Ian J. Kremenic

Reconstruction of the Coracoclavicular Ligaments with Tendon Grafts A Comparative Biomechanical Study

Background Numerous surgical techniques have been described to address injuries to the coracoclavicular ligaments. Purpose To compare the biomechanical properties of tendon graft reconstructions with those of the native coracoclavicular ligaments and various other repair methods. Study Design Controlled laboratory study. Methods Eleven fresh-frozen human cadaveric shoulders were tensile tested to failure to compare the biomechanical properties of the native coracoclavicular ligaments, coracoacromial ligament transfer, No. 5 Mersilene suture repair, 5-mm Mersilene tape repair, and tendon graft reconstructions with gracilis, semitendinosus, and long toe extensor tendons. Results Reconstructions with semitendinosus, gracilis, or long toe extensor tendon grafts were found to have superior initial biomechanical properties compared with coracoacromial ligament transfer; failure strengths were as strong as those of the native coracoclavicular ligaments. Failure of the tendon grafts occurred through the midsubstance of the tendon graft, not at the fixation site. Conclusions Tendon graft reconstruction may be an alternative to coracoacromial ligament transfer and may provide a permanent biologic reconstruction with superior initial biomechanical properties, including that of tensile strength. Clinical Relevance Use of tendon graft reconstruction may limit the need for postoperative immobilization and lead to an accelerated rehabilitation program.

The Role of Passive Muscle Stiffness in Symptoms of Exercise-Induced Muscle Damage

We examined whether passive stiffness of an eccentrically exercising muscle group affects the subsequent symptoms of muscle damage. Passive hamstring muscle stiffness was measured during an instrumented straight-leg-raise stretch in 20 subjects (11 men and 9 women) who were subsequently classified as “stiff” (N 7), “normal” (N 6), or “compliant” (N 7). Passive stiffness was 78% higher in the stiff subjects (36.2 3.3 N m rad 1) compared with the compliant subjects (20.3 1.8 N m rad 1). Subjects then performed six sets of 10 isokinetic (2.6 rad s 1) submaximal (60% maximal voluntary contraction) eccentric actions of the hamstring muscle group. Symptoms of muscle damage were documented by changes in isometric hamstring muscle strength, pain, muscle tenderness, and creatine kinase activity on the following 3 days. Strength loss, pain, muscle tenderness, and creatine kinase activity were significantly greater in the stiff compared with the compliant subjects on the days after eccentric exercise. Greater symptoms of muscle damage in subjects with stiffer hamstring muscles are consistent with the sarcomere strain theory of muscle damage. The present study provides experimental evidence of an association between flexibility and muscle injury. Muscle stiffness and its clinical correlate, static flexibility, are risk factors for more severe symptoms of muscle damage after eccentric exercise.

The role of mechanical and neural restraints to joint range of motion during passive stretch

UNLABELLED Musculoskeletal flexibility is typically characterized by maximum range of motion (ROM) in a joint or series of joints. Resistance to passive stretch in the mid-range of motion is a function of the passive mechanical restraints to motion. However, an active contractile response may contribute resistance at terminal ROM. PURPOSE The purpose of this study was to examine whether maximum straight leg raise (SLR) ROM was limited by passive mechanical forces or stretch-induced contractile responses to stretch. METHODS An instrumented SLR stretch was applied to the right leg of 16 subjects ending at the point of discomfort. Torque was measured with a load cell attached to the ankle. An electrogoniometer was placed on the hip, and the knee was braced in extension. Surface electrodes were placed over the rectus and biceps femoris muscles. Following the instrumented SLR test, maximum ROM was measured goniometrically by a physical therapist using the standard SLR test (PT SLR ROM). Torque/ROM curves were plotted for each subject. RESULTS PT SLR ROM was positively related to total energy absorbed (area under the curve) (r = 0.49, P = 0.044), negatively related to the increase in torque from 20 to 50 degrees (r = -0.81, P < 0.0001) and negatively related to energy absorbed from 20 to 50 degrees (r = -0.73, P < 0.001). Minimal stretch-induced hamstring activity was elicited (3 +/- 1% MVC), and the EMG activity was unrelated to PT SLR ROM (r = -0.06, P = 0.8). A combination of the increase in torque from 20 to 50 degrees and total energy absorbed improved the relationship to PT SLR ROM (r = 0.89, P = 0.001). Seventy-nine percent of the variability in maximum SLR ROM could be explained by the passive mechanical response to stretch. CONCLUSIONS These data lend support to the concept that musculoskeletal flexibility can be explained in mechanical terms rather than by neural theories.

Comparison of Landing Biomechanics Between Male and Female Professional Dancers

Background The incidence of anterior cruciate ligament injuries among dancers is much lower than that among team sport athletes and no clear gender disparity has been reported in the dance population. Although numerous studies have observed differences in lower extremity landing biomechanics between male and female athletes, there is currently little research examining the landing biomechanics of male and female dancers. Comparing landing biomechanics within this population may help explain the lower overall anterior cruciate ligament injury rates and the lack of gender disparity. Hypothesis Due to the fact that dancers receive jump-specific and balance-specific training from a very young age, we hypothesized that there would be no gender differences in drop-landing biomechanics in professional dancers. Study Design Controlled laboratory study. Methods Kinematics and ground-reaction forces were recorded as 33 professional modern and ballet dancers (12 men and 21 women) performed single-legged drop landings from a 30-cm platform. Joint kinematics and kinetics were compared between genders. Results No gender differences in joint kinematics or kinetics were found during landings (multivariate analysis of variance: P = .490 and P = .175, respectively). A significant relationship was found between the age at which the dancers began training and the peak hip adduction angle during landing (r = .358, P = .041). Conclusion In executing a 30-cm drop landing, male and female dancers exhibited similar landing strategies and avoided landing patterns previously associated with increased injury rates. Clinical Relevance Commonly reported biomechanical differences between men and women, as well as the gender disparity among athletes in the incidence of ACL injuries, may be the result of inadequate experience in proper balance and landing technique rather than intrinsic gender factors. Beginning jump-specific and balance-specific training at an early age may counteract the potentially harmful adaptations in landing biomechanics observed in female athletes after maturity.

Optimizing Achilles Tendon Repair: Effect of Epitendinous Suture Augmentation on the Strength of Achilles Tendon Repairs

Background Epitendinous suture augmentation has been shown to increase gap resistance and overall strength in flexor tendon repairs of the hand. The purpose of this study was to evaluate the effect of various suture augmentation techniques in Achilles tendon repair. Materials and Methods Eighteen fresh-frozen cadaveric Achilles tendons were transected and repaired with a 4-strand Krackow core stitch. Suture augmentation was performed with 3 figure-of-eight stitches in 6 specimens and a running cross-stitch weave in 6 specimens. The other 6 specimens were not augmented. Each tendon was loaded to failure on an MTS. Force to failure (defined as peak force or force at 5 mm gapping), gapping resistance, stiffness, and elongation were compared. Results Force to failure (p < 0.001), stiffness (p < 0.01) and gapping resistance (p < 0.05) were increased by suture augmentation. Additionally failure force and gapping resistance for the cross-stitch augmentation was higher than the figure-of-eight augmentation (p < 0.05). Conclusion Cross-stitch augmentation of Achilles tendon repair yields a stronger and stiffer repair with greater resistance to gapping. Clinical Relevance Achilles tendon repairs augmented with a cross stitch weave will be able to withstand substantially higher forces than non-augmented repairs.

Cyclical Loading of Coracoclavicular Ligament Reconstructions: A Comparative Biomechanical Study

Background Reconstruction for injuries to the acromioclavicular joint remains controversial. Hypothesis A coracoclavicular ligament reconstruction with a semitendinosus tendon would have superior performance to the classic coracoacromial ligament transfer with or without augmentation. Study Design Controlled laboratory study. Methods Five cadaveric shoulders were used to reconstruct the coracoclavicular ligaments with 3 methods: coracoacromial ligament transfer without augmentation, coracoacromial ligament transfer augmented with No. 5 Ethibond suture, and a semitendinosus tendon. Each reconstruction was cyclically loaded at 40 N to 80 N for 2500 cycles, then from 40 N to 210 N for 2500 cycles, followed by loading to failure. The number of cycles to 50% and 100% loss of acromioclavicular joint reduction were recorded. Results During the 40 N to 80 N-loading cycle, the coracoacromial transfer without augmentation failed (15 ± 16 cycles). The augmented coracoacromial ligament transfer and the semitendinosus reconstruction did not fail (P = .008). During the 40 N to 210 N-loading cycle, the augmented coracoacromial ligament transfer failed (207 ± 399 cycles). The semitendinosus reconstruction survived through both loading cycles (P < .01). Conclusion Coracoclavicular ligament reconstruction with a semitendinosus graft is a biomechanically superior construct in a cyclically loaded setting to a coracoacromial ligament transfer augmented with a No. 5 Ethibond suture. Clinical Relevance The semitendinosus graft is a strong, biologic option for reconstruction of the coracoclavicular ligaments.

Cyclic Loading of 3 Achilles Tendon Repairs Simulating Early Postoperative Forces

Background Accelerated rehabilitation has been advocated after Achilles tendon repair, but it produces significant forces at the repair site. Hypothesis Stresses applied to the repaired Achilles tendon simulating postoperative forces may exceed the strength of some repairs. Study Design Controlled laboratory study. Methods Fifteen Achilles tendons were incised 4 cm proximal to the calcaneal insertion, then were repaired using either a percutaneous, 4-strand Krackow, or an epitendinous augmented 4-strand Krackow technique. Tendons were cyclically loaded to 1000 cycles each at 100, 190, and 369 N. The number of cycles to initial gapping, 5-mm gapping, and total failure were compared using Mann-Whitney U tests with adjustments for multiple comparisons. Results Gap resistance was significantly greater for augmented Krackow repairs (2208 cycles to initial gapping) versus nonaugmented repairs (502 cycles, P = .024) and for nonaugmented Krackow repairs versus percutaneous repairs (5 cycles, P = .024). All percutaneous repairs failed during the 100-N cycling (102 ± 135 cycles). All nonaugmented Krackow repairs failed during the 190-N cycles (total cycles to failure: 1268 ± 345). All augmented Krackow repairs were intact (no gapping) after the 190-N cycles. Four failed during 369-N cycling (total cycles to failure, 2017 ± 11), and 1 remained intact for 3000 cycles. Conclusion Epitendinous cross-stitch weave augmentation of Achilles tendon repairs significantly increased repair strength and gap resistance. Clinical Relevance Epitendinous cross-stitch weave augmentation of Achilles tendon repairs may better allow for early stretching and ambulation after Achilles tendon repair.

Similar improvement in gait parameters following direct anterior & posterior approach total hip arthroplasty.

We compared gait parameters prior to, at 6 months and 1 year following total hip arthroplasty (THA) performed via direct anterior approach (DAA) and posterior approach (PA) by a single surgeon in 22 patients. A gait analysis system involving reflective markers, infrared cameras and a multicomponent force plate was utilized. Postoperatively, the study cohort demonstrated improvement in flexion/extension range of motion (ROM) (P = 0.001), peak flexion (P = 0.005) and extension (P = 0.002) moments with no differences between groups. Internal/external ROM improved significantly in the DAA group (P = 0.04) with no change in the PA group. THA performed via DAA and PA offers similar improvement in gait parameters with the exception of internal/external ROM which might be related to the release and repair of external rotators during PA THA.

Comparison of Landing Biomechanics Between Male and Female Dancers and Athletes, Part 1 Influence of Sex on Risk of Anterior Cruciate Ligament Injury

Background: The incidence of anterior cruciate ligament (ACL) injuries among dancers is much lower than among team sport athletes, and no clear disparity between sexes has been reported in the dance population. Although numerous studies have observed differences in landing biomechanics of the lower extremity between male and female team sport athletes, there is currently little research examining the landing biomechanics of male and female dancers and none comparing athletes to dancers. Comparing the landing biomechanics within these populations may help explain the lower overall ACL injury rates and lack of sex disparity. Hypothesis: The purpose was to compare the effects of sex and group (dancer vs team sport athlete) on single-legged drop-landing biomechanics. The primary hypothesis was that female dancers would perform a drop-landing task without demonstrating typical sex-related risk factors associated with ACL injuries. A secondary hypothesis was that female team sport athletes would display typical ACL risk factors during the same task. Study Design: Controlled laboratory study. Methods: Kinematics and kinetics were recorded as 40 elite modern and ballet dancers (20 men and 20 women) and 40 team sport athletes (20 men and 20 women) performed single-legged drop landings from a 30-cm platform. Joint kinematics and kinetics were compared between groups and sexes with a group-by-sex multivariate analysis of variance (MANOVA) followed by pairwise t tests. Results: Dancers of both sexes and male team sport athletes landed similarly in terms of frontal-plane knee alignment, whereas female team sport athletes landed with a significantly greater peak knee valgus (P = .007). Female dancers were found to have a lower hip adduction torque than those of the other 3 groups (P = .003). Dancers (male and female) exhibited a lower trunk side flexion (P = .002) and lower trunk forward flexion (P = .032) compared with team sport athletes. Conclusion: In executing a 30-cm drop landing, female team sport athletes displayed a greater knee valgus than did the other 3 groups. Dancers exhibited better trunk stability than did athletes. Clinical Relevance: These biomechanical findings may provide insight into the cause of the epidemiological differences in ACL injuries between dancers and athletes and the lack of a sex disparity within dancers.

Comparison of landing biomechanics between male and female dancers and athletes, part 2: Influence of fatigue and implications for anterior cruciate ligament injury.

Background: Fatigue is strongly linked to an increased risk of injuries, including anterior cruciate ligament (ACL) ruptures. Part 1 of this study identified differences in the biomechanics of landing from a jump between dancers and team athletes, particularly female athletes, which may explain the epidemiological differences in ACL injuries between dancers and team athletes and the lack of a sex disparity within dancers. However, it is not known if these biomechanical variables change differently between team athletes and dancers in the face of fatigue. Purpose/Hypothesis: The purpose of this study was to compare dancers’ and team athletes’ resistance to fatigue and its effect on the biomechanics of single-legged drop landings. The primary hypotheses were that dancers may be more resistant than team athletes to the onset of fatigue and/or may have different biomechanical responses than athletes in landing tasks once fatigue has been achieved. Study Design: Controlled laboratory study. Methods: Kinematics and kinetics were recorded as 40 elite modern and ballet dancers (20 men and 20 women) and 40 team sport athletes (20 men and 20 women; National Collegiate Athletic Association Division I-III) performed single-legged drop landings from a 30-cm platform before and after a fatigue protocol consisting of step-ups and vertical jumps. Unfatigued and fatigued joint kinematics and kinetics were compared between groups and sexes with multivariate analyses of variance, followed by pairwise t tests as appropriate. Results: Dancers took longer (P = .023) than team athletes to reach a similar state of fatigue. Multiple kinetic (eg, increased peak knee valgus moment; P < .001) and kinematic (eg, increased lateral and forward trunk flexion; P < .001 and P = .002, respectively) parameters of landing changed with fatigue, such that both fatigued dancers and athletes landed with mechanics that were more at risk for ACL injuries as compared with before fatigue. Conclusion: Dancers took significantly longer to reach fatigue than team athletes. Female athletes consistently exhibited landing patterns associated with a risk for ACL injuries when compared with the other 3 groups. Fatigue changed landing mechanics similarly in both dancers and athletes, such that all groups landed with worse alignment after being fatigued. Clinical Relevance: Dancers are more resistant to lower extremity fatigue than athletes, and this may partially explain the lower incidence of ACL injuries in both male and female dancers compared to team athletes. The extensive training in landing technique and daily practice that dancers undergo from a young age may be responsible for the higher levels of endurance.