint provided by the ACL at various tibial rotation and adduction positions. The purposes of this study were to evaluate multiaxis muscle strength in ACL deficient and reconstructed knees and to gain insights into potential compensatory mechanisms adopted by the patients. METHODS: Muscle strength in tibial internal-external rotation, abduction-adduction, and flexion-extension were investigated in 19 chronic ACL deficient, 18 acute ACL deficient, 21 ACL reconstructed, and 23 normal subjects. The strength ratios of flexion/extension, abduction/adduction, and internal/external rotation were determined for each subject and compared across the different populations. RESULTS: The chronic ACL deficient patients showed significantly lower strength ratio in internal/external rotation than that of the normal controls and acute ACL deficient subjects (P = 0.02), indicating a compensatory mechanism developed by the patients to unload the ACL and/or to avoid unstable knee positions. For ACL reconstructed patients, the internal/external rotation strength ratio became closer to their counterparts in normal controls than that of chronic ACL deficient patients, presumably reflecting the reduced need for compensation after reconstruction. Furthermore, compared with strength reduction in knee extension, reductions in tibial rotation and abduction strength following ACL reconstruction were less severe and more easy to recover. CONCLUSION: A better understanding of changes in multiaxis muscle strength and the associated compensatory mechanism will help us evaluate treatment outcome more accurately and develop more effective treatment modalities with focus on muscles that help protect and unload the ACL.